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<h1>The Steam Engine<br />Explained and Illustrated</h1>

<div class="front">
<div class="figcenter" style="width: 300px;">
  <img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_002.png" width="300" height="400" alt="" />
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<div class="caption">
  <div class="fsize2">WATT.</div>
  <div class="fsize4">Engraved by H. Adlard, from a Drawing by H.
      Corbould,<br />
      taken with the permission of James Watt, Esq.</div>
  <div>FROM THE STATUE BY CHANTREY.</div>
</div> <!--end of Caption div-->

<div style="margin-top:3em;margin-bottom:1em;text-align:center;">
 London: Taylor &#38; Walton, Upper Gower Street.
</div></div>

<div class="front">
<div class="fsize4">THE</div>

<div class="fsize1">STEAM ENGINE</div>

<div class="fsize2 gap1">EXPLAINED AND ILLUSTRATED;<br /><br /></div>

<div class="fsize4">WITH<br />
AN ACCOUNT OF ITS INVENTION AND PROGRESSIVE<br />
IMPROVEMENT,</div>

<div class="fsize4">AND ITS APPLICATION TO</div>

<div class="fsize2">NAVIGATION AND RAILWAYS;</div>

<div class="fsize4"><br />INCLUDING ALSO</div>

<div class="fsize3 gothic">A Memoir of Watt.</div>

<div class="fsize3 gap1">BY</div>

<div class="fsize2">DIONYSIUS LARDNER, D.C.L. F.R.S.<br />
<small>&#38;c. &#38;c.</small></div>

<div class="fsize3 gap1"><b>SEVENTH EDITION</b>,</div>

<div class="fsize4">ILLUSTRATED BY ENGRAVINGS ON WOOD.<br />&nbsp;</div>

<div class="fsize3 gap1">LONDON:</div>

<div class="fsize3">PRINTED FOR TAYLOR AND WALTON,</div>
<div class="fsize4">28. UPPER GOWER STREET.</div>

<div class="fsize4">MDCCCXL.</div>
</div>

<div class="front">
<div class="fsize4"><strong class="m1">London</strong>:</div>

<div class="fsize4">Printed by <strong class="m1">A.
 Spottiswoode</strong>,</div>

<div class="fsize4">New-Street-Square.</div>
</div>



<div class="front">
<div class="fsize4">TO</div>

<div class="fsize4">THE RIGHT HONOURABLE</div>

<div class="fsize3">HENRY LORD BROUGHAM AND VAUX,</div>

<div class="fsize4">FELLOW OF THE ROYAL SOCIETY,</div>

<div class="fsize4">AND</div>

<div class="fsize4">MEMBER OF THE NATIONAL INSTITUTE OF FRANCE,</div>

<div class="fsize4 gap1">AS A MARK OF PUBLIC RESPECT</div>

<div class="fsize4">AND</div>

<div class="fsize4">A TESTIMONY OF PRIVATE REGARD,</div>

<div class="fsize4 gap1">THIS WORK</div>

<div class="fsize4">INSCRIBED, BY HIS ATTACHED FRIEND,</div>

<div class="fsize4">THE AUTHOR.</div>
</div>

<div class="front">
<div class="fsize2">ADVERTISEMENT.</div>

<p>The Drawings for several of the Cuts in this
Volume have been taken, by the permission of
Mr. Weale, from the admirable Plates annexed to
the last edition of Tredgold on the Steam Engine
and on Steam Navigation. This acknowledgment is
especially due for the Illustrations which abound in
this Volume.</p>

<p>&#160;&#160;&#160;&#160;&#160;&#160;<i>London, June, 1840.</i></p>
</div>

<div class="figcenter" style="width: 600px;">
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_009.png" width="600" height="458" alt="" />
<div class="caption">LONDON ENTRANCE TO THE BIRMINGHAM RAIL-ROAD.</div>
</div>

<h2><a name="CONTENTS" id="CONTENTS">CONTENTS.</a></h2>

<div class="contents">

<ul><li class="lvl1"><a href="#CHAPTER_I">CHAPTER I.</a></li>

<li class="lvl1a">PRELIMINARY MATTER.</li>

<li class="lvl2">The Steam Engine, a Subject of popular Interest
 <span class="rghtpush"><a href="#Pg004">4</a></span></li>

<li class="lvl2">Effects of Steam
 <span class="rghtpush"><a href="#Pg005">5</a></span></li>

<li class="lvl2">Great Power of Steam
 <span class="rghtpush"><a href="#Pg007">7</a></span></li>

<li class="lvl2">Object of this Work
 <span class="rghtpush"><a href="#Pg009">9</a></span></li>

<li class="lvl2">Disputes respecting the Invention
 <span class="rghtpush"><a href="#Pg011">11</a></span></li>

<li class="lvl2">Hero of Alexandria's Machine
 <span class="rghtpush"><a href="#Pg013">13</a></span></li>

<li class="lvl2">Blasco De Garay's Proposition to propel Vessels by a
 Machine
 <span class="rghtpush"><a href="#Pg016">16</a></span></li>

<li class="lvl2">Solomon De Caus
 <span class="rghtpush"><a href="#Pg017">17</a></span></li>

<li class="lvl2">Giovanni Branca proposes to work Mills by Steam
 <span class="rghtpush"><a href="#Pg022">22</a></span></li>

<li class="lvl2">Marquis of Worcester
 <span class="rghtpush"><a href="#Pg023">23</a></span></li>

<li class="lvl2">Mechanical Properties of Fluids
 <span class="rghtpush"><a href="#Pg025">25</a></span></li>

<li class="lvl2">Elastic and Inelastic Fluids
 <span class="rghtpush"><a href="#Pg025">25</a></span></li>

<li class="lvl2">Elasticity of Gases
 <span class="rghtpush"><a href="#Pg028">28</a></span></li>

<li class="lvl2">Effects of Heat
 <span class="rghtpush"><a href="#Pg029">29</a></span></li>

<li class="lvl2">Application of these Principles to the Engines of
 Hero, De Caus, and Lord Worcester
 <span class="rghtpush"><a href="#Pg030">30</a></span></li>

<li class="lvl2">Sir Samuel Morland
 <span class="rghtpush"><a href="#Pg034">34</a></span></li>

<li class="lvl2">Denis Papin
 <span class="rghtpush"><a href="#Pg036">36</a></span></li>

<li class="lvl2">Atmospheric Pressure
 <span class="rghtpush"><a href="#Pg038">38</a></span></li>

<li class="lvl2">Weight of Air
 <span class="rghtpush"><a href="#Pg039">39</a></span></li>

<li class="lvl2">Pressure of Air
 <span class="rghtpush"><a href="#Pg041">41</a></span></li>

<li class="lvl2">Barometer
 <span class="rghtpush"><a href="#Pg041">41</a></span></li>

<li class="lvl2">Elastic Force of Air and Gases
 <span class="rghtpush"><a href="#Pg042">42</a></span></li>

<li class="lvl2">Force obtained by a Vacuum
 <span class="rghtpush"><a href="#Pg043">43</a></span></li>

<li class="lvl2">Common Pump
 <span class="rghtpush"><a href="#Pg043">43</a></span></li>

<li class="lvl2">Rarefaction by Heat
 <span class="rghtpush"><a href="#Pg044">44</a></span></li>

<li class="lvl2">Process of filling Thermometers
 <span class="rghtpush"><a href="#Pg044">44</a></span></li>

<li class="lvl2">Papin's Method of producing a Vacuum
 <span class="rghtpush"><a href="#Pg044">44</a></span></li>

<li class="lvl2">His Discovery of the Condensation of Steam
 <span class="rghtpush"><a href="#Pg045">45</a></span></li>

<li class="lvl2">Thomas Savery
 <span class="rghtpush"><a href="#Pg047">47</a></span></li>


<li class="lvl1"><a href="#CHAP_II">CHAP. II.</a></li>

<li class="lvl1a center">ENGINES OF SAVERY AND NEWCOMEN.</li>

<li class="lvl2">Savery's Engine
 <span class="rghtpush"><a href="#Pg049">49</a></span></li>

<li class="lvl2">Boilers and their Appendages
 <span class="rghtpush"><a href="#Pg050">50</a></span></li>

<li class="lvl2">Working Apparatus described
 <span class="rghtpush"><a href="#Pg051">51</a></span></li>

<li class="lvl2">Mode of Operation
 <span class="rghtpush"><a href="#Pg052">52</a></span></li>

<li class="lvl2">Defects of Savery's Engine
 <span class="rghtpush"><a href="#Pg058">58</a></span></li>

<li class="lvl2">Newcomen's Engine described by Papin
 <span class="rghtpush"><a href="#Pg062">62</a></span></li>

<li class="lvl2">Newcomen and Cawley obtain a Patent for Atmospheric
  Engine
 <span class="rghtpush"><a href="#Pg065">65</a></span></li>

<li class="lvl2">Accidental Discovery of Condensation by Injection
 <span class="rghtpush"><a href="#Pg069">69</a></span></li>

<li class="lvl2">Potter's Discovery of the Method of working the Valves
 <span class="rghtpush"><a href="#Pg071">71</a></span></li>

<li class="lvl2">His Contrivance improved by the Substitution of a Plug Frame
 <span class="rghtpush"><a href="#Pg072">72</a></span></li>

<li class="lvl2">Advantages of the Atmospheric Engine over that of Savery
 <span class="rghtpush"><a href="#Pg072">72</a></span></li>

<li class="lvl2">The Power of Savery's Engine restricted
 <span class="rghtpush"><a href="#Pg073">73</a></span></li>

<li class="lvl2">It contained no new Principle
 <span class="rghtpush"><a href="#Pg073">73</a></span></li>

<li class="lvl2">Its practical Superiority
 <span class="rghtpush"><a href="#Pg073">73</a></span></li>


<li class="lvl1"><a href="#CHAP_III">CHAP. III.</a></li>

<li class="lvl1a">EARLY CAREER AND DISCOVERIES OF JAMES WATT.</li>

<li class="lvl2">Atmospheric Engine improved by Beighton
 <span class="rghtpush"><a href="#Pg075">75</a></span></li>

<li class="lvl2">Smeaton's Improvements in the Atmospheric Engine
 <span class="rghtpush"><a href="#Pg076">76</a></span></li>

<li class="lvl2">Brindley obtains a Patent for Improvement in
 <span class="rghtpush"><a href="#Pg076">76</a></span></li>

<li class="lvl2">Invents the Self-regulating Feeder
 <span class="rghtpush"><a href="#Pg076">76</a></span></li>

<li class="lvl2">Infancy of James Watt
 <span class="rghtpush"><a href="#Pg077">77</a></span></li>

<li class="lvl2">His Descent and Parentage
 <span class="rghtpush"><a href="#Pg077">77</a></span></li>

<li class="lvl2">Anecdotes of his Boyhood
 <span class="rghtpush"><a href="#Pg078">78</a></span></li>

<li class="lvl2">His early Acquirements
 <span class="rghtpush"><a href="#Pg079">79</a></span></li>

<li class="lvl2">Goes to London
 <span class="rghtpush"><a href="#Pg080">80</a></span></li>

<li class="lvl2">Returns to Glasgow
 <span class="rghtpush"><a href="#Pg080">80</a></span></li>

<li class="lvl2">Appointed Instrument-maker to the University
 <span class="rghtpush"><a href="#Pg081">81</a></span></li>

<li class="lvl2">Opens a Shop in Glasgow
 <span class="rghtpush"><a href="#Pg081">81</a></span></li>

<li class="lvl2">His Friends and Patrons
 <span class="rghtpush"><a href="#Pg081">81</a></span></li>

<li class="lvl2">Professor Robison's Remarks on Watt's personal
 Character
 <span class="rghtpush"><a href="#Pg082">82</a></span></li>

<li class="lvl2">His industrious and studious Habits
 <span class="rghtpush"><a href="#Pg082">82</a></span></li>

<li class="lvl2">His Attention first directed to Steam
 <span class="rghtpush"><a href="#Pg083">83</a></span></li>

<li class="lvl2">Experiments on High-pressure Engine
 <span class="rghtpush"><a href="#Pg083">83</a></span></li>

<li class="lvl2">Repairs an Atmospheric Model
 <span class="rghtpush"><a href="#Pg084">84</a></span></li>

<li class="lvl2">Experimental Inquiry consequent on this
 <span class="rghtpush"><a href="#Pg084">84</a></span></li>

<li class="lvl2">Its Results
 <span class="rghtpush"><a href="#Pg084">84</a></span></li>

<li class="lvl2">Observes great Defects in the Atmospheric Engine
 <span class="rghtpush"><a href="#Pg085">85</a></span></li>

<li class="lvl2">His first Attempt to improve it
 <span class="rghtpush"><a href="#Pg085">85</a></span></li>

<li class="lvl2">His early Experiments on Steam
 <span class="rghtpush"><a href="#Pg087">87</a></span></li>

<li class="lvl2">Discovery by Experiment of the Expansion which Water
 undergoes in Evaporation
 <span class="rghtpush"><a href="#Pg090">90</a></span></li>

<li class="lvl2">Discovers the latent Heat of Steam
 <span class="rghtpush"><a href="#Pg091">91</a></span></li>

<li class="lvl2">Informed by Dr. Black of the Theory of latent Heat
 <span class="rghtpush"><a href="#Pg093">93</a></span></li>

<li class="lvl2">His Improvement not due to Black
 <span class="rghtpush"><a href="#Pg093">93</a></span></li>


<li class="lvl1"><a href="#CHAP_IV">CHAP. IV.</a></li>

<li class="lvl1a">EXPOSITION OF PHYSICAL PRINCIPLES.</li>

<li class="lvl2">Construction of Thermometer
 <span class="rghtpush"><a href="#Pg098">98</a></span></li>

<li class="lvl2">Method of graduating it
 <span class="rghtpush"><a href="#Pg099">99</a></span></li>

<li class="lvl2">Freezing and boiling Points
 <span class="rghtpush"><a href="#Pg099">99</a></span></li>

<li class="lvl2">Latent Heat of Water
 <span class="rghtpush"><a href="#Pg101">101</a></span></li>

<li class="lvl2">Quantity of Heat necessary to convert Ice into Water,
 first noticed by Dr. Black
 <span class="rghtpush"><a href="#Pg101">101</a></span></li>

<li class="lvl2">Examination of the analogous Effects produced by the
continued Application of Heat to Water in the liquid
State
 <span class="rghtpush"><a href="#Pg102">102</a></span></li>

<li class="lvl2">Process of Boiling
 <span class="rghtpush"><a href="#Pg104">104</a></span></li>

<li class="lvl2">Reconversion of Steam into Water
 <span class="rghtpush"><a href="#Pg104">104</a></span></li>

<li class="lvl2">Conversion of Water into Steam
 <span class="rghtpush"><a href="#Pg105">105</a></span></li>

<li class="lvl2">Latent Heat of Steam
 <span class="rghtpush"><a href="#Pg107">107</a></span></li>

<li class="lvl2">Boiling Point varies
 <span class="rghtpush"><a href="#Pg108">108</a></span></li>

<li class="lvl2">Different in different Places
 <span class="rghtpush"><a href="#Pg109">109</a></span></li>

<li class="lvl2">Inquiry whether a Diminution of Pressure will produce a
corresponding Effect on the boiling Point
 <span class="rghtpush"><a href="#Pg112">112</a></span></li>

<li class="lvl2">Table showing the Temperature at which Water will boil
under different Pressures of the Atmosphere
 <span class="rghtpush"><a href="#Pg113">113</a></span></li>

<li class="lvl2">Mechanical Force of Steam
 <span class="rghtpush"><a href="#Pg115">115</a></span></li>

<li class="lvl2">Facts to be observed in
 <span class="rghtpush"><a href="#Pg117">117</a></span></li>


<li class="lvl1"><a href="#CHAP_V">CHAP. V.</a></li>

<li class="lvl1a">FURTHER DISCOVERIES OF WATT.</li>

<li class="lvl2">Watt finds that Condensation in the Cylinder is incompatible
with a due Economy of Fuel
 <span class="rghtpush"><a href="#Pg119">119</a></span></li>

<li class="lvl2">Conceives the Notion of condensing out of the Cylinder
 <span class="rghtpush"><a href="#Pg120">120</a></span></li>

<li class="lvl2">Discovers separate Condensation
 <span class="rghtpush"><a href="#Pg121">121</a></span></li>

<li class="lvl2">Invents the Air Pump
 <span class="rghtpush"><a href="#Pg123">123</a></span></li>

<li class="lvl2">Substitutes Steam Pressure for Atmospheric Pressure
 <span class="rghtpush"><a href="#Pg123">123</a></span></li>

<li class="lvl2">Invents the Steam Case, or Jacket
 <span class="rghtpush"><a href="#Pg124">124</a></span></li>

<li class="lvl2">His first Experiments to realise these Inventions
 <span class="rghtpush"><a href="#Pg125">125</a></span></li>

<li class="lvl2">His experimental Apparatus
 <span class="rghtpush"><a href="#Pg125">125</a></span></li>

<li class="lvl2">His experimental Models fitted up at Delft House, in Glasgow
 <span class="rghtpush"><a href="#Pg128">128</a></span></li>

<li class="lvl2">Difficulties of bringing the improved Engines into Use
 <span class="rghtpush"><a href="#Pg129">129</a></span></li>

<li class="lvl2">Watt first employed by Roebuck as a Civil Engineer
 <span class="rghtpush"><a href="#Pg130">130</a></span></li>

<li class="lvl2">His Partnership with Roebuck
 <span class="rghtpush"><a href="#Pg130">130</a></span></li>

<li class="lvl2">His first Patent
 <span class="rghtpush"><a href="#Pg130">130</a></span></li>

<li class="lvl2">Experimental Engine at Kinneal
 <span class="rghtpush"><a href="#Pg131">131</a></span></li>

<li class="lvl2">Abstract of the Act of Parliament for the Extension of his
Patent
 <span class="rghtpush"><a href="#Pg132">132</a></span></li>

<li class="lvl2">Description of his single-acting Steam Engine
 <span class="rghtpush"><a href="#Pg133">133</a></span></li>


<li class="lvl1"><a href="#CHAP_VI">CHAP. VI.</a></li>

<li class="lvl1a">WATT'S ENGINES.</li>

<li class="lvl2">Correspondence of Watt with Smeaton
 <span class="rghtpush"><a href="#Pg145">145</a></span></li>

<li class="lvl2">Failure of Condensation by Surface
 <span class="rghtpush"><a href="#Pg146">146</a></span></li>

<li class="lvl2">Improvements in Construction of Piston
 <span class="rghtpush"><a href="#Pg147">147</a></span></li>

<li class="lvl2">Method of Packing
 <span class="rghtpush"><a href="#Pg148">148</a></span></li>

<li class="lvl2">Improvements in boring the Cylinder
 <span class="rghtpush"><a href="#Pg149">149</a></span></li>

<li class="lvl2">Disadvantages of the new compared with the old Engines
 <span class="rghtpush"><a href="#Pg150">150</a></span></li>

<li class="lvl2">Greatly increased Economy of Fuel
 <span class="rghtpush"><a href="#Pg150">150</a></span></li>

<li class="lvl2">Economy of the Engine
 <span class="rghtpush"><a href="#Pg151">151</a></span></li>

<li class="lvl2">Expedients to force the new Engines into Use
 <span class="rghtpush"><a href="#Pg151">151</a></span></li>

<li class="lvl2">Correspondence of Boulton
 <span class="rghtpush"><a href="#Pg153">153</a></span></li>

<li class="lvl2">Correspondence with Smeaton
 <span class="rghtpush"><a href="#Pg155">155</a></span></li>

<li class="lvl2">Efficiency of Fuel in the new Engines
 <span class="rghtpush"><a href="#Pg156">156</a></span></li>

<li class="lvl2">Discovery of the expansive Action of Steam
 <span class="rghtpush"><a href="#Pg157">157</a></span></li>

<li class="lvl2">Watt states it in a Letter to Dr. Small
 <span class="rghtpush"><a href="#Pg157">157</a></span></li>

<li class="lvl2">Its Principle explained
 <span class="rghtpush"><a href="#Pg158">158</a></span></li>

<li class="lvl2">Mechanical Effects resulting from it
 <span class="rghtpush"><a href="#Pg162">162</a></span></li>

<li class="lvl2">Computed Effect of cutting off Steam at different Portions
of the Stroke
 <span class="rghtpush"><a href="#Pg163">163</a></span></li>

<li class="lvl2">Produces a variable Power
 <span class="rghtpush"><a href="#Pg163">163</a></span></li>

<li class="lvl2">Expedients for equalising the Power
 <span class="rghtpush"><a href="#Pg164">164</a></span></li>

<li class="lvl2">Expansive Principle in Watt's Engines limited
 <span class="rghtpush"><a href="#Pg165">165</a></span></li>

<li class="lvl2">Its more extensive Application in the Cornish Engines
 <span class="rghtpush"><a href="#Pg165">165</a></span></li>


<li class="lvl1"><a href="#CHAP_VII">CHAP. VII.</a></li>

<li class="lvl1a">DOUBLE-ACTING ENGINE.</li>

<li class="lvl2">Common Steam
 <span class="rghtpush"><a href="#Pg168">168</a></span></li>

<li class="lvl2">Superheated Steam
 <span class="rghtpush"><a href="#Pg170">170</a></span></li>

<li class="lvl2">Laws of Dalton and Gay Lussac
 <span class="rghtpush"><a href="#Pg171">171</a></span></li>

<li class="lvl2">Law of Mariotte
 <span class="rghtpush"><a href="#Pg171">171</a></span></li>

<li class="lvl2">Relation between Temperature and Pressure of common
Steam
 <span class="rghtpush"><a href="#Pg171">171</a></span></li>

<li class="lvl2">Effects of the Expansion of common Steam
 <span class="rghtpush"><a href="#Pg173">173</a></span></li>

<li class="lvl2">Mechanical Effects of Steam
 <span class="rghtpush"><a href="#Pg173">173</a></span></li>

<li class="lvl2">Method of equalising the expansive Force
 <span class="rghtpush"><a href="#Pg174">174</a></span></li>

<li class="lvl2">Hornblower's Engine
 <span class="rghtpush"><a href="#Pg175">175</a></span></li>

<li class="lvl2">Woolf's Engine
 <span class="rghtpush"><a href="#Pg176">176</a></span></li>

<li class="lvl2">Watt's Attempts to extend the Steam Engine to Manufactures
 <span class="rghtpush"><a href="#Pg178">178</a></span></li>

<li class="lvl2">Papin's projected Applications of the Steam Engine
 <span class="rghtpush"><a href="#Pg178">178</a></span></li>

<li class="lvl2">Savery's Application of the Engine to move Machinery
 <span class="rghtpush"><a href="#Pg180">180</a></span></li>

<li class="lvl2">Jonathan Hull's Application to Water Wheels
 <span class="rghtpush"><a href="#Pg180">180</a></span></li>

<li class="lvl2">Champion of Bristol applies the Atmospheric Engine to
raise Water
 <span class="rghtpush"><a href="#Pg181">181</a></span></li>

<li class="lvl2">Stewart's Application of the Engine to Mill-work
 <span class="rghtpush"><a href="#Pg182">182</a></span></li>

<li class="lvl2">Wasbrough's Application of the Fly-wheel and Crank
 <span class="rghtpush"><a href="#Pg183">183</a></span></li>

<li class="lvl2">Reasons why Watt's single-acting Steam Engine was not
adapted to produce continuous uniform Motion of Rotation
 <span class="rghtpush"><a href="#Pg184">184</a></span></li>

<li class="lvl2">Watt's Second Patent
 <span class="rghtpush"><a href="#Pg186">186</a></span></li>

<li class="lvl2">Sun-and-Planet Wheels
 <span class="rghtpush"><a href="#Pg187">187</a></span></li>

<li class="lvl2">Valves of double-acting Engine
 <span class="rghtpush"><a href="#Pg189">189</a></span></li>


<li class="lvl1"><a href="#CHAP_VIII">CHAP. VIII.</a></li>

<li class="lvl1a">DOUBLE-ACTING ENGINE.</li>

<li class="lvl2">Methods of connecting the Piston-rod and Beam in the
double-acting Engine
 <span class="rghtpush"><a href="#Pg193">193</a></span></li>

<li class="lvl2">Rack and Sector
 <span class="rghtpush"><a href="#Pg194">194</a></span></li>

<li class="lvl2">Parallel Motion
 <span class="rghtpush"><a href="#Pg195">195</a></span></li>

<li class="lvl2">Connection of Piston-rod and Beam
 <span class="rghtpush"><a href="#Pg195">195</a></span></li>

<li class="lvl2">Connecting Rod and Crank
 <span class="rghtpush"><a href="#Pg203">203</a></span></li>

<li class="lvl2">Fly-wheel
 <span class="rghtpush"><a href="#Pg205">205</a></span></li>

<li class="lvl2">Throttle-valve
 <span class="rghtpush"><a href="#Pg207">207</a></span></li>

<li class="lvl2">Governor
 <span class="rghtpush"><a href="#Pg209">209</a></span></li>

<li class="lvl2">Construction and Operation of the double-acting Engine
 <span class="rghtpush"><a href="#Pg216">216</a></span></li>

<li class="lvl2">Eccentric
 <span class="rghtpush"><a href="#Pg225">225</a></span></li>

<li class="lvl2">Cocks and Valves
 <span class="rghtpush"><a href="#Pg227">227</a></span></li>

<li class="lvl2">Single-clack Valves
 <span class="rghtpush"><a href="#Pg227">227</a></span></li>

<li class="lvl2">Double-clack Valves
 <span class="rghtpush"><a href="#Pg228">228</a></span></li>

<li class="lvl2">Conical Valves
 <span class="rghtpush"><a href="#Pg228">228</a></span></li>

<li class="lvl2">Slide Valves
 <span class="rghtpush"><a href="#Pg229">229</a></span></li>

<li class="lvl2">Murray's Slides
 <span class="rghtpush"><a href="#Pg229">229</a></span></li>

<li class="lvl2">D Valves
 <span class="rghtpush"><a href="#Pg230">230</a></span></li>

<li class="lvl2">Seaward's Slides
 <span class="rghtpush"><a href="#Pg235">235</a></span></li>

<li class="lvl2">Single Cock
 <span class="rghtpush"><a href="#Pg238">238</a></span></li>

<li class="lvl2">Two-way Cock
 <span class="rghtpush"><a href="#Pg239">239</a></span></li>

<li class="lvl2">Four-way Cock
 <span class="rghtpush"><a href="#Pg239">239</a></span></li>

<li class="lvl2">Pistons
 <span class="rghtpush"><a href="#Pg242">242</a></span></li>

<li class="lvl2">Common hemp-packed Piston
 <span class="rghtpush"><a href="#Pg242">242</a></span></li>

<li class="lvl2">Woolf's Piston
 <span class="rghtpush"><a href="#Pg243">243</a></span></li>

<li class="lvl2">Metallic Pistons
 <span class="rghtpush"><a href="#Pg244">244</a></span></li>

<li class="lvl2">Cartwright's Engine
 <span class="rghtpush"><a href="#Pg245">245</a></span></li>

<li class="lvl2">Cartwright's Piston
 <span class="rghtpush"><a href="#Pg247">247</a></span></li>

<li class="lvl2">Barton's Piston
 <span class="rghtpush"><a href="#Pg248">248</a></span></li>


<li class="lvl1"><a href="#CHAP_IX">CHAP. IX.</a></li>

<li class="lvl1a">BOILERS AND FURNACES.</li>

<li class="lvl2">Analysis of Coal
 <span class="rghtpush"><a href="#Pg252">252</a></span></li>

<li class="lvl2">Process of Combustion
 <span class="rghtpush"><a href="#Pg253">253</a></span></li>

<li class="lvl2">Heat evolved in it
 <span class="rghtpush"><a href="#Pg254">254</a></span></li>

<li class="lvl2">Form and Structure of Boiler
 <span class="rghtpush"><a href="#Pg255">255</a></span></li>

<li class="lvl2">Waggon Boiler
 <span class="rghtpush"><a href="#Pg255">255</a></span></li>

<li class="lvl2">Furnace
 <span class="rghtpush"><a href="#Pg256">256</a></span></li>

<li class="lvl2">Method of feeding it
 <span class="rghtpush"><a href="#Pg257">257</a></span></li>

<li class="lvl2">Combustion of Gas in Flues
 <span class="rghtpush"><a href="#Pg260">260</a></span></li>

<li class="lvl2">Williams's Patent for Method of consuming unburned Gases
 <span class="rghtpush"><a href="#Pg260">260</a></span></li>

<li class="lvl2">Construction of Grate and Ash-pit
 <span class="rghtpush"><a href="#Pg261">261</a></span></li>

<li class="lvl2">Magnitude of heating Surface of Boiler
 <span class="rghtpush"><a href="#Pg262">262</a></span></li>

<li class="lvl2">Steam-space and Water-space in Boiler
 <span class="rghtpush"><a href="#Pg263">263</a></span></li>

<li class="lvl2">Position of Flues
 <span class="rghtpush"><a href="#Pg264">264</a></span></li>

<li class="lvl2">Method of feeding Boiler
 <span class="rghtpush"><a href="#Pg265">265</a></span></li>

<li class="lvl2">Method of indicating the Level of Water in Boiler
 <span class="rghtpush"><a href="#Pg266">266</a></span></li>

<li class="lvl2">Level Gauges
 <span class="rghtpush"><a href="#Pg266">266</a></span></li>

<li class="lvl2">Self-regulating Feeders
 <span class="rghtpush"><a href="#Pg267">267</a></span></li>

<li class="lvl2">Steam Gauge
 <span class="rghtpush"><a href="#Pg270">270</a></span></li>

<li class="lvl2">Barometer Gauge
 <span class="rghtpush"><a href="#Pg272">272</a></span></li>

<li class="lvl2">Watt's Invention of the Indicator
 <span class="rghtpush"><a href="#Pg274">274</a></span></li>

<li class="lvl2">Counter
 <span class="rghtpush"><a href="#Pg278">278</a></span></li>

<li class="lvl2">Safety-valve
 <span class="rghtpush"><a href="#Pg279">279</a></span></li>

<li class="lvl2">Fusible Plugs
 <span class="rghtpush"><a href="#Pg280">280</a></span></li>

<li class="lvl2">Self-regulating Damper
 <span class="rghtpush"><a href="#Pg281">281</a></span></li>

<li class="lvl2">Brunton's Self-regulating Furnace
 <span class="rghtpush"><a href="#Pg283">283</a></span></li>

<li class="lvl2">Gross and useful Effect of an Engine
 <span class="rghtpush"><a href="#Pg285">285</a></span></li>

<li class="lvl2">Power and Duty of Engines
 <span class="rghtpush"><a href="#Pg287">287</a></span></li>

<li class="lvl2">Horse-power of Steam Engines
 <span class="rghtpush"><a href="#Pg289">289</a></span></li>

<li class="lvl2">Evaporation proportional to Horse-power
 <span class="rghtpush"><a href="#Pg290">290</a></span></li>

<li class="lvl2">Sources of Loss of Power
 <span class="rghtpush"><a href="#Pg292">292</a></span></li>

<li class="lvl2">Absence of good practical Rules for Power
 <span class="rghtpush"><a href="#Pg292">292</a></span></li>

<li class="lvl2">Common Rules followed by Engine-makers
 <span class="rghtpush"><a href="#Pg292">292</a></span></li>

<li class="lvl2">Duty distinguished from Power
 <span class="rghtpush"><a href="#Pg294">294</a></span></li>

<li class="lvl2">Duty of Boilers
 <span class="rghtpush"><a href="#Pg294">294</a></span></li>

<li class="lvl2">Proportion of Stroke to Diameter of Cylinder
 <span class="rghtpush"><a href="#Pg295">295</a></span></li>

<li class="lvl2">Duty of Engines
 <span class="rghtpush"><a href="#Pg296">296</a></span></li>

<li class="lvl2">Cornish System of Inspection
 <span class="rghtpush"><a href="#Pg297">297</a></span></li>

<li class="lvl2">Table showing the Improvement of Cornish Engines
 <span class="rghtpush"><a href="#Pg298">298</a></span></li>

<li class="lvl2">Beneficial Effects of Cornish Inspection
 <span class="rghtpush"><a href="#Pg299">299</a></span></li>

<li class="lvl2">Successive Improvements on which the increased Duty of
Engines depends, traced by John Taylor in his "Records
of Mining"
 <span class="rghtpush"><a href="#Pg299">299</a></span></li>


<li class="lvl1"><a href="#CHAP_X">CHAP. X.</a></li>

<li class="lvl1a">LIFE OF WATT.</li>

<li class="lvl2">Watt's Friends and Associates at Birmingham
 <span class="rghtpush"><a href="#Pg302">302</a></span></li>

<li class="lvl2">His Invention of the Copying Press
 <span class="rghtpush"><a href="#Pg302">302</a></span></li>

<li class="lvl2">Heating Apartments and Buildings by Steam
 <span class="rghtpush"><a href="#Pg303">303</a></span></li>

<li class="lvl2">Watt's Machine for drying Linen
 <span class="rghtpush"><a href="#Pg303">303</a></span></li>

<li class="lvl2">His Share in the Discovery of the Composition of Water
 <span class="rghtpush"><a href="#Pg303">303</a></span></li>

<li class="lvl2">The Merit of this Discovery shared between Cavendish,
Lavoisier, and Watt
 <span class="rghtpush"><a href="#Pg305">305</a></span></li>

<li class="lvl2">Anecdote of Watt's Activity of Mind
 <span class="rghtpush"><a href="#Pg309">309</a></span></li>

<li class="lvl2">His Introduction of the Use of Chlorine in Bleaching
 <span class="rghtpush"><a href="#Pg310">310</a></span></li>

<li class="lvl2">One of the Founders of the Pneumatic Institution at Clifton
 <span class="rghtpush"><a href="#Pg310">310</a></span></li>

<li class="lvl2">His first Marriage
 <span class="rghtpush"><a href="#Pg311">311</a></span></li>

<li class="lvl2">Death of his first Wife
 <span class="rghtpush"><a href="#Pg311">311</a></span></li>

<li class="lvl2">His second Marriage
 <span class="rghtpush"><a href="#Pg311">311</a></span></li>

<li class="lvl2">Death of his younger Son
 <span class="rghtpush"><a href="#Pg311">311</a></span></li>

<li class="lvl2">Extracts from his Letters
 <span class="rghtpush"><a href="#Pg312">312</a></span></li>

<li class="lvl2">Character of Watt by Lord Brougham
 <span class="rghtpush"><a href="#Pg313">313</a></span></li>

<li class="lvl2">Extract from Sir Walter Scott's "Monastery" on the Character
of Watt
 <span class="rghtpush"><a href="#Pg314">314</a></span></li>

<li class="lvl2">Sketch of the Life of Watt from the
"<cite>Scotsman</cite>" by Lord Jeffrey
 <span class="rghtpush"><a href="#Pg315">315</a></span></li>

<li class="lvl2">Occupation of his old Age
 <span class="rghtpush"><a href="#Pg318">318</a></span></li>

<li class="lvl2">His Invention of Machine for copying Sculpture
 <span class="rghtpush"><a href="#Pg318">318</a></span></li>

<li class="lvl2">His last Days
 <span class="rghtpush"><a href="#Pg318">318</a></span></li>

<li class="lvl2">Monuments to his Memory
 <span class="rghtpush"><a href="#Pg319">319</a></span></li>

<li class="lvl2">Inscription by Lord Brougham on the Pedestal of the Monument
in Westminster Abbey
 <span class="rghtpush"><a href="#Pg320">320</a></span></li>


<li class="lvl1"><a href="#CHAP_XI">CHAP. XI.</a></li>

<li class="lvl1a">LOCOMOTIVE ENGINES ON RAILWAYS.</li>

<li class="lvl2">High-pressure Engines
 <span class="rghtpush"><a href="#Pg322">322</a></span></li>

<li class="lvl2">One of the earliest Forms of the Steam Engine
 <span class="rghtpush"><a href="#Pg322">322</a></span></li>

<li class="lvl2">Description of Leupold's Engine
 <span class="rghtpush"><a href="#Pg323">323</a></span></li>

<li class="lvl2">Non-condensing Engine of Messrs. Trevethick and Vivian
 <span class="rghtpush"><a href="#Pg324">324</a></span></li>

<li class="lvl2">Construction of a Machine for moving Carriages on Railroads
 <span class="rghtpush"><a href="#Pg328">328</a></span></li>

<li class="lvl2">Effects of Railway Transport
 <span class="rghtpush"><a href="#Pg329">329</a></span></li>

<li class="lvl2">Moral and political Consequences of
 <span class="rghtpush"><a href="#Pg334">334</a></span></li>

<li class="lvl2">History of the Locomotive Engine
 <span class="rghtpush"><a href="#Pg337">337</a></span></li>

<li class="lvl2">Construction of Locomotive Engine by Blinkensop
 <span class="rghtpush"><a href="#Pg337">337</a></span></li>

<li class="lvl2">Messrs. Chapman's Contrivance
 <span class="rghtpush"><a href="#Pg337">337</a></span></li>

<li class="lvl2">Walking Engine
 <span class="rghtpush"><a href="#Pg337">337</a></span></li>

<li class="lvl2">Mr. Stephenson's Engines at Killingworth
 <span class="rghtpush"><a href="#Pg339">339</a></span></li>

<li class="lvl2">Liverpool and Manchester Railway
 <span class="rghtpush"><a href="#Pg342">342</a></span></li>

<li class="lvl2">The Directors offer a Prize for the best Locomotive Engine
 <span class="rghtpush"><a href="#Pg344">344</a></span></li>

<li class="lvl2">Experimental Trial
 <span class="rghtpush"><a href="#Pg344">344</a></span></li>

<li class="lvl2">The "Rocket," "Sanspareil," and "Novelty"
 <span class="rghtpush"><a href="#Pg344">344</a></span></li>

<li class="lvl2">Admirable Arrangement in the Rocket
 <span class="rghtpush"><a href="#Pg345">345</a></span></li>

<li class="lvl2">Description of the "Sanspareil"
 <span class="rghtpush"><a href="#Pg347">347</a></span></li>

<li class="lvl2">Description of the "Novelty"
 <span class="rghtpush"><a href="#Pg349">349</a></span></li>

<li class="lvl2">The Superiority of the "Rocket"
 <span class="rghtpush"><a href="#Pg350">350</a></span></li>

<li class="lvl2">Method of subdividing the Flue into Tubes
 <span class="rghtpush"><a href="#Pg353">353</a></span></li>

<li class="lvl2">Progressive Improvement of Locomotive Engines
 <span class="rghtpush"><a href="#Pg354">354</a></span></li>

<li class="lvl2">Dr. Lardner's Experiments in 1832
 <span class="rghtpush"><a href="#Pg357">357</a></span></li>

<li class="lvl2">Adoption of Brass Tubes
 <span class="rghtpush"><a href="#Pg360">360</a></span></li>

<li class="lvl2">Great Expense of Locomotive Power
 <span class="rghtpush"><a href="#Pg361">361</a></span></li>

<li class="lvl2">Mr. Booth's Report
 <span class="rghtpush"><a href="#Pg362">362</a></span></li>

<li class="lvl2">Detailed Description of the most improved Locomotive
Engines
 <span class="rghtpush"><a href="#Pg365">365</a></span></li>

<li class="lvl2">Substitution of Brass for Copper Tubes ascribed to Mr.
Dixon
 <span class="rghtpush"><a href="#Pg370">370</a></span></li>

<li class="lvl2">Power of Locomotive Engines
 <span class="rghtpush"><a href="#Pg379">379</a></span></li>

<li class="lvl2">Position of the Eccentrics
 <span class="rghtpush"><a href="#Pg379">379</a></span></li>

<li class="lvl2">Pressure of Steam in the Boiler
 <span class="rghtpush"><a href="#Pg401">401</a></span></li>

<li class="lvl2">Dr. Lardner's Experiments in 1838
 <span class="rghtpush"><a href="#Pg406">406</a></span></li>

<li class="lvl2">Resistance to Railway Trains
 <span class="rghtpush"><a href="#Pg407">407</a></span></li>

<li class="lvl2">Dr. Lardner's Experiments on the Great Western Railway
 <span class="rghtpush"><a href="#Pg408">408</a></span></li>

<li class="lvl2">Experiments on Resistance
 <span class="rghtpush"><a href="#Pg409">409</a></span></li>

<li class="lvl2">Restrictions on Gradients
 <span class="rghtpush"><a href="#Pg410">410</a></span></li>

<li class="lvl2">Compensating Effect of Gradients
 <span class="rghtpush"><a href="#Pg412">412</a></span></li>

<li class="lvl2">Experiment with the "Hecla"
 <span class="rghtpush"><a href="#Pg412">412</a></span></li>

<li class="lvl2">Disposition of Gradients should be uniform
 <span class="rghtpush"><a href="#Pg415">415</a></span></li>

<li class="lvl2">Methods of surmounting steep Inclinations
 <span class="rghtpush"><a href="#Pg415">415</a></span></li>


<li class="lvl1"><a href="#CHAP_XII">CHAP. XII.</a></li>

<li class="lvl1a">LOCOMOTIVE ENGINES ON TURNPIKE ROADS.</li>

<li class="lvl2">Railways and Stone Roads compared
 <span class="rghtpush"><a href="#Pg420">420</a></span></li>

<li class="lvl2">Gurney's Steam Carriage
 <span class="rghtpush"><a href="#Pg423">423</a></span></li>

<li class="lvl2">The Boiler of Gurney's Engine
 <span class="rghtpush"><a href="#Pg423">423</a></span></li>

<li class="lvl2">His Method of cleansing Boilers
 <span class="rghtpush"><a href="#Pg428">428</a></span></li>

<li class="lvl2">Convenience and Safety of Steam Carriages
 <span class="rghtpush"><a href="#Pg432">432</a></span></li>

<li class="lvl2">Two Methods of applying Locomotive Engines upon common
Roads
 <span class="rghtpush"><a href="#Pg434">434</a></span></li>

<li class="lvl2">Horse Carriages compared with Steam
 <span class="rghtpush"><a href="#Pg435">435</a></span></li>

<li class="lvl2">Extract from Mr. Farey's Evidence before the House of
Commons
 <span class="rghtpush"><a href="#Pg435">435</a></span></li>

<li class="lvl2">Hancock's Steam Carriage
 <span class="rghtpush"><a href="#Pg436">436</a></span></li>

<li class="lvl2">How it differs from that of Mr. Gurney
 <span class="rghtpush"><a href="#Pg437">437</a></span></li>

<li class="lvl2">Ogle's Locomotive Carriage
 <span class="rghtpush"><a href="#Pg438">438</a></span></li>

<li class="lvl2">Dr. Church's Steam Engine
 <span class="rghtpush"><a href="#Pg439">439</a></span></li>


<li class="lvl1"><a href="#CHAP_XIII">CHAP. XIII.</a></li>

<li class="lvl1a">STEAM NAVIGATION.</li>

<li class="lvl2">Form and Arrangement of Marine Engines
 <span class="rghtpush"><a href="#Pg441">441</a></span></li>

<li class="lvl2">Arrangement of the Engine-room
 <span class="rghtpush"><a href="#Pg446">446</a></span></li>

<li class="lvl2">Marine Boilers
 <span class="rghtpush"><a href="#Pg448">448</a></span></li>

<li class="lvl2">Effects of Sea Water in Boilers
 <span class="rghtpush"><a href="#Pg450">450</a></span></li>

<li class="lvl2">Remedies for them
 <span class="rghtpush"><a href="#Pg451">451</a></span></li>

<li class="lvl2">Blow-off Cocks
 <span class="rghtpush"><a href="#Pg452">452</a></span></li>

<li class="lvl2">Indicators of Saltness
 <span class="rghtpush"><a href="#Pg453">453</a></span></li>

<li class="lvl2">Seaward's Indicator
 <span class="rghtpush"><a href="#Pg454">454</a></span></li>

<li class="lvl2">His Method of blowing out
 <span class="rghtpush"><a href="#Pg454">454</a></span></li>

<li class="lvl2">Field's Brine Pumps
 <span class="rghtpush"><a href="#Pg456">456</a></span></li>

<li class="lvl2">Tubular Condensers applied by Mr. Watt
 <span class="rghtpush"><a href="#Pg457">457</a></span></li>

<li class="lvl2">Hall's Condensers
 <span class="rghtpush"><a href="#Pg458">458</a></span></li>

<li class="lvl2">Substitution of Copper for Iron Boilers
 <span class="rghtpush"><a href="#Pg460">460</a></span></li>

<li class="lvl2">Process of Stoking
 <span class="rghtpush"><a href="#Pg462">462</a></span></li>

<li class="lvl2">Watt's Expedient of attaching Felt to the Boiler Surface
 <span class="rghtpush"><a href="#Pg463">463</a></span></li>

<li class="lvl2">Means of economising Fuel
 <span class="rghtpush"><a href="#Pg463">463</a></span></li>

<li class="lvl2">Number and Arrangement of Furnaces and Flues
 <span class="rghtpush"><a href="#Pg463">463</a></span></li>

<li class="lvl2">Howard's Marine Engine
 <span class="rghtpush"><a href="#Pg464">464</a></span></li>

<li class="lvl2">Application of the expansive Principle in Marine Engines
 <span class="rghtpush"><a href="#Pg466">466</a></span></li>

<li class="lvl2">Recent Improvements of Messrs. Maudslay and Field
 <span class="rghtpush"><a href="#Pg467">467</a></span></li>

<li class="lvl2">Humphrey's Marine Engine
 <span class="rghtpush"><a href="#Pg470">470</a></span></li>

<li class="lvl2">Common Paddle-wheel
 <span class="rghtpush"><a href="#Pg472">472</a></span></li>

<li class="lvl2">Feathering Paddles
 <span class="rghtpush"><a href="#Pg474">474</a></span></li>

<li class="lvl2">Galloway's Patent for a Paddle-wheel with movable Paddles
 <span class="rghtpush"><a href="#Pg476">476</a></span></li>

<li class="lvl2">Split Paddle
 <span class="rghtpush"><a href="#Pg478">478</a></span></li>

<li class="lvl2">Proportion of Power to Tonnage
 <span class="rghtpush"><a href="#Pg480">480</a></span></li>

<li class="lvl2">Improved Efficiency of Marine Engines
 <span class="rghtpush"><a href="#Pg482">482</a></span></li>

<li class="lvl2">Iron Steam Vessels
 <span class="rghtpush"><a href="#Pg483">483</a></span></li>

<li class="lvl2">Steam Navigation to India
 <span class="rghtpush"><a href="#Pg484">484</a></span></li>


<li class="lvl1"><a href="#CHAP_XIV">CHAP. XIV.</a></li>

<li class="lvl1a">AMERICAN STEAM NAVIGATION.</li>

<li class="lvl2">Steam Navigation first established in America
 <span class="rghtpush"><a href="#Pg487">487</a></span></li>

<li class="lvl2">Circumstances which led to it
 <span class="rghtpush"><a href="#Pg488">488</a></span></li>

<li class="lvl2">Attempts of Fitch and Rumsey to apply the single-acting
Engine to the Propulsion of Vessels
 <span class="rghtpush"><a href="#Pg489">489</a></span></li>

<li class="lvl2">Stevens of Hoboken commences Experiments in Steam
Navigation
 <span class="rghtpush"><a href="#Pg489">489</a></span></li>

<li class="lvl2">Experiments of Livingstone and Fulton
 <span class="rghtpush"><a href="#Pg489">489</a></span></li>

<li class="lvl2">Fulton's first Boat
 <span class="rghtpush"><a href="#Pg490">490</a></span></li>

<li class="lvl2">The Hudson navigated by Steam
 <span class="rghtpush"><a href="#Pg491">491</a></span></li>

<li class="lvl2">Extension and Improvement of River Navigation
 <span class="rghtpush"><a href="#Pg492">492</a></span></li>

<li class="lvl2">American Steamers
 <span class="rghtpush"><a href="#Pg494">494</a></span></li>

<li class="lvl2">Difference between them and European Steamers
 <span class="rghtpush"><a href="#Pg494">494</a></span></li>

<li class="lvl2">Steamers on the Hudson
 <span class="rghtpush"><a href="#Pg494">494</a></span></li>

<li class="lvl2">American Paddle-wheels
 <span class="rghtpush"><a href="#Pg495">495</a></span></li>

<li class="lvl2">Sea-going American Steamers
 <span class="rghtpush"><a href="#Pg496">496</a></span></li>

<li class="lvl2">Speed attained by American Steamers
 <span class="rghtpush"><a href="#Pg497">497</a></span></li>

<li class="lvl2">Lake Steamers
 <span class="rghtpush"><a href="#Pg499">499</a></span></li>

<li class="lvl2">The Mississippi and its Tributaries
 <span class="rghtpush"><a href="#Pg499">499</a></span></li>

<li class="lvl2">Steam-boats navigating it
 <span class="rghtpush"><a href="#Pg500">500</a></span></li>

<li class="lvl2">Their Structure and Machinery
 <span class="rghtpush"><a href="#Pg500">500</a></span></li>

<li class="lvl2">New Orleans Harbour
 <span class="rghtpush"><a href="#Pg503">503</a></span></li>

<li class="lvl2">Steam Tugs
 <span class="rghtpush"><a href="#Pg503">503</a></span></li>

<li class="lvl1"><a href="#APPENDIX">APPENDIX.</a></li>

<li class="lvl1a">
 <i>On the Relation between the Temperature, Pressure, and Density of
 Common Steam.</i></li>

<li class="lvl2">
 Empirical Formula of Biot, showing the Relation between the Pressure
and Temperature
 <span class="rghtpush"><a href="#Pg505">505</a></span></li>

<li class="lvl2">Empirical formula of</li>
<li class="lvl2"><span style="padding-left:4em;">Southern</span>
 <span class="rghtpush"><a href="#Pg506">506</a></span></li>
<li class="lvl2"><span style="padding-left:4em;">Tredgold</span>
 <span class="rghtpush"><a href="#Pg506">506</a></span></li>
<li class="lvl2"><span style="padding-left:4em;">Mellet</span>
 <span class="rghtpush"><a href="#Pg506">506</a></span></li>
<li class="lvl2"><span style="padding-left:4em;">De Pambour</span>
 <span class="rghtpush"><a href="#Pg506">506</a></span></li>
<li class="lvl2"><span style="padding-left:4em;">MM. Dulong and Arago</span>
 <span class="rghtpush"><a href="#Pg506">506</a></span></li>

<li class="lvl2">Law of the Expansion of elastic Fluids, discovered by
 Dalton and Gay Lussac
 <span class="rghtpush"><a href="#Pg506">506</a></span></li>

<li class="lvl2">Formula for the Relation between the Volumes and Temperatures
 <span class="rghtpush"><a href="#Pg507">507</a></span></li>

<li class="lvl2">Law of Mariotte
 <span class="rghtpush"><a href="#Pg507">507</a></span></li>

<li class="lvl2">Table of Pressures, Temperatures, Volumes, and Mechanical Effects
of Steam
 <span class="rghtpush"><a href="#Pg509">509</a></span></li>

<li class="lvl2">Empirical FormulÃ¦ for the Relation between the Volume of Water
and that of the Steam produced by its Evaporation under given
Pressures
 <span class="rghtpush"><a href="#Pg511">511</a></span></li>

<li class="lvl2">Formula of Navier
 <span class="rghtpush"><a href="#Pg511">511</a></span></li>

<li class="lvl2">Modified by De Pambour
 <span class="rghtpush"><a href="#Pg511">511</a></span></li>

<li class="lvl2 center"><i>On the Expansive Action of Steam.</i></li>

<li class="lvl2">Mechanical Effect produced during a given Extent of Expansion
 <span class="rghtpush"><a href="#Pg511">511</a></span></li>

<li class="lvl2">Mechanical Effect produced during Evaporation and subsequent
Expansion
 <span class="rghtpush"><a href="#Pg512">512</a></span></li>

<li class="lvl2">Application to double-acting Engines
 <span class="rghtpush"><a href="#Pg513">513</a></span></li>

<li class="lvl2">Formula for Pressure of Steam in Cylinders
 <span class="rghtpush"><a href="#Pg514">514</a></span></li>

<li class="lvl2">Formula for total Mechanical Effect per Minute of Steam when cut
off at any proposed Part of the Stroke
 <span class="rghtpush"><a href="#Pg514">514</a></span></li>

<li class="lvl2">FormulÃ¦ exhibiting the Relation between the Resistance of the
Load, the Resistances of the Engine, the Evaporation, the Speed
of the Piston, and the Magnitude of the Cylinder
 <span class="rghtpush"><a href="#Pg515">515</a></span></li>

<li class="lvl2">FormulÃ¦ showing the Relation between the Power of the Engine,
the Evaporation, and the useful Load
 <span class="rghtpush"><a href="#Pg516">516</a></span></li>

<li class="lvl2">FormulÃ¦ for the <em>useful Effect</em> and the <em>Duty</em>
 <span class="rghtpush"><a href="#Pg517">517</a></span></li>

<li class="lvl2">Estimates of the several Sources of Resistances
 <span class="rghtpush"><a href="#Pg518">518</a></span></li>

<li class="lvl2">Tables to facilitate the Computation of the Effects of Expansive
Engines
 <span class="rghtpush"><a href="#Pg519">519</a></span></li>

<li class="lvl2">Table of the Areas of Pistons
 <span class="rghtpush"><a href="#Pg520">520</a></span></li>

<li class="lvl2"><strong class="m1">Examples</strong> of the Application of these FormulÃ¦
 <span class="rghtpush"><a href="#Pg521">521</a></span></li>

<li class="lvl1"><a href="#INDEX">INDEX.</a></li>
</ul>

</div> <!--end of "contents" division-->

<div class="figcenter" style="width: 600px;">
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_022.png" width="600" height="496" alt="" />
<div class="caption">VIADUCT, NEAR WATFORD, BIRMINGHAM RAIL-ROAD.</div>
</div>

<div class="front">
<div class="fsize3">THE</div>
<div class="fsize1">STEAM ENGINE.</div>
</div>

<div class="figcenter" style="width: 420px;">
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_025.png" width="420" height="487" alt="" />
<div class="caption">HERO OF ALEXANDRIA.</div>
</div>

<h2><a name="CHAPTER_I" id="CHAPTER_I">CHAPTER I.</a></h2>

<p class="right"><a class="refpn" id="Pg003">[Pg003]</a><br />
<a href="#CONTENTS"><small>TOC</small></a>&#160;&#160;<a
href="#INDEX"><small>INX</small></a>
</p>

<div class="chapheader">
THE STEAM ENGINE, A SUBJECT OF POPULAR INTEREST.â€”THE OBJECT
OF THIS WORK.â€”DISPUTES RESPECTING THE INVENTION.â€”HERO.â€”DE
GARAY.â€”DE CAUS.â€”BRANCA.â€”MARQUIS OF WORCESTER.â€”PHYSICAL
PRINCIPLES.â€”ELASTIC AND INELASTIC FLUIDS.â€”THEIR PROPERTIES.â€”APPLICATION
OF THESE PRINCIPLES TO THE ENGINES OF HERO, DE
CAUS, AND LORD WORCESTER.â€”SIR SAMUEL MORLAND.â€”PAPIN.â€”ATMOSPHERIC
PRESSURE.â€”THE WEIGHT OF AIR.â€”LESS AT GREATER
HEIGHTS.â€”BAROMETER.â€”PRESSURE OF AIR.â€”ELASTIC FORCE OF
AIR AND GASES.â€”FORCE PRODUCED BY A VACUUM.â€”COMMON PUMP.â€”RAREFACTION
BY HEAT.â€”PAPIN'S METHODS OF PRODUCING A
VACUUM.â€”HIS DISCOVERY OF THE CONDENSATION OF STEAM.â€”SAVERY.</div>


<div class="ph3fst">
<h3>(1.)</h3> That the history of the invention of a piece of mechanism,
and the description of its structure, operation, and
 <a class="refpn" id="Pg004">[Pg004]</a>
uses, should be capable of being rendered the subject matter of
a volume, destined not alone for the instruction of engineers
or machinists, but for the information and amusement of the
public in general, is a statement which at no very remote
period would have been deemed extravagant and incredible.
</div>

<p>Advanced as we are in the art of rendering knowledge
popular, and cultivated as the public taste is in the appreciation
of the expedients by which science ministers to
the uses of life, there is still perhaps but one machine of
which such a proposition can be truly predicated: it is needless
to say that that machine is the <strong>STEAM ENGINE</strong>. There
are many circumstances attending this extraordinary piece of
mechanism which impart to it an interest so universally felt.
Whether we regard the details of its structure and operation,
the physical principles which it calls into play, and the beautiful
contrivances by which these physical principles are rendered
available;â€”or, passing over these <em>means</em>, we direct our
attention to the <em>ends</em> which they attain, we are equally
filled with astonishment and admiration. The history of the
steam engine offers to our notice a series of contrivances
which, for exquisite and refined ingenuity, stand without any
parallel in the annals of mechanical science. These admirable
inventions, unlike other results of scientific inquiry, have also
this peculiarity, that, to understand their excellence and
to perceive their beauty, no previous or subsidiary knowledge
is necessary, save what may be imparted with facility and
clearness in the progress of the explanation and development
of the machine itself. A simple and clear exposition, divested
of needless technicalities and aided by well-selected diagrams,
is all that is necessary to render the construction and operation
of the steam engine, in all its forms, intelligible to
persons of plain understanding and moderate information.</p>

<p>But if the contrivances by which this vast power is
brought to bear on the arts and manufactures, be rendered
attractive by their great mechanical beauty, how much more
imposing will the subject become when the effects which
the steam engine has produced upon the well-being of the
human race are considered. It has penetrated the crust
of the earth, and drawn from beneath it boundless treasures
<a class="refpn" id="Pg005">[Pg005]</a>
of mineral wealth, which, without its aid, would have been
rendered inaccessible; it has drawn up, in measureless quantity,
the fuel on which its own life and activity depend; it
has relieved men from their most slavish toils, and reduced
labour in a great degree to light and easy superintendence.
To enumerate its present effects, would be to count almost
every comfort and every luxury of life. It has increased
the sum of human happiness, not only by calling new
pleasures into existence, but by so cheapening former enjoyments
as to render them attainable by those who before could
never have hoped to share them: the surface of the land, and
the face of the waters, are traversed with equal facility by
its power; and by thus stimulating and facilitating the intercourse
of nation with nation, and the commerce of people
with people, it has knit together remote countries by bonds of
amity not likely to be broken. Streams of knowledge and
information are kept flowing between distant centres of population,
those more advanced diffusing civilisation and improvement
among those that are more backward. The press
itself, to which mankind owes in so large a degree the rapidity
of their improvement in modern times, has had its power
and influence increased in a manifold ratio by its union with
the steam engine. It is thus that literature is cheapened,
and, by being cheapened, diffused; it is thus that Reason has
taken the place of Force, and the pen has superseded the
sword; it is thus that war has almost ceased upon the earth,
and that the differences which inevitably arise between people
and people are for the most part adjusted by peaceful negotiation.</p>

<p>Deep as the interest must be with which the steam engine
will be regarded in every civilised country, it presents peculiar
claims upon the attention of the people of Great Britain.
Its invention and progressive improvement are the work of
our own time and our own country; it has been produced
and matured almost within the last century, and is the exclusive
offspring of British genius, fostered and sustained by
British enterprise and British capital.</p>

<p>The steam engine is a mechanical contrivance, by which
coal, wood, or other fuel is rendered capable of executing any
<a class="refpn" id="Pg006">[Pg006]</a>
kind of labour. <strong class="m1">Coals</strong> are by it made to spin, weave, dye,
print and dress silks, cottons, woollens, and other cloths; to
make paper, and print books upon it when made; to convert
corn into flour; to express oil from the olive, and wine from
the grape; to draw up metal from the bowels of the earth;
to pound and smelt it, to melt and mould it; to forge it; to
roll it, and to fashion it into every desirable form; to transport
these manifold products of its own labour to the doors
of those for whose convenience they are produced; to carry
persons and goods over the waters of rivers, lakes, seas, and
oceans, in opposition alike to the natural difficulties of wind
and water; to carry the wind-bound ship out of port; to place
her on the open deep ready to commence her voyage; to throw
its arms around the ship of war, and place her side by side
with the enemy; to transport over the surface of the deep
persons and information, from town to town, and from country
to country, with a speed as much exceeding that of the ordinary
wind, as the ordinary wind exceeds that of a common
pedestrian.</p>

<p>Such are the virtues, such the powers, which the steam
engine has conferred upon <strong>COALS</strong>. The means of calling
these powers into activity are supplied by a substance which
nature has happily provided in unbounded quantity in every
part of the earth; and though it has no price, it has inestimable
value: this substance is <strong>WATER</strong>.</p>

<p>A pint of water may be evaporated by two ounces of coals.
In its evaporation it swells into two hundred and sixteen
gallons of steam, with a mechanical force sufficient to raise
a weight of thirty-seven tons a foot high. The steam thus
produced has a pressure equal to that of common atmospheric
air; and by allowing it to expand, by virtue of its elasticity,
a further mechanical force may be obtained, at least equal
in amount to the former. A pint of water, therefore, and two
ounces of common coal, are thus rendered capable of doing as
much work as is equivalent to seventy-four tons raised a foot
high.</p>

<p>The circumstances under which the steam engine is worked
on a railway are not favourable to the economy of fuel. Nevertheless
a pound of coke burned in a locomotive engine
<a class="refpn" id="Pg007">[Pg007]</a>
will evaporate about five pints of water. In their evaporation
they will exert a mechanical force sufficient to draw two tons
weight on the railway a distance of one mile in two minutes.
Four horses working in a stage-coach on a common road are
necessary to draw the same weight the same distance in six
minutes.</p>

<p>A train of coaches weighing about eighty tons, and transporting
two hundred and forty passengers with their luggage,
has been taken from Liverpool to Birmingham, and back from
Birmingham to Liverpool, the trip each way taking about four
hours and a quarter, stoppages included. The distance between
these places by the railway is ninety-five miles. This double
journey of one hundred and ninety miles is effected by the
mechanical force produced in the combustion of four tons
of coke, the value of which is about five pounds. To carry
the same number of passengers daily between the same places
by stage-coaches on a common road, would require twenty
coaches and an establishment of three thousand eight hundred
horses, with which the journey in each direction would be
performed in about twelve hours, stoppages included.</p>

<p>The circumference of the earth measures twenty-five
thousand miles; and if it were begirt with an iron railway,
such a train as above described, carrying two hundred and
forty passengers, would be drawn round it by the combustion
of about thirty tons of coke, and the circuit would be accomplished
in five weeks.</p>

<p>In the drainage of the Cornish mines the economy of fuel
is much attended to, and coals are there made to do more
work than elsewhere. A bushel of coals usually raises forty
thousand tons of water a foot high; but it has on some occasions
raised sixty thousand tons the same height. Let us
take its labour at fifty thousand tons raised one foot high.
A horse worked in a fast stage-coach pulls against an average
resistance of about a quarter of a hundred weight. Against
this he is able to work at the usual speed through about
eight miles daily: his work is therefore equivalent to one
thousand tons raised one foot. A bushel of coals consequently,
as used in Cornwall, performs as much labour as a
day's work of one hundred such horses.
<a class="refpn" id="Pg008">[Pg008]</a></p>

<p>The great pyramid of Egypt stands upon a base measuring
seven hundred feet each way, and is five hundred feet high,
its weight being twelve thousand seven hundred and sixty
millions of pounds. Herodotus states, that in constructing it
one hundred thousand men were constantly employed for
twenty years. The materials of this pyramid would be raised
from the ground to their present position by the combustion
of about four hundred and eighty tons of coals.</p>

<p>The Menai Bridge consists of about two thousand tons of
iron, and its height above the level of the water is one
hundred and twenty feet. Its mass might be lifted from the
level of the water to its present position by the combustion of
four bushels of coal.</p>

<p>The enormous consumption of coals produced by the application
of the steam engine in the arts and manufactures, as
well as to railways and navigation, has of late years excited
the fears of many as to the possibility of the exhaustion of
our coal-mines. Such apprehensions are, however, altogether
groundless. If the present consumption of coal be estimated
at sixteen millions of tons annually, it is demonstrable that
the coal-fields of this country would not be exhausted for
many centuries.</p>

<p>But in speculations like these, the probable, if not certain
progress of improvement and discovery ought not be overlooked;
and we may safely pronounce that, long before
such a period of time shall have rolled away, other and
more powerful mechanical agents will supersede the use of
coal. Philosophy already directs her finger at sources of
inexhaustible power in the phenomena of electricity and
magnetism. The alternate decomposition and recomposition
of water, by magnetism and electricity, has too close an
analogy to the alternate processes of vaporisation and condensation,
not to occur at once to every mind: the development
of the gases from solid matter by the operation
of the chemical affinities, and their subsequent condensation
into the liquid form, has already been essayed as a source
of power. In a word, the general state of physical science
at the present moment, the vigour, activity, and sagacity
with which researches in it are prosecuted in every civilised
<a class="refpn" id="Pg009">[Pg009]</a>
country, the increasing consideration in which scientific
men are held, and the personal honours and rewards which
begin to be conferred upon them, all justify the expectation
that we are on the eve of mechanical discoveries still greater
than any which have yet appeared; and that the steam engine
itself, with the gigantic powers conferred upon it by the
immortal Watt, will dwindle into insignificance in comparison
with the energies of nature which are still to be revealed; and
that the day will come when that machine, which is now extending
the blessings of civilisation to the most remote skirts
of the globe, will cease to have existence except in the page
of history.</p>


<div class="ph3"><h3>(2.)</h3> The object of the present volume will be to deliver, in
an easy and familiar style, an historical view of the invention
of the steam engine, and an exposition of its structure and
operation in the various forms in which it is now used,
and of its most important applications in the arts of life,
especially in transport by land and water. It is hoped
that the details of these subjects may be rendered easily intelligible
to all persons of ordinary information, whether
urged by that natural and laudable spirit of inquiry awakened
by contemplating effects on the material and social condition
of our species, so rapid and so memorable as those which have
followed the invention of the steam engine, and by the pleasure
which results from the perception of the numerous instances
of successful contrivances and beautiful applications of
science to art which it unfolds,â€”or impelled by the exigencies
of trade or profession to acquire an acquaintance with a
machine on which, more than any other, the prosperity of
our commercial and manufacturing interests depends. It will
be our aim to afford to the former class all the information
which they can require; and, if this work be not as comprehensive
in its scope, and as minute in its details, as some of
the latter may wish, it will at least serve as an easy and
convenient introduction to other works more voluminous,
costly, and detailed, but less elementary in their matter, and
less familiar in their style.</div>

<p>In explaining the different forms of steam engine which
have been proposed in the course of the progressive improvement
<a class="refpn" id="Pg010">[Pg010]</a>
of that machine from its early rude and imperfect state
to its present comparatively perfect form, it will be necessary
to advert to various physical phenomena and mechanical
principles, which, however obvious to those who are conversant
with matters of science, must necessarily be at least imperfectly
known by the great majority of our readers. To
refer for information on such topics to other works on
Mechanics and general Physics, would be with most readers
ineffectual, and with all unsatisfactory. In former editions of
the present work, we consigned these necessary general principles
of physics and mechanics to a preliminary chapter;
but it appears, on the whole, more convenient not to remove
the exposition of the principle from the place where its application
is required. We shall therefore pause as we proceed,
where these difficulties occur, to give such explanation and
illustration as may seem best suited to render them intelligible
and interesting to the unscientific reader.</p>

<p>The history of the arts and manufactures affords no example
of any invention the credit for which has been claimed
by so many different nations and individuals as that of the
steam engine. The advocates of the competitors for this
honour have urged their pretensions, and pressed their claims,
with a zeal which has occasionally outstripped the bounds of
discretion, and the contest has not unfrequently been tinged
with prejudices, national and personal, and characterised by
a degree of asperity altogether unworthy of so noble a cause,
and beneath the dignity of science.</p>

<p>"When a question is clearly proposed, it is already half
resolved." Let us see whether a careful attention to this
maxim will aid us in the investigation of the origin of the
steam engine. The source of the power of that machine is
found in the following natural phenomena.</p>

<ol class="nomarker">
<li><em>First.</em> When fire is applied to water, the liquid swells
into vapour, and in undergoing this change exerts, as has
been already stated, a considerable amount of mechanical
force. This force may, by proper means, be rendered applicable
to any purpose for which labour or power is needful.</li>

<li><em>Second.</em> The vapour so produced is endowed with the
property of elasticity, in virtue of which it is capable of
<a class="refpn" id="Pg011">[Pg011]</a>
swelling or expanding into increased dimensions, exerting, as
it expands, a force, the energy of which is gradually diminished
as the dimensions of the vapour are increased. This mechanical
force is likewise capable of being applied to any
useful purpose for which labour or power is necessary.</li>

<li><em>Third.</em> This vapour is capable, by proper means, of being
reconverted into water; and when so reconverted, it shrinks
into its original dimensions, deserting the large space which
it occupied as vapour, and leaving that space a vacuum. It
is known in physics, that when a vacuum is produced, surrounding
bodies have a tendency to rush into it with a definite
amount of force. Consequently any agent which produces a
vacuum, becomes a source of a considerable amount of mechanical
power. By its reconversion into water, therefore,
steam again becomes a mechanical agent.</li>
</ol>

<p>Such are the natural phenomena in which are found the
original sources of all steam power. In some forms of steam
engine one of these is used, and in some another, and in
some the application of all of them is combined; but in no
existing form of steam engine whatever is there any other
source of mechanical power.</p>

<p>Neither these nor any other natural forces can be applied
<em>immediately</em> to any useful purpose. The interposition of
mechanism is indispensable; on the invention and contrivance
of that mechanism depends altogether the useful application
of these natural forces.</p>

<p>The world owes the steam engine then partly to <em>discovery</em>,
and partly to <em>invention</em>.</p>

<p>He that discovered the fact, that mechanical force was
produced in the conversion of water into steam, must be justly
held to be a sharer in the merit of the steam engine, even
though he should never have practically applied his discovery.
The like may be said of him who first discovered the
source of the mechanical power arising from the expansion
of steam.</p>

<p>The discoverer of the fact, that steam being reconverted
into water greatly contracted its dimensions, and thereby
produced a vacuum, is likewise entitled to a share of the
credit.
<a class="refpn" id="Pg012">[Pg012]</a></p>

<p>The mechanism by which these natural forces have been
rendered so universally available as a moving power, is very
various and complicated, and cannot be traced to one inventor.
"If a watchmaker," says M. Arago, "well instructed
in the history of his art, were required to give a categorical
answer to the question, Who has invented watches? he would
remain mute; but the question would be divested of much
of its difficulty if he were required separately to declare who
discovered the use of the main spring, the different forms of
escapement, or the balance wheel." So it is with the steam
engine. It is a combination of a great variety of contrivances,
distinct from each other, which are the production of several
inventors. If, however, one name more than the rest be
entitled to special notice; if <i>he</i> is entitled to the chief
credit of the invention who by the powers of his mechanical
genius has imparted to the steam engine that form,
and conferred upon it those qualities, on which mainly
depends its present extensive utility, and by which it has
become an agent of transcendant power, spreading its beneficial
effects throughout every part of the civilised globe,
then the universal voice will, as it were by acclamation,
award the honour to one individual, whose pre-eminent
genius places him far above all other competitors, and from
the application of whose mental energies to this machine
may be dated those grand effects which render it a topic of
interest to all for whom the progress of civilisation has any
attractions. Before the era rendered memorable by the discoveries
of <strong class="m1">James Watt</strong>, the steam engine, which has since
become an object of such universal interest, was a machine
of extremely limited power, inferior in importance and usefulness
to most other mechanical agents used as prime
movers; but, from that epoch, it is scarcely necessary here
to state, that it became a subject not of British interest only,
but one having an important connection with the progress of
the human race.</p>

<p class="txthead3">Hero of Alexandria, 120 B. C.</p>

<div class="figright" style="width: 300px;">
<a id="Fig001"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_035.png" width="300" height="242" alt="" />
<div class="caption figure">Fig. 1.</div>
</div>

<div class="ph3"><h3>(3.)</h3>
The discovery of the fact, that a mechanical force is
produced when water is evaporated by the application of heat,
<a class="refpn" id="Pg013">[Pg013]</a>
must be considered as the first capital step in the invention
of the steam engine. It is recorded in a work entitled <cite>Spiritalia
seu Pneumatica</cite>, that Hero of Alexandria contrived a
machine, 120 years before the Christian era, which was moved
by the mechanical force of the vapour of water. The principle
of this machine admits of easy explanation: When a
fluid issues from any vessel in which it is confined, that vessel
suffers a force equal to that with which the fluid escapes from
it, and in the opposite direction. If water issues from an
orifice, a pressure is produced behind the orifice corresponding
to the force with which the water escapes. If a man discharge
a gun, the gases produced by the explosion of the
powder issue with a certain force from the muzzle, and his
shoulder is driven backwards by the recoil with a corresponding
force. If the muzzle, instead of being presented forwards,
were turned at right angles to the length of the gun, then, as
the gases of explosion would escape sideways, the recoil would
likewise take place sideways, and the shooter, instead of being
driven backward, would be made to spin round as a dancer
pirouettes. This was the principle of Hero's steam engine.
A small globe or ball was
placed on pivots at <strong>A</strong> and
<strong>B</strong> (<a href="#Fig001"><i>fig.</i> 1.</a>), on which it was
capable of revolving: steam
was supplied through one
of these pivots from one of
the tubes <strong>D C E F</strong>, which
communicated with the
boiler. This steam filled the
globe <strong>A I B K</strong>, and also the
arms <strong>I H</strong> and <strong>K G</strong>.
A lateral orifice, represented at <strong>G</strong>, near
the end of these arms, allowed the steam to escape in a jet,
and the reaction, producing a recoil, had a tendency to drive
the arm round. A small orifice at <strong>H</strong>,
on the other side
of the tube, produced a like effect. In the same manner,
any convenient number of arms might be provided, surrounding
the globe and communicating with its interior like the
spokes of a wheel. Thus these arms, having lateral orifices
for the escape of the steam, all placed so that the recoil may
<a class="refpn" id="Pg014">[Pg014]</a>
tend to turn the globe in the same direction, a rotatory
motion might be communicated to any machinery which it
was desired to move.</div>

<p>After having been allowed to slumber for nearly two thousand
years, this machine has recently been revived, and
engines constructed similar to it are now working in these
countries. In the proper place we shall describe Avery's
Rotatory Engine, which it will be seen is, not only in its
principle, but almost in its details, the machine of <strong class="m1">Hero of
Alexandria</strong>.</p>

<p>Although the elastic force of steam was not reduced to numerical
measure by the ancients, nor brought under control,
nor applied to any useful purpose, yet it appears to have been
recognised in vague and general terms. Aristotle, Seneca, and
other ancient writers, accounted for earthquakes by the sudden
conversion of water into steam within the earth. This change,
according to them, was effected by subterranean heat. Such
tremendous effects being ascribed to steam, it can scarcely be
doubted that the Greeks and Romans were acquainted with the
fact, that water in passing into vapour exercises considerable
mechanical power. They were aware that the earthquakes,
which they ascribed to this cause, exerted forces sufficiently
powerful to extend the natural limits of the ocean; to overturn
from their foundations the most massive monuments of
human labour; to raise islands in the midst of seas; and to
heave up the surface of the land of level continents so as to
form lofty mountains.</p>

<p>Such notions, however, resulted not as consequences of any
exact or scientific principles, but from vague analogies derived
from effects which could not fail to have been manifested
in the arts, such as those which commonly occurred in the
process of casting in metal the splendid statues which adorned
the temples, gardens, and public places of Rome and Athens.
The artisan was liable to the same accidents to which modern
founders are exposed, produced by the casual presence of a
little water in the mould into which the molten metal is
poured. Under such circumstances, the sudden formation
of steam of an extreme pressure produces, as is well known,
explosions attended with destructive effects. The Grecian
<a class="refpn" id="Pg015">[Pg015]</a>
and Roman artisans were subject to such accidents; and the
philosopher, generalising such a fact, would arrive at a solution
of the grander class of phenomena of earthquakes and volcanoes.</p>

<p>Before natural phenomena are rendered subservient to purposes
of utility, they are often made to minister to the objects
of superstition. The power of steam is not an exception to
this rule. It is recorded in the Chronicles, that upon the
banks of the Weser the ancient Teutonic gods sometimes
marked their displeasure by a sort of thunderbolt, which was
immediately succeeded by a cloud that filled the temple. An
image of the god <i>Busterich</i>, which was found in some excavations,
clearly explains the manner in which this prodigy
was accomplished by the priests. The head of the metal god
was hollow, and contained within it a pot of water: the
mouth, and another hole, above the forehead, were stopped
by wooden plugs; a small stove, adroitly placed in a cavity
of the head under the pot, contained charcoal, which, being
lighted, gradually heated the liquid contained in the head.
The vapour produced from the water, having acquired sufficient
pressure, forced out the wooden plugs with a loud report,
and they were immediately followed by two jets of steam,
which formed a dense cloud round the god, and concealed him
from his astonished worshippers.<a name="FNanchor_1_1"
id="FNanchor_1_1"></a><a href="#Footnote_1_1" class="fnanchor">[1]</a></p>

<p>Among other amusing anecdotes showing the knowledge
which the ancients had of the mechanical force of steam, it is
related that Anthemius, the architect of Saint Sophia, occupied
a house next door to that of Zeno, between whom and
Anthemius there existed a feud. To annoy his neighbour,
Anthemius placed on the ground floor of his own house several
close digesters, or boilers, containing water. A flexible tube
proceeded from the top of each of these, which was conducted
through a hole made in the wall between the houses, and
which communicated with the space under the floors of the
rooms in the house of Zeno. When Anthemius desired to annoy
his neighbour, he lighted fires under his boilers, and the
steam produced by them rushed in such quantity and with
<a class="refpn" id="Pg016">[Pg016]</a>
such force under Zeno's floors, that they were made to heave
with all the usual symptoms of an earthquake.<a name="FNanchor_2_2"
id="FNanchor_2_2"></a><a href="#Footnote_2_2" class="fnanchor">[2]</a></p>

<p class="txthead3">Blasco de Garay, A. D. 1543.</p>

<div class="ph3">
<h3>(4.)</h3> In the year 1826, M. de Navarrete published, in Zach's
Astronomical Correspondence, a communication from Thomas
Gonzales, Director of the royal archives of Simancas, giving
an account of an experiment reported to have been made in
the year 1543, in which a vessel was propelled by a machine
having the appearance of a steam engine.</div>

<p>Blasco de Garay, a sea captain, proposed in that year to
the Emperor Charles V. to propel vessels by a machine which
he had invented, even in time of calm, without oars or
sails. Notwithstanding the apparent improbability attending
this project, the Emperor ordered the experiment to be
made in the port of Barcelona, and the 17th of June, 1543,
was the day appointed for its trial. The commissioners appointed
by Charles V. to attend and witness the experiment
were Don Henry of Toledo, Don Pedro of Cardona, the treasurer
Ravago, the vice chancellor and intendant of Catalonia,
and others. The vessel on which the experiment was made
was the Trinity, 200 tons burthen, which had just discharged a
cargo of corn at Barcelona. Garay concealed the nature of
his machinery, even from the commissioners. All that could
be discovered during the trial was, that it consisted of a large
boiler containing water, and that wheels were attached to each
side of the vessel, by the revolution of which it was propelled.
The commissioners having witnessed the experiment, made a
report to the king, approving generally of the invention, particularly
on account of the ease and promptitude with which
the vessel could be put about by it.</p>

<p>The treasurer Ravago, who was himself hostile to the project,
reported that the machine was capable of propelling a
vessel at the rate of two leagues in three hours; but the
other commissioners stated that it made a league an hour at
the least, and that it put the vessel about as speedily as would
be accomplished with a galley worked according to the common
<a class="refpn" id="Pg017">[Pg017]</a>
method. Ravago reported that the machinery was too
complicated and expensive, and that it was subject to the
danger of the boiler bursting.</p>

<p>After the experiment was made, Garay took away all the
machinery, leaving nothing but the framing of wood in the
arsenals of Barcelona.</p>

<p>Notwithstanding the opposition of Ravago, the invention
was approved, and the inventor was promoted and received a
pecuniary reward, besides having all his expenses paid.</p>

<p>From the circumstance of the nature of the machinery
having been concealed, it is impossible to say in what this
machine consisted; but as a boiler was used, it is probable,
though not certain, that steam was the agent. There have
been various machines proposed, of which a furnace and
boiler form a part, and in which the agency of steam is
not used. The machine of Amontons furnishes an example
of this. It is most probable that the contrivance of Garay
was identical with that of Hero. The low state of the arts
in Spain in the sixteenth century would be incompatible with
the construction of any machine requiring great precision of
execution. But the simplicity of Hero's contrivance would
have rendered its construction and operation quite practicable.
As to the claims to the invention of the steam engine advanced
by the advocates of De Garay, founded on the above
document, a refutation is supplied by the admission, that
though he was rewarded and promoted by the government of
the day, in consequence of the experiment, and although the
great usefulness of the contrivance in towing ships out of
port, &#38;c., was admitted, yet it does not appear that a second
experiment was ever tried, much less that the machine was
ever brought into practical use.</p>

<p class="txthead3">Solomon de Caus, 1615.</p>

<div class="ph3"><h3>(<a id="h3-5"></a>5.)</h3>
Solomon De Caus was engineer and architect to
Louis XIII., king of France, before the year 1612. In that
year he entered the service of the Elector Palatine, who
married the daughter of King James I., with whom he came
to England. He was there employed by the Prince of
Wales in ornamenting the gardens of his house at Richmond.
<a class="refpn" id="Pg018">[Pg018]</a>
During his sojourn in England he composed and published at
London, in the same year, a Treatise on Perspective. This
person was the author of a work entitled, "<cite>Les Raisons des
Forces Mouvantes, avec diverses Machines tant utiles que
plaisantes</cite>," which was apparently composed at Heidelburg,
but published at Franckfort, in 1615. The same work was
subsequently republished in Paris in 1623.
</div>

<p>The treatise commences with definitions of what were then
considered the four elements: earth, air, fire, and water.
Air is defined to be a cold, dry, and light element, capable of
compression, by which it may be rendered very violent. He
says, "The violence will be great when water exhales in air
by means of fire, and that the said air is enclosed: as, for
example, take a ball of copper of one or two feet diameter,
and one inch thick, which being filled with water by a small
hole, which shall be strongly stopped with a peg, so that
neither air nor water can escape, it is certain that if we put
the said ball upon a great fire, so that it will become very
hot, that it will cause a compression so violent, that the ball
will burst in pieces, with a noise like a petard."</p>

<p>The effect which is here described is due to the combined
pressure of the heated air contained in the ball and the high
pressure steam raised from the water, but much more to the
latter than to the former. It is evident, however, from the
language of De Caus, that he ascribes the force entirely to
the air, and seems to consider that the force of the air proceeded
from the water which exhaled in it.</p>

<p>The first theorem is, "that the parts of the elements mix
together for a time, and then each returns to its place" (the
elements here referred to being apparently air and water).
Upon this subject the following is an example: "Take a
round vessel of copper, soldered close on every side, and
with a tube, whereof one end approaches nearly to the
bottom of the vessel, and the other end, which projects on
the outside of the vessel, has a stop-cock; there is also a hole
in the top of the vessel, with a plug to stop it. If this vessel
will contain three pots of water, then pour in one pot of
water, and place the vessel on the fire about three or four
minutes, leaving the hole open; then take the vessel off the
<a class="refpn" id="Pg019">[Pg019]</a>
fire, and a little after pour out the water at the hole, and it
will be found that a part of the said water has been evaporated
by the heat of the fire. Then pour in one pot of
water as before, and stop up the hole and the cock, and
put the vessel on the fire for the same time as before; then
take it off, and let it cool of itself, without opening the plug,
and after it is quite cold pour out the water, and it will be
found exactly the same quantity as was put in. Thus we see
that the water which was evaporated (the first time that the
vessel was put on the fire) is returned into water the second
time when that vapour has been shut up in the vessel, and
cooled of itself."</p>

<p>In the description of these experiments, the processes of
evaporation and condensation are obscurely indicated; but
there is no intimation that the author possessed any knowledge
of the elastic force of steam. His theorem is, that the
parts of the element water mix for a time with the parts of
the element air; that fire causes this mixture, and that on
removing the fire, and dissipating the heat, then the parts of
the water mixed with air return to their proper place, forming
again part of the water. There is no indication of a
<em>change of property</em> of the water in passing into vapour. It
is difficult to conceive, if De Caus had been aware that the
vapour of water possessed the same violent force which he
distinctly and in terms ascribes to air, or if he had been
aware that in effect the vapour of the water produced by the
fire was a fluid, possessing exactly the same mechanical
qualities, and producing the same mechanical effects as air,
that he would not have expressed himself clearly on the
subject.</p>

<p>He proceeds to give another demonstration that heat will
cause the particles of water to mix with those of air.</p>

<p>"After having put the measure of water into the vessel,
and shut the vent-hole, and opened the cock, put the vessel
on the fire, and put the pot under the cock; then the water
of the vessel, raising itself by the heat of the fire, will run
out through the cock; but about one sixth or one eighth
part of the water will not run out, because the violence of
the vapour which causes the water to rise proceeds from the
<a class="refpn" id="Pg020">[Pg020]</a>
said water; which vapour goes out through the cock after the
water with great violence. There is also another example in
quicksilver, or mercury, which is a fluid mineral, but being
heated by fire, exhales in vapour, and mixes with the air for
a time; but after the said vapour is cooled, it returns to its
first nature of quicksilver. The vapour of water is much
lighter, and therefore it rises higher," &#38;c. &#38;c.</p>

<p>In this second demonstration there appears to be some
obscure indication of the force of steam in the words "because
of the violence of the vapour which causes the water
to rise," &#38;c.</p>

<p>The fifth theorem is the following:â€”</p>

<p>"<em>Water will mount by the help of fire higher than its level</em>,"
which is explained and proved in the following terms:â€”</p>

<div class="figleft" style="width: 225px;">
<a id="Fig002"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_042.png" width="225" height="302" alt="" />
<div class="caption figure">Fig. 2.</div>
</div>

<p>"The third method of raising water is by the aid of fire.
On this principle may be constructed various machines: I
shall here describe one. Let a ball
of copper marked <strong>A</strong>; well soldered in
every part, to which is attached a
tube and stop-cock marked <strong>D</strong>, by
which water may be introduced; and
also another tube marked <strong>B C</strong>, which
will be soldered into the top of the
ball, and the lower end <strong>C</strong> of which
shall descend nearly to the bottom of
the ball without touching it. Let
the said ball be filled with water
through the tube <strong>D</strong>, then shutting the stop-cock
<strong>D</strong>, and
opening the stop-cock in the vertical tube <strong>B C</strong>, let the ball be
placed upon a fire the heat acting upon the said ball will
cause the water to rise in the tube <strong>B C</strong>."</p>

<p>In the apparatus as here described, the space enclosed in
the boiler above the surface of the water is filled with air.
By the action of the fire, two effects are produced: first, the
air enclosed above the water, being heated, acquires increased
elasticity, and presses with a corresponding force on the surface
of the water. By this means a column of water will be
driven up the tube <strong>A B</strong> at such a height as will balance the
elasticity of the heated air confined in the boiler; but besides
<a class="refpn" id="Pg021">[Pg021]</a>
this the water contained in the boiler being heated, will produce
steam, which being mixed with air contained in the
boiler, will likewise press with its proper elasticity on the
surface of the water, and will combine with the air in raising
a column of water in the tube <strong>A B</strong>. In the above description
of the machine, the force which raises the water in the tube
<strong>A B</strong> is ascribed to the fire, no mention being made of the
water, or of the vapour or steam produced from it having any
agency in raising the water in the tube <strong>A B</strong>.</p>

<p>Antecedently to the date of this invention, the effect of
heat in increasing the elastic force of air was known, and so
far as the above description goes, the whole operation might
be ascribed to the air by a person having no knowledge
whatever of the elasticity of steam. M. Arago, however,
who, on the grounds of this passage in the work of De Caus,
claims for him a share of the honour of the invention of the
steam engine, contends that the agency of steam in this
apparatus was perfectly known to De Caus, although no
mention is made of steam in the above description, because
in the second demonstration above quoted he uses the words,
"the violence of the vapour which causes the water to rise
proceeds from the said water; which vapour goes out from the
cock after the water with great violence." By these words
M. Arago considers that De Caus expresses the quality of
elasticity proper to the vapour, and that the context justifies
the inference, that to this elasticity he ascribed the elevation
of the water in the tube <strong>C B</strong>.</p>

<p>There appears to be some uncertainty attending the birthplace
of De Caus. In the <cite>Biographie Universelle</cite> he is said
to have been born and to have died in Normandy. M. Arago
assigns Dieppe, or its neighbourhood, as his birthplace.</p>

<p>There was another engineer and architect, Isaac De Caus,
a native of Dieppe, who published a work in folio, entitled
"<cite>Nouvelle Invention de Lever l'Eau plus haut que sa Source,
avec quelque Machines mouvantes, par le Moyen de l'Eau, et
un Discours de la Conduite d'Icelle</cite>." This volume is without
a date, but from the nature of its contents it would appear to
have been published before the work of Solomon De Caus already
cited. The drawings and machines described in both
<a class="refpn" id="Pg022">[Pg022]</a>
are exactly the same; but the definitions and theorems quoted
above on raising water by fire are not given in the work of
Isaac. It seems, therefore, that Solomon De Caus re-published,
with additions, the work of Isaac De Caus. From the
same birthplace being assigned to both these authors, as well
as from the similarity of their pursuits, it is likely they were
members of the same family, and from their christian names
they were probably Jews.</p>

<p>The work cited above, was dedicated to Louis XIII., and
in the dedication Solomon De Caus calls himself the subject
of that monarch; and in the privilege prefixed to the work
he is designated, "Our well-beloved Solomon De Caus, master
engineer, being at present in the service of our dear and
well-beloved cousin, the Prince Elector Palatine, has made
known to us," &#38;c.â€”"we, desiring to gratify the said De
Caus, he being our subject," &#38;c.</p>

<p>It is therefore certain, whatever may have been the
birthplace of De Caus, that he was at least a subject of
France. The circumstance of his work being written in
French, though published beyond the Rhine, is also an argument
in favour of his being a native of that country.</p>

<p class="txthead3">Giovanni Branca, 1629.</p>

<div class="ph3"><h3>(6.)</h3> Giovanni Branca of Loretto in Italy, an engineer and
architect, proposed to work mills of different kinds by steam
issuing from a large Ã¦olopile, and blowing against the vanes of
a wheel. Branca was the author of many ingenious mechanical
inventions, a collection of which he dedicated to M. Cenci,
the governor of Loretto. These were published in a work
printed at Rome in 1629. It is a thin quarto, entitled "<cite>Le
Machine volume nuovo, et di molto artificio da fare effetti maravigliosi
tanto Spiritali quanto di Animale Operatione, arichito
di bellissime figure. Del Sig. Giovanni Branca, Cittadino Romano.
In Roma, 1629.</cite>" The work contains sixty-three engravings,
accompanied by descriptions in Italian and Latin.
Branca's steam engine, represented in the twenty-fifth plate,
consists of a wheel furnished with flat vanes upon its rim, like
the boards of a paddle wheel. The steam is produced in a
close vessel, and made to issue with violence from the extremity
<a class="refpn" id="Pg023">[Pg023]</a>
of a pipe directed against the vanes, and causes
the wheel to revolve. This motion being imparted by the
usual mechanical contrivances, any machinery may be impelled
by it. Different useful applications of this power are
contained in the work, viz. pestles and mortars for pounding
materials to make gunpowder, and rolling stones for grinding
the same; machines for raising water by buckets, for sawing
timbers, for driving piles, &#38;c. &#38;c.
</div>

<p>This method of applying the force of steam has no analogy
to any application of steam in modern engines.</p>

<p class="txthead3">Edward Somerset, Marquis of Worcester, 1663.</p>

<div class="ph3">
<h3>(<a id="h3-7"></a>7.)</h3> Of all the names which figure in the early annals of
steam, by far the most remarkable is that of the Marquis of
Worcester, who has left a description of a machine in a work,
entitled "<cite>The Scantling of One Hundred Inventions</cite>," which
has been generally in this country considered as giving him a
right to the honour of having been the inventor of the steam
engine.</div>

<p>Lord Worcester having been engaged on the side of the
Royalists in the civil wars of the revolution, lost his fortune,
and went to Ireland, where he was imprisoned. He escaped
from thence, and reached France; from that country he ventured
to London, as a secret agent of Charles II., but was
detected, and imprisoned in the Tower, where he remained
until the restoration, when he was set at liberty. Tradition
has connected the invention of the steam engine with the
following anecdote:â€”One day, during his imprisonment,
Lord Worcester observed the lid of the pot in which his
dinner was being cooked, suddenly forced upwards by the
vapour of the water which was boiling in it. Reflecting on
this, it occurred to him that the same force which raised the
cover of the pot might be rendered, when properly applied, a
useful and convenient moving power. After he recovered
his liberty, he accordingly proceeded to carry into effect this
conception. The contrivance to which he was ultimately led
is described in the following terms in the sixty-eighth invention,
in the work above named:â€”</p>

<p>"I have invented an admirable and forcible way to drive
<a class="refpn" id="Pg024">[Pg024]</a>
up water by fire; not by drawing or sucking it upwards, for
that must be, as the philosopher terms it, <i>infra sphÅ“rum
activitatis</i>, which is but at such a distance. But this way
hath no bounder if the vessels be strong enough. For I have
taken a piece of whole cannon whereof the end was burst,
and filled it three quarters full of water, stopping and screwing
up the broken end, as also the touch-hole, and making a
constant fire under it; within twenty-four hours, it burst
and made a great crack. So that, having a way to make my
vessels so that they are strengthened by the force within
them, and the one to fill after the other, I have seen the
water run like a constant fountain stream forty feet high.
One vessel of water rarefied by fire driveth up forty of cold
water, and a man that tends the work has but to turn two
cocks; that one vessel of water being consumed, another
begins to force and refill with cold water, and so successively;
the fire being tended and kept constant, which the self-same
person may likewise abundantly perform in the interim between
the necessity of turning the said cocks."</p>

<p>Since the date of the publication of the "Century of Inventions"
was the year 1663, the experiments here mentioned
must have been made before that year. The description of
the machine here given, as well as others in the same work,
was intended by the author, not to convey a knowledge of the
nature of the mechanism which he used, but only to express
the effects produced, and to indicate the physical principle on
which they depended. It should also be observed, that an
air of mystery was thrown by Worcester over the accounts of
all the machines which he described; and therefore any obscurity
in the above description ought not to be regarded as an
evidence against his claim to the discovery of the mechanical
agency of steam, so far as that agency is indicated by the
effects said by him to be produced. The above account is,
however, sufficiently distinct and explicit to enable any one
possessing a knowledge of the mechanical qualities of steam
to perceive the general nature of the machine described. To
render this machine, and that of De Caus, previously described,
intelligible to those who are not familiar with physical science,
we must here explain some general principles on which their
agency depends.
<a class="refpn" id="Pg025">[Pg025]</a></p>


<div class="ph3">
<h3>(8.)</h3> Fluid bodies are of two kinds, inelastic fluids, or liquids,
and elastic fluids, or gases. Of the former of these
classes, water is the most familiar example, and of the latter,
air.</div>

<p>These two species of fluids are each distinguished by peculiar
mechanical properties.</p>

<div class="figright" style="width: 240px;">
<a id="Fig003"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_047.png" width="240" height="196" alt="" />
<div class="caption figure">Fig. 3.</div>
</div>

<div class="ph3"><h3>(9.)</h3> The constituent particles of a liquid are distinguished
from those of solids by having little or no coherence; so that
unless the mass be confined by the sides of the vessel which
contains it, the particles will fall asunder by their gravity. A
mass of liquid, therefore, unlike a solid, can never retain any
particular form, but will accommodate itself to the form of
the vessel in which it is placed. It will press against the bottom
of the vessel which contains it with the whole force of
its weight, and it will press against the sides with a force proportional
to the depth of the particles in contact with the
sides measured from the surface of the liquid above. This
lateral pressure also distinguishes liquids from solids. Let
us take for illustration the case of a
square or a cubical vessel, <strong>A B C D</strong>,
<a href="#Fig003"><i>fig.</i> 3.</a> If a solid body, such as a
piece of lead, be cut to the shape of
this vessel, so as to fit in it without
pressing with any force against its
sides, the mechanical effect which
would be produced by it when placed
in the vessel, would be merely a pressure upon the bottom,
<strong>B C</strong>, the amount of which would be equal to the weight of the
metallic mass. No pressure would be exerted against the
sides; for the coherence of the particles of the solid maintaining
them in their position, the removal of the sides would
not subject the solid body contained in the vessel to any
change.
</div>

<p>Now let us suppose this solid mass of lead to be rendered
liquid by being melted. The constituent particles will then
be deprived of that cohesion by which they were held together;
they will accordingly have a tendency to separate, and
fall asunder by their gravity, and will only be prevented from
actually doing so by the support afforded to them by the sides,
<a class="refpn" id="Pg026">[Pg026]</a>
<strong>A B</strong>, <strong>D C</strong>, of the vessel. They
will therefore produce a pressure
against the sides, which was not produced by the lead
in its solid state. This pressure will vary at different depths:
thus a part of the side of the vessel at <strong>P</strong> will receive a pressure
proportional to the depth of the point <strong>P</strong> below the surface
of the lead. If, for example, we take a square inch of
the inner surface of the side of the vessel at <strong>P</strong>, it will sustain
an outward pressure equal to the weight of a column of lead
having a square inch for its base, and a height equal to <strong>P A</strong>.
And, in like manner, every square inch of the sides of the
vessel will sustain an outward pressure equal to the weight of
a column of lead having a square inch for its base, and a
height equal to the depth of the point below the surface of
the lead.</p>


<div class="ph3"><h3>(10.)</h3> We have here proceeded upon the supposition that
no force acts on the upper surface <strong>A D</strong> of the lead. If any
force presses <strong>A D</strong> downwards, that force would be transferred
to the bottom by the lead, and would produce a pressure on
the bottom <strong>B C</strong> equal to its own amount in addition to the
weight of the lead; and if the lead were solid, this would be
the only additional mechanical effect which such a force acting
on the surface <strong>A D</strong> of the lead would produce. But if, on
the other hand, the lead were liquified, then the force now adverted
to, acting on the surface <strong>A D</strong>, would not only produce
a pressure on the bottom <strong>B C</strong>, equal to its own amount in addition
to the weight of the lead, but it would also produce a
pressure against every part of the sides of the vessel, equal to
that which it would produce upon an equal magnitude of the
surface <strong>A D</strong>.</div>

<p>Thus if we suppose any mechanical cause producing a pressure
on the surface <strong>A D</strong> amounting to ten pounds on each
square inch, the effect which would be produced, if the lead
were solid, would be an additional pressure on the base <strong>B C</strong>
amounting to ten pounds per square inch. But if the lead
were liquid, besides this pressure on each square inch of the
base <strong>B C</strong>, there would likewise be a pressure of ten pounds on
every square inch of the sides of the vessel.</p>

<p>All that has been here stated with respect to a square or
a cubical vessel will be equally applicable to a vessel of any
other form.
<a class="refpn" id="Pg027">[Pg027]</a></p>


<div class="ph3"><h3>(11.)</h3> The second class of fluids are distinguished from liquids
by the particles not merely being destitute of cohesion,
but having a tendency directly the reverse, to repel each other,
and fly asunder with more or less force. Thus if a vessel, such
as that represented in <a href="#Fig003"><i>fig.</i> 3.</a>, were filled with a fluid of this
kind, being open at the top, and not being restrained by any
pressure incumbent upon it, the particles of the fluid would
not rest in the vessel by their gravity, as those of the liquid
would do; but they would, by their mutual repulsion, fly asunder,
and rise out of the vessel, as smoke is seen to rise from a
chimney, or steam from the spout of a kettle. Let us suppose,
then, that the vessel in which an elastic fluid is contained
is closed on every side by solid surfaces. In fact, let
us imagine that the square or cubical vessel represented in
<a href="#Fig003"><i>fig.</i> 3.</a> is closed by a square lid at the top <strong>A D</strong>,
having contained
in it an elastic fluid, such as atmospheric air.</div>

<p>If such a cover, or lid, had been placed upon a liquid, the
cover would sustain no pressure from the fluid, nor would any
mechanical effect be produced, save those already described
in the case of the open vessel; but when the fluid contained
in the vessel is elastic, as is the case with air, then the elasticity
(by which name is expressed the tendency of the particles
of the fluid to fly asunder) will produce peculiar mechanical
effects, which have no existence whatever in the case of
a liquid.</p>

<p>It is true that, supposing the fluid to be air or any other
gas or vapour, a pressure will be produced upon the bottom
<strong>B C</strong> of the vessel equivalent to the weight of such fluid, and
lateral pressures will be produced on the different points of
the sides by the weight of that part of the fluid which is above
these points; but gases and vapours are bodies of such extreme
levity, that these effects due to their weight are neglected
in practice.</p>

<p>Putting, then, the weight of the air contained in the vessel
out of the question, let us consider the effect of its elasticity.
If the vessel, as already described, be supposed to
contain atmospheric air in its ordinary state, the tendency of
the constituent particles to fly asunder will be such as to produce
on every square inch of the inner surface of the vessel
<a class="refpn" id="Pg028">[Pg028]</a>
a pressure amounting to fifteen pounds; this pressure being,
as already stated, quite independent of the weight of the air.
In fact, this pressure would continue to exist if the air contained
in the vessel actually ceased to have weight by being
removed from the neighbourhood of the earth, which is the
cause of its gravity.</p>


<div class="ph3">
<h3>(12.)</h3> Different gases are endowed with different degrees of
elasticity, and the same gas may have its elasticity increased
or diminished, either by varying the space within which it is
confined, or by altering the temperature to which it is exposed.</div>

<p>If the space within which an elastic fluid is enclosed be enlarged,
its elasticity is found to diminish in the same proportion.
Thus if the air contained in the vessel <strong>A B C D</strong>
(<a href="#Fig003"><i>fig.</i> 3.</a>) be allowed to pass into a vessel of twice the magnitude,
the elasticity of the particles will cause them to repel
each other, so that the same quantity of air shall diffuse itself
throughout the larger vessel, assuming double its former bulk.
Under such circumstances, the pressure which it would exert
upon the sides of the larger vessel would be only half that
which it had exerted on the sides of the smaller vessel. If,
on the other hand, it were forced into a vessel of half the
magnitude of <strong>A B C D</strong>, as it might be, then its elasticity would
be double, and it would press on the inner surface of that
vessel with twice the force with which it pressed on that of
the vessel <strong>A B C D</strong>.</p>

<p>This power of swelling and contracting its dimensions according
to the dimensions of the vessel in which it is confined,
or to the force compressing it, is a quality which results
immediately from elasticity, and is consequently one which is
peculiar to the gases or elastic fluids, and does not at all appertain
to liquids. If the liquid contained in the vessel <strong>A B C D</strong>
were transferred to a vessel of twice the magnitude, it would
only occupy half the capacity of that vessel, and it could not
by any means be transferred, as we have supposed the air or
gas to be, to a vessel of half the dimensions, since it is inelastic
and incompressible.</p>


<div class="ph3"><h3>(13.)</h3> The elasticity of gases is likewise varied by varying
the temperature to which they are exposed; thus, in general,
<a class="refpn" id="Pg029">[Pg029]</a>
if air or any other gas be augmented in temperature, it will
likewise be increased in elasticity; and if, on the other hand,
it be diminished in temperature, it will be likewise diminished
in its elastic force. The more heated, therefore, any air or
gas confined in a vessel becomes, the greater will be the
force with which it will press on the inner surface of that
vessel, and tend to burst it.</div>


<div class="ph3"><h3>(14.)</h3> The same body may, by the agency of heat, be made
to pass successively through the different states of solid, liquid,
and gas, or vapour. The most familiar and obvious example
of these successive transitions is presented by water. Exposed
to a certain temperature, water can only exist as a
solid; as the temperature is increased, the ice, or solid water,
is liquefied; and by the continued application of heat, this
water again undergoes a change, and assumes the form, and
acquires the mechanical qualities, of air or gas: in such a
state it is called <strong>STEAM</strong>.
</div>

<p>This is a common property of all liquids. If they be exposed
for a sufficient length of time to a sufficient degree of
heat, they will always be converted into elastic fluids. These
are usually distinguished from air and other permanent gases,
which never are known to exist in the liquid form, by the
term <em>vapour</em>, by which, therefore, must be understood an elastic
fluid which at common temperatures exists in the liquid or
solid state; by <em>steam</em> is expressed the vapour of water; and by
<em>gases</em>, those elastic fluids which like air are never knownâ€”at
least, under ordinary circumstancesâ€”to exist in any other
but the elastic form.</p>


<div class="ph3">
<h3>(15.)</h3> When a liquid is caused, by the application of heat, to
take the form of an elastic fluid, or is evaporated, besides
acquiring the property of elasticity, it always undergoes a
considerable change of bulk. The amount of this change is
different with different liquids, and even with the same liquid
it varies with the circumstances under which the change is
produced.</div>

<div class="ph3"><h3>(16.)</h3> When water is evaporated under ordinary
circumstances,â€”that
is, when exposed to no other external pressure
than that of the atmosphere,â€”it increases its volume about
seventeen-hundred-fold. Thus a cubic inch of liquid
<a class="refpn" id="Pg030">[Pg030]</a>
water would form about seventeen hundred cubic inches of
common steam. If, however, the water be confined by a
greater pressure than that produced by the common atmosphere,
then the increase of volume which takes place in its
evaporation would be less in proportion.
</div>

<p>These important physical circumstances are now only indicated
in a general way. As we proceed with our account
of the invention and improvement of the steam engine, they
will be developed more fully and accurately.</p>


<div class="ph3"><h3>(<a id="h3-17"></a>17.)</h3> After duly considering
what has been just explained,
no difficulty will be found in comprehending the
principles on which the first rude attempts at the mechanical
application of steam already stated depend. In the apparatus
ascribed to <i>Hero</i> of Alexandria, the elasticity of the vapour
contained in the arms of the revolving ball causes that vapour
to issue from the lateral orifices in the arms, such as that of
<strong>G</strong>, <a href="#Fig001"><i>fig.</i> 1.</a> As these orifices, however, are exposed to the
common atmosphere pressing inwards with a force, the mean
amount of which has been stated to be about fifteen pounds
per square inch, it follows that the steam cannot escape from
these orifices until its pressure or elasticity exceeds this
amount, and that when it does, the force with which it will
so escape will be the excess of its elasticity above that of the
atmosphere; and it is the reaction produced by this difference
of pressure, causing the arms to recoil, which will give
motion to the machine.</div>

<p>In the case of the apparatus of <cite>De Caus</cite>
(<a href="#h3-5">5</a>.), the heat of
the fire acting on the vessel <strong>D C</strong> (<a href="#Fig002"><i>fig.</i> 2.</a>) will
raise the temperature
of the water contained in it, and also of the air
confined within it above the surface of that water. This air,
as it is increased in temperature, will also increase in elasticity;
it will therefore press on the surface of the water
with increased force, and will gradually force the water upwards
in the tube; and this effect would continue until all
the water in the vessel would be forced up the tube.</p>

<p>But at the same time that the heat acting on the vessel
increases the temperature of the air above the water, it also
produces a partial evaporation of the water, so that more or
less steam is mixed with the air in the vessel above the surface
<a class="refpn" id="Pg031">[Pg031]</a>
of the water; and this steam possessing elasticity, unites
with the air in pressing on the surface of the water, and in
raising it in the tube.</p>

<div class="figleft" style="width: 384px;">
<a id="Fig004-5-6"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i053.png" width="384" height="440" alt="" />
<div class="caption figure">Figs. 4, 5, and 6.</div>
</div>

<p>Let us now revert to the brief account of the engine of the
Marquis of Worcester, described in "<cite>The Century of Inventions</cite>."
We collect from that description that the vessel
in which the water was evaporated was separate from those
which contained the water to be elevated; also that there
were two vessels of the like description, the contents of which
were alternately elevated by the pressure of the "water
rarefied by the fire;" in other words by steam; and that the
water was raised in an uninterrupted stream, by the management
of two cocks communicating with these vessels and with
the boiler. The following is such an apparatus as would
answer this description.
Let <strong>E</strong> (<a href="#Fig004-5-6"><i>fig.</i> 4.</a>)
be the vessel containing
the water
to be evaporated,
placed over a proper
furnace <strong>A</strong>; let <strong>S</strong> be
a pipe to allow the
steam produced from
the boiling water in
<strong>E</strong> to pass into the
vessels where its
mechanical action
is required. Let <strong>R</strong>
represent a cock or
regulator, having in
it a curved passage,
leading from <strong>S</strong> to the tube <strong>T</strong>, when the lever or handle
<strong>L</strong> is
in the position represented by the cut; but leading to the
tube <strong>Tâ€²</strong>, when the lever <strong>L</strong> is turned one quarter of a revolution
to the right, as represented in <a href="#Fig004-5-6"><i>fig.</i> 5.</a> By the shifting
of this lever, therefore, the steam pipe <strong>S</strong> may be made to
communicate alternately with the tubes <strong>T</strong> and <strong>Tâ€²</strong>. The tubes
<strong>T</strong> and <strong>Tâ€²</strong> are carried respectively to
two vessels <strong>V</strong> and <strong>Vâ€²</strong>, which
are filled with the water required to be raised. In these
<a class="refpn" id="Pg032">[Pg032]</a>
vessels tubes enter at <strong>C</strong> and <strong>Câ€²</strong>, descending nearly to the bottom:
these tubes have valves at <strong>B</strong> and <strong>Bâ€²</strong>, opening upwards,
by which water will be allowed to pass into the vertical tube
<strong>F</strong>, but which will not allow it to return downwards, the valves
<strong>B</strong> and <strong>Bâ€²</strong> being then closed by the weight of the water above
them.</p>

<p>Let <strong>G Gâ€²</strong> be a pipe entering the sides of the
vessels <strong>V</strong> and <strong>Vâ€²</strong>,
for the purpose of filling them with the water to be raised:
let <strong>K</strong> be a cock having a curved passage similar to the cock <strong>R</strong>,
and leading to a tube by which water is supplied from the
reservoir or other source from which the water to be raised is
drawn. When the cock <strong>K</strong> is placed as represented in <a href="#Fig004-5-6"><i>fig.</i> 4.</a>,
the water from the reservoir will flow through the curved
passage in the cock <strong>K</strong> into the tube <strong>Gâ€²</strong>, and thence into the
vessel <strong>Vâ€²</strong>; but when this cock is turned one quarter round,
by shifting the lever to the left, it will take the position
represented in <a href="#Fig004-5-6"><i>fig.</i> 6.</a>, and the water will flow through the
curved passage into the tube <strong>G</strong>, and thence into the vessel <strong>V</strong>.
Let us now suppose the vessel <strong>V</strong> already filled with water to
be elevated, and the vessel <strong>Vâ€²</strong> to have discharged its contents.
The cock <strong>R</strong> is turned, so as to allow the steam generated in
the boiler <strong>E</strong> to pass into the tube <strong>T</strong>, and thence into the
upper part of the vessel <strong>V</strong>, while the cock <strong>K</strong> is turned so as to
allow the water from the reservoir to pass into the tube <strong>Gâ€²</strong>,
and thence into the vessel <strong>Vâ€²</strong>. The steam collecting in the
upper part of the vessel <strong>Vâ€²</strong> presses with its elastic force on the
surface of the water therein, and forces the water upwards in
the tube <strong>C</strong>; it passes through the valve <strong>B</strong>, which it opens by
the upward pressure received from the action of the steam,
and thence into the tube <strong>F</strong>, its descent into the tube <strong>Câ€²</strong> being
prevented by the valve <strong>Vâ€²</strong>, which can only be opened upwards.
As the steam is gradually supplied from the boiler <strong>E</strong>, the
water in the vessel <strong>V</strong> is forced up the tube <strong>C</strong>, through the
valve <strong>B</strong>, and into the tube <strong>F</strong>, until all the contents of the
vessel <strong>V</strong> above the lower end of the tube <strong>C</strong> have been raised.
In the meanwhile, the vessel <strong>Vâ€²</strong> has been filled with water,
through the cock <strong>K</strong>: when this has been accomplished, the
man who attends the machine shifts the cocks <strong>R</strong> and <strong>K</strong>, so as
to give them the position represented in <a href="#Fig004-5-6"><i>fig.</i> 5.</a> and <a href="#Fig004-5-6"><i>fig.</i> 6.</a>
<a class="refpn" id="Pg033">[Pg033]</a>
In this position, the steam from the boiler, being excluded
from the tube <strong>T</strong>, will be conducted to the tube <strong>Tâ€²</strong>, and thence
to the vessel <strong>Vâ€²</strong>,
while the water
from the reservoir
will be excluded
from the tube <strong>Gâ€²</strong>, and
conducted through
the tube <strong>G</strong> to the
vessel <strong>V</strong>. The vessel
<strong>V</strong> will thus be
replenished and, by
a process similar to
that already described,
the contents
of the vessel
<strong>Vâ€²</strong> will be forced
up the tube <strong>Câ€²</strong>,
through the valve
<strong>Bâ€²</strong>, and into the tube <strong>F</strong>; its descent
into the tube <strong>C</strong> being
prevented by the valve <strong>B</strong>, which will then be closed.
After the contents of the vessel <strong>Vâ€²</strong> have thus been raised,
and the vessel <strong>V</strong> replenished, the two cocks
<strong>R</strong> and <strong>K</strong> are
once more shifted, and the contents of <strong>V</strong> raised while <strong>Vâ€²</strong> is
replenished, and so on.</p>

<div class="figleft" style="width: 384px;">
<a id="Fig004-5-6-second"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i055.png" width="384" height="440" alt="" />
<div class="caption figure">Fig. 4, 5, and 6.</div>
</div>

<p>If, having comprehended the apparatus here described, the
reader refers to the description of the Marquis of Worcester's
machine, he will find that all the conditions therein laid down
are fulfilled by it. One vessel (<strong>E</strong>) of "water rarefied by fire"
may by such means "drive up forty (or more) of cold water;
and the man that tends the work has but to turn two cocks,
that one vessel (<strong>V</strong>) of water being consumed, another (<strong>Vâ€²</strong>)
begins to force and refill with cold water, and so on successively,
the fire being tended and kept constant; which the
self-same person may likewise abundantly perform, in the
interim between the necessity of turning the said cocks."</p>

<p>On comparing this with the contrivance previously suggested
by De Caus, it will be observed, that even if De Caus
<a class="refpn" id="Pg034">[Pg034]</a>
knew the physical agent by which the water was driven upwards
in the apparatus described by him, still it was only a
method of causing a vessel of boiling water to empty itself;
and before a repetition of the process could be made, the
vessel should be refilled, and again boiled. In the contrivance
of Lord Worcester, on the other hand, the agency
of the steam was employed in the same manner as it is in the
steam engines of the present day, being generated in one
vessel, and used for mechanical purposes in another. Nor
must this distinction be regarded as trifling or insignificant,
because on it depends the whole practicability of using steam
as a mechanical agent. Had its action been confined to the
vessel in which it was produced, it never could have been
employed for any useful purpose.</p>

<p>Although many of the projects contained in Lord Worcester's
work were in the highest degree extravagant and absurd,
yet the engine above described is far from being the only
practicable and useful invention proposed in it. On the contrary,
many of his inventions have been reproduced, and some
brought into general use since his time. Among these may
be mentioned, stenography, telegraphs, floating baths, speaking
statues, carriages from which horses can be disengaged if
unruly, combination locks, secret escutcheons for locks, candle
moulds, the rasping mill, the gravel engine, &#38;c.</p>


<p class="txthead3">Sir Samuel Morland, 1683.</p>


<div class="ph3">
<h3>(18.)</h3> Sir Samuel Morland was the son of a baronet of the
same name, who had received his title at the restoration for
some services to the royalist party, performed by him during
the wars of the Commonwealth. He appears to have devoted
much attention to mechanics, in which he attained some
celebrity. He was the reputed inventor of several ingenious
contrivances, such as the drum capstan for ships, the plunger
pump, &#38;c. He also investigated various questions in acoustics,
and among others, the determination of the best form for the
speaking-trumpet.</div>

<p>In 1680, Sir Samuel Morland was appointed Master
<a class="refpn" id="Pg035">[Pg035]</a>
of the Works to Charles II., and in the following year was
sent to France, to execute some waterworks for Louis XIV.
In 1683, while in France, he wrote in the French language,
a work entitled "<cite>Elevation des Eaux par toute sorte de Machines,
reduite Ã  la Mesure, au Poids et Ã  la Balance. PresentÃ©e
Ã  sa MajestÃ© trÃ¨s Chrestienne, par le Chevalier Morland,
Gentilhomme Ordinaire de la Chambre PrivÃ©e, et Maistre des
MÃ©chaniques du Roi de la Grande BrÃ©tagne, 1683.</cite>" This
book is preserved in manuscript in the Harleian Collection in
the British Museum. It is written on vellum, and consists
of only thirty-eight pages. It contains tables of measures
and weights, theorems for the calculation of the volumes of
cylinders, the weights of columns of water, the thickness
of lead for pipes, and is concluded by a chapter on steam,
consisting of four pages, of which the following is a translation:â€”</p>

<p>"<em>The principles of the new force of fire invented by Chevalier
Morland in 1682, and presented to His Most Christian
Majesty in 1683</em>:â€”</p>

<p>"'Water being converted into vapour by the force of
fire, these vapours shortly require a greater space (about
2000 times) than the water before occupied, and sooner
than be constantly confined would split a piece of cannon.
But being duly regulated according to the rules of statics,
and by science reduced to measure, weight, and balance,
then they bear their load peaceably (like good horses),
and thus become of great use to mankind, particularly for
raising water, according to the following table, which shows
the number of pounds that may be raised 1800 times per
hour to a height of six inches by cylinders half filled with
water, as well as the different diameters and depths of the
said cylinders.'"</p>

<p>There is nothing in the description here given which can
indicate the form of the machine by which Morland proposed
to render the force of steam a useful mover. It is, however,
remarkable, that at this early period, before experiments had
been made on the expansion which water undergoes in evaporation,
he should have given so near an approximation to
<a class="refpn" id="Pg036">[Pg036]</a>
the actual amount of that expansion. It is scarcely supposable
that such an estimate could be obtained by him otherwise
than by experiment.</p>

<p>The work containing the above description was not printed;
but a work bearing nearly the same title, containing, however,
no mention of the force of steam, was published by him in
Paris in the year 1685. In this he describes various experiments
made by him at St. Germains on the weight of the
water of the Seine, and gives weights of the columns of water,
the contents of cylinders, &#38;c.</p>

<p>Soon after the publication of this work, Morland returned
to England, and resided near the court till his death. The
celebrated John Evelyn mentioned having paid a visit to him
at his house at Hammersmith, in 1695, when he had become
aged and blind, but was still remarkable for his mechanical
ingenuity. "On the 25th of October," says Evelyn, "the
Archbishop and myself went to Hammersmith to visit Sir
Samuel Morland, who was entirely blind; a very mortifying
sight. He showed us his invention of writing (short-hand),
which was very ingenious; also his wooden kalendar, which
instructed him all by feeling; and other pretty and useful
inventions of mills, pumps, &#38;c.; and the pump he had
erected, that serves water to his garden and to passengers,
with an inscription, and brings from a filthy part of the
Thames near it a most perfect and pure water."<a
name="FNanchor_3_3" id="FNanchor_3_3"></a><a href="#Footnote_3_3"
class="fnanchor">[3]</a></p>

<p>He died at Hammersmith, in January 1696; and before
his death, as a penance for his past life, was guilty of the eccentricity
of burying in the ground six feet deep a great collection
of music which he possessed.<a name="FNanchor_4_4" id="FNanchor_4_4"></a><a
href="#Footnote_4_4" class="fnanchor">[4]</a></p>


<p class="txthead3">Denis Papin, 1688.</p>


<div class="ph3"><h3>(19.)</h3> Denis Papin, a native of Blois in France, and professor
of mathematics at Marbourg, is the name which stands
next recorded in the progressive invention of the steam engine.
To this philosopher is due the discovery of one of the
qualities of steam, to the proper management of which is
owing much of the efficacy of the modern steam engine.
<a class="refpn" id="Pg037">[Pg037]</a></div>

<p>Papin was born at Blois in France. He devoted his
youth to the study of medicine, in which he took a degree at
Paris. The revocation of the Edict of Nantes having driven
him into exile, he went to England, where the celebrated
Boyle associated him in several of his experiments with the
air-pump, and caused him to be elected a fellow of the Royal
Society in 1681. Having been invited to Germany by the
Landgrave of Hesse, he discharged during several years the
duties of professor of mathematics at the university of Marbourg,
where he died in 1710. Notwithstanding his discoveries
respecting the agency of steam, he never received
any mark of distinction in his own country. The truth
is, the importance and value of these investigations were
not apparent until long afterwards.</p>

<p>This philosopher conceived the idea of producing a moving
power by means of a piston working in a cylinder, in the
manner which we shall now briefly explain.</p>

<div class="figleft" style="width: 120px;">
<a id="Fig007"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_059.png" width="120" height="260" alt="" />
<div class="caption figure">Fig. 7.</div>
</div>

<p>Let <strong>A B</strong> (<a href="#Fig007"><i>fig.</i> 7.</a>) be a cylinder open at the top, and let a
piston <strong>P</strong> be fitted into it, so as to move in it air tight. At
the bottom of the cylinder suppose an opening provided,
which can be closed at pleasure, by a stop-cock, or otherwise,
so that the communication may be opened and closed at will
between the interior of the cylinder and the external air.
This stop-cock being opened, let the piston be drawn upwards
till it reach the top of the cylinder. Let the stop-cock
at the bottom be then removed, and imagine that some means
can be supplied by which the air within the
cylinder can be suddenly annihilated. The
piston, now at the top, will have above it the
pressure of the atmosphere; and having no
air below, it will be resisted in its descent by
no force save that arising from its friction with
the cylinder. If, then, the force of the air
above the piston be greater than the resistance
arising from this friction, the piston will
descend with the excess of this force, and
will continue so to descend until it reach the
bottom of the cylinder. Having attained that position, let us
<a class="refpn" id="Pg038">[Pg038]</a>
suppose the stop-cock in the bottom opened, so as to allow
the external air to pass freely below the piston. The piston
may now be drawn to the top of the cylinder again, offering
no resistance save that of its weight, and its friction with the
cylinder. Having reached the top of the cylinder once more,
let the stop-cock be closed, and the air included within the
cylinder once more annihilated. A second descent of the
piston will take place, with the same force as before, and in
like manner the process may be continued indefinitely.</p>

<p>Now, if it should appear that means could be provided suddenly
and repeatedly to annihilate the air within the cylinder,
and that the pressure of the atmosphere above the piston
should exert a force compared with which the weight of the
piston and its friction are trifling, it is evident that a moving
power would be obtained which would be capable, by proper
mechanism, of being applied to any useful purpose, but
which would more especially be applicable to the working of
pumps, the motion of which corresponds with that which has
been just ascribed to the piston in the cylinder. Such were
the first ideas of Papin. But in order to enable those who
are not conversant with physical science fully to appreciate
their importance, it will be necessary here to explain some of
the mechanical properties of atmospheric air.</p>


<div class="ph3"><h3>(20.)</h3> The atmosphere is the thin, transparent, colourless,
and therefore invisible, fluid in which we live and move,
which by respiration sustains animal life, and is otherwise
connected with various important functions of organised matter.
This fluid is so light and attenuated, that it might at
first be doubted whether it be really a body at all; and, indeed,
the name expressing incorporeal beings, <i>spirit</i>, is a word
in its origin signifying <i>air</i>.<a name="FNanchor_5_5"
id="FNanchor_5_5"></a><a href="#Footnote_5_5" class="fnanchor">[5]</a>
The air, however, is light only
as compared with other material substances, which exist in
a more condensed state: it possesses the quality of weight
as absolutely as the most solid and massive bodies in nature,
and to render this quality manifest, it is only necessary to
submit a sufficient quantity of air to any of the usual tests of
gravitation.
<a class="refpn" id="Pg039">[Pg039]</a></div>

<p>A direct demonstration of this may be given by the following
experiment:â€”On the mouth of a flask let a stop-cock
be fastened so as to be air-tight. The interior of the
flask may then be put into free communication with the external
air, or that communication may be cut off at pleasure,
by opening or closing the stop-cock. If a syringe be
applied to the mouth of the flask, the stop-cock being open
a part of the air contained in it may be drawn out. After
this, the stop-cock being closed, and the syringe detached, let
the flask be placed in the dish of a good balance, and accurately
counterpoised by weights in the other dish. This
counterpoise will then represent the weight of the flask,
and of the air which has remained in it. If the stop-cock be
now opened, air will immediately rush in, and replace that
which the syringe had withdrawn from the flask; and immediately
the dish of the balance containing the flask will sink
by the effect of the weight of the air thus admitted into the
flask.</p>

<p>If the weight of quantity of air so small as to be capable
of being withdrawn by a syringe from an ordinary flask be
thus of sensible amount, it may be easily imagined that the
vast mass of atmosphere extending from the surface of the
earth upwards, to a height not ascertained with precision, but
certainly not being less than thirty miles, must be very considerable.
Such a force, pressing as it must constantly do,
upon the surfaces of all bodies, whether solid or fluid, and
resisting and modifying their movements, would play an important
part in all mechanical phenomena; and it is, therefore,
not sufficient merely to have recognised its existence,
but it is most needful to measure its amount with that degree
of certainty and precision, which will enable us to estimate
its effects on those phenomena which we shall have to
investigate.</p>


<div class="ph3">
<h3>(21.)</h3> The amount of the pressure of the atmosphere on
each square inch of horizontal surface on which it rests, is
obviously the weight of the column of air extending from that
square inch of surface upwards to the top of the atmosphere.
This force is measured by the following means:â€”</div>

<div class="figleft" style="width: 219px;">
<a id="Fig008-9"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_062.png" width="219" height="390" alt="" />
<div class="caption figure">Figs. 8., 9.</div>
</div>

<p>Take a glass tube, <strong>A B</strong> (<a href="#Fig008-9"><i>fig.</i> 8.</a>), above 32 inches long, open
at one end <strong>A</strong>, and closed at the other end <strong>B</strong>, and let it
<a class="refpn" id="Pg040">[Pg040]</a>
be filled with mercury (quicksilver).
Let a glass vessel or cistern <strong>C</strong>, containing
a quantity of mercury, be also
provided. Applying the finger at <strong>A</strong>, so
as to prevent the mercury in the tube
from falling out, let the tube be inverted,
and the end, stopped by the
finger, plunged into the mercury in <strong>C</strong>.
When the end of the tube is below
the surface of the mercury in <strong>C</strong> (<a href="#Fig008-9"><i>fig.</i> 9.</a>),
let the finger be removed. It will be
found that the mercury in the tube
will not, as might be expected, fall to
the level of the mercury in the cistern
<strong>C</strong>, which it would do were the end <strong>B</strong> open, so as to admit the
air into the upper part of the tube. On the other hand, the
level <strong>D</strong> of the mercury in the tube will be nearly 30 inches
above the level <strong>C</strong> of the mercury in the cistern.</p>

<p>The cause of this effect is, that the weight of the atmosphere
rests on the surface <strong>C</strong> of the mercury in the cistern,
and tends thereby to press it up, or rather to resist its fall in
the tube; and as the fall is not assisted by the weight of the
atmosphere on the surface <strong>D</strong> (since <strong>B</strong> is closed), it follows,
that as much mercury remains suspended in the tube above
the level <strong>C</strong>, as the weight of the atmosphere is able to support.</p>

<p>If the section of the tube were equal to the magnitude
of a square inch, the weight of the column of mercury in
the tube above the level <strong>C</strong> would be exactly equal to the
weight of the atmosphere on each square inch of the surface <strong>C</strong>.</p>


<div class="ph3">
<h3>(22.)</h3> If such an apparatus be observed from time to time,
it will be found that the column of mercury sustained in the
tube will be subject to variation between certain limits,
never falling below twenty-eight inches, and never rising
above thirty-one inches. This variation of the mercurial column
is produced by a corresponding variation in the weight
of the atmosphere.</div>

<p>If the apparatus be transported to any height above its
ordinary position, it will have a less quantity of atmosphere
above it, and therefore the surface of the mercury in the cistern
will be pressed by a less weight, and consequently the
<a class="refpn" id="Pg041">[Pg041]</a>
column of mercury will fall proportionally. In virtue of this
effect, such an instrument has been rendered a means of
measuring heights, such as the heights of mountains, the ascents
of balloons, &#38;c. &#38;c.</p>

<div class="ph3"><h3>(23.)</h3> If a proper scale be attached to the tube containing
the mercurial column, showing the absolute height of the
column sustained at any time, and indicating its changes of
height, the instrument becomes a <strong class="m1">Barometer</strong>.</div>

<p>Two cubic inches of mercury weigh very nearly one pound
avoirdupois.<a name="FNanchor_6_6" id="FNanchor_6_6"></a><a
href="#Footnote_6_6" class="fnanchor">[6]</a> Hence, when the
barometric column measures
thirty inches, the weight of the atmosphere resting on
each square inch of surface is about fifteen pounds.</p>


<div class="ph3">
<h3>(24.)</h3> It is an established property of fluids, that they press
equally in all directions; and air, like every other fluid, participates
in this quality. Hence, it follows, that when the
downward pressure or weight of the atmosphere is fifteen
pounds on the square inch, the lateral, upward, and oblique
pressures are of the same amount. But, independently of the
general principle, it may be satisfactory to give experimental
proof of this.</div>

<div class="figleft" style="width: 300px;">
<a id="Fig010"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_063.png" width="300" height="413" alt="" />
<div class="caption figure">Fig. 10.</div>
</div>

<p>Let four glass tubes, <strong>A</strong>, <strong>B</strong>,
<strong>C</strong>, <strong>D</strong> (<a href="#Fig010"><i>fig.</i> 10.</a>), be constructed of
sufficient length, closed at one end, <strong>A</strong>, <strong>B</strong>,
<strong>C</strong>, <strong>D</strong>, and open at the
other. Let the open ends of three of them be bent, as represented
in the tubes <strong>B</strong>, <strong>C</strong>, <strong>D</strong>.
Being previously filled with
mercury, let them all be
gently inverted, so as to have
their closed ends up, as here
represented. It will be found
that the mercury will be sustained
in all, and that the
difference of the levels in all
will be the same.<a name="FNanchor_7_7" id="FNanchor_7_7"></a><a
href="#Footnote_7_7" class="fnanchor">[7]</a> Thus, the
mercury is sustained in <strong>A</strong> by
the upward pressure of the
atmosphere; in <strong>B</strong>, by its horizontal
or lateral pressure; in
<strong>C</strong>, by its downward pressure;
<a class="refpn" id="Pg042">[Pg042]</a>
and in <strong>D</strong>, by its oblique pressure: and, as the difference
of the levels is the same in all, these pressures are exactly
equal.</p>


<div class="ph3">
<h3>(25.)</h3> The same arrangement by which the pressure of the
atmosphere is measured by a mercurial column of equivalent
weight, also supplies the means of measuring the pressure or
elasticity of atmospheric air, or any other gas or vapour,
whether in a more or less compressed or rarefied state; and
as instruments constructed on this principle are of considerable
use in steam engines, we shall take this occasion to
explain their principle and application.</div>

<p>In the experiments described in (21), the space <strong>D B</strong> in the
top of the barometer-tube, from which the mercury descended,
is a vacuum. If, however, it were occupied by a
quantity of air in a rarefied state, or any other gas or vapour,
such gas or vapour would press on the surface of the mercury
at <strong>D</strong>, with a force determined by its elasticity. In that case,
the atmospheric pressure acting on the surface of the mercury
<strong>C</strong> in the cistern, would be balanced by the combined forces
of the weight of the mercurial column sustained in the tube,
and the elasticity of the gas or vapour in the upper part of
it. Now if we know the actual amount of the atmospheric
pressure,â€”that is to say, the height of the column of mercury
which it would be capable of sustaining,â€”we should then
be able to determine the pressure of the rarefied air in the
space <strong>C D</strong>.</p>

<p>For example, let us suppose that the barometric column,
when <strong>B D</strong> (<a href="#Fig008-9"><i>fig.</i> 9.</a>) is a vacuum, measures thirty inches: the atmospheric
pressure, therefore, would be equal to the weight of
a column of mercury of that height. Let us suppose that the
elasticity of the gas or vapour occupying the upper part of
the tube <strong>D B</strong> causes the column to fall to the height of
twenty-six inches: it is evident, then, that the pressure of
the air in the top of the tube would be equal to the weight
of a column of mercury of four inches. In fine, to determine
the pressure of the rarefied gas or vapour in the top of the
tube, it is only necessary to observe the difference between
the height of the column of mercury actually sustained in
the tube, and the column sustained at the same time and
<a class="refpn" id="Pg043">[Pg043]</a>
place in a common barometer: the difference of the two will
be the column of mercury whose weight will represent the
pressure of the vapour or gas in the top of the tube.</p>


<div class="ph3">
<h3>(26.)</h3> Whenever the air contained in any vessel or other
enclosed space has by any means had its pressure reduced so
as to be rendered less than that of the external air, the external
air will have a tendency to rush into such vessel or
enclosed space with a force proportionate to the excess of the
pressure of such external air over that of the air within;
and if any communication be opened between the interior of
such vessel or enclosed space, and the external air, the latter
will rush in until an equilibrium be established between the
pressures within and without. It is evident that the force
thus obtained by diminishing the pressure of air within a vessel
may be applied to any mechanical purpose.</div>

<p>It is by such means that water is raised in an ordinary
pump. A portion of the air contained between the piston
of the pump and the surface of the water below, is withdrawn
by the action of the piston, and the pressure of the
air remaining under the piston is thereby diminished. The
superior pressure of the atmosphere upon the external surface
of the water in the well then forces up a column of water in
the pump-barrel, and this is continued as the air is more
and more rarefied by the action of the piston. By whatever
means, therefore, the air can be wholly or partially
withdrawn from any space, a mechanical power will be
thereby developed, proportional in its amount and efficacy
to the quantity of air so withdrawn. If, however, such air
be withdrawn by any mechanical process, such as by a
syringe, by a common pump, or by an air-pump, the quantity
of force expended in withdrawing it is always equivalent
to the amount of mechanical power obtained by the vacuum
or partial vacuum so produced. Indeed the power expended
is greater than the power so obtained, inasmuch as
the friction, leakage, &#38;c. of the exhausting apparatus must
be allowed for.</p>


<div class="ph3"><h3>(27.)</h3> There are, however, various other means by which air
may be partially expelled from a vessel besides the direct
application of mechanical force. Thus if heat be applied to
<a class="refpn" id="Pg044">[Pg044]</a>
the vessel, the air, as has been already explained, will acquire
increased elasticity, and will rush from the vessel with a force
proportionate to the excess of its elasticity above that of the
external air, and this process may be continued by increasing
the heat to which the vessel is exposed, until a very considerable
portion of the air has been expelled. If the orifice by
which the air has escaped be then closed, and the vessel be
allowed to cool, the air within, by having its temperature
reduced to that of the external air, will lose all the elasticity
which it had gained from the heat, and will be in the same
condition as if an equivalent quantity of air had been withdrawn
by any mechanical agent. The external air, therefore,
will have a tendency to rush in with a force corresponding to
the difference of pressures.</div>

<p>The process of filling thermometers with mercury shows
one use of producing a high degree of rarefaction by heat.
To construct the instrument it is necessary to fill the bulb
and a part of the tube with mercury; but the bore of the tube
is so small that the mercury cannot be introduced by any
ordinary means. It is therefore held over flame until heated
to a high temperature. The air within it gradually increasing
in pressure as its temperature is raised, is forced through the
small bore of the tube, until the pressure of the air within
becomes no more than equal to the pressure of the external
atmosphere; this air being so rarefied that quantity in the
bulb bears a very small proportion to its contents at common
temperatures. The mouth of the tube is then plunged into
mercury, and as the bulb cools, the air within it loses its
elasticity, and the superior pressure upon the external surface
forces the mercury into the tube. This continues until
the air remaining within the bulb has been so contracted, that
its pressure combined with the weight of the mercury, shall
balance the atmospheric pressure. The tube is then reversed,
and the air which remained rises in a bubble to the surface,
and escapes.</p>


<div class="ph3"><h3>(28.)</h3> Let us now return to the proceedings of Papin. How
great a power would result from such a machine as he conceived,
will be apparent, if it be considered that the unresisted
atmosphere exercises a pressure of about fifteen pounds on
<a class="refpn" id="Pg045">[Pg045]</a>
each square inch of surface exposed to it, and that if the
piston in the cylinder imagined by Papin, had a diameter of
only one foot, its superficial magnitude would be about
114 square inches. The pressure of the atmosphere upon it,
therefore, would be 114 times fifteen pounds, or 1710 pounds.
Papin first proposed to produce the vacuum under the piston
by means of common air pumps, worked by a water-wheel;
and by such means he conceived that the power of a river,
stream, or waterfall might be conveyed by pipes to a distance.
While he was in England, in 1687, he laid his contrivance
before the Royal Society of London, but was met
by objections and difficulties, the nature of which he does
not explain.</div>

<p>It is, however, apparent, from what has been already explained,
that such a method of proceeding would amount to
a mere transfer of power, and would not, properly speaking,
be itself a moving force: the moving power would, in reality,
be the force of the water by which the water-wheel would be
driven; and the air-pumps, tubes, together with the piston
and cylinder, would be merely means of conveying the
power of the water-wheel to the objects to be moved, or
the machinery to be driven. Papin states, that, long before
this, he had attempted to expel the air from his cylinder by
means of gunpowder; but, notwithstanding all the precautions
which he could take, there always remained a considerable
quantity; so much, indeed, as to deprive the vacuum of more
than half its proper force. At length he adopted an expedient
for the production of a vacuum which forms a most
important step in the progressive invention of the steam
engine, and which gives to Papin's name a high place in the
history of that machine. This method is explained in the
following paragraph of a work published by Papin in 1695, at
Cassel, entitled "<cite>Recueil de diverses PiÃ¨ces touchant quelques
nouvelles Machines</cite>", p. 53.</p>

<p>"I have endeavoured," says he, "to attain this end (viz.
the production of a vacuum in the cylinder) in another way.
As water has the property of elasticity, when converted into
steam by heat, and afterwards of being so completely recondensed
by cold, that there does not remain the least
<a class="refpn" id="Pg046">[Pg046]</a>
appearance of this elasticity, I have thought that it would
not be difficult to work machines in which, by means of a
moderate heat and at a small cost, water might produce
that perfect vacuum which has vainly been sought by means
of gunpowder."</p>

<p>This remarkable passage is given in the work just cited, as
an extract from the "<cite>Leipsic Acts</cite>," of August, 1690.</p>

<p>Let us pause here to explain more fully this important
discovery.</p>

<div class="ph3">
<h3>(29.)</h3> We have explained that, in its conversion into vapour,
by the application of heat, water, besides acquiring the property
of elasticity, undergoes a vast enlargement of bulk, filling,
under ordinary circumstances, about 1700 times more
space than it occupied in the liquid form. This fact was
known generally, though not with numerical accuracy, by
Papin, having been the foundation of the machines previously
invented and published by De Caus and Lord Worcester;
the happy idea of reversing the process occurred to him. If
water in its conversion into steam swelled into many hundred
times its original bulk, it would necessarily follow, that
steam, being reconverted into water, would shrink into its
primitive dimensions. Papin therefore saw, that if he could
by any means expel the air from his cylinder under the
piston, and replace it by the pure vapour of water, he could
cause that vapour to be reconverted into a comparatively
minute quantity of water by depriving it of the heat which
sustained it in the state of steam, and that by accomplishing
this, the space in the cylinder under the piston would become
a vacuum; that by such means, the pressure of the atmosphere
above the piston would take full effect, and would
urge the piston down; that by introducing more steam under
the piston, it might be again raised by the elastic force of the
steam, the destruction of which by cold water would again
produce the descent of the piston with the same mechanical
force; and that in this way the alternate ascent and descent of
the piston might be continued indefinitely.</div>

<p>In accordance with these ideas, Papin constructed a model
consisting of a small cylinder, in which was placed a solid piston;
<a class="refpn" id="Pg047">[Pg047]</a>
and in the bottom of the cylinder under the piston was
contained in a small quantity of water. The piston being in
immediate contact with this water, so as to exclude the atmospheric
air, on applying fire to the bottom of the cylinder,
steam was produced, the elastic force of which raised the piston
to the top of the cylinder; the fire being then removed,
and the cylinder being cooled by the surrounding air, the
steam was condensed and reconverted into water, leaving a
vacuum in the cylinder into which the piston was pressed by
the force of the atmosphere. The fire being applied and subsequently
removed, another ascent and descent were accomplished;
and in the same manner the alternate motion of the
piston might be continued. Papin described no other form
of machine by which this property could be rendered available
in practice; but he states generally, that the same end
may be attained by various forms of machines easy to be
imagined.<a name="FNanchor_8_8" id="FNanchor_8_8"></a><a
href="#Footnote_8_8" class="fnanchor">[8]</a></p>

<p class="txthead3">Thomas Savery, 1698.</p>

<div class="ph3">
<h3>(30.)</h3> The discovery of the method of making a vacuum
by the condensation of steam was reproduced, before 1698, by
Captain Thomas Savery, to whom a patent was granted in that
year for a steam engine to be applied to the raising of water,
&#38;c. Savery proposed to combine the machine described
by the Marquis of Worcester with an apparatus for raising
water by suction into a vacuum produced by the condensation
of steam.</div>

<p>Savery appears to have been ignorant of the publication of
Papin, and stated that his discovery of the condensing principle
arose from the following circumstance:â€”</p>

<p>Having drunk a flask of Florence at a tavern, and flung the
empty flask on the fire, he called for a basin of water to wash
his hands. A small quantity which remained in the flask began
to boil, and steam issued from its mouth. It occurred to
him to try what effect would be produced by inverting the
flask and plunging its mouth in the cold water. Putting on
a thick glove to defend his hand from the heat, he seized the
<a class="refpn" id="Pg048">[Pg048]</a>
flask, and the moment he plunged its mouth in the water the
liquid immediately rushed up into the flask and filled it.</p>

<p>Savery stated that this circumstance immediately suggested
to him the possibility of giving effect to the atmospheric pressure
by creating a vacuum in this manner. He thought that
if, instead of exhausting the barrel of a pump by the usual
laborious method of a piston and sucker, it was exhausted by
first filling it with steam, and then condensing the same steam,
the atmospheric pressure would force the water from the well
into the pump-barrel, and into any vessel connected with it,
provided that vessel were not more than about thirty-four feet
above the elevation of the water in the well. He perceived
also, that, having lifted the water to this height, he might use
the elastic force of steam in the manner described by the Marquis
of Worcester to raise the same water to a still greater
elevation, and that the same steam which accomplished this
mechanical effect would serve, by its subsequent condensation,
to reproduce the vacuum, and draw up more water. It was
on this principle that Savery constructed the first engine in
which steam was ever brought into practical operation.</p>

<div class="figcenter" style="width: 445px;">
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_070.png" width="445" height="355" alt="" />
<div class="caption">BRANCA'S ENGINE.</div>
</div>

<div class="footnotes"><h3>FOOTNOTES:</h3>

<div class="footnote">

<p><a name="Footnote_1_1" id="Footnote_1_1"></a><a href="#FNanchor_1_1"><span
class="label">[1]</span></a> Arago, Eloge historique de James Watt; p. 22.</p></div>

<div class="footnote">

<p><a name="Footnote_2_2" id="Footnote_2_2"></a><a href="#FNanchor_2_2"><span
class="label">[2]</span></a> Ibid., p. 21. note.</p></div>

<div class="footnote">

<p><a name="Footnote_3_3" id="Footnote_3_3"></a><a href="#FNanchor_3_3"><span
class="label">[3]</span></a> Farey, Treatise on the Steam Engine, p. 93.</p></div>

<div class="footnote">

<p><a name="Footnote_4_4" id="Footnote_4_4"></a><a href="#FNanchor_4_4"><span
class="label">[4]</span></a> Arago, sur les Machines Ã  Vapeur, Annuaire, 1829, p. 165</p></div>

<div class="footnote">

<p><a name="Footnote_5_5" id="Footnote_5_5"></a><a href="#FNanchor_5_5"><span
class="label">[5]</span></a> <strong class="m1">Spiritus</strong>, <em>breath</em> or <i>air</i>.</p></div>

<div class="footnote">

<p><a name="Footnote_6_6" id="Footnote_6_6"></a><a href="#FNanchor_6_6"><span
class="label">[6]</span></a> Exactly 15Â·68 oz. = 0Â·98 lb.</p></div>

<div class="footnote">

<p><a name="Footnote_7_7" id="Footnote_7_7"></a><a href="#FNanchor_7_7"><span
class="label">[7]</span></a> This experiment with the tube <strong>A</strong>
requires to be very carefully executed,
and the tube should be one of small bore.</p></div>

<div class="footnote">

<p><a name="Footnote_8_8" id="Footnote_8_8"></a><a href="#FNanchor_8_8"><span
class="label">[8]</span></a> Recueil de diverses PiÃ¨ces touchant quelques
nouvelles Machines,
p. 38.</p></div></div>

<div class="figcenter" style="width: 550px;">
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_071.png" width="550" height="688" alt="" />
<div class="caption">SAVERY'S ENGINE.</div>
</div>

<h2><a name="CHAP_II" id="CHAP_II">CHAP. II.</a></h2>

<p class="fsize2 center">ENGINES OF SAVERY AND NEWCOMEN.</p>

<p class="right"><a class="refpn" id="Pg049">[Pg049]</a><br />
<a href="#CONTENTS"><small>TOC</small></a>&#160;&#160;<a
href="#INDEX"><small>INX</small></a></p>

<div class="chapheader">
SAVERY'S ENGINE.â€”BOILERS AND THEIR APPENDAGES.â€”WORKING APPARATUS.â€”MODE
OF OPERATION.â€”DEFECTS OF THE ENGINE.â€”NEWCOMEN
AND CAWLEY.â€”ATMOSPHERIC ENGINE.â€”ACCIDENTAL DISCOVERY
OF CONDENSATION BY INJECTION.â€”HUMPHREY POTTER MAKES
THE ENGINE WORK ITSELF.â€”ADVANTAGES OF THE ATMOSPHERIC
ENGINE OVER THAT OF SAVERY.â€”IT CONTAINED NO NEW PRINCIPLE.â€”ITS
PRACTICAL SUPERIORITY.</div>


<div class="ph3fst"><h3>(<a id="h3-31"></a>31.)</h3> The steam engine contrived
by Savery, like every
other which has since been constructed, consists of two parts,
essentially distinct. The first is that which is employed to
<a class="refpn" id="Pg050">[Pg050]</a>
generate the steam, which is called the boiler; and the second,
that in which the steam is applied as a moving power.</div>

<div class="figleft" style="width: 365px;">
<a id="Fig011"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_072.png" width="365" height="271" alt="" />
<div class="caption figure">Fig. 11.</div>
</div>

<p>The former apparatus in Savery's engine consists of two
strong boilers, sections of which are represented at <strong>D</strong> and <strong>E</strong> in
<a href="#Fig011"><i>fig.</i> 11.</a>; <strong>D</strong> the greater
boiler, and <strong>E</strong> the less.
The tubes <strong>T</strong> and <strong>Tâ€²</strong>
communicate with the
working apparatus,
which we shall presently
describe. A thin
plate of metal <strong>R</strong>, is applied
closely to the top
of the great boiler <strong>D</strong>,
turning on a centre <strong>C</strong>, so that by moving a lever applied to
the axis <strong>C</strong> on the outside of the top, the sliding plate <strong>R</strong> can be
brought from the mouth of the one tube to the mouth of the
other alternately. This sliding valve is called the <em>regulator</em>,
since it is by it that the communications between the boiler
and two steam vessels (hereafter described) are alternately
opened and closed, the lever which effects this being moved
at intervals by the hand of the attendant.</p>

<p>Two <em>gauge cocks</em> are represented at <strong>G</strong>, <strong>Gâ€²</strong>,
the use of which
is to determine the depth of water in the boiler. One, <strong>G</strong>, has
its lower aperture a little above the proper depth; and the
other, <strong>Gâ€²</strong>, a little below it. Cocks are attached to the upper
ends <strong>G</strong>, <strong>Gâ€²</strong>, which can be opened or closed at pleasure. The
steam collected in the top of the boiler pressing on the surface
of the water, forces it up in the tubes <strong>G</strong>, <strong>Gâ€²</strong>, if their lower
ends be immersed. Upon opening the cocks <strong>G</strong>, <strong>Gâ€²</strong>, if water
be forced from both, there is too much water in the boiler,
since the mouth of <strong>G</strong> is <em>below</em> its level. If steam issue from
both, there is too little water in the boiler, since the mouth
of <strong>Gâ€²</strong> is <em>above</em> its level. But if steam issue from <strong>G</strong>, and water
from <strong>Gâ€²</strong>, the water in the boiler is at its proper level. This
ingenious contrivance for determining the level of the water
in the boiler is the invention of Savery, and is used in many
instances at the present day.</p>

<p>The mouth of the pipe <strong>G</strong> should be at a level of a little less
<a class="refpn" id="Pg051">[Pg051]</a>
than one third of the whole depth, and the mouth of <strong>Gâ€²</strong> at a
level little lower than one third; for it is requisite that about
two thirds of the boiler should be kept filled with water. The
tube <strong>I</strong> forms a communication between the greater boiler <strong>D</strong>
and the lesser or feeding boiler <strong>E</strong>, descending nearly to the
bottom of it. This communication can be opened and closed
at pleasure by the cock <strong>K</strong>. A gauge pipe is inserted similar
to <strong>G</strong>, <strong>Gâ€²</strong>, but extending nearly to the bottom. From this
boiler a tube <strong>F</strong> extends, which is continued to a cistern <strong>C</strong>
(<a href="#Fig012"><i>fig.</i> 12.</a>), and a cock is placed at <strong>M</strong>, which, when opened,
allows the water from the cistern to flow into the feeding
boiler <strong>E</strong>, and which is closed when that boiler is filled. The
manner in which this cistern is supplied will be described
hereafter.</p>

<p>Let us now suppose that the principal boiler is filled to the
level between the gauge pipes, and that the subsidiary boiler
is nearly full of water, the cock <strong>K</strong> and the gauge cocks <strong>G Gâ€²</strong>
being all closed. The fire being lighted beneath <strong>D</strong>, and the
water boiled, steam is produced, and is transmitted through
one or other of the tubes <strong>T</strong>, <strong>Tâ€²</strong>, to the working apparatus.
When evaporation has reduced the water in <strong>D</strong> below the level
of <strong>Gâ€²</strong>, it will be necessary to replenish the boiler <strong>D</strong>. This is
effected thus:â€”A fire being lighted beneath the feeding
boiler <strong>E</strong>, steam is produced in it above the surface of the
water, which, having no escape, presses on the surface so as to
force it up in the pipe <strong>I</strong>. The cock <strong>K</strong> being then opened, the
boiling water is forced into the principal boiler <strong>D</strong>, into which
it is allowed to flow until water issues from the gauge cock <strong>Gâ€²</strong>.
When this takes place, the cock <strong>K</strong> is closed, and the fire removed
from <strong>E</strong> until the great boiler again wants replenishing.
When the feeding boiler <strong>E</strong> has been exhausted, it is replenished
from the cistern <strong>C</strong> (<a href="#Fig012"><i>fig.</i> 12.</a>), through the pipe <strong>F</strong>, by
opening the cock <strong>M</strong>.</p>


<div class="ph3">
<h3>(32.)</h3> We shall now describe the working apparatus in
which the steam is used as a moving power.</div>

<p>Let <strong>V Vâ€²</strong> (<a href="#Fig012"><i>fig.</i> 12.</a>) be two steam vessels communicating by
the tubes <strong>T Tâ€²</strong> (marked by the same letters in <a href="#Fig011"><i>fig.</i> 11.</a>) with the
greater boiler <strong>D</strong>.</p>

<div class="figleft" style="width: 300px;">
<a id="Fig012"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_074.png" width="300" height="394" alt="" />
<div class="caption figure">Fig. 12.</div>
</div>

<p>Let <strong>S</strong> be a pipe, called the <em>suction pipe</em>, descending into
<a class="refpn" id="Pg052">[Pg052]</a>
the well or reservoir from which the water is to be raised, and
communicating with each of
the steam vessels through
tubes <strong>D Dâ€²</strong>, by valves <strong>A Aâ€²</strong>,
which open upwards. Let
<strong>F</strong> be a pipe continued from
the level of the engine to
whatever higher level it is
intended to elevate the water.
The steam vessels <strong>V Vâ€²</strong> communicate
with the <em>force-pipe</em>
<strong>F</strong> by valves <strong>B Bâ€²</strong>, which open
upwards, through the tubes
<strong>E Eâ€²</strong>. Over the steam vessels
and on the force-pipe is placed
a small cistern <strong>C</strong>, already
mentioned, which is kept
filled with cold water from the force-pipe, and from the
bottom of which proceeds a pipe terminated with a cock <strong>G</strong>.
This is called the <em>condensing pipe</em>, and can be brought alternately
over each steam vessel. From this cistern another
pipe communicates with the feeding boiler (<a href="#Fig011"><i>fig.</i> 11.</a>), by the
cock <strong>M</strong>.<a name="FNanchor_9_9" id="FNanchor_9_9"></a><a href="#Footnote_9_9" class="fnanchor">[9]</a></p>

<p>The communication of the pipes <strong>T Tâ€²</strong> with the boiler can be
opened and closed alternately, by the regulator <strong>R</strong> (<a href="#Fig011"><i>fig.</i> 11.</a>),
already described.</p>

<p>Now suppose the steam vessels and tubes to be all filled
with common atmospheric air, and that the regulator be
placed so that the communication between the tube <strong>T</strong> and the
boiler be opened, the communication between the other tube
<strong>Tâ€²</strong> and the boiler being closed, steam will flow into <strong>V</strong> through
<strong>T</strong>. At first, while the vessel <strong>V</strong> is cold, the steam will be condensed,
and will fall in drops of water on the bottom and sides
of the vessel. The continued supply of steam from the boiler
will at length impart such a degree of heat to the vessel <strong>V</strong>,
that it will cease to condense it. Mixed with the heated air
<a class="refpn" id="Pg053">[Pg053]</a>
contained in the vessel <strong>V</strong>, it will have an elastic force greater
than the atmospheric pressure, and will therefore force open
the valve <strong>B</strong>, through which a mixture of air and steam will be
driven until all the air in the vessel <strong>V</strong> will have passed out,
and it will contain nothing but the pure vapour of water.</p>

<p>When this has taken place, suppose the regulator be moved
so as to close the communication between the tube <strong>T</strong> and the
boiler, and to stop the further supply of steam to the vessel
<strong>V</strong>; and at the same time let the condensing pipe <strong>G</strong> be brought
over the vessel <strong>V</strong>, and the cock opened so as to let a stream of
cold water flow upon it. This will cool the vessel <strong>V</strong>, and the
steam with which it is filled will be condensed and fall in a
few drops of water, leaving the interior of the vessel a vacuum.
The valve <strong>B</strong> will be kept closed by the atmospheric pressure.
But the elastic force of the air between the valve <strong>A</strong> and the
surface of the water in the well, or reservoir, will open <strong>A</strong>, so
that a part of this air will rush in, and occupy the vessel <strong>V</strong>.
The air in the suction pipe <strong>S</strong>, being thus allowed an increased
space, will be proportionally diminished in its elastic force,
and its pressure will no longer balance that of the atmosphere
acting on the external surface of the water in the reservoir.
This pressure will, therefore, force water up in the tube
<strong>S</strong> until its weight, together with the elastic force of the air
above it, balances the atmospheric pressure. When this
has taken place, the water will cease to ascend.</p>

<p>Let us now suppose that, by shifting the regulator, the
communication is opened between <strong>T</strong> and the boiler, so that
steam flows again into <strong>V</strong>. The condensing cock <strong>G</strong> being removed,
the vessel will be again heated as before, the air expelled,
and its place filled by the steam. The condensing
pipe being again allowed to play upon the vessel <strong>V</strong>, and the
further supply of steam being stopped, a vacuum will be produced
in <strong>V</strong>, and the atmospheric pressure will force the
water through the valve <strong>A</strong> into the vessel <strong>V</strong>, which it will
nearly fill, a small quantity of air, however, remaining above
it.</p>

<p>Thus far the mechanical agency employed in elevating the
water is the atmospheric pressure; and the power of steam
is no further employed than in the production of a vacuum.
<a class="refpn" id="Pg054">[Pg054]</a>
But, in order to continue the elevation of the water through
the force pipe <strong>F</strong>, above the level of the steam vessel, it will be
necessary to use the elastic pressure of the steam. The
vessel <strong>V</strong> is now nearly filled by the water which has been
forced into it by the atmosphere. Let us suppose that, the
regulator being shifted again, the communication between the
tube <strong>T</strong> and the boiler is opened, the condensing cock removed,
and that steam flows into <strong>V</strong>. At first, coming in contact with
the cold surface of the water and that of the vessel, it is condensed;
but the vessel is soon heated, and the water formed
by the condensed steam collects in a sheet or film upon the
surface of the water in <strong>V</strong>, so as to form a surface as hot as
boiling water.<a name="FNanchor_10_10" id="FNanchor_10_10"></a><a href="#Footnote_10_10" class="fnanchor">[10]</a> The steam then being no longer condensed,
presses on the surface of the water with its elastic force; and
when that pressure becomes greater than the atmospheric
pressure, the valve <strong>B</strong> is forced open, and the water issuing
through it, passes through <strong>E</strong> into the force-pipe <strong>F</strong>; and this is
continued until the steam has forced all the water from <strong>V</strong>,
and occupies its place.</p>

<p>The further admission of steam through <strong>T</strong> is once more
stopped by moving the regulator; and the condensing pipe
being again allowed to play on <strong>V</strong>, so as to condense the steam
which fills it, produces a vacuum. Into this vacuum, as before,
the atmospheric pressure will force the water, and
fill the vessel <strong>V</strong>. The condensing pipe being then closed, and
steam admitted through <strong>T</strong>, the water in <strong>V</strong> will be forced by its
pressure through the valve <strong>B</strong> and tube <strong>E</strong> into <strong>F</strong>, and so the
process is continued.</p>

<p>We have not yet noticed the other steam vessel <strong>Vâ€²</strong>, which,
as far as we have described, would have remained filled with
common atmospheric air, the pressure of which on the valve
<strong>Aâ€²</strong> would have prevented the water raised in the suction pipe
<strong>S</strong> from passing through it. However, this is not the case; for,
during the entire process which has been described in <strong>V</strong>,
similar effects have been produced in <strong>Vâ€²</strong>, which we have only
omitted to notice to avoid the confusion which the two processes
might produce. It will be remembered, that after the
steam, in the first instance, having flowed from the boiler
<a class="refpn" id="Pg055">[Pg055]</a>
through <strong>T</strong>, has blown the air out of <strong>V</strong> through <strong>B</strong>, the communication
between <strong>T</strong> and the boiler is closed. Now the same
motion of the regulator which closes this, opens the communication
between <strong>Tâ€²</strong> and the boiler; for the sliding plate <strong>R</strong>
(<a href="#Fig011"><i>fig.</i> 11.</a>) is moved from the one tube to the other, and at the
same time, as we have already stated, the condensing pipe is
brought to play on <strong>V</strong>. While, therefore, a vacuum is being
formed in <strong>V</strong> by condensation, the steam, flowing through <strong>Tâ€²</strong>,
blows out the air through <strong>Bâ€²</strong>, as already described in the other
vessel <strong>V</strong>; and while the air in <strong>S</strong> is rushing up through <strong>A</strong> into
<strong>V</strong>, followed by the water raised in <strong>S</strong> by the atmospheric pressure,
the vessel <strong>V</strong>â€² is being filled with steam, and the air
is completely expelled from it.</p>

<p>The communication between <strong>T</strong> and the boiler is now again
opened, and the communication between <strong>Tâ€²</strong> and the boiler
closed by moving the regulator <strong>R</strong> (<a href="#Fig011"><i>fig.</i> 11.</a>) from the tube
<strong>T</strong> to <strong>Tâ€²</strong>; at the same time the condensing pipe is removed
from over <strong>V</strong>, and brought to play upon <strong>Vâ€²</strong>. While the steam
once more expels the air from <strong>V</strong> through <strong>B</strong>, a vacuum is
formed by condensation in <strong>Vâ€²</strong>, into which the water in <strong>S</strong>
rushes through the valve <strong>Aâ€²</strong>. In the mean time <strong>V</strong> is again
filled with steam. The communication between <strong>T</strong> and the
boiler is now closed, and that between <strong>Tâ€²</strong> and the boiler is
opened, and the condensing pipe removed from <strong>Vâ€²</strong>, and brought
to play on <strong>V</strong>. While the steam from the boiler forces the
water in <strong>Vâ€²</strong> through <strong>Bâ€²</strong> into the force-pipe <strong>F</strong>, a vacuum is being
produced in <strong>V</strong>, into which water is raised by the atmospheric
pressure.</p>

<p>Thus each of the vessels <strong>V</strong> <strong>Vâ€²</strong> is alternately filled from <strong>S</strong>,
and the water thence forced into <strong>F</strong>. The same steam which
forces the water from the vessels into <strong>F</strong>, having done its duty,
is condensed, and brings up the water from <strong>S</strong>, by giving effect
to the atmospheric pressure.</p>

<p>During this process, two alternate motions or adjustments
must be constantly made; the communication between <strong>T</strong> and
the boiler must be opened, and that between <strong>Tâ€²</strong> and the boiler
closed, which is done by one motion of the regulator. The
condensing pipe at the same time must be brought from <strong>V</strong> to
play on <strong>Vâ€²</strong>, which is done by the lever placed upon it. Again
<a class="refpn" id="Pg056">[Pg056]</a>
the communication between <strong>Tâ€²</strong> and the boiler is to be opened,
and that between <strong>T</strong> and the boiler closed; this is done by
moving back the regulator. The condensing pipe is brought
from <strong>Vâ€²</strong> to <strong>V</strong> by moving back the other lever, and so on
alternately.</p>

<p>For the clearness and convenience of description, some
slight and otherwise unimportant changes have been made in
the position of the parts. A perspective view of this engine
is represented at the head of this chapter. The different
parts already described will easily be recognised.</p>

<p>The engine of Savery was very clearly described in a small
work published in London in 1702, entitled, <cite>The Miner's
Friend, or an Engine to raise Water by Fire described, and
the Manner of Fixing it in Mines; with an Account of the
several Uses it is applicable unto, and an Answer to the Objection
made against it; by Thomas Savery, Gentleman</cite>. This
volume was dedicated to William III. (to whom the engine
had been exhibited at Hampton Court palace), to the Royal
Society, and to the mining adventurers of England. The
following are the uses to which Savery proposed the engine
should be applied: <em>First</em>, to raise water for turning all sorts
of mills; <em>second</em>, supplying palaces and houses with water,
and supplying means of extinguishing fire therein by the
water so raised; <em>third</em>, the supplying cities and towns with
water; <em>fourth</em>, draining fens or marshes; <em>fifth</em>, for ships;
<em>sixth</em>, the drainage of mines.</p>

<p>Dr. Harris, in his <cite>Lexicon Technicum, or Dictionary of
Arts and Sciences</cite>, mentions a machine of Savery's for propelling
a vessel in a calm, by paddle-wheels placed at the
side; but it does not appear that Savery contemplated the
application of a steam engine to work these wheels.</p>

<p>It is only from scattered passages in publications of the day
that it can be ascertained to what extent the engines of
Savery were practically applied. In his address to the Royal
Society, he speaks of the "difficulties and expense which he
encountered in instructing artisans to make engines according
to his wish; but that after much experience the workmen
had become such masters of the thing, that they bound
themselves to deliver the engines 'exactly tight and fit for
<a class="refpn" id="Pg057">[Pg057]</a>
service, and such as he (Savery) dare warrant them to every
one that has occasion for them.'"</p>

<p>In his address to the miners of England he also says,
"that the frequent disorders and cumbersomeness of water
engines then in use encouraged him to invent engines to
work by this new force; that though they were obliged to
encounter the oddest and almost insuperable difficulties, yet
he spared neither time, pains, nor money, till he had conquered
them."</p>

<p>In Bradley's <cite>Improvements of Planting and Gardening</cite>, 1718,
the author thus speaks of an engine erected by Savery:â€”</p>

<p>"Supposing the situation of a house or garden to be a
considerable height above any pond, river, or spring, and
that it has at present no other conveniency of water than
what is brought continually by men or horses to it. In this
case, the wonderful invention of the late Mr. Savery, F.R.S.,
for raising water by fire, will not only supply the defect, by
flinging up as much water as may be desired, but may be
maintained with very little trouble and very small expense.</p>

<p>"It is now about six years since Mr. Savery set up one
of them for that curious gentleman Mr. Balle, at Cambden
House, Kensington, near London, which has succeeded so
well that there has not been any want of water since it has
been built; and, with the improvements since made to it, I
am apt to believe will be less subject to be out of order than
any engine whatever."</p>

<p>It is remarkable that, notwithstanding the high pressure
steam necessary for the operation of Savery's engine, he does
not appear to have adopted the obvious expedient of a safety
valve. The safety valve had been previously known, having
been invented about the year 1681, by Papin, for his digester,
which was a close boiler, contrived by him for stewing meat
and digesting bones, by submitting them to a higher temperature
than that of water boiling in an open vessel.</p>

<p>The safety valve which has ever since been used for steam
boilers of every kind is a valve which opens outwards, and is
fitted to an aperture in the boiler, so as to be steam tight. It
is pressed down by a weight, the amount of which is regulated
by the maximum pressure to which it is intended the steam
<a class="refpn" id="Pg058">[Pg058]</a>
shall be limited. Thus, if the magnitude of the valve be a
square inch, and the pressure of the steam be limited to 10 lbs.
per square inch above the pressure of the atmosphere, then
the valve would be loaded with a weight of 10 lbs.; but as it
was found necessary to vary from time to time the limiting
pressure of the steam, or the load of the safety valve, these
valves were usually constructed so as to be held down by the
pressure of a lever having a sliding weight upon it. By moving
the weight on the arm of the lever, the pressure on the valve
could be increased or diminished at the discretion of the
engineer. This contrivance was first applied to Savery's
engines, by Desaguliers, about the year 1717, before which
year Savery died.</p>

<p>It is justly observed by Mr. Farey, in his treatise on the
steam engine, that, "when a comparison is made between
Captain<a name="FNanchor_11_11" id="FNanchor_11_11"></a><a
href="#Footnote_11_11" class="fnanchor">[11]</a>
Savery's engine and those of his predecessors, the
result will be in every respect favourable to his character as
an inventor, and as a practical engineer; all the details of his
invention are made out in a masterly style, and accidents and
contingencies are provided for, so as to render it a real working
engine; whereas De Caus, the Marquis of Worcester,
Sir Samuel Morland, and Papin, though ingenious philosophers,
only produced mere outlines, which required great
labour and skill of subsequent inventors to fill up, and make
them sufficiently complete to be put in execution."</p>

<p>About the year 1718 further improvements were made in
the construction of Savery's engine, by Dr. Desaguliers; but
it is probable that some of these were suggested by the proceedings
of the inventors of the atmospheric engine, which
shall presently describe.</p>


<div class="ph3"><h3>(33.)</h3> In order duly to appreciate
the value of improvements,
it is necessary first to perceive the defects which
these improvements are designed to remove. Savery's steam
engine, considering how little was known of the value and
properties of steam, and how low the general standard of
mechanical knowledge was in his day, is certainly highly
<a class="refpn" id="Pg059">[Pg059]</a>
creditable to his genius. Nevertheless it had very considerable
defects, and was finally found to be inefficient for the
most important purposes to which he proposed applying it.</div>

<p>At the time of this invention, the mines in England had
greatly increased in depth, and the process of draining them
had become both expensive and difficult; so much so, that it
was found in many instances that their produce did not cover
the cost of working them. The drainage of these mines was
the most important purpose to which Savery proposed to
apply his steam engine.</p>

<p>It has been already stated that the pressure of the atmosphere
amounts to about fifteen pounds on every square inch.
Now, a column of water, whose base is one square inch, and
whose height is thirty-four feet, weighs about fifteen pounds.
If we suppose that a perfect vacuum were produced in the steam
vessels <strong>V Vâ€²</strong> (<a href="#Fig012"><i>fig.</i> 12.</a>) by condensation, the atmospheric pressure
would fail to force up the water, if the height of the top of these
vessels above the water to be raised exceeded thirty-four feet.
It is plain, therefore, that the engine cannot be more than
thirty-four feet above the water which it is intended to elevate.
But in fact it cannot be so much; for the vacuum produced
in the steam vessels <strong>V Vâ€²</strong> is never perfect. Water, when not
submitted to the pressure of the atmosphere, will vaporise at
a very low temperature, as we shall hereafter explain; and
it was found that a vapour possessing a considerable elasticity
would, notwithstanding the condensation, remain in the vessels
<strong>V Vâ€²</strong> and the pipe <strong>S</strong>, and would oppose the ascent of the
water. In consequence of this, the engine could never be
placed with practical advantage at a greater height than
twenty-six feet above the level of the water to be raised.</p>


<div class="ph3"><h3>(34.)</h3> When the water is elevated to the engine, and the
steam vessels filled, if steam be introduced above the water
in <strong>V</strong>, it must first balance the atmospheric pressure, before it
can force the water through the valve <strong>B</strong>. Here, then, is a
mechanical pressure of fifteen pounds per square inch expended,
without any water being raised by it. If steam of
twice that elastic force be used, it will elevate a column in <strong>F</strong>
of thirty-four feet in height; and if steam of triple the force
be used, it will raise a column of sixty-eight feet high,
<a class="refpn" id="Pg060">[Pg060]</a>
which, added to twenty-six feet raised by the atmosphere,
gives a total lift of ninety-four feet.</div>

<p>In effecting this, steam of a pressure equal to three times
that of the atmosphere acts on the inner surface of the
vessels <strong>V Vâ€²</strong>. One third of this bursting pressure is balanced
by the pressure of the atmosphere on the external
surface of the vessels; but an effective pressure of thirty
pounds per square inch still remains, tending to burst the
vessels. It was found that the apparatus could not be constructed
to bear more than this with safety; and, therefore,
in practice, the lift of such an engine was limited to about
ninety perpendicular feet. In order to raise the water from
the bottom of the mine by these engines, therefore, it was
necessary to place one at every ninety feet of the depth; so
that the water raised by one through the first ninety feet
should be received in a reservoir, from which it was to be
elevated the next ninety feet by another, and so on.</p>

<p>Besides this, it was found that sufficient strength could not
be given to those engines, if constructed upon a large scale.</p>

<p>They were, therefore, necessarily very limited in their dimensions,
and were incapable of raising the water with sufficient
speed. Hence arose a necessity for several engines at
each level, which greatly increased the expense.</p>


<div class="ph3"><h3>(35.)</h3> These, however, were not the only defects of Savery's
engines. The consumption of fuel was enormous, the proportion
of heat wasted being much more than what was used in
either forcing up the water, or producing a <em>vacuum</em>. This
will be very easily understood by attending to the process of
working the engine already described.</div>

<p>When the steam is first introduced from the boiler into
the steam vessels <strong>V Vâ€²</strong>, preparatory to the formation of a vacuum,
it is necessary that it should heat these vessels up to
the temperature of the steam itself; for until then the steam
will be condensed the moment it enters the vessel by the
cold surface. All this heat, therefore, spent in raising the
temperature of the steam vessels is wasted. Again, when the
water has ascended and filled the vessels <strong>V Vâ€²</strong>, and steam is
introduced to force this water through <strong>B Bâ€²</strong> into <strong>F</strong>, it is immediately
condensed by the cold surface in <strong>V Vâ€²</strong>, and does not
<a class="refpn" id="Pg061">[Pg061]</a>
begin to act until a quantity of hot water, formed by condensed
steam, is collected on the surface of the cold water
which fills these vessels. Hence another source of the waste
of heat arises.</p>

<p>When the steam begins to act upon the surface of the water
in <strong>V Vâ€²</strong>, and to force it down, the cold surface of the vessels
is gradually exposed to the steam, and must be heated while
the steam continues its action; and when the water has been
forced out of the vessel, the vessel itself has been heated to
the temperature of the steam which fills it, all which heat is
dissipated by the subsequent process of condensation. It
must thus be evident that the steam used in forcing up
the water in <strong>F</strong>, and in producing a vacuum, bears a very small
proportion indeed to what is consumed in heating the apparatus
after condensation.</p>


<div class="ph3"><h3>(36.)</h3> There is also another circumstance which increases
the consumption of fuel. The water must be forced through
<strong>B</strong>, not only against the atmospheric pressure, but also against
a column of sixty-eight feet of water. Steam is therefore
required of a pressure of forty-five pounds on the square
inch. Consequently the water in the boiler must be boiled
under this pressure. That this should take place, it is necessary
that the water should be raised to a temperature considerably
above 212Â°, even so high as 275Â°; and thus an increased
heat must be given to the boiler. Independently of
the other defects, this intense heat weakened and gradually
destroyed the apparatus.</div>

<p>Savery was the first who suggested the method of expressing
the power of an engine with reference to that of
horses. In this comparison, however, he supposed each horse
to work but eight hours a day, while the engine works for
twenty-four hours. This method of expressing the power of
steam engines will be explained hereafter.</p>


<div class="ph3"><h3>(37.)</h3> The failure of the engines proposed by Captain Savery
in the work of drainage, from the causes which have been
just mentioned, and the increasing necessity for effecting this
object, arising from the large property in mines which became
every year unproductive by being flooded, stimulated the ingenuity
<a class="refpn" id="Pg062">[Pg062]</a>
of mechanics to contrive some means of rendering those
powers of steam exhibited in Savery's engine available.</div>

<p>Thomas Newcomen, the reputed inventor of the atmospheric
engine, was an ironmonger, or, according to some, a
blacksmith, in the town of Dartmouth in Devonshire. From
his personal acquaintance and intercourse with Dr. Hooke,
the celebrated natural philosopher, it is probable that he was
a person of some education, and therefore likely to be above
the position of a blacksmith. Being in the habit of visiting
the tin mines in Cornwall, Newcomen became acquainted
with the engine invented by Savery, and with the causes
which led to its inefficiency for the purposes of drainage.</p>

<p>It has been stated that Papin, about the year 1690, proposed
the construction of an engine working by the atmospheric
pressure acting on one side of a piston against a
vacuum produced by the condensation of steam on the other
side. Papin was not conscious of the importance of this
principle; for, so far from ever having attempted to apply it
to practical purposes, he probably never constructed, even on
a small scale, any machine illustrating it. On the contrary,
he abandoned the project the moment he was informed of
the principle and structure of the steam engine of Savery;
and he then proposed an engine for raising water, acting by
the expansive force of steam similar to Savery's, but abandoning
the method of working by a vacuum.</p>

<p>This engine is described by Papin in a work published in
1707.</p>

<div class="figcenter" style="width: 550px;">
<a id="Fig013"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_085.png" width="550" height="434" alt="" />
<div class="caption figure">Fig. 13.</div>
</div>

<p><strong>A</strong> (<a href="#Fig013"><i>fig.</i> 13.</a>) is an oval boiler, having a safety-valve <strong>B</strong>, which
limits the pressure of the steam. It is connected with a cylinder
<strong>C</strong>, by a curved pipe having a stop-cock at <strong>D</strong>. A pipe
with a stop-cock <strong>G</strong> opens from the top of the cylinder into
the atmosphere, and a safety-valve <strong>F</strong> is placed upon the cylinder.
A hollow copper piston <strong>H</strong> moves freely in the cylinder,
and floats upon the water. <strong>O</strong> is a funnel with a valve <strong>L</strong>
in the bottom, opening downwards, through which the cylinder
<strong>C</strong> may be filled with water to the level of the top of the
funnel. A close air-vessel communicates with the cylinder
<strong>C</strong> by the curved tube, and has a valve <strong>K</strong> opening upwards.
The force-pipe through which the water is raised communicates
<a class="refpn" id="Pg063">[Pg063]</a>
with the air-vessel <strong>I</strong>. If the cock <strong>D</strong> be shut, and the
cock <strong>G</strong> opened, water poured into the funnel <strong>O</strong> will rise into
the cylinder <strong>C</strong>, the air which fills the cylinder escaping
through the open pipe <strong>G</strong>. When the cylinder is thus filled
with water, let the cock <strong>G</strong> be closed, and the cock <strong>D</strong> opened.
The steam from the boiler, after heating the metal of the
cylinder, will force the piston downwards, and drive the water
through the curved tube into the vessel <strong>I</strong>, from which its return
is prevented by the valve <strong>K</strong>, which is closed by its
weight. The air which filled the vessel <strong>I</strong> will then be compressed,
and by its elasticity will drive a column of water up
the pipe <strong>N</strong>. After the contents of the cylinder have been
thus discharged it may be refilled in the same manner, and
the process repeated.</p>

<p>It will be perceived that this project is nothing more than a
reproduction of the engine of the Marquis of Worcester. In
the preface to the work containing this description, Papin
gives an extract from a letter addressed by him to Leibnitz
in 1698, from which it appears that he had abandoned his
idea of working the piston by the atmospheric pressure acting
against a vacuum, considering it to be a contrivance inferior
<a class="refpn" id="Pg064">[Pg064]</a>
to the engine now described. "We now raise water,"
he says, "by the force of fire, <em>in a more advantageous
manner than that which I had published some years before</em>;
for besides the suction, we now also use the pressure which
the water exerts upon other bodies in dilating itself by heat;
instead of which I before employed the suction only, the effects
of which are more limited."</p>

<p>From documents which have been preserved in the Royal
Society, it appears that Newcomen was acquainted with
Papin's writings, and therefore probably first derived from
them the suggestion which he subsequently realised in the
atmospheric engine. Among some papers of Dr. Hooke's
have been found notes for the use of Newcomen, on Papin's
method of transmitting the force of a stream or fall of water
to a distance by pipes. Hooke dissuaded Newcomen from
attempting any machine on this principle, which, as first proposed
by Papin, was impracticable. He exposed the fallacy
of Papin's first project in several discourses before the Royal
Society, and considered his improved edition of it, though free
from fallacy, as impracticable.</p>

<p>Papin's project for producing a vacuum under a piston by
condensing the steam having been published in the <cite>ActÃ¦
Eruditorum</cite>, in Latin, in 1690, and in French, at Cassel, in
1695, and subsequently, in the <cite>Philosophical Transactions</cite>, in
England in 1697, cannot be supposed to be unknown to Dr.
Hooke; and if known to him, would probably have been communicated
to Newcomen. Dr. Hooke died in 1703, some
years before the date of Newcomen's invention.</p>

<p>John Cawley, who was the associate of Newcomen in his
experiments and inquiries, was a plumber and glazier of the
same town. Newcomen and Cawley obtained a patent for the
atmospheric engine in 1705, in which Savery was associated,
he having previously obtained a patent for the method of producing
a vacuum by the condensation of steam, which was
essential to Newcomen's contrivance. It was not, however,
until about the year 1711 that any engine had been constructed
under this patent.</p>

<p>In the latter end of that year, according to Desaguliers, the
patentees "made proposals to drain a colliery at Griff, in
<a class="refpn" id="Pg065">[Pg065]</a>
Warwickshire, in which work five hundred horses were constantly
employed. This proposal not being accepted, they
contracted, in the following March, to drain water for Mr.
Back of Wolverhampton, where, after many laborious attempts,
they succeeded in making their engine work; but not
being either philosophers to understand the reason, or mathematicians
enough to calculate the power and proportions
of the parts, they very luckily, by accident, found what they
sought for."</p>

<div class="figcenter" style="width: 550px;">
<a id="Fig014"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_087.png" width="550" height="621" alt="" />
<div class="caption figure">Fig. 14.</div>
</div>

<p>Newcomen resumed the old method of raising the water
from the mines by ordinary pumps, but conceived the idea
of working these pumps by some moving power less expensive
than that of horses. The means whereby he proposed
effecting this, was by connecting the end of the
pump-rod <strong>D</strong> (<a href="#Fig014"><i>fig.</i> 14.</a>) by a chain with the arch head <strong>A</strong> of a
<a class="refpn" id="Pg066">[Pg066]</a>
working-beam <strong>A B</strong>, playing on an axis <strong>C</strong>. The other arch
head <strong>B</strong> of this beam was connected by a chain with the rod
<strong>E</strong> of a solid piston <strong>P</strong>, which moved air-tight in a cylinder <strong>F</strong>.
If a vacuum be created beneath the piston <strong>P</strong>, the atmospheric
pressure acting upon it will press it down with a force of
fifteen pounds per square inch; and the end <strong>A</strong> of the beam
being thus raised, the pump-rod <strong>D</strong> will be drawn up. If a
pressure equivalent to the atmosphere be then introduced
below the piston, so as to neutralise the downward pressure,
the piston will be in a state of indifference as to the rising or
falling; and if in this case the rod <strong>D</strong> be made heavier than the
piston and its rod, so as to overcome the friction, it will
descend, and elevate the piston again to the top of the cylinder.
The vacuum being again produced, another descent of
the piston, and consequent elevation of the pump-rod, will
take place; and so the process may be continued.</p>

<p>Such was Newcomen's first conception of the <em>atmospheric
engine</em>; and the contrivance had much, even at the first view,
to recommend it. The power of such a machine would
depend entirely on the magnitude of the piston; and being
independent of highly elastic steam, would not expose the
materials to the destructive heat which was necessary for
working Savery's engine. Supposing a perfect vacuum to
be produced under the piston in the cylinder, an effective
downward pressure would be obtained, amounting to fifteen
times as many pounds as there are square inches in the
section of the piston.<a name="FNanchor_12_12" id="FNanchor_12_12"></a><a href="#Footnote_12_12" class="fnanchor">[12]</a> Thus, if the base of the piston were
100 square inches, a pressure equal to 1500 pounds would
be obtained.</p>


<div class="ph3"><h3>(38.)</h3> In order to accomplish this, two things were necessary:
1. To make a speedy and effectual vacuum below the
<a class="refpn" id="Pg067">[Pg067]</a>
piston in the descent; and, 2. To contrive a counterpoise for
the atmosphere in the ascent.</div>

<p>The condensation of steam immediately presented itself as
the most effectual means of accomplishing the former; and
the elastic force of the same steam previous to condensation
an obvious method of effecting the latter. Nothing now
remained to carry the design into execution, but the contrivance
of means for the alternate introduction and condensation
of the steam; and Newcomen and Cawley were
accordingly granted a patent in 1707, in which Savery was
united, in consequence of the principle of condensation for
which he had previously received a patent being necessary to
the projected machine. We shall now describe the <em>atmospheric
engine</em>, as first constructed by Newcomen:â€”</p>

<p>The boiler <strong>K</strong> (<a href="#Fig014"><i>fig.</i> 14.</a>) is placed over a furnace <strong>I</strong>, the flue of
which winds round it, so as to communicate heat to every part
of the bottom of it. In the top, which is hemispherical, two
gauge-cocks <strong>G Gâ€²</strong> are placed, as in Savery's engine, and a
<em>puppet valve</em> <strong>V</strong>, which opens upward, and is loaded at one
pound per square inch; so that when the steam produced in
the boiler exceeds the pressure of the atmosphere by more
than one pound on the square inch, the valve <strong>V</strong> is lifted, and
the steam escapes through it, and continues to escape until
its pressure is sufficiently diminished, when the valve <strong>V</strong> again
falls into its seat. This valve performs the office of the safety-valve
in modern engines.</p>

<p>The great steam-tube is represented at <strong>S</strong>, which conducts
steam from the boiler to the cylinder; and a feeding pipe <strong>T</strong>,
furnished with a cock, which is opened and closed at pleasure,
proceeds from a cistern <strong>L</strong> to the boiler. By this pipe the
boiler may be replenished from the cistern, when the gauge
cock <strong>Gâ€²</strong> indicates that the level has fallen below it. The
cistern <strong>L</strong> is supplied with hot water, by means which we shall
presently explain.</p>


<div class="ph3"><h3>(39.)</h3> To understand the mechanism necessary to work the
piston, let us consider how the supply and condensation of
steam must be regulated. When the piston has been forced
to the bottom of the cylinder by the atmospheric pressure
acting against a vacuum, in order to balance that pressure,
<a class="refpn" id="Pg068">[Pg068]</a>
and enable it to be drawn up by the weight of the pump-rod,
it is necessary to introduce steam from the boiler. This is
accomplished by opening the cock <strong>R</strong> in the steam pipe <strong>S</strong>.
The steam being thus introduced from the boiler, its pressure
balances the action of the atmosphere upon the piston, which
is immediately drawn to the top of the cylinder by the
weight of the pump-rod <strong>D</strong>. It then becomes necessary to
condense this steam, in order to produce a vacuum. To
accomplish this, the further supply of steam must be cut
off, which is done by closing the cock <strong>R</strong>. The supply of
steam from the boiler being thus suspended, the application
of cold water on the external surface of the cylinder becomes
necessary to condense the steam within it. This was
done by enclosing the cylinder within another, leaving a
space between them.<a name="FNanchor_13_13" id="FNanchor_13_13"></a><a href="#Footnote_13_13" class="fnanchor">[13]</a> Into this space cold water was allowed
to flow from a cock <strong>M</strong> placed over it, supplied by a pipe from
the cistern <strong>N</strong>. This cistern is supplied with water by a
pump <strong>O</strong>, which is worked by the engine.</div>

<p>The cold water supplied from <strong>M</strong>, having filled the space
between the two cylinders, abstracts the heat from the inner
one; and condensing the steam, produces a vacuum, into
which the piston is forced by the atmospheric pressure.
Preparatory to the next descent, the water which thus
fills the space between the cylinders, and which is warmed
by the heat abstracted from the steam, must be discharged,
in order to give room for a fresh supply of cold water
from <strong>M</strong>. An aperture, furnished with a cock, is accordingly
provided in the bottom of the cylinder, through which the
water is discharged into the cistern <strong>L</strong>; and being warm, is
adapted for the supply of the boiler through <strong>T</strong>, as already
mentioned.</p>

<p>The cock <strong>R</strong> being now again opened, steam is admitted
below the piston, which, as before, ascends, and the descent
is again accomplished by closing the cock <strong>R</strong>, and opening the
cock <strong>M</strong>, admitting cold water between the cylinders, and
thereby condensing the steam below the piston.</p>

<p>The condensed steam, thus reduced to water, will collect
<a class="refpn" id="Pg069">[Pg069]</a>
in the bottom of the cylinder, and resist the descent of the
piston. It is therefore necessary to provide an exit for it,
which is done by a valve opening <em>outwards</em> into a tube which
leads to the feeding cistern <strong>L</strong>, into which the condensed steam
is driven.</p>

<p>That the piston should continue to be air-tight, it was
necessary to keep a constant supply of water over it; this
was done by a cock similar to <strong>M</strong>, which allowed water to
flow from the pipe M on the piston.</p>


<div class="ph3">
<h3>(40.)</h3> Soon after the first construction of these engines, an
accidental circumstance suggested to Newcomen a much better
method of condensation than the application of cold water
on the external surface of the cylinder. An engine was
observed to work several strokes with unusual rapidity, and
without the regular supply of the condensing water. Upon
examining the piston, a hole was found in it, through which
the water, which was poured on to keep it air-tight, flowed,
and instantly condensed the steam under it.</div>

<p>On this suggestion Newcomen abandoned the external
cylinder, and introduced a pipe <strong>H</strong>, furnished with a cock <strong>Q</strong>,
into the bottom of the cylinder, so that, on turning the cock,
the pressure of the water in the pipe <strong>H</strong>, from the level of the
water in the cistern <strong>N</strong>, would force the water to rise as a jet
into the cylinder, and would instantly condense the steam.
This method of condensing by injection formed a very important
improvement in the engine, and is still used.</p>


<div class="ph3">
<h3>(41.)</h3> Having taken a general view of the parts of the atmospheric
engine, let us now consider more particularly its
operation.</div>

<p>When the engine is not working, the weight of the pump-rod
<strong>D</strong> (<a href="#Fig014"><i>fig.</i> 14.</a>) draws down the beam <strong>A</strong>, and draws the piston to
the top of the cylinder, where it rests. Let us suppose all the
cocks and valves closed, and the boiler filled to the proper depth.
The fire being lighted beneath it, the water is boiled until the
steam acquires sufficient force to lift the valve <strong>V</strong>. When this
takes place, the engine may be started. For this purpose the
regulating valve <strong>R</strong> is opened. The steam rushes in, and is first
condensed by the cold cylinder. After a short time the cylinder
acquires the temperature of the steam, which then
<a class="refpn" id="Pg070">[Pg070]</a>
ceases to be condensed, and mixes with the air which filled
the cylinder. The steam and heated air, having a greater
force than the atmospheric pressure, will open a valve placed
at the end <strong>X</strong> of a small tube in the bottom of the cylinder,
and which opens outwards. From this (which is called the
<em>blowing valve</em><a name="FNanchor_14_14" id="FNanchor_14_14"></a><a href="#Footnote_14_14" class="fnanchor">[14]</a>) the steam and air rush in a constant stream,
until all the air has been expelled, and the cylinder is filled
with the pure vapour of water. This process is called <em>blowing</em>
the engine preparatory to starting it.</p>

<p>When it is about to be started, the engine-man closes the
regulator <strong>R</strong>, and thereby suspends the supply of steam from
the boiler. At the same time he opens the <em>condensing valve</em>
<strong>H</strong><a name="FNanchor_15_15" id="FNanchor_15_15"></a><a href="#Footnote_15_15" class="fnanchor">[15]</a>; and thereby throws up a jet of cold water into the cylinder.
This immediately condenses the steam contained in
the cylinder, and produces the vacuum. (The atmosphere
cannot enter the <em>blowing</em> valve, because it opens <em>outwards</em>, so
that no air can enter to vitiate the vacuum.) The atmospheric
pressure above the piston now takes effect, and forces
it down in the cylinder. The descent being completed, the
engine-man closes the condensing valve <strong>H</strong>, and opens the regulator,
<strong>R</strong>. By this means he stops the play of the jet within
the cylinder, and admits the steam from the boiler. The first
effect of the steam is to expel the condensing water and condensed
steam which are collected in the bottom of the cylinder,
through the tube <strong>Y</strong>, containing a valve which opens <em>outwards</em>
(called the <em>eduction valve</em>), which leads to the hot cistern <strong>L</strong>,
into which this water is therefore discharged.</p>

<p>When the steam admitted through <strong>R</strong> ceases to be condensed,
it balances the atmospheric pressure above the piston, and thus
permits it to be drawn to the top of the cylinder by the weight
of the rod <strong>D</strong>. This ascent of the piston is also assisted by the
circumstance of the steam being somewhat stronger than the
atmosphere.</p>

<p>When the piston has reached the top, the regulating valve
<strong>R</strong> is closed, and the condensing valve <strong>H</strong> opened, and another
descent produced, as before, and so the process is continued.
<a class="refpn" id="Pg071">[Pg071]</a></p>

<p>The manipulation necessary in working this engine was,
therefore, the alternate opening and closing of two valves; the
regulating and condensing valves. When the piston reached
the top of the cylinder, the former was to be closed, and the
latter opened; and, on reaching the bottom, the former was
to be opened, and the latter closed.</p>


<div class="ph3"><h3>(42.)</h3> The duty of working the engine requiring no great
amount of labour, or skill, was usually entrusted to boys,
called, <em>cock boys</em>. It happened that one of the most important
improvements which has ever been made in the working
of steam engines was due to the ingenuity of one of these
boys. It is said that a lad, named <em>Humphrey Potter</em>, was
employed to work the cocks of an atmospheric engine, and
being tempted to escape from the monotonous drudgery to
which his duty confined him, his ingenuity was sharpened so
as to prompt him to devise some means by which he might
indulge his disposition to play without exposing himself to
the consequences of suspending the performance of the engine.
On observing the alternate ascending and descending
motion of the beam above him, and considering it in reference
to the labour of his own hands, in alternately raising and
lowering the levers which governed the cocks, he perceived a
relation which served as a clue to a simple contrivance, by
which the steam engine, for the first time, became an automaton.
When the beam arrived at the top of its play, it was
necessary to open the steam valve by raising a lever, and to
close the injection valve by raising another. This he saw
could be accomplished by attaching strings of proper length
to these levers, and tying them to some part of the beam.
These levers required to be moved in the opposite direction
when the beam attained the lowest point of its play. This
he saw could be accomplished by strings, either connected
with the outer arm of the beam, or conducted over rods or
pulleys. In short, he contrived means of so connecting the
levers which governed the two cocks by strings with the
beam, that the beam opened and closed these cocks with the
most perfect regularity and certainty as it moved upwards
and downwards.</div>

<p>Besides rendering the machine independent of manual
<a class="refpn" id="Pg072">[Pg072]</a>
superintendence, this process conferred upon it much greater
regularity of performance than any manual superintendence
could ensure.</p>

<p>This contrivance of Potter was very soon improved by the
substitution of a bar, called a <em>plug frame</em>, which was suspended
from the arm of the beam, and which carried upon it
pins, by which the arms of the levers governing the cocks
were struck as the plug-frame ascended and descended, so as
to be opened and closed at the proper times.</p>

<p>The engine thus improved required no other attendance
except to feed the boiler occasionally by the cock <strong>T</strong>, and to
attend the furnace.</p>


<div class="ph3"><h3>(43.)</h3> However the merit of the discovery of the physical
principles on which the mechanical application of steam depends
may be awarded, it must be admitted that the engine
contrived by Newcomen and his associates, considered as a
practical machine, was immeasurably superior to that which
preceded it; superior, indeed, to such a degree, that while the
one was incapable of any permanently useful application, the
other soon became a machine of extensive utility in the
drainage of mines; and, even at the present time, the atmospheric
engine is not unfrequently used in preference to the
modern steam engine, in districts where fuel is abundant
and cheap; the expense of constructing and maintaining it
being considerably less than that of an improved steam engine.
The low pressure of the steam used in working
it, rendered it perfectly safe. While Savery's engine, to
work with effect, required that the steam confined in the
vessels should have a bursting pressure amounting to about
thirty pounds per square inch, the pressure of steam in the
boiler and cylinder of the atmospheric engine required only
a pressure about one pound per square inch. The high
pressure also of the steam used in Savery's engine, was necessarily
accompanied, as we shall presently explain, by a
greatly increased temperature. The effect of this was, to
weaken and gradually destroy the vessels, especially those
which, like the steam vessels <strong>V</strong> and <strong>Vâ€²</strong> (<a href="#Fig012"><i>fig.</i> 12.</a>), were alternately
heated and cooled.</div>

<p>Besides these defects, the power of Savery's engines was
<a class="refpn" id="Pg073">[Pg073]</a>
also very restricted, both as to the quantity of water raised
and as to the height to which it was elevated. On the other
hand, the atmospheric engine was limited in its power only
by the dimensions of its piston. Another considerable
advantage which the atmospheric engine possessed over that
of Savery, was the facility with which it was capable of
driving machinery by means of the working-beam. The
merit, however, of Newcomen's engine, regarded as an invention,
and apart from merely practical considerations, must
be ascribed principally to its mechanism and combinations.
We find in it no new principle, and scarcely even a novel
application of a principle. The agency of the atmospheric
pressure acting against a vacuum, or partial vacuum, had
been long known: the method of producing a vacuum by
the condensation of steam had been suggested by Papin, and
carried into practical effect by Savery. The mechanical
power obtained from the direct pressure of the elastic force
of steam, used in the atmospheric engine to balance the
atmosphere during the ascent of the piston, was suggested
by De Caus and Lord Worcester. The boiler,
gauge pipes, and the regulator, were all borrowed from
the engine of Savery. The idea of using the atmospheric
pressure against a vacuum or partial vacuum, to work a
piston in a cylinder, had been suggested by Otto Guericke,
an ingenious German philosopher, who invented the air-pump;
and this, combined with the production of a vacuum
by the condensation of steam, was subsequently suggested
by Papin. The use of a working-beam could not have been
unknown. Nevertheless, the judicious combination of these
scattered principles must be acknowledged to deserve considerable
credit. In fact, the mechanism contrived by Newcomen
rendered a machine which was before altogether
inefficient, highly efficient: and, as observed by Tredgold,
such a result, considered in a practical sense, should be more
highly valued than the fortuitous discovery of a physical
principle. The method of condensing the steam by the
sudden injection of water, and of expelling the air and water
from the cylinder by the injection of steam, are two contrivances
not before in use, which are quite essential to the
<a class="refpn" id="Pg074">[Pg074]</a>
effective operation of the engine. These processes, which
are still necessary to the operation of the improved steam
engine, appear to be wholly due to the inventors of the
atmospheric engine.</p>

<div class="figcenter" style="width: 400px;">
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_096.png" width="400" height="421" alt="" />
<div class="caption">ATMOSPHERIC ENGINE.</div>
</div>

<div class="footnotes"><h3>FOOTNOTES:</h3>

<div class="footnote">

<p><a name="Footnote_9_9" id="Footnote_9_9"></a><a href="#FNanchor_9_9"><span class="label">[9]</span></a> This pipe is represented as proceeding from the force-pipe above the
cistern <strong>C</strong>, in the perspective view of Savery's engine at the head of this
chapter.</p></div>

<div class="footnote">

<p><a name="Footnote_10_10" id="Footnote_10_10"></a><a href="#FNanchor_10_10"><span class="label">[10]</span></a> Hot water being lighter than cold, floats on the surface.</p></div>

<div class="footnote">

<p><a name="Footnote_11_11" id="Footnote_11_11"></a><a href="#FNanchor_11_11"><span class="label">[11]</span></a> "Captain" is a title given in Cornwall to the superintendent of the
works connected with a mine.</p></div>

<div class="footnote">

<p><a name="Footnote_12_12" id="Footnote_12_12"></a><a
href="#FNanchor_12_12"><span class="label">[12]</span></a> As the calculation of the power of an engine depends on the number
of square inches in the section of the piston, it may be useful to give a
rule for computing the number of square inches in a circle. The following
rule will always give the dimensions with sufficient accuracy:â€”<em>Multiply
the number of inches in the diameter by itself; divide the product
by 14, and multiply the quotient thus obtained by 11, and the result will be
the number of square inches in the circle</em>. Thus, if there be 12 inches in the
diameter, this multiplied by itself gives 144, which divided by 14 gives
<span class="fraction">10<sup>4</sup>â„<sub>44</sub>,</span> which multiplied by 11 gives 115, neglecting fractions. There are,
therefore, 115 square inches in a circle whose diameter is 12 inches.</p></div>

<div class="footnote">

<p><a name="Footnote_13_13" id="Footnote_13_13"></a><a href="#FNanchor_13_13"><span class="label">[13]</span></a> The external cylinder is not represented in the diagram.</p></div>

<div class="footnote">

<p><a name="Footnote_14_14" id="Footnote_14_14"></a><a href="#FNanchor_14_14"><span class="label">[14]</span></a> Also called the <em>snifting</em> valve, from the peculiar noise made by the
air and steam escaping from it.</p></div>

<div class="footnote">

<p><a name="Footnote_15_15" id="Footnote_15_15"></a><a href="#FNanchor_15_15"><span class="label">[15]</span></a> Also called the <em>injection valve</em>.</p></div></div>

<div class="figcenter" style="width: 600px;">
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_097.png" width="600" height="406" alt="" />
<div class="caption">GREENOCK, IN 1824.</div>
</div>

<h2><a name="CHAP_III" id="CHAP_III">CHAP. III.</a></h2>

<p class="right"><a class="refpn" id="Pg075">[Pg075]</a><br />
<a href="#CONTENTS"><small>TOC</small></a>&#160;&#160;<a
href="#INDEX"><small>INX</small></a></p>

<div class="chapheader">
PROGRESS OF THE ATMOSPHERIC ENGINE.â€”SMEATON'S IMPROVEMENTS.â€”BRINDLEY,
ENGINEER OF THE BRIDGEWATER CANAL.â€”INVENTS THE
SELF-REGULATING FEEDER.â€”JAMES WATT.â€”HIS DESCENT AND
PARENTAGE.â€”ANECDOTES OF HIS BOYHOOD.â€”HIS EARLY ACQUIREMENTS.â€”GOES
TO LONDON.â€”RETURNS TO GLASGOW.â€”IS APPOINTED
INSTRUMENT-MAKER TO THE UNIVERSITY.â€”OPENS A SHOP IN GLASGOW.â€”HIS
FRIENDS AND PATRONS.â€”ADAM SMITH.â€”DR. BLACK.â€”ROBERT
SIMSON.â€”PROFESSOR ROBISON.â€”WATT'S PERSONAL CHARACTER.â€”INDUSTRIOUS
AND STUDIOUS HABITS.â€”HIS ATTENTION FIRST
DIRECTED TO STEAM.â€”EXPERIMENTS ON HIGH-PRESSURE STEAM.â€”REPAIRS
AN ATMOSPHERIC MODEL.â€”EXPERIMENTAL INQUIRY CONSEQUENT
ON THIS.â€”ITS RESULTS.â€”DISCOVERS THE GREAT DEFECTS
OF THE ATMOSPHERIC ENGINE.â€”DISCOVERY BY EXPERIMENT OF THE
EXPANSION WHICH WATER UNDERGOES IN EVAPORATION.â€”DISCOVERS
THE LATENT HEAT OF STEAM.â€”IS INFORMED BY DR. BLACK OF
THE THEORY OF LATENT HEAT.</div>


<div class="ph3fst"><h3>(44.)</h3> The atmospheric engine was brought to a state of considerable
efficiency and improvement by Mr. Beighton, in 1718.
From that time it continued in use without any change in its
<a class="refpn" id="Pg076">[Pg076]</a>
principle, and with little improvement in its structure, for
half a century. Although engines of this kind continued
to be extensively constructed, they were usually executed
by ordinary mechanics, incapable of applying to them the
just principles of practical science; and, consequently, little
attention was paid to their proportions. It was not until
about the year 1772, that Mr. John Smeaton, the celebrated
engineer, applied the powers of his mind to the investigation
of this machine, as he had previously done with such
success to wind and water mills. Although he did not introduce
any new principle into the atmospheric engine, yet
it derived greatly augmented power from the proportions
which he established for engines of different magnitudes.</div>

<p>In 1759, Mr. James Brindley, whose name is so celebrated
as the engineer of the Duke of Bridgewater's canal, obtained
a patent for some improvements in the atmospheric engine.
He proposed that the boiler should be made of wood and
stone, with a stove or fire-place of cast iron within it, so that
the fire should be surrounded on every side by water. The
chimney was to be an iron pipe or tube, conducted through
the boiler; so that the heated air, in passing from the fire,
should impart a portion of its heat to the water. He also
proposed a method of feeding the boiler, which, by self-acting
machinery, would keep the water in the boiler at a fixed level,
independently of any attention on the part of the engine-man.
This was to be accomplished by a buoy or float upon the surface
of the water in the boiler, which should communicate
with a valve in the feed-pipe, so that when the level of the
water in the boiler fell, the float or buoy, falling with it, would
open the valve and supply the feed. It is stated, in the
<cite>Biographia Britannica</cite>, that Mr. Brindley, in 1756, undertook
to erect an engine at Newcastle-under-Lyne; but he is
said to have been discouraged by the obstacles which were
thrown in his way, and to have abandoned the steam
engine.</p>

<p>The interval between the invention of the atmospheric
engine, and the amelioration it received at the hands of
Smeaton, has been rendered memorable by the advent of one
who was destined to work a mighty change in the condition
<a class="refpn" id="Pg077">[Pg077]</a>
of the human race by the application of his vast genius to
the adaptation of steam power to the uses of life.</p>


<div class="ph3"><h3>(45.)</h3> <strong class="m1">James Watt</strong>
was born at Greenock, in Scotland, on
the nineteenth day of January, in the year 1736.<a name="FNanchor_16_16"
id="FNanchor_16_16"></a><a href="#Footnote_16_16"
class="fnanchor">[16]</a></div>

<p>The great-grandfather of Watt, a farmer in Aberdeenshire,
was killed in one of the battles of Montrose. The victorious
party, not thinking death a sufficient expiation for the
political opinions in support of which he had fought and bled,
punished him in the person of his son, by confiscating his
little property. Thomas Watt, the son, thus deprived of
support, was received by distant relations, and, for a time,
applied himself to study, by which he was enabled, after the
restoration of tranquillity, to establish himself at Greenock
as a teacher of practical mathematics and navigation. He
resided in the burgh or barony of Crawford's Dyke, and attained
a position of sufficient respectability to be elected to
the office of baron-baillie, or chief magistrate, and died in
1734, at the advanced age of ninety-two years.</p>

<p>Thomas Watt had two sons. The elder, John, adopted
the profession of his father, and was a teacher of mathematics
and navigation at Glasgow: he died in 1737, at the age
of fifty years. The second son, James, the father of the
celebrated engineer, was, during a quarter of a century,
treasurer of the town council of Greenock, and a local magistrate.
He was remarked for the ardent zeal and enlightened
spirit with which he discharged his public duties. His business
was that of a ship-chandler, builder, and general merchant;
but, unhappily, notwithstanding his active industry, he
lost, in the decline of his life, by unsuccessful commercial speculations,
a part of the property which he had so honourably
acquired. He died in 1782, at the age of eighty-four years.</p>

<p><strong class="m1">James Watt</strong>, to whom the world is so largely indebted for
the extension and improvement of steam power, had from his
birth an extremely delicate constitution. From his mother,
<a class="refpn" id="Pg078">[Pg078]</a>
whose family name was Muirhead, he received his first lessons
in reading, and he learned from his father writing and arithmetic.
Although he was entered as a pupil in the grammar
school of Greenock, yet such was his delicate state of health,
that his attendance there was so interrupted by constant indisposition
that he could derive but little benefit from the
opportunities of instruction which it afforded. For a great
period of the year he was confined to his room, where he devoted
himself to study without the aid of instruction. It was
in the retirement of the sick chamber that the high intellectual
faculties of Watt, which were destined to produce such
precious fruits, began to unfold themselves. He was too
sickly to be subjected to the restraints which the business of
education usually imposes on children. His parents, therefore,
found it necessary to leave him at liberty to choose his
occupations and amusements. The following anecdotes will
show the use he made of this freedom.</p>

<p>A friend of his father found the boy one day stretched upon
the hearth tracing with chalk various lines and angles. "Why
do you permit this child," said he, "to waste his time so;
why not send him to school?" Mr. Watt replied, "You judge
him hastily; before you condemn us, ascertain how he is employed."
On examining the boy, then six years of age, it
was found that he was engaged in the solution of a problem
of Euclid!</p>

<p>Having observed the tendency of his son's mind, Mr. Watt
placed at his disposal a collection of tools. These he soon
learned to use with the greatest skill. He took to pieces and
put together, again and again, all the children's toys which he
could procure; and he was constantly employed in making
new ones. Subsequently he used his tools in constructing a
little electrical machine, the sparks proceeding from which
became a great subject of amusement to all the playfellows
of the poor invalid.</p>

<p>Though endowed with great retentive powers, Watt would
probably never have figured among the prodigies of a common
school: he would have been slow to commit his lessons
to memory, from the repugnance which he would feel to
repeat like a parrot anything which he did not perfectly
<a class="refpn" id="Pg079">[Pg079]</a>
understand. The natural tendency of his mind to meditate
on whatever came before it, would give him, to superficial
observers, the appearance of dullness. Happily, however, he
had a parent who was sufficiently clear-sighted, and who entertained
high hopes of the growing faculties of his son. More
distant and less sagacious relations were not so sanguine.
One day Mrs. Muirhead, the aunt of the boy, reproaching
him for what she conceived to be listless idleness, desired
him to take a book and occupy himself usefully. "More than
an hour has now passed away," said she, "and you have not
uttered a single word. Do you know what you have been doing
all this time? You have taken off, and put on, repeatedly, the
lid of the tea-pot; you have been holding the saucers and
the spoons over the steam, and you have been endeavouring to
catch the drops of water formed on them by the vapour. Is it
not a shame for you to waste your time so?"</p>

<p>Mrs. Muirhead was little aware that this was the first experiment
in the splendid career of discovery which was subsequently
to immortalise her little nephew. She did not see,
as we now can, in the little boy playing with the tea-pot, the
great engineer preluding to those discoveries which were destined
to confer on mankind benefits so inestimable.</p>

<p>One of the social qualities of mind which was remarkable
throughout his life, was the singular felicity and grace with
which he related anecdotes. This power was manifested even
in his earliest childhood. The following is an extract from a
letter written by Mrs. Marion Campbell, his cousin, and the
playfellow of his childhood:â€”</p>

<p>"He was not fourteen when his mother brought him to
Glasgow to visit a friend of hers; his brother John accompanied
him. On Mrs. Watt's return to Glasgow, some weeks
after, her friend said, 'You must take your son James home;
I cannot stand the degree of excitement he keeps me in; I
am worn out for want of sleep. Every evening before ten
o'clock, our usual hour of retiring to rest, he contrives to
engage me in conversation, then begins some striking tale,
and, whether humorous or pathetic, the interest is so overpowering
that the family all listen to him with breathless
attention, and hour after hour strikes unheeded.'"
<a class="refpn" id="Pg080">[Pg080]</a></p>

<p>Watt had a younger brother, John, who was subsequently
lost by shipwreck, in a voyage from Scotland to the United
States. This lad, having determined on following the business
of his father, left James more completely at liberty to choose
his own occupation. But such a choice was difficult for a
student who commanded equal success in every thing to which
he directed his attention.</p>

<p>The excursions which he was in the habit of making on the
Scottish mountains surrounding Loch Lomond, naturally directed
his attention to botany and mineralogy, in each of
which he attained considerable knowledge. His love of anecdote
and romance was likewise gratified by the scenery which
he enjoyed in these walks; and the traditions and popular
songs with which they made him acquainted. When from ill-health,
as constantly happened, he was confined to the house,
he devoted himself to chemistry, natural philosophy, and even
to medicine and surgery. In chemistry he acquired some experimental
skill, and studied with eager zeal the elements of
natural philosophy by S'. Gravesande. His own unhappy maladies
prompted him to read works on surgery and medicine;
and to such an extent did the activity of his mind impel him
on these subjects, that he was found one day dissecting, in his
room, the head of a child, who had died of some unknown
disease, with a view to ascertain the cause of its death.</p>

<p>In 1775, at the age of nineteen, at the recommendation of
Dr. Dick, professor of natural philosophy in the university
of Glasgow, he went to London, where he employed himself
in the house of Mr. John Morgan, a mathematical instrument
maker, in Finch Lane, Cornhill, to whom he apprenticed
himself for three years. He remained, however, only
a year, at the expiration of which (probably owing to his
delicate state of health) he was released from his apprenticeship,
and returned to Glasgow, with the intention of
establishing himself in business as an optician and mathematical
instrument maker. In the fulfilment of this intention,
however, he was obstructed by the interposition of
the Corporation of Trades in that town, who regarded him
as an intruder, not qualified by the necessary apprenticeship
to carry on business. All means of conciliation being
<a class="refpn" id="Pg081">[Pg081]</a>
exhausted, the Professors of the University interfered, and gave
him the use of three apartments within the college, for carrying
on his business, and likewise appointed him mathematical
instrument maker to the University. Soon afterwards the
opposition of the local trades seems to have given way, and
he opened a shop in Glasgow for the sale of mathematical
instruments.</p>

<p>After the celebrity at which he has arrived, it will be easily
believed that every trace of his earlier connection with Glasgow
college is carefully cherished. There are accordingly
preserved at that place little instruments and pieces of apparatus
of exquisite workmanship, which were executed entirely
by the hand of Watt, at a time when he was not in a condition
to command the aid of workmen under him.</p>

<p>At the time of obtaining this appointment in the University,
Watt was in his twenty-first year. His natural
talents and winning manners were speedily the means of
gaining for him the esteem and friendship of all those eminent
persons connected at the time with that university
whose regard was most valued. Among these the earliest of
his friends and patrons wereâ€”<strong class="m1">Adam Smith</strong>, the author of
"The Wealth of Nations;" <strong class="m1">Black</strong>, afterwards celebrated for
his chemical discoveries, and more especially for his theory of
latent heat; and <strong class="m1">Robert Simson</strong>, rendered illustrious by his
works on ancient geometry. In releasing Watt from the
persecution of the Glasgow corporation, these distinguished
persons first imagined that they were conferring a benefit
merely on an industrious and clever artisan, whose engaging
manners won their regard; but a short acquaintance with
him was sufficient to convince them how superior his mind
was to his position, and they conceived towards him the most
lively friendship. His shop became the common rendezvous,
the afternoon lounge, of all who were most distinguished
for literary and scientific attainments among the professors
and students. There they met to discuss the topics of the
day in art, science, and literature. Among these students,
the name which afterwards attained the highest distinctions,
and among these distinctions, not the least, the lasting personal
friendship and esteem of Watt himself, was <strong class="m1">Robison</strong>,
<a class="refpn" id="Pg082">[Pg082]</a>
the author of a well known work on Mechanics, and one of
the contributors to the <cite>EncyclopÅ“dia Britannica</cite>.</p>

<p>The following extract from an unpublished manuscript by
Robison himself will show at once the estimation in which
Watt was held, and will illustrate one of the most interesting
traits of his personal character:â€”</p>

<p>"I had always, from my earliest youth, a great relish for the
natural sciences, and particularly for mathematical and mechanical
philosophy, when I was introduced by Drs. Simson, Dick,
and Moor, gentlemen eminent for their mathematical abilities,
to Mr. Watt. I saw a workman, and expected no more; but
was surprised to find a philosopher as young as myself, and
always ready to instruct me. I had the vanity to think
myself a pretty good proficient in my favourite study, and was
rather mortified at finding Mr. Watt so much my superior.. .. Whenever
any puzzle came in the way of any of the
young students, we went to Mr. Watt. He needed only to be
prompted, for every thing became to him the beginning of a
new and serious study, and we knew that he would not quit it
till he had either discovered its insignificancy, or had made
something of it. He learnt the German language in order
to peruse Leupold's 'Theatrum Machinarum;' so did I, to
know what he was about. Similar reasons made us both learn
the Italian language.
<span class="no-wrap">&#160;&#160;&#160;*&#160;&#160;&#160;*&#160;&#160;&#160;*&#160;&#160;&#160;</span>
When to his superiority
of knowledge is added the <i>naÃ¯ve</i> simplicity and candour of
Mr. Watt's character, it is no wonder that the attachment of
his acquaintances was strong. I have seen something of the
world, and am obliged to say I never saw such another instance
of general and cordial attachment to a person whom
all acknowledged to be their superior. But that superiority
was concealed under the most amiable candour, and a liberal
allowance of merit to every man. Mr. Watt was the first to
ascribe to the ingenuity of a friend things which were nothing
but his own surmises, followed out and embodied by another.
I am the more entitled to say this, as I have often experienced
it in my own case."</p>

<p>Watt never permitted the inquiries which arose out of
these reunions to interfere with the discharge of the duties
of his workshop. There he passed the day, devoting the
<a class="refpn" id="Pg083">[Pg083]</a>
night to study. Every inquiry appeared to him to be attractive
in proportion to its difficulty, and to have charms
in proportion as it was removed from the common routine
of his business. As an example of this may be mentioned
the fact, that, being himself so insensible to the charms of
music that he could not distinguish one note from another,
he was actually induced to undertake the construction of an
organ, in which he was nevertheless completely successful. The
instrument he constructed, as might have been expected, contained
many improvements in its mechanism; but what is much
more remarkable, its tone and its musical qualities commanded
the admiration of all the professional musicians who heard
it. In the construction of this instrument Watt showed that
vigorous spirit of investigation which characterised all the
subsequent labours of his life. He made out the scale of
temperament by the aid of the phenomena of beats, of
which he could only obtain a knowledge by a profound but
obscure work published by Dr. Robert Smith of Cambridge.</p>

<p>The earliest occasion on which the attention of Watt is
said to have been called to the agency of steam, was in the
year 1759, when his friend Robison entertained some speculations
for applying that agent as a means of propelling
wheel carriages; and he consulted Watt on the subject.
No record, however, has been preserved of any experiments
which were tried on this occasion; nor does it appear that the
inquiry was carried farther than a verbal discussion, such as
habitually took place on other subjects of science between
Watt and his friends.</p>


<div class="ph3"><h3>(46.)</h3> In 1762, Watt tried some experiments on the force of
steam at a high pressure, confined in a close digester; and
he then constructed a small model to show how motion could
be obtained from that power. The practicability of what has
since been called the <em>High Pressure Engine</em>, was demonstrated
by him on this occasion; but he did not pursue the inquiry,
on account of the supposed danger of working with such
compressed steam as was required.</div>

<p>It is usual to provide, in the cabinets of experimental apparatus
for the instruction of the students of universities,
<a class="refpn" id="Pg084">[Pg084]</a>
small working models of the most useful machines. In the
collection for the illustration of the lectures delivered to the
Natural Philosophy class in the University of Glasgow was
a working model of Newcomen's atmospheric engine, applied
to a pump for raising water; which, however, had never been
found to work satisfactorily. The Professor of Experimental
Philosophy of that day, Dr. John Anderson (the founder of
the celebrated Andersonian Institution), sent this model in
1763 to Watt's workshop, to be repaired. Its defects soon
disappeared, and it was made to work to the satisfaction of
the professor and students.</p>

<p>This simple discharge of his duty, however, did not satisfy
the artisan; and his wonted activity of mind rendered this
model a subject of profound meditation, and led him into a
course of practical inquiry respecting it, which formed the
commencement of a most brilliant career of mechanical
discovery. The improvementâ€”we might almost say the
creationâ€”of the steam engine, by this great man, must
not therefore be regarded, as so often happens with mechanical
discoveries, as the result of fortuitous observation, or
even of a felicitous momentary inspiration. Watt, on the
other hand, conducted his investigation by a course of deep
thought, and of experiments marked by the last refinement
of delicacy and address. If he had received a more extended
and liberal education, one would have thought that he had
adopted for his guide the celebrated maxim of Bacon:â€”</p>

<p>"To write, speak, meditate, or act, when we are not provided
with <em>facts</em> to direct our thoughts, is to navigate a coast
full of dangers without a pilot, and to launch into the immensity
of the ocean without either rudder or compass."</p>

<p>The model which he had repaired, had a cylinder of only
two inches diameter, and six inches stroke. After he had
put it in complete order, he found, that although the boiler
was much larger in proportion to the cylinder than those of
real engines, yet, that it was incapable of supplying the
cylinder with steam in sufficient quantity to keep it at work.
To enable it to continue to move, he found it necessary to
lessen the quantity of water raised by its pump, so as to
<a class="refpn" id="Pg085">[Pg085]</a>
reduce the load on its piston very much below the proper
standard according to the common rules for large engines.</p>

<p>He ascribed the great inferiority in the performance of the
model, compared with the performance of the large engines,
to the small size of the cylinder, and to its material. The
cylinder of the model was brass, while those of large engines
were of cast iron; and brass being a better conductor of heat
than iron, he concluded that more heat in proportion was lost
from this cause in the model, than in the larger engines. He
observed that the small cylinder was so heated when the
steam was admitted into it, that it could not be touched by
the hand; but, nevertheless, that this heat contributed nothing
to its performance, inasmuch as before the piston descended,
the cylinder required to be cooled.</p>


<div class="ph3">
<h3>(47.)</h3> His first attempt to improve the engine, was by
using a wooden cylinder instead of an iron one. He accordingly
made a model with a cylinder of wood, soaked in
linseed oil, and baked to dryness. With this he made numerous
experiments, and found that it required a less quantity
of water to be thrown into the cylinder to condense the
steam, and that it was worked with a less supply of steam
from the boiler than was necessary with the metallic cylinder.</div>

<p>Still he found that the force with which the piston descended
was considerably less than that which the atmospheric
pressure ought to supply, supposing a tolerably
perfect vacuum to be produced under the piston. This
led him to suspect that the water injected into the cylinder
was not perfectly effectual in condensing the steam. The
experiments which he had previously made on the increased
temperature at which water boils under pressures greater
than that of the atmosphere, led him by analogy to the conclusion
that it would boil at lower temperatures if it were
submitted to a pressure less than the atmosphere, and he was
aware that Dr. Cullen and others had then recently discovered
that in vacuo, water would boil at so low a temperature as
100Â°. These notions suggested the probability that the
water injected into the cylinder being heated by the condensed
steam, might produce vapour of a low temperature
<a class="refpn" id="Pg086">[Pg086]</a>
and reduced pressure under the piston, which would account
for the deficiency he observed in the power of the engine.</p>

<p>No means occurred to him by which he could ascertain,
by direct experiment, the temperatures at which water would
boil under pressures less than that of the atmosphere. He
sought, however, to determine it by the following method.
Having ascertained, by repeating and multiplying the experiments
which he had tried in 1762, on high-pressure steam,
he obtained a table of the temperatures at which water boils
at various pressures greater than that of the atmosphere.
These results he laid down in a series forming a curve, of
which the abscissa represented the temperatures, and the
ordinates the pressures. He then continued this curve,
backwards as it were, and obtained, by analogy, an approximation
to the boiling temperatures, corresponding to
pressures less than that of the atmosphere. In other words,
having obtained by his experiments a notion, however imperfect,
of the law or rule observed by the temperatures at
which water boils at different pressures <em>greater</em> than that of
the atmosphere, he calculated by the same law or rule what
the pressures would be at different pressures <em>less</em> than that
of the atmosphere.</p>

<p>Applying these results to the interior of the cylinder of
the atmospheric engine, he obtained an approximation to the
pressure of the vapour which would be produced from the
warm water formed by the cold water injected into the cylinder,
and the steam condensed by it; and he accordingly found
that vapour, having a pressure seriously injurious to the
power of the engine would be produced in the cylinder, unless
considerably more water of injection was thrown in than
was customary.</p>

<p>It was apparent that the actual quantity of steam usefully
employed in the cylinder at each stroke, was only the quantity
which filled the cylinder; and therefore, in order to
ascertain the quantity of steam lost by the imperfections of
the machine, it was necessary to compare the actual quantity
of steam transmitted by the boiler to the cylinder at each
stroke, with the quantity which would just fill the cylinder.
The difference would of course be wasted. But to determine
<a class="refpn" id="Pg087">[Pg087]</a>
the actual quantity of steam supplied by the boiler to the
cylinder, there was no other means than by observing the
quantity of water evaporated in the boiler. That being observed,
it was necessary to know the quantity of steam which
that water formed; and it was therefore necessary to determine
the quantity or volume of steam which a given volume
of water produced.</p>


<div class="ph3">
<h3>(48.)</h3> On considering more attentively the operation of the
machine, the following circumstances gradually unfolded themselves
to him.</div>

<p>Let us suppose the piston at the top of the cylinder, and
the space in the cylinder below it, filled with steam so as to
balance the pressure of the atmosphere above the piston.
Under such circumstances the steam, as will presently be explained,
must have the temperature of boiling water. But that
the steam should have, and should maintain, this temperature,
it was evidently necessary that the inner surface of the cylinder
in contact with it should have the same temperature: for
if it had a lower temperature, it would take heat from the
steam, and reduce the temperature of the latter. Now the cylinder
being a mass of metal, has a quality in virtue of which
heat passes freely through its dimensions, so that its inner
surface could not be maintained at a temperature more elevated
than that of its dimensions extending from the inner
surface to the outer surface. Therefore, to maintain the
steam contained in the cylinder at the proper temperature, it
was essential that the whole of the solid metal composing
the cylinder should be itself at that temperature.</p>

<p>Things being in this state, it was required that a vacuum
should be produced under the piston to give effect to the atmospheric
pressure above it, by relieving it from the pressure
below. This, indeed, would appear to have been attained by
introducing as much cold water within the cylinder as would
be sufficient to reconvert the steam contained in it into water;
but Watt found, in his experiments on the atmospheric model,
that the piston would not descend with the proper force,
unless a vastly greater quantity of water were introduced into
the cylinder than the quantity which he had ascertained to be
<a class="refpn" id="Pg088">[Pg088]</a>
necessary for the reconversion of the steam into water. The
cause of this he perceived and fully explained.</p>

<p>If we suppose as much, and no more, cold water introduced
into the cylinder as would reconvert the steam contained in
it into water, then we should have in the bottom of the cylinder
a quantity of warm water with a vacuum above it: but
the entire mass of metal composing the cylinder itself, which
was previously at the temperature of boiling water, would
still be at the same temperature. The warm water, resting in
contact with this metal in the bottom of the cylinder, would
be immediately heated by it, and would rise in its temperature,
while the metal of the cylinder itself would be somewhat
lowered in temperature by the heat which it would thus impart
to the warm water contained in it. Under these circumstances,
as we shall presently explain, steam would be produced
from the water, which would fill the cylinder; and
although such steam would not have a mechanical pressure
equal in amount to the atmosphere, and therefore would not
altogether prevent the piston from descending if it had no
load to move, yet it would deprive the engine of so great a
portion of its legitimate power as to render it altogether inefficient.
But this defect would be removed by throwing into
the cylinder a sufficient quantity of cold water, not only to
destroy the steam contained in it, but also to cool the entire
mass of metal composing the cylinder itself, until it would be
reduced to such a temperature that the vapour proceeding
from the water contained in it would have so small a pressure
that it would not seriously or injuriously obstruct the descent
of the piston.</p>

<p>The piston being made to descend with such force as to
render the machine practically efficient, it would then be necessary
again to make it ascend; and to accomplish this, Watt
found that the boiler should supply a quantity of steam many
times greater than was necessary to fill the cylinder. Mature
reflection on the circumstances which have been just explained,
enabled him to discover how this undue quantity of
steam was rendered necessary.</p>

<p>Let it be recollected, that when the piston has reached the
bottom of the cylinder, the whole mass of the cylinder, and
<a class="refpn" id="Pg089">[Pg089]</a>
the piston itself, are reduced to so low a temperature that the
vapour of water, having the same temperature, has no pressure
sufficiently great to obstruct the action of the machine. When,
in order to make the piston ascend, steam is introduced from the
boiler into the cylinder under the piston, this steam encounters,
in the first instance, the cold surfaces of the metal forming the
bottom of the cylinder and the bottom of the piston. The
first effect of this is to convert the steam which comes from
the boiler into water, an effect which is produced by that
steam imparting its heat to the metal with which it comes into
contact. This destruction of steam continues until the metal
exposed to contact with it has been heated up to the temperature
of boiling water. Then, and not till then, the steam
below the piston will have a pressure equal to that of the
atmosphere above it, and the piston will begin to ascend. As
it ascends, however, the sides of the cylinder which it exposes
to the contact of the steam are cold, and partially destroy the
steam. Steam, therefore, must be supplied from the boiler
to replace the steam thus destroyed; nor can the piston reach
the top of the cylinder until such a quantity of steam shall
have flowed from the boiler into the cylinder, as shall be sufficient
not only to fill the cylinder under the piston, but likewise,
by its condensation, to raise the whole mass of the
cylinder and piston to the temperature of boiling water.</p>

<p>Such were the circumstances which forced themselves upon
the attention of Watt, in the course of repairing, and subsequently
trying, the model of the atmospheric engine, at Glasgow.
Being informed generally of the uses of the engine in the
drainage of mines, and of the vast expense attending its operation,
by reason of the quantity of fuel which it consumed, he
saw how important any improvement would be by which the
extensive sources of waste which had thus presented themselves
could be removed. He saw also, that all that portion
of steam which was expended, not in filling the cylinder under
the piston, but in heating the great mass of metal composing
the cylinder and piston, from a low temperature to that of
boiling water, upon each stroke of the piston, was so much
heat lost, and that the proportion of the fuel expended in
evaporating the steam thus wasted would be saved, if by any
<a class="refpn" id="Pg090">[Pg090]</a>
expedient <em>he could make the piston descend without cooling
the cylinder</em>. But in order to estimate the full amount of
this waste, and to discover the most effectual means of preventing
it, it was necessary to investigate the quantity of heat
necessary for the evaporation of a given quantity of water;
also, the quantity of steam which a given quantity of water
would produce, as well as other circumstances connected with
the temperature and pressure of steam. He, therefore, applied
himself to make experiments with a view to elucidate
these questions; and succeeded in obtaining results which led
to the discovery of some of the most important of those physical
phenomena, on the due application of which, the efficacy
of the steam engine, which he afterwards invented, depended,
and which also form striking facts in the general physics
of heat.</p>


<div class="ph3"><h3>(49.)</h3> The first question to which he directed his experiments,
was the determination of the extent to which water enlarged
its volume, or magnitude, when it passed into steam. To ascertain
this, he filled a thin Florence flask with steam, of a
pressure equal to the atmosphere, and weighed it accurately.
The same flask was then filled with water, and weighed again.
Finally, the weight of the flask itself was ascertained. It is
evident, that by such means, the exact weight of the steam
which filled the flask, and of the same bulk of water, would be
obtained. He found that the water weighed about eighteen
hundred times more than the steam; from whence he inferred
that the steam which filled the flask contained about eighteen
hundred times less water than the flask would contain.<a
name="FNanchor_17_17" id="FNanchor_17_17"></a><a href="#Footnote_17_17"
class="fnanchor">[17]</a></div>

<p><a class="refpn" id="Pg091">[Pg091]</a>
 Having once ascertained this point, he was able, by observing
the quantity of water evaporated in the boiler of the atmospheric
model, to compute the volume of steam which was
supplied to the cylinder. It was evident, that for every cubic
inch of water evaporated in the boiler, eighteen hundred
cubic inches of steam were supplied to the cylinder. Having
accurately observed the evaporation of the boiler for a short
time, and the number of strokes made by the piston in the
same time, he found that the quantity of water evaporated
in the boiler would supply about four times as much steam
as the cylinder would require. He consequently inferred,
that about three-fourths of the steam produced was wasted.</p>

<p>The next question to which he directed his experiments,
was to ascertain the quantity of cold water necessary to be
injected into the cylinder, in order to condense the steam contained
in it. To ascertain this, he attached a pipe to a boiler,
by which he was enabled to conduct the steam from the boiler
into a glass jar containing cold water at fifty-two degrees of
temperature. The steam, as it passed from the boiler through
the pipe, was condensed by the cold water, and continued to
be so condensed, until, by the heat which it imparted to the
water, the latter began to boil, and would then condense no
more steam. On comparing the water in the glass jar, when
boiling, with the water originally contained in it at fifty-two
<a class="refpn" id="Pg092">[Pg092]</a>
degrees, the quantity was found to be increased in the proportion
of six to seven, very nearly; from which he inferred, that
to reduce one ounce of steam to water, it was necessary to
mix about six ounces of cold water with it.</p>

<p>He was further led to the conclusion, that steam contains
a vast quantity of heat, by the following experiment. He
heated, in a close digester, a quantity of water several degrees
above the common boiling point. When thus heated, by
opening a stop-cock, he allowed the compressed steam to escape
into a cold vessel; in three or four seconds, he found
that the heat of the water in the digester was reduced from
a very high temperature to the common boiling point; yet,
that all the steam which escaped from it, and which carried
off with it the superabundant heat, formed only a few drops
of water when condensed; from which he inferred, that this
small quantity of water, in the form of steam, contained as
much heat as was sufficient to raise all the water in the digester
from the boiling point to the temperature at which it
was before the steam was allowed to escape.</p>

<p>Having thus ascertained the exact quantity of cold water
which ought to be injected into the cylinder in order to condense
the steam which filled the cylinder, he found, on comparing
the quantity necessary to be injected in order to enable
the piston to descend, that this quantity was about four
times as great as that which was necessary to condense the
steam. This led him to the conclusion, that about four times
as much heat was destroyed in the cylinder as needed to be
destroyed, if the object were the mere condensation of the
steam. This result fully corroborated the other conclusion,
deduced, from the proportion which he found between the
quantity of steam supplied by the boiler and the actual contents
of the cylinder.</p>


<div class="ph3">
<h3>(50.)</h3> Watt was forcibly struck with these circumstances, not
only on account of their importance in an economical point of
view, when their relation to steam power was considered, but
still more so, as indicating phenomena in the physics of
heat altogether novel to him.</div>

<p>He, therefore, eagerly sought his friend Dr. Black, to whom
he communicated these results. Then, for the first time, he
<a class="refpn" id="Pg093">[Pg093]</a>
was informed, by Black, of the theory of <strong>LATENT HEAT</strong>, which
had recently been discovered by him, and of which these very
phenomena formed the basis.</p>

<p>Some passages in the works of Dr. Robison produced an erroneous
impression, that a large share of the merit of the discoveries
of Watt which have been just explained was due to Dr.
Black, to whose instructions on the subject of latent heat Watt
was represented to have owed the knowledge of those facts
which led to his principal inventions and improvements. We
shall here give, in the words of Watt himself, his explanation of
the circumstances which led to this error. This explanation
is given in a letter addressed by Watt to Dr. Brewster, in
May 1814, and prefixed to the third volume of Brewster's
edition of <cite>Robison's Mechanical Philosophy</cite>:â€”</p>

<div class="blockquot">
<p>"The representations of friends whose opinions I highly
value induce me to avail myself of this opportunity of noticing
an error into which not only Dr. Robison, but apparently
also Dr. Black, has fallen, in relation to the <em>origin</em> of my improvements
upon the steam engine, and which not having been
publicly controverted by me, has, I am informed, been adopted
by almost every subsequent writer upon the subject of latent
heat.</p>

<p>"Dr. Robison, in the article Steam Engine, after passing
an encomium upon me, dictated by the partiality of friendship,
qualifies me as the '<em>pupil</em> and intimate friend of Dr. Black,'â€”a
description which not being there accompanied with any
inference, did not particularly strike me at the time of its
first perusal. He afterwards, in the dedication to me of his
edition of Dr. Black's lectures upon chemistry, goes the length
of supposing me to have professed to owe my improvements
upon the steam engine to the instructions and information I
had received from that gentleman, which certainly was a misapprehension;
as, though I have always felt and acknowledged
my obligations to him for the information I had received
from his conversation, and particularly for the knowledge
of the doctrine of latent heat, I never did nor <em>could</em>
consider my improvements as originating in those communications.
He is also mistaken in his assertion (p. 8. of the
preface to the above work), that 'I had attended two courses
<a class="refpn" id="Pg094">[Pg094]</a>
of the doctor's lectures;' for, unfortunately for me, the necessary
avocations of my business prevented me from attending
his or any other lectures at college; and as Dr. Robison
was himself absent from Scotland for four years at the period
referred to, he must have been misled by erroneous information.
In p. 184. of the lectures, Dr. Black says, 'I have
the pleasure of thinking that the knowledge we have acquired
concerning the nature of elastic vapours, in consequence
of my fortunate observation of what happens in its
formation and condensation, has contributed in no inconsiderable
degree to the public good by <em>suggesting</em> to my friend
Mr. Watt of Birmingham, then of Glasgow, his improvement
on this useful engine' (meaning the steam engine of which
he is then speaking). There can be no doubt from what follows
in his description of the engine, and from the very
honourable mention which he has made of me in various
parts of his lectures, that he did not mean to lessen any
merit that might attach to me as an inventor; but, on the
contrary, he was always disposed to give me fully as much
praise as I deserved.</p>

<p>"And were that otherwise doubtful, it would, I think, be
evident from the following quotation from a letter of his to
me, dated 13th February 1783, where, speaking of an intended
publication by a friend of mine, on subjects connected
with the history of steam, he says, 'I think it is very proper
for you to give him a short account of your discoveries and
speculations; <em>and particularly to assert clearly and fully
your sole right to the honour of the improvements of the steam
engine</em>.' And in a written testimonial which he very kindly
gave me, on the occasion of a trial at law against a piracy
of my invention in 1796-7, after giving a short account of the
invention, he adds, '<em>Mr. Watt was the sole inventor of the
capital improvement and contrivance above mentioned.</em>'</p>

<p>"Under this conviction of his candour and friendship, it is
very painful to me to controvert any assertion or opinion of
my revered friend; yet, in the present case I find it necessary
to say, that he appears to me to have fallen into an error;
and I hope, in addition to my assertion, to make that appear
by the short history I have given of my invention, in my
<a class="refpn" id="Pg095">[Pg095]</a>
notes upon Dr. Robison's essay, as well as by the following
account of the state of my knowledge previous to my receiving
any explanation of the doctrine of latent heat; and
also from that of the facts which principally guided me in the
invention.</p>

<p>"It was known very long before my time, that steam was
condensed by coming into contact with cold bodies, and that
it communicated heat to them; witness the common still,
&#38;c. &#38;c.</p>

<p>"It was known, by some experiments of Dr. Cullen and
others, that water and other liquids boiled in vacuo at very
low heats; water below 100Â°.</p>

<p>"It was known to some philosophers that the capacity or
equilibrium of heat, as we then called it, was much smaller
in mercury and tin than in water.</p>

<p>"It was also known that evaporation caused the cooling of
the evaporating liquid, and bodies in contact with it.</p>

<p>"I had myself made experiments to determine the following
facts:â€”</p>

<p>"First, the capacities of heat for iron, copper, and some
sorts of wood, comparatively with water.</p>

<p>"Second, the bulk of steam compared with that of water.</p>

<p>"Third, the quantity of water evaporated in a certain boiler
by a pound of coals.</p>

<p>"Fourth, the elasticities of steam at various temperatures
greater than that of boiling water, and an approximation to
the law which it followed at other temperatures.</p>

<p>"Fifth, how much water in the form of steam was required
every stroke by a small Newcomen's engine, with a wooden
cylinder six inches diameter, and twelve inches stroke.</p>

<p>"Sixth, the quantity of cold water required in every stroke
to condense the steam in that cylinder, so as to give it a working
power of about 7 lb. on the inch.</p>

<p>"Here I was at a loss to understand how so much cold
water could be heated so much by so small a quantity of water
in the form of steam; and I accordingly applied to Dr. Black,
and then first understood what was called latent heat.</p>

<p>"But this theory, though useful in determining the
quantity of injection necessary where the quantity of water
<a class="refpn" id="Pg096">[Pg096]</a>
evaporated by the boiler, and used by the cylinder, was known,
and in determining, by the quantity and heat of the hot water
emitted by Newcomen's engines, the quantity of steam required
to work them did not lead to the improvements I afterwards
made in the engine. These improvements proceeded upon the
old established fact, that steam was condensed by the contact
of cold bodies; and the later known one, that water boiled in
vacuo at heats below 100Â°, and consequently that a vacuum
could not be obtained unless the cylinder and its contents
were cooled every stroke to below that heat."</p>
</div>

<div class="figcenter" style="width: 600px;">
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_118.png" width="600" height="404" alt="" />
<div class="caption">LOCH LOMOND.</div>
</div>

<div class="footnotes"><h3>FOOTNOTES:</h3>

<div class="footnote">

<p><a name="Footnote_16_16" id="Footnote_16_16"></a><a
href="#FNanchor_16_16"><span class="label">[16]</span></a>
We are indebted for many of the anecdotes of the life of Watt to the
<cite>Eloge Historique</cite>, recently published by M. Arago, who was furnished
with all the documents and circumstances relating to this celebrated person
which were considered proper for publication, by his son, the present
James Watt, Esq., of Aston Hall, near Birmingham, and to the notes
added to this memoir by Mr. Muirhead, a relative of Mr. Watt.</p></div>

<div class="footnote">

<p><a name="Footnote_17_17" id="Footnote_17_17"></a><a
href="#FNanchor_17_17"><span class="label">[17]</span></a>
The following is the account of these experiments given in Watt's
own words:â€”</p>

<p>"It being evident that there was a great error in Dr. Desagulier's calculations
of Mr. Beighton's experiments on the bulk of steam, a Florence
flask, capable of containing about a pound of water, had about one ounce
of distilled water put into it; a glass tube was fitted into its mouth, and
the joining made tight by lapping that part of the tube with packthread
covered with glazier's putty. When the flask was set upright, the tube
reached down near to the surface of the water, and in that position the
whole was placed in a tin reflecting oven before a fire until the water was
wholly evaporated, which happened in about an hour, and might have been
done sooner, had I not wished the heat not much to exceed that of boiling
water. As the air in the flask was heavier than the steam, the latter ascended
to the top, and expelled the air through the tube. When the
water was all evaporated, the oven and flask were removed from the fire,
and a blast of cold air was directed against one side of the flask, to collect
the condensed steam in one place. When all was cold, the tube was removed,
the flask and its contents were weighed with care; and the flask
being made hot, it was dried by blowing into it by bellows, and when
weighed again was found to have lost rather more than four grains, estimated
at <span class="fraction">4<sup>1</sup>â„<sub>3</sub></span>
grains. When the flask was filled with water, it was found to
contain about <span class="fraction">17<sup>1</sup>â„<sub>8</sub></span>
ounces avoirdupois of that fluid which gave about 1800
for the expansion of water converted into steam of the heat of boiling water.</p>

<p>"This experiment was repeated with nearly the same result, and in
order to ascertain whether the flask had been wholly filled with steam, a
similar quantity of water was for the third time evaporated; and, while
the flask was still cold, it was placed inverted with its mouth (contracted
by the tube) immersed in a vessel of water, which it sucked in as it cooled,
until in the temperature of the atmosphere it was filled to within half an
ounce measure of water.</p>

<p>"In repetitions of this experiment at a later date, I simplified the
apparatus by omitting the tube, and laying the flask upon its side in the
oven, partly closing its mouth by a cork, having a notch on one side, and
otherwise proceeding as has been mentioned.</p></div></div>

<div class="figcenter" style="width: 500px;">
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_119.png" width="500" height="394" alt="" />
<div class="caption">GLASGOW.</div>
</div>

<h2><a name="CHAP_IV" id="CHAP_IV">CHAP. IV.</a></h2>

<p class="right"><a class="refpn" id="Pg097">[Pg097]</a><br />
<a href="#CONTENTS"><small>TOC</small></a>&#160;&#160;<a
href="#INDEX"><small>INX</small></a></p>

<div class="chapheader">
EXPOSITION OF PHYSICAL PRINCIPLES.â€”THERMOMETER.â€”METHOD OF
GRADUATING IT.â€”FREEZING AND BOILING POINTS.â€”LATENT HEAT
OF WATER.â€”QUANTITY OF HEAT NECESSARY TO CONVERT ICE INTO
WATER.â€”QUANTITY OF HEAT GIVEN OUT BY WATER IN BEING CONVERTED
INTO ICE.â€”PROCESS OF BOILING.â€”OF RECONVERSION OF
STEAM INTO WATER.â€”QUANTITY OF HEAT NECESSARY TO CONVERT
WATER INTO STEAM.â€”BOILING POINT OF WATER.â€”DIFFERENT IN DIFFERENT
PLACES.â€”DEPENDS ON THE BAROMETER.â€”VARIES WITH THE
PRESSURE.â€”EXPERIMENTAL PROOF OF THIS.â€”BOILS AT LOWER TEMPERATURES
THAN 212Â° UNDER PRESSURES LESS THAN THE ATMOSPHERE.â€”SUM
OF LATENT AND SENSIBLE HEAT OF STEAM ALWAYS THE SAME.â€”THE
FUEL NECESSARY TO EVAPORATE WATER THE SAME, WHATEVER BE
THE TEMPERATURE OR PRESSURE AT WHICH IT IS EVAPORATED.â€”MECHANICAL
FORCE OBTAINED BY EVAPORATION.â€”THIS FORCE NEARLY
THE SAME UNDER ALL CIRCUMSTANCES.</div>


<div class="ph3fst"><h3>(51.)</h3> We shall pause here to put the reader in possession of
the physical and mechanical principles connected with the
evaporation of water and other liquids, which are necessary
to enable him to understand the full extent of the value and
the merit of the discoveries of Watt, and to comprehend the
<a class="refpn" id="Pg098">[Pg098]</a>
structure and operation of the steam engine in its improved
form, as it has passed to us from his hands.</div>

<p>As we shall frequently have occasion to refer to the indications
of a thermometer, we shall first explain the principle
of that instrument as it is commonly used in this country.</p>

<p>The thermometer is an instrument used for the purpose of
measuring and indicating the temperature or sensible heat of
material substances.</p>

<p>Heat, like all other physical agents, can only be measured
by its effects. One of these effects best suited for this purpose,
is the change of dimension which all bodies undergo
in consequence of their change of temperature. In general,
when heat is applied to a material substance, that substance
undergoes an enlargement of bulk; and if heat be abstracted
from it, it suffers a diminution of bulk. This variation of
magnitude is not always in the same proportion as the
increase or diminution of temperature; but it is so when
applied to certain substances and between certain limits.
One of the substances whose expansion and contraction
through an extensive range of temperature has been found
to be nearly uniform, and which is attended with other convenient
qualities for a thermometer, is the liquid called
<em>mercury</em> or <em>quicksilver</em>. A mercurial thermometer is constructed
in the following way:â€”</p>

<p>A glass tube is made with a small and uniform bore: upon
the end of this tube, a bulb is blown, having a magnitude
very great compared with the bore of the tube. Let us
suppose this bulb and a part of the tube to be filled with
mercury. If the mercury contained in the bulb be heated, it
will expand, and being more susceptible of expansion than
the glass which contains it, the bulb will be too small for its
augmented volume: the mercury in the bulb can only,
therefore, obtain room for its increased bulk by pressing the
mercury in the tube upwards, which it will accordingly do.
The increase of volume which the mercury in the bulb
therefore undergoes, will be exhibited by the increased
length of the column in the tube. Since the bore of the
tube is made so exceedingly minute compared with the magnitude
of the bulb, a very small quantity of mercury forced
<a class="refpn" id="Pg099">[Pg099]</a>
from the bulb into the tube, will cause a considerable increase
of the length of the column. Small degrees of expansion
will therefore be rendered very apparent, and may be accurately
measured. The following is the method by which the
thermometer called <em>Fahrenheit's thermometer</em> is graduated.</p>

<p>The tube and bulb being prepared and supplied with
mercury, as already explained, let the instrument be plunged
in a vessel of melting ice. It will be found that the mercury
will stand in the tube at a certain point, from which it
will not vary so long as any ice remains not completely
melted in the vessel. Let a mark be made on the tube, or
on a scale attached to the tube, at the point corresponding
to the top of the column: the point thus marked is called
the <em>freezing point</em>.</p>

<p>Now let the instrument be immersed in a vessel of boiling
water, the barometer at the time having the height of thirty
inches. It will be found that so long as the water is kept
boiling, the column of mercury in the tube will remain
stationary. Let the point corresponding with the top of the
column be marked on the tube, or on the scale attached to
it. This is called the <em>boiling point</em>. Let the space on the
scale between the freezing and boiling points be now divided
into 180 equal parts: each of these parts is called a <em>degree</em>.
Let the same divisions be continued upon the scale below
the freezing point, until thirty-two divisions be taken; let
the lowest division be then marked 0, and let the successive
divisions upwards from that be numbered 1, 2, 3, &#38;c. In like
manner, let the same divisions be continued above the boiling
point, as far as the tube will admit.</p>

<p>It is evident that, under these circumstances, the freezing
point will be marked by 32, and the boiling point by 212.
It is usual to express the degrees of a thermometer in the
same manner as the degrees of a circle, by placing a small Â°
above the number. Thus the freezing point is expressed by
32Â°, and the boiling point by 212Â°.</p>

<p>The reason the degrees were commenced at 32Â° below the
freezing point was, because, when the thermometer was
invented, that temperature was supposed to be the lowest
degree of cold possible, being that of a certain mixture of
<a class="refpn" id="Pg100">[Pg100]</a>
snow and salt. This, however, has since been found to be an
error, very much lower temperatures being obtained by
various physical expedients.</p>

<p>The temperature of a body is, then, that elevation to which
the thermometer would rise when immersed in that body.
Thus, if in plunging the thermometer in water we found the
mercury to rise or fall to the division marked 100, we should
then say, the temperature of the water was 100Â°.</p>

<p>Let us suppose a spirit lamp, or other regular source of
heat, applied to a bath of mercury, so as to maintain the mercury
at a fixed temperature of 200Â°, and let another vessel,
containing a quantity of ice at a temperature of 20Â° be immersed
in the mercury. Let a thermometer be placed in the
mercury, and another in the ice. The following effects will
then ensue. The thermometer immersed in the ice will be
observed gradually to rise from 20Â° upwards, until it indicates
the temperature of 32Â°. It will then become stationary, and
the ice which had hitherto remained in a solid state will begin
to melt and be converted into water. This process of liquefaction
will continue for a considerable time, during which
the thermometer immersed in the ice will constantly be maintained
at 32Â°. At the moment, however, when the last portion
of ice is liquefied, the thermometer will begin again to
rise. The coincidence of this ascent of the thermometer
with the completion of the liquefaction of the ice, may be
very easily observed, because the ice being lighter, bulk for
bulk, than water, will float on the surface, and so long as a
particle of it remains unmelted it will be distinctly seen.</p>

<p>Now it cannot be doubted that, during the whole of this
process, the mercury, supposed to be maintained at 200Â°, constantly
imparts heat to the ice; yet, from the moment the
liquefaction begins, until it is completed, no increased temperature
is exhibited by the thermometer immersed in the
melting ice. If during this part of the process no heat were
received by the ice from the mercury, the consequence would
be, that the application of the lamp would cause the temperature
of the mercury to rise above 200Â°, which may be easily
demonstrated by withdrawing the vessel of ice from the mercurial
bath during the process of liquefaction. The moment
<a class="refpn" id="Pg101">[Pg101]</a>
it is withdrawn, the thermometer immersed in the mercury,
instead of remaining fixed at 200Â°, will begin to rise, although
the action of the lamp remains the same as before; from
which it is evident that the heat which now causes the mercury
to rise above 200Â° was before received by the melting
ice.</p>

<p>The heat which thus enters ice in the process of liquefaction,
and which is not indicated by the thermometer, is for
this reason called <em>latent heat</em>. It will be perceived that this
phrase is the name of a fact, and not of an hypothesis. That
heat really enters the water, and is contained in it, has been
established by the experiments; and to declare that it is present
there, is to declare an established fact. To call it by the name
<em>latent</em> heat, is to declare another established fact, viz., that it
is not sensible to the thermometer.</p>

<p>These facts show us that heat is capable of existing in bodies
in two distinct states, in one of which it is sensible to the
thermometer, and in the other not. Heat which is sensible to
the thermometer is called, for distinction, <em>sensible</em> or <em>free heat</em>.
It may be here observed, that heat which is sensible to the
thermometer is also perceptible by the senses, and heat not
sensible to the thermometer is not perceptible by the senses.
Thus, ice at 32Â° and water at 32Â° <em>feel</em> equally cold, and yet
we have seen that the latter contains considerably more heat
than the former.</p>

<p>Dr. Black, who first noticed the remarkable fact to which
we have now alluded, inferred that ice is converted into water
by communicating to it a certain quantity or dose of heat,
which enters into combination with it in a manner analogous
to that which takes place when bodies combine chemically.
The heat, thus combined with the solid ice, loses its property of
affecting the senses or the thermometer, and the effects therefore
bear a resemblance to those cases of chemical combination
in which the constituent elements change their sensible
properties when they form the compound.</p>

<p>The fact that the thermometer immersed in the ice remains
stationary only as long as the process of liquefaction is going
on, shows that this absorption of heat is necessarily connected
with that process, and that, were it not for the conversion of
<a class="refpn" id="Pg102">[Pg102]</a>
the solid ice into liquid water, the heat which is so received
would be sensible, and would cause the thermometer immersed
in the ice to rise. Before the time of Black it was supposed
that the slightest addition of heat would cause solid ice to be
converted into water, and that the thermometer would immediately
pass from the freezing temperature to higher degrees.
The experiments above described, however, show the falsehood
of such a supposition. If, while the mercurial bath, in
which the ice is immersed, is maintained at the temperature
of 200Â°, the length of time necessary to complete the liquefaction
of the ice be observed, it would be found that that time
is about twenty-eight times the length of time which it would
take to raise the liquid water from 32Â° to 37Â°; and if it be assumed
that the same quantity of heat is imparted to the ice,
during the process of liquefaction, during each minute, as is
imparted to the water, during each minute, in rising from 32Â°
to 37Â°, it will follow, that to liquefy the ice requires twenty-eight
times as much heat as is necessary to raise the water
from 32Â° to 37Â°. It appears, therefore, that, instead of a
small quantity of heat being necessary to melt the ice, a
very considerable portion is absorbed in that process.</p>

<p>Having ascertained the remarkable fact, that heat is absorbed
in a large quantity in the conversion of ice into water,
without rendering the body so absorbing it warmer, let us now
inquire what the exact quantity of heat so absorbed is. We
have already stated that, if the quantity communicated in
equal times be the same, the heat necessary to liquefy a given
weight of ice would be twenty-eight times as much as would
be necessary to raise the same weight of water from 32Â° to
37Â°; or, if the heat necessary to raise water through every 5Â°
be the same, that quantity of heat would be sufficient to raise
water from 32Â° to 172Â°: and hence we infer, that as much
heat is absorbed in the liquefaction of a given quantity of ice
as would raise the same quantity of water through 140 degrees
of the thermometric scale.</p>


<div class="ph3">
<h3>(52.)</h3> Let us now examine the analogous effects produced by
the continued application of heat to water in the liquid state.</div>

<p>Let a small quantity of water be placed in a glass flask of
considerable size, and then closed so as to prevent the escape
<a class="refpn" id="Pg103">[Pg103]</a>
of any vapour. Let this vessel be now placed over the flame
of a spirit lamp, so as to cause the water it contains to boil.
For a considerable time the water will be observed to boil, and
apparently to diminish in quantity, until at length all the
water disappears, and the vessel is apparently empty. If the
vessel be now removed from the lamp, and suspended in a cool
atmosphere, the whole of the interior of its surface will presently
appear to be covered with a dewy moisture; and at
length a quantity of water will collect in the bottom of it,
equal to that which had been in it at the commencement of
the process. That no water has at any period of the experiment
escaped from it, may be easily determined, by performing
the experiment with the glass flask suspended from the
arm of a balance, counterpoised by a sufficient weight suspended
from the other arm. The equilibrium will be preserved
throughout, and the vessel will be found to have the same
weight, when to all appearance it is empty, as when it contains
the liquid water. It is evident, therefore, that the water
exists in the vessel in every stage of the process, but that it
becomes invisible when the process of boiling has continued
for a certain length of time; and it may be shown that it will
continue to be invisible, provided the flask be exposed to a
temperature considerably elevated. Thus, for example, if it
be suspended in a vessel of boiling water, the water which it
contains will continue to be invisible; but the moment it is
withdrawn from the boiling water, and exposed to the cold
air, the water will again become visible, as above mentioned,
forming a dew on the inner surface, and finally collecting in
the bottom, as in the commencement of the experiment.</p>

<p>In fact, the liquid has, by the process of boiling, been converted
into <em>vapour</em>, or <em>steam</em>, which is a body similar in its
leading properties to common air, and, like it, is invisible.
It will hereafter appear that it likewise possesses the property
of elasticity, and other mechanical qualities enjoyed by gases
in general.</p>


<div class="ph3"><h3>(53.)</h3> Again, let an open vessel be filled with water at 60Â°,
and placed in a mercurial bath, which is maintained, by a fire or
lamp applied to it, at the temperature of 230Â°. Place a thermometer
in the water, and it will be observed gradually to
<a class="refpn" id="Pg104">[Pg104]</a>
rise as the temperature of the water is increased by the heat
which it receives from the mercury in which it is immersed.
The water will steadily rise in this manner until it attains the
temperature of 212Â°; but here the thermometer immersed in
it will become stationary. At the same time the water contained
in the vessel will become agitated, and its surface will
present the same appearance as if bubbles of air were rising
from the bottom, and issuing at the top. A cloudy vapour
will be given off in large quantities from its surface. This
process is called <em>ebullition</em> or <em>boiling</em>. If it be continued for
any considerable time, the quantity of water in the vessel will
be sensibly diminished; and at length every particle of it will
disappear, and the vessel will remain empty. During the
whole of this process, the thermometer immersed in the water
will remain stationary at 212Â°.</div>

<p>Now, it will be asked, what has become of the water? It
cannot be imagined that it has been annihilated. We shall be
able to answer this by adopting means to prevent the escape
of any particle of matter from the vessel containing the water,
into the atmosphere or elsewhere. Let us suppose that the
top of the vessel containing the water is closed, with the exception
of a neck communicating with a tube, and let that tube
be carried into another close vessel removed from the cistern
of heated mercury, and plunged in another cistern of cold
water. Such an apparatus is represented in <a href="#Fig015"><i>fig.</i> 15.</a></p>

<div class="figcenter" style="width: 400px;">
<a id="Fig015"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_126.png" width="400" height="177" alt="" />
<div class="caption figure">Fig. 15.</div>
</div>

<p><strong>A</strong> is a cistern of heated mercury, in which the glass vessel
<strong>B</strong>, containing water, is immersed. From the top of the vessel
<strong>B</strong> proceeds a glass tube <strong>C</strong>, inclining downwards, and entering
a glass vessel <strong>D</strong>, which is immersed in a cistern <strong>E</strong> of cold water.
If the process already described be continued until the water
by constant ebullition has disappeared, as already mentioned,
<a class="refpn" id="Pg105">[Pg105]</a>
from the vessel <strong>B</strong>, it will be found that a quantity of water
will be collected in the vessel <strong>D</strong>; and if this water be weighed,
it will be found to have exactly the same weight as the water
had which was originally placed in the vessel <strong>B</strong>. It is, therefore,
quite apparent that the water has passed by the process
of boiling from the one vessel to the other; but, in its passage,
it was not perceptible by the sight. The tube <strong>C</strong> and
the upper part of the vessel <strong>B</strong>, had the same appearance,
exactly, as if they had been filled with atmospheric air.
That they are not merely filled with atmospheric air may,
however, be easily proved. When the process of boiling
first commences, it will be found that the tube <strong>C</strong> is cold, and
the inner surface dry. When the process of ebullition has
continued a short time, the tube <strong>C</strong> will become gradually
heated, and the inner surface of it covered with moisture.
After a time, however, this moisture disappears, and the tube
attains the temperature 212Â°. In this state it continues until
the whole of the water is discharged from the vessel <strong>B</strong> to the
vessel <strong>D</strong>.</p>


<div class="ph3"><h3>(54.)</h3> These effects are easily explained. The water in the
vessel <strong>B</strong> is incapable of receiving any higher temperature than
212Â°, consistently with its retaining the liquid form. Small
portions, therefore, are constantly converted into steam by the
heat received from the surrounding mercury, and bubbles of
steam are formed on the bottom and sides of the vessel <strong>B</strong>.
These bubbles, being very much lighter, bulk for bulk, than
water, rise rapidly through the water, just in the same manner
as bubbles of air would, and produce that peculiar agitation
at its surface which has been taken as the external indication
of boiling. They escape from the surface, and collect in the
upper part of the vessel. The steam thus collected, when it
first enters the tube <strong>C</strong>, is cooled below the temperature of
212Â° by the surface of the tube; and consequently, being incapable
of remaining in the state of vapour at any lower temperature
than 212Â°, it is reconverted into water, and forms the
dewy moisture which is observed in the commencement of the
process on the interior of the tube <strong>C</strong>. At length, however,
the whole of the tube <strong>C</strong> is heated to the temperature of 212Â°,
and the moisture which was previously collected upon its inner
<a class="refpn" id="Pg106">[Pg106]</a>
surface is again converted into steam. As the quantity of
steam evolved from the water in <strong>B</strong> increases, it drives before
it the steam previously collected in the tube <strong>C</strong>, and forces it
into the vessel <strong>B</strong>. Here it encounters the inner surface of
this vessel, which is kept constantly cold by being surrounded
with the cold water in which it is immersed; and the vapour,
being thus immediately reduced below the temperature of
212Â°, is reconverted into water. At first it collects in a dew
on the surface of the vessel <strong>D</strong>; but as this accumulates, it
drops into the bottom of the vessel, and forms a more considerable
quantity. As the quantity of water is observed to be
gradually diminished in the vessel <strong>B</strong>, the quantity will be
found to be gradually increased in the vessel <strong>D</strong>; and if the
operation be suspended at any stage of the process, and the
water in the two vessels weighed, it will be found that the
weight of the water in <strong>D</strong> is exactly equal to the weight which
the water in <strong>B</strong> has lost.</div>


<div class="ph3"><h3>(55.)</h3> The demonstration is, therefore, perfect, that the gradual
diminution of the boiling water in the vessel <strong>B</strong> is produced
by the conversion of that water into steam by the heat. In
the process first described, when the top of the vessel <strong>B</strong> was
supposed to be open, this steam made its escape into the air,
where it was first dispersed, and subsequently cooled in separate
particles, and was deposited in minute globules of moisture
on the ground and on surrounding objects.</div>


<div class="ph3"><h3>(56.)</h3> In reviewing this process, we are struck by the fact,
that the continued application of heat to the vessel <strong>B</strong> is incapable
of raising the temperature of the water contained in it
above 212Â°. This presents an obvious analogy to the process of
liquefaction, and leads to inquiries of a similar nature, which
are attended with a like result. We must either infer, that
the water, having arrived at 212Â°, received no more heat from
the mercury; or that such heat, if received, is incapable of
affecting the thermometer; or, finally, that the steam which
passes off carries this heat with it. That the water receive
heat from the mercury, will be proved by the fact, that, if the
vessel <strong>B</strong> be removed from the mercury, other things remaining
as before, the temperature of the mercury will rapidly rise, and
if the fire be continued, it will even boil; but so long as the
<a class="refpn" id="Pg107">[Pg107]</a>
vessel <strong>B</strong> remains immersed, it prevents the mercury from increasing
in temperature. It therefore receives that heat which
would otherwise raise the temperature of the quicksilver.</div>

<div class="figright" style="width: 245px;">
<a id="Fig016"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_129.png" width="245" height="171" alt="" />
<div class="caption figure">Fig. 16.</div>
</div>

<p>If a thermometer be immersed in the steam which collects
in the upper part of the vessel <strong>B</strong>, it will show the same temperature
(of 212Â°) as the water from which it is raised. The
heat, therefore, received from the mercury, is clearly not imparted
in a sensible form to the steam, which has the same
temperature in the form of steam as it had in the form of
water. What has been already explained respecting liquefaction
would lead us, by analogy, to suspect that the heat imparted
by the mercury to the water has become latent in the steam,
and is instrumental to the conversion of water into steam,
in the same manner as heat has been shown to be instrumental
to the conversion of ice into water. As the fact was in
that case detected by mixing ice with water, so we shall, in the
present instance, try it by a like test, viz. by mixing water
with steam. Let about five ounces and a half of water, at the
temperature of 32Â°, be placed in a
vessel <strong>A</strong> (<a href="#Fig016"><i>fig.</i> 16.</a>), and let another
vessel <strong>B</strong>, in which water is kept constantly
boiling at the temperature of
212Â°, communicate with <strong>A</strong> by a pipe
<strong>C</strong> proceeding from the top, so that
the steam may be conducted from <strong>B</strong>,
and escape from the mouth of the pipe at some depth below
the surface of the water in <strong>A</strong>. As the steam issues from the
pipe, it will be immediately reconverted into water by the cold
water which it encounters; and, by continuing this process, the
water in <strong>A</strong> will be gradually heated by the steam combined
with it and received through the pipe <strong>C</strong>. If this process be
continued until the water in <strong>A</strong> is raised to the temperature of
212Â°, it will boil. Let it then be weighed, and it will be
found to weigh six ounces and a half: from whence we infer,
that one ounce of water has been received from the vessel <strong>B</strong>
in the form of steam, and has been reconverted into water by
the inferior temperature of the water in <strong>A</strong>. Now, this ounce
of water received in the form of steam into the vessel <strong>A</strong> had,
when in that form, the temperature of 212Â°. It is now
<a class="refpn" id="Pg108">[Pg108]</a>
converted into the liquid form, and still retains the same temperature
of 212Â°; but it has caused the five ounces and a half
of water with which it has been mixed, to rise from the temperature
of 32Â° to the temperature of 212Â°,â€”and this, <em>without
losing any temperature itself</em>. It follows, therefore, that,
in returning to the liquid state, it has parted with as much
heat as is capable of raising five times and a half its own
weight of water from 32Â° to 212Â°. This heat was combined
with the steam, though not sensible to the thermometer; and
was, therefore, <em>latent</em>. Had it been sensible in the water in
<strong>B</strong>, it would have caused the water to have risen through a
number of thermometric degrees, amounting to five times and
a half the excess of 212Â° above 32Â°; that is, through five
times and a half 180Â°; for it has caused five times and a half
its own weight of water to receive an equal increase of temperature.
But five times and a half 180Â° is 990Â°, or, to use
round numbers (for minute accuracy is not here our object),
1000Â°. It follows, therefore, that an ounce of water, in passing
from the liquid state at 212Â° to the state of steam at 212Â°,
receives as much heat as would be sufficient to raise it through
1000 thermometric degrees, if that heat, instead of becoming
latent, had been sensible.</p>


<div class="ph3">
<h3>(57.)</h3> In order to derive all the knowledge from these experiments
which they are capable of imparting, it will be
necessary to examine very carefully how water comports
itself under a variety of different circumstances.</div>

<p>If water be boiled in an open vessel, with a thermometer
immersed, on different days, it will be observed that the fixed
temperature which it assumes in boiling will be subject to a
variation within certain small limits. Thus, at one time, it
will be found to boil at the temperature of 210Â°; while, at
others, the thermometer immersed in it will rise to 213Â°; and,
on different occasions, it will fix itself at different points within
these limits. It will also be found, if the same experiment
be performed at the same time in distant places, that the
boiling points will be subject to a like variation. Now, it is
natural to inquire what cause produces this variation; and we
shall be led to the discovery of the cause, by examining what
other physical effects undergo a simultaneous change.
<a class="refpn" id="Pg109">[Pg109]</a></p>

<p>If we observe the height of the barometer at the time of
making each experiment, we shall find a very remarkable correspondence
between it and the boiling temperature. Invariably,
whenever the barometer stands at the same height,
the boiling temperature will be the same. Thus, if the barometer
stands at 30 inches, the boiling temperature will be
212Â°. If the barometer fall to
<span class="fraction">29<sup>1</sup>â„<sub>2</sub></span> inches, the thermometer
stands at a small fraction above 211Â°. If the barometer rise
to <span class="fraction">30<sup>1</sup>â„<sub>2</sub></span> inches, the boiling temperature rises to nearly 213Â°.
The variation in the boiling temperature is, then, accompanied
by a variation in the pressure of the atmosphere indicated
by the barometer; and it is constantly found that the
boiling point will remain unchanged, so long as the atmospheric
pressure remains unchanged, and that every increase
in the one causes a corresponding increase in the other.</p>


<div class="ph3">
<h3>(58.)</h3> From these facts it must be inferred, that the pressure
excited on the surface of the water has a tendency to resist its
ebullition, and to make it necessary, before it can boil, that
it should receive a higher temperature; and, on the contrary,
that every diminution of pressure on the surface of the water
will give an increased facility to the process of ebullition, or
will cause that process to take place at a lower temperature.
As these facts are of the utmost importance in the theory of
heat, it may be useful to verify them by direct experiment.</div>

<p>If the variable pressure excited on the surface of the water
by the atmosphere be the cause of the change in the boiling
temperature, it must happen, that any change of pressure
produced by artificial means on the surface of the water must
likewise change the boiling point, according to the same law.
Thus, if a pressure considerably greater than the atmospheric
pressure be excited on a liquid, the boiling point may
be expected to rise considerably above 212Â°; and, on the
other hand, if the surface of the water be relieved from the
pressure of the atmosphere, and be submitted to a considerably
diminished pressure, the water would boil below 212Â°.</p>

<div class="figright" style="width: 213px;">
<a id="Fig017"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_132.png" width="213" height="596" alt="" />
<div class="caption figure">Fig. 17.</div>
</div>

<p>Let <strong>B</strong> (<a href="#Fig017"><i>fig.</i> 17.</a>) be a strong spherical vessel of brass, supported
on a stand <strong>S</strong>, under which is placed a large spirit
lamp <strong>L</strong>, or other means of heating it. In the top of this
vessel are three apertures, in two of which are screwed a
<a class="refpn" id="Pg110">[Pg110]</a>
thermometer <strong>T</strong>, the bulb of which enters the hollow brass
sphere, and a stop-cock <strong>C</strong>, which may be closed or opened at
pleasure, to confine the steam, or allow
it to escape. In the third aperture
at the top, is screwed a long barometer
tube, open at both ends. The lower
end of this tube extends nearly to the
bottom of the spherical vessel <strong>B</strong>. In
the bottom of this vessel is placed a
quantity of mercury, the surface of
which rises to some height above the
lower end of the tube <strong>A</strong>. Over the
mercury is poured a quantity of water,
so as to half fill the vessel <strong>B</strong>. Matters
being thus arranged, the screws are
made tight, so as to confine the water,
and the lamp is allowed to act on the
vessel; the temperature of the water is
raised, and steam is produced, which,
being confined within the vessel, exerts
its pressure on the surface of the water,
and resists its ebullition. The pressure
of the steam acting on the surface of
the water is communicated to the surface
of the mercury, and it forces a portion of
the mercury into the tube <strong>A</strong>, which presently rises above
the point where the tube is screwed into the top of the
vessel <strong>B</strong>. As the action of the lamp continues, the thermometer
<strong>T</strong> exhibits a gradually increasing temperature;
while the column of mercury in <strong>A</strong> shows the force with which
the steam presses on the surface of the water in <strong>B</strong>,â€”this
column being balanced by the pressure of the steam. Thus,
the temperature and pressure of the steam at the same moment
may always be observed by inspecting the thermometer
<strong>T</strong> and the tube <strong>A</strong>. When the column in the tube <strong>A</strong> has risen
to the height of 30 inches above the level of the mercury in
the vessel <strong>B</strong>, then the pressure of the steam will be equivalent
to double the pressure of the atmosphere, because, the
tube <strong>A</strong> being open at the top, the atmosphere presses on the
<a class="refpn" id="Pg111">[Pg111]</a>
surface of the mercury in it. The thermometer <strong>T</strong> will be observed
gradually to rise until it attains the temperature of
212Â°; but it will not stop there, as it would do if immersed
in water boiled in an open vessel. It will, on the other hand,
continue to rise; and when the column of mercury in <strong>A</strong> has
attained the height of 30 inches, the thermometer <strong>T</strong> will have
risen to 251Â°,â€”being 39Â° above the ordinary boiling point.</p>

<p>During the whole of this process, the surface of the water
being submitted to a constantly increasing pressure, its ebullition
is prevented, and it continues to receive heat without
boiling. That it is the increased pressure which resists its
ebullition, and causes it to receive a temperature above 212Â°,
may be easily shown. Let the stop-cock <strong>C</strong> be opened; immediately
the steam in <strong>B</strong>, having a pressure considerably
greater than that of the atmosphere, will rush out, and will
continue to issue from <strong>C</strong>, until its pressure is balanced by the
atmosphere. At the same time the column of mercury in <strong>A</strong>
will be observed rapidly to fall, and to sink below the orifice
by which it is inserted in the vessel <strong>B</strong>. The thermometer <strong>T</strong>
will also fall until it attains the temperature of 212Â°. At that
point, however, it will remain stationary; and the water will
now be distinctly heard to be in a state of rapid ebullition. If
the stop-cock <strong>C</strong> be once more closed, the thermometer will
begin to rise, and the column of mercury ascending in <strong>A</strong> will
be again visible.</p>

<p>If, instead of a stop-cock being at <strong>C</strong>, the aperture were
made to communicate with a valve, like the safety-valve of a
steam engine, loaded with a certain weight,â€”say at the rate of
15 lbs. on the square inch,â€”then the thermometer <strong>T</strong>, and the
mercury in the tube <strong>A</strong>, would not rise indefinitely as before.
The thermometer would continue to rise till it attained the
temperature of 251Â°; and the mercury in the tube <strong>A</strong> would
rise to the height of 30 inches. At this limit the resistance
of the valve would be balanced by the pressure of the steam;
and as fast as the water would have a tendency to produce
steam of a higher pressure, the valve would be raised and the
steam suffered to escape; the thermometer <strong>T</strong> and the column
of mercury in <strong>A</strong> remaining stationary during this process. If
the valve were loaded more heavily, the phenomena would be
<a class="refpn" id="Pg112">[Pg112]</a>
the same, only that the mercury in <strong>T</strong> and <strong>A</strong> would become
stationary at certain heights. But, on the other hand, if the
valve were loaded at a less pressure than 15 lbs. on the
square inch, then the mercury in the two tubes would become
stationary at lower points.</p>


<div class="ph3">
<h3>(59.)</h3> These experiments show that every increase of pressure
above the ordinary pressure of the atmosphere causes an
increase in the temperature at which water boils. We shall
now inquire whether a diminution of pressure will produce
a corresponding effect on the boiling point.</div>

<p>This may be easily accomplished by the aid of an air pump.
Let water at the temperature of 200Â° be placed in a glass vessel
under the receiver of an air pump, and let the air be gradually
withdrawn. After a few strokes of the pump, the water
will boil; and if the mercurial gauge of the pump be observed,
it will be found that its altitude will be about
<span class="fraction">23<sup>1</sup>â„<sub>2</sub></span> inches.
Thus the pressure to which the water is submitted has been
reduced from the ordinary pressure of the atmosphere expressed
by the column of 30 inches of mercury, to a diminished
pressure expressed by
<span class="fraction">23<sup>1</sup>â„<sub>2</sub></span>
inches; and we find that the
temperature at which the water boils has been lowered from
212Â° to 200Â°. Let the same experiment be repeated with
water at the temperature of 180Â°, and it will be found that a
further rarefaction of the air is necessary, but the water will
at length boil. If the gauge of the pump be now observed, it
will be found to stand at about fifteen inches, showing, that at
the temperature of 180Â° water will boil under half the ordinary
pressure of the atmosphere. These experiments may be
varied and repeated; and it will be always found, that, as the
pressure is diminished or increased, the temperature at which
the water will boil will be also diminished or increased.</p>


<div class="ph3"><h3>(60.)</h3> The same effects may be exhibited in a striking manner
without an air pump, by producing a vacuum by the condensation
of steam. Let a small quantity of water be placed in a
thin glass flask, and let it be boiled by holding it over a spirit
lamp. When the steam is observed to issue abundantly from
the mouth of the flask, let it be quickly corked and removed
from the lamp. The process of boiling will then cease, and
the water will become quiescent; but if the flask be plunged
<a class="refpn" id="Pg113">[Pg113]</a>
in a vessel of cold water, the water it contains will again pass
into a state of violent ebullition, thus exhibiting the singular
fact of water being boiled by cooling it. This effect is produced
by the cold medium in which the flask is immersed,
causing the steam above the surface of the water in it to be
condensed, and therefore relieving the water from its pressure.
The water, under these circumstances, boils at a lower temperature
than when submitted to the pressure of the uncondensed
vapour.</div>


<div class="ph3">
<h3>(61.)</h3> There is no limit to the temperature to which water may
be raised, if it be submitted to a sufficient pressure to resist
its tendency to take the vaporous form. If a strong metallic
vessel be nearly filled with water, so as to prevent the liquid
from escaping by any force which it can exert, the water thus
inclosed may be heated to any temperature whatever without
boiling; in fact, it may be made red-hot; and the temperature
to which it may be raised will have no limit, except the strength
of the vessel containing it, or the point at which the metal of
which it is formed may begin to soften or to be fused.</div>


<div class="ph3">
<h3>(62.)</h3> The following table will show the temperature at which
water will boil under different pressures of the atmosphere
corresponding to the altitudes of the barometer between 26
and 31 inches.</div>

<table summary="water boiling point vs pressure">
<tr><th align="right">Barometer.<br />inches</th><th align="right">Boiling<br />Point.</th></tr>
<tr>
 <td align="right">26&#160;&#160;</td>
 <td align="right">204Â°Â·91</td></tr>
<tr>
 <td align="right">26Â·5</td>
 <td align="right">205Â°Â·79</td></tr>
<tr>
 <td align="right">27&#160;&#160;</td>
 <td align="right">206Â°Â·67</td></tr>
<tr>
 <td align="right">27Â·5</td>
 <td align="right">207Â°Â·55</td></tr>
<tr>
 <td align="right">28&#160;&#160;</td>
 <td align="right">208Â°Â·43</td></tr>
<tr>
 <td align="right">28Â·5</td>
 <td align="right">209Â°Â·31</td></tr>
<tr>
 <td align="right">29&#160;&#160;</td>
 <td align="right">210Â°Â·19</td></tr>
<tr>
 <td align="right">29Â·5</td>
 <td align="right">211Â°Â·07</td></tr>
<tr>
 <td align="right">30&#160;&#160;</td>
 <td align="right">212Â°&#160;&#160;&#160;</td></tr>
<tr>
 <td align="right">30Â·5</td>
 <td align="right">212Â°Â·88</td></tr>
<tr>
 <td align="right">31&#160;&#160;</td>
 <td align="right">213Â°Â·76</td></tr>
</table>

<p>From this table it appears, that, for every tenth of an inch
which the barometric column varies between these limits, the
boiling temperature changes by the fraction of a degree expressed
by the decimal Â·176, or nearly by the vulgar fraction
<span class="fraction"><sup>1</sup>â„<sub>6</sub>.</span></p>

<div class="ph3"><h3>(63.)</h3> In the experiment already described, by which the latent
<a class="refpn" id="Pg114">[Pg114]</a>
heat of steam was determined, the water was supposed
to be boiled under the ordinary pressure of the atmosphere.
Having seen, however, that water may boil at different temperatures,
under different pressures, the inquiry presents itself,
whether the heat absorbed in vaporisation at different
temperatures, and under different pressures, is subject to any
variation? Experiments of the same nature as those already
described, instituted upon water in a state of ebullition at different
temperatures, as well below as above 212Â°, have led to
the discovery of a very remarkable fact in the theory of vapour.
It has been found that the heat absorbed by vaporisation
is always less, the higher the temperature at which the
ebullition takes place; and less, by the same amount as the
temperature of ebullition is increased. Thus, if water boil at
312Â°, the heat absorbed in ebullition will be less by 100Â° than
if it boiled at 212Â°; and again, if water be boiled under a diminished
pressure, at 112Â°, the heat absorbed in vaporisation
will be 100Â° more than the heat absorbed by water boiled at
212Â°. It follows, therefore, that the actual consumption of
heat in the process of vaporisation must be the same, whatever
be the temperature at which the vaporisation takes place;
for whatever heat is saved in the sensible form, is consumed in
the latent form, and <i>vice versÃ¢</i>.</div>

<p>Let us suppose a given weight of water at the temperature
of 32Â° to be exposed to any regular source by which heat may
be supplied to it. If it be under the ordinary atmospheric
pressure, the first 180Â° of heat which it receives will raise it
to the boiling point, and the next 1000Â° will convert it into
steam. Thus, in addition to the heat which it contains at
32Â°, the steam at 212Â° contains 1180Â° of heat. But if the
same water be submitted to a pressure equal to half the atmospheric
pressure, then the first 148Â° of heat which it receives
will cause it to boil, and the next 1032Â° will convert
it into vapour. Thus, steam at the temperature of 180Â° contains
a quantity of heat more than the same quantity of water
at 32Â°, by 1032Â° added to 148Â°, which gives a sum of 1180Â°.
Steam, therefore, raised under the ordinary pressure of the
atmosphere at 212Â°, and steam raised under half that pressure
at 180Â°, contain the same quantity of heat,â€”with this difference
<a class="refpn" id="Pg115">[Pg115]</a>
onlyâ€”that the one has more latent heat, and less sensible
heat, than the other.</p>

<p>From this fact, that the sum of the latent and sensible heats
of the vapour of water is constant, it follows that the same
quantity of heat is necessary to convert a given weight of water
into steam, at whatever temperature, or under whatever pressure,
the water may be boiled. It follows, also, that, in the
steam engine, equal weights of high-pressure and low-pressure
steam are produced by the same consumption of fuel; and
that, in general, the consumption of fuel is proportional to the
quantity of water vaporised, whatever the pressure of the
steam may be.<a name="FNanchor_18_18" id="FNanchor_18_18"></a><a href="#Footnote_18_18" class="fnanchor">[18]</a></p>


<div class="ph3">
<h3>(64.)</h3> Having explained the conditions under which, by supplying
heat to water, it is converted into steam, and, by abstracting
heat from steam, it may be reconverted into water,
let us now consider the mechanical force which is developed in
these phenomena.</div>

<div class="figleft" style="width: 146px;">
<a id="Fig018"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_137.png" width="146" height="389" alt="" />
<div class="caption figure">Fig. 18.</div>
</div>

<p>Let <strong>A B</strong> (<a href="#Fig018"><i>fig.</i> 18.</a>) be a tube, or cylinder, the base of which is
equal to a square inch, and let a piston <strong>P</strong> move
in it so as to be steam-tight. Let it be supposed,
that under this piston there is, in the
bottom of the cylinder, a cubic inch of water between
the bottom of the piston and the bottom
of the tube; let the piston be counterbalanced
by a weight <strong>W</strong> acting over a pulley, which
will be just sufficient to counterpoise the
weight of the piston, so as leave no force
tending to keep the piston down, except the
force of the atmosphere acting above it.
Under the circumstances here supposed, the
piston being in contact with the water, and
all air being excluded, it will be pressed down
by the weight of the atmosphere, which we
will suppose to be fifteen pounds, the magnitude
of the piston being a square inch.
<a class="refpn" id="Pg116">[Pg116]</a></p>

<p>Now let the flame of a lamp be applied at the bottom of
the tube; the water under the piston having its temperature
thereby gradually raised, and being submitted to no pressure
save that of the atmosphere above the piston, it will begin to
be converted into steam when it has attained the temperature
of 212Â°. According as it is converted into steam, it will cause
the piston to ascend in the tube until all the water has been
evaporated. If the tube were constructed of sufficient length,
the piston then would be found to have risen to the height of
about seventeen hundred inches, or one hundred and forty-two
feet; since, as has been already explained, water passing
into steam under the ordinary pressure of the atmosphere
undergoes an increase of bulk in the proportion of about
seventeen hundred to one.</p>

<p>Now in this process, the air above the piston, which presses
on it with a force equal to fifteen pounds, has been raised one
hundred and forty-two feet. It appears, therefore, that, by
the evaporation of a cubic inch of water under a pressure
equal to fifteen pounds per square inch, a mechanical force of
this amount is developed.</p>

<p>It is evident that fifteen pounds raised one hundred and
forty-two feet successively, is equivalent to one hundred and
forty-two times fifteen pounds raised one foot. Now, one
hundred and forty-two times fifteen is two thousand one hundred
and thirty, and therefore the force thus obtained is equal
to two thousand one hundred and thirty pounds raised one
foot high. This being within about 110 pounds of a ton,
it may be stated, in round numbers, that, by the evaporation
of a cubic inch of water under these circumstances, a force is
obtained equal to that which would raise a ton weight a foot
high.</p>

<p>The augmentation of volume which water undergoes in
passing into steam under the pressure here supposed, may be
easily retained in the memory, from the accidental circumstance
that a cubic inch of water is converted into a cubic
foot of steam, very nearly. A cubic foot contains one thousand
seven hundred and twenty-eight cubic inches,â€”which
is little different from the proportion which steam bears to
water, when raised under the atmospheric pressure.
<a class="refpn" id="Pg117">[Pg117]</a></p>


<div class="ph3">
<h3>(65.)</h3> It will, therefore, be an advantage to retain in memory
the following general facts:â€”</div>

<p>1. <em>A cubic inch of water evaporated under the ordinary atmospheric
pressure, is converted into a cubic foot of steam.</em></p>

<p>2. <em>A cubic inch of water evaporated under the atmospheric
pressure, gives a mechanical force equal to what would raise
about a ton weight a foot high.</em></p>


<div class="ph3"><h3>(<a id="h3-66"></a>66.)</h3> Let us, again,
suppose the piston <strong>P</strong> (<a href="#Fig023"><i>fig.</i> 23.</a>) to be restored
to its original position, with the liquid water beneath it;
and, in addition to the weight of the atmosphere which before
pressed it down, let us suppose another weight of fifteen
pounds laid upon it, so that the water below shall be pressed
by double the weight of the atmosphere. If the lamp were
now applied, and at the same time a thermometer were immersed
in the water, it would be found that the water would
not begin to be converted into steam until it attained the temperature
of about 250Â°. The piston would then begin, as before,
to ascend, and the water to be gradually converted into
vapour. The water being completely evaporated, it would be
found that the piston would be raised to a height little more
than half its former height, or 72 feet. The mechanical
effect, therefore, thus obtained, will be equivalent to double
the former weight raised half the former height.</div>

<p>In like manner, if the piston were loaded with thirty
pounds in addition to the atmosphere, the whole pressure
on the water being then three times the pressure first supposed,
the piston would be raised to somewhat more than
one third of its first height by the evaporation of the water.
This would give a mechanical force equivalent to three times
the original weight raised a little more than one third of the
original height.</p>

<p>In general, as the pressure on the piston is increased, the
height to which the piston would be raised by the evaporation
of the water will be diminished in a proportion somewhat less
than the proportion in which the pressure on the piston is
increased. If the temperature at which the water is converted
into steam under these different pressures were the
same, then the height to which the piston would be raised by
the evaporation of the water would be diminished in precisely
<a class="refpn" id="Pg118">[Pg118]</a>
the same proportion as the pressure on the piston is increased;
and, in that case, the whole mechanical force developed by the
evaporation of the water would remain exactly the same
under whatever pressure the water might be boiled. We
shall explain hereafter the extent to which the variation of
temperature in the water and steam corresponding to the
variation of pressure modifies this law; but, as the effect of
the difference of temperatures is not considerable, it will be
convenient to register in the memory the following important
practical conclusion:â€”</p>


<div class="ph3"><h3>(<a id="h3-67"></a>67.)</h3> <em>A cubic inch of water converted into steam will supply
a mechanical force very nearly equal to a ton weight raised a
foot high; and this force will not be subject to considerable
variation, whatever be the temperature or pressure at which
the water may be evaporated.</em></div>

<div class="figcenter" style="width: 466px;">
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_140.png" width="466" height="387" alt="" />
<div class="caption">GLASGOW.</div>
</div>

<div class="footnotes"><h3>FOOTNOTES:</h3>

<div class="footnote">

<p><a name="Footnote_18_18" id="Footnote_18_18"></a><a href="#FNanchor_18_18"><span class="label">[18]</span></a> The preceding paragraphs, and some other parts of the present volume
on the general properties of Heat, are taken from my Treatise on Heat, in
the <cite>Cabinet CyclopÅ“dia</cite>, to which those who desire more detailed explanation
and more copious illustration should refer.</p></div></div>

<div class="figcenter" style="width: 411px;">
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_141.png" width="411" height="464" alt="" />
<div class="caption">GLASGOW COLLEGE.</div>
</div>

<h2><a name="CHAP_V" id="CHAP_V">CHAP. V.</a></h2>

<p class="right"><a class="refpn" id="Pg119">[Pg119]</a><br />
<a href="#CONTENTS"><small>TOC</small></a>&#160;&#160;<a
href="#INDEX"><small>INX</small></a></p>

<div class="chapheader">
WATT FINDS THAT CONDENSATION IN THE CYLINDER IS INCOMPATIBLE
WITH A DUE ECONOMY OF FUEL.â€”CONCEIVES THE NOTION OF CONDENSING
OUT OF THE CYLINDER.â€”DISCOVERS SEPARATE CONDENSATION.â€”INVENTS
THE AIR-PUMP.â€”SUBSTITUTES STEAM PRESSURE
FOR ATMOSPHERIC PRESSURE.â€”INVENTS THE STEAM CASE, OR JACKET.â€”HIS
FIRST EXPERIMENTS TO REALISE THESE INVENTIONS.â€”HIS
EXPERIMENTAL APPARATUS.â€”DIFFICULTIES OF BRINGING THE IMPROVED
ENGINES INTO USE.â€”WATT PRACTISES AS A CIVIL ENGINEER.â€”HIS
PARTNERSHIP WITH ROEBUCK.â€”HIS FIRST PATENT.â€”DESCRIPTION
OF HIS SINGLE-ACTING STEAM ENGINE.</div>


<div class="ph3fst"><h3>(68.)</h3> At the period to which we have now brought the history
of the invention of the steam engine, Watt had obtained,
chiefly by his own experiments, a sufficient knowledge of the
phenomena which have been just explained, to enable him
to arrive at the conclusion that a very small proportion of the
whole mechanical effect attending the evaporation was really
rendered available by the atmospheric engine; and that,
<a class="refpn" id="Pg120">[Pg120]</a>
therefore, extensive and injurious sources of waste existed in its
machinery.</div>

<p>He perceived that the principal source of this wasteful expenditure
of power consisted in the quantity of steam which
was condensed at each stroke of the piston, in heating the
cylinder previous to the ascent of the piston. Yet, as it was
evident that that ascent could not be accomplished in a cold
cylinder, it was apparent that this waste of power must be
inevitable, unless some expedient could be devised, by which
<em>a vacuum could be maintained in the cylinder, without cooling
it</em>. But, to produce such a vacuum, the steam must be condensed;
and, to condense the steam, its temperature must
be lowered to such a point that the vapour proceeding from
it shall have no injurious pressure; yet, if condensed steam
be contained in a cylinder at a high temperature, it will
return to the temperature of the cylinder, recover its elasticity,
and resist the descent of the piston.</p>

<p>Having reflected on these circumstances, it became apparent
to Watt, that a vice was inherent in the structure of
the atmospheric engine, which rendered a large waste of
power inevitable; this vice arising from the fact, that the
condensation of the steam was incompatible with the condition
of maintaining the elevated temperature of the cylinder
in which that condensation took place. It followed,
therefore, either that the steam must be imperfectly condensed,
or that the condensation could not take place in the
cylinder. It was in 1765, that, pondering on these circumstances,
the happy idea occurred to him, that the production
of a vacuum could be equally effected, though <em>the place</em> where
the condensation of the steam took place were not the cylinder
itself. He saw, that if a vessel in which a vacuum was
produced were put into communication with another containing
an elastic fluid, the elastic fluid would rush into the
vacuum, and diffuse itself through the two vessels; but if, on
rushing into such vacuum, this elastic fluid, being vapour, were
there condensed, or restored to the liquid form, that then the
space within the two vessels would be equally rendered a vacuum;â€”that,
under such circumstances, one of the vessels
might be maintained at any temperature, however high, while
<a class="refpn" id="Pg121">[Pg121]</a>
the other might be kept at any temperature, however low.
This felicitous conception formed the first step in that splendid
career of invention and discovery which has conferred immortality
on the name of Watt. He used to say, that the moment
the idea of separate condensation occurred to him,â€”that is,
of condensing, in one vessel kept cold, the steam coming from
another vessel kept hot,â€”all the details of his improved engine
rushed into his mind in such rapid succession, that, in
the course of a day, his invention was so complete that he
proceeded to submit it to experiment.</p>

<div class="figleft" style="width: 231px;">
<a id="Fig019"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_143.png" width="231" height="296" alt="" />
<div class="caption figure">Fig. 19.</div>
</div>

<p>To explain the first conception of this memorable invention;
let a tube or pipe, <strong>S</strong> (<a href="#Fig019"><i>fig.</i> 19.</a>), be imagined to proceed
from the bottom of the
cylinder <strong>A B</strong> to a vessel, <strong>C</strong>,
having a stop-cock, <strong>D</strong>, by
which the communication
between the cylinder and
the vessel <strong>C</strong> may be opened
or closed at pleasure. If
we suppose the piston <strong>P</strong> at
the top of the cylinder, and
the space below it filled
with steam, the cylinder
and steam being at the
usual temperature, while
the vessel <strong>C</strong> is a vacuum,
and maintained at a low
temperature. Then, on
opening the cock <strong>D</strong>, the steam will rush from the cylinder
<strong>A B</strong> through the tube <strong>S</strong>, and, passing into the cold vessel <strong>C</strong>,
will be condensed by contact with its cold sides. This process
of condensation will be rendered instantaneous if a jet
of cold water is allowed to play in the vessel <strong>C</strong>. When the
steam thus rushing into <strong>C</strong>, has been destroyed, and the space
in the cylinder <strong>A B</strong> becomes a vacuum, then the pressure of
the atmosphere being unobstructed, the piston will descend
with the force due to the excess of the pressure of the
atmosphere above the friction. When it has descended,
suppose the stop-cock <strong>D</strong> closed, and steam admitted from
<a class="refpn" id="Pg122">[Pg122]</a>
the boiler through a proper cock or valve below the piston,
the cylinder and piston being still at the same temperature
as before. The steam on entering the cylinder, not being
exposed to contact with any surface below its own temperature,
will not be condensed, and therefore will immediately
cause the piston to rise, and the piston will have attained
the top of the cylinder when as much steam shall have been
supplied by the boiler as will fill the cylinder. When this
has taken place, suppose the communication with the boiler
cut off, and the cock <strong>D</strong> once more opened: the steam will
again rush through the pipe <strong>S</strong> into the vessel <strong>C</strong>, where encountering
the cold surface and the jet of cold water, it
will be condensed, and the vacuum, as before, will be produced
in the cylinder <strong>A B</strong>; that cylinder still maintaining
its temperature, the piston will again descend, and so the
process may be continued.</p>


<div class="ph3"><h3>(69.)</h3> Having carried the invention to this point, Watt saw
that the vessel <strong>C</strong> would gradually become heated by the steam
which would be continually condensed in it. To prevent
this, as well as to supply a constant jet of cold water, he proposed
to keep the vessel <strong>C</strong> submerged in a cistern of cold
water, from which a pipe should conduct a jet to play within
the vessel, so as to condense the steam as it would pass from
the cylinder.</div>

<p>But here a difficulty presented itself, against which it was
necessary to provide. The cold water admitted through the
jet to condense the steam, mixed with the condensed steam
itself, would gradually collect in the vessel <strong>C</strong>, and at length
choke it. To prevent this, Watt proposed to put the vessel
<strong>C</strong> in communication with a pump <strong>F</strong>, which might be wrought
by the engine itself, and by which the water, which would
collect in the bottom of the vessel <strong>C</strong>, would be constantly
drawn off. This pump would be evidently rendered the more
necessary, since more or less atmospheric air, always combined
with water in its common state, would enter the vessel <strong>C</strong> by the
condensing jet. This air would be disengaged in the vessel <strong>C</strong>
by the heat of the steam condensed therein; and it would rise
through the tube <strong>S</strong>, and vitiate the vacuum in the cylinder;â€”an
effect which would be rendered the more injurious,
<a class="refpn" id="Pg123">[Pg123]</a>
inasmuch as, unlike steam, this elastic fluid would be incapable
of being condensed by cold. The pump <strong>F</strong>, therefore, by
which Watt proposed to draw off the water from the vessel <strong>C</strong>,
might also be made to draw off the air, or the principal part
of it.</p>

<p>The vessel <strong>C</strong> was subsequently called a <em>condenser</em>; and, from
the circumstances just adverted to, the pump <strong>F</strong> has been called
the <em>air-pump</em>.</p>

<p>Theseâ€”namely, the cylinder, the condenser, and the air-pumpâ€”were
the three principal parts in the invention, as it
first presented itself to the mind of Wattâ€”and even before it
was reduced to a model, or submitted to experiment. But, in
addition to these, other two improvements offered themselves
in the very first stage of its progress.</p>

<p>In the atmospheric engine, the piston was maintained steam-tight
in the cylinder by supplying a stream of cold water above
it, by which the small interstices between the piston and
cylinder would be stopped. It is evident that the effect of
this water as the piston descended would be to cool the cylinder,
besides which any portion of it which might pass between
the piston and cylinder and which would pass below the
piston, would boil the moment it would fall into the cylinder,
which itself would be maintained at the boiling temperature.
This water, therefore, would produce steam, the pressure of
which would resist the descent of the piston.</p>

<p>Watt perceived, that even though this inconvenience were
removed by the use of oil or tallow upon the piston, still, that
as the piston would descend in the cylinder, the cold atmosphere
would follow it; and would, to a certain extent, lower the
temperature of the cylinder. On the next ascent of the piston,
this temperature would have to be again raised to 212Â°
by the steam coming from the boiler, and would entail upon
the machine a proportionate waste of power.</p>

<p>If the atmosphere of the engine-house could be kept heated
to the temperature of boiling water, this inconvenience would
be removed. The piston would then be pressed down by air
as hot as the steam to be subsequently introduced into it. On
further consideration, however, it occurred to Watt that it
would be still more advantageous if the cylinder itself could be
<a class="refpn" id="Pg124">[Pg124]</a>
worked in an atmosphere of steam, having only the same pressure
as the atmosphere. Such steam would press the piston
down as effectually as the air would; and it would have the
further advantage over air, that if any portion of it leaked
through between the piston and cylinder, it would be condensed,
which could not be the case with atmospheric air.
He therefore determined on surrounding the cylinder by an
external casing, the space between which and the cylinder he
proposed to be filled with steam supplied from the boiler.
The cylinder would thus be enclosed in an atmosphere of its
own, independent of the external air, and the vessel so enclosing
it would only require to be a little larger than the
cylinder, and to have a close cover at the top, the centre of
which might be perforated with a hole to admit the rod of the
piston to pass through, the rod being made smooth, and so
fitted to the perforation that no steam should escape between
them. This method would be attended also with the advantage
of keeping the cylinder and piston always heated, not
only inside but outside; and Watt saw that it would be
further advantageous to employ the pressure of steam to drive
the piston in its descent instead of the atmosphere, as its
intensity or force would be much more manageable; for, by
increasing or diminishing the heat of the steam in which the
cylinder was enclosed, its pressure might be regulated at
pleasure, and it might be made to urge the piston with any
force that might be required. The power of the engine would
therefore be completely under control, and independent of all
variations in the pressure of the atmosphere.</p>


<div class="ph3"><h3>(70.)</h3> This was a step which totally changed the character
of the machine, and which rendered it a <strong>STEAM ENGINE</strong> instead
of an <strong>ATMOSPHERIC ENGINE</strong>. Not only was the vacuum
below the piston now produced by the property of steam,
in virtue of which it is reconverted into water by cold; but
the pressure which urged the piston into this vacuum was due
to the elasticity of steam.</div>

<p>The external cylinder, within which the working cylinder
was enclosed, was called <strong>THE JACKET</strong>, and is still very generally
used.</p>

<div class="figcenter" style="width: 479px;">
<a id="Fig020"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_147.png" width="479" height="469" alt="" />
<div class="caption figure">Fig. 20.</div>
</div>

<div class="ph3"><h3>(71.)</h3> The first experiment in which Watt attempted to
<a class="refpn" id="Pg125">[Pg125]</a>
realise, on a small scale, his conceptions, was made in the following
manner. The cylinder of the engine was represented by
a brass syringe <strong>A B</strong> (<a href="#Fig020"><i>fig.</i> 20.</a>) an inch and a third in diameter,
and ten inches in length, to which a top and a bottom of tin
plate was fitted. Steam was conveyed by a pipe, <strong>S</strong>, from a
small boiler into the lower end of this syringe, a communication
being made with the upper end of the syringe by a
branch pipe <strong>D</strong>. For the greater convenience of the experiment,
it was found desirable to invert the position of the
cylinder, so that the steam should press the piston <strong>P</strong> upwards
instead of downwards. The piston-rod <strong>R</strong> therefore was presented
downwards. An eduction pipe <strong>E</strong> was also inserted in
the top of the cylinder, which was carried to the condenser.
The piston-rod was made hollow, or rather a hole was drilled
longitudinally through it, and a valve was fitted at its lower
end, to carry off the water produced by the steam, which
<a class="refpn" id="Pg126">[Pg126]</a>
would be condensed in the cylinder in the commencement of
the process. The condenser used in this experiment operated
without injection, the steam being condensed by the contact
of cold surfaces. It consisted of two thin pipes <strong>F, G</strong> of tin,
ten or twelve inches in length, and the sixth of an inch in
diameter, standing beside each other perpendicularly, and
communicating at the top with the eduction pipe, which was
provided with a valve opening upwards. At the bottom these
two pipes communicated with another tube <strong>I</strong> of about an inch
in diameter, by a horizontal pipe, having in it a valve, <strong>M</strong>, opening
towards <strong>I</strong>, fitted with a piston <strong>K</strong>, which served the office
of the air-pump, being worked by the hand. This piston, <strong>K</strong>,
had valves in it opening upwards. These condensing pipes
and air-pump were immersed in a small cistern, filled with
cold water. The steam was conveyed by the steam-pipe <strong>S</strong> to
the bottom of the cylinder, a communication between the top
and bottom of the cylinder being occasionally opened by a
cock, <strong>C</strong>, placed in the branch pipe. The eduction pipe leading
to the condenser also had a cock, <strong>L</strong>, by which the communication
between the top of the cylinder and the condenser
might be opened and closed at pleasure. In the commencement
of the operation, the cock <strong>N</strong> admitting steam from the
boiler, and the cock <strong>L</strong> opening a communication between the
cylinder and the condenser, and the cock <strong>C</strong> opening a communication
between the top and bottom of the cylinder, being
all open, steam rushed from the boiler, passing through all the
pipes, and filling the cylinder. A current of mixed air and
steam was thus produced through the eduction pipe <strong>E</strong>, through
the condensing pipes <strong>F</strong> and <strong>G</strong>, and through the air-pump <strong>I</strong>,
which issued from the valve <strong>H</strong> in the eduction pipe, and
from the valve in the air-pump piston, all of which opened
upwards. The steam also in the cylinder passed through the
hole drilled in the piston-rod, and escaped, mixed with air,
through the valve in the lower end of that rod. This process
was continued until all the air in the cylinder, pipes, and
condenser, was blown out, and all these spaces filled with pure
steam. The cocks <strong>L</strong>, <strong>C</strong>, and <strong>N</strong>, were then closed, and the
atmospheric pressure closed the valve <strong>H</strong> and the valves in the
air-pump piston. The cold surfaces condensing the steam in
<a class="refpn" id="Pg127">[Pg127]</a>
the pipes <strong>F</strong> and <strong>G</strong>, and in the lower part of the air-pump, a
vacuum was produced in these spaces. The cock C being
now closed, and the cocks <strong>L</strong> and <strong>N</strong> being open, the steam
in the upper part of the cylinder rushed through the pipe
E into the condenser, where it was reduced to water, so that
a vacuum was left in the upper part of the cylinder. The
steam from the boiler passing below the piston, pressed it
upwards with such force, that it lifted a weight of eighteen
pounds hung from the end of the piston-rod. When the
piston reached the top of the cylinder, the cocks <strong>L</strong> and <strong>N</strong> were
closed, and the cock <strong>C</strong> opened. All communication between
the cylinder and the boiler, as well as between the cylinder and
the condenser, were now cut off, and the steam in the cylinder
circulated freely above and below the piston, by means of the
open tube <strong>D</strong>. The piston, being subject to equal forces
upwards and downwards, would therefore descend by its own
weight, and would reach the bottom of the cylinder. The
air-pump piston meanwhile being drawn up, the air and the
condensed steam in the tubes <strong>F</strong> and <strong>G</strong> were drawn into the
air-pump <strong>I</strong>, through the open horizontal tube at the bottom.
Its return was stopped by the valve <strong>M</strong>. By another stroke of
the air-pump, this water and air were drawn out through valves
in the piston, which opened upwards. The cock <strong>C</strong> was now
closed, and the cocks <strong>L</strong> and <strong>N</strong> opened, preparatory to another
stroke of the piston. The steam in the upper part of the
cylinder rushed, as before, into the tubes <strong>F</strong> and <strong>G</strong>, and was
condensed by their cold surfaces, while steam from the boiler
coming through the pipe <strong>S</strong>, pressed the piston upwards. The
piston again ascended with the same force as before, and in
the same manner the process was continually repeated.</div>


<div class="ph3"><h3>(72.)</h3> The quantity of steam expended in this experimental
model in the production of a given number of strokes of the
piston was inferred from the quantity of water evaporated in
the boiler; and on comparing this with the magnitude of the
cylinder and the weight raised by the pressure of the steam,
the contrivance was proved to affect the economy of steam, as
far as the imperfect conditions of such a model could have permitted.
A larger model was next constructed, having an outer
cylinder, or steam case, surrounding the working cylinder, and
<a class="refpn" id="Pg128">[Pg128]</a>
the experiments made with it fully realised Watt's expectations,
and left no doubt of the great advantages which would
attend his invention. The weights raised by the piston proved
that the vacuum in the cylinder produced by the condensation
was almost perfect; and he found that when he used water
in the boiler which by long boiling had been well cleared of
air, the weight raised was not much less than the whole
amount of the pressure of the steam upon the piston. In this
larger model, the cylinder was placed in the usual position,
with a working lever and other apparatus similar to that employed
in the Atmospheric Engine.</div>


<div class="ph3">
<h3>(73.)</h3> It was in the beginning of the year 1765, Watt
being then in the twenty-ninth year of his age, that he
arrived at these great discoveries. The experimental models
just described, by which his invention was first reduced to
a rude practical test, were fitted up at a place called Delft
House, in Glasgow. It will doubtless, at the first view, be a
matter of surprise that improvements of such obvious importance
in the economy of steam power, and capable of being
verified by tests so simple, were not immediately adopted
wherever atmospheric engines were used. At the time, however,
referred to, Watt was an obscure artisan, in a provincial
town, not then arrived at the celebrity to which it has since
attained, and the facilities by which inventions and improvements
became public were much less than they have since
become. It should also be considered that all great and sudden
advances in the useful arts are necessarily opposed by the
existing interests with which their effects are in conflict.
From these causes of opposition, accompanied with the usual
influence of prejudice and envy, Watt was not exempt,
and was not therefore likely suddenly to revolutionise the arts
and manufactures of the country by displacing the moving
powers employed in them, and substituting an engine, the
efficacy and power of which depended mainly on physical
principles, then altogether new and but imperfectly understood.</div>

<p>Not having the command of capital, and finding it impracticable
to inspire those who had, with the same confidence in
the advantages of his invention which he himself felt, he was
<a class="refpn" id="Pg129">[Pg129]</a>
unable to take any step towards the construction of engines on
a large scale. Soon after this, he gave up his shop in Glasgow,
and devoted himself to the business of a Civil Engineer. In
this capacity he was engaged to make a survey of the river
Clyde, and furnished an elaborate and valuable Report upon
its projected improvements. He was also engaged in making
a plan of the canal, by which the produce of the Monkland
Colliery was intended to be carried to Glasgow, and in superintending
the execution of that work. Besides these, several
other engineering enterprises occupied his attention, among
which may be mentioned, the navigable canal across the isthmus
of Crinan, afterwards completed by Rennie; improvements
proposed in the ports of Ayr, Glasgow, and Greenock;
the construction of the bridges at Hamilton, and at Rutherglen;
and the survey of the country through which the celebrated
Caledonian canal was intended to be carried.</p>

<p>"If, forgetful of my duties as the organ of this academy,"
says M. Arago (whose eloquent observations on the delays of
this great invention, addressed to the assembled members of
the National Institute of France, we cannot forbear to quote),
"I could think of making you smile, rather than expressing
useful truths, I would find here matter for a ludicrous
contrast. I would call to your recollection the authors, who
at our weekly sittings demand with all their might and main
(<i>Ã  cor et Ã  cris</i>) an opportunity to communicate some little
remarkâ€”some small reflectionâ€”some trifling note, conceived
and written the night before; I would represent them to you
cursing their fate, when according to your rules, the reading
of their communication is postponed to the next meeting,
although during this cruel week, they are assured that their
important communication is deposited in our archives in a
sealed packet. On the other hand, I would point out to you
the creator of a machine, destined to form an epoch in the
annals of the world, undergoing patiently and without murmur,
the stupid contempt of capitalists,â€”conscious of his exalted
genius, yet stooping for eight years to the common labour of
laying down plans, taking levels, and all the tedious calculations
connected with the routine of common engineering.
While in this conduct you cannot fail to recognise the serenity,
<a class="refpn" id="Pg130">[Pg130]</a>
the moderation, and the true modesty of his character, yet such
indifference, however noble may have been its causes, has
something in it not altogether blameless. It is not without
reason that society visits with severe reprobation those who
withdraw gold from circulation and hoard it in their coffers.
Is he less culpable who deprives his country, his fellow citizens,
his age, of treasures a thousand times more precious than
the produce of the mine; who keeps to himself his immortal
inventions, sources of the most noble and purest enjoyment of
the mind, who abstains from conferring upon labour those
powers, by which would be multiplied in an infinite proportion
the products of industry, and by which, with advantage to civilisation
and human nature, he would smooth away the inequalities
of the conditions of man."<a name="FNanchor_19_19" id="FNanchor_19_19"></a><a href="#Footnote_19_19" class="fnanchor">[19]</a></p>


<div class="ph3"><h3>(74.)</h3> Although Watt was thus attracted by pursuits foreign
to his recent investigations respecting the improvement of
steam power, he never lost sight of that object. It was not
until the year 1768, three years after his great discoveries, that
any step was taken to enable him to carry them into effect on
a large scale. At that time his friends brought him into
communication with Dr. Roebuck, the proprietor of the
Carron Iron Works, who rented extensive coal works at
Kinneal from the Duchess of Hamilton. Watt was first employed
by Roebuck as a civil engineer; but when he made
known to him the improvements he had projected in the
steam engine, Roebuck proposed to take out a patent for an
engine on the principle of the model which had been fitted
up at Delft House, and to join Watt in a partnership, for the
construction of such engines. Sensible of the advantages to
be derived from the influence of Roebuck, and from his
command of capital, Watt agreed to cede to him two thirds
of the advantages to be derived from the invention. A patent
was accordingly taken out on the fifth of January, 1769,
nearly four years after the invention had been completed;
and an experimental engine on a large scale was constructed
by him, and fitted up at Kinneal House. In the first trial
this machine more than fulfilled Watt's anticipations. Its
<a class="refpn" id="Pg131">[Pg131]</a>
success was complete. In the practical details of its construction,
however, some difficulties were still encountered,
the greatest of which consisted in packing the piston, so as to
be steam-tight. The principle of the new engine did not
admit of water being kept upon the piston, to prevent leakage,
as in the old engines; he was therefore obliged to have
his cylinders much more accurately bored, and more truly
cylindrical, and to try a great variety of soft substances for
packing the piston, which would make it steam-tight without
great friction, and maintain it so in a situation perfectly
dry, and at the temperature of boiling water.</div>

<p>While Watt was endeavouring to overcome these and
other difficulties, in the construction of the machine, his
partner, Dr. Roebuck, became embarrassed, by the failure of
his undertaking in the Borrowstowness coal and salt works;
and he was unable to supply the means of prosecuting with
the necessary vigour the projected manufacture of the new
engines.</p>

<p>The important results of Watt's labours having happily at
this time become more publicly known, Mr. Matthew Boulton,
whose establishment at Soho, near Birmingham, was at
that time the most complete manufactory for metal-work in
England, and conducted with unexampled enterprise and
spirit, proposed to purchase Dr. Roebuck's interest in the
patent. This arrangement was effected in the year 1773,
and in the following year Mr. Watt removed to Soho, where
a portion of the establishment was allotted to him, for the
erection of a foundery, and other works necessary to realise
his inventions on a grand scale.</p>

<p>The patent which had been granted in 1769 was limited to
a period of fourteen years, and would consequently expire
about the year 1783. From the small progress which had
hitherto been made in the construction of engines upon the
new principle, and from the many difficulties still to be
encountered, and the large expenditure of capital which
must obviously be incurred before any return could be obtained,
it was apparent that unless an extension of the patent
right could be obtained, Boulton and Watt could never
expect any advantage adequate to the risk of their great
<a class="refpn" id="Pg132">[Pg132]</a>
enterprise. In the year 1774 an application was accordingly
made to parliament for an extension of the patent, which was
supported by the testimony of Dr. Roebuck, Mr. Boulton,
and others, as to the merits and probable utility of the invention.
An Act was accordingly passed, in 1775, extending
the term of the patent until the year 1800.</p>


<div class="ph3">
<h3>(75.)</h3> The following abstract of this Act may not be uninteresting
at this time, when the anticipations expressed in it
have been so successfully and extensively realised:â€”</div>

<p>"An Act for vesting in James Watt, engineer, his executors,
administrators, and assigns, the sole use and property
of certain steam engines, commonly called fire engines, of his
invention, throughout his majesty's dominions, for a limited
time:</p>

<p>"And whereas the said James Watt hath employed many
years, and a considerable part of his fortune, in making experiments
upon steam engines, commonly called fire engines,
with a view to improve those very useful machines, by which
several very considerable advantages over the common steam
engines are acquired; but upon account of the many difficulties
which always arise in the execution of such large and
complex machines, and of the long time requisite to make
the necessary trials, he could not complete his intention
before the end of the year 1774, when he finished some large
engines as specimens of his construction, which have succeeded,
so as to demonstrate the utility of the said invention:</p>

<p>"And whereas, in order to manufacture these engines with
the necessary accuracy, and so that they may be sold at
moderate prices, a considerable sum of money must be previously
expended in erecting mills and other apparatus; and
as several years and repeated proofs will be required before
any considerable part of the public can be fully convinced of
the utility of the invention, and of their interest to adopt the
same, the whole term granted by the said letters patent may
probably elapse before the said James Watt can receive an
advantage adequate to his labour and invention:</p>

<p>"And whereas, by furnishing mechanical power at much
less expense, and in more convenient forms, than has hitherto
been done, his engines may be of great utility, in facilitating
<a class="refpn" id="Pg133">[Pg133]</a>
the operations in many great works and manufactures of this
kingdom; yet it will not be in the power of the said James
Watt to carry his invention into that complete execution
which he wishes, and so as to render the same of the highest
utility to the public of which it is capable, unless the term
granted by the said letters patent be prolonged, and his property
in the said invention secured for such time as may
enable him to obtain an adequate recompense for his labour,
time, and expense:</p>

<p>"To the end, therefore, that the said James Watt may be
enabled and encouraged to prosecute and complete his said
invention, so that the public may reap all the advantages to
be derived therefrom in their fullest extent: it is enacted,</p>

<p>"That from and after the passing of this Act, the sole
privilege and advantage of making, constructing, and selling
the said engines hereinbefore particularly described, within
the kingdom of Great Britain, and his majesty's colonies and
plantations abroad, shall be, and are hereby declared to be,
vested in the said James Watt, his executors, administrators,
and assigns, for and during the term of twenty-five years,"
&#38;c. &#38;c.</p>


<div class="ph3"><h3>(76.)</h3> Thus protected and supported, Watt now directed
the whole vigour of his mind to perfect the practical details
of his invention, and the result was, the construction on a
large scale of the engine which has since been called his
<strong class="m1">Single acting Steam Engine</strong>.</div>

<p>It is necessary to recollect, that notwithstanding the extensive
and various application of steam power in the arts
and manufactures, at the time to which our narrative has
now reached, the steam engine had never been employed
for any other purpose save that of raising water by working
pumps. The motion, therefore, which was required was
merely an upward force, such as was necessary to elevate the
piston of a pump, loaded with the column of water which it
raised. The following then is a description of the improved
engine of Watt, by which such work was proposed to be
performed:â€”</p>

<div class="figcenter" style="width: 550px;">
<a id="Fig021"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_156.png" width="550" height="778" alt="" />
<div class="caption figure">Fig. 21.</div>
</div>

<p>In the cylinder represented at <strong>C</strong> (<a href="#Fig021"><i>fig.</i> 21.</a>), the piston <strong>P</strong>
moves steam-tight. It is closed at the top, and the piston
<a class="refpn" id="Pg134">[Pg134]</a>
rod, being accurately turned, runs in a steam-tight collar, <strong>B</strong>,
furnished with a stuffing-box, and is constantly lubricated
with melted tallow. A funnel is screwed into the top of
the cylinder, through which, by opening a stop-cock, melted
<a class="refpn" id="Pg135">[Pg135]</a>
tallow is permitted from time to time to fall upon the piston
within the cylinder, so as to lubricate it, and keep it steam-tight.
Two boxes, <strong>A A</strong>, called the upper and lower steam boxes,
contain valves by which steam from the boiler may be
admitted and withdrawn. These steam boxes are connected
by a tube of communication <strong>T</strong>, and they communicate with
the cylinder at the top and bottom by short tubes represented
in the figure. The upper steam box <strong>A</strong> contains one valve,
by which a communication with the boiler may be opened or
closed at pleasure. The lower valve box contains two valves.
The lower valve <strong>I</strong> communicates with the tube <strong>Tâ€²</strong>, leading to
the condenser <strong>D</strong>, which being opened or closed, a communication
is made or cut off at pleasure, between the cylinder <strong>C</strong>
and the condenser <strong>D</strong>. A second valve, or upper valve <strong>H</strong>,
which is represented closed in the figure, may be opened so
as to make a free communication between the cylinder <strong>C</strong> and
the tube <strong>T</strong>, and by that means between the cylinder <strong>C</strong>, below
the piston and the space above the piston. The condenser
<strong>D</strong> is submerged in a cistern of cold water. At the side there
enters it a tube, <strong>E</strong>, governed by a cock, which being opened
or closed to any required extent, a jet of cold water may be
allowed to play in the condenser, and may be regulated or
stopped, at pleasure. This jet, when playing, throws the
water upwards in the condenser towards the mouth of the
tube <strong>Tâ€²</strong>, as water issues from the rose of a watering pot.
The tube <strong>S</strong> proceeds from the boiler, and terminates in
the steam box <strong>A</strong>, so that the steam supplied from the boiler
constantly fills that box. The valve <strong>G</strong> is governed by levers,
whose pivots are attached to the framing of the
engine, and is opened or closed at pleasure, by raising or
lowering the lever <strong>Gâ€²</strong>. The valve <strong>G</strong>, when open, will therefore
allow steam to pass from the boiler through the short
tube to the top of the piston, and this steam will also fill
the tube <strong>T</strong>. If the lower valve <strong>H</strong> be closed, its circulation
beyond that point will be stopped; but if the valve <strong>H</strong> be
open, the valve <strong>I</strong> being closed, then the steam will circulate
equally in the cylinder, above and below the piston. If
the valve <strong>I</strong> be open, then steam will rush through the tube
<strong>Tâ€²</strong> into the condenser; but this escape of the steam will be
<a class="refpn" id="Pg136">[Pg136]</a>
stopped, if the valve <strong>I</strong> be closed. The valve <strong>H</strong> is worked by
the lever <strong>Hâ€²</strong>, and the valve <strong>I</strong> by the lever <strong>Iâ€²</strong>.</p>

<p>The valve <strong>G</strong> is called the upper steam valve, <strong>H</strong> the lower
steam valve, <strong>I</strong> the exhausting valve, and <strong>E</strong> the condensing
valve.</p>

<p>From the bottom of the condenser <strong>D</strong> proceeds a tube
leading to the air-pump, which is also submerged in the
cistern of cold water. In this tube is a valve <strong>M</strong>, which opens
outwards from the condenser towards the air-pump. In the
piston of the air-pump <strong>N</strong> is a valve which opens upwards.
The piston-rod <strong>Q</strong> of the air-pump is attached to a beam of
wood called a plug frame, which is connected with the working
beam by a flexible chain playing on the small arch-head
immediately over the air-pump. From the top of the air-pump
barrel above the piston proceeds a pipe or passage
leading to a small cistern, <strong>B</strong>, called the hot well. The pipe
which leads to this well, is supplied with a valve, <strong>K</strong>, which
opens outwards from the air pump barrel towards the well.
From the nature of its construction, the valve <strong>M</strong> admits the
flow of water from the condenser towards the air-pump, but
prevents its return; and, in like manner, the valve <strong>K</strong> admits
the flow of water from the upper part of the air-pump barrel
into the hot well <strong>B</strong>, but obstructs its return.</p>

<p>Let us now consider how these valves should be worked in
order to move the piston upwards and downwards with the
necessary force. It is in the first place necessary that all the
air which fills the cylinder, the tubes and the condenser shall
be expelled. To accomplish this it is only necessary to open
at once the three valves <strong>G</strong>, <strong>H</strong>, and <strong>I</strong>. The steam then rushing
from the boiler through the steam-pipe <strong>S</strong>, and the open valve
<strong>G</strong> will pass into the cylinder above the piston, will fill the
tube <strong>T</strong>, pass through the lower steam valve <strong>H</strong>, will fill the
cylinder <strong>C</strong> below the piston, and will pass through the open
valve <strong>I</strong> into the condenser. If the valve <strong>E</strong> be closed so that
no jet shall play in the condenser, the steam rushing into it
will be partially condensed by the cold surfaces to which it
will be exposed; but if the boiler supply it through the pipe
<strong>S</strong> in sufficient abundance, it will rush with violence through
the cylinder and all the passages, and its pressure in the
<a class="refpn" id="Pg137">[Pg137]</a>
condenser <strong>D</strong>, combined with that of the heated air with which it
is mixed, will open the valve <strong>M</strong>, and it will rush through
mixed with the air into the air-pump barrel <strong>N</strong>. It will press
the valves in the air-pump piston upwards, and, opening them,
will rush through, and will collect in the air-pump barrel
above the piston. It will then, by its pressure, open the
valve <strong>K</strong>, and will escape into the cistern <strong>B</strong>.</p>

<p>Throughout this process the steam, which mixed with the
air fills the cylinder, condenser and air-pumps will be only
partially condensed in the last two, and it will escape mixed
with air through the valve <strong>K</strong>, and this process will continue
until all the atmospheric air which at first filled the cylinder,
tubes, condenser and air-pump barrel shall be expelled
through the valve <strong>K</strong>, and these various spaces shall be filled
with pure steam. When that has happened let us suppose
all the valves closed. In closing the valve <strong>I</strong> the flow of
steam to the condenser will be stopped, and the steam contained
in it will speedily be condensed by the cold surface of
the condenser, so that a vacuum will be produced in the condenser,
the condensed steam falling in the form of water to
the bottom. In like manner, and for like reasons, a vacuum
will be produced in the air-pump. The valve <strong>M</strong>, and the
valves in the air-pump piston will be closed by their own
weight.</p>

<p>By this process, which is called <em>blowing through</em>, the atmospheric
air, and other permanent gases, which filled the
cylinder, tubes, condenser and air-pump are expelled, and
these spaces will be a vacuum. The engine is then prepared
to be started, which is effected in the following manner:â€”The
upper steam valve <strong>G</strong> is opened, and steam allowed to
flow from the boiler through the passage leading to the top
of the cylinder. This steam cannot pass to the bottom of
the cylinder, since the lower steam valve <strong>H</strong> is closed. The
space in the cylinder below the piston being therefore a
vacuum, and the steam pressing above it the piston will be
pressed downwards with a corresponding force. When it has
arrived at the bottom of the cylinder the steam valve <strong>G</strong> must
be closed, and at the same time the valve <strong>H</strong> opened. The
valve <strong>I</strong> leading to the condenser being also closed, the steam
<a class="refpn" id="Pg138">[Pg138]</a>
which fills the cylinder above the piston is now admitted to
circulate through the open valve <strong>H</strong> below the piston, so that
the piston is pressed equally upwards and downwards by
steam, and there is no force to resist its movement save its
friction with the cylinder. The weight of the pump rods on
the opposite end of the beam being more than equivalent to
overcome this the piston is drawn to the top of the cylinder,
and pushes before it the steam which is drawn through the
tube <strong>T</strong>, and the open valve <strong>H</strong>, and passes into the cylinder <strong>C</strong>
below the piston.</p>

<p>When the piston has thus arrived once more at the top of the
cylinder, let the valve <strong>H</strong> be closed, and at the same time the
valves <strong>G</strong> and <strong>I</strong> opened, and the condensing cock <strong>E</strong> also opened,
so as to admit the jet to play in the condenser. The steam which
fills the cylinder <strong>C</strong> below the piston, will now rush through
the open valve <strong>I</strong> into the condenser which has been hitherto a
vacuum, and there encountering the jet, will be instantly converted
into water, and a mixture of condensed steam and injected
water will collect in the bottom of the condenser. At
the same time, the steam proceeding from the boiler by the
steam pipe <strong>S</strong> to the upper steam box <strong>A</strong>, will pass through the
open steam valve <strong>G</strong> to the top of the piston, but cannot pass
below it because of the lower steam valve <strong>H</strong> being closed. The
piston, thus acted upon above by the pressure of the steam, and
the space in the cylinder below it being a vacuum, its downward
motion is resisted by no force but the friction, and it is therefore
driven to the bottom of the cylinder. During its descent
the valves <strong>G</strong>, <strong>I</strong>, and <strong>E</strong> remained open. At the moment it arrives
at the bottom of the cylinder, all these three valves are closed,
and the valve <strong>H</strong> opened. The steam which fills the cylinder
above the piston is now permitted to circulate below it, by the
open valve <strong>H</strong>, and the piston being consequently pressed equally
upwards and downwards will be drawn upwards as before by
the preponderance of the pump rods at the opposite end of the
beam. The weight of these rods must also be sufficiently
great to draw the air-pump piston <strong>N</strong> upwards. As this
piston rises in the air-pump, it leaves a vacuum below it into
which the water and air collected in the condenser will be
drawn through the valve <strong>M</strong>, which opens outwards. When the
<a class="refpn" id="Pg139">[Pg139]</a>
air-pump piston has arrived at the top of the barrel, which it
will do at the same time that the steam piston arrives at the
top of the cylinder, the water and the chief part of the air or
other fluids which may have been in the condenser will be
drawn into the barrel of the air-pump, and the valve <strong>M</strong> being
closed by its own weight, assisted by the pressure of these
fluids they cannot return into the condenser. At the moment
the steam piston arrives at the top of the cylinder, the valve
<strong>H</strong> is closed, and the three valves <strong>G</strong>, <strong>I</strong>, and <strong>E</strong> are opened. The
effect of this change is the same as was already described in
the former case, and the piston will in the same manner and
from the same causes be driven downwards. The air-pump
piston will at the same time descend by the force of its own
weight, aided by the weight of the plug-frame attached to its
rod. As it descends, the air below it will be gradually compressed
above the surface of the water in the bottom of the
barrel, until its pressure becomes sufficiently great to open
the valves in the air-pump piston. When this happens, the
valves in the air-pump
piston, as represented
on a large
scale in <a href="#Fig022"><i>fig.</i> 22.</a>, will
be opened, and the
air will pass through
them above the piston.
When the piston
comes in contact
with the water
in the bottom of the
barrel, this water
will likewise pass
through the open
valves. When the
piston has arrived
at the bottom of
the air-pump barrel, the valves in it will be closed by the
pressure of the fluids above them. The next ascent of the
steam piston will draw up the air-pump piston, and with
it the fluids in the pump barrel above it. As the air-pump
<a class="refpn" id="Pg140">[Pg140]</a>
piston approaches the top of its barrel, the air and water above
it will be drawn through the valve <strong>K</strong> into the hot cistern <strong>B</strong>.
The air will escape in bubbles through the water in that cistern,
and the warm water will be deposited in it.</p>

<div class="figright" style="width:322px;">
<a id="Fig022"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_161.png" width="322" height="354" alt="" />
<div class="caption figure">Fig. 22.</div>
</div>

<p>The magnitude of the opening in the condensing valve <strong>E</strong>,
must be regulated by the quantity of steam admitted to the
cylinder. As much water ought to be supplied through the
injection valve as will be sufficient to condense the steam contained
in the cylinder, and also to reduce the temperature of
the water itself, when mixed with the steam, to a sufficiently
low degree to prevent it from producing vapour of a pressure
which would injuriously affect the working of the piston. It
has been shown, that five and a half cubic inches of ice-cold
water mixed with one cubic inch of water in the state of
steam would produce six and a half cubic inches of water at
the boiling temperature. If then the cylinder contained one
cubic inch of water in the state of steam, and only five
and a half cubic inches of water were admitted through the
condensing jet, supposing this water, when admitted, to be at
the temperature of 32Â°, then the consequence would be that
six and a half cubic inches of water at the boiling temperature
would be produced in the condenser. Steam would immediately
arise from this, and at the same time the temperature
of the remaining water would be lowered by the amount of
the latent heat taken up by the steam so produced. This vapour
would rise through the open exhausting valve <strong>I</strong>, would
fill the cylinder below the piston, and would impair the efficiency
of the steam above pressing it down. The result of the
inquiries of Watt respecting the pressure of steam at different
temperatures, showed, that to give efficiency to the steam acting
upon the piston it would always be necessary to reduce
the temperature of the water in the condenser to 100Â°.</p>

<p>Let us then see what quantity of water at the common
temperature would be necessary to produce these effects.</p>

<p>If the latent heat of steam be taken at 1000Â°, a cubic inch
of water in the state of steam may be considered for the purposes
of this computation, as equivalent to one cubic inch of
water at 1212Â°. Now the question is, how many cubic inches
of water at 60Â° must be mixed with this, in order that the
<a class="refpn" id="Pg141">[Pg141]</a>
mixture may have the temperature of 100Â°? This will be
easily computed. As the cubic inch of water at 1212Â° is to
be reduced to 100Â°, it must be deprived of 1112Â° of its temperature.
On the other hand, as many inches of water at
60Â° as are to be added, must be raised in the same mixture
to the temperature of 100Â°, and therefore each of these must
receive 40Â° of temperature. The number of cubic inches of
water necessary to be added will therefore be determined by
finding how often 40Â° are contained in 1112Â°. If 1112 be
divided by 40, the quotient will be 27Â·8. Hence it appears,
that to reduce the water in the condenser to the temperature
of 100Â°, supposing the temperature of the water injected to
be 60Â°, it will be necessary to supply by the injection cock
very nearly twenty-eight times as much water as passes
through the cylinder in the state of steam; and therefore if
it be supposed that all the water evaporated in the boiler
passes through the cylinder, it follows that about twenty-eight
times as much water must be thrown into the condenser
as is evaporated in the boiler.</p>

<p>From these circumstances it will be evident that the cold
cistern in which the condenser and air-pump are submerged,
must be supplied with a considerable quantity of water. Independently
of the quantity drawn from it by the injection
valve, as just explained, the water in the cistern itself must
be kept down to a temperature of about 60Â°. The interior of
the condenser and air-pump being maintained by the steam
condensed in them at a temperature not less than 100Â°; the
outer surfaces of these vessels consequently impart heat to the
water in the cold cistern, and have therefore a tendency to
raise the temperature of that water. To prevent this, a pump
called the <em>cold pump</em>, represented at <strong>L</strong> in <a href="#Fig021"><i>fig.</i> 21.</a>, is provided.
By this pump water is raised from any convenient reservoir,
and driven through proper tubes into the cold cistern. This
cold pump is wrought by the engine, the rod being attached
to the beam. Water being, bulk for bulk, heavier the
lower its temperature, it follows that the water supplied
by the cold pump to the cistern will have a tendency to
sink to the bottom, pressing upwards the warmer water
contained in it. A waste-pipe is provided, by which this
<a class="refpn" id="Pg142">[Pg142]</a>
water is drained off, and the cistern therefore maintained
at the necessary temperature.</p>

<p>From what has been stated, it is also evident that the hot
well <strong>B</strong>, into which the warm water is thrown by the air-pump,
will receive considerably more water than is necessary to feed
the boiler. A waste-pipe, to carry off this, is also provided;
and the quantity necessary to feed the boiler is pumped up by
a small pump, <strong>O</strong>, the rod of which is attached to the beam, as
represented in <a href="#Fig021"><i>fig.</i> 21.</a>, and which is worked by the engine.
The water raised by this pump is conducted to a reservoir
from which the boiler is fed, by means which will be hereafter
explained.</p>

<p>We shall now explain the manner in which the machine
is made to open and close the valves at the proper times. By
referring to the explanation already given, it will be perceived
that at the moment the piston reaches the top of the
cylinder, the upper steam valve <strong>G</strong> must be open, to admit the
steam to press it down; while the exhausting valve <strong>I</strong> must be
opened, to allow the steam to pass to the condenser; and the
condensing valve <strong>E</strong> must be opened, to let in the water
necessary for the condensation of the steam; and at the same
time the lower steam valve <strong>H</strong> must be closed, to prevent the
passage of the steam which has been admitted through <strong>G</strong>.
The valves <strong>G</strong>, <strong>I</strong>, and <strong>E</strong> must be kept open, and the valve <strong>H</strong>
kept closed, until the piston arrives at the bottom of the
cylinder, when it will be necessary to close all the three
valves, <strong>G</strong>, <strong>I</strong>, and <strong>E</strong>, and to open the valve <strong>H</strong>, and the same
effects must be produced each time the piston arrives at the
top and bottom of the cylinder. All this is accomplished by
a system of levers, which are exhibited in <a href="#Fig021"><i>fig.</i> 21.</a> The
pivots on which these levers play are represented on the
framing of the engine, and the arms of the levers <strong>Gâ€²</strong>, <strong>Hâ€²</strong>, and
<strong>Iâ€²</strong>, communicating with the corresponding valves <strong>G</strong>, <strong>H</strong>, and <strong>I</strong>,
are represented opposite a bar attached to the rod of the air-pump,
called the <em>plug frame</em>. This bar carries certain pegs
and detents, which act upon the arms of the several levers in
such a manner that, on the arrival of the beam at the extremities
of its play upwards and downwards, the levers are
so struck that the valves are opened and closed at the proper
<a class="refpn" id="Pg143">[Pg143]</a>
times. It is needless to explain all the details of this arrangement.
Let it be sufficient, as an example of all, to
explain the method of working the upper steam valve <strong>G</strong>.
When the piston reaches the top of the cylinder, a pin strikes
the arm of the lever <strong>Gâ€²</strong>, and throws it upwards: this, by
means of the system of levers, pulls the arm of the valve <strong>G</strong>
downwards, by which the upper steam valve is raised out of
its seat, and a passage is opened from the steam pipe to the
cylinder. The valve is maintained in this state until the
piston reaches the bottom of the cylinder, when the arm <strong>Gâ€²</strong>
is pressed downwards, by which the arm <strong>G</strong> is pressed upwards,
and the valve restored to its seat. By similar methods
the levers governing the other three valves, <strong>H</strong>, <strong>I</strong>, and <strong>E</strong>, are
worked.</p>

<div class="figleft" style="width: 91px;">
<a id="Fig023"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_165a.png" width="91" height="154" alt="" />
<div class="caption figure">Fig. 23.</div>
</div>

<div class="figleft" style="width: 240px;">
<a id="Fig024"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_165b.png" width="240" height="199" alt="" />
<div class="caption figure">Fig. 24.</div>
</div>

<p>The valves used in these engines were of the kind called
<em>spindle valves</em>. They consisted of a flat circular
plate of bell metal, <strong>A B</strong>, <a href="#Fig023"><i>fig.</i> 23.</a>, with a
round spindle passing perpendicularly through
its centre, and projecting above and below it.
This valve, having a conical form, was fitted
very exactly, by grinding into a corresponding
circular conical seat, <strong>A B C D</strong>, <a href="#Fig024"><i>fig.</i> 24.</a>, which
forms the passage which it is the office of the
valve to open and close. When the valve falls into its seat,
it fits the aperture like a plug, so as entirely to stop it. The
spindle plays in sockets or
holes, one above and the
other below the aperture
which the valve stops; these
holes keep the valve in its
proper position, so as to
cause it to drop exactly into
its place.</p>

<p>In the experimental engine
made by Mr. Watt at Kinneal,
he used cocks, and sometimes sliding covers, like the regulator
described in the old engines; but these he found very
soon to become leaky. He was, therefore, obliged to change
them for the spindle valves just described, which, being truly
<a class="refpn" id="Pg144">[Pg144]</a>
ground, and accurately fitted in the first instance, were not so
liable to go out of order. These valves are also called <em>puppet
clacks</em>, or <em>button valves</em>.</p>

<p>In the earlier engines constructed by Watt, the condensation
was produced by the contact of cold surfaces,
without injection. The reason of rejecting the method of
condensing by injection was, doubtless, to avoid the injurious
effects of the air, which would always enter the condenser, in
combination with the water of condensation, and vitiate the
vacuum. It was soon found, however, that a condenser
acting by cold surfaces without injection, being necessarily
composed of narrow pipes or passages, was liable to incrustation
from bad water, by which the conducting power of the
material of the condenser was diminished; so that, while its
outer surface was kept cold by the water of the cold cistern,
the inner surface might, nevertheless, be so warm that a very
imperfect condensation would be produced.</p>

<div class="figcenter" style="width: 496px;">
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_166.png" width="496" height="301" alt="" />
<div class="caption">SOHO, BIRMINGHAM.</div>
</div>

<div class="footnotes"><h3>FOOTNOTES:</h3>
<div class="footnote">
<p><a name="Footnote_19_19" id="Footnote_19_19"></a><a
href="#FNanchor_19_19"><span class="label">[19]</span></a>
Eloge, p. 308.</p></div></div>

<div class="figcenter" style="width: 500px;">
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_167.png" width="500" height="325" alt="" />
<div class="caption">BIRMINGHAM.</div>
</div>

<h2><a name="CHAP_VI" id="CHAP_VI">CHAP. VI.</a></h2>

<p class="right"><a class="refpn" id="Pg145">[Pg145]</a><br />
<a href="#CONTENTS"><small>TOC</small></a>&#160;&#160;<a
href="#INDEX"><small>INX</small></a></p>

<div class="chapheader">
CORRESPONDENCE OF WATT WITH SMEATON.â€”FAILURE OF CONDENSATION
BY SURFACE.â€”IMPROVEMENTS IN CONSTRUCTION OF PISTON.â€”METHOD
OF PACKING.â€”IMPROVEMENTS IN BORING THE CYLINDERS.â€”DISADVANTAGES
OF THE NEW COMPARED WITH THE OLD
ENGINES.â€”GREATLY INCREASED ECONOMY OF FUEL.â€”EXPEDIENTS
TO FORCE THE NEW ENGINES INTO USE.â€”CORRESPONDENCE WITH
SMEATON.â€”EFFICIENCY OF FUEL IN THE NEW ENGINES.â€”DISCOVERY
OF THE EXPANSIVE ACTION OF STEAM.â€”WATT STATES IT
IN A LETTER TO DR. SMALL.â€”ITS PRINCIPLE EXPLAINED.â€”MECHANICAL
EFFECT RESULTING FROM IT.â€”COMPUTED EFFECT OF
CUTTING OFF STEAM AT DIFFERENT PORTIONS OF THE STROKE.â€”PRODUCES
A VARIABLE POWER.â€”EXPEDIENTS FOR EQUALISING THE
POWER.â€”LIMITATION OF THE EXPANSIVE PRINCIPLE IN WATT'S
ENGINES.â€”ITS MORE EXTENSIVE APPLICATION IN THE CORNISH ENGINES.</div>


<div class="ph3fst"><h3>(77.)</h3> In a letter addressed by Watt to Smeaton, dated April,
1766, Watt refers to some of these practical difficulties which
he had to encounter. "I have been," says he, "tormented
with exceedingly bad health, resulting from the operation of
an anxious mind, the natural consequence of staking everything
<a class="refpn" id="Pg146">[Pg146]</a>
upon the cast of a die; for in that light I look upon
every project which has not received the sanction of repeated
success.</div>

<p>"I have made considerable alterations in our engine lately,
particularly in the condenser. That which I used at first
was liable to be impaired, from incrustations from bad water;
therefore we have substituted one which works by an injection.
In pursuing this idea I have tried several kinds,
and have at last come to one, which I am not inclined to
alter. It consists of a jack-head pump, shut at bottom, with
a common clack bucket, and a valve in the cover of the
pump, to discharge the air and water. The eduction steam
pipe, which comes from the cylinder, communicates with this
pump both above and below the bucket, and has valves to
prevent anything from going back from the pump to the
eduction pipe. The bucket descends by its own weight, and
is raised by the engine when the great piston descends, being
hung to the outer end of the great lever: the injection is
made both into the upper part of this pump and into the
eduction pipe, and operates beyond my ideas in point of
quickness and perfection."</p>

<p>Besides the difficulty arising from incrustation, Watt
found the tubulated condensers, and indeed all other expedients
for condensing by cold surfaces, subject to a fatal
objection. They did not condense instantaneously, and
although they were capable of ultimately effecting the condensation,
yet that process was not completed until a
great part of the stroke of the piston was made. Thus
during more or less of the stroke the uncondensed steam
resisted the piston, and robbed the moving power of a part
of its effect. This objection has ever attended condensation
by surface.</p>

<div class="figright" style="width: 172px;">
<a id="Fig025"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_169a.png" width="172" height="291" alt="" />
<div class="caption figure">Fig. 25.</div>
</div>

<div class="figright" style="width: 207px;">
<a id="Fig026"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_169b.png" width="207" height="179" alt="" />
<div class="caption figure">Fig. 26.</div>
</div>

<div class="ph3"><h3>(78.)</h3> Another source of difficulty arose from the necessity of
constructing the piston and cylinder with greater precision
than had been usual in the old engines. To fit the cover to
the cylinder so as to be steam-tight; to construct the piston
rod so as to move through it without allowing the escape of
steam, and yet at the same time without injurious friction;
to connect the piston rod with the piston, so as to drive the
<a class="refpn" id="Pg147">[Pg147]</a>
latter through the cylinder with a perfectly straight and
parallel motion; to make such connection perfectly centrical
and firm, and yet to allow the piston in its ascent to come
nearly into contact with the cover of the cylinderâ€”were all
difficulties peculiar to the new engine. In the atmospheric
engine the shank of the piston rod was rough and square,
and the rod was secured to the piston by two or four
branches or stays, as represented in
<a href="#Fig025"><i>fig.</i> 25.</a> It is evident that such a
construction would be inadmissible
in an engine in which the piston in
its ascent must be brought nearly
into contact with the close cover of
the cylinder. Besides this the piston
rod of an atmospheric engine
might throughout its whole length
have any form which was most convenient,
and required no other property
than the strength necessary to
work the beam. In the new engine,
on the contrary, it was necessary that
it should be accurately turned and
finely polished, so as to pass through the hole in the top
of the cylinder, and be maintained in it steam-tight. This was
effected by a contrivance called a <em>stuffing-box</em> <strong>B</strong>, represented in
<a href="#Fig026"><i>fig.</i> 26.</a> A hole is made in the
cover of the cylinder very little
greater in magnitude than the
diameter of the piston rod.
Above this hole is a cup in
which, around the piston, is
placed a stuffing of hemp or tow,
which is saturated with oil or
melted tallow. This collar of
hemp is pressed down by another piece, also perforated with
a hole through which the piston rod plays, and which is
screwed down on the said collar of hemp.</div>


<div class="ph3"><h3>(<a id="h3-79"></a>79.)</h3> Although the imperfect manner in which the interior of
the cylinders was then formed impaired the efficiency of the
<a class="refpn" id="Pg148">[Pg148]</a>
new engines, yet such imperfections were not so injurious as
in the old atmospheric engines. Any imperfection of form of
the inner surface of the cylinder would necessarily cause more
or less steam or air to escape between the piston and cylinder.
In the improved engine this steam passing into the vacuum
below the piston would rush into the condenser, and be there
condensed, so that its effect in resisting the motion of the
piston would necessarily be trifling. But on the other hand,
any escape of air between the piston and cylinder of an
atmospheric engine would introduce an elastic fluid under
the piston, which would injuriously affect the action of the
machine.</div>

<div class="figleft" style="width: 265px;">
<a id="Fig027"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_170.png" width="265" height="136" alt="" />
<div class="caption figure">Fig. 27.</div>
</div>

<p>To make the pistons move sufficiently steam-tight in these
early imperfect cylinders, Watt contrived a packing formed
of a collar of hemp, or
tow, as represented in
<a href="#Fig027"><i>fig.</i> 27.</a> The bottom of
the piston was formed
of a circular plate of a
diameter nearly, but not
altogether equal to the
interior diameter of the cylinder. The part of the piston above
this was considerably less in diameter, so that the piston was
surrounded by a circular groove or channel two inches wide,
into which hemp or soft rope, called <em>gasket</em>, was run, so as
to form the packing. The top of the piston was placed over
this, having a rim or projecting part, which entered the circular
groove and pressed upon the packing, the cover being
pressed downwards by screws passing through the piston.
The lower part of the groove round the piston was rounded
with a curve, so that the pressure on the packing might force
the latter against the inner surface of the cylinder. This
packing was kept supplied with melted tallow, as already
described, from the funnel, screwed into the top of the
cylinder. The metallic edges of the piston were by this
means prevented from coming into contact with the surface
of the cylinder, which was only pressed upon by the stuffing
or packing projecting beyond these.</p>


<div class="ph3"><h3>(80.)</h3> Improved methods of boring soon, however, relieved
<a class="refpn" id="Pg149">[Pg149]</a>
the engine from a part of these imperfections, and Watt writes
to Mr. Smeaton in the letter above quoted as follows:â€”</div>

<p>"Mr. Wilkinson has improved the art of boring cylinders;
so that I promise, upon a 72 inch cylinder, being not further
distant from absolute truth than the thickness of a thin sixpence
in the worst part. I am labouring to improve the
regulators; my scheme is to make them acute conical valves,
shut by a weight, and opened by the force of the steam.
They bid fair for success, and will be tried in a few days."</p>

<p>The person here alluded to was Mr. John Wilkinson, of
Bersham near Chester, who, about the year 1775, contrived
a new machine for accurately boring the insides of cylinders.
The cylinder being first obtained from the foundery with a
surface as accurate as the process of casting would admit,
had its inner surface reduced to still greater accuracy by this
machine, which consists of a straight central bar extended
along the axis of the cylinder, which was made to revolve
slowly round it. During the operation of boring,
the borer or cutter was fitted to slide along this bar, which
being perfectly straight, served as a sort of ruler to guide
the borer or cutter in its progress through the cylinder.
In this manner the interior surface of the cylinder was rendered
not only true and straight in its longitudinal direction,
but also perfectly circular in its cross section.</p>

<p>The grease found to be most eligible for lubrication was
the tallow of beef or mutton; but in the earlier cylinders
this was soon consumed by reason of the imperfection of the
boring, and the piston being left dry ceased to be steam-tight.
To prevent this, Watt sought for some substance,
which while it would thicken the tallow, and detain it around
the piston, would not be subject to decomposition by heat.
Black lead dust was used for this purpose, but was soon
found to wear the cylinder. In the mean while, however,
the improved method of boring supplied cylinders which rendered
this expedient unnecessary.</p>

<p>When the inner surface of the cylinder is perfectly true
and smooth, the packing of the piston is soon rendered solid
and hard, being moulded to the cylinder by working, so as
to fit it perfectly. When by wear it became loose, it was
<a class="refpn" id="Pg150">[Pg150]</a>
only necessary to tighten the screws by which the top and
bottom of the piston were held together. The packing being
compressed by those means, was forced outwards towards the
surface of the cylinder, so as to be rendered steam-tight.</p>


<div class="ph3">
<h3>(81.)</h3> It was not until about the year 1778, nine years after
the date of the patent, and thirteen after the invention of
separate condensation, that any impression was produced on
the mining interests by the advantages which were presented
to them by these vast improvements. This long
interval, however, had not elapsed without considerable
advantage; for although all the great leading principles of
the contrivance were invented so early as the year 1765,
yet the details of construction had been in a state of progressive
and continued improvement from the time Watt
joined Dr. Roebuck, in 1769, to the period now adverted to.</div>

<p>The advantages which the engine offered in the form in
which it has been just described, were numerous and important,
as compared even with the most improved form of
the atmospheric engine; and it should be remembered, that
that machine had also gone on progressively improving, and
was probably indebted for some of its ameliorations to hints
derived from the labours of Watt, and to the adoption of
such of his expedients as were applicable to this imperfect
machine, and could be adopted without an infraction of his
patent.</p>

<p>In the most improved forms to which the atmospheric
engine had then attained, the quantity of steam wasted at
each stroke of the piston was equal to the contents of the
cylinder. Such engines, therefore, consumed twice the fuel
which would be requisite, if all sources of waste could have
been removed. In Watt's engines, the steam consumed at each
stroke of the piston amounted only to
<span class="fraction">1<sup>1</sup>â„<sub>4</sub></span>
times the contents
of the cylinder. The waste steam, therefore, per stroke, was
only a quarter of what was usefully employed. The absolute
waste, therefore, of the best atmospheric engines was four
times that of the improved engine, and consequently the
saving of fuel in the improved engines amounted to about
three eighths of all the fuel consumed in atmospheric engines
of the same power.
<a class="refpn" id="Pg151">[Pg151]</a></p>


<div class="ph3">
<h3>(82.)</h3> But independently of this saving of steam, which would
otherwise be wasted, the power of Watt's engine, as compared
with the atmospheric engine, was so much augmented
that the former would work against a resistance of ten pounds
on the square inch under the same circumstances in which
the latter would not move against more than seven pounds.
The cause of this augmentation of power is easily explained.
In the atmospheric engine the temperature of the condensed
steam could not be reduced below 152Â° without incurring a
greater loss than would be compensated by the advantage to
be obtained from any higher degree of condensation. Now
steam raised from water at 152Â° has a pressure of nearly four
pounds per square inch. This pressure, therefore, acted
below the piston resisting the atmospheric pressure above.
In Watt's engine, however, the condenser was kept at a
temperature of about 100Â°, at which temperature steam has
a pressure of less than one pound per square inch. A resisting
force upon the piston of three pounds per square inch
was therefore saved in Watt's engine as compared with the
atmospheric engine.</div>


<div class="ph3"><h3>(83.)</h3> Besides these direct sources of economy, there were
other advantages incidental to Watt's engine. An atmospheric
engine possessed very limited power of adaptation to a varying
load. The moving power being the atmospheric pressure,
was not under control, and, on the other hand, was subject
to variations from day to day and from hour to hour, according
to the changes of the barometer. In the first construction
of such an engine, therefore, its power being necessarily
adapted to the greatest load which it would have to move,
whenever the load upon its pumps was diminished, the motion
of the piston in descending would be rapidly accelerated in
consequence of the moving power exceeding the resistance.
By this the machinery would be subject to sudden shocks,
which were productive of rapid wear, and exposed the machinery
to the danger of fracture. To remedy this inconvenience,
the following expedient was provided in the atmospheric
engine: whenever the load on the engine was materially
diminished, the quantity of water admitted through the
injection valve to condense the steam was proportionally
<a class="refpn" id="Pg152">[Pg152]</a>
diminished. An imperfect condensation being therefore produced,
vapour remained in the cylinder under the piston, the pressure
of which resisted the atmosphere, and mitigated the force
of the machine. Besides this, a cock was provided in the bottom
of the cylinder, called an <em>air cock</em>, by which atmospheric
air could be admitted to resist the piston whenever the
motion was too rapid.</div>

<p>These expedients, however, were all attended with a waste
of fuel in relation to the work done by the engine; for it is
evident that the consumption of steam was necessarily the
same, whether the engine was working against its full load or
against a reduced resistance.</p>

<p>On the other hand, in the improved engine of Watt, when
the load, to work against which the engine exerted its full
power, was diminished, a cock or valve was provided in the
steam pipe leading from the boiler, which was called a <em>throttle
valve</em>, by adjusting which the passage in that pipe could be
more or less contracted. By regulating this cock the supply
of steam from the boiler was checked, and the quantity transmitted
to the cylinder diminished, so that its effect upon the
piston might be rendered equal to the amount of the diminished
resistance. By this means the quantity of steam transmitted
to the cylinder was rendered exactly proportional to
the work which the engine had to perform. If, under such
circumstances, the boiler was worked to its full power, so as
to produce steam as fast as it would when the engine was
working at full power, then no saving of fuel would be effected,
since the surplus steam produced in the boiler would
necessarily escape at the safety valve. But in such case the
fireman was directed to limit the fuel of the furnace until the
discharge at the safety valve ceased.</p>

<p>By these expedients, the actual consumption of fuel in one
of these improved engines was always in the exact proportion
of the work which it performed, whether it worked at full
power or at any degree under its regular power.</p>


<div class="ph3"><h3>(84.)</h3> Notwithstanding these and other advantages attending
the new engines, Boulton and Watt experienced difficulties
all but insurmountable in getting them into use. No manufactory
existed in the country possessing machinery capable of
<a class="refpn" id="Pg153">[Pg153]</a>
executing with the necessary precision the valves and other
parts which required exact execution, and the patentees were
compelled to construct machinery at Soho for this purpose;
and even after they succeeded in getting the cylinders properly
bored, the piston rods exactly turned and polished, the
spindle valves constructed so as to be steam-tight, and every
other arrangement completed which was necessary for the
efficiency of the machine, the novelty of the engine, and the
difficulty which was supposed to attend its maintenance in
good working order, formed strong objections to its adoption.</div>

<p>To remove such objections, great sacrifices were necessary
on the part of Boulton and Watt; and they accordingly resolved
to undertake the construction of the new engines without
any profit, giving them to the parties requiring their use
at first cost, on the condition of being remunerated by a small
share of what they would save in fuel.</p>

<p>"We have no objection," writes Mr. Boulton, "to contract
with the Carron Company to direct the making of an engine
to return the water for their mills.
<span class="no-wrap">&#160;&#160;&#160;*&#160;&#160;&#160;*&#160;&#160;&#160;*&#160;&#160;&#160;*&#160;&#160;&#160;</span>
We do not aim at profits in engine building, but shall take our
profits out of the saving of fuel; so that if we save nothing,
we shall take nothing. Our terms are as follows: we will
make all the necessary plans, sections, and elevations for the
building, and for the engine with its appurtenances, specifying
all cast and forged iron work, and every other particular
relative to the engine. We will give all necessary directions
to your workmen, which they must implicitly obey. We will
execute, for a stipulated price, the valves, and all other parts
which mayÂ·require exact execution, at Soho; we will see that
all the parts are put together, and set to work, properly; we
will keep our own work in repair for one year, and we have
no other objection to seven years than the inconvenience of
the distance. We will guarantee that the engine so constructed
shall raise at least 20,000 cubic feet of water twenty-four
feet high with each hundred weight of coals burnt.</p>

<p>"When all this is done, a fair and candid comparison
shall be made between it, and your own engine, or any other
engine in Scotland, from which comparison the amount of
savings in fuel shall be estimated, and that amount being
<a class="refpn" id="Pg154">[Pg154]</a>
divided into three parts, we shall be entitled to one of those
parts, in recompense for our patent licence, our drawings,
&#38;c. &#38;c. Our own share of savings shall be estimated in
money, according to the value of your coals delivered under
the boiler, and you shall annually pay us that sum, during
twenty-five years from the day you begin to work; provided
you continue the use of the engine so long. And in case you
sell the engine, or remove it to any other place, you must
previously give us notice, for we shall then be entitled to our
third of the savings of fuel, according to the value of coals
at such new place. This is a necessary condition, otherwise
the engine which we make for you at an expense of two
thousand pounds may be sold in Cornwall for ten thousand
pounds.</p>

<p>"Such parts of the engine as we execute at Soho we will
be paid for at a fair price; I conclude, from all the observations
I have had an opportunity of making, that our engines
are four times better than the common engines. In boilers,
which are a very expensive article, the savings will be in proportion
to the savings of coal. If you compare our engine
with the common engine (not in size, but in power), you will
find the original expense of erecting one to be nearly the
same.</p>

<p>"Mr. Wilkinson has bored us several cylinders, almost
without error; that of fifty inches diameter, which we put up
at Tipton, does not err the thickness of an old shilling in any
part; so that you must either improve your method of boring,
or we must furnish the cylinder to you."</p>

<p>The reluctance of mining companies to relinquish the old
engines, even on these terms, led them to propose to Mr.
Watt to grant them a licence for the use of his condenser,
to be applied to the atmospheric engine, without the introduction
of other improvements. Such a proposition was
made to him by Mr. Smeaton, in the year 1778, to which he
returned the following answer:â€”</p>

<p>"I have several times considered the propriety of the
application of my condensers to common engines, and have
made experiments with that view upon our engine at Soho,
but have never found such results as would induce me to try
<a class="refpn" id="Pg155">[Pg155]</a>
it any where else; and, in consequence, we refused to make
that application to Wheal Virgin engines in Cornwall, and to
some others; our reasons were, that though it might have
enabled them to have gone deeper with their present engines,
yet, the savings of fuel would not have been great, in comparison
to the complete machine. By adding condensers to
engines that were not in good order, our engine would have
been introduced into that country (which we look upon as
our richest mine) in an unfavourable point of view, and
without such profits as would have been satisfactory either
to us or to the adventurers; and if we had granted the
use of condensers to one, we must have done so to all, and
thereby have curtailed our profits, and perhaps injured our
reputation. Besides, where a new engine is to be erected,
and to be equally well executed in point of workmanship and
materials, an engine of the same power cannot be constructed
materially cheaper on the old plan than on ours; for our
boiler and cylinder are much smaller, and the building, the
lever, the chains, together with all the pump and pit work,
are only the same.
<span class="no-wrap">&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;
*&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;
*&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;
*&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;*
&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;</span>
</p>

<p>"We charge our profits in proportion to the saving
made in fuel by our engine, when compared with a common
one which burns the same kind of coals; we ask
one third of these savings to be paid us annually, or half
yearly; the payment being redeemable in the option of our
employer, at ten years' purchase; and when the coals are low
priced, we should also make some charge as engineers. In
all these comparisons our own interest has made us except
your (Mr. Smeaton) improved engines, unless we were allowed
a greater proportion of the savings."</p>

<p>Their exertions to improve the manufacture of engines at
Soho is shown by the following letter from Mr. Boulton, in
the same correspondence to Mr. Smeaton:â€”</p>

<p>"We are systematising the business of engine making, as
we have done before in the button manufactory; we are training
up workmen, and making tools and machines to form the
different parts of Mr. Watt's engines with more accuracy, and
at a cheaper rate than can possibly be done by the ordinary
methods of working. Our workshop and apparatus will be of
<a class="refpn" id="Pg156">[Pg156]</a>
sufficient extent to execute all the engines which are likely to
be soon wanted in this country; and it will not be worth the
expense for any other engineers to erect similar works, for that
would be like building a mill to grind a bushel of corn.</p>

<p>"I can assure you from experience, that our small engine
at Soho is capable of raising 500,000 cubic feet of water
1 foot high with every 112 lbs. of coals, and we are in hopes
of doing much more. Mr. Watt's engine has a very great
advantage in mines, which are continually working deeper:
suppose, for instance, that a mine is 50 fathoms deep, you
may have an engine which will be equal to draining the
water when the mine is worked, to 100 fathoms deep, and
yet you can constantly adapt the engine to its load, whether
it be 50 or 100 fathoms, or any intermediate depth; and the
consumption of coals will be less in proportion when working
at the lesser than at the greater depths; supposing it works,
as our engines generally do, at 11 lbs. per square inch, when
the mine becomes 100 fathoms deep."</p>


<div class="ph3">
<h3>(85.)</h3> The great improvement which has been introduced
within the last half century, in the details of Watt's steam
engine, will be rendered manifest by comparing the effects of
a given weight of fuel here supplied by Mr. Boulton with the
effects which the same weight of fuel is now known to produce
in the best pumping engines worked in Cornwall. One of these
engines, in good working order, has been known to raise
125,000,000 lbs. 1 foot high, by the combustion of a bushel
of coals. But the average performance of even the best
engines is below this amount. If we take it at 90,000,000,
this will be equivalent to the weight of about
<span class="fraction">1<sup>1</sup>â„<sub>2</sub></span> million
cubic feet of water, a bushel of coals being
<span class="fraction"><sup>3</sup>â„<sub>4</sub></span> cwt. It will
therefore follow that, with the present engines, one hundred
weight of coals is capable of raising about two million cubic
feet of water one foot high, being a duty four times that
assigned to the early engines by Mr. Boulton.</div>


<div class="ph3"><h3>(86.)</h3> At the time that Watt, in conjunction with Dr. Roebuck,
obtained the patent for his improved engine, the idea
occurred to him, that the steam which had impelled the piston
in its descent rushed from the cylinder with a mechanical
force much more than sufficient to overcome any resistance
<a class="refpn" id="Pg157">[Pg157]</a>
which it had to encounter in its passage to the condenser;
and that such force might be rendered available as a moving
power, in addition to that already obtained from the steam
during the stroke of the piston. This notion involved the
whole principle of the expansive action of steam, which
subsequently proved to be of such importance in the performance
of steam engines. Watt was, however, so much
engrossed at that time, and subsequently, by the difficulties
he had to encounter in the construction of his engines,
that he did not attempt to bring this principle into operation.
It was not until after he had organised that part of
the establishment at Soho which was appropriated to the
manufacture of steam engines, that he proceeded to apply the
expansive principle. Since the date of the patent which he
took out for this (1782), was subsequent to the application of
the same principle by another engineer, named Hornblower, it
is right to state, that the claim of Mr. Watt to this important
step in the improvement of the steam engine, is established
by a letter addressed by him to Dr. Small, of Birmingham,
dated Glasgow, May, 1769:â€”</div>

<p>"I mentioned to you a method of still doubling the effect
of the steam, and that tolerably easy, by using the power of
steam rushing into a vacuum, at present lost. This would do
little more than double the effect, but it would too much
enlarge the vessels to use it all: it is peculiarly applicable to
wheel engines, and may supply the want of a condenser,
where the force of steam only is used; for open one of the
steam valves, and admit steam until one fourth of the distance
between it and the next valve is filled with steam, then shut
the valve, and the steam will continue to expand, and to
press round the wheel, with a diminishing power, ending in
one fourth of its first exertion. The sum of the series you
will find greater than one half, though only one fourth of
steam was used. The power will indeed be unequal, but this
can be remedied by a fly, or by several other means."</p>

<p>In 1776 the engine, which had been then recently erected
at Soho, was adapted to act upon the principle of expansion.
When the piston had been pressed down in the cylinder for
a certain portion of the stroke, the further supply of steam
<a class="refpn" id="Pg158">[Pg158]</a>
from the boiler was cut off, by closing the upper steam valve,
and the remainder of the stroke was accomplished by the
expansive power of the steam which had already been introduced
into the cylinder.</p>


<div class="ph3">
<h3>(87.)</h3> To make this method of applying the force of steam
intelligible, some previous explanation of mechanical principles
will be necessary.</div>

<p>If a body which offers a certain resistance be urged by a
certain moving force, the motion which it will receive will
depend on the relation between the energy of the moving
force and the amount of the resistance opposed to it. If the
moving force be precisely equal to the resistance, the motion
which the body will receive will be perfectly uniform.</p>

<p>If the energy of the moving force be greater than the
resistance, then its surplus or excess above the amount of
resistance will be expended in imparting momentum to the
mass of the body moved, and the latter will, consequently,
continually acquire augmented speed. The motion of the
body will, therefore, be in this case accelerated.</p>

<p>If the energy of the moving force be less in amount than
the resistance, then all that portion of the resistance which
exceeds the amount of the moving force will be expended in
depriving the mass of the body of momentum, and the body
will therefore be moved with continually diminished speed
until it be brought to rest.</p>


<div class="ph3">
<h3>(88.)</h3> Whenever, therefore, a uniform motion is produced in
a body, it may be taken as an indication of the equality of the
moving force to the resistance; and, on the other hand,
according as the speed of the body is augmented or diminished,
it may be inferred that the energy of the moving
force has been greater or less than the resistance.</div>

<p>It is an error to suppose that rest is the only condition possible
for a body to assume when under the operation of two
or more mechanical forces which are in equilibrium. By the
laws of motion the state of a body which is not under the
operation of any external force must be either in a state of
rest or of uniform motion. Whichever be its state, it will
suffer no change if the body be brought under the operation
of two or more forces which are in equilibrium; for to suppose
<a class="refpn" id="Pg159">[Pg159]</a>
such forces to produce any change in the state of the
body, whether from rest to motion, or <i>vice versÃ¢</i>, or in the
velocity of the motion which the body may have previously
had, would be equivalent to a supposition that the forces
applied to the body being in equilibrium were capable of
producing a dynamical effect, which would be a contradiction
in terms. This, though not always clearly understood by
mere practical men, or by persons superficially informed, is,
in fact, among the fundamental principles of mechanical
science.</p>


<div class="ph3"><h3>(89.)</h3> When the piston is at the top of the cylinder, and about
to commence its motion downwards, the steam acting upon it
will have not only to overcome the resistance arising from
the friction of the various parts of the engine, but will also
have to put in motion the whole mass of matter of the piston
pump rods, pump pistons, and the column of water in the
pump barrels. Besides imparting to this mass the momentum
corresponding to the velocity with which it will be moved, it
will also have to encounter the resistance due to the preponderance
of the weight of the water and pump rods over that
of the steam piston. The pressure of steam, therefore, upon
the piston at the commencement of the stroke must, in accordance
with the mechanical principles just explained, have
a greater force than is equal to all the resistances which it
would have to overcome, supposing the mass to be moving at
a uniform velocity. The moving force, therefore, being
greater than the resistance, the mass, when put in motion,
will necessarily move with a gradually augmented speed, and
the piston of the engine which has been described in the last
chapter would necessarily move from the top to the bottom
of the cylinder with an accelerated motion, having at the
moment of its arrival at the bottom a greater velocity than at
any other part of the stroke. As the piston and all the
matter which it has put in motion must at this point come to
rest, the momentum of the moving mass must necessarily
expend itself on some part of the machinery, and would be
so much mechanical force lost. It is evident, therefore,
independently of any consideration of the expansive principle,
to which we shall presently refer, that the action of the
<a class="refpn" id="Pg160">[Pg160]</a>
moving power in the descent of the piston ought to be suspended
before the arrival of the piston at the bottom of
the cylinder, in order to allow the momentum of the mass
which is in motion to expend itself, and to allow the piston
to come gradually to rest at the termination of the stroke.</div>

<p>Thus, if we were to suppose that after the piston had descended
through three fourths of the whole length of the cylinder,
and had acquired a certain velocity, the steam above it
were suddenly condensed, so as to leave a vacuum both above
and below it, the piston, being then subject to no impelling
force, would still move downwards, in virtue of the momentum
it had acquired, until the resistance would deprive it of
that momentum, and bring it to rest; and if the remaining
fourth part of the cylinder were necessary for the accomplishment
of this, then it is evident that that part of the stroke
would be accomplished without further expenditure of the
moving power.</p>

<p>In fact, this part of the stroke would be made by the
expenditure of that excess of moving power, which, at the
commencement of the stroke, had been employed in putting
the machinery and its load in motion, and in subsequently
accelerating that motion.</p>

<p>Although under such circumstances the resistance, during
the operation of the moving power, shall not have been at
any time equal to the moving power, since while the motion
was accelerated it was less, and while retarded greater than
that power, yet as the whole moving power has been expended
upon the resistance, the mechanical effect which the moving
power has produced under such circumstances will be equal
to the actual amount of that power. If in an engine of this
kind the steam was not cut off till the conclusion of the
stroke, a part of the moving power would be lost upon those
fixed points in the machinery which would sustain the shock
produced by the instantaneous cessation of motion at the end
of the stroke.</p>

<p>Independently, therefore, of any consideration of the expansive
principle, it appears that, in an engine of this kind,
the steam ought to be cut off before the completion of the
stroke.
<a class="refpn" id="Pg161">[Pg161]</a></p>

<div class="figright" style="width: 132px;">
<a id="Fig028"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_183.png" width="132" height="271" alt="" />
<div class="caption figure">Fig. 28.</div>
</div>

<div class="ph3"><h3>(90.)</h3> To render the expansive action of steam intelligible, let
<strong>A B</strong> (<a href="#Fig028"><i>fig.</i> 28.</a>) represent a cylinder whose area we will suppose,
for the sake of illustration, to be a square
foot, and whose length, <strong>A B</strong>, shall also be
a foot. If steam of a pressure equal to
the atmosphere be supplied to this cylinder,
it will exert a pressure of about
one ton on the piston; and if such steam
be uniformly supplied from the boiler, the
piston will be moved from <strong>A</strong> to <strong>B</strong> with the
force of one ton, and that motion will be
uniform if the piston be opposed throughout
the same space by a resistance equal
to a ton. When the piston has arrived at
<strong>B</strong>, let us suppose that the further supply of
steam from the boiler is stopped by closing
the upper steam valve, and let us also suppose the cylinder to be
continued downwards so that <strong>B C</strong> shall be equal to <strong>A B</strong>, and suppose
that <strong>B C</strong> has been previously in communication with the
condenser, and is therefore a vacuum. The piston at <strong>B</strong> will then
be urged with a force of one ton downwards, and as it descends
the steam above it will be diffused through an increased volume,
and will consequently acquire a diminished pressure. We shall,
for the present, assume that this diminution of pressure
follows the law of elastic fluids in general; that it will be decreased
in the same proportion as the volume of the steam is
augmented. While the piston, therefore, moves from <strong>B</strong>
downwards it will be urged by a continually decreasing force.
Let us suppose, that by some expedient, it is also subject to a
continually decreasing resistance, and that this resistance decreases
in the same proportion as the force which urges the
piston. In that case the motion of the piston would continue
uniform. When the piston would arrive at <strong>Pâ€²</strong>, the middle of
the second cylinder, then the space occupied by the steam
being increased in the proportion of 2 to 3, the pressure on
the piston would be diminished in the proportion of 3 to 2,
and the pressure at B being one ton, it would be two-thirds of
a ton at <strong>Pâ€²</strong>. In like manner when the piston would arrive at
<strong>C</strong>, the space occupied by the steam being double that which
<a class="refpn" id="Pg162">[Pg162]</a>
it occupied when the piston was at <strong>B</strong>, the pressure of the
steam would be half its pressure at <strong>B</strong>, and therefore at the
termination of the stroke, the pressure on the piston would be
half a ton.</div>

<p>If the space from <strong>B</strong> to <strong>C</strong>, through which the steam is here
supposed to act expansively, be divided into ten equal parts,
the pressure on the piston at the moment of passing each of
those divisions would be calculated upon the same principle
as in the cases now mentioned. After moving through the
first division, the volume of the steam would be increased in
the proportion of 10 to 11, and therefore its pressure would
be diminished in the proportion of 11 to 10. The pressure,
therefore, driving the piston at the end of the first of these
ten divisions would be
<span class="fraction"><sup>10</sup>â„<sub>11</sub>ths</span> of a ton. In like manner, its
pressure at the second of the divisions would be
<span class="fraction"><sup>10</sup>â„<sub>12</sub>ths</span> of a
ton, and the third
<span class="fraction"><sup>10</sup>â„<sub>13</sub>ths</span> of a ton; and so on, as indicated in
the figure.</p>

<p>Now if the pressure of the steam through each of these
divisions were to continue uniform, and, instead of gradually
diminishing, to suffer a sudden change in passing from one
division to another, then the mechanical effect produced from
<strong>B</strong> to <strong>C</strong>
would be obtained by taking a mean or average of the
several pressures throughout each of the ten divisions. In
the present case it has been supposed that the force on the
piston at <strong>B</strong> was 2240 pounds. To
obtain the pressure in
pounds corresponding to each of the successive divisions, it
will therefore only be necessary to multiply 2240 by 10, and
to divide it successively by 11, 12, 13, &#38;c. The pressures,
therefore, in pounds, at each of the ten divisions, will be as
follows:â€”</p>

<table summary="pressure, in pounds, at each of ten divisions">
<tr>
 <td align="right"> 1st</td>
 <td align="right">2036Â·3</td></tr>
<tr>
 <td align="right"> 2d&#160;</td>
 <td align="right">1866Â·6</td></tr>
<tr>
 <td align="right"> 3d&#160;</td>
 <td align="right">1723Â·1</td></tr>
<tr>
 <td align="right"> 4th</td>
 <td align="right">1600Â·0</td></tr>
<tr>
 <td align="right"> 5th</td>
 <td align="right">1493Â·3</td></tr>
<tr>
 <td align="right"> 6th</td>
 <td align="right">1400Â·0</td></tr>
<tr>
 <td align="right"> 7th</td>
 <td align="right">1317Â·6</td></tr>
<tr>
 <td align="right"> 8th</td>
 <td align="right">1244Â·4</td></tr>
<tr>
 <td align="right"> 9th</td>
 <td align="right">1179Â·0</td></tr>
<tr>
 <td align="right">10th</td>
 <td align="right">1120Â·0</td></tr>
</table>

<p>If the mean of these be taken by adding them together
<a class="refpn" id="Pg163">[Pg163]</a>
and dividing by 10, it will be found to be 1498 pounds. It
appears, therefore, that the pressures through each of the ten
divisions being supposed to be uniform (which however,
strictly, they are not,) the mechanical effect of the steam from
<strong>B</strong> to <strong>C</strong> would be the same as if it acted uniformly throughout
that space upon the piston with a force of about 1500
pounds, being rather less than three-fourths of its whole
effect from <strong>A</strong> to <strong>B</strong>.</p>

<p>But it is evident that this principle will be equally applicable
if the second cylinder had any other proportion to the
first. Thus it might be twice the length of the first; and
in that case, a further mechanical effect would be obtained
from the expansion of the steam.</p>

<p>The more accurate method of calculating the effect of the
expansion from <strong>B</strong> to <strong>C</strong>, would involve more advanced mathematical
principles than could properly be introduced here;
but the result of such a computation would be that the actual
average effect of the steam from <strong>B</strong> to <strong>C</strong> would be equal to a
uniform pressure through that space, amounting to one thousand
five hundred and forty-five pounds, being greater than
the result of the above computation, the difference being due
to the expansive action through each of the ten divisions,
which was omitted in the above computation.</p>


<div class="ph3"><h3>(91.)</h3> It is evident that the expansive principle, as here explained,
involves the condition of a variation in the intensity
of the moving power. Thus, if the steam act with a uniform
energy on the piston so long as its supply from the boiler continues,
the moment that supply is stopped, by closing the steam
valve, the steam contained in the cylinder will fill a gradually
increasing volume by the motion of the piston, and therefore
will act above the piston with a gradually decreasing energy.
If the resistance to the moving power produced by the load,
friction, &#38;c. be not subject to a variation corresponding precisely
to such variation in the moving power, then the consequence
must be that the motion imparted to the load will
cease to be uniform. If the energy of the moving power at
any part of the stroke be greater than the resistance, the
motion produced will be accelerated; if it be less, the motion
will be retarded; and if it be at one time greater, and another
<a class="refpn" id="Pg164">[Pg164]</a>
time less, as will probably happen, then the motion will be
alternately accelerated and retarded. This variation in the
speed of the body moved will not, however, affect the mechanical
effect produced by the power, provided that the
momentum imparted to the moving mass be allowed to
expend itself at the end of the stroke, so that the piston
may be brought to rest as nearly as possible by the resistance
of the load, and not by any shock on any fixed points in the
machine. This is an object which, consequently, should
be aimed at with a view to the economy of power, independently
of other considerations connected with the wear
and tear of the machinery. So long as the engine is only
applied to the operation of pumping water, great regularity of
motion is not essential, and, therefore, the variation of speed
which appears to be an almost inevitable consequence of any
extensive application of the expansive principle, is of little
importance. In the patent which Watt took out for the
application of the expansive principle, he specified several
methods of producing a uniform effect upon a uniform resistance,
notwithstanding the variation of the energy of the power
which necessarily attended the expansion of the steam. This
he proposed to accomplish by various mechanical means, some
of which had been previously applied to the equalisation of a
varying power. One consisted in causing the piston to act on
a lever, which should have an arm of variable length, the
length increasing in the same proportion as the energy of the
moving power diminished. This was an expedient which had
been already applied in mechanics for the purpose of equalising
a varying power. A well-known example of it is presented
in the main-spring and fuzee of a watch. According as the
watch goes down, the main-spring becomes relaxed, and its
force is diminished; but, at the same time, the chain by which
it drives the fuzee acts upon a wheel or circle, having a
diameter increased in the same proportion as the energy of
the spring is diminished.</div>

<p>Another expedient consisted in causing the moving power,
when acting with greatest energy, to lift a weight which
should be allowed to descend again, assisting the piston when
the energy of the moving force was diminished.
<a class="refpn" id="Pg165">[Pg165]</a></p>

<p>Another method consisted in causing the moving force, when
acting with greatest energy, to impart momentum to a mass of
inert matter, which should be made to restore the same force
when the moving power was more enfeebled. We shall not
more than allude here to these contrivances proposed by
Watt, since their application has never been found advantageous
in cases where the expansive principle is used.</p>


<div class="ph3">
<h3>(92.)</h3> The application of the expansive principle in the
engines constructed by Boulton and Watt, was always very
limited, by reason of their confining themselves to the use of
steam having a pressure not much exceeding that of the atmosphere.
If the principle of expansion, as above explained, be
attentively considered, it will be evident that the extent of
its application will mainly depend on the density and pressure
of the steam admitted from the boiler. If the density and
pressure be not considerable when the steam is cut off, the
extent of its subsequent expansion will be proportionally
limited. It was in consequence of this, that this principle
from which considerable economy of power has been derived,
was applied with much less advantage by Mr. Watt than it
has since been by others, who have adopted the use of steam
of much higher pressure. In the engines of Boulton and
Watt, where the expansive principle was applied, the steam
was cut off after the piston had performed from one half to
two thirds of the stroke, according to the circumstances
under which the engine was worked. The decreasing pressure
produced by expansion was, in this case, especially
with the larger class of engines, little more than would be
necessary to allow the momentum of the mass moved to
spend itself, before the arrival of the piston at the end of
the stroke.</div>

<p>Subsequently, however, boilers producing steam of much
higher pressure were applied, and the steam was cut off when
the piston had performed a much smaller part of the whole
stroke. The great theatre of these experiments and improvements
has been the mining districts in Cornwall, where,
instead of working with steam of a pressure not much exceeding
that of the atmosphere, it has been found advantageous
to use steam whose pressure is at least four times as great as
<a class="refpn" id="Pg166">[Pg166]</a>
that of the atmosphere; and instead of limiting its expansion
to the last half or fourth of the stroke, it is cut off after the
piston has performed one fourth part of the stroke or less,
all the remainder of the stroke being accomplished by the
expansive power of the steam, and by momentum.</p>

<div class="figcenter" style="width: 464px;">
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_188.png" width="464" height="345" alt="" />
<div class="caption">BRIDGE OVER THE CLYDE AT HAMILTON,
<br />DESIGNED BY WATT.</div>
</div>

<div class="figcenter" style="width: 432px;">
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_189.png" width="432" height="513" alt="" />
<div class="caption">DOUBLE-ACTING ENGINE,
<br />ZINC WORKS, CITY ROAD, LONDON.</div>
</div>

<h2><a name="CHAP_VII" id="CHAP_VII">CHAP. VII.</a></h2>

<p class="right"><a class="refpn" id="Pg167">[Pg167]</a><br />
<a href="#CONTENTS"><small>TOC</small></a>&#160;&#160;<a
href="#INDEX"><small>INX</small></a></p>

<div class="chapheader">
PROPERTIES OF STEAM.â€”COMMON STEAM.â€”SUPERHEATED STEAM.â€”LAW
OF DALTON AND GAY LUSSAC.â€”LAW OF MARIOTTE.â€”RELATION
BETWEEN TEMPERATURE AND PRESSURE OF COMMON STEAM.â€”EFFECTS
OF THE EXPANSION OF COMMON STEAM.â€”MECHANICAL
EFFECTS OF STEAM.â€”METHOD OF EQUALISING THE EXPANSIVE FORCE.â€”HORNBLOWER'S
ENGINE.â€”WOOLF'S ENGINE.â€”WATT'S ATTEMPTS
TO EXTEND THE STEAM ENGINE TO MANUFACTURES.â€”PAPIN'S PROJECTED
APPLICATIONS OF THE STEAM ENGINE.â€”SAVERY'S APPLICATIONS
OF THE ENGINE TO MOVE MACHINERY.â€”JONATHAN HULL'S
APPLICATION TO WATER WHEELS.â€”STEWART'S APPLICATION OF THE
ENGINE TO MILL WORK.â€”WASHBOROUGH'S APPLICATION OF THE FLY
WHEEL AND CRANK.â€”WATT'S SECOND PATENT.â€”DOUBLE-ACTION VALVES.</div>

<div class="ph3fst"><h3>(93.)</h3> Since the application of the expansive action of steam
involves the consideration of its properties when it ceases to
be in contact with the water from which it was produced,
and likewise the variation of its pressure in different states of
<a class="refpn" id="Pg168">[Pg168]</a>
density and at different temperatures, it is necessary here to explain
some of the most important of these properties of vapour.</div>

<p>Steam may exist in two states, distinguished from each
other by the following circumstances:â€”</p>

<p>1st. It may be such that the abstraction from it of any
portion of heat, however small, will cause its partial condensation.</p>

<p>2d. It may be such as to admit of the abstraction of heat
from it without undergoing any other change than that which
air would undergo under like circumstances, viz. a diminution
of temperature and pressure.</p>


<div class="ph3"><h3>(<a id="h3-94"></a>94.)</h3>
We shall call, for distinction, the former <em>Common
Steam</em>, and the latter <em>Superheated Steam</em>.</div>

<div class="figleft" style="width: 85px;">
<a id="Fig029"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_190.png" width="85" height="279" alt="" />
<div class="caption figure">Fig. 29.</div>
</div>

<p>To explain the circumstances out of which these properties
arise, let <strong>B</strong> (<a href="#Fig029"><i>fig.</i> 29.</a>) be imagined to be a vessel filled with
water, communicating by a pipe and stopcock
with another vessel <strong>A</strong>, which in the commencement
of the process may be conceived to be filled
with air. Let <strong>D</strong> be a pipe and stopcock at the
top of this vessel. If the vessel <strong>B</strong> be heated, and
the two cocks be opened, the steam proceeding
from the water in <strong>B</strong> will blow the air out of the
vessel <strong>A</strong> through the open stopcock <strong>D</strong>, in the
same manner as air is blown from a steam engine.
When the vessel <strong>A</strong> by these means has been filled
with pure steam, let both stopcocks be closed.
If the steam in <strong>A</strong>, under these circumstances, have
a pressure of 15 lbs. per square inch, its temperature
will be found to be 213Â°. Now, if any
heat be abstracted from this steam, its temperature will fall,
and a portion of it will be reconverted into water.</p>

<p>Again, suppose the vessel <strong>A</strong> to be filled with pure steam
which has been produced from the heated water in <strong>B</strong>, the
stopcock <strong>C</strong> being open. Let the stopcock <strong>C</strong> be then closed,
and the water in <strong>B</strong> be heated to a higher temperature, the
temperature and pressure of the steam in <strong>A</strong> being observed.
If the stopcock <strong>C</strong> be now opened, the steam in <strong>A</strong> will be
immediately observed to rise to the more elevated temperature
which has been imparted to the water in <strong>B</strong>, and at the
same time it will acquire an increased pressure.
<a class="refpn" id="Pg169">[Pg169]</a></p>

<p>The increase of temperature which it has received would
of itself produce an increased pressure; but that this is not
the sole cause of the augmented pressure in the present case
might be proved by weighing the vessel <strong>A</strong>. It would be
found to have increased weight, which could only arise from
its having received from the water in <strong>B</strong> an additional quantity
of vapour. The increased pressure therefore, which the steam
in <strong>A</strong> has acquired, is due conjointly to its increased density
and its increased temperature. In general, if the water in
the vessel <strong>B</strong> be raised or lowered in temperature, the steam
in the vessel <strong>A</strong> will rise and fall in temperature in a corresponding
manner, always having the same temperature as
the water in <strong>B</strong>. If the weight of the vessel <strong>A</strong> were observed,
it would be found to increase with every increase of temperature,
and to diminish with every diminution of temperature,
proving that the augmented temperature of the water in <strong>B</strong>
produces an augmented density of the steam in <strong>A</strong>. The same
pressure would be found always to correspond to the same
temperature and density, so that if the numerical amount of
any one of the three quantities, the temperature, the pressure,
or the density, were known, the other two must necessarily
be determined, the same temperature always corresponding
to the same pressure, and <i>vice versÃ¢</i>. And in like manner,
steam produced under these circumstances of the same density
cannot have different pressures. It must be observed
that the steam here produced receives all the heat which it
possesses from the water from which it is raised. Now it is
easily demonstrable, that this is the least quantity of heat
which is compatible with the steam maintaining the vaporous
form; for if the stopcock <strong>C</strong> be closed so as to separate the
steam in <strong>A</strong> from the water in <strong>B</strong>, and that any portion of heat,
however small, be then abstracted from the steam in <strong>A</strong>, some
portion of the steam will be reconverted into water.</p>

<p>This then, according to the definition already given, is
<em>Common Steam</em>.</p>


<div class="ph3"><h3>(95.)</h3> Let us now suppose that the vessel <strong>A</strong>, being in communication
with the vessel <strong>B</strong> by the open stopcock, has been
filled with pure steam of any given temperature. The steam
which it thus contains will be common steam, and, as has been
<a class="refpn" id="Pg170">[Pg170]</a>
shown (<a href="#h3-94">94</a>.), it cannot lose any portion of heat, however small,
without being partially condensed; but let the stopcock <strong>C</strong> be
closed, and let the steam in <strong>A</strong> be then exposed to any source
of heat by which its temperature may be raised any required
number of degrees. From the steam thus obtained heat may
be abstracted without producing any condensation; and such
abstraction of heat may be continued without producing condensation,
until the steam is cooled down to that temperature
at which it was raised from the water in <strong>B</strong>, when the stopcock
<strong>C</strong> was opened. Any further reduction of temperature would
be attended with condensation.</div>

<p>If after increasing the temperature of the steam in <strong>A</strong>, the
stopcock <strong>C</strong> being shut so as to render it superheated steam,
its pressure be observed, the pressure will be found to be
increased, but not to that amount which it would have been
increased had the steam in <strong>A</strong> been raised to the same temperature
by heating the water in <strong>B</strong> to that temperature, and
keeping the stopcock open. In fact, its present augmented
pressure will be due only to its increased temperature, since
its density remains unchanged. But if in these circumstances
the stopcock <strong>C</strong> be suddenly opened, the pressure of the steam
in <strong>A</strong> will as suddenly rise to that pressure which in common
steam corresponds to its temperature; and if the vessel <strong>A</strong>
were weighed, it would be found to have increased in weight,
proving that the steam contained in it has received increased
density by an increased quantity of vapour proceeding from
the water in <strong>A</strong>. In fact, by opening the stopcock the steam
which was before superheated steam, has become common
steam. It has the greatest density which steam of that temperature
can have; and consequently, if any heat be abstracted
from it, a partial condensation will ensue.</p>

<p>To render these general principles more intelligible, let us
suppose that the water in <strong>B</strong> is raised to the temperature of
213Â°, the stopcock <strong>C</strong> being open; the vessel <strong>A</strong> will then be
filled with steam of the same temperature, and having a
pressure of 15 lbs. per square inch. This will be common
steam. If the stopcock be now closed, and the whole apparatus
be exposed to the temperature of 243Â°; the steam in <strong>A</strong>
will preserve the same density, but its pressure will be
<a class="refpn" id="Pg171">[Pg171]</a>
increased from 15 lbs. to a little more than 16 lbs. per square
inch. Let the stopcock <strong>C</strong> be then opened and while the temperature
of the steam in <strong>A</strong> shall continue to be 243Â°, the
pressure will suddenly rise from 16 lbs. to about 26 lbs. per
square inch. The weight of the steam in <strong>A</strong> will be at the
same time increased in the same proportion of 16 to 26 as its
pressure. The steam thus produced in <strong>A</strong> will then be common
steam, and any abstraction of heat from it would be
attended with partial condensation.</p>


<div class="ph3">
<h3>(<a id="h3-96"></a>96.)</h3>
The law, according to which the pressure of elastic
fluids in general, whether gases or vapours, increases with
their temperature, was simultaneously discovered by Dalton
and Gay Lussac. If the pressure which the gas or vapour
would have at the temperature of melting ice, were expressed
by 10,000, then the increase of pressure which it would
receive for every degree of temperature by which it would be
raised, its volume being supposed to be preserved, would be
expressed by
<span class="fraction">208<sup>1</sup>â„<sub>3</sub></span>.
Thus, if the pressure of gas, or vapour,
on a surface of a certain magnitude at the temperature of 32Â°
were 10,000 ounces, then the same gas or vapour would
acquire an additional pressure of
<span class="fraction">208<sup>1</sup>â„<sub>3</sub></span> ounces for every
degree of temperature which would be imparted to it above
32Â°. This law is common to all gases and vapours.</div>

<p>It may be objected that water cannot exist in the state of
vapour under the usual pressures at so low a temperature as
melting ice. This, however, does not hinder the application
of the above law, for that law will equally hold good by computing
the pressure which the vapour would have if it were a
permanent gas, and if it could therefore exist in the elastic
form at that low temperature.</p>


<div class="ph3"><h3>(<a id="h3-97"></a>97.)</h3> Another law, common to all elastic fluids, and of
equal importance with the former, was discovered by Mariotte.
By this law it appears that every gas or vapour,
so long as its temperature is unchanged, will have a pressure
directly proportional to its density. If therefore, while
we compress steam into half its volume, we could preserve
its temperature unaltered, we should increase its
pressure in a two-fold proportion; but if the process of
compression should cause its temperature to increase,
<a class="refpn" id="Pg172">[Pg172]</a>
then its increase of pressure will be greater than its
increase of density, since it will be due conjointly to the
increase of density and to the increase of temperature. In
this case the increased pressure may be deduced from the
combined application of the two laws just explained; that of
Mariotte will determine that increase of pressure which is
due to the increase of density, and that of Dalton and Gay
Lussac will determine the further increase of pressure which
will be due to the increase of temperature. The full investigation
of these effects, and the formulÃ¦ expressing them,
will be found in the Appendix to this volume.</div>


<div class="ph3">
<h3>(98.)</h3> The fixed relations which exist between the temperatures
of common steam and its pressure and density,
have never been discovered from any general physical principles.
The pressures and the densities however, which
correspond to a great variety of temperatures throughout the
thermometric scale, have been ascertained by extensive series
of experiments instituted by philosophers of this and other
countries. From a comparison of the temperatures and
pressures thus found by experiment, empirical formulÃ¦ have
been constructed, which exhibit, with an approximation
sufficiently close for practice, this relation; and these formulÃ¦
may accordingly be used for the computation of tables
exhibiting the pressures, temperatures, and densities of common
steam; and such tables will have sufficient numerical
accuracy for all practical purposes. These formulÃ¦, and the
tables resulting from them, will be found in the Appendix
to this volume.</div>


<div class="ph3"><h3>(99.)</h3> It has been explained, that to effect the conversion of
water into steam, it is only necessary to impart to it as much
heat as, added to the temperature which it has, would, if it
continued in the liquid form, raise it to the temperature of
1212Â°. This condition is necessary, and sufficient to effect
the transition of water into vapour. If, for example, as much
heat were imparted to the water evaporated, as would maintain
it in the liquid state to 1300Â°, then the steam so produced
would be superheated steam, having 80Â° of heat more
than is necessary to maintain it in the vaporous form. From
such steam, therefore, 80Â° of heat may be abstracted without
producing any condensation.
<a class="refpn" id="Pg173">[Pg173]</a></div>


<div class="ph3"><h3>(100.)</h3> Common steam being raised from water at any pressure
and temperature, and being afterwards separated from the
water, if the same steam be compressed into a small volume,
or allowed to expand into a greater volume, it will still maintain
its quality of common steam, and will have the same
pressure and temperature, whatever volume it may assume, as
it would have if immediately raised from water at that pressure.
Thus if steam be raised from water under a pressure
of 30 lbs. per square inch, and, being separated from the
water, be allowed to dilate, until its pressure is reduced to
15 lbs. per square inch, its temperature will then be reduced
to 213Â°, which is that temperature which it would have if
immediately raised from water under a pressure of 15 lbs.
per square inch; and if any heat be abstracted from such
steam, whether under its original pressure, or under the
diminished pressure of 15 lbs. per square inch, a condensation
will be produced, the amount of which will be the
same, if the same quantity of heat be abstracted from the
steam. These are consequences which immediately flow
from the fact, that the sum of the latent and sensible heats
of steam is always the same.<a name="FNanchor_20_20" id="FNanchor_20_20"></a><a href="#Footnote_20_20" class="fnanchor">[20]</a></div>

<p>It appears, therefore, that supposing the steam used in an
engine to receive no additional heat after it leaves the boiler,
however it may be changed in its density by subsequent
expansion, it will still retain its character of common steam,
and cannot lose any portion of heat, however small, without
suffering partial condensation. The mechanical force also
exerted by such steam, after expansion, must be computed in
the same manner as if it were raised immediately.</p>


<div class="ph3"><h3>(101.)</h3> If the law of Mariotte were strictly applicable to
steam, its mechanical effect would be the same as has been
already explained in all states of density; but since its temperature
will rise and fall as its density is increased or diminished,
a corresponding change will be produced in its
<a class="refpn" id="Pg174">[Pg174]</a>
mechanical efficacy. It is therefore necessary in the calculation
of the mechanical effect of steam, whether it be used at
a uniform pressure without the principle of expansion, or
with the application of that principle to any given extent,
to take into account the combined operation of the laws
of Mariotte and Dalton. FormulÃ¦ exhibiting the relation
between the temperatures, pressures, volumes, and densities
of steam, and the mechanical effect produced by the evaporation
of water, whether acting with or without expansion,
together with the tables necessary for the practical application
of these, will be found in the Appendix.</div>


<div class="ph3">
<h3>(102.)</h3> One of the methods of equalising the varying force of
expanding steam, would be to work it at the same time in
two cylinders connected with the same beam; so that while its
force in one would be augmented, its force in the other would
be diminished, the combination of the two producing a
uniform effect. Soon after the expansive principle was promulged
by Mr. Watt, this expedient was accordingly resorted
to by an engineer named Hornblower.</div>

<div class="figleft" style="width: 250px;">
<a id="Fig030"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_196.png" width="250" height="355" alt="" />
<div class="caption figure">Fig. 30.</div>
</div>

<p>In the year 1781, Hornblower conceived the notion of
working an engine with two
cylinders of different sizes,
by allowing the steam to
flow freely from the boiler
until it fills the smaller cylinder,
and then permitting
it to expand into the greater
one, employing it thus to
press down two pistons in
the following manner.</p>

<p>Let <strong>C</strong>, <a href="#Fig030"><i>fig.</i> 30.</a>, be the
centre of the great working-beam,
carrying two arch
heads, on which the chains
of the piston rods play.
The distances of these arch
heads from the centre <strong>C</strong> must
be in the same proportion as the length of the cylinders, in
order that the same play of the beam may correspond to
<a class="refpn" id="Pg175">[Pg175]</a>
the plays of both pistons. Let <strong>F</strong> be the steam-pipe from the
boiler, and <strong>G</strong> a valve to admit the steam above the lesser
piston. <strong>H</strong> is a tube by which a communication may be
opened by the valve <strong>I</strong>, between the top and bottom of the
lesser cylinder <strong>B</strong>. <strong>K</strong> is a tube communicating by the valve
<strong>L</strong>, between the bottom of the lesser cylinder <strong>B</strong> and the top
of the greater cylinder <strong>A</strong>. <strong>M</strong> is a tube communicating, by the
valve <strong>N</strong>, between the top and bottom of the greater cylinder
<strong>A</strong>; and <strong>P</strong> a tube leading to the condenser by the exhausting
valve <strong>O</strong>.</p>

<p>At the commencement of the operation, suppose all the
valves opened, and steam allowed to flow through the engine
until the air be completely expelled, and then let all the
valves be closed. To start the engine, let the exhausting
valve <strong>O</strong> and the steam valves <strong>G</strong> and
<strong>L</strong> be opened, as in <a href="#Fig030"><i>fig.</i> 30.</a>
The steam will flow freely from the boiler, and press upon
the lesser piston, and at the same time the steam below the
greater piston will flow into the condenser, leaving a vacuum
in the greater cylinder. The valve <strong>L</strong> being opened, the
steam which is under the piston in the lesser cylinder will
flow through <strong>K</strong>, and press on the greater piston, which, having
a vacuum beneath it, will consequently descend. At the
commencement of the motion, the lesser piston is as much
resisted by the steam below it, as it is urged by the steam above
it; but after a part of the descent has been effected, the steam
below the piston, in the lesser cylinder, passing into the
greater, expands into an increased space, and therefore loses
part of its elastic force. The steam above the lesser piston
retaining its full force by having a free communication with
the boiler by the valve <strong>G</strong>, the lesser piston will be urged by
a force equal to the excess of the pressure of this steam
above the diminished pressure of the expanded steam below
it. As the pistons descend, the steam which is between
them is continually increasing in its bulk, and therefore decreasing
in its pressure, from whence it follows, that the
force which resists the lesser piston is continually decreasing,
while that which presses it down remains the same, and therefore
the effective force which impels it must be continually
increasing.
<a class="refpn" id="Pg176">[Pg176]</a></p>

<p>On the other hand, the force which urges the greater piston
is continually decreasing, since there is a vacuum below it,
and the steam which presses it is continually expanding into
an increased bulk.</p>

<div class="figleft" style="width: 191px;">
<a id="Fig031"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_198.png" width="191" height="154" alt="" />
<div class="caption figure">Fig. 31.</div>
</div>

<p>Impelled in this way, let us suppose the pistons to have
arrived at the bottoms of the cylinders, and let the valves
<strong>G</strong>, <strong>L</strong>, and <strong>O</strong>, be closed, and the
valves <strong>I</strong> and <strong>N</strong> opened. No steam
is allowed to flow from the boiler,
<strong>G</strong> being closed, nor any allowed to
pass into the condenser, since <strong>O</strong> is
closed, and all communication between
the cylinders is stopped by
closing <strong>L</strong>. By opening the valve <strong>I</strong>,
a free communication is made between the top and bottom
of the lesser piston through the tube <strong>H</strong>, so that the steam
which presses above the lesser piston will exert the same
pressure below it, and the piston is in a state of indifference.
In the same manner the valve <strong>N</strong> being open, a free communication
is made between the top and bottom of the
greater piston, and the steam circulates above and below the
piston, and leaves it free to rise. A counterpoise attached to
the pump-rods, in this case, draws up the piston, as in Watt's
single engine; and when they arrive at the top, the valves <strong>I</strong>
and <strong>N</strong> are closed, and <strong>G</strong>, <strong>L</strong>, and <strong>O</strong>, opened, and the next
descent of the pistons is produced in the manner already
described, and so the process is continued.</p>

<p>The valves are worked by the engine itself, by means
similar to some of those already described. By computation,
we find the power of this engine to be nearly the same as a
similar engine on Watt's expansive principle. It does not,
however, appear, that any adequate advantage was gained by
this modification of the principle, since no engines of this construction
are now made.</p>


<div class="ph3"><h3>(103.)</h3> The use of two cylinders was revived by Arthur Woolf
in 1804, who, in this and the succeeding year, obtained patents
for the application of steam raised under a high pressure to
double-cylinder engines. The specification of his patent
states, that he has proved by experiment that steam raised
<a class="refpn" id="Pg177">[Pg177]</a>
under a safety-valve loaded with any given number of pounds
upon the square inch will, if allowed to expand into as many
times its bulk as there are pounds of pressure on the square
inch, have a pressure equal to that of the atmosphere. Thus,
if the safety-valve be loaded with four pounds on the square
inch, the steam, after expanding into four times its bulk, will
have the atmospheric pressure; if it be loaded with 5, 6, or
10 lbs. on the square inch, it will have the atmospheric
pressure when it has expanded into 5, 6, or 10 times
its bulk, and so on. It was, however, understood in this
case, that the vessel into which it was allowed to expand
should have the same temperature as the steam before it
expands.</div>

<p>It is very unaccountable how a person of Mr. Woolf's
experience in the practical application of steam could be led
into errors so gross as those involved in the averments of this
patent; and it is still more unaccountable how the experiments
could have been conducted which led him to conclusions
not only incompatible with all the established properties of
elastic fluids, but even involving in themselves palpable contradiction
and absurdity. If it were admitted that every additional
pound avoirdupois which should be placed upon the
safety-valve would enable steam, by its expansion into a proportionally
enlarged space, to attain a pressure equal to the
atmosphere, the obvious consequence would be, that a physical
relation would subsist between the atmospheric pressure
and the pound avoirdupois! It is wonderful that it did not
occur to Mr. Woolf, that, granting his principle to be true
at any given place, it would necessarily be false at another
place, where the barometer would stand at a different height!
Thus, if the principle were true at the foot of a mountain, it
would be false at the top of it; and if it were true in fair
weather, it would be false in foul weather, since these circumstances
would be attended by a change in the atmospheric
pressure, without making any change in the pound avoirdupois.<a name="FNanchor_21_21" id="FNanchor_21_21"></a><a href="#Footnote_21_21" class="fnanchor">[21]</a></p>

<p class="right"><a class="refpn" id="Pg178">[Pg178]</a></p>

<div class="ph3">
<h3>(104.)</h3> For several years after the extension of Watt's first
patent had been obtained from parliament, he was altogether
engrossed by the labour of bringing to perfection the application
of the steam-engine to the drainage of mines, and in
surmounting the numerous difficulties which presented themselves
to its general adoption, even after its manifold advantages
were established and admitted. When, however, these
obstacles had been overcome, and the works for the manufacture
of engines for pumping water, at Soho, had been
organised and brought into active operation, he was relieved
from the pressure of these anxieties, and was enabled to turn
his attention to the far more extensive and important uses of
which he had long been impressed with the conviction that
the engine was capable. His sagacious mind enabled him to
perceive that the machine he had created was an infant force,
which by the fostering influence of his own genius would one
day extend its vast power over the arts and manufactures,
the commerce and the civilisation of the world. Filled with
such aspirations, he addressed his attention about the year
1779, to the adaptation of the steam-engine to move machinery,
and thereby to supersede animal power, and the natural
agents, wind and water.</div>

<p>The idea that steam was capable of being applied extensively
as a prime mover, had prevailed from a very
early period; and now that we have seen its powers so extensively
brought to bear, it will not be uninteresting to revert
to the faint traces by which its agency was sketched in the
crude speculations of the early mechanical inventors.</p>


<div class="ph3">
<h3>(105.)</h3> Papin, to whom the credit of discovering the method
of producing a vacuum by the condensation of steam is due, was
the earliest and most remarkable of those projectors. With
very limited powers of practical application, he was, nevertheless,
peculiarly happy in his mechanical conceptions; and
had his experience and opportunities been proportionate to
the clearsighted character of his mind, he would doubtless
have anticipated some of the most memorable of his successors
in the progressive improvement of the steam engine.</div>

<p>In his work already cited, after describing his method of
imparting an alternate motion to a piston by the atmospheric
<a class="refpn" id="Pg179">[Pg179]</a>
pressure acting against a vacuum produced by the condensation
of steam, he stated that his invention, besides being
applicable to pumping water, could be available for rowing
vessels against wind and tide, which he proposed to accomplish
in the following manner.</p>

<p>Paddle-wheels, such as have since been brought into
general use, were to be placed at the sides, and attached to
a shaft extending across the vessel. Within the vessel, and
under this shaft, he proposed to place several cylinders
supplied with pistons, to be worked by the atmospheric
pressure. On the piston-rods were to be constructed racks
furnished with teeth: these teeth were to work in the teeth
of wheels or pinions, placed on the shaft of the paddle-wheels.
These pinions were not to be fixed on the shaft,
but to be connected with it by a ratchet; so that when they
turned in one direction, they would revolve without causing
the shaft to revolve; but when driven in the other direction,
the catch of the ratchet-wheel would act upon the shaft so
as to compel the shaft and paddle-wheels to revolve with the
motion of the pinion or wheel upon it. By this arrangement,
whenever the piston of any cylinder was forced down by the
atmospheric pressure, the rack descending would cause the
corresponding pinion of the paddle-shaft to revolve; and the
catch of the ratchet wheel, being thus in operation, would
cause the paddle-shaft and paddle-wheels also to revolve; but
whenever the piston would rise, the rack driving the pinion
in the opposite direction, the catch of the ratchet wheel
would merely fall from tooth to tooth, without driving the
paddle-shaft.</p>

<p>It is evident that by such an arrangement a single cylinder
and piston would give an intermitting motion to the paddle-shaft,
the motion of the wheel being continued only during
the descent of the piston; but if several cylinders were provided,
then their motion might be so managed, that when one
would be performing its ascending stroke, and therefore
giving no motion to the paddle-shaft, another should be performing
its descending stroke, and therefore driving the
paddle-shaft. As the interval between the arrival of the
piston at the bottom of the cylinder and the commencement
<a class="refpn" id="Pg180">[Pg180]</a>
of its next descent would have been, in the imperfect machine
conceived by Papin, much longer than the time of the descent,
it was evident that more than two cylinders would be necessary
to insure a constantly acting force on the paddle-shaft,
and, accordingly, Papin proposed to use several cylinders.</p>

<p>In addition to this, Papin proposed to construct a boiler
having a fireplace surrounded on every side by water, so that
the heat might be imparted to the water with such increased
rapidity as to enable the piston to make four strokes per
minute. These projects were promulged in 1690, but it
does not appear that they were ever reduced to experiment.</p>


<div class="ph3"><h3>(106.)</h3> Savery proposed, in his original patent, in 1698, to
apply his steam engine as a general prime mover for all sorts
of machinery, by causing it to raise water to make an artificial
fall, by which overshot water-wheels might be driven. This
proposal was not acted on during the lifetime of Savery, but
it was at a subsequent period partially carried into effect.
Mr. Joshua Rigley erected several steam engines on this principle
at Manchester, and other parts of Lancashire, to impel
the machinery of some of the earliest manufactories and cotton
mills in that district. The engines usually raised the water
from sixteen to twenty feet high, from whence it was conveyed
to an overshot wheel, to which it gave motion. The
same water was repeatedly elevated by the engine, so that no
other supply was necessary, save what was sufficient to make
good the waste. These engines continued in use for some
years, until superseded by improved machines.<a name="FNanchor_22_22" id="FNanchor_22_22"></a><a href="#Footnote_22_22" class="fnanchor">[22]</a></div>


<div class="ph3">
<h3>(107.)</h3> In 1736, Jonathan Hulls obtained a patent for a method
of towing ships into or out of harbour against wind and
tide. This method was little more than a revival of that proposed
by Papin in 1690. The motion, however, was to be communicated
to the paddle-shaft by a rope passing over a pulley
fixed on an axis, and was to be maintained during the returning
stroke of the piston by the descent of a weight which was
elevated during the descending stroke. There is no record,
however, of this plan, any more than that of Papin, ever having
been reduced to experiment.</div>


<div class="ph3"><h3>(108.)</h3> During the early part of the last century the
<a class="refpn" id="Pg181">[Pg181]</a>
manufactures of this country had not attained to such an extent as
to render the moving power supplied by water insufficient or
uncertain to any inconvenient degree; and accordingly mills,
and other works in which machinery required to be driven by a
moving power, were usually built along the streams of rivers.
About the year 1750 the general extension of manufactures,
and their establishment in localities where water power was not
accessible, called the steam engine into more extensive operation.
In the year 1752, Mr. Champion, of Bristol, applied
the atmospheric engine to raise water, by which a number of
overshot wheels were driven. These were applied to move
extensive brass-works in that neighbourhood, and this application
was continued for about twenty years, but ultimately
given up on account of the expense of fuel and the improved
applications of the steam engine.</div>

<p>About this time Smeaton applied himself with great
activity and success to the improvement of wind and water
mills, and succeeded in augmenting their useful effect in a
twofold proportion with the same supply of water. From the
year 1750 until the year 1780 he was engaged in the construction
of his improved water mills, which he erected in
various parts of the country, and which were imitated so extensively
that the improvement of such mills became general.
In cases where a summer drought suspended the supply of
water, horse machinery was provided, either to work the mill
or to throw back the water. These improvements necessarily
obstructed for a time the extension of steam power to mill
work; but the increase of manufactures soon created a demand
for power greatly exceeding what could be supplied by
such limited means.</p>

<p>In the manufacture of iron, it is of great importance to
keep the furnaces continually blown, so that the heat may
never be abated by day or night. In the extensive ironworks
at Colebrook Dale, several water-wheels were used in
the different operations of the manufacture of iron, especially
in driving the blowers of the iron furnaces. These wheels
were usually driven by the water of a river, but in the summer
months the supply became so short that it was insufficient to
work them all. Steam engines were accordingly erected to
<a class="refpn" id="Pg182">[Pg182]</a>
return the water for driving these wheels. This application
of the engine as an occasional power for the supply of water-wheels
having been found so effectual, returning engines were
soon adopted as the permanent and regular means of supplying
water-wheels. The first attempt of this kind is recorded to
have been made by Mr. Oxley, in 1762, who constructed a
machine to draw coals out of a pit at Hartley colliery, in
Northumberland. It was originally intended to turn the
machine by a continuous circular motion received from the
beam of the engine; but that method not being successful,
the engine was applied to raise water for a wheel by which the
machine was worked. This engine was continued in use for
several years, and though it was at length abandoned, on account
of its defective construction, it nevertheless established
the practicability of using steam power as a means of driving
water wheels.<a name="FNanchor_23_23" id="FNanchor_23_23"></a><a href="#Footnote_23_23" class="fnanchor">[23]</a></p>


<div class="ph3"><h3>(109.)</h3> In the year 1777, Mr. John Stewart read a paper before
the Royal Society, describing a method for obtaining a continued
circular motion for turning all kinds of mills from the
reciprocating motion of a steam engine. He proposed to accomplish
this by means of two endless chains passing over pulleys,
which should be moved upwards and downwards by the
motion of the engine, in the manner of a window sash. The
joint pins of the links of the two chains worked in teeth at
the opposite sides of a cog wheel, to which they imparted a
circular motion, first by one chain, and then by the other,
acting alternately on opposite sides of the wheel. One chain
impelled it during the descent of the piston, and the other
during the ascent; but one of these chains always passed over
its pulleys so as to produce no effect on one side of the cog
wheel, whilst the other chain worked on the opposite side to
turn it round. For this purpose each chain was provided
with a catch, to prevent its circulating over its pulleys in one
direction, but to allow it free motion in the other. The cog
wheel thus kept in revolution might be applied to the axis of
any mill which the engine was required to work. Thus, if it
were applied to a flour-mill, the millstone itself would perform
the office of a fly-wheel to regulate the intermission of
<a class="refpn" id="Pg183">[Pg183]</a>
the power, and in other mills a fly-wheel might be added
for this purpose.</div>

<p>The hints obtained by Mr. Stewart from Papin's contrivance,
before mentioned, will not fail to be perceived. In
Mr. Stewart's paper he notices indirectly the method of obtaining
a continued circular motion from a reciprocating motion
by means of a crank or winch, which, he says, occurs naturally
in theory, but in practice would be impossible, from the
nature of the motion of the engine, which depends on the
force of the steam, and cannot be ascertained in its length.
Therefore, on the first variation, the machine would be either
broken in pieces or turned back. Such an opinion, pronounced
by a man of considerable mechanical knowledge and
ingenuity, against a contrivance which, as will presently appear,
proved in practice, not less than in theory, to be the
most effectual means of accomplishing the end here pronounced
to be impossible, is sufficiently remarkable. It
might cast some doubt on the extent of Mr. Stewart's practical
knowledge, if it did not happen to be in accordance with
a judgment so generally unimpeachable as that of Mr.
Smeaton. This paper of Mr. Stewart's was referred by the
council of the Royal Society to Mr. Smeaton, who remarked
upon the difficulty arising from the absolute stopping of the
whole mass of moving power, whenever the direction of the
motion is changed; and observed, that although a fly-wheel
might be applied to regulate the motion, it must be such a
large one as would not be readily controlled by the engine
itself; and he considered that the use of such a fly-wheel
would be a greater incumbrance to a mill than a water-wheel
to be supplied by water pumped up by the engine. This engineer,
illustrious as he was, not only fell into the error of
Mr. Stewart in respect of the crank, but committed the
further blunder of condemning the very expedient which has
since rendered the crank effectual. It will presently appear
that the combination of the crank and fly-wheel have been the
chief means of establishing the dominion of the steam engine
over manufactures.</p>


<div class="ph3"><h3>(110.)</h3> In 1779, Mr. Matthew Wasbrough, an engineer at
Bristol, took out a patent for the application of a steam engine
<a class="refpn" id="Pg184">[Pg184]</a>
to produce a continuous circular motion by means of ratchet
wheels, similar to those previously used by Mr. Oxley, at
Hartley colliery; to which, however, Mr. Wasbrough added
a fly-wheel to maintain and regulate the motion. Several
machines were constructed under this patent; and among
others, one was erected at Mr. Taylor's saw-mills and block
manufactory at Southampton. In 1780, one was erected at
Birmingham, where the ratchet work was found to be subject
to such objections, that one of the persons about the works
substituted for it the simple crank, which has since been invariably
used. A patent was taken out for this application
of the crank in the same year, by Mr. James Pickard, of
Birmingham. It will presently appear, however, that the
suggestion of this application of the crank was derived from
the proceedings of Watt, who was at the same time engaged
in similar experiments.</div>


<div class="ph3">
<h3>(111.)</h3> The single-acting steam engine, as constructed by
Watt, was not adapted to produce continuous uniform motion
of rotation, for the following reasons:â€”</div>

<ol class="nomarker">
<li><em>First.</em> The effect required was that of an uniformly acting
force. The steam engine, on the other hand, supplied an intermitting
force. Its operation was continued during the descending
motion of the piston, but it was suspended during
the ascent of the piston. To produce the continued effect
now required, either its principle of operation should be
altered, or some expedient should be devised for maintaining
the motion of the revolving shaft during the ascent of the
piston, and the consequent suspension of the moving power.</li>

<li><em>Secondly.</em> The action of the steam engine was rectilinear.
It was a power which acted in a straight line, viz., in the direction
of the cylinder. The motion, however, required to be
produced, was a circular motionâ€”a motion of rotation around
the axis or shaft of the mill.</li>
</ol>

<p>The steps by which Watt proceeded to accomplish these
objects have been recorded by himself as follows, in his notes
upon Dr. Robison's article on the steam engine:â€”</p>

<p>"I had very early turned my mind to the producing of
continued motion round an axis; and it will be seen, by reference
to my first specification in 1769, that I there described
<a class="refpn" id="Pg185">[Pg185]</a>
a steam wheel, moved by the force of steam, acting in a circular
channel against a valve on one side, and against a
column of mercury, or some other fluid metal, on the other
side. This was executed upon a scale of about six feet
diameter at Soho, and worked repeatedly, but was given
up, as several practical objections were found to operate
against it; similar objections lay against other rotative engines,
which had been contrived by myself and others, as well
as to the engines producing rotatory motions by means of
ratchet wheels.</p>

<p>"Having made my single reciprocating engines very regular
in their movements, I considered how to produce rotative motions
from them in the best manner; and amongst various
schemes which were subjected to trial, or which passed
through my mind, none appeared so likely to answer the purpose
as the application of the crank, in the manner of the
common turning lathe; but as the rotative motion is produced
in that machine by impulse given to the crank in the descent
of the foot only, it requires to be continued in its ascent by
the energy of the wheel, which acts as a fly; being unwilling
to load my engine with a fly-wheel heavy enough to continue
the motion during the ascent of the piston (or with a fly-wheel
heavy enough to equalise the motion, even if a counterweight
were employed to act during that ascent), I proposed
to employ two engines, acting upon two cranks fixed on the
same axis, at an angle of 120Â° to one another, and a weight
placed upon the circumference of the fly-wheel at the same
angle to each of the cranks, by which means the motion
might be rendered nearly equal, and only a very light fly-wheel
would be requisite.</p>

<p>"This had occurred to me very early; but my attention
being fully employed in making and erecting engines for
raising water, it remained <i>in petto</i> until about the year 1778
or 1789, when Mr. Wasbrough erected one of his ratchet-wheel
engines at Birmingham, the frequent breakages and
irregularities of which recalled the subject to my mind, and
I proceeded to make a model of my method, which answered
my expectations; but having neglected to take out a patent,
the invention was communicated by a workman employed to
<a class="refpn" id="Pg186">[Pg186]</a>
make the model, to some of the people about Mr. Wasbrough's
engine, and a patent was taken out by them for the
application of the crank to steam engines. This fact the said
workman confessed, and the engineer who directed the works
acknowledged it; but said, nevertheless, that the same idea
had occurred to him prior to his hearing of mine, and that he
had even made a model of it before that time; which might
be a fact, as the application to a single crank was sufficiently
obvious.</p>

<p>"In these circumstances, I thought it better to endeavour
to accomplish the same end by other means, than to enter
into litigation; and if successful, by demolishing the patent,
to lay the matter open to every body. Accordingly, in 1781,
I invented and took out a patent for several methods of producing
rotative motions from reciprocating ones; amongst
which was the method of the sun-and-planet wheels. This
contrivance was applied to many engines, and possesses the
great advantage of giving a double velocity to the fly-wheel;
but is perhaps more subject to wear, and to be broken under
great strains, than a simple crank, which is now more commonly
used, although it requires a fly-wheel of four times the
weight, if fixed upon the first axis; my application of the
double engine to these rotative machines rendered the counterweight
unnecessary, and produced a more regular motion."</p>


<div class="ph3">
<h3>(112.)</h3> Watt's second patent here referred to, was dated 25th
October, 1781, and was entitled "<cite>A patent for certain
new methods of applying the vibrating or reciprocating
motions of steam or fire engines to produce a continued
rotative or circular motion round an axis or centre, and
thereby to give motion to the wheels of mills and other
machines</cite>."</div>

<p>All the methods specified in this patent were intended to
be worked by the single-acting engine, already described, a
counterweight being applied to impel the machinery during
the returning stroke of the engine, which weight would be
elevated during the descent of the piston. There were five different
expedients proposed in the specification for producing
a rotatory motion; but, of these five, two only were ever applied
in practice.
<a class="refpn" id="Pg187">[Pg187]</a></p>


<div class="ph3">
<h3>(113.)</h3> Suppose a rod or bar attached by a pin or joint at the
upper extremity to the working end of the beam of the engine,
and by a similar pin or joint at the lower extremity to an iron
wheel fixed on the extremity of the axis of the fly-wheel.
One half of this wheel is formed of a solid semicircle of cast
iron, while the other half is constructed of open spokes, so as
to be as light as is consistent with strength. The position of
the wheel on the axis is such that during the returning stroke
of the piston, when the operation of the steam is suspended,
the heavy semicircle of the wheel will be descending, and by
its weight will draw down the connecting bar, and thereby
draw down the working end of the beam, and draw up the
piston in the cylinder. When the piston descends and is
driven by the power of the steam, the heavy semicircle of the
above-mentioned wheel will be drawn upwards, and in the
same way the motion will be continued.</div>

<div class="figright" style="width: 355px;">
<a id="Fig032"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i209.png" width="355" height="296" alt="" />
<div class="caption figure">Fig. 32.</div>
</div>

<div class="ph3"><h3>(114.)</h3> The second method of producing a rotatory motion,
which was subsequently continued for many years in practical
operation, was that which was called the <em>Sun-and-planet Wheels</em>.
A toothed wheel <strong>A</strong>
(<a href="#Fig032"><i>fig.</i> 32.</a>), called the
sun wheel, was fixed
on the axle of the
fly-wheel, to which
rotation was to be
imparted. The wheel
<strong>B</strong>, called the planet
wheel, having an
equal diameter, was
fastened on the end
<strong>I</strong> of the connecting
rod <strong>H I</strong>, so as to be
incapable of revolving. During the descent of the piston,
the working end of the beam was drawn upwards, and the
end <strong>I</strong> of the connecting rod travelled from <strong>C</strong> to <strong>D</strong>, through
the dotted semicircle <strong>C I D</strong>. The wheel <strong>B</strong> not being capable
of revolving on the centre <strong>I</strong>, would, during this motion, drive
the sun wheel <strong>A</strong>. During the ascent of the steam piston, the
working end of the beam would descend, and the centre <strong>I</strong> of
<a class="refpn" id="Pg188">[Pg188]</a>
the planet wheel <strong>B</strong> would be driven downwards from <strong>D</strong> to <strong>C</strong>,
through the other dotted semicircle, and would consequently
continue to drive the sun wheel round in the same direction.</div>

<p>This contrivance, although in the main inferior to the more
simple one of the crank, is not without some advantages;
among others, it gives to the sun wheel double the velocity
which would be communicated by the crank; for in the crank
one revolution only on the axle is produced by one revolution
of the crank, but in the sun-and-planet wheel, two revolutions
of the sun wheel are produced by one of the planet wheel;
thus a double velocity is obtained from the same motion of
the beam. This will be evident from considering that when
the planet wheel is in its highest position, its lowest tooth is
engaged with the highest tooth of the sun wheel; as the planet
wheel passes from the highest position, its teeth drive
those of the sun wheel before them, and when it comes into
the lowest position, the highest tooth of the planet wheel is
engaged with the lowest of the sun wheel: but then half of
the sun wheel has <em>rolled off</em> the planet wheel, and, therefore,
the tooth which was engaged with it in its highest position,
must now be distant from it by half the circumference
of the wheel, and must, therefore, be again in the highest
position; so that while the planet wheel has been carried from
the top to the bottom, the sun wheel has made a complete
revolution.</p>

<p>This advantage of giving an increased velocity may be
obtained also by the crank, by placing toothed wheels on its
axle. Independently of the greater expense attending the
construction of the sun-and-planet wheel, its liability to go
out of order, and the rapid wear of the teeth, and other
objections, rendered it inferior to the crank, which has entirely
superseded it.</p>


<div class="ph3"><h3>(115.)</h3> Although by these contrivances Watt succeeded in
obtaining a continuous circular motion from the reciprocating
motion of the steam engine, the machine was still
one of intermitting, instead of continuous action. The expedient
of a counterweight, elevated during the descending
stroke, and giving back the power expended on it in the
interval of the returning stroke, did not satisfy the
<a class="refpn" id="Pg189">[Pg189]</a>
fastidious mechanical taste of Watt. He soon perceived that
all which he proposed to accomplish by the application
of two cylinders and pistons working alternately, could be
attained with greater simplicity and effect by a single cylinder,
if he could devise means by which the piston might be
impelled by steam upwards as well as downwards. To
accomplish this, it was only necessary to throw the lower
end of the cylinder into alternate communication with
the boiler, while the upper end would be put into communication
with the condenser. If, for example, during the
descent of the piston, the upper end of the cylinder communicated
with the boiler, and the lower end with the condenser;
and, on the other hand, during the ascent of the piston, the
lower end communicated with the boiler, and the upper end
with the condenser; then the piston would be driven continually,
whether upwards or downwards, by the power of
steam acting against a vacuum. Watt obtained his third
patent for this contrivance, on the 12th of March, 1782.</div>

<p>This change in the principle of the machine involved several
other changes in the details of its mechanism.</p>

<div class="figright" style="width: 143px;">
<a id="Fig033"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_211.png" width="143" height="226" alt="" />
<div class="caption figure">Fig. 33.</div>
</div>

<div class="ph3"><h3>(<a id="h3-116"></a>116.)</h3> It was necessary, in the first place, to provide means
for admitting and withdrawing the steam at either end of the
cylinder. For this purpose let <strong>B</strong> and <strong>Bâ€²</strong>
(<a href="#Fig033"><i>fig.</i> 33.</a>) be two steam-boxes, <strong>B</strong> the upper,
and <strong>Bâ€²</strong> the lower, communicating
respectively with the top and bottom of
the cylinder by proper passages <strong>D Dâ€²</strong>.
Let two valves be placed in <strong>B</strong>, one, <strong>S</strong>,
above the passage <strong>D</strong>, and the other, <strong>C</strong>,
below it; and in like manner two other
valves in the lower valve-box, <strong>Bâ€²</strong>, one, <strong>Sâ€²</strong>,
above the passage <strong>Dâ€²</strong>, and the other, <strong>Câ€²</strong>,
below it. Above the valve <strong>S</strong> in the upper
steam-box is an opening at which
the steam-pipe from the boiler enters, and below the valve <strong>C</strong> is
another opening, at which enters the exhausting-pipe leading
to the condenser. In like manner, above the valve <strong>Sâ€²</strong> in the
lower steam-box enters a steam-pipe leading from the boiler,
and below the valve <strong>Câ€²</strong> enters an exhausting-pipe leading to
<a class="refpn" id="Pg190">[Pg190]</a>
the condenser. It is evident, therefore, that steam can always
be admitted above the piston by opening the valve <strong>S</strong>, and below
it by opening the valve <strong>Sâ€²</strong>; and, in like manner, steam can
be withdrawn from the cylinder above the piston, and allowed
to pass to the condenser, by opening the valve <strong>C</strong>, and from
below it by opening the valve <span class="no-wrap"><strong>Câ€²</strong>.</span></div>

<div class="figright" style="width: 147px;">
<a id="Fig034"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_212.png" width="147" height="230" alt="" />
<div class="caption figure">Fig. 34.</div>
</div>

<p>Supposing the piston <strong>P</strong> to be at the top of the cylinder,
and the cylinder below the piston to be filled with pure
steam, let the valves <strong>S</strong> and <strong>Câ€²</strong> be
opened, the valves <strong>C</strong> and <strong>Sâ€²</strong>
being closed as represented in <a href="#Fig034"><i>fig.</i> 34.</a>
Steam from the boiler will, therefore, flow
in through the open valve <strong>S</strong>, and will press
the piston downwards, while the steam that
has filled the cylinder below the piston will
pass through the open valve <strong>Câ€²</strong> into the
exhausting-pipe leading to the condenser,
and being condensed will leave the cylinder
below the piston a vacuum. The piston
will, therefore, be pressed downwards by
the action of the steam above it, as in the
single-acting engine. Having arrived at
the bottom of the cylinder, let the valves <strong>S</strong> and <strong>Câ€²</strong> be both
closed, and the valves <strong>Sâ€²</strong> and <strong>C</strong> be opened, as represented in
<a href="#Fig034"><i>fig.</i> 34.</a> Steam will now be admitted through the open valve
<strong>Sâ€²</strong> and through the passage <strong>Dâ€²</strong> below the piston, while the
steam which has just driven the piston downwards, filling the
cylinder above the piston, will be drawn off through the open
valve <strong>C</strong>, and the exhausting-pipe, into the condenser, leaving
the cylinder above the piston a vacuum. The piston will,
therefore, be pressed upwards by the action of the steam
below it, against the vacuum above it, and will ascend with
the same force as that with which it had descended.</p>

<p>This alternate action of the piston upwards and downwards
may evidently be continued by opening and closing the valves
alternately in pairs. Whenever the piston is at the top of
the cylinder, as represented in <a href="#Fig033"><i>fig.</i> 33.</a>, the valves <strong>S</strong> and <strong>Câ€²</strong>,
that is, the upper steam-valve and the lower exhausting-valve,
are opened, and the valves <strong>C</strong> and <strong>Sâ€²</strong>, that is, the upper
exhausting-valve and the lower steam-valve, are closed; and
<a class="refpn" id="Pg191">[Pg191]</a>
when the piston has arrived at the bottom of the cylinder, as
represented in <a href="#Fig034"><i>fig.</i> 34.</a>, the valves <strong>C</strong> and <strong>Sâ€²</strong>, that is, the upper
exhausting-valve and the lower steam-valve, are opened, and
the valves <strong>S</strong> and <strong>Câ€²</strong>, that is, the upper steam-valve and the
lower exhausting-valve, are closed.</p>

<p>If these valves, as has been here supposed, be opened and
closed at the moments at which the piston reaches the top
and bottom of the cylinder, it is evident that they may be all
worked by a single lever connected with them by proper
mechanism. When the piston arrives at the top of the
cylinder, this lever would be made to open the valves <strong>S</strong> and
<strong>Câ€²</strong>, and at the same time to close the valves <strong>Sâ€²</strong> and <strong>C</strong>; and
when it arrives at the bottom of the cylinder, it would be
made to close the valves <strong>S</strong> and <strong>Câ€²</strong>, and to open the valves
<strong>Sâ€²</strong> and <strong>C</strong>.</p>

<p>If, however, it be desired to cut off the steam before the
arrival of the piston at the termination of its stroke, whether
upwards or downwards, then the steam-valves must be closed
before the arrival of the piston at the end of its stroke; and
as the exhausting-valve ought to be left open until the stroke
is completed, these valves ought to be moved at different
times. In that case separate levers should be provided for
the different valves. We shall, however, return again to the
subject of the valves which regulate the admission of steam
to the cylinder and its escape to the condenser.</p>


<div class="ph3">
<h3>(117.)</h3> It will be remembered that in the single-acting engine
the process of condensation was suspended while the piston
ascended in the cylinder, and therefore the play of the jet of
cold water in the condenser was stopped during this interval.
In the double-acting engine, however, the flow of steam from
the cylinder to the condenser is continued, whether the piston
ascends or descends, and therefore a constant condensation of
steam must be produced. The condensing jet, therefore,
does not in this case, as in the former, play with intervals of
intermission. A constant jet of cold water must be maintained
in the condenser.</div>

<p>It will presently appear that in the double-acting engine
applied to manufactures, the motion of the piston was subject
to more or less variation of speed, and the quantity of steam
<a class="refpn" id="Pg192">[Pg192]</a>
admitted to the cylinder was subject to a corresponding
change. The quantity of steam, therefore, drawn into the
condenser was subject to variation, and required a considerable
change in the quantity of cold water admitted through
the jet to condense it. To regulate this, the valve or cock
by which the water was admitted into the condenser was
worked in the double-acting engine by a lever furnished with
an index, by which the quantity of condensing water admitted
into the condenser could be regulated. This index
played upon a graduated arch, by which the engine-man was
enabled to regulate the supply.</p>

<div class="figcenter" style="width: 447px;">
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_214.png" width="447" height="356" alt="" />
<div class="caption">HEATHFIELD HOUSE, NEAR BIRMINGHAM,
THE RESIDENCE OF WATT.</div>
</div>

<div class="footnotes"><h3>FOOTNOTES:</h3>
<div class="footnote">
<p><a name="Footnote_20_20" id="Footnote_20_20"></a><a href="#FNanchor_20_20"><span class="label">[20]</span></a> These effects are explained in my Treatise on Heat; and they have
lately been verified by experiments made with locomotive engines by
M. de Pambour, who found that the steam raised from the boiler of a locomotive
engine, under a pressure of above 50 lbs. per square inch, was
in the state of common steam as it issued from the chimney at a very
diminished pressure and at a lower pressure.</p></div>

<div class="footnote">
<p><a name="Footnote_21_21" id="Footnote_21_21"></a><a
href="#FNanchor_21_21"><span class="label">[21]</span></a>
It is strange that this absurdity has been repeatedly given as unquestionable
fact in various encyclopÃ¦dias, as well as in by far the greater
number of treatises expressly on the subject.</p></div>

<div class="footnote">
<p><a name="Footnote_22_22" id="Footnote_22_22"></a><a
href="#FNanchor_22_22"><span class="label">[22]</span></a>
Farey, Treatise on the Steam Engine, p. 122.</p></div>

<div class="footnote">
<p><a name="Footnote_23_23" id="Footnote_23_23"></a><a
href="#FNanchor_23_23"><span class="label">[23]</span></a>
Farey on the Steam Engine, p. 297.</p></div></div>

<div class="figcenter" style="width: 467px;">
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_215.png" width="467" height="525" alt="" />
<div class="caption">DOUBLE-ACTING ENGINE.â€”CITY SAW-MILLS.</div>
</div>

<h2><a name="CHAP_VIII" id="CHAP_VIII">CHAP. VIII.</a></h2>

<p class="right"><a class="refpn" id="Pg193">[Pg193]</a><br />
<a href="#CONTENTS"><small>TOC</small></a>&#160;&#160;<a
href="#INDEX"><small>INX</small></a></p>

<div class="chapheader">
METHODS OF CONNECTING THE PISTON-ROD AND BEAM IN THE DOUBLE-ACTING
ENGINE.â€”RACK AND SECTOR.â€”PARALLEL MOTION.â€”CONNECTING
ROD AND CRANK.â€”FLY-WHEEL.â€”THROTTLE-VALVE.â€”GOVERNOR.â€”CONSTRUCTION
AND OPERATION OF THE DOUBLE-ACTING
ENGINE.â€”ECCENTRIC.â€”COCKS AND VALVES.â€”SINGLE-CLACK VALVE.â€”DOUBLE-CLACK
VALVE.â€”CONICAL VALVES.â€”SLIDE VALVES.â€”MURRAY'S
SLIDES.â€”THE D VALVE.â€”SEAWARD'S SLIDES.â€”SINGLE
COCK.â€”FOUR-WAY COCK.â€”PISTONS.â€”COMMON HEMP-PACKED PISTON.â€”WOOLFE'S
PISTON.â€”METALLIC PISTONS.â€”CARTWRIGHT'S ENGINE.â€”CARTWRIGHT'S
PISTON.â€”BARTON'S PISTON.</div>


<div class="ph3fst"><h3>(118.)</h3> In the single-acting engine, the force of the piston
acted on the beam only during its descent; and this force was
transmitted from the piston to the beam, as we have seen, by
a flexible chain, extended from the end of the piston-rod,
<a class="refpn" id="Pg194">[Pg194]</a>
and playing upon the arch head of the beam. In the double-acting
engine, however, the force of the steam pressing the
piston upwards must likewise be transmitted to the beam,
so as to drive the latter upwards while the piston ascends.
This action could not be accomplished by a chain connecting
the piston with the arch head of the beam.</div>

<p>Where the mechanical action to be transmitted is a
<em>pull</em>, and not a <em>push</em>, a flexible chain, cord, or strap, is
sufficient; but if a <em>push</em> or <em>thrust</em> is required to be transmitted,
then the flexibility of the medium of mechanical
communication afforded by a chain renders it inapplicable.
In the double-acting engine, during the descent, the piston-rod
still pulls the beam down; and so far a chain connecting
the piston-rod with the beam would be sufficient to transmit
the action of the one to the other; but in the ascent, the beam
no longer pulls up the piston-rod, but is pushed up by it.
A chain from the piston-rod to the arch head, as described
in the single-acting engine, would fail to transmit this force.
If such a chain were used with the double engine, where
there is no counterweight on the opposite end of the beam,
the consequence would be, that in the ascent of the piston
the chain would slacken, and the beam would still remain
depressed. It is therefore necessary that some other mechanical
connection be contrived between the piston-rod and the
beam, of such a nature that in the <em>descent</em> the piston-rod may
<em>pull</em> the beam down, and may <em>push</em> it up in the <em>ascent</em>.</p>

<div class="figleft" style="width: 61px;">
<a id="Fig035"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_216.png" width="61" height="133" alt="" />
<div class="caption figure">Fig. 35.</div>
</div>

<p>Watt first proposed to effect this by attaching to the end
of the piston-rod a straight rack, faced with teeth, which
should work in corresponding teeth raised on the arch head of
the beam, as represented in <a href="#Fig035"><i>fig.</i> 35.</a> If his improved steam
engines required no further precision of operation
and construction than the atmospheric engines, this
might have been sufficient; but in these engines it
was indispensably necessary that the piston-rod should
be guided with a smooth and even motion through
the stuffing-box in the top of the cylinder, otherwise
any shake or irregularity would cause it to work
loose in the stuffing-box, and either to admit the air, or to let
the steam escape. Under these circumstances, the motion of
<a class="refpn" id="Pg195">[Pg195]</a>
the rack and toothed arch head were inadmissible, since it
was impossible by such means to impart to the piston-rod that
smooth and equable motion which was requisite. Another
contrivance which occurred to Watt was, to attach to the top
of the piston-rod a bar, which should extend above the beam,
and to use two chains or straps, one extending from the top
of the bar to the lower end of the arch head, and the other
from the bottom of the bar to the upper end of the arch head.
By such means the latter strap would pull the beam down
when the piston would descend, and the former would pull the
beam up when the piston would ascend. These contrivances,
however, were superseded by the celebrated mechanism since
called the <em>Parallel Motion</em>, one of the most ingenious
mechanical combinations connected with the history of the
steam engine.</p>

<div class="ph3">
<h3>(119.)</h3> It will be observed that the object was to connect by
some inflexible means the end of the piston-rod with the extremity
of the beam, and so to contrive the mechanism, that
while the end of the beam would move alternately up and down
in part of a circle, the end of the piston-rod connected with the
beam should move up and down in a straight line. If the end of
the piston-rod were fastened upon the end of the beam by a
pivot without any other connection, it is evident that, being
moved up and down in the arch of a circle, it would be drawn
to the left and the right alternately, and would consequently
either be broken or bent, or would work loose in the stuffing-box.
Instead of connecting the end of the rod immediately
with the end of the beam by a pivot, Watt proposed to connect
them by certain moveable rods, so arranged that, as the
end of the beam would move up and down in the circular
arch, the rods would so accommodate themselves to that motion,
that the end connected with the piston-rod should not
be disturbed from its rectilinear course.</div>

<p>To explain the principle of the mechanism called the parallel
motion, let us suppose that <strong>O P</strong> (<a href="#Fig036"><i>fig.</i> 36.</a>) is a rod or lever
moveable on a centre <strong>O</strong>, and that the end <strong>P</strong> of this rod
shall move through a circular arch <strong>P Pâ€² Pâ€³ Pâ€´</strong> a vertical
plane, and let its play be limited by two stops <strong>S</strong>, which shall
prevent its ascent above the point <strong>P</strong>, and its descent below
<a class="refpn" id="Pg196">[Pg196]</a>
the point <strong>Pâ€´</strong>. Let the position of the rod and the limitation
of its play be such that the straight line <strong>A B</strong> drawn through
<strong>P</strong> and <strong>Pâ€´</strong>, the extreme positions of the lever <strong>O P</strong>, shall be a
vertical line.</p>

<div class="figcenter" style="width: 356px;">
<a id="Fig036"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_218.png" width="356" height="632" alt="" />
<div class="caption figure">Fig. 36.</div>
</div>

<p>Let <i>o</i> be a point on the other side of the vertical line <strong>A B</strong>,
and let the distance of <strong>O</strong> to the right of <strong>A B</strong> be the same as
the distance of <i>o</i> to the left of <strong>A B</strong>. Let <i>o p</i> be a rod equal
in length to <strong>O P</strong>, moving like <strong>O P</strong> on the centre <i>o</i>, so that its
<a class="refpn" id="Pg197">[Pg197]</a>
extremity <i>p</i> shall play upwards and downwards through the
arch <i>p pâ€² pâ€³ pâ€´</i>, its play being limited in like manner by
stops <i>s</i>.</p>

<p>Now, let us suppose that the ends <strong>P</strong> <i>p</i> of these two rods are
joined by a link <strong>P</strong> <i>p</i>, the connection being made by a pivot,
so that the angles formed by the link and the rods shall be
capable of changing their magnitude. This link will make
the motion of one rod depend on that of the other, since it
will preserve their extremities <strong>P</strong> <i>p</i> always at the same distance
from each other. If, therefore, we suppose the rod <strong>O P</strong> to be
moved to the position <strong>O Pâ€´</strong>, its extremity <strong>P</strong> tracing the arch
<strong>P Pâ€² Pâ€³ Pâ€´</strong>, the link connecting the rods will at the same time
drive the extremity <i>p</i> of the rod <i>o p</i> through the arch
<i>p pâ€² pâ€³ pâ€´</i> so that when the extremity of the one rod
arrives at <strong>Pâ€´</strong>, the extremity of the other rod will arrive at
<i>pâ€´</i>. By this arrangement, in the simultaneous motion of the
rods, whether upwards or downwards, through the circular
arches to which their play is limited, the extremities of the
link joining them will deviate from the vertical line <strong>A B</strong> in
opposite directions. At the limits of their play, the extremities
of the link will always be in the line <strong>A B</strong>; but in all
intermediate positions, the lower extremity of the link will be
to the right of <strong>A B</strong>, and its upper extremity to the left of <strong>A B</strong>.
So far as the derangement of the lower extremity of the link
is concerned, the matter composing the link would be transferred
to the right of <strong>A B</strong>, and so far as the upper extremity
of the link is concerned, the matter composing it would be
transferred to the left of <strong>A B</strong>.</p>

<p>By the combined effects of these contrary derangements of
the extremities of the link from the vertical line, it might be
expected that a point would exist, in the middle of the link,
where the two contrary derangements would neutralise each
other, and which point would therefore be expected to be
disturbed neither to the right nor to the left, but to be moved
upwards and downwards in the vertical line <strong>A B</strong>. Such is
the principle of the parallel motion; and in fact the middle
point of the link will move for all practical purposes accurately
in the vertical line <strong>A B</strong>, provided that the angular
play of the levers <strong>O P</strong> and <i>o p</i> does not exceed a certain
<a class="refpn" id="Pg198">[Pg198]</a>
limit, within which, in practice, their motion may always be
restrained.</p>

<p>To trace the motion of the middle point of the link more
minutely, let <strong>P Pâ€² Pâ€³ Pâ€´</strong> be four positions of the lever <strong>O P</strong>, and
let <i>p pâ€² pâ€³ pâ€´</i> be the four corresponding positions of the lever
<i>o p</i>. In the positions <strong>O P</strong> <i>o p</i>, the link will take the position
<strong>P</strong> <i>p</i>, in which the entire link will be vertical, and its
middle point <i>x</i> will therefore be in the vertical line <strong>A B</strong>.</p>

<p>When the one rod takes the position <strong>O Pâ€²</strong>, the other rod
will have the position <i>o pâ€²</i>; and the link will have the position
<strong>Pâ€²</strong> <i>pâ€²</i>. The middle point of the link will be at <i>xâ€²</i>, which will
be found to be on the vertical line <strong>A B</strong>. Thus one half of
the link <strong>Pâ€²</strong> <i>xâ€²</i> will be to the left of the vertical line <strong>A B</strong>;
while the other half, <i>pâ€² xâ€²</i>, will be to the right of the vertical
line; the derangement from the vertical line affecting each
half of the link in contrary directions.</p>

<p>Again, taking the one rod in the position <strong>O Pâ€³</strong>, the corresponding
position of the other rod will be <i>o pâ€³</i>, and the
position of the link will be <strong>Pâ€³</strong> <i>pâ€³</i>. If the middle point of the
link in this position be taken, it will be found to be at <i>xâ€³</i>, on
the vertical line <strong>A B</strong>; and, as before, one half of the link
<strong>Pâ€³</strong> <i>xâ€³</i> will be thrown to the left of the vertical line, while
the other half <i>pâ€³ xâ€³</i>, will be thrown to the right of the vertical
line.</p>

<p>Finally, let the one rod be in its lowest position, <strong>O Pâ€´</strong>,
while the other rod shall take the corresponding position,
<i>o pâ€´</i>. The direction of the link <strong>Pâ€´</strong> <i>pâ€´</i> will now coincide
with the vertical line; and its middle point <i>xâ€´</i> will therefore
be upon that line. The previous derangement of the extremities
of the rod, to the right and to the left, are now redressed,
and all the parts of the rod have assumed the vertical
position.</p>

<p>It is plain, therefore, that by such means the alternate
motion of a point such as <strong>P</strong> or <i>p</i>, upwards and downwards in
a circular arch, may be made to produce the alternate motions
of another point <i>x</i>, upwards and downwards in a straight
line.</p>


<div class="ph3"><h3>(<a id="h3-120"></a>120.)</h3> Although the guidance of the air-pump rod in a true
vertical line is not so necessary as that of the steam piston,
<a class="refpn" id="Pg199">[Pg199]</a>
and as the air-pump piston is always brought down by its own
weight and that of its rod, the connection of the air-pump
piston-rod with the beam, by any contrivance of the kind
now described, was not so necessary. Nevertheless, by a
slight addition to the mechanical contrivance which has been
just described, Watt obtained the means of at once preserving
the true rectilinear motion of both piston-rods.</div>

<div class="figcenter" style="width: 384px;">
<a id="Fig037"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_221.png" width="384" height="300" alt="" />
<div class="caption figure">Fig. 37.</div>
</div>

<p>Let the lever represented by <strong>O P</strong> in <a href="#Fig036"><i>fig.</i> 36.</a> be conceived to
be prolonged to twice its length, as represented in <a href="#Fig037"><i>fig.</i> 37.</a>, so
that <strong>O Pâ€²</strong> shall be twice <strong>O P</strong>. Let the points <strong>P</strong> <i>p</i> be connected
by a link as before. Let a link <strong>Pâ€²</strong> <i>xâ€²</i>, equal in length to the
link <strong>P</strong> <i>p</i> be attached to the point <strong>Pâ€²</strong>, and let the extremity <i>xâ€²</i>
of this link be connected with the point <i>p</i> by another link,
equal in length to <strong>P Pâ€²</strong>, by pivots at <i>xâ€²</i> and <i>p</i>, so that the figure
<strong>P Pâ€²</strong> <i>xâ€² p</i> shall be a jointed parallelogram, the angles of which
will be capable of altering their magnitude with every change
of position of the rods <i>o p</i> and <strong>O P</strong>. Thus, when the rod <strong>O P</strong>
descends, the angles of the parallelogram at <strong>P</strong> and <i>xâ€²</i> will be
diminished in magnitude, while the angles at <strong>Pâ€²</strong> and <i>p</i> will be
increased in magnitude. Now, let a line be conceived to
be drawn from <strong>O</strong> to <i>xâ€²</i>. It is evident that that line will
pass through the middle point of the link <i>p</i> <strong>P</strong>, for the triangle
<strong>O P</strong> <i>x</i> is in all respects similar to the greater triangle
<strong>O Pâ€²</strong> <i>xâ€²</i> only on half the scale, so that every side of the one is
<a class="refpn" id="Pg200">[Pg200]</a>
half the corresponding side of the other. Therefore <strong>P</strong> <i>x</i> is
half the length of <strong>Pâ€²</strong> <i>xâ€²</i>; but <strong>Pâ€²</strong> <i>xâ€²</i> was made equal to <strong>P</strong> <i>p</i>, and
therefore <i>p</i> <i>x</i> is half of <strong>P</strong> <i>p</i>, that is to say, <i>x</i> is the middle
point of <strong>P</strong> <i>p</i>.</p>

<p>It has been already shown, that in the alternate motion of
the rods <i>o p</i>, <strong>O P</strong> in ascending and descending, the point <i>x</i> is
moved upwards and downwards in a true vertical line. Now
since the triangle <strong>O P</strong> <i>x</i> is in all respects similar to <strong>O Pâ€²</strong> <i>xâ€²</i>,
and subject to a similar motion during the ascent and descent
of the rods, it is apparent that the point <i>xâ€²</i> must be
subject to a motion in all respects similar to that which affects
the points <i>x</i>, except that the point <i>xâ€²</i> will move through
double the space. In fact, the principle of the mechanism is
precisely similar to that of the common pantograph, where two
rods are so connected as that the motion of the one governs
the motion of the other, so that whatever line or figure may
be described by one, a similar line or figure must be described
by the other. Since, then, the point <i>x</i> is moved upwards and
downwards in a vertical straight line, the point <i>xâ€²</i> will also be
moved in a vertical straight line of double the length.</p>

<p>If such an arrangement of mechanism as has been here described
can be connected with the beam of the steam engine,
so that while the point <i>xâ€²</i> is attached to the top of the steam
piston, and the space through which it ascends and descends
shall be equal to the length of the stroke of that piston, the
point <i>x</i> shall be attached to the rod of the air-pump piston,
the stroke of the latter being half that of the steam piston,
then the points <i>xâ€²</i> and <i>x</i> will guide the motion of the two pistons
so as to preserve them in true vertical straight lines.</p>

<p>The manner in which these ideas are reduced to practice
admits of easy explanation: let the point <strong>O</strong> be the centre of
the great working beam, and let <strong>O Pâ€²</strong> be the arm of the beam
on the side of the steam cylinder. Let <strong>P</strong> be a pivot upon the
beam, at the middle point between its centre <strong>O</strong> and its extremity
<strong>Pâ€²</strong>; and let the links <strong>P</strong> p, <strong>Pâ€²</strong> <i>xâ€²</i>, and <strong>P</strong> <i>p</i> be jointed together,
as already described. Let the point or pivot <i>o</i> be attached
to some part of the fixed framing of the engine or engine
house, and let the rod <i>o p</i>, equal to half the arm of the beam,
be attached by a pivot to the corner of the parallelogram at
<a class="refpn" id="Pg201">[Pg201]</a>
<i>p</i>. Let the end of the steam piston-rod be attached to the
corner of the parallelogram <i>xâ€²</i>, and let the end of the air-pump
be attached to the middle point <i>x</i> of the link <strong>P</strong> <i>p</i>;
by which arrangement it is evident that the rectilinear motion
of the two piston-rods will be rendered compatible with
the alternate circular motions of the points <strong>Pâ€²</strong> and <strong>P</strong> on the
beam.</p>

<p>Among the many mechanical inventions produced by the
fertile genius of Watt, there is none which has excited such
universal, such unqualified, and such merited admiration as
that of the parallel motion. It is indeed impossible, even
for an eye unaccustomed to view mechanical combinations, to
behold the beam of a steam engine moving the pistons,
through the instrumentality of the parallel motion, without
an instinctive feeling of pleasure at the unexpected fulfilment
of an end by means having so little apparent connection
with it. When this feeling was expressed to Watt himself,
by those who first beheld the performance of this exquisite
mechanism, he exclaimed with his usual vivacity, that he
himself, when he first beheld his own contrivance in action,
was affected by the same sense of pleasure and surprise at its
regularity and precision. He said, that he received from it
the same species of enjoyment that usually accompanies the
first view of the successful invention of another person.</p>

<p>"Among the parts composing the steam engine, you have
doubtless," says M. Arago, "observed a certain articulated
parallelogram. At each ascent and descent of the piston, its
angles open and close with the sweetnessâ€”I had almost said
with the graceâ€”which charms you in the gestures of a consummate
actor. Follow with your eye alternately the progress
of its successive changes, and you will find them subject
to the most curious geometrical conditions. You will see, that
of the four angles of the jointed parallelogram, three describe
circular arches, but the fourth which holds the piston-rod
is moved nearly in a straight line. The immense utility of
this result strikes mechanicians with even less force than the
simplicity of the means by which Watt has attained it."</p>

<p>The parallel motion, of which there are several other varieties,
depending, however, generally upon the same
<a class="refpn" id="Pg202">[Pg202]</a>
principle, formed part of a patent which Mr. Watt obtained in the
year 1784, another part of which patent was for a locomotive
engine, by which a carriage was to be propelled on a road.
In a letter to Mr. Smeaton dated 22d October, in the same
year, Watt says,â€”</p>

<p>"I have lately contrived several methods of getting entirely
rid of all the chains and circular arches about the great levers
of steam engines, and nevertheless making the piston-rods
ascend and descend perpendicularly, without any sliding motions
or right-lined guides, merely by combinations of motions
about centres; and with this further advantage, that they
answer equally well to push upwards as to pull downwards,
so that this method is applicable to our double engines which
act both in the ascent and descent of their pistons.</p>

<p>"A rotative engine of this species with the new motion
which is now at work in our manufactory (but must be sent
away very soon) answers admirably. It has cost much brain
work to contrive proper working gear for these double engines,
but I have at last done it tolerably well, by means of
the circular valves, placed in an inverted position, so as to be
opened by the force of the steam; and they are kept shut by
the working gear. We have erected an engine at Messrs.
Goodwyne and Co.'s brewery, East Smithfield, London."</p>

<div class="figright" style="width: 297px;">
<a id="Fig038"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_225.png" width="297" height="581" alt="" />
<div class="caption figure">Fig. 38.</div>
</div>

<div class="ph3"><h3>(121.)</h3> By the contrivance which has been explained above,
the force of the piston in ascending and descending would be
conveyed to the working end of the beam; and the next problem
which Watt had to solve was, to produce by the force
exerted by the working end of the beam in ascending and descending
a continuous motion of rotation. In the first instance
he proposed to accomplish this by a crank placed upon
the axle to which rotation was to be imparted, and driven by
a rod connecting it with the working end of the beam. Let
<strong>K</strong> (<a href="#Fig038"><i>fig.</i> 38.</a>) be the centre, to which motion is to be imparted
by the working end <strong>H</strong> of the beam. On the axle <strong>K</strong> suppose
a short lever <strong>K I</strong> to be fixed so that when <strong>K I</strong> is turned round
the centre <strong>K</strong>, the axle must turn with it. Let an iron rod,
the weight of which shall balance the piston and piston-rod
at the other end of the beam, be connected by joints with
the working end <strong>H</strong> of the beam, and the extremity <strong>I</strong> of the
<a class="refpn" id="Pg203">[Pg203]</a>
lever <strong>K I</strong>. As the end <strong>H</strong> of the beam is moved upwards and
downwards, the lever <strong>K I</strong> will be turned round the centre <strong>K</strong>,
taking successively
the positions represented
by faint lines
in the figure; and thus
a motion of continued
rotation will be imparted
to the axle <strong>K</strong>.</div>

<p>This simple and
effectual expedient
of producing a continued
rotatory motion
by a crank was
abandoned by Watt,
as already explained,
by reason of a patent
having been obtained
upon information of
his experiments surreptitiously
procured.
To avoid litigation,
he therefore substituted
for the crank
the sun and planet
wheel already described;
but at the
expiration of the
patent, which restricted
the use of
the crank, the sun and planet wheel was discontinued in
Watt's engine, and the crank restored.</p>


<div class="ph3"><h3>(122.)</h3> Whether the crank or the sun and planet wheel be
used, there is still a difficulty in the maintenance of a regular
motion of rotation. In the various positions which the crank
and connecting rod assume throughout a complete revolution,
there are two in which the moving power loses all influence
in impelling the crank. These positions are those which the
crank assumes when the piston is at the top and bottom of the
<a class="refpn" id="Pg204">[Pg204]</a>
cylinder, and is just about to change the direction of its motion.
When the piston is at the bottom of the cylinder,
the pivot <strong>I</strong> (<a href="#Fig038"><i>fig.</i> 38.</a>), by which the connecting rod <strong>H I</strong> is attached
to the end of the crank, is immediately over the axle
<strong>K</strong> of the crank, and under the pivot <strong>H</strong>, which joins the upper
end of the connecting rod with the beam. In fact, in this
position the connecting rod and crank are in the same
straight line, extending from the end of the beam to the axle
of the crank. The steam, on entering the cylinder below the
piston, and pressing it upwards, would produce a corresponding
downward force on the connecting rod at <strong>H</strong>, which would
be continued along the connecting rod and crank to the axle
<strong>K</strong>. It is evident that such a force could have no tendency to
turn the crank round, but would expend its whole energy in
pressing the axle <strong>K</strong> downwards.</div>

<p>The other position in which the power loses its effect upon
the crank is when the piston is at the top of the cylinder. In
this case, the working end of the beam will be at the lowest
point of its play, and the crank-pin <strong>I</strong> will be immediately
below the axle <strong>K</strong>; so that <strong>K</strong> will be placed immediately between
<strong>H</strong> and <strong>I</strong>. When the steam presses on the top of the
piston, it will expend its force in drawing the end <strong>H</strong> of the
connecting rod upwards, by which the crank-pin <strong>I</strong> will likewise
be drawn upwards. It is evident that this force can have
no effect in turning the crank round, but will expend its whole
energy in producing an upward strain on the axle <strong>K</strong>.</p>

<p>If the crank were absolutely at rest in either of the positions
above described, it is apparent that the engine could not be
put in motion by the steam; but if the engine has been
previously in motion, then the mass of matter forming the
crank, and the axle on which the crank is formed, having already
had a motion of rotation, will have a tendency to preserve
the momentum it has received, and this tendency will
be sufficient to throw the crank <strong>K I</strong> out of either of those critical
positions which have been described. Having once escaped
these dead points, then the connecting rod forming an
angle, however obtuse or acute, with the crank, the pressure
or pull upon the former will have a tendency to produce rotation
in the latter. As the crank revolves, however, the influence
<a class="refpn" id="Pg205">[Pg205]</a>
of the connecting rod upon it will vary according to the
angle formed by the connecting rod and crank. When that
angle is a right angle, then the effect of the connecting rod
on the crank is greatest, since the force upon it has the advantage
of the whole leverage of the crank; but according as
the angle formed by the crank and connecting rod becomes
more or less acute or obtuse in the successive attitudes which
they assume in the revolution of the crank, the influence of the
connecting rod over the crank varies, changing from nothing
at the two dead points already described, to the full effect
produced in the two positions where they are at right angles.
In consequence of this varying leverage, by which the force
with which the connecting rod is driven by the steam is transmitted
to the axle on which the crank revolves, a corresponding
variation of speed would necessarily be produced in the
motion imparted to the crank. The speed at the dead points
would be least, being due altogether to the momentum already
imparted to the revolving mass of the crank and axle; and it
would gradually increase and be greatest at the points where
the effect of the crank on the connecting rod is greatest.
Although this change of speed would not affect the actual mechanical
efficacy of the machine, and although the same quantity
of steam would perform the same work at the varying
velocity as it would do if the velocity were regulated, yet this
variation of speed would be incompatible with the purposes
to which it was now proposed that the steam engine should
be applied in manufactures. In these a regular uniform motion
should be imparted to the main axle.</p>


<div class="ph3"><h3>(123.)</h3> One of the expedients which Watt proposed for the
attainment of this end was, by placing two cranks on the same
axle, in different positions, to be worked by different cylinders,
so that while one crank should be at its dead points, the
other should be in the attitude most favourable for its action.
This expedient has since, as we shall see, been carried into
effect in steam vessels; but one more simple and efficient
presented itself in the use of a <em>fly-wheel</em>.</div>

<p>On the main axle driven by the crank Watt placed a large
wheel of metal, as represented in <a href="#Fig043"><i>fig.</i> 43.</a>, called a <em>fly-wheel</em>.
This wheel being well constructed, and nicely balanced on its
<a class="refpn" id="Pg206">[Pg206]</a>
axle, was subject to very little resistance from friction; any
moving force which it would receive it would therefore
retain, and would be ready to impart such moving force to
the main axle whenever that axle ceased to be driven by the
power. When the crank, therefore, is in those positions in
which the action of the power upon it is most efficient, a
portion of the energy of the power is expended in increasing
the velocity of the mass of matter composing the fly-wheel.
As the crank approaches the dead points, the effect of the
moving power upon the axle and upon the crank is gradually
enfeebled, and at these points vanishes altogether. The
momentum which has been imparted to the fly-wheel then
comes into play, and carries forward the axle and crank out
of the dead points with a velocity very little less than that
which it had when the crank was in the most favourable
position for receiving the action of the moving power.</p>

<p>By this expedient, the motion of revolution received by
the axle from the steam piston is subject to no other variation
than just the amount of change of momentum in the great
mass of the fly-wheel, which is sufficient to extricate the crank
twice in every revolution from the mechanical dilemma to
which its peculiar form exposes it; and this change of velocity
may be reduced to as small an amount as can be requisite by
giving the necessary weight and magnitude to the fly-wheel.</p>


<div class="ph3"><h3>(124.)</h3> By such arrangements the motion imparted to the
main axle <strong>K</strong> would be uniform, provided that the moving
power of the engine be always proportionate to the load which
it drives. But in the general application of the steam engine
to manufactures it was evident that the amount of the resistance
to which any given machine would be subject must be liable
to variation. If, for example, the engine drive a cotton-mill,
it will have to impart motion to all the spinning frames in that
mill. The operation of one or more of these may from time
to time be suspended, and the moving power would be relieved
from a corresponding amount of resistance. If, under
such circumstances, the energy of the moving power remained
the same, the velocity with which the machines would be
driven would be subject to variation, being increased whenever
the operation of any portion of the machines usually
<a class="refpn" id="Pg207">[Pg207]</a>
driven by it is suspended; and, on the other hand, diminished
when any increased number of machines are brought into
operation. In fine, the speed would vary nearly in the inverse
proportion of the load driven, increasing as the load is diminished,
and <i>vice versÃ¢</i>.</div>

<p>On the other hand, supposing that no change took place in
the amount of the load driven by the engine, and that the
same number of machines of whatever kind would have to be
continually driven, the motion imparted to the main axle
would still be subject to variation by the changes inevitable
to the moving power. The piston of the engine being subject
to an unvaried resistance, a uniform motion could only be imparted
to it, by maintaining a corresponding uniformity in
the impelling power. This would require a uniform supply
of steam from the boiler, which would further imply a uniform
rate of evaporation in the boiler, unless means were provided
in the admission of steam from the boiler to the cylinder to
prevent any excess of steam which might be produced in the
boiler from reaching the cylinder.</p>

<div class="figleft" style="width: 126px;">
<a id="Fig039"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_229.png" width="126" height="108" alt="" />
<div class="caption figure">Fig. 39.</div>
</div>

<div class="figleft" style="width: 142px;">
<a id="Fig040"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_229b.png" width="142" height="171" alt="" />
<div class="caption figure">Fig. 40.</div>
</div>

<p>This end was attained by a contrivance afterwards called the
<em>throttle-valve</em>. An axis <strong>A B</strong> (<i>figs.</i> 39, 40.)
was placed across
the steam pipe in a ring of cast-iron <strong>D E</strong>,
of proper thickness. On this axis was fastened
a thin circular plate <strong>T</strong>, of nearly
the same diameter as the steam pipe. On
the outer end <strong>B</strong> of this axle was placed a
short lever or handle <strong>B C</strong>, by which it
could be turned. When the circular plate
<strong>T</strong> was turned into such a position as to be
at right angles to the length of the tube,
it stopped the passage within the tube
altogether, so that no steam could pass
from the boiler to the engine. On the other
hand, when the handle was turned through
a fourth of a revolution from this position,
then the circular plate <strong>T</strong> had its plane in the direction of the
length of the tube, so that its edge would be presented
towards the current of steam flowing from the boiler to the
cylinder. In that position the passage within the tube
<a class="refpn" id="Pg208">[Pg208]</a>
would be necessarily unobstructed by the throttle-valve.
In intermediate positions of the valve, as that represented in
<i>figs.</i> 39, 40., the passage might be left more or less opened, so
that steam from the boiler might be admitted to the
cylinder in any regulated quantity according to the position
given to the lever <strong>B C</strong>.</p>

<p>A view of the throttle-valve taken by a section across the
steam pipe is exhibited in <a href="#Fig040"><i>fig.</i> 40.</a>, and a section of it through
the axis of the steam pipe is represented in <a href="#Fig039"><i>fig.</i> 39.</a> The
form of the valve is such, that, if accurately constructed, the
steam in passing from the boiler would have no effect by its
pressure to alter any position which might be given to the
valve; and any slight inaccuracy of form which might give a
tendency to the steam to alter the position would be easily
counteracted by the friction of the valve upon its axle. The
latter might be regulated at pleasure.</p>

<p>By this expedient, however the evaporation of water in the
boiler might vary within practical limits, the supply of steam
to the cylinder would be rendered regular and uniform. If
the boiler became too active, and produced more steam than
was necessary to move the engine with its load at the requisite
speed, then the throttle-valve was shifted so as to contract
the passage and limit the supply of steam. If, on the other
hand, the process of evaporation in the boiler was relaxed,
then the throttle-valve was placed with its edge more directed
towards the steam. Independently of the boiler, if the load
on the engine was lightened, then the same supply of steam to
the cylinder would unduly accelerate the motion. In this
case, likewise, the partial closing of the throttle-valve would
limit the supply of steam and regulate the motion; and if, on
the other hand, the increase of load upon the engine rendered
necessary an increased supply of steam, then the opening of
the throttle-valve would accomplish the purpose. By these
means, therefore, a uniform motion might be maintained,
provided the vigilance of the engine-man was sufficient
for the due management of the lever <strong>B C</strong>, and provided that
the furnace under the boiler was kept in sufficient activity to
supply the greatest amount of steam which would be necessary
<a class="refpn" id="Pg209">[Pg209]</a>
for the maintenance of a uniform motion with the throttle-valve
fully opened.</p>


<div class="ph3"><h3>(125.)</h3> Watt, however, soon perceived that the proper
manipulation of the lever <strong>B C</strong> would be impracticable with
any degree of vigilance and skill which could be obtained
from the persons employed to attend the engine. He, therefore,
adapted to this purpose a beautiful application of a piece
of mechanism, which had been previously used in the regulation
of mill-work, and which has since been well known
by the name of the <em>Governor</em>, and has always been deservedly
a subject of much admiration.</div>

<p>The governor is an apparatus by which the axle of the
fly-wheel is made to regulate the throttle-valve, so that the
moment that the axle begins to increase its velocity, it shifts
the position of the throttle-valve, so as to limit the supply of
steam from the boiler, and thereby to check the increase of
speed. And on the other hand, whenever the velocity of the
axle is diminished, the lever <strong>B C</strong> is moved in the contrary
direction, so as to open more fully the passage for the steam,
and accelerate the motion of the engine.</p>

<p>A small grooved wheel <strong>A B</strong> (<a href="#Fig041"><i>fig.</i> 41.</a>) is attached to a vertical
spindle supported in pivots or sockets <strong>C</strong> and <strong>D</strong>, in which it is
capable of revolving. An endless cord works in the groove
<strong>A B</strong>, and is carried over proper pulleys to the axle of the fly-wheel,
where it likewise works in a groove. When this cord
is properly tightened the motion of the fly-wheel will give
motion to the wheel <strong>A B</strong>, so that the velocity of the one will
be subject to all the changes incidental to the velocity of
the other. By this means the speed of the grooved wheel
<strong>A B</strong> may be considered as representing the speed of the fly-wheel,
and of the machinery which the axle of the fly-wheel
drives.</p>

<div class="figcenter" style="width: 422px;">
<a id="Fig041"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_232.png" width="422" height="324" alt="" />
<div class="caption figure">Fig. 41.</div>
</div>

<p>It is evident that the same end might be attained by substituting
for the grooved wheel <strong>A B</strong> a toothed wheel, which
might be connected by other toothed wheels, and proper
shafts, and axles with the axle of the fly-wheel.</p>

<p>A ring or collar <strong>E</strong> is placed on the upright spindle, so as
to be capable of moving freely upwards and downwards. To
this ring are attached by pivots two short levers, <strong>E F</strong>, the
<a class="refpn" id="Pg210">[Pg210]</a>
pivots or joints at <strong>E</strong> allowing these levers to play upon them.
At <strong>F</strong> these levers are joined by pivots to other levers <strong>F G</strong>,
which cross each other at <strong>H</strong>, where an axle or pin passes
through them, and attaches them to the upright spindle <strong>C D</strong>.
These intersecting levers are capable, however, of playing on
this axle or pin <strong>H</strong>. To the ends <strong>G</strong> of these levers are
attached two heavy balls of metal <strong>I</strong>. The levers <strong>F G</strong> pass
through slits in a metallic arch attached to the upright spindle,
so as to be capable of revolving upon it. If the balls <strong>I</strong> are
drawn outwards from the vertical axis, it is evident that the
ends <strong>F</strong> of the levers will be drawn down, and therefore the
pivots <strong>E</strong> likewise drawn down. In fact, the angles <strong>E F H</strong> will
become more acute, and the angle <strong>F E F</strong> more obtuse. By
these means the sliding ring <strong>E</strong> will be drawn down. To this
sliding ring <strong>E</strong>, and immediately above it, is attached a grooved
collar, which slides on the vertical spindle upwards and downwards
with the ring <strong>E</strong>. In the grooved collar are inserted the
prongs of a fork <strong>K</strong>, formed at the end of the lever <strong>K L</strong>, the
fulcrum or pivot of the lever being at <strong>L</strong>. By this arrangement,
when the divergence of the balls <strong>I</strong> causes the collar <strong>E</strong> to
be drawn down, the fork <strong>K</strong>, whose prongs are inserted in the
groove of that collar, is likewise drawn down; and, on the
other hand, when, by reason of the balls <strong>I</strong> falling towards the
<a class="refpn" id="Pg211">[Pg211]</a>
vertical spindle, the collar <strong>E</strong> is raised, the fork <strong>K</strong> is likewise
raised.</p>

<p>The ascent and descent of the fork <strong>K</strong> necessarily produce
a contrary motion in the other end <strong>N</strong> of the lever. This
end is connected by a rod, or system of rods, with the
end <strong>M</strong> of the short lever which works the throttle-valve
<strong>T</strong>. By such means the motion of the balls <strong>I</strong>, towards or from
the vertical spindle, produces in the throttle-valve a corresponding
motion; and they are so connected that the divergence
of the balls <strong>I</strong> will cause the throttle-valve to close, while
their descent towards the vertical spindle will cause it to
open.</p>

<p>These arrangements being comprehended, let us suppose
that, either by reason of a diminished load upon the engine
or an increased activity of the boiler, the speed has a tendency
to increase. This would impart increased velocity to the
grooved wheel <strong>A B</strong>, which would cause the balls <strong>I</strong> to revolve
with an accelerated speed. The centrifugal force which
attends their motion would therefore give them a tendency to
move from the axle, or to diverge. This would cause, by
the means already explained, the throttle-valve <strong>T</strong> to be
partially closed, by which the supply of steam from the boiler
to the cylinder would be diminished, and the energy of the
moving power, therefore, mitigated. The undue increase of
speed would thereby be prevented.</p>

<p>If, on the other hand, either by an increase of the load, or
a diminished activity in the boiler, the speed of the machine
was lessened, a corresponding diminution of velocity would
take place in the grooved wheel <strong>A B</strong>. This would cause the
balls <strong>I</strong> to revolve with less speed, and the centrifugal force
produced by their circular motion would be diminished. This
force being thus no longer able fully to counteract their
gravity, they would fall towards the spindle, which would
cause, as already explained, the throttle-valve to be more fully
opened. This would produce a more ample supply of steam
to the cylinder, by which the velocity of the machine would be
restored to its proper amount.</p>

<div class="figcenter" style="width: 371px;">
<a id="Fig042"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_234.png" width="371" height="250" alt="" />
<div class="caption figure">Fig. 42.</div>
</div>

<div class="ph3"><h3>(126.)</h3> The principle which renders the governor so perfect
a regulator of the velocity of the machine is difficult to be
<a class="refpn" id="Pg212">[Pg212]</a>
explained without having recourse to the aid of the technical
language of mathematical physics. As, however, this instrument
is of such great practical importance, and has attracted
such general admiration, it may be worth while here to
attempt to render intelligible the mechanical principles which
govern its operation. Let <strong>S</strong> (<a href="#Fig042"><i>fig.</i> 42.</a>) be the point of suspension
of a common pendulum <strong>S P</strong>, and let <strong>P O Pâ€²</strong> be the arch
of its vibration, so that the ball <strong>P</strong> shall swing or vibrate
alternately to the east and to the west of the lowest point <strong>O</strong>,
through the arches <strong>O Pâ€²</strong> and <strong>O P</strong>. It is a property of such an
instrument that, provided the arch in which it vibrates be not
considerable in magnitude, the time of its vibration will be
the same whether the arch be long or short. Thus, for example,
if the pendulum, instead of vibrating in the arch <strong>P Pâ€²</strong>,
vibrated in the arch <i>p pâ€²</i>, the time which it would take to
perform its vibrations would be the same. If, however, the
magnitude of the arch of vibration be increased, then a variation
will take place in the time of vibration; but unless the
arch of vibration be considerably increased, this variation will
not be great.</div>

<p>Now let it be supposed that while the pendulum <strong>P Pâ€²</strong> continues
to vibrate east and west through the arch <strong>P Pâ€²</strong>, it shall
receive such an impulse from north and south as would,
if it were not in a state of previous vibration, cause it to
vibrate between north and south, in an arch similar to the
arch <strong>P Pâ€²</strong>. This second vibration between north and south
<a class="refpn" id="Pg213">[Pg213]</a>
would not prevent the continuance of the other vibration between
east and west; but the ball <strong>P</strong> would be at the same
time affected by both vibrations. While, in virtue of the
vibration from east to west, the ball would swing from <strong>P</strong> to
<strong>Pâ€²</strong>, it would, in virtue of the other vibration, extend its motion
towards the north to a distance from the line <strong>W E</strong> equal to
half a vibration, and will return from that distance again to
the position <strong>Pâ€²</strong>. While returning from <strong>Pâ€²</strong> to <strong>P</strong>, its second
vibration will carry it towards the south to an equal distance
on the southern side of <strong>W E</strong>, and it will return again to the
position <strong>P</strong>. If the combination of these two motions or
vibrations be attentively considered, it will be perceived that
the effect on the ball will be a circular motion, precisely
similar to the circular motion of the balls of the governor
already described.</p>

<p>Now the time of vibration of the pendulum <strong>S P</strong> between
east and west will not in any way be affected by the second
vibration, which it is supposed to receive between north and
south, and therefore the time the pendulum takes in moving
from <strong>P</strong> to <strong>Pâ€²</strong> and back again from <strong>Pâ€²</strong> to <strong>P</strong> will be the same
whether it shall have simultaneously or not the other vibration
between north and south. Hence it follows that the time of
revolution of the circular pendulum will be equal to the time
of similar vibrations of the same pendulum, if, instead of
having a circular motion, it were allowed to vibrate in the
manner of a common pendulum.</p>

<p>If this point be understood, and if it also be remembered
that the time of vibration of a common pendulum is necessarily
the same whether the arch of vibration be small or
great, it will be easily perceived that the revolving pendulum
or governor will have nearly the same time of revolution
whether it revolve in a large circle or a small one: in other
words, whether the balls revolve at a greater or a less distance
from the central spindle or axis. This, however, is to be understood
only approximately. When the angle of divergence
of the balls is as considerable as it usually is in governors,
the time of revolution at different distances from the axis will
therefore be subject to some variation, but to a very small
one.
<a class="refpn" id="Pg214">[Pg214]</a></p>

<p>The centrifugal force (which is the name given in mechanics
to that influence which makes a body revolving in a circle fly
from the centre) depends conjointly on the velocity of revolution,
and on the distance of the revolving body from the
centre of the circle. If the velocity of revolution be the
same, then the centrifugal force will increase in the same proportion
as the distance of the revolving body from the centre.
If, on the other hand, the distance of the revolving body from
the centre remain the same, the centrifugal force will increase
in the same proportion as the square of the time of vibration
diminishes, or, in other words, it will increase in the same
proportion as the square of the number of revolutions per
minute. It follows from this, therefore, that the greater is
the divergence of the balls of the governor, and the more
rapidly they revolve, the greater will be their centrifugal
force. Now this centrifugal force, if it were not counterbalanced,
would give the balls a constant tendency to recede
from the centre; but from the construction of the apparatus,
the further they are removed from the centre the greater will
be the effect of their gravitation in resisting the centrifugal
force.</p>

<p>It is evident that the ball at <strong>P</strong> will have a greater tendency
to fall by gravitation towards <strong>O</strong> than it would have at <i>p</i>, because
the acclivity of the arch descending towards <strong>O</strong> at <strong>P</strong> is
greater than its acclivity at <i>p</i>. The gravitation, therefore, or
tendency of the ball to fall towards the central axis being
greater at <strong>P</strong> than at <i>p</i> it will be able to resist a greater centrifugal
force. This increased centrifugal force, which the
ball would have revolving at the distance <strong>P</strong> above what it
would have at the distance <i>p</i>, is produced partly by the
greater distance of the ball from the central axis, and partly
by the greater velocity of its motion. But it will be evident
that the time of its revolution may nevertheless be the same,
or nearly the same, at both distances. If it should appear
that the actual velocity of its motion of revolution at <strong>P</strong> be
greater than its velocity at <i>p</i>, in the same proportion as the
circles in which they revolve, then it is evident that the time
of revolution would be as much increased by the greater
space which <strong>P</strong> will have to travel over, as it will have to be
<a class="refpn" id="Pg215">[Pg215]</a>
diminished by the greater speed with which that space is
traversed. The time of revolution, therefore, may be the
same, or nearly the same, in both cases.</p>

<p>If this explanation be comprehended, it will not be difficult
to apply it to the actual case of the governor. If a sudden
increase of the energy of the moving power, or a diminution
of the load, should give the machine an increased velocity,
then the increased speed of the balls of the governor will give
them an increased centrifugal force, which for the moment
will be greater than the tendency of their gravitation to make
them fall towards the vertical axis. This centrifugal force,
therefore, prevailing, the balls will recede from the axis; but
as they recede, their gravitation towards the vertical axis
will, as has been already explained, be increased, and will
become equal to the centrifugal force produced by the
increased velocity, provided that velocity do not exceed
a certain limit. When the balls, by diverging, get such
increased gravitation as to balance the centrifugal force, then
they will continue to revolve at a fixed distance from the
vertical axis. When this happens, the time of the revolution
must be nearly the same as it was before their increased
divergence; in other words, the proportion of the moving
power to the load will be so restored by the action of the
levers of the governor on the throttle-valve that the machine
will move at its former velocity, or nearly so.</p>

<p>The principle on which the governor acts, as just explained,
necessarily supposes temporary disarrangements of the speed.
In fact, the governor, strictly speaking, does not maintain
a uniform velocity, but restores it after it has been disturbed.
When a sudden change of motion of the engine
takes place, the governor being immediately affected will
cause a corresponding alteration in the throttle-valve; and
this will not merely correct the change of motion, but it will,
as it were, overdo it, and will cause a derangement of speed
of the opposite kind. Thus if the speed be suddenly increased
to an undue amount, then the governor being affected
will first close the throttle-valve too much, so as to reduce
the speed below the proper limit. This second error will
again affect the governor in the contrary way, and the speed
<a class="refpn" id="Pg216">[Pg216]</a>
will again be increased rather too much. In this way a
succession of alterations of effect will ensue until the governor
settles down into that position in which it will maintain the
engine at the proper speed.</p>

<p>To prevent the inconvenience which would attend any
excess of such variations, the governor is made to act with
great delicacy on the throttle-valve, so that even a considerable
change in the divergence of the balls shall not produce
too much alteration in the opening of that valve: the steam
in the boiler should have at least 2 lbs. per square inch
pressure more than is generally required in the cylinder.
This excess is necessary to afford scope for that extent of
variation of the power which it is the duty of the throttle-valve
to regulate.</p>

<p>The governor is usually so adjusted as to make thirty-six
revolutions per minute, when in uniform motion; but if the
motion is increased to the rate of thirty-nine revolutions, the
balls will fly to the utmost extent allowed them, being the
limitation of the grooves in which their rods move; and if, on
the other hand, the speed be diminished to thirty-four revolutions
per minute, they will collapse to the lowest extent of
their play. The duty of the governor, therefore, is to correct
smaller casual derangements of the velocity; but if any permanent
change to a considerable extent be made either in
the load driven by the machine or in the moving power supplied
to it from the boiler, then a permanent change is
necessary to be made in the connection between the governor
and the throttle-valve, so as to render the governor capable of
regulating those smaller changes to which the speed of the
machine is liable.</p>


<div class="ph3"><h3>(127.)</h3> Having thus explained the principal mechanical contrivances
provided by Watt for the maintenance and regulation
of the rotatory motion to be produced by his double-acting
steam engine, let us now consider the machine as a whole, and
investigate the process of its operation. A section of this
engine is represented in <a href="#Fig043"><i>fig.</i> 43.</a></div>

<div class="figcenter" style="width: 481px;">
<a id="Fig043"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_240.png" width="481" height="539" alt="" />
<div class="caption figure">Fig. 43.</div>
</div>

<p>Steam is supplied from the boiler to the cylinder by the
steam pipe <strong>S</strong>. The throttle-valve <strong>T</strong> in that pipe, near the
cylinder, is regulated by a system of levers connected with
<a class="refpn" id="Pg217">[Pg217]</a>
the governor. The piston <strong>P</strong> is accurately fitted in the steam
cylinder <strong>C</strong> by packing, as already described in the single-acting
engine. This piston, as it moves, divides the cylinder
into two compartments, between which there is no communication
by which steam or any other elastic fluid can pass.
The upper steam box <strong>B</strong> is divided into three compartments
by the two valves. Above the upper steam valve <strong>V</strong> is a compartment
communicating with the steam pipe; below the upper
exhausting valve <strong>E</strong> is another compartment communicating
with the eduction pipe which leads to the condenser. By the
valves <strong>V</strong> and <strong>E</strong> a communication may be opened or closed
between the boiler on the one hand, or the condenser on the
other, and the top of the cylinder. The continuation <strong>Sâ€²</strong> of
the steam pipe leads to the lower box <strong>Bâ€²</strong>, which, like
the upper, is divided into three compartments by two
valves <strong>Vâ€²</strong> and <strong>Eâ€²</strong>. The upper compartment communicates
with the steam pipe, and thereby with the boiler; and the
lower compartment communicates with the eduction pipe,
and thereby with the condenser. By means of the two valves
<strong>Vâ€²</strong> and <strong>Eâ€²</strong>, a communication may be opened or closed between
the steam pipe on the one hand, or the exhausting pipe on
the other, and the lower part of the cylinder. The four
valves <strong>V</strong>, <strong>E</strong>, <strong>Vâ€²</strong>, and <strong>Eâ€²</strong> are connected by a system of levers
with a handle or spanner <i>m</i>, which, being driven downwards
or upwards, is capable of opening or closing the valves in
pairs, in the manner already described (<a href="#h3-116">116</a>.). The condensers,
the air-pump, and the hot-water pump, are in all
respects similar to those already described in the single-acting
engine, except that the condensing jet is governed by a lever
<strong>I</strong>, by which it is allowed to play continually in the condenser,
and by which the quantity of water admitted through it is
regulated. The cold-water pump <strong>N</strong> is worked by the engine
as already described in the single-acting engine, and supplies
the cistern in which the air-pump and condenser are submerged,
so as to keep down its temperature to the proper
limit. On the air-pump rod <strong>R</strong> are two pins properly placed,
so as to strike the spanner <i>m</i>, upwards and downwards, at the
proper times, when the piston approaches the termination of
the stroke at the top or bottom of the cylinder. The pump <strong>L</strong>
<a class="refpn" id="Pg218">[Pg218]</a>
conducts the warm water drawn by the air-pump from the
condenser to a proper reservoir for feeding the boiler. The
vertical motion of the piston-rod in a straight line is rendered
compatible with the circular motion of the end of the beam
by the parallel motion already described. The point <i>b</i>, on
the beam, moves upwards and downwards in a circular arch,
of which the axis of the beam is the centre. In like manner
the point <i>d</i> of the rod <i>d c</i> moves upwards and downwards, in
a similar arch of which the fixed pivot <i>c</i> is the centre. The
joint or bar <i>d b</i>, which joins these two pivots, will be moved
so that its middle point <i>e</i> will ascend and descend nearly in
a straight line, as has been already explained
(<a href="#h3-120">120</a>.); <a class="refpn" id="Pg219">[Pg219]</a>
opposite this point <i>e</i> is attached the piston-rod of the air-pump,
which is accordingly guided upwards and downwards by this
means. The jointed parallelogram <i>b d g f</i> is attached to the
beam by pivots; and, as has been explained (<a href="#h3-120">120</a>.), the
point <i>g</i> will be moved upwards and downwards in a straight
line, through twice the space through which the point <i>e</i> is
moved. To the point <i>g</i> the rod of the steam piston is attached.
Thus, the rods of the steam piston and air-pump
are moved by the same system of jointed bars, and moved
through spaces which are in the proportion of two to one.</p>

<p>Although this system of jointed rods forming the parallel
motion, appears in the figure to consist only of one parallelogram
<i>b d g f</i>, and one rod <i>c d</i>, called the <em>radius rod</em>, it is, in
fact, double, a similar parallelogram and radius rod being attached
to corresponding points, and in the same manner on
the other side of the beam; but from the view given in the
cut, the one set of rods hides the other. The two systems
of rods thus attached to opposite sides of the beam at several
inches asunder, are connected by cross rods, the ends of which
form the pivots or joints, and extend between the parallelograms.
The ends of these rods are only visible in the figure.
It is to the middle of one of these rods, the end of which is
represented at <i>e</i>, that the air-pump piston-rod is attached;
and it is to the middle of another, the end of which is represented
at <i>g</i>, that the steam piston-rod is attached. These two
piston-rods, therefore, are driven, not immediately by either
of the parallelograms forming the parallel motion, but by the
bars extending between them.</p>

<p>To the working end of the beam <strong>H</strong> is attached a rod of cast-iron
<strong>O</strong>, called the <em>connecting rod</em>, the lower end of which is
attached to the crank by a pivot. The weight of the connecting
rod is so made, that it shall balance the weight of the
piston-rods of the air-pump and cylinder on the other side of
the beam; and the weight of the piston-rod of the cold-water
pump <strong>N</strong> nearly balances the weight of the piston-rod of the
hot-water pump <strong>L</strong>. Thus, so far as the weights of the machinery
are concerned, the engine is in equilibrium, and the
piston would rest in any position indifferently in the cylinder.</p>

<p>The axis of the fly-wheel on which the crank is formed is
<a class="refpn" id="Pg220">[Pg220]</a>
square in the middle part, where the fly-wheel is attached to it,
but has cylindrical necks at each end, which rest in sockets or
bearings supported by the framing of the machine, in which
sockets the axis revolves freely. On the axle of the crank
is placed the fly-wheel, and connected with its axle is the
governor <strong>Q</strong>, which regulates the throttle-valve <strong>T</strong> in the manner
already described.</p>

<p>Let us now suppose the engine to be in full operation.
The piston being at the top of the cylinder, the spanner <i>m</i>
will be raised by the lower pin on the air-pump rod, and the
upper steam valve <strong>V</strong>, and the lower exhausting valve <strong>Eâ€²</strong>, will
be opened, while the upper exhausting valve <strong>E</strong> and the lower
steam valve <strong>Vâ€²</strong> are closed. Steam will, therefore, be admitted
above the piston, and the steam which filled the cylinder below
it will be drawn off to the condenser, where it will be converted
into water. The piston will, therefore, be urged by
the pressure of the steam above it to the bottom of the
cylinder. As it approaches that limit, the spanner <i>m</i> will be
struck downwards by the upper pin on the air-pump rod, and
the valves <strong>V</strong> and <strong>Eâ€²</strong> will be closed, and at the same time the
lower steam valve <strong>Vâ€²</strong> and the upper exhausting valve <strong>E</strong> will be
opened. Steam will, therefore, be admitted below the piston,
while the steam above it will be drawn off into the condenser,
and converted into water. The pressure of the steam, therefore,
below the piston will urge it upwards, and in the same
manner the motion will be continued.</p>

<p>While this process is going on in the cylinder and the condenser,
the water formed in the condenser will be gradually
drawn off by the operation of the air-pump piston, in the same
manner as explained in the single-acting engine; and at the
same time the hot water thrown into the hot well by the air-pump
piston will be carried off by the hot-water pump <strong>L</strong>.</p>

<p>Such are the chief circumstances attending the continuance
of the operation of the double-acting engine. It is only
necessary here to recall what has been already explained
respecting the operation of the fly-wheel. The commencement
of the motion of the piston from the top and bottom of
the cylinder is produced, not by the pressure of the steam
upon it upwards or downwards, which must, for the reasons
<a class="refpn" id="Pg221">[Pg221]</a>
already explained, be entirely inefficient; but by the momentum
of the fly-wheel, which extricates the crank from
those positions in which the moving power cannot affect it.</p>

<p>The manner in which the motion of the crank affects the
connecting rod at the dead points produces an effect of great
importance in the operation of the engine. When the crank-pin
is approaching the lowest point of its play, and therefore
the piston approaching the top of the cylinder, the motion of
the crank-pin becomes nearly horizontal, and consequently its
effect in drawing the connecting rod and the working end of
the beam downwards and the piston upwards, is extremely
small. The consequence of this is, that as the piston approaches
the top of the cylinder, its motion becomes very
rapidly retarded; and as the motion of the crank-pin at its
lowest point is actually horizontal, the piston is brought to a
state of rest by this gradually retarded motion at the top of
the cylinder. In like manner, when the crank-pin moves
from its dead point upwards, its motion at first is very nearly
horizontal, and consequently its effect in driving the working
end of the beam upwards, and the piston downwards, is at
first very small, but gradually accelerated. The effect of this
upon the piston is, that it arrives at and departs from the top
of the stroke with a very slow motion, being absolutely
brought to rest at that point.</p>

<p>The same effect is produced when the piston arrives at
the bottom of the cylinder. This retardation and suspension
of the motion of the piston at the termination of the stroke
affords time for the process of condensation to be effected, so
that when the moving power of the steam upon the piston
can come into action, the condensation shall be sufficiently
complete. As the piston approaches the top of the cylinder,
and its motion becomes slow, the working gear is made to
open the lower exhausting valve; the steam enclosed in the
cylinder below the piston, and which has just driven the
piston upwards, presses with an elastic force of 17 lbs. per
square inch on every part of the interior of the cylinder,
while the uncondensed vapour in the condenser presses with
a force of about 2 lbs. per square inch. The steam, therefore,
will have a tendency to rush from the cylinder to the
<a class="refpn" id="Pg222">[Pg222]</a>
condenser through the open exhausting valve, with an excess
of pressure amounting to 15 lbs. per square inch, while
the piston pauses at the top of the cylinder. This process
goes on, and when the piston has descended by the motion
of the fly-wheel, a sufficient distance from the top of the
cylinder to call the moving force of the steam into action, the
exhaustion will be complete, and the pressure of the uncondensed
vapour in the cylinder will become the same as in the
condenser.</p>

<p>The pressure of steam in the cylinder, and of uncondensed
vapour in the condenser, varies, within certain limits, in different
engines, and therefore the amount here assigned to
them must be taken merely as an example.</p>

<p>The size of the valves by which the steam is allowed to
pass from the cylinder to the condenser should be such as to
cause the condensation to take place in a sufficiently short
time, to be completed when the steam impelling the piston is
called into action.</p>

<p>Watt, in the construction of his engines, made the exhaustion-valves
with a diameter which was one fifth of the
diameter of the cylinder, and therefore the actual magnitude
of the aperture for the escape of the steam was one twenty-fifth
of the magnitude of the cylinder; but the spindle of the
valve diminished this so that the available space for the
escape of steam did not exceed one twenty-seventh of the
magnitude of the cylinder. This was found to produce a
sufficiently rapid condensation.</p>

<p>It was usual to make the steam valves of the same magnitude
as the exhausting valves, but the flow of steam
through the former was resisted by the throttle-valve, while
no obstruction was opposed to its passage through the latter.</p>

<p>The rapidity with which the cylinder must be exhausted
by the condenser will, however, depend upon the velocity
with which the piston is moved in it. The magnitude, therefore,
of the exhausting valves which would be sufficient for
an engine which acts with a slow motion would be too small
where a rapid motion is required.</p>

<p>In the single-acting steam engine, where the moving force
always acted downwards on the piston, the pressure upon
<a class="refpn" id="Pg223">[Pg223]</a>
all the joints of the machinery by which the force of the
piston was conveyed to the working parts, always took
place in the same direction, and consequently whatever
might be the mechanical connection by which the several
joints were formed, the pins by which they were connected,
must always come to a bearing in their respective
sockets, however loosely they may have been fitted. For
the same reason, however, that the arch head and chain
were abandoned as a means of connecting the steam piston
with the beam, and the parallel motion substituted, it
was also necessary in the double-acting engine, where all
joints whatever were driven alternately in opposite directions,
to fit the connecting pins with the greatest accuracy
in their sockets, and to abandon all connection of the
parts by chains. If any sensible looseness was left in the
joints, a violent jerk would be produced every time the motion
of the piston was reversed. Any looseness either in the
pivots or joints of the parallel motion of the working beam,
the connecting rod, or crank, would, at every change of stroke,
be so accumulated as to produce upon the machinery the
effects of percussion, and would consequently be attended
with the danger of straining and breaking the moveable parts
of the mechanism.</p>

<p>To secure, therefore, the necessary accuracy of the joints,
Watt contrived that every joint in the engine should admit
of the size of the socket being exactly adapted to the size
of the pin, so as always to make a good fitting by closing
the socket upon the pin, when any looseness would be produced
by wear. With this view, all the joints were fitted
with sockets made of brass or gun-metal, capable of adjustment.
Each socket was composed of two pieces, accurately
fitted into a cell or groove, in which one of the brasses can
be moved towards the other by means of a wedge or screw.
Each brass has in it a semi-cylindrical cavity, and the two
cavities being opposed to each other, form a socket for the
joint-pin. One of the two brasses can always be tightened
round that pin, so as to enclose it tight between the two semi-cylindrical
cavities, and to prevent any looseness taking place.
The brasses, and other parts of such a joint, are represented
<a class="refpn" id="Pg224">[Pg224]</a>
in <a href="#Fig044"><i>fig.</i> 44.</a> These joints still continue to be used in the
engines as now constructed.</p>

<div class="figleft" style="width: 110px;">
<a id="Fig044"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_246.png" width="110" height="172" alt="" />
<div class="caption figure">Fig. 44.</div>
</div>

<p>The motion of the working beam, and the pump-rods
which it drives, and of the connecting rod, ought, if the
whole were constructed with perfect precision, to
take place in the same or parallel vertical planes;
but this supposes a perfection of execution which
could hardly have been expected in the early
manufacture of such engines, whatever may have
been attained by improvements which have been
since made. In the details of construction, Watt
saw that there would be a liability to lateral strain, owing to
the planes of the different motions not being truly vertical and
truly parallel, and that if a provision were not made for such
lateral motion, the machinery would be subject to constant
strain in its joints and rapid wear. He provided against this
by constructing the main joints by which the great working
lever was connected with the pistons and connecting rod, so
as to form universal joints, giving freedom of motion laterally
as well as vertically.</p>

<p>The great lever, or working beam, was so called from being
originally made from a beam of oak. It is now, however,
universally constructed of cast-iron. The connecting rod is
also made of cast-iron, and attached to the beam and to the
crank by axles or pivots.</p>

<p>The mechanism by which the four valves are opened and
closed, is subject to considerable variation in different engines.
They have been described above as being opened and
closed simultaneously by a single lever. Sometimes, however,
they are opened alternately in pairs by two distinct
levers driven by two pins attached to the air-pump rod. One
pin strikes the lever, which opens and closes the upper steam
valve, and lower exhausting valve; the other strikes that
which opens and closes the lower steam valve and upper exhausting
valve.</p>

<p>Since the date of the earlier double-acting engines, constructed
by Boulton and Watt, a great variety of mechanical
expedients have been practised for working the valves, by
which the steam is admitted to and withdrawn from the
<a class="refpn" id="Pg225">[Pg225]</a>
cylinder. We shall here describe a few of these methods:â€”</p>


<div class="ph3"><h3>(128.)</h3> The method of working the valves by pins on the air-pump
rod driving levers connected with the valves has been, in
almost all modern double-acting machines, superseded by an
apparatus called an <em>eccentric</em>, by which the motion of the
axle of the fly-wheel is made to open and close the valves at
the proper times.</div>

<div class="figcenter" style="width: 456px;">
<a id="Fig045"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_247.png" width="456" height="266" alt="" />
<div class="caption figure">Fig. 45.</div>
</div>

<p>An eccentric is a metallic circle attached to a revolving
axle, so that the centre of the circle shall not coincide with
the centre round which the axle revolves. Let us suppose
that <strong>G</strong> (<a href="#Fig045"><i>fig.</i> 45.</a>), is a square revolving shaft. Let a circular
plate of metal <strong>B D</strong>, having its centre at <strong>C</strong>, have a square hole
cut in it, corresponding to the shaft <strong>G</strong>, and let the shaft <strong>G</strong>
pass through this square aperture, so that the circular plate
<strong>B D</strong> shall be fastened upon the shaft, and capable of revolving
with it as the shaft revolves. The centre <strong>C</strong> of the circular
plate <strong>B D</strong> will be carried round the centre <strong>G</strong> of the revolving
shaft, and will describe round it a circle, the radius of which
will be the distance of the centre <strong>C</strong> of the circular plate from
the centre of the shaft. Such circular plate so placed upon a
shaft, and revolving with it, is <em>an eccentric</em>.</p>

<p>Let <strong>E F</strong> be a metallic ring, formed of two semicircles of
metal screwed together at <strong>H</strong>, so as to be capable, by the
adjustment of the screws, of having the circular aperture
formed by the ring enlarged and diminished within certain
<a class="refpn" id="Pg226">[Pg226]</a>
small limits. Let this circular aperture be supposed to be
equal to the magnitude of the eccentric <strong>B D</strong>. To the circular
ring <strong>E F</strong> let an arm <strong>L M</strong> be attached. If the ring <strong>E F</strong> be placed
around the eccentric <strong>B D</strong>, and that the screws <strong>H</strong> be so adjusted
as to allow the eccentric <strong>B D</strong> to revolve within the ring <strong>E F</strong>,
then while the eccentric revolves, the ring not partaking of
its revolution, the arm <strong>L M</strong> will be alternately driven to the
right and to the left, by the motion of the centre <strong>C</strong> of the
eccentric as it revolves round the centre <strong>G</strong> of the axle.
When the centre <strong>C</strong> of the eccentric is in the same horizontal
line with the centre <strong>G</strong>, and to the left of it, then the position
of <strong>L M</strong> will be that which is represented in <a href="#Fig045"><i>fig.</i> 45.</a>; but when,
after half a revolution of the main axle, the centre <strong>C</strong> of the
eccentric is thrown on the other side of the centre <strong>G</strong>, then
the point <strong>M</strong> will be transferred to the right, to a distance
equal to twice the distance <strong>C G</strong>. Thus as the eccentric <strong>B D</strong>
revolves within the ring <strong>E F</strong>, that ring, together with the arm
<strong>L M</strong>, will be alternately driven, right and left, through a space
equal to twice the distance between the centre of the eccentric
and the centre of the revolving shaft.</p>

<p>If we suppose a notch formed at the extremity of the arm
<strong>L M</strong>, which is capable of embracing a lever <strong>N M</strong>, moveable on a
pivot at <strong>N</strong>, the motion of the eccentric would give to such a lever
an alternate motion from right to left, and <i>vice versÃ¢</i>. If we suppose
another lever <strong>N O</strong> connected with <strong>N M</strong>, and at right angles
to it, forming what is called a bell-crank, then the alternate
motion received by <strong>M</strong>, from right to left, would give a corresponding
motion to the extremity <strong>O</strong> of the lever <strong>N O</strong>, upwards
and downwards. If this last point <strong>O</strong> were attached to
a vertical arm or shaft, it would impart to such arm or shaft
an alternate motion upwards and downwards, the extent of
which would be regulated by the length of the levers respectively.</p>

<p>By such a contrivance the revolution of the fly-wheel shaft
is made to give an alternate vertical motion of any required
extent to a vertical shaft placed near the cylinder, which
may be so connected with the valves as to open and close
them. Since the upward and downward motion of this vertical
shaft is governed by the alternate motion of the centre
<a class="refpn" id="Pg227">[Pg227]</a>
<strong>C</strong> to the right and to the left of the centre <strong>G</strong>, it is evident
that by the adjustment of the eccentric upon the fly-wheel
shaft, the valves may be opened and closed at any required
position of the fly-wheel and crank, and therefore at any
required position of the piston in the cylinder.</p>

<p>Such is the contrivance by which the valves, whatever form
may be given to them, are now almost universally worked in
double-acting steam engines.</p>

<hr />

<p>Having described the general structure and operation of the
steam engine as improved by Watt, we shall now explain, in
a more detailed manner, some parts of its machinery which
have been variously constructed, and in which more or less
improvements have been made.</p>

<p class="txthead3">Of the Cocks and Valves.</p>

<div class="ph3">
<h3>(129.)</h3> In the steam engine, as well as in every other machine
in which fluids act, it is necessary to open or close, occasionally,
the tubes or passages through which these fluids move.
The instruments by which this is accomplished are called
cocks or valves.</div>

<p>Cocks or valves may be classified by the manner in which
they are opened: 1st, they may be opened by a motion
similar to the lid of a box upon its hinges; 2d, they may
be opened by being raised directly upwards, in the same
manner as the lid of a pot or kettle; 3d, they may be opened
by a sliding motion, like that of the sash of a window or the
lid of a box which slides in grooves; 4th, they may be
opened by a motion of revolution, in the same manner as the
cock of a beer-barrel is opened or closed. The term <em>valve</em> is
more properly applied to the first and second of these classes;
the third class are usually called <em>slides</em>, and the fourth <em>cocks</em>.</p>


<div class="ph3"><h3>(130.)</h3> The single clack valve is the most simple example of
the first class. It is usually constructed by attaching to a plate
of metal larger than the aperture which the valve is intended
to stop, a piece of leather, and to the under side of this leather
another piece of metal smaller than the aperture. The leather
<a class="refpn" id="Pg228">[Pg228]</a>
extending on one side beyond the larger metallic plate, and
being flexible, forms the hinge on which the valve plays. Such
a valve is usually closed by its own weight, and opened by the
pressure of the fluid which passes through it. It is also held
closed more firmly by the pressure of the fluid whose return
it is intended to obstruct. An example of this valve occurs
in the steam engine, in the passage between the condenser
and the air-pump. The aperture which it stops is there a
seat inclined at an angle whose inclination is such as to render
the weight of the valve sufficient to close it. In cases where
the valve is exposed to heat, as in the example just mentioned,
where it is continually in contact with the hot water
flowing from the condenser to the air-pump, the use of leather
is inadmissible, and in that case the metallic surface of the
valve is ground smooth to fit its seat.</div>

<p>The extent to which such a valve should be capable of
opening, ought to be such that the aperture produced by it
shall be equal to the aperture which it stops. This will be
effected if the angle through which it rises be about 30Â°.</p>

<div class="figleft" style="width: 77px;">
<a id="Fig046"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_250.png" width="77" height="106" alt="" />
<div class="caption figure">Fig. 46.</div>
</div>

<p>The valve by which the air and water collected
in the bottom of the air-pump are admitted to
pass through the air-pump piston is a double
clack, consisting of two semicircular plates, having
the hinges on the diameters of these semicircles,
as represented in <a href="#Fig046"><i>fig.</i> 46.</a></p>

<div class="ph3">
<h3>(131.)</h3> Of the valves which are opened by a motion perpendicular
to their seat, the most simple is a flat metallic
plate, made larger than the orifice which it is intended to
stop, and ground so as to rest in steam-tight contact with
the surface surrounding the aperture. Such a valve is
usually guided in its perpendicular motion by a spindle
passing through its centre, and sliding in holes made in cross
bars extending above and below the seat of the valve.</div>

<p>The conical steam-valves, which have been already described
(<a href="#h3-116">116</a>.), usually called spindle-valves, are the most common
of this class. The best angle to be given to the conical seat
is found in practice to be 45Â°. With a less inclination the
valve has a tendency to be fastened in its seat, and a greater
inclination would cause the top of the valve to occupy
<a class="refpn" id="Pg229">[Pg229]</a>
unnecessary space in the valve-box. The area, or transverse
section of the valve-box, should be rather more than double
the magnitude of the upper surface of the valve, in order to
allow a sufficiently free passage for the steam, and the play
of the valve should be such as to allow it to rise from its seat
to a height not less than one fourth of the diameter of its
upper surface.</p>

<p>The valves coming under this class are sometimes formed
as spheres or hemispheres resting in a conical seat, and in
such cases they are generally closed by their own weight, and
opened by the pressure of the fluid which passes through
them.</p>


<div class="ph3">
<h3>(132.)</h3> One of the advantages attending the use of slides,
compared with the other form of valves, is the simplicity with
which the same slide may be made to govern several passages,
so that a single motion with a slide may perform the
office of two or more motions imparted to independent valves.</div>

<p>In most modern engines the passage of the steam to and
from the cylinder is governed by slides of various forms, some
of which we shall now explain.</p>

<div class="figright" style="width: 130px;">
<a id="Fig047"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_251.png" width="130" height="324" alt="" />
<div class="caption figure">Fig. 47.</div>
</div>

<div class="ph3"><h3>(<a id="h3-133"></a>133.)</h3> In <i>figs.</i> 47. and 48. is represented a slide-valve contrived
by Mr. Murray of Leeds. <strong>A B</strong> is a steam-tight case attached
to the side of the cylinder; <strong>E F</strong> is a rod, which
receives an alternate motion, upwards and
downwards, from the eccentric, or from whatever
other part of the engine is intended to
move the slide. This rod, passing through
a stuffing-box, moves the slide <strong>G</strong> upwards
and downwards. <strong>S</strong> is the mouth of the
steam pipe coming from the boiler; <strong>T</strong> is
the mouth of a tube or pipe leading to the
condenser; <strong>H</strong> is a passage leading to the top,
and <strong>I</strong> to the bottom, of the cylinder. In the
position of the slide represented in <a href="#Fig047"><i>fig.</i> 47.</a>,
the steam coming from the boiler through <strong>S</strong>
passes through the space <strong>H</strong> to the top of the
cylinder, while the steam from the bottom
of the cylinder passes through the space <strong>I</strong>
into the tube <strong>T</strong>, and goes to the condenser. When the rod
<a class="refpn" id="Pg230">[Pg230]</a>
<strong>E F</strong> is raised to the position represented in <a href="#Fig048"><i>fig.</i> 48.</a>, then the
passage <strong>H</strong> is thrown into communication with
the tube <strong>T</strong>, while the passage <strong>I</strong> is made to
communicate with the tube <strong>S</strong>. Steam, therefore,
passes from the boiler through <strong>I</strong> below
the piston, while the steam which was above
the piston, passing through <strong>H</strong> into <strong>T</strong>, goes
to the condenser. Thus the single slide <strong>G</strong>
performs the office of the four valves described
in (<a href="#h3-116">116</a>.).</div>

<div class="figright" style="width: 118px;">
<a id="Fig048"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_252.png" width="118" height="313" alt="" />
<div class="caption figure">Fig. 48.</div>
</div>

<div class="ph3"><h3>(134.)</h3> The slide <strong>G</strong> has always steam of a
full pressure behind it, while the steam in
front of it escaping to the condenser, exerts
but little pressure upon it. It is therefore
always forcibly pressed against the surfaces
in contact with which it moves, and
is thereby maintained steam-tight. Indeed
this pressure would rapidly wear the rubbing surfaces, unless
they were made sufficiently extensive, and hardened so as
to resist the effects of the friction. Where fresh water
is used, as in land boilers, the slide may be made of hardened
steel; and in the case of marine boilers, it may be
constructed of gun-metal. In this and all other contrivances
in which the apertures by which the steam is admitted to
and withdrawn from the piston are removed to any considerable
distance from the top and bottom of the cylinder, there
is a waste of steam, for the steam consumed at each stroke of
the piston is not only that which would fill the capacity of
the cylinder, but also the steam which fills the passage
between the slide <strong>G</strong> and the top or bottom of the cylinder.
Any arrangement which would throw the passages <strong>H</strong> and <strong>I</strong>
on the other side of the slide <strong>G</strong>, that is, between <strong>S</strong> and <strong>G</strong>,
instead of being, as they are, between <strong>G</strong> and the top and
bottom of the cylinder, would remove this defect. This is
accomplished by a slide, which is usually called the <strong>D</strong> valve,
because, being semi-cylindrical in its form, and hollow, its
cross section resembles the letter <strong>D</strong>. This slide, which is
that which at present is in most general use, is represented
in <a href="#Fig049-50"><i>figs.</i> 49</a>, <a href="#Fig049-50">50</a>.; <strong>E</strong> is the rod by which the slide is moved, passing
<a class="refpn" id="Pg231">[Pg231]</a>
through a stuffing-box <strong>F</strong>; <strong>G G</strong> is the slide represented by a
vertical section, <i>a a</i> being a passage in it extending from the
top to the bottom; <strong>S</strong> is the mouth of the great steam pipe
coming from the boiler;
<strong>P</strong> is the pipe leading
to the condenser;
<strong>T H</strong> is a hollow space
formed in the slide
always in communication
with the steam
pipe <strong>S</strong>, and consequently
always filled
with steam from the
boiler. A transverse
section of the slide and
cylinder is represented in <a href="#Fig051"><i>fig.</i> 51.</a>, where <i>a</i> represents the
top of the passage marked <i>a</i> in <a href="#Fig049-50"><i>fig.</i> 49.</a> In the position of
the slide represented in <a href="#Fig049-50"><i>fig.</i> 49.</a>, the steam filling
the space <strong>T H</strong> has access to the top of the
cylinder, but is excluded from the bottom. The
steam which was below the piston, passing up
the passage <i>a</i>, escapes through the tube <strong>P</strong> to the
condenser. When the piston has descended, the
rod <strong>E</strong> moves the slide downwards, so as to give
it the position represented in <a href="#Fig049-50"><i>fig. 50.</i></a> The steam in <strong>T H</strong> has
now access to the bottom of the cylinder, while the steam
above the piston passing through <strong>P</strong> escapes to the condenser.
In this way the operation of the piston is continued
and the steam consumed at each stroke only exceeds the
capacity of the cylinder by what is necessary to fill the
passages between the slide and the cylinder.</div>

<div class="figleft" style="width: 281px;">
<a id="Fig049-50"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_253a.png" width="281" height="230" alt="" />
<div class="caption figure">Figs. 49., 50.</div>
</div>

<div class="figleft" style="width: 93px;">
<a id="Fig051"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_253b.png" width="93" height="129" alt="" />
<div class="caption figure">Fig. 51.</div>
</div>

<p>In a slide constructed in this manner, the steam filling the
space <strong>T H</strong> has a tendency to press the slide back, so as to
break the contact of the rubbing surfaces, and thereby to
cause the steam to leak from the space <strong>T H</strong> to the back of the
slide. This is counteracted by the packing <i>x</i>, at the back of
the slide.</p>

<p>In engines of very long stroke, the extent of the rubbing
surfaces of slides of this kind renders it difficult to keep
<a class="refpn" id="Pg232">[Pg232]</a>
them in steam-tight contact and to insure their uniform
wear. In such cases, therefore, separate slides, upon the same
principle, are provided at the top and bottom of the cylinder,
moved, however, by a single rod of communication.</p>


<div class="ph3"><h3>(135.)</h3> In slides, as we have here described them, the same
motion which admits steam to either end of the cylinder, withdraws
it from the other end. Such an arrangement is only compatible
with the operation of a cylinder which works without
expansion; for in such a cylinder the full flow of steam to
the piston is only interrupted for a moment during the
change of position of the slide. But if the steam act expansively,
it would be necessary to move the slide, so as to
stop its flow to one end of the cylinder, without at the same
time obstructing the escape of steam from the other end to
the condenser. It would therefore be necessary that the
slide should close the passage leading to the cylinder at one
end, without at the same time obstructing the communication
between the passage from the cylinder to the condenser at the
other end. On the arrival of the piston, however, at the
bottom of the cylinder, it would be necessary immediately to
put the lower passage to the cylinder in communication with
the steam pipe, and the upper passage in communication
with the condenser. This would necessarily suppose two
motions of the slide as well as some modifications in its
length. Let the length of the slide be such that when the
passage to the top of the cylinder is stopped, the lower
part of the slide shall not reach the passage to the lower
part of the cylinder; and let such a provision be made in
the mechanism by which the rod <strong>E</strong> governing the slide is
driven that it shall receive two motions during the descent
of the piston, the first to be imparted to it at the
moment the steam is to be cut off, and the second just before
the termination of the stroke. Let the position of the slide,
at the commencement of the stroke, be represented in <a
href="#Fig052-53-54"><i>fig.</i> 52.</a>,
and let it be required that the steam shall be cut off at
one half of the stroke. When the piston has made half the
stroke, the rod governing the slide is moved downwards, so
as to throw the slide into the position represented in <a
href="#Fig052-53-54"><i>fig.</i> 53.</a>
The passage between the steam pipe and the cylinder is
<a class="refpn" id="Pg233">[Pg233]</a>
now stopped at both ends; but the passage from the bottom
of the cylinder to the condenser remains open. During the
remainder of the stroke, therefore, the steam in the cylinder
works expansively. As the piston approaches the bottom
of the cylinder, another motion is imparted to the rod governing
the slide, by which the latter is thrown into the
position represented in <a href="#Fig052-53-54"><i>fig.</i> 54.</a>
Steam now flows below the
piston while the steam above it passes to the condenser. In
a similar manner, by two motions successively imparted to the
slide during the ascent of the piston, the steam may be cut
off at half stroke; and it is evident that by regulating the
time at which these motions are given to the slide, the steam
may be worked expansively, to any required extent.</div>

<div class="figcenter" style="width: 377px;">
<a id="Fig052-53-54"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_255.png" width="377" height="268" alt="" />
<div class="caption figure">Figs. 52., 53., 54.</div>
</div>

<p>It is easy to conceive various mechanical means by which,
in the same engine, the point at which the steam is cut off
may be regulated at pleasure.</p>

<p>In cases where the motion of the piston is very rapid, as in locomotive
engines, it is desirable that the passages to and from
the cylinder should be opened very suddenly. This is difficult
to be accomplished with any form of slide consisting of a
single aperture; but if, instead of admitting the steam to the
cylinder by a single aperture, the same magnitude of opening
were divided among several apertures, then a proportionally
less extent of motion in the slide would clear the passage for
the steam, and consequently greater suddenness of opening
would be effected.
<a class="refpn" id="Pg234">[Pg234]</a></p>

<p>The great advantages in the economy of fuel resulting
from the application of the expansive principle have, of late
years forced themselves on the attention of engineers, and
considerable improvements have been made in its application,
especially in the case of marine engines used for long voyages,
in which the economy of fuel has become an object of the
last importance. The mechanism by which expansive slides
are moved, is made capable of adjustment, so that the part
of the stroke at which the steam is cut off, can be altered at
pleasure. The working power of the engine, therefore, instead
of being controlled by the throttle-valve, is regulated
by the greater or less extent to which the expansive principle
is applied. Steam of the same pressure is admitted to the
cylinder in all cases; but it is cut off at a greater or less
portion of the stroke, according to the power which the
engine is required to exert.</p>

<p>The last degree of perfection has been conferred on this
principle by connecting the governor with the mechanism by
which the slide is moved, so that the governor instead of
acting on the throttle-valve, is made to act upon the slide.
By this means when, by reason of any diminution of the
resistance, the motion of the engine is accelerated, the balls
of the governor diverging shift the cam or lever which
governs the slide, so that the steam is cut off after a shorter
portion of the stroke, the expansive principle is brought into
greater play, and the quantity of steam admitted to the
cylinder at each stroke is diminished. If, on the other hand,
the resistance to the machine be increased, so as to diminish
the velocity of the engine, then the balls collapsing the levers
of the governor shift the cam which moves the slides, so as
to increase the portion of the stroke made by the piston
before the steam is cut off, and thereby to increase the amount
of mechanical power developed in the cylinder at each stroke.
The extent to which the expansive principle is capable of
being applied, more especially in marine engines, has been
hitherto limited by the necessity of using steam of very high
pressure, whenever the steam is cut off after the piston has
performed only a small part of the stroke. A method, however,
is now (March, 1840) under experimental trial, by
<a class="refpn" id="Pg235">[Pg235]</a>
Messrs. Maudsley and Field, by which the expansive principle
may be applied to any required extent without raising
the steam in the boiler above the usual pressure of from
three to five pounds per square inch. This method consists
in the use of a piston of great magnitude. The force urging
the piston is thus obtained not by an excessive pressure on
a limited surface, but by a moderate pressure diffused over a
large surface. The entire moving force acting on the piston
before the steam is cut off, is considerably greater than the
resistance; but during the remainder of the stroke this force
is gradually enfeebled until the piston is brought to the
extremity of its play.</p>

<div class="figcenter" style="width: 315px;">
<a id="Fig055"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_257.png" width="315" height="294" alt="" />
<div class="caption figure">Fig. 55.</div>
</div>

<div class="ph3"><h3>(136.)</h3> Mr. Samuel Seaward, of the firm of Messrs. Seawards,
engineers, has contrived an improved system of slides,
for which he has obtained a patent. A section of Seaward's
slides is represented in <a href="#Fig055"><i>fig.</i> 55.</a> The steam pipe proceeding
from the boiler to the cylinder is represented at <strong>A A</strong>, and
it communicates with passages <strong>S</strong> and <strong>Sâ€²</strong> leading to the top
and bottom of the cylinder. These passages are formed in
nozzles of iron or other hard metal cast upon the side of the
cylinder. These nozzles present a smooth face outwards,
upon which the slides <strong>B Bâ€²</strong>, also formed with smooth faces,
play. The slides <strong>B Bâ€²</strong> are attached by knuckle-joints to
rods <strong>E Eâ€²</strong>, which move through stuffing-boxes, and the
<a class="refpn" id="Pg236">[Pg236]</a>
connection of these rods with the slides is such that the slides
have play so as to detach their surfaces easily from the
smooth surfaces of the nozzles when not pressed against
these surfaces. The steam in the steam pipe <strong>A A</strong> will press
against the backs of the slides <strong>B Bâ€²</strong>, and keep their faces
in steam-tight contact with the smooth surfaces of the
nozzles. These slides may be opened or closed by proper
mechanism at any point of the stroke. When steam is to be
admitted to the top of the cylinder, the upper slide is raised
and the passage <strong>S</strong> opened; and when it is to be admitted to
the bottom of the cylinder, the lower slide is raised and the
passage <strong>Sâ€²</strong> opened; and its communication to the top or
bottom of the cylinder is stopped by the lowering of these
slides respectively. On the other side of the cylinder are
provided two passages <strong>C Câ€²</strong> leading to a pipe <strong>G</strong>, which is
continued to the condenser. On this pipe are cast nozzles of
iron or other metal presenting smooth faces towards the
cylinder, and having passages <strong>D Dâ€²</strong> communicating between the
top and bottom of the cylinder respectively and the pipe <strong>G G</strong>
leading to the condenser. Two slides <i>b b'</i>, having smooth faces
turned from the cylinder, and pressing upon the faces of the
nozzles <strong>D Dâ€²</strong>, are governed by rods playing through stuffing-boxes,
in the same manner as already described. The faces
of these slides being turned from the cylinder, the steam in the
cylinder having free communication with them, has a tendency
to keep them by its pressure in steam-tight contact with the
surfaces in which the apertures leading to the condenser are
formed. These two slides may be opened or closed whenever
it is necessary.</div>

<p>When the piston commences its descent, the upper steam
slide is raised, so as to open the passage <strong>S</strong>, and admit steam
above the piston; and the lower exhausting slide <i>bâ€²</i> is also
raised, so as to allow the steam below the piston to escape
through <strong>G</strong> to the condenser, the other two passages <strong>Sâ€²</strong> and <strong>C</strong>
being closed by their respective slides. The slide which
governs <strong>S</strong> is lowered at that part of the stroke at which the
steam is intended to be cut off, the other slides remaining
unchanged; and when the piston has reached the bottom of
the cylinder, the lower steam slide opens the passage <strong>Sâ€²</strong>, and
<a class="refpn" id="Pg237">[Pg237]</a>
the upper exhausting slide opens the passage <strong>C</strong>; and at the
same time the lower exhausting slide closes the passage <strong>Câ€²</strong>.
Steam being admitted below the piston through <strong>Sâ€²</strong>, and at the
same time the steam above it being drawn away to the
condenser through the open passage <strong>C</strong> and the tube <strong>G</strong>, the
piston ascends. When it has reached that point at which
the steam is intended to be cut off, the slide which governs <strong>Sâ€²</strong>
is lowered, the other slides remaining unaltered, and the
upward stroke is completed in the same manner as the
downward.</p>

<p>These four slides may be governed by a single lever, or
they may be moved by separate means. From the small
spaces between the several slides and the body of the
cylinder, it will be evident that the waste of steam by this
contrivance will be very small.</p>

<p>In the slide valves commonly used, the packing of hemp at
the back of the slide, by which the pressure necessary to keep
the slide in steam-tight contact is obtained, requires constant
attention from the engine-man while the engine is at work.
Any neglect of this will produce a corresponding loss in the
power of the engine; and accordingly it is found that in
many cases where engines work inefficiently, the defect is
owing either to ignorance or want of attention on the part of
the engine-man in the packing of the slides. In Seaward's
slides no hemp packing is used, nor is any attention on the
part of the engine-man required after the slides are first
adjusted. The slides receive the pressure necessary to keep
them in steam-tight contact with the surfaces of the nozzles
from the steam itself, which acts behind them.</p>

<p>The eduction and steam slides being independent of each
other, they may be adjusted so that the engine shall work
expansively in any required degree; and this may be accomplished
either by working the slides by separate mechanism,
or by a single eccentric.</p>

<p>One of the advantages claimed by the patentees for these
slides is, that the engines are secured from the accidents
which arise from the accumulation of water within the steam
cylinder. If such a circumstance should occur, the action of
the piston will press the water against the faces of the steam
<a class="refpn" id="Pg238">[Pg238]</a>
slides, and the play allowed to them by their connection
with the rods which move them permits their faces to be raised
from the surfaces of the nozzles, so that the water collected
in the cylinder shall be driven into the steam pipe, and sent
back from thence to the boiler.</p>

<div class="figright" style="width: 209px;">
<a id="Fig056"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_260a.png" width="209" height="149" alt="" />
<div class="caption figure">Fig. 56.</div>
</div>

<div class="ph3"><h3>(137.)</h3> Of the cocks or valves
which are opened and closed by
the motion of an axis passing
through their centre, the throttle-valve,
whether worked by
hand or by the governor, is an
example. But the most common
form for cocks is that of a
cylindrical or slightly conical plug (<a href="#Fig056"><i>fig.</i> 56.</a>), inserted in an
aperture of corresponding magnitude passing across the
pipe or passage which the cock is intended to open or
close. One or more holes are pierced transversely in the
cock, and when the cock is turned so that these holes run in
the direction of the tube, the passage through the tube is
opened; but when the passage through the cock is placed at
right angles to the tube, then the sides of the tube stop the
ends of the passage in the cock, and the passage through the
tube is obstructed. The simple cock is designed to open or
close the passage through a single tube. When the cock is
turned, as in <a href="#Fig057-58"><i>fig.</i> 57.</a>, so that the passage through the cock
shall be at right angles to the length of the tube, then the
passage through the tube is stopped; but when the cock is
turned from that position through a quarter of a revolution,
as in <a href="#Fig057-58"><i>fig.</i> 58.</a>, then the passage through the cock takes the direction
of the passage through the tube, and the cock is
opened, and the passage through the tube unobstructed. In
such a cock the passage may be more or less <em>throttled</em> by
<a class="refpn" id="Pg239">[Pg239]</a>
adjusting the position of the cock, so that a part of the opening
in it shall be covered by the side of the tube.</div>

<div class="figcenter" style="width: 335px;">
<a id="Fig057-58"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_260b.png" width="335" height="116" alt="" />
<div class="caption figure">Figs. 57., 58.</div>
</div>

<div class="ph3"><h3>(<a id="h3-138"></a>138.)</h3> It is sometimes required to put one tube or passage
alternately in communication with two others. This is
accomplished by a <em>two-way cock</em>. In this cock the passage is
curved, opening usually at points on the surface of the cock,
at right angles to each other. Such a cock has already been
described, and its use illustrated in the description of the
Marquis of Worcester's engine (<a href="#h3-17">17</a>.); the two-way cock,
as represented at <strong>K</strong> and <strong>R</strong> (<a href="#Fig004-5-6"><i>fig.</i> 4.</a>), being the means by which
steam and water are alternately supplied to the two forcing
vessels.</div>

<div class="figright" style="width: 169px;">
<a id="Fig059-60"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_261.png" width="169" height="337" alt="" />
<div class="caption figure">Figs. 59., 60.</div>
</div>

<div class="ph3"><h3>(139.)</h3> When it is required to put four passages alternately
in communication by pairs, a <em>four-way cock</em> is used. Such a
cock has two curved passages (<i>fig.</i>
59.), each similar to the curved passage
in the two-way cock. Let <strong>S C B T</strong>
be the four tubes which it is required
to throw alternately into communication
by pairs. When the cock
is in the position <a href="#Fig059-60"><i>fig.</i> 59.</a>, the tube <strong>S</strong>
communicates with <strong>T</strong>, and the tube <strong>C</strong>
with <strong>B</strong>. By turning the cock through
a quarter of a revolution, as in <a href="#Fig059-60"><i>fig.</i> 60.</a>,
the tube <strong>S</strong> is made to communicate
with <strong>B</strong>, and the tube <strong>C</strong> with <strong>T</strong>; and if
the cock continue to be turned at intervals
through a quarter of a revolution,
these changes of communication
will continue to be alternately
made. It is evident that this may be accomplished by turning
the cock continually in the same direction.</div>

<p>The four-way cock is sometimes used as a substitute for
the valves or slides in a double-acting steam engine to conduct
the steam to and from the cylinder. If <strong>S</strong> represent a
pipe conducting steam from the boiler, <strong>C</strong> that which leads to the
condenser, <strong>T</strong> the tube which leads to the top of the cylinder,
and <strong>B</strong> that which leads to the bottom, then when the cock is
in the position (<a href="#Fig059-60"><i>fig.</i> 59.</a>), steam would flow from the boiler to
<a class="refpn" id="Pg240">[Pg240]</a>
the top of the piston, while the steam below it would be
drawn off to the condenser; and in the position (<a href="#Fig059-60"><i>fig.</i> 60.</a>),
steam would flow from the boiler to the bottom of the
piston, while the steam above it would be drawn off to the
condenser. Thus by turning the cock through a quarter of a
revolution towards the termination of each stroke, the operation
of the machine would be continued.</p>

<p>One of the disadvantages which is inseparable from the use
of a four-way cock for this purpose is the loss of the steam at
each stroke, which fills the tubes between the cock and the
ends of the cylinder. This disadvantage could only be avoided
by the substitution of two two-way cocks (<a href="#h3-138">138</a>.) instead of a
four-way cock. A two-way cock at the top of the cylinder
would open an alternate communication between the cylinder
and steam pipe, and the cylinder and condenser, while
a similar office would be performed by another two-way
cock at the other end.</p>

<p>The friction on cocks of this description is more than on
other valves; but this is in some degree compensated by the
great simplicity of the instrument. When the cock is truly
ground into its seat, being slightly conical in its form, the
pressure of the steam has a tendency to keep the surfaces in
contact; but this pressure also increases the friction, and has
a tendency to wear the seat of the cock into an elliptical
shape. Consequently, such cocks require to be occasionally
ground and refitted.</p>


<div class="ph3">
<h3>(140.)</h3> The four-way cock, as above described, admits the
steam to one end of the piston at the same moment that it
stops it at the other end. It would therefore be inapplicable
where steam is worked expansively. A slight modification,
however, analogous to that already described in the slides,
will adapt it to expansive action. This will be accomplished
by giving to one of the passages through the cock one aperture
larger than the other, and working the cock so that this
passage shall always be used to conduct steam to the cylinder;
also by enlarging both apertures of the other passage, and
using it always to conduct steam from the cylinder. The
effect of such an arrangement will be readily understood.</div>

<div class="figleft" style="width: 161px;">
<a id="Fig061-62"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_263a.png" width="161" height="307" alt="" />
<div class="caption figure">Figs. 61., 62.</div>
</div>

<p>Let the position of the cock at the commencement of the
<a class="refpn" id="Pg241">[Pg241]</a>
descending stroke be represented in <a href="#Fig061-62"><i>fig.</i> 61.</a> Steam flows
from <strong>S</strong> through <strong>T</strong> to the top of the cylinder,
while it escapes from <strong>B</strong> through <strong>C</strong>
from the bottom of the cylinder. When
the piston has arrived at that point at
which the steam is to be cut off, let the
cock be shifted to the position represented
in <a href="#Fig061-62"><i>fig.</i> 62.</a> The passage of steam from
the boiler is now stopped, but the escape
of steam from the bottom of the cylinder through <strong>C</strong> continues,
and the cock is maintained in this
position until the piston approaches the
bottom of the cylinder, when it is further
shifted to the position represented
in <a href="#Fig063-64"><i>fig.</i> 63.</a> Steam now flows from <strong>S</strong>
through <strong>B</strong> to the bottom of the cylinder,
while the steam from the top of the
cylinder escapes through <strong>C</strong> to the condenser.
When the piston has arrived at that point where
the steam is to be cut off, the cock is shifted to the position
represented in <a href="#Fig063-64"><i>fig.</i> 64.</a>
The communication between the
steam and the bottom of the piston is now stopped, while
the communication between the top of the cylinder and the
condenser is still open. During the next double stroke of
the piston the position of the cock is similarly changed, but
in the contrary direction, and in the same way the motion
is continued. Under these circumstances the cock, instead
<a class="refpn" id="Pg242">[Pg242]</a>
of being moved constantly in the same direction, as in the
case of the common four-way cock, will require to be moved
alternately in opposite directions.</p>

<div class="figcenter" style="width: 418px;">
<a id="Fig063-64"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_263b.png" width="418" height="188" alt="" />
<div class="caption figure">Figs. 63., 64.</div>
</div>

<p class="txthead3">Pistons.</p>

<div class="ph3"><h3>(<a id="h3-141"></a>141.)</h3> The office of a piston being to divide a cylinder into
two compartments by a movable partition which shall obstruct
the passage of any fluid from one compartment to the
other, it is evident that the two conditions which such an instrument
ought to fulfil are, <em>first</em>, that the contact of its sides
with the surface of the cylinder shall be so close and tight
throughout its entire play that no steam or other fluid can
pass between them; <em>secondly</em>, that it shall be so free from
friction, notwithstanding this necessary tightness, that it shall
not absorb any injurious quantity of the moving power.</div>

<p>Since, however accurately the surfaces of the piston and
cylinder may be constructed, there will always be in practice
more or less imperfection of form, it is evident that the contact
of the surface of the piston with the cylinder throughout
the stroke can only be maintained by giving to the circumference
of the piston sufficient elasticity to accommodate
itself to such inequalities of form. The substance, whatever
it may be, used for this purpose, and by which the piston is
surrounded, is called <em>packing</em>.</p>

<p>In steam pistons the material used for packing must be
such as is capable of resisting the united effects of heat and
moisture. Hence leather and other animal substances are inapplicable.</p>

<p>The packing used for steam pistons is therefore of two
kinds, <em>vegetable packing</em>, usually hemp, or <em>metallic packing</em>.</p>

<p>The common hemp-packed piston has been already in part
described (<a href="#h3-79">79</a>.). The bottom of the piston is a circular plate
just so much less in diameter than the cylinder as is sufficient
to allow its free motion in ascending and descending. A little
above its lowest point this plate begins gradually to diminish
in thickness, until its diameter is reduced to from one to two
inches less than that of the cylinder, leaving therefore around
<a class="refpn" id="Pg243">[Pg243]</a>
it a hollow space, as represented in <a href="#Fig065"><i>fig.</i> 65.</a> The cover of the
piston is a plate similarly
formed, being in
like manner gradually
reduced in thickness
downwards, so as to
correspond with the
lower plate. In the hollow
space which thus surrounds the piston a packing of
unspun hemp or soft rope, called <em>gasket</em>, is introduced by
winding it round the piston so as to render it an even and
compact mass. When the space is thus filled up, the top of
the piston is attached to the bottom by screws. The curved
form of the space within which the hempen packing is
confined is such that when the screws are tightened, that
part of the packing which is nearest to the top and bottom
of the piston is forced against the cylinder, so as to produce
upon the two parallel rings as much pressure as is necessary
to render it steam-tight. When by use the packing
is worn down so as to produce leakage, the cover of the
cylinder must be removed, and the screws connecting the
top and bottom of the piston tightened: this will force out
the packing and render the piston steam-tight. This packing
is lubricated by melted tallow let down upon the piston
from the funnel inserted in the top of the cylinder, furnished
with a stop-cock to prevent the escape of steam.
The lower end of the piston-rod is formed slightly conical, the
thickest part of the cone being downward. It is passed
up through the piston, and a nut or wedge between the top
and bottom is inserted so as to secure the piston in its position
upon the rod.</p>

<div class="figright" style="width: 267px;">
<a id="Fig065"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_265.png" width="267" height="142" alt="" />
<div class="caption figure">Fig. 65.</div>
</div>

<p>The process of removing the top of the cylinder for the
purpose of tightening the screws in the piston is one of so
laborious a nature, that the men entrusted with the superintendence
of these machines are tempted to allow the engine
to work notwithstanding injurious leakage at the piston,
rather than incur the labour of tightening the screws as often
as it is necessary to do so.</p>

<p>To avoid this inconvenience, the following method of
<a class="refpn" id="Pg244">[Pg244]</a>
tightening the packing of the piston without removing the
lid of the cylinder, was contrived by Woolf. The head of
each of the screws was formed into a toothed pinion, and as
these screws were placed at equal distances from the centre
of the piston, these several pinions were driven by a large
toothed wheel, revolving on the piston-rod as an axis. By
such an arrangement it is evident that if any one of the
screws be turned, a like motion will be imparted to all the
others through the medium of the large central wheel. Woolf
accordingly formed, on the head of one of the screws, a square
end. When the piston was brought to the top of the cylinder,
this square end entered an aperture made in the under side of
the cover of the cylinder. This aperture was covered by a small
circular piece screwed into the top of the cylinder, which was
capable of being removed so as to render the square head of
the screw accessible. When this was done, a proper key
being applied to the square head of the screw, it was turned;
and by being turned, all the other screws were in like manner
moved. In this way, instead of having to remove the cover of
the cylinder, which in large cylinders was attended with great
labour and loss of time, the packing was tightened by merely
unscrewing a piece in the top of the cylinder not much
greater in magnitude than the head of one of the screws.</p>

<p>This method was further simplified by causing the great
circular wheel already described to move upon the piston-rod,
not as an axis, but as a screw, the thread being cut upon a
part of the piston-rod which worked in a corresponding
female screw cut upon the central plate. By such means,
the screw whose head was let into the cover of the cylinder
which turned, would cause this circular plate to be pressed
downwards by the force of the screw constructed on the piston-rod.
This circular plate thus pressed downwards, acted
upon pins or plugs which pressed together the top and bottom
of the cylinder in the same manner as they were pressed
together by the screws connecting them as already described.</p>

<p class="txthead3">Metallic Pistons.</p>

<div class="ph3"><h3>(142.)</h3> The notion of constructing a
piston so as to move steam-tight
in the cylinder without the use of packing of vegetable
<a class="refpn" id="Pg245">[Pg245]</a>
matter was first suggested by the Rev. Mr. Cartwright, a
gentleman well known for other mechanical inventions. A
patent was granted in 1797 for a new form of steam engine,
in which he proposed to use the vapour of alcohol to work the
piston instead of the steam of water: and since the principle
of the engine excluded the use of lubrication by oil or tallow,
he substituted a piston formed of metallic rings pressed against
the surface of the cylinder by springs, so as to be maintained
in steam-tight contact with it, independently either of packing
or lubrication. Although the engine for which this form of
piston was intended never came into practical use, yet it
is so simple and elegant in its structure, and forms a link so
interesting in the history of the steam engine, that some explanation
of it ought not to be omitted in this work.</div>

<p>The steam-pipe from the boiler is represented cut off at <strong>B</strong>
(<a href="#Fig066"><i>fig.</i> 66.</a>); <strong>T</strong> is a spindle-valve, for admitting steam above the
piston, and <strong>R</strong> is a spindle-valve in the piston; <strong>D</strong> is a curved
pipe forming a communication between the cylinder and the
condenser, which is of very peculiar construction. Cartwright
proposed effecting a condensation without a jet, by exposing
the steam to contact with a very large quantity of cold surface.
For this purpose, he formed his condenser by placing
two cylinders nearly equal in size, one within the other, allowing
the water of the cold cistern in which they were placed
to flow through the inner cylinder, and to surround the outer
one. Thus, the thin space between the two cylinders formed
the condenser.</p>

<div class="figcenter" style="width: 426px;">
<a id="Fig066"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_268.png" width="426" height="608" alt="" />
<div class="caption figure">Fig. 66.</div>
</div>

<p>The air-pump is placed immediately under the cylinder,
and the continuation of the piston-rod works its piston, which
is solid and without a valve. <strong>F</strong> is the pipe from the condenser
to the air-pump, through which the condensed steam
is drawn off through the valve <strong>G</strong> on the ascent of the piston,
and on the descent this is forced through a tube into a hot
well <strong>H</strong>, for the purpose of feeding the boiler through the
feed-pipe <strong>I</strong>. In the top of the hot well <strong>H</strong> is a valve which
opens inwards, and is kept closed by a ball floating on the
surface of the liquid. The pressure of the condensed air
above the surface of the liquid in <strong>H</strong> forces it through <strong>I</strong> into
the boiler. When the air accumulates in too great a degree
<a class="refpn" id="Pg246">[Pg246]</a>
in <strong>H</strong>, the surface of the liquid is pressed so low that the ball
falls and opens the valve, and allows it to escape. The air
in <strong>H</strong> is that which is pumped from the condenser with the
liquid, and from which it was disengaged.</p>

<p>Let us suppose the piston at the top of the cylinder: it
strikes the tail of the valve <strong>T</strong>, and raises it, while the stem
of the piston-valve <strong>R</strong> strikes the top of the cylinder, and is
pressed into its seat. A free communication is at the same
time open between the cylinder, below the piston and the
condenser, through the tube <strong>D</strong>. The pressure of the steam
<a class="refpn" id="Pg247">[Pg247]</a>
thus admitted above the piston acting against the vacuum
below it, will cause its descent. On arriving at the bottom
of the cylinder, the tail of the piston-valve <strong>R</strong> will strike the
bottom, and it will be lifted from its seat, so that a communication
will be opened through it with the condenser. At
the same moment, a projecting spring <strong>K</strong>, attached to the
piston-rod, strikes the stem of the steam-valve <strong>T</strong>, and presses
it into its seat. Thus while the further admission of steam
is cut off, the steam above the piston flows into the condenser,
and the piston being relieved from all pressure, is drawn up
by the momentum of the fly-wheel, which continues the
motion it received from the descending force. On the arrival
of the piston again at the top of the cylinder, the valve <strong>T</strong> is
opened and <strong>R</strong> closed, and the piston descends as before, and
so the process is continued.</p>

<p>The mechanism by which motion is communicated from
the piston to the fly-wheel is peculiarly elegant. On the
axis of the fly-wheel is a small wheel with teeth, which work
in the teeth of another larger wheel <strong>L</strong>. This wheel is turned
by a crank, which is worked by a cross-piece attached to the
end of the piston-rod. Another equal-toothed wheel <strong>M</strong> is
turned by a crank, which is worked by the other end of the
cross-arm attached to the piston-rod.</p>

<p>One of the peculiarities of this engine is, that the liquid
which is used for the production of steam in the boiler
circulates through the machine without either diminution or
admixture with any other fluid, so that the boiler never
wants more feeding than what can be supplied from the
hot well <strong>H</strong>. This circumstance forms an important feature
in the machine, as it allows of ardent spirits being used in
the boiler instead of water, which, since they boil at low
heats, promised a saving of fuel. The inventor proposed
that the engine should be used as a still, as well as a mechanical
power, in which case the whole of the fuel would be
saved.</p>

<div class="figright" style="width: 261px;">
<a id="Fig067"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_270a.png" width="261" height="260" alt="" />
<div class="caption figure">Fig. 67.</div>
</div>

<div class="figright" style="width: 258px;">
<a id="Fig068"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_270b.png" width="258" height="158" alt="" />
<div class="caption figure">Fig. 68.</div>
</div>

<div class="ph3"><h3>(143.)</h3> That part of Cartwright's piston which in the common
piston is occupied by the packing of gasket, already explained
(<a href="#h3-141">141</a>.), was filled by a number of rings, one placed
within and above another, and divided into three or four
<a class="refpn" id="Pg248">[Pg248]</a>
segments. Two rings of brass were made of the full size of the
cylinder, and so ground as to fit the cylinder nearly steam-tight.
These were cut into several segments <strong>A A A</strong> (<a href="#Fig067"><i>fig.</i> 67.</a>), and
were placed one above
the other, so as to fill the
space between the top and
bottom plates of the piston.
The divisions of the
segments of the one ring
were made to fit between
the divisions of the other.
Within these another
series of rings, <strong>B B B</strong>, were
placed, similarly constructed,
so as to fit
within the first series in
the same manner as the first series were made to fit within
the cylinder. The joints of the upper series of each set of
rings are exhibited in the plan (<a href="#Fig067"><i>fig.</i> 67.</a>); the places of the
joints of the lower series are shown by dotted lines; the
position of the rings of each series one above the other is
shown in the section (<a href="#Fig068"><i>fig.</i> 68.</a>). The joints of the inner series
of rings are so placed as
to lie between those of the
outer series, to prevent
the escape of steam which
would take place by one
continued joint from top
to bottom of the packing.
The segments into which
the rings are divided are pressed outwards by steel springs
in the form of the letter V, the springs which act upon the
outer series of segments abutting upon the inner series, and
those which act on the inner series abutting upon the solid
centre of the piston: these springs are represented in <a href="#Fig067"><i>fig.</i> 67.</a></div>

<div class="figright" style="width: 259px;">
<a id="Fig069"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_271a.png" width="259" height="158" alt="" />
<div class="caption figure">Fig. 69.</div>
</div>

<div class="ph3"><h3>(144.)</h3> An improved form was given to the metallic piston
by Barton. Barton's piston consists of a solid cylinder of cast
iron, represented at <strong>A</strong> in section in <a href="#Fig069"><i>fig.</i> 69.</a>, and in plan in
<a class="refpn" id="Pg249">[Pg249]</a>
<a href="#Fig070"><i>fig.</i> 70.</a> In the centre of this is a conical hole, increasing in
magnitude downwards, to
receive the piston-rod, in
which the latter is secured
by a cross-pin <strong>B</strong>. A deep
groove, square in its section,
is formed around the
piston, so that while the
top and bottom of the piston
form circles equal in magnitude to the section of the
cylinder, the intermediate part of the body of the piston
forms a circle less than the former by the depth of the
groove. Let a ring of brass, cast iron, or cast steel, be
made to correspond in magnitude and form with this groove,
and let it be divided as represented in <a href="#Fig070"><i>fig.</i> 70.</a>, into four segments
<strong>C C C C</strong>, and four corresponding angular pieces <strong>D D D D</strong>.
Let the groove which surrounds the piston be filled by the
four segments with the four wedge-like angular pieces within
them, and let the latter be urged against the former by eight
spiral springs, as represented in <a href="#Fig069"><i>fig.</i> 69.</a> and <a href="#Fig070"><i>fig.</i> 70.</a> These
springs will abut against the solid centre by the piston, and
will urge the segments <strong>C</strong> against the cylinder. The spiral
springs which urge the wedges are confined in their action
by steel pins which pass through their centre, and by being
<a class="refpn" id="Pg250">[Pg250]</a>
confined in cylindrical cavities worked into the wedges and
into corresponding parts of the solid centre of the piston, as
the segments <strong>C</strong> wear, the springs urge the wedges outwards,
and the points of the latter protruding, are gradually worn
down so as to fill up the spaces left between the segments,
and thus to complete the outer surface of the piston.</div>

<div class="figcenter" style="width: 259px;">
<a id="Fig070"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_271b.png" width="259" height="254" alt="" />
<div class="caption figure">Fig. 70.</div>
</div>

<p>Various other forms of metallic pistons have been proposed,
but as they do not differ materially in principle from
those we have just described, it will not be necessary here to
describe them.</p>

<div class="figcenter" style="width: 448px;">
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_272.png" width="448" height="359" alt="" />
<div class="caption">ENGINE AT THE CITY SAW MILLS.</div>
</div>

<div class="figcenter" style="width: 453px;">
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_273.png" width="453" height="356" alt="" />
<div class="caption">FURNACE AT THE CITY SAW MILLS.</div>
</div>

<h2><a name="CHAP_IX" id="CHAP_IX">CHAP. IX.</a></h2>

<p class="right"><a class="refpn" id="Pg251">[Pg251]</a><br />
<a href="#CONTENTS"><small>TOC</small></a>&#160;&#160;<a
href="#INDEX"><small>INX</small></a></p>

<div class="chapheader">
CONSTITUENTS OF COAL.â€”PROCESS OF COMBUSTION.â€”HEAT EVOLVED
IN IT.â€”FORM AND STRUCTURE OF BOILER.â€”WAGGON BOILER.â€”FURNACE.â€”METHOD
OF FEEDING IT.â€”COMBUSTION OF GAS IN FLUES.â€”CONSTRUCTION
OF GRATE AND ASH-PIT.â€”MAGNITUDE OF HEATING
SURFACE OF BOILER.â€”STEAM-SPACE AND WATER-SPACE IN BOILER.â€”POSITION
OF FLUES.â€”METHOD OF FEEDING BOILER.â€”LEVEL
GAUGES.â€”SELF-REGULATING FEEDERS.â€”STEAM-GAUGE.â€”BAROMETER-GAUGE.â€”
INDICATOR.â€”COUNTER.â€”SAFETY-VALVE.â€”FUSIBLE PLUGS.â€”SELF-REGULATING
DAMPER.â€”SELF-REGULATING FURNACE.â€”POWER AND DUTY OF ENGINES.â€”HORSE-POWER
OF STEAM ENGINES.â€”EVAPORATION
PROPORTIONAL TO HORSE-POWER.â€”SOURCES OF LOSS OF
POWER.â€”ABSENCE OF GOOD PRACTICAL RULES FOR POWER.â€”COMMON
RULES FOLLOWED BY ENGINE MAKERS.â€”DUTY DISTINGUISHED FROM
POWER.â€”DUTY OF BOILERS.â€”PROPORTION OF STROKE TO DIAMETER
OF CYLINDER.â€”DUTY OF ENGINES.â€”CORNISH SYSTEM OF INSPECTION.â€”ITS
GOOD EFFECTS.â€”HISTORICAL DETAIL OF THE DUTY OF
CORNISH ENGINES.</div>


<div class="ph3fst"><h3>(145.)</h3> The machinery which has been explained in the
preceding chapters, consisting of the cylinder with its passages
and valves, the piston-rod, parallel motion, beam,
connecting-rod and crank, together with the condenser, air-pump,
and other appendages, having no source of moving
power in themselves, must be regarded as mere instruments
by which the mechanical effect developed by the furnace and
the boiler is transmitted to the working point and so
<a class="refpn" id="Pg252">[Pg252]</a>
modified as to be adapted to the uses to which the machine is
applied. The boiler is at once a magazine in which the
moving power is stored in sufficient quantity to supply the
demands of the engine and an apparatus in which that
power is fabricated. The mechanical effect evolved in the
conversion of water into steam by heat, is the process by
which the power of the steam-engine is produced, and space
is provided in the boiler, capacious enough to contain as much
steam as is necessary for the engine, besides a sufficient
quantity of water to continue that supply undiminished,
notwithstanding the constant drafts made upon it by the
cylinder: even the water itself, from the evaporation of which
the mechanical power is produced, ought to be regarded as
an instrument by which the effect of the heat of the combustible
is rendered mechanically efficient, inasmuch as the
same heat, applied not only to other liquids but even to
solids, would likewise be productive of mechanical effects.
The boiler and its furnace are therefore parts of the steam-engine,
the construction and operation of which are entitled
to especial attention.</div>


<div class="ph3"><h3>(146.)</h3> <strong class="m1">Coal</strong>, the combustible almost universally used in
steam-engines, is a substance, the principal constituents of
which are <em>carbon</em> and <em>hydrogen</em>, occasionally mixed with sulphur
in a small proportion, and earthy incombustible matter.
In different sorts of coal the proportions of these constituents
vary, but in coal of good quality about three quarters of the
whole weight of the combustible is carbon.</div>

<p>When carbon is heated to a temperature of about 700Â° in
an atmosphere of pure oxygen, it will combine chemically
with that gas, and the product will be the gas called <em>carbonic
acid</em>. The volume of carbonic acid produced by this combination,
will be exactly equal to that of the oxygen combined
with the carbon, and therefore the weight of a given
volume of the gas will be increased by the weight of carbon
which enters the combination. It is found that two parts
by weight of oxygen combined with three of carbon, form
carbonic acid. The weight of the carbonic acid, therefore,
produced in the combustion, will be greater than the weight
of the oxygen, bulk for bulk, in the proportion of five to
two, the volume being the same and the gases being
<a class="refpn" id="Pg253">[Pg253]</a>
compared at the same temperatures and under equal pressures.
In this combination heat is evolved in very large quantities.
This effect arises from the heat previously latent in the
carbon and oxygen being rendered sensible in the process
of combustion. The carbonic acid proceeding from the
combustion is by such means raised to a very high temperature,
and the carbon during the process acquires a heat
so intense as to become luminous; no flame, however, is
produced.</p>

<p>Hydrogen, heated to a temperature of about 1000Â°, in contact
with oxygen will combine with the latter, and a great evolution
of heat will attend the process; the gases will be rendered
luminous, and flame will be produced. The product of
this process will be water, which being exposed to the intense
heat of combustion, will be immediately converted into
steam. Hydrogen combines with eight times its own weight
of oxygen, producing nine times its own weight of water.</p>

<p>Hydrogen gas is, however, not usually disengaged from
coal in a simple form, but combined chemically with a certain
portion of carbon, the combination being called carburetted
hydrogen. Pure hydrogen burns with a very faintly luminous
blue flame, but carburetted hydrogen gives that bright
flame occasionally having an orange or reddish tinge, which
is seen to issue from burning coals: this is the gas used for
illumination, being expelled from the coal by the process
of coking, and conducted to the various burners through
proper pipes.</p>

<p>The sulphur, which in a very small proportion is contained
in coals, is also combustible, and combines in the process of
combustion with oxygen, forming sulphurous acid: it is also
sometimes evolved in combination with hydrogen, forming
sulphuretted hydrogen.</p>

<p>Atmospheric air consists of two gases, azote and oxygen,
mixed together in the proportion of four to one; five cubic
feet of atmospheric air consisting of four cubic feet of azote
and one of oxygen. Any combustible will combine with the
oxygen contained in atmospheric air, if raised to a temperature
somewhat higher than that which is necessary to cause
its combustion in an atmosphere of pure oxygen.</p>

<p>If coals, therefore, or other fuel exposed to atmospheric
<a class="refpn" id="Pg254">[Pg254]</a>
air, be raised to a sufficiently high temperature, their combustible
constituents will combine with the oxygen of the
atmospheric air, and all the phenomena of combustion will
ensue. In order, however, that the combustion should be
continued, and should be carried on with quickness and activity,
it is necessary that the carbonic acid, and other products,
should be removed from the combustible as they are
produced, and fresh portions of atmospheric air brought into
contact with it; otherwise the combustible would soon be
surrounded by an atmosphere composed chiefly of carbonic
acid to the exclusion of atmospheric air, and therefore of uncombined
oxygen, and consequently the combustion would
cease, and the fuel be extinguished. To maintain the combustion,
therefore, a current of atmospheric air must be constantly
carried through the fuel: the quantity and force of
this current must depend on the quantity and quality of the
fuel to be consumed. It must be such that it shall supply
sufficient oxygen to the fuel to maintain the combustion, and
not more than sufficient, since any excess would be attended
with the effect of absorbing the heat of combustion, without
contributing to the maintenance of that effect.</p>

<p>Heat is communicated from body to body in two ways, by
radiation and by contact.</p>

<p>Rays of heat issue from a heated body, and are dispersed
through the surrounding space in a manner, and according to
laws, similar to those which govern the radiation of light.
The heat thus radiated meeting other bodies is imparted to
them, and penetrates them with more or less facility according
to their physical qualities.</p>

<p>A heated body also brought into contact with another body
of lower temperature, communicates heat to that other body,
and will continue to do so until the temperature of the two
bodies in contact shall be equalised. Heat proceeds from fuel
in a state of combustion in both these ways: the heated fuel
radiates heat in all directions around it, and the heat thus
radiated will be imparted to all parts of the furnace which
are exposed to the fuel.</p>

<p>The gases, which are the products of the combustion, escape
from the fuel at a very high temperature, and consequently,
in acquiring that temperature they absorb a considerable
<a class="refpn" id="Pg255">[Pg255]</a>
quantity of the heat of combustion. But besides the gases
actually formed in the process of combustion, the azote forming
four fifths of the air carried through the fuel to support
the combustion, absorbs heat from the combustible, and
rises into the upper part of the furnace at a high temperature.
These various gases, if conducted directly to the chimney,
would carry off with them a considerable quantity of the
heat. Provision should therefore be made to keep them in
contact with the boiler such a length of time as will enable
them to impart such a portion of the heat which they have
absorbed from the fuel, as will still leave them at a temperature
sufficient, and not more than sufficient, to produce
the necessary draft in the chimney.</p>


<div class="ph3"><h3>(<a id="h3-147"></a>147.)</h3> The forms of boiler which have been proposed as
the most convenient for the attainment of all these requisite
purposes have been very various. If strength alone were
considered, the spherical form would be the best; and the
early boilers were very nearly hemispheres, placed on a
slightly concave base. The form adopted by Watt, called
the waggon boiler, consists of a semi-cylindrical top, flat perpendicular
sides, flat ends, and a slightly concave bottom.
The steam intended to be used in boilers of this description
did not exceed the pressure of the external atmosphere by
more than from 3 to 5 lbs. per square inch; and the flat
sides and ends, though unfavourable to strength, could be constructed
sufficiently strong for this purpose. In a boiler of
this sort, the air and smoke passing through the flues that
are carried round it, are in contact at one side only with the
boiler. The brickwork, or other materials forming the flue,
must therefore be non-conductors of heat, that they may not
absorb any considerable portion of heat from the air passing
in contact with them. A boiler of this form is represented
in <a href="#Fig071"><i>fig.</i> 71.</a></div>

<div class="figcenter" style="width: 445px;">
<a id="Fig071"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_278.png" width="445" height="482" alt="" />
<div class="caption figure">Fig. 71</div>
</div>

<p>The grate and a part of the flues are rendered visible by
the removal of a portion of the surrounding masonry in which
the boiler is set. The interior of the boiler is also shown by
cutting off one half of the semi-cylindrical roof. A longitudinal
vertical section is shown in <a href="#Fig072"><i>fig.</i> 72.</a>, and a cross section
in <a href="#Fig073"><i>fig.</i> 73.</a> A horizontal section taken above the level of the
grate, and below the level of the water in the boiler, showing
<a class="refpn" id="Pg256">[Pg256]</a>
the course of the flues, is given in <a href="#Fig074"><i>fig.</i> 74.</a> The corresponding
parts in all the figures are marked by the same letters.</p>

<div class="figcenter" style="width: 439px;">
<a id="Fig072"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_279.png" width="439" height="423" alt="" />
<div class="caption figure">Fig. 72.</div>
</div>

<p>The door by which fuel is introduced upon the grate is
represented at <strong>A</strong>, and the door leading to the ash-pit at <strong>B</strong>.
The fire bars at <strong>C</strong> slope downwards from the front at an angle
of about 25Â°, giving a tendency to the fuel to move from the
front towards the back of the grate. The ash-pit <strong>D</strong> is constructed
of such a magnitude, form, and depth, as to admit a
current of atmospheric air to the grate-bars, sufficient to sustain
the combustion. The form of the ash-pit is usually
wide below, contracting towards the top.</p>

<p>The fuel when introduced at the fire-door <strong>A</strong>, should be laid
on that part of the grate nearest to the fire-door, called the
dead plates: there it is submitted to the process of coking, by
which the gases and volatile matter which it contains are
expelled, and being carried by a current of air, admitted
<a class="refpn" id="Pg257">[Pg257]</a>
through small apertures in the fire-door over the burning fuel
in the hinder part of the grate, they are burnt. When the
fuel in front of the grate has been thus <em>coked</em>, it is pushed
back, and a fresh feed introduced in front. The coal thus
pushed back soon becomes vividly ignited, and by continuing
this process, the fuel spread over the grate is maintained in
the most active state of combustion at the hinder part of the
grate. By such an arrangement, the smoke produced by the
combustion of the fuel may be burnt before it enters the
flues. The flame and heated air proceeding from the burning
fuel arising from the grate, and rushing towards the back of
the furnace, passes over the <em>fire-bridge</em> <strong>E</strong>, and is carried
through the flue <strong>F</strong> which passes under the boiler. This flue
(the cross section of which is shown in <a href="#Fig073"><i>fig.</i> 73.</a>, by the dark
shade put under the boiler) is very nearly equal in width to
the bottom of the boiler, the space at the bottom of the
boiler, near the corners, being only what is sufficient to give
the weight of the boiler support on the masonry forming the
<a class="refpn" id="Pg258">[Pg258]</a>
sides of the flue. The bottom of the boiler being concave,
the flame and heated air as they pass along the flue rise to
the upper part by the effects of their high temperature, and
<em>lick</em> the bottom of the boiler from the fire-bridge at <strong>E</strong> to the
further end <strong>G</strong>.</p>

<div class="figcenter" style="width: 394px;">
<a id="Fig073"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_280a.png" width="394" height="388" alt="" />
<div class="caption figure">Fig. 73.</div>
</div>

<p>At <strong>G</strong> the flue rises to <strong>H</strong>, and turning to the side of the
boiler at <strong>I I</strong>, conducts the flame in contact with the side from
the back to the front; it then passes through the flue <strong>K</strong>
across the front, and returns to the back by the other side
<a class="refpn" id="Pg259">[Pg259]</a>
flue <strong>L</strong>. The side flue is represented, stripped of the masonry,
in <a href="#Fig071"><i>fig.</i> 71.</a>, and also appears in the plan in <a href="#Fig074"><i>fig.</i> 74.</a>, and in the
cross section in <a href="#Fig073"><i>fig.</i> 73.</a> The course of the air is represented
in <a href="#Fig074"><i>fig.</i> 74.</a> by the arrows. From the flue <strong>L</strong> the air is conducted
into the chimney at <strong>M</strong>.</p>

<div class="figcenter" style="width: 441px;">
<a id="Fig074"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_280b.png" width="441" height="236" alt="" />
<div class="caption figure">Fig. 74.</div>
</div>

<p>By such an arrangement, the flame and heated air proceeding
from the grate are made to circulate round the boiler,
and the length and magnitude of the flues through which
it is conducted should be such, that when it shall arrive at
the chimney its temperature shall be reduced, as nearly as is
consistent with the maintenance of draught in the chimney,
to the temperature of the water with which it is in contact.</p>

<p>The method of feeding the furnace, which has been described
above, is one which, if conducted with skill and care,
would produce a much more perfect combustion of the fuel
than would attend the common method of filling the grate
from the back to the front with fresh fuel, whenever the furnace
is fed. This method, however, is rarely observed in the
management of the furnace. It requires the constant attention
of the stokers (such is the name given to those who feed
the furnaces). The fuel must be supplied, not in large
quantities, and at distant intervals, but in small quantities
and more frequently. On the other hand, the more common
practice is to allow the fuel on the grate to be in a great
degree burned away, and then to heap on a large quantity of
fresh fuel, covering over with it the burning fuel from the back
to the front of the grate. When this is done, the heat of the
ignited coal acting upon the fresh fuel introduced, expels the
gases combined with it and, mixed with these, a quantity of
carbon, in a state of minute division, forming an opaque black
smoke. This is carried through the flues and drawn up the
chimney. The consequence is, that not only a quantity
of solid fuel is sent out of the chimney unconsumed, but
the hydrogen and other gases also escape unburned, and a
proportional waste of the combustible is produced; besides
which, the nuisance of an atmosphere filled with smoke
ensues. Such effects are visible to all who observe the chimneys
of steam-vessels, while the engine is in operation. When
the furnaces are thus filled with fresh fuel, a large volume of
<a class="refpn" id="Pg260">[Pg260]</a>
dense black smoke is observed to issue from the chimney.
This gradually subsides as the fuel on the grate is ignited,
and does not reappear until a fresh feed is introduced.</p>

<p>This method of feeding, by which the furnace would
be made to consume its own smoke, and the combustion
of the fuel be rendered complete, is not however
free from counteracting effects. In ordinary furnaces the
feed can only be introduced by opening the fire-doors, and
during the time the fire-doors are opened a volume of cold
air rushes in, which passing through the furnace is carried
through the flues to the chimney. Such is the effect of this
in lowering the temperature of the flues, that in many cases
the loss of heat occasioned is greater than any economy
of fuel obtained by the complete consumption of smoke.
Various methods, however, may be adopted by which fuel
may be supplied to the grate without opening the fire-doors,
and without disturbing the supply of air to the fire. A
hopper built into the front of the furnace, with a moveable
bottom or valve, by which coals may be allowed to drop in
from time to time upon the front of the grate, would accomplish
this.</p>


<div class="ph3">
<h3>(148.)</h3> In order to secure the combustion of the gases evolved
from the coals placed in the front of the grate, it is necessary
that a supply of atmospheric air should be admitted
with them over the burning fuel. This is effected by small
apertures or regulators, provided in the fire-doors, governed
by sliding-plates, by which they may be opened or closed to
any required extent.</div>

<p>A patent has recently been granted to Mr. Williams,
one of the directors of the City of Dublin Steam Navigation
Company, for a method of consuming the unburned gases
which escape from the grate, and are carried through the
flues. This method consists in introducing into the flue
tubes placed in a vertical position, the lower ends of which
being inserted in the bottom of the flue are made to communicate
with the ash-pit, and the upper ends of which
are closed. The sides and tops of these tubes are pierced
with small holes, through which atmospheric air drawn from
the ash-pit issues in jets. The oxygen supplied by this air
immediately combines with the carburetted hydrogen, which
<a class="refpn" id="Pg261">[Pg261]</a>
having escaped from the furnace unburned is carried through
the flues at a sufficient temperature to enter into combination
with the oxygen admitted through holes in the tubes. A
number of jets of flame thus proceed from these holes, having
an appearance similar to the flame of a gas-lamp.</p>

<p>It is evident that such tubes must be inefficient unless
they are placed in the flues so near the furnace, that the
temperature of the unburned gases shall be sufficiently high
to produce their combustion.</p>


<div class="ph3"><h3>(149.)</h3> The magnitude of the grate and ash-pit must be determined
by the rate at which the evaporation is required to be
conducted in the boiler and the quality of the fuel. It must
be a matter of regret, that the proportions of the various
parts of steam-engines, with their boilers and furnaces, have
not been determined by any exact or satisfactory experiments;
and those who project and manufacture the engines
themselves, are not less in ignorance on those points than
others. With coals of the common quality a certain average
proportion must exist between the necessary magnitude of
the grate-surface and the quantity of water to be evaporated
in a given time in the boiler. But what that proportion
is for any given quality of fuel, is at present unascertained.
Each engine-maker follows his own rule, and
the rule thus followed is in most cases a matter of bare conjecture,
unsupported by any experimental evidence. Some engine-makers
will allow a square foot of grate-surface for every
cubic foot of water per hour, which is expected to be evaporated
in the boiler; others allow only half a square foot:
and practice varies between these limits. Bituminous coals
which melt and cake, and which burn with much flame and
smoke, must be spread more thinly on the grate than other
descriptions of fuel, otherwise a considerable quantity of
combustible gases would be dismissed into the flues unburnt.
Such coals therefore, other circumstances being the same,
require a larger portion of grate-surface; and the same may
be said of coals which produce clinkers in their combustion,
and form lumps of vitrified matter on the grate, by which the
spaces between the grate-bars are speedily closed up. When
such fuel is used, the grate-bars require to be frequently raked
<a class="refpn" id="Pg262">[Pg262]</a>
out, otherwise the spaces between them being obstructed,
the draught would become insufficient for the due combustion
of the fuel.</div>

<p>To facilitate the raking out of the grate, the bars are
placed with their ends towards the fire-door: they are usually
made of cast-iron, from two to two inches and a half wide on
the upper surface, with intervals of nearly half an inch
between them. The bars taper downwards, their under
surfaces being much narrower than their upper, the spaces
between them thus widening, to facilitate the fall of the
ashes between them. The grate-bars slope downwards from
the front to the back. The height of the centre of the
bottom of the boiler, above the front of the grate, is usually
about two feet, and about three feet above the back of it.
The concave bottom of the boiler, however, brings its surfaces
at the slide closer to the grate.</p>


<div class="ph3"><h3>(150.)</h3> Between the evaporating power of the boiler, and the
magnitude of surface it exposes to the action of the furnace,
there is a relation which, like that of the grate surface,
has never been ascertained by any certain or satisfactory
experimental investigation; much less have the different
degrees of efficiency attending different parts of the boiler-surface
been determined. That part of the surface of the
boiler immediately over and around the grate, is exposed to
the immediate radiation of the burning fuel, and is therefore
probably the most efficient in the production of steam. The
tendency of flame and heated air to rise, would naturally
bring them in the flues into closer contact with those
parts of the boiler-surface which are horizontal in their position,
and which form the tops of the flues, than with those which
are lateral or vertical in their position, and which form the
sides of the flues. In a boiler constructed like that already
described, the flue-surface therefore, which would be most
efficient, would be the concave bottom of the boiler extending
from the fire-bridge to its remote end. In some boilers,
especially those in which steam of high pressure is produced,
the form is cylindrical, the middle flue being formed into
an elliptical tube the greater axis of which is horizontal
from end to end of the boiler. It seems doubtful, however,
<a class="refpn" id="Pg263">[Pg263]</a>
whether in such a boiler the heat produces any useful effect
on the water below the flue, the water above being always at
a higher temperature, and therefore lighter than that below,
and consequently no currents being established between the
upper and lower strata of the water.</div>

<p>It was considered by Mr. Watt, but we are not aware on
what experimental grounds, that from eight to ten square
feet of heating surface were sufficient to produce the evaporation
of one cubic foot of water per hour. The practice
of engine-makers since that time has been to increase the
allowance of heating surface for the same rate of evaporation.
Engine-builders have varied very much in this
respect, some allowing twelve, fifteen, and even eighteen
square feet of surface for the same rate of evaporation. It
must, however, still be borne in mind, that whether this
increased allowance did or did not produce the actual evaporation
imputed to it, has not been, as far as we are
informed, ever accurately ascertained. The production of a
given rate of evaporation by a moderate heat diffused over
a larger surface, rather than by a fiercer temperature confined
to a smaller surface, is attended with many practical advantages.
The plates of the boiler acted upon by the fire are
less exposed to oxydisation, and the boiler will be proportionally
more durable.</p>


<div class="ph3"><h3>(151.)</h3> Besides presenting to the action of the fire a sufficient
surface to produce steam at the required rate, the capacity
of the boiler must be proportioned to the quantity of water to
be evaporated. The space within the boiler is appropriated
to a twofold purpose: 1st, To contain the water to be evaporated;
2dly, To contain a quantity of ready made steam
for the supply of the cylinder. If the space appropriated to
the steam did not bear a considerable proportion to the
magnitude of the cylinder, the momentary expansion of the
steam passing to the cylinder from the boiler at each stroke
would reduce the pressure of the steam in a great proportion,
and unless the pressure in the boiler were considerably
greater than that which the steam is intended to
have in the cylinder, the pressure in the latter would be
reduced below the proper amount. The proportion of the
<a class="refpn" id="Pg264">[Pg264]</a>
steam space in the boiler to the magnitude of the cylinder
has been very variously estimated, nor can it be said that
any practical rule of a general kind has been adopted. It is
held by some that the steam-space will be sufficient if it
contain five times the quantity of steam consumed at each
stroke, while others maintain that it should contain at least
ten times that quantity, and opinions vary between these
limits.</div>


<div class="ph3">
<h3>(152.)</h3> The proportion of water-space in the boiler to its
evaporating power should also be regulated, so that the introduction
of the feed at a comparatively low temperature may
not unduly chill the water in the boiler. Supposing the
feed to be introduced in a low pressure boiler at the temperature
of 100Â°, and that the necessary temperature within the
boiler be 225Â°, the quantity of water it contains should be
about five times the quantity evaporated, and therefore also
five times the quantity introduced through the feed per hour.
For every cubic foot of water per hour therefore, intended
to be evaporated by the boiler, water-space for five cubic feet
should be provided. It is, however, right to repeat that this
(like almost every other so called rule) is the result not of any
exact general calculation, but one deduced from the custom
which has obtained among the manufacturers of steam-engines.</div>


<div class="ph3"><h3>(153.)</h3> The surface of the water in the boiler should always
be above the range of the flues. When the heated air in the
flues acts upon a part of the boiler within which water is
contained, the water within receiving an increased temperature
becomes, bulk for bulk, lighter than the strata of water
above it, and ascends. It is replaced by the descending
strata, which, in their turn receiving increased temperature,
rise to the surface; or if the action of the heat convert the
water into steam, the bubbles of steam rise to the surface,
fresh portions of water continually coming into contact with
the boiler-plates on which the heated air or flame acts. By
this process the boiler-plates are continually cooled, either by
being successively washed by water at a lower temperature,
or by the heat taken from them becoming latent in the steam
bubbles formed in contact with them. But if the heat act
<a class="refpn" id="Pg265">[Pg265]</a>
upon a part of the boiler containing steam within it, which
steam being a slow recipient of heat, and no currents being
established, nor any phenomenon produced in which heat is
rendered latent, the heat of the fire communicated to the
boiler-plates accumulates in them, and raises their temperature
to an injurious degree. The plates may by this means
be softened, so as to cause the boiler to burst, or the difference
between the expansion of the highly heated plates thus
exposed to fire in contact with steam and that of the plates
which are cooled by contact with water, may cause the
joinings of the boiler-plates to open, and the boiler to leak.
By whatever means, therefore, the boiler be fed, care should
be taken that the evaporation should not be allowed to reduce
the level of the water in it below the highest flue.</div>


<div class="ph3">
<h3>(154.)</h3> As the water by which the boiler is fed must always
have a much lower temperature than that at which the boiler
is maintained, the supply of the feed will have a constant
tendency to lower the temperature of the water, and this
tendency will be determined by the proportion between the
magnitude of the feed and the quantity of water in the
boiler.</div>

<p>Since it is requisite that the level of the water in the
boiler shall not suffer any considerable change, it is evident
that the magnitude of the feed must be equal to the quantity
of water evaporated. If it were less, the level of the water
would continually fall by reason of the excess of the evaporation
over the feed; and if it were greater, the level would
rise by the accumulation of water in the boiler. If therefore
the quantity of water-space allowed in the boiler be five
times the volume of water evaporated per hour, the quantity
introduced by the feed per hour, whether continuously or at
intervals, must be of the same amount. Since the process
of evaporation is continuous, the variation of level of water
in the boiler will be entirely dependent on the intervals
between the successive feeds. If the feed be continuous,
and always equal to the evaporation, then the level of
the water in the boiler will undergo no change; but if
while the evaporation is continuous the feed be made at
intervals, then the change of level of water in the boiler as
<a class="refpn" id="Pg266">[Pg266]</a>
well as its change of temperature, will be subject to a variation
proportional to the intervals between the successive
feeds. It is manifest, therefore, that the feed should either
be uninterrupted or be supplied at short intervals, so that the
change of level and temperature of the water in the boiler
should not be considerable.</p>


<div class="ph3"><h3>(155.)</h3> Different methods have been, from time to time,
suggested for indicating the level of the water in the boiler.
We have already mentioned the two gauge-pipes used in the
earlier steam-engines (<a href="#h3-31">31</a>.), and which are still generally
continued. There are, however, some other methods which
merit our attention.</div>

<div class="figleft" style="width: 173px;">
<a id="Fig075"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_288.png" width="173" height="203" alt="" />
<div class="caption figure">Fig. 75.</div>
</div>

<p>A weight <strong>F</strong> (<a href="#Fig075"><i>fig.</i> 75.</a>), half immersed in the water in the
boiler, is supported by a wire, which,
passing steam-tight through a small
hole in the top, is connected by a
flexible string, or chain, passing over
a wheel <strong>W</strong>, with a counterpoise <strong>A</strong>,
which is just sufficient to balance <strong>F</strong>
when half immersed. If <strong>F</strong> be raised
above the water, <i>A</i> being lighter
will no longer balance it, and <strong>F</strong> will
descend pulling up <strong>A</strong>, and turning
the wheel <strong>W</strong>. If, on the other hand, <strong>F</strong> be plunged deeper
in the water, <strong>A</strong> will more than balance it, and will pull it up,
so that the only position in which <strong>F</strong> and <strong>A</strong> will balance each
other is, when <strong>F</strong> is half immersed. The wheel <strong>W</strong> is so
adjusted, that when two pins placed on its rim are in the
horizontal position, the water is at its proper level. Consequently
it follows, that if the water rise above this level,
the weight <strong>F</strong> is lifted and <strong>A</strong> falls, so that the pins come
into another position. If, on the other hand, the level of
the water fall, <strong>F</strong> falls and <strong>A</strong> rises, so that the pins assume
a different position. Thus, in general, the position of the
pins becomes an indication of the quantity of water in the
boiler.</p>


<div class="ph3"><h3>(<a id="h3-156"></a>156.)</h3> Another method is to place a glass tube
(<a href="#Fig076"><i>fig.</i> 76.</a>), with
one end <strong>T</strong> entering the boiler above the proper level, and
the other end <strong>Tâ€²</strong> entering it below the proper level. It must
<a class="refpn" id="Pg267">[Pg267]</a>
be evident that the water in the tube
will always stand at the same level as the
water in the boiler, since the lower part
has a free communication with that
water, while the surface is submitted to
the pressure of the same steam as the
water in the boiler. This and the last-mentioned
gauge have the advantage of addressing the eye
of the engineer at once, without any adjustment; whereas
the gauge-cocks must be both opened, whenever the depth is
to be ascertained.</div>

<div class="figleft" style="width: 135px;">
<a id="Fig076"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_289a.png" width="135" height="115" alt="" />
<div class="caption figure">Fig. 76.</div>
</div>

<p>These gauges, however, require the frequent attention of
the engine-man; and it becomes desirable either to find some
more effectual means of awakening that attention, or to
render the supply of the boiler independent of any attention.
In order to enforce the attention of the engine-man to
replenish the boiler when partially exhausted by evaporation,
a tube was sometimes inserted at the lowest level to which it
was intended that the water should be permitted to fall.
This tube was conducted from the boiler into the engine-house,
where it terminated in a mouth-piece or whistle, so
that whenever the water fell below the level at which this
tube was inserted in the boiler, the steam would rush
through it, and issuing with great velocity at the mouth-piece,
would summon the engineer to his duty with a call
that would rouse him even from sleep.</p>

<div class="figright" style="width: 206px;">
<a id="Fig077"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_289b.png" width="206" height="232" alt="" />
<div class="caption figure">Fig. 77.</div>
</div>

<div class="ph3">
<h3>(157.)</h3> In the most effectual of
these methods, the task of replenishing
the boiler should still
be executed by the engineer; and
the utmost that the boiler itself
was made to do, was to give due
notice of the necessity for the
supply of water. The consequence
was, among other inconveniences,
that the level of the
water was subject to constant
variation.</div>

<p>To remedy this a method has been invented, by which
<a class="refpn" id="Pg268">[Pg268]</a>
the engine is made to feed its own boiler. The pipe <strong>G</strong>
(<a href="#Fig077"><i>fig.</i> 77.</a>), which leads from the hot water pump, terminates
in a small cistern <strong>C</strong> in which the water is received. In the
bottom of this cistern, a valve <strong>V</strong> is placed, which opens
upwards, and communicates with a feed-pipe, which descends
into the boiler below the level of the water in it.
The stem of the valve <strong>V</strong> is connected with a lever turning on
the centre <strong>D</strong>, and loaded with a weight <strong>F</strong> dipped in the
water in the boiler in a manner similar to that described
in <a href="#Fig075"><i>fig.</i> 75.</a>, and balanced by a counterpoise <strong>A</strong> in exactly the
same way. When the level of the water in the boiler falls,
the float <strong>F</strong> falls with it, and pulling down the arm of the
lever raises the valve <strong>V</strong>, and lets the water descend into the
boiler from the cistern <strong>C</strong>. When the boiler has thus been
replenished, and the level raised to its former place, <strong>F</strong> will
again be raised, and the valve <strong>V</strong> closed by the weight <strong>A</strong>. In
practice, however, the valve <strong>V</strong> adjusts itself by means of the
effect of the water on the weight <strong>F</strong>, so as to permit the water
from the feeding-cistern <strong>C</strong> to flow in a continued stream,
just sufficient in quantity to supply the consumption from
evaporation, and to maintain the level of the water in the
boiler constantly the same.</p>

<p>By this arrangement the boiler is made to replenish itself,
or, more properly speaking, it is made to receive such a
supply, as that it never wants replenishing, an effect which
no effort of attention on the part of an engine-man could
produce. But this is not the only good effect produced by
this contrivance. A part of the steam which originally left
the boiler, and having discharged its duty in moving the
piston, was condensed and reconverted into water, and lodged
by the air-pump in the hot well (<a href="#Fig077"><i>fig.</i> 77.</a>), is here again
restored to the source from which it came, bringing back all
the unconsumed portion of its heat preparatory to being once
more put in circulation through the machine.</p>

<p>The entire quantity of hot water pumped into the cistern
<strong>C</strong>, is not always necessary for the boiler. A waste-pipe may
be provided for carrying off the surplus, which may be
turned to any purpose for which it may be required; or it
may be discharged into a cistern to cool, preparatory to
<a class="refpn" id="Pg269">[Pg269]</a>
being restored to the cold cistern, in case water for the
supply of that cistern be not sufficiently abundant.</p>

<div class="figcenter" style="width: 345px;">
<a id="Fig078"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_291.png" width="345" height="524" alt="" />
<div class="caption figure">Fig. 78.</div>
</div>

<div class="ph3"><h3>(158.)</h3> Another method of arranging a self-regulating feeder
is shown in <a href="#Fig078"><i>fig.</i> 78.</a> <strong>A</strong> is a hollow ball of metal attached to
the end of a lever, whose fulcrum is at <strong>B</strong>. The other arm of
the lever <strong>C</strong> is connected with the stem of a spindle-valve,
communicating with a tube which receives water from the
feeding-cistern. Thus, when the level of the water in the
boiler subsides, the ball <strong>A</strong> preponderating over the weight of
the opposite arm, the lever falls, the arm <strong>C</strong> rises and opens
the valve, and admits the feeding water. This apparatus
will evidently act in the same manner and on the same principles
as that already described.
<a class="refpn" id="Pg270">[Pg270]</a></div>

<p>The mouth of the tube by which the feed is introduced
should be placed at that part of the boiler which is nearest
the end of the flues which issue into the chimney. By such
means the temperature of the water in contact with those
flues will be lowest at the place where the temperature of
the heated air intended to act upon it is also lowest. The
difference of the temperatures will therefore be greater than
it would be if the point of the boiler containing water of
a higher temperature was left in contact with this part of
the flue.</p>

<div class="figright" style="width: 199px;">
<a id="Fig079"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_292.png" width="199" height="332" alt="" />
<div class="caption figure">Fig. 79.</div>
</div>

<div class="ph3"><h3>(159.)</h3> It is necessary to have a ready method of ascertaining
at all times the pressure of the steam which is used in
working the engine. For this purpose a bent tube containing
mercury is inserted into some part of the apparatus,
which has free communication with
the steam. Let <strong>A B C</strong> (<a href="#Fig079"><i>fig.</i> 79.</a>)
be such a tube. The pressure of
the steam forces the mercury down
in the leg <strong>A B</strong>, and up in the leg
<strong>B C</strong>. If the mercury in both legs
be at exactly the same level, the
pressure of the steam must be
exactly equal to that of the atmosphere;
because the steam pressure
on the mercury in <strong>A B</strong> balances
the atmospheric pressure on the
mercury in <strong>B C</strong>. If, however, the
level of the mercury in <strong>B C</strong> be
above the level of the mercury in
<strong>B A</strong>, the pressure of the steam will
exceed that of the atmosphere.
The excess of its pressure above that of the atmosphere may
be found by observing the difference of the level of the
mercury in the tubes <strong>B C</strong> and <strong>B A</strong>, allowing a pressure of
one pound on each square inch for every two inches in the
difference of the levels.</div>

<p>If, on the contrary, the level of the mercury in <strong>B C</strong> should
fall below its level in <strong>A B</strong>, the atmospheric pressure will
<a class="refpn" id="Pg271">[Pg271]</a>
exceed that of the steam, and the quantity of the excess may
be ascertained exactly in the same way.</p>

<p>If the tube be glass, the difference of levels of the mercury
would be visible; but it is most commonly made of iron;
and in order to ascertain the level, a thin wooden rod with
a float is inserted in the open end of <strong>B C</strong>, so that the portion
of the stick within the tube indicates the distance of the level
of the mercury from its mouth. A bulb or cistern of mercury
might be substituted for the leg <strong>A B</strong>, as in the common barometer.
This instrument is called the <em>steam-gauge</em>.</p>

<p>If the steam-gauge be used as a measure of the strength
of the steam which presses on the piston, it ought to be on
the same side of the throttle-valve (which is regulated by the
governor) as the cylinder; for if it were on the same side of
the throttle-valve with the boiler, it would not be affected by
the changes which the steam may undergo in passing through
the throttle-valve, when partially closed by the agency of the
governor.</p>

<p>For boilers in which steam of very high pressure is used,
as in those of locomotive engines, a steam-gauge, constructed
on the above principle, would have inconvenient or impracticable
length. In such boilers the pressure of the steam is
equal to four or five times that of the atmosphere, to indicate
which the column of mercury in the steam-gauge would
be four or five feet in height. In such cases a thermometer-gauge
may be used with advantage. The principle of
this gauge is founded on the fact, that between the pressure
and temperature of steam produced in contact with water
there is a fixed relation, the same temperature always corresponding
to the same pressure. If, therefore, a thermometer
be immersed in the boiler which shall show the
temperature of the steam, a scale may be attached to it, on
which shall be engraved the corresponding pressures. Such
gauges are now very generally used on locomotive engines.</p>

<div class="figright" style="width: 65px;">
<a id="Fig080"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_294.png" width="65" height="184" alt="" />
<div class="caption figure">Fig. 80.</div>
</div>

<div class="ph3"><h3>(160.)</h3> The force with which the piston is pressed depends
on two things, 1st, the actual strength of the steam which
presses on it; and, 2dly, on the actual strength of the vapour
which resists it. For although the vacuum produced by the
method of separate condensation be much more perfect than
<a class="refpn" id="Pg272">[Pg272]</a>
what had been produced in the atmospheric engines, yet still
some vapour of a small degree of elasticity is found to be
raised from the hot water in the bottom of the condenser
before it can be extracted by the air-pump. One of these
pressures is indicated by the steam-gauge already described;
but still, before we can estimate the force with which the
piston descends, it is necessary to ascertain the force of the
vapour which remains uncondensed, and resists the motion
of the piston. Another gauge, called the barometer-gauge, is
provided for this purpose. A glass tube <strong>A B</strong> (<a href="#Fig080"><i>fig.</i> 80.</a>), more
than thirty inches long and open at both ends, is
placed in an upright or vertical position, having the
lower end <strong>B</strong> immersed in a cistern of mercury <strong>C</strong>.
To the upper end is attached a metal tube, which
communicates with the condenser, in which a constant
vacuum, or rather high degree of rarefaction,
is sustained. The same vacuum must therefore
exist in the tube <strong>A B</strong>, above the level of the mercury,
and the atmospheric pressure on the surface
of the mercury in the cistern <strong>C</strong> will force the
mercury up in the tube <strong>A B</strong>, until the column which
is suspended in it is equal to the difference between the
atmospheric pressure and the pressure of the uncondensed
steam. The difference between the column of mercury sustained
in this instrument and in the common barometer, will
determine the strength of the uncondensed steam, allowing a
force proportional to one pound per square inch for every
two inches of mercury in the difference of the two columns.
In a well-constructed engine which is in good order, there is
very little difference between the altitude in the barometer-gauge
and the common barometer.</div>

<p>To compute the force with which the piston descends, thus
becomes a very simple arithmetical process. First, ascertain
the difference of the levels of the mercury in the steam-gauge;
this gives the excess of the steam pressure above the
atmospheric pressure. Then find the height of the mercury
in the barometer-gauge; this gives the excess of the atmospheric
pressure above the uncondensed steam. Hence, if
these two heights be added together, we shall obtain the
<a class="refpn" id="Pg273">[Pg273]</a>
excess of the impelling force of the steam from the boiler, on
the one side of the piston, above the resistance of the uncondensed
steam on the other side: this will give the effective
impelling force. Now, if one pound be allowed for every
two inches of mercury in the two columns just mentioned,
we shall have the number of pounds of impelling pressure
on every square inch of the piston. Then, if the number of
square inches in the section of the piston be found, and multiplied
by the number of pounds on each square inch, the
force with which it moves will be obtained.</p>

<p>From what we have stated it appears that, in order to
estimate the force with which the piston is urged, it is necessary
to refer to both the barometer and the steam-gauge.
This double computation may be obviated by making one
gauge serve both purposes. If the end <strong>C</strong> of the steam-gauge
(<a href="#Fig079"><i>fig.</i> 79.</a>), instead of communicating with the atmosphere
were continued to the condenser, we should have the pressure
of the steam acting upon the mercury in the tube <strong>B A</strong>, and
the pressure of the uncondensed vapour which resists the
piston acting on the mercury in the tube <strong>B C</strong>. Hence the
difference of the levels of the mercury in the tubes would at
once indicate the difference between the force of the steam
and that of the uncondensed vapour, which is the effective
force with which the piston is urged.</p>


<div class="ph3"><h3>(161.)</h3> But these methods of determining the effective
force by which the piston is urged, can only be regarded as
approximations, and not very perfect ones. If the condensation
of steam on one side of the piston were instantaneously
effected, or the uncondensed vapour were of the
same tension during the whole stroke; and if, besides this,
the pressure of steam on the piston were of uniform intensity
from the beginning to the end of the stroke, then the steam
and barometer gauges taken together would become an accurate
index of the effective force of steam on the piston: but
such is not the case. When the steam is first admitted through
the steam-valve it acts on the piston with a pressure which is
first slightly diminished, and afterwards a little increased,
until it arrives at that part of the stroke at which the steam-valve
is closed, after which the pressure is diminished. The
<a class="refpn" id="Pg274">[Pg274]</a>
pressure, therefore, urging the piston is subject to variation;
but the pressure of the uncondensed vapour on the other
side of the piston is subject to still greater change. At the
moment the exhausting-valve is opened, the piston is relieved
from the pressure upon it by the commencement of the condensation;
but this process during the descent of the piston
is gradual, and the vacuum is rendered more and more perfect,
until the piston has nearly attained the limit of its play.
These variations, both as well of the force urging the piston
as of the force resisting it, are such as not to be capable of
being accurately measured by a mercurial column, since they
would produce oscillations in such a column, which would
render any observations of its mean height impracticable.</div>

<p>To measure the mean efficient force of the piston, taking
into account these circumstances, Mr. Watt invented an
instrument, which, like all his mechanical inventions, has
answered its purpose perfectly, and is still in general
use. This instrument, called an <em>indicator</em>, consists of a
cylinder of about
<span class="fraction">1<sup>3</sup>â„<sub>4</sub></span>
inch in diameter, and 8 inches in
length. It is bored with great accuracy, and fitted with a
solid piston moving steam-tight in it with very little friction.
The rod of this piston is guided in the direction of the axis
of the cylinder through a collar in the top, so as not to be
subject to friction in any part of its play. At the bottom
of the cylinder is a pipe governed by a stop-cock and turned
in a screw, by which the instrument may be screwed on the
top of the steam-cylinder of the engine. In this position, if
the stop-cock of the indicator be opened, a free communication
will be made between the cylinder of the indicator
and that of the engine. The piston-rod of the indicator is
attached to a spiral spring, which is capable of extension
and compression, and which by its elasticity is capable of
measuring the force which extends or compresses it in the
same manner as a spring steel-yard or balance. If a scale be
attached to the instrument at any point on the piston-rod
to which an index might be attached, then the position of
that index upon the scale would be governed by the position
of the indicator-piston in its cylinder. If any force pressed
the indicator-piston upwards, so as to compress the spring,
<a class="refpn" id="Pg275">[Pg275]</a>
the index would rise upon the scale; and if, on the other
hand, a force pressed the indicator-piston downwards, then
the spiral spring would be extended, and the index on the
piston-rod descend upon the scale. In each case the force
of the spring, whether compressed or extended, would be
equal to the force urging the indicator-piston, and the scale
might be so divided as to show the amount of this force.</p>

<p>Now, let the instrument be supposed to be screwed upon
the top of the cylinder of a steam-engine, and the stop-cock
opened so as to leave a free communication between the
cylinder of the indicator below its piston and the cylinder of
the steam-engine above the steam-piston. At the moment
the upper steam-valve is opened, the steam rushing in upon
the steam-piston will also pass into the indicator, and press
the indicator-piston upwards: the index upon its piston-rod
will point upon the scale to the amount of pressure thus
exerted. As the steam-piston descends, the indicator-piston
will vary its position with the varying pressure of the steam
in the cylinder, and the index on the piston-rod will play
upon the scale, so as to show the pressure of the steam at
each point during the descent of the piston.</p>

<p>If it were possible to observe and record the varying
position of the index on the piston-rod of the indicator, and
to refer each of these varying positions to the corresponding
point of the descending stroke, we should then be able to
declare the actual pressure of the steam at every point of the
stroke. But it is evident that such an observation would
not be practicable. A method, however, was contrived by
Mr. Southern, an assistant of Messrs. Boulton and Watt, by
which this is perfectly effected. A square piece of paper,
or card, is stretched upon a board, which slides in grooves
formed in a frame. This frame is placed in a vertical position
near the indicator, so that the paper may be moved in
a horizontal direction backwards and forwards, through a
space of fourteen or fifteen inches. Instead of an index a
pencil is attached to the indicator of the piston-rod: this
pencil is lightly pressed by a spring against the paper above
mentioned, and as the paper is moved in a horizontal direction
<a class="refpn" id="Pg276">[Pg276]</a>
under the pencil, would trace upon the paper a line.
If the pencil were stationary this line would be straight and
horizontal, but if the pencil were subject to a vertical motion,
the line traced on the paper moved under the pencil horizontally
would be a curve, the form of which would depend
on the vertical motion of the pencil. The board thus supporting
the paper is put into connexion by a light cord
carried over pulleys with some part of the parallel motion, by
which it is alternately moved to the right and to the left.
As the piston ascends or descends, the whole play of the
board in the horizontal direction will therefore represent
the length of the stroke, and every fractional part of that
play will correspond to a proportional part of the stroke of
the steam-piston.</p>

<div class="figcenter" style="width: 357px;">
<a id="Fig081"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_299.png" width="357" height="147" alt="" />
<div class="caption figure">Fig. 81.</div>
</div>

<p>The apparatus being thus arranged, let us suppose the
steam-piston at the top of the cylinder commencing its descent.
As it descends, the pencil attached to the indicator
piston-rod varies its height according to the varying pressure
of the steam in the cylinder. At the same time the paper is
moved uniformly under the pencil, and a curved line is traced
upon it from right to left. When the piston has reached the
bottom of the cylinder, the upper exhausting-valve is opened,
and the steam drawn off to the condenser. The indicator-piston
being immediately relieved from a part of the pressure
acting upon it descends, and with it the pencil also descends;
but at the same time the steam-piston has begun to ascend,
and the paper to return from left to right under the pencil.
While the steam-piston continues to ascend, the condensation
becomes more and more perfect, and the vacuum in the cylinder,
and therefore also in the indicator, being gradually increased
in power, the atmospheric pressure above the indicator-piston
presses it downwards and stretches the spring.
The pencil meanwhile, with the paper moving under it from
right to left, traces a second curve. As the former curve
showed the actual pressure of the steam impelling the piston
in its descent, this latter will show the pressure of the uncondensed
steam raising the piston in its ascent, and a comparison
of the two will exhibit the effective force on the
piston. <a href="#Fig081"><i>Fig.</i> 81.</a> represents such a diagram as would be
<a class="refpn" id="Pg277">[Pg277]</a>
produced by this instrument. <strong>A B C</strong> is the curve traced by the
pencil during the descent of the piston, and <strong>C D E</strong> that during
its ascent. <strong>A</strong> is the position of the pencil at the moment the
piston commences its descent, <strong>B</strong> is its position at the middle
of the stroke, and <strong>C</strong> at the termination of the stroke. On
closing the upper steam-valve and closing the exhausting-valve,
the indicator-piston being gradually relieved from the
pressure of the steam the pencil descends, and at the same
time the paper moving from left to right, the pencil traces the
curve <strong>C D E</strong>, the gradual descent of this curve showing the
progressive increase of the vacuum. As the atmospheric pressure
constantly acts above the piston of the indicator, its position
will be determined by the difference between the atmospheric
pressure and the pressure of the steam below it; and
therefore the difference between the heights of the pencil at
corresponding points in the ascending and descending stroke,
will express the difference between the pressure of the steam
impelling the piston in the ascent and resisting it in the descent
at these points. Thus at the middle of the stroke, the
line <strong>B D</strong> will express the extent to which the spring governing
the indicator-piston would be stretched by the difference between
the force of steam impelling the piston at the middle of
the descending stroke, and the force of steam resisting it at
the middle of the ascending stroke. The force therefore
measured by the line <strong>B D</strong> will be the effective force on the
piston at that point; and the same may be said of every part
of the diagram produced by the indicator.</p>

<p>The whole mechanical effect produced by the stroke of the
piston being composed of the aggregate of all its varying
effects throughout the stroke, the determination of its amount
<a class="refpn" id="Pg278">[Pg278]</a>
is a matter of easy calculation by the measurement of the
diagram supplied by the indicator. Let the horizontal play
of the pencil from <strong>A</strong> to <strong>C</strong> be divided into any proposed number
of equal parts, say ten: at the middle of the stroke, <strong>B D</strong>
expresses the effective force on the piston, and if this be considered
to be uniform through the tenth part of the stroke, as
from <i>f</i> to <i>g</i>, then the number of pounds expressed by <strong>B D</strong>
multiplied by the tenth part of the stroke expressed in parts
of a foot, will be the mechanical effect through that part of the
stroke expressed in pounds' weight raised one foot. In like
manner <i>m n</i> will express the effective force on the piston after
three fourths of the stroke have been performed, and if this
be multiplied by a tenth part of the stroke as before, the mechanical
effect similarly expressed will be obtained; and the
same process being applied to any successive tenth part of
the stroke, and the numerical results thus obtained being
added together, the whole effect of the stroke will be obtained,
expressed in pounds' weight raised one foot.</p>


<div class="ph3"><h3>(162.)</h3> By means of the indicator, the actual mechanical
effect produced by each stroke of the engine can be obtained,
and if the actual number of strokes made in any given time
be known, the whole effect of the moving power would be
determined. An instrument called a <em>counter</em> was also contrived
by Watt, to be attached either to the working beam or
to any other reciprocating part of the engine. This instrument
consisted of a train of wheel-work with governing hands
or indices moved upon divided dials, like the hand of a
clock. A record of the strokes was preserved by means
precisely similar to those by which the hands of a clock
or time-piece indicated and recorded the number of vibrations
of the pendulum or balance-wheel.</div>


<div class="ph3"><h3>(163.)</h3> To secure the boiler from accidents arising from the
steam contained in it acquiring an undue pressure, a safety-valve
is used, similar in principle to those adopted in the early
engines. This valve is represented in <a href="#Fig071"><i>fig.</i> 71.</a> at <strong>N</strong>. It is a
conical valve, kept down by a weight sliding on a rod upon
it. When the pressure of the steam overcomes the force of
this weight, it raises the valve and escapes, being carried off
through the tube.
<a class="refpn" id="Pg279">[Pg279]</a></div>

<p>With a view to the economy of heat, this waste steam
tube is sometimes conducted into the feeding cistern, where
the steam carried off by it is condensed, and heats the feeding
water.</p>

<p>The magnitude of the safety-valve should be such that,
when open, steam should be capable of passing through it as
rapidly as it is generated in the boiler. The superficial magnitude,
therefore, of such valves must be proportional to the
evaporating power of the boiler. In low pressure boilers the
steam is generally limited to five or six pounds' pressure per
square inch, and consequently the load over the safety-valve
in pounds would be found by multiplying the superficial
magnitude of its smallest part by these numbers. In boilers
in which the steam is maintained at a higher pressure, it would
be inconvenient to place upon the safety-valve the necessary
weight. In such cases a lever is used, the shorter arm of which
presses down the valve, and the longer arm is held down by
a weight capable of adjustment, so that the pressure on the
valve may be regulated at discretion. Two safety-valves
should be provided on all boilers, one of which should be
locked up, so that the persons in care of the engine should
have no power to increase the load upon it. In such case,
however, it is necessary that a handle connected with the
valve should project outside the box containing it, so that it
may always be possible for the engineer to ascertain that the
valve is not locked in its seat, a circumstance which is liable
to happen.</p>

<p>Sometimes also two safety-valves are provided, one loaded
a little heavier than the other. The escape of steam from
the lighter valve in this case gives notice to the engine-man
of the growing increase of pressure, and warns him to check
the production of steam. The lever by which the safety-valve
is held down is sometimes acted on by a spiral spring,
capable of being so adjusted as to produce any required
pressure on the valve. This arrangement is adopted in locomotive
engines, where steam of very high pressure is used;
and in such cases also there are always provided two such
valves, one of which cannot be increased in its pressure.</p>

<p>The pipe by which the boiler is fed with water will
<a class="refpn" id="Pg280">[Pg280]</a>
necessarily act as a safety-valve, for when the pressure of the steam
increases in an undue degree, it will press the water in the
boiler up through the feed-pipe, so as to discharge it into the
feed-cistern, a circumstance which would immediately give
notice of the internal state of the boiler. The steam-gauge,
already described (<a href="#Fig079"><i>fig.</i> 79.</a>), would also act as a safety-valve;
for if the pressure of steam in the boiler should be so augmented
as to blow the mercury out of the steam-gauge, the
steam would then issue through the gauge, and the pressure
of the boiler be reduced, provided that the magnitude of the
tube forming the steam-gauge were sufficient for this purpose.</p>


<div class="ph3">
<h3>(164.)</h3> In high pressure boilers which are exposed to extreme
temperatures and pressures, and which are therefore subject
to danger of explosion, a plug of metal is sometimes inserted,
which is capable of being fused at a temperature above which
the boiler should not be permitted to be raised. If the
pressure of steam increase beyond the proper limit, the temperature
of the water and steam will undergo a corresponding
increase; and if the metal of the plug be capable of being
fused at such a temperature, the plug will fall out of the
boiler, and the steam and water will issue from it. Various
alloys of metal are fusible at temperatures sufficiently low for
this purpose. An alloy composed of one part of lead, three
of tin, and five of bismuth, will fuse at the common temperature
of boiling water; and alloys of the same metals, in
various proportions, will fuse at different temperatures from
200Â° to 400Â°.</div>

<p>Although fusible plugs may be used, in addition to other
means of insuring safety, they ought not to be exclusively
relied on at the ordinary working pressure of the boiler. The
fusible plug ought to be capable of more than resisting
the pressure; but if it be so, its point of fusion would be
one at which the steam would have a pressure of at least two
atmospheres above its working pressure. The plug would
therefore be capable of being fused only as soon as the steam
would acquire a pressure of 30 lbs. per inch above its regular
working pressure.</p>

<p>When a boiler ceases to be worked, and the furnace has
been extinguished, the space within it appropriated to steam
<a class="refpn" id="Pg281">[Pg281]</a>
will be left a vacuum by the condensation of the steam with
which it was previously filled. The external pressure of the
atmosphere acting on the boiler would, under such circumstances,
have a tendency to crush it inwards. To prevent
this, a safety-valve is provided, opening inwards, and balanced
by a weight sufficient to keep it closed until it be relieved
from the pressure of the steam below.</p>

<p>A large aperture closed by a flange secured with screws,
represented at <strong>O</strong> in <a href="#Fig071"><i>fig.</i> 71.</a>, called the <em>man-hole</em>, is provided
to admit persons into the boiler for the purpose of cleaning
or repairing its interior.</p>


<div class="ph3"><h3>(165.)</h3> The manner in which the governor regulates the
supply of steam from the boiler to the cylinder, proportioning
the quantity to the work to be done, and thereby sustaining
a uniform motion, has been already explained
(p. 125.). Since then the <em>consumption</em> of steam in the engine
is subject to variation, owing to the various quantities of work
it may have to perform, it is evident that the <em>production</em> of
steam in the boiler should be subject to a proportional variation.
For otherwise, one of two effects would ensue: the
boiler would either fail to supply the engine with steam, or
steam would accumulate in the boiler from being produced in
too great abundance, and would escape at the safety-valve,
and thus be wasted.</div>

<p>In order to vary the production of steam in proportion to
the demands of the engine, it is necessary to stimulate or
mitigate the furnace, as the evaporation is to be augmented
or diminished.</p>

<p>The activity of the furnace must depend on the current of
air which is drawn through the grate-bars, and this will depend
on the magnitude of the space afforded for the passage
of that current through the flues. A plate called a <em>damper</em>
is accordingly placed with its plane at right angles to the flue,
so that by raising and lowering it in the same manner as the
sash of a window is raised or lowered, the space allowed
for the passage of air through the flue may be regulated.
This plate might be regulated by the hand, so that by
raising or lowering it the draught might be increased or
diminished, and a corresponding effect produced on the
<a class="refpn" id="Pg282">[Pg282]</a>
evaporation in the boiler: but the force of the fire is rendered
uniformly proportional to the rate of evaporation by
the following arrangement, without the intervention of the
engineer. The column of water sustained in the feed-pipe
(<i>figs.</i> 71, 72.) represents by its weight the difference
between the pressure of steam within the boiler and that
of the atmosphere. If the engine consumes steam faster
than the boiler produces it, the steam contained in the
boiler acquires a diminished pressure, and consequently the
column of water in the feed-pipe will fall. If, on the other
hand, the boiler produce steam faster than the engine consumes
it, the accumulation of steam in the boiler will cause
an increased pressure on the water it contains, and thereby
increase the height of the column of water sustained in the
feed-pipe. This column therefore necessarily rises and falls
with every variation in the rate of evaporation in the boiler.
A hollow float <strong>P</strong> is placed upon the surface of the water of this
column; a chain connected with this float is carried upwards, and
passed over two pulleys, after which it is carried downwards
through an aperture leading to the flue which passes beside
the boiler: to this chain is attached the damper. By such
an arrangement it is evident that the damper will rise when
the float <strong>P</strong> falls, and will fall when the float <strong>P</strong> rises, since the
weight of the damper is so adjusted, that it will only balance
the float <strong>P</strong> when the latter rests on the surface of the water.</p>

<p>Whenever the evaporation of the boiler is insufficient, it is
evident from what has been stated, that the float <strong>P</strong> will fall
and the damper will rise, and will afford a greater passage for
air through the flue. This will stimulate the furnace, will
augment its heating power, and will therefore increase the rate
of evaporation in the boiler. If, on the other hand, the production
of steam in the boiler be more than is requisite for
the supply of the engine, the float will be raised and the
damper let down, so as to contract the flue, to diminish the
draught, to mitigate the fire, and therefore to check the evaporation.
In this way the excess, or defect, of evaporation in
the boiler is made to act upon the fire, so as to render the
heat proceeding from the combustion as nearly as possible
proportional to the wants of the engine.
<a class="refpn" id="Pg283">[Pg283]</a></p>


<div class="ph3">
<h3>(166.)</h3> The method of feeding the furnace by hand through
the fire-door being subject to the double objection of admitting
more cold air over the fuel than is necessary for its combustion,
and the impracticability of insuring that regular attendance
on the part of the stokers, directed the attention of
engineers to the construction of self-regulating furnaces. The
most effectual of these, and that which has come into most
general use, was invented by Mr. William Brunton of Birmingham.</div>

<p>The advantages proposed to be attained by him were those
expressed in his patent:â€”</p>

<p>"First, I put the coal upon the grate by small quantities,
and at very short intervals, say every two or three seconds.
2dly, I so dispose of the coals upon the grate, that the smoke
evolved must pass over that part of the grate upon which the
coal is in full combustion, and is thereby consumed. 3dly,
As the introduction of coal is uniform in short spaces of time,
the introduction of air is also uniform, and requires no attention
from the fireman.</p>

<p>"As it respects economy: 1st, The coal is put upon the
fire by an apparatus driven by the engine, and so contrived
that the quantity of coal is proportioned to the quantity of
work which the engine is performing; and the quantity of air
admitted to consume the smoke is regulated in the same
manner. 2dly, The fire-door is never opened, excepting to
clean the fire; the boiler, of course, is not exposed to that
continual irregularity of temperature which is unavoidable in
the common furnace, and which is found exceedingly injurious
to boilers. 3dly, The only attention required is to
fill the coal-receiver every two or three hours, and clean the
fire when necessary. 4thly, The coal is more completely
consumed than by the common furnace, as all the effect of
what is termed stirring up the fire (by which no inconsiderable
quantity of coal is passed into the ash-pit), is attained
without moving the coal upon the grate."</p>

<p>A circular grate is placed on a vertical revolving shaft; on
the lower part of this shaft, under the ash-pit, is placed a
toothed wheel driven by a pinion. This pinion is placed on
another vertical shaft, which ascends above the boiler; and
<a class="refpn" id="Pg284">[Pg284]</a>
on the other end of this is placed a bevelled wheel driven by
a pinion. This pinion is attached to a shaft, which takes its
motion from the axis of the fly-wheel, or any other revolving
shaft connected with the engine. A constant motion of
revolution is therefore imparted to the circular grate, and its
velocity being proportional to that of the engine, will necessarily
be also proportional to the quantity of fuel which
ought to be consumed. Through that part of the boiler
which is over the fire-grate a vertical tube or opening is
made directly over that part of the furnace which is most
distant from the flues. Over this opening a hopper is placed,
which contains the fuel by which the boiler is to be fed; and
in the bottom of this hopper is a sliding valve, capable of
being opened or closed, so as to regulate the quantity of fuel
supplied to the fire-grate. The fuel dropping in in small
quantities through this open valve falls on the grate, and is
carried round by it, so as to leave a fresh portion of the grate
to receive succeeding feeds. The coals admitted through
the hopper are previously broken to a proper size; and in
some forms of this apparatus there are two rollers, at a regulated
distance asunder, the surfaces of which are formed into
blunt angular points, and which are kept in slow revolution
by the engine. Between these rollers the coals must pass
before they reach the valve through which the furnace is fed,
and they are thus broken and reduced to a regulated size.
The valve which regulates the opening through which the
feed is admitted, is connected by chains and pulleys with the
self-regulating damper already described, so that in proportion
as the damper is raised, the valve governing the feed may be
opened. Thus, while the quantity of air admitted by the
damper is increased according to the demands of the engine,
the quantity of fuel admitted for the feed is increased by
opening the valve in the bottom of the hopper in the same
proportion. Apertures are also provided in the front of the
grate, governed by regulators, by which the quantity of air
necessary and sufficient to produce the combustion of the gas
evolved from the fuel is admitted, these openings being also
connected with the self-regulating damper.</p>

<p>A considerable portion of the heat imparted to the water
<a class="refpn" id="Pg285">[Pg285]</a>
in the boiler escapes by radiation from the surface of the
boiler, steam-pipes, and other parts of the machinery in
contact with the steam and hot water. The effects of this
are rendered very apparent in marine engines, where a large
quantity of water is found to be condensed in the great
steam-pipes leading from the boiler to the cylinder. In stationary
land boilers this loss of heat is usually diminished,
and in some cases in a great degree removed, by surrounding
the boiler with non-conducting substances. In some cases
the boiler is built round in brick work. In Cornwall, where
the economy is regarded perhaps to a greater extent than
elsewhere, the boiler and steam-pipes are surrounded with a
packing of sawdust, which being almost a non-conductor of
heat, is impervious to the heat proceeding from the surfaces
with which it is in contact, and consequently confines all the
heat within the boiler. In marine boilers it has been the
practice recently to clothe the boiler and steam-pipes with a
coating of felt, which is attended with a similar effect.
When these remedies are properly applied, the loss of heat
proceeding from the radiation of the boiler is reduced to an
extremely small amount. The engine-houses of some of the
Cornish engines, where the boiler generates steam at a very
high temperature, are nevertheless frequently maintained at
a lower temperature than the external air, and on entering
them they have in a great degree the effect of a cave.</p>


<div class="ph3">
<h3>(167.)</h3> All mechanical action is measured by the amount
of force exercised, or resistance overcome, and the space
through which that force has acted, or through which the
resistance has been moved.</div>

<p>The gross amount of mechanical action developed by the
moving power of an engine, is expended partly on moving
the engine itself, and partly on overcoming the resistance on
which the engine is intended to act. That part of the mechanical
energy of the moving power which is expended on
the resistance or load which the engine moves exclusively,
and of the power expended on moving the engine itself, is
called <em>the useful effect</em> of the machine.</p>

<p>The <em>gross effect</em>, therefore, exceeds the <em>useful effect</em> by the
<a class="refpn" id="Pg286">[Pg286]</a>
amount of power spent in moving the engine, or which may
be wasted or destroyed in any way by the engine.</p>

<p>It is usual to express and estimate all mechanical effect
whatever by nature of the resistance overcome, by an equivalent
weight raised a certain height. Thus, if an engine exerts
a certain power in driving a mill, in drawing a carriage on a
road, or in propelling a vessel on water, the resistance against
which it has to act must be equal to a definite amount of
weight. If a carriage be drawn, the traces are stretched by
the tractive power, by the same tension that would be given
to them if a certain weight were appended to them. If the
paddle-wheels of a boat are made to revolve, the water opposes
to them a resistance equal to that which would be produced,
if instead of moving the water the wheel had to raise
some certain weight. In any case, therefore, weight becomes
the exponent of the energy of the resistance against which
the moving power acts.</p>

<p>But the amount of mechanical effect depends conjointly on
the amount of resistance, and the space through which that
resistance is moved. The quantity of this effect, therefore,
will be increased in the same proportion, whether the quantity
of resistance or the space through which that resistance
is moved be augmented. Thus, a resistance of one hundred
pounds, moved through two feet, is mechanically equivalent
to a resistance of two hundred pounds moved through one
foot, or of four hundred pounds moved through six inches.
To simplify, therefore, the expression of mechanical effect,
it is usual to reduce it invariably to a certain weight raised one
foot. If the resistance under consideration be equivalent to
a certain weight raised through ten feet, it is always expressed
by ten times the amount of that weight raised
through one foot.</p>

<p>It has also been usual in the expression of mechanical effect,
to take the pound weight as the unit of weight, and the
foot as the unit of length, so that all mechanical effect whatsoever
is expressed by a certain number of pounds raised one
foot.</p>


<div class="ph3"><h3>(168.)</h3> The gross effect of the moving power in a steam-engine,
is the whole mechanical force developed by the evaporation
<a class="refpn" id="Pg287">[Pg287]</a>
of water in the boiler. A part of this effect is lost by
the partial condensation of the steam before it acts upon the
piston, and by the imperfect condensation of it subsequently:
another portion is expended on overcoming the friction of the
different moving parts, and in acting against the resistance
which the air opposes to the machine. If the motion be
subject to sudden shocks, a portion of the power is then lost
by the destruction of momentum which such shocks produce.
But if those parts of the machine which have a reciprocating
motion be, as they ought to be, brought gradually to rest at
each change of direction, then no power is absorbed in this
way.</div>


<div class="ph3"><h3>(169.)</h3> The useful effect of an engine is variously denominated
according to the relation under which it is considered.
If it be referred to the time during which it is produced, it
is called <strong>POWER</strong>.</div>


<div class="ph3"><h3>(170.)</h3> If it be referred to the fuel, by the combustion of
which the evaporation has been effected, it is called <strong>DUTY</strong>.</div>


<div class="ph3"><h3>(171.)</h3> When steam-engines were first brought into use,
they were commonly applied to work pumps for mills
which had been previously worked or driven by horses.
In forming their contracts, the first steam-engine builders
found themselves called upon to supply engines capable
of executing the same work as was previously executed
by some certain number of horses. It was therefore convenient,
and indeed necessary, to be able to express the
performance of these machines by comparison with the
animal power to which manufacturers, miners, and others,
had been so long accustomed. When an engine, therefore,
was capable of performing the same work in a given
time as any given number of horses of average strength
usually performed, it was said to be an engine of so many
horses' power. Steam-engines had been in use for a considerable
time before this term had acquired any settled or
uniform meaning, and the nominal power of engines was
accordingly very arbitrary. At length, however, the use of
steam-engines became more extended, and the confusion and
inconvenience arising out of all questions respecting the performance
of engines, rendered it necessary that some fixed
<a class="refpn" id="Pg288">[Pg288]</a>
and definite meaning should be assigned to the terms by
which the powers of this machine were expressed. To have
abandoned the term <em>horse-power</em>, which had been so long in
use, would have been obviously inconvenient; nor could
there be any objection to its continuance, provided all
engine-makers, and all those who used engines, could be
brought to agree upon some standard by which the unit of
horse-power might be defined. The performance of a horse
of average strength working for eight hours a day was
therefore selected as a standard, or unit, of steam-engine
power. Smeaton estimated that such an animal, so working,
was capable of performing a quantity of work equal in its
mechanical effect to 22,916 lbs. raised one foot per minute,
while Desaguliers estimated the same power at 27,500 lbs.
raised through the same height in the same time. The discrepancy
between these estimates probably arose from their
being made from the performances of different classes of
horses. Messrs. Boulton and Watt caused experiments to
be made with the strong horses used in the breweries in
London, and from the result of these trials they assigned
33,000 lbs. raised one foot per minute, as the value of a
horse's power. This is the unit of engine-power now universally
adopted; and when an engine is said to be of so
many horses' power, what is meant is, that that engine, in
good working order and properly managed, is capable of
moving a resistance equal to 33,000 lbs. through one foot per
minute. Thus an engine of ten horse-power is one that
would raise 330,000 lbs. weight one foot per minute.</div>

<p>Whether this estimate of an average horse's power be
correct or not, in reference to the actual work which the
animal is capable of executing, is a matter of no present
importance in its application to steam-power. The steam-engine
is no longer used to replace the power of horses, and
therefore no contracts are based upon such a comparison.
The term horse-power, therefore, as applied to steam-engines,
must be understood to have no reference whatever to
the actual animal power, but must be taken as a term having
no other meaning than the expression of the ability of the
<a class="refpn" id="Pg289">[Pg289]</a>
machine to move the amount of resistance above mentioned
through one foot per minute.</p>


<div class="ph3"><h3>(172.)</h3>
It has been already explained (<a href="#h3-67">67</a>.) that the conversion
of a given volume of water into steam is productive of a
certain definite amount of mechanical force, this amount
depending on the pressure under which the water is evaporated,
and the extent to which the expansive principle is
used in working the steam. It is evident that this amount
of mechanical effect is a major limit, which cannot be
exceeded by the power of the engine.</div>

<p>If the steam be not worked expansively, then the whole
power of the water, transmitted in the form of steam from
the boiler to the working machinery, will be a matter of easy
calculation, when the pressure at which the steam is worked
is known. A table, exhibiting the mechanical power of a
cubic foot of water converted into steam at various pressures,
expressed in an equivalent number of pounds' weight raised one
foot high, is given in the Appendix to this volume. Where
much accuracy is sought for, the pressure at which the steam
is used must be taken into account; but by reference to
the table it will be seen, that when steam is worked without
expansion, its mechanical effect varies very little with
the pressure. It may therefore be assumed, as has been
already stated, that for every cubic inch of water transmitted
in the form of steam to the cylinders, a force is
produced, represented by a ton weight raised a foot high.
Now, as 33,000 lbs. is very nearly 15 tons, it follows that 15
cubic inches of water converted into steam per minute, or
900 cubic inches per hour, will produce a mechanical force
equal to one horse. If, therefore, to 900 cubic inches be
added the quantity of water per hour necessary to move the
engine itself, independently of its load, we shall obtain the
quantity of water per hour which must be supplied by the
boiler to the engine for each horse-power, and this will be
the same whatever may be the magnitude or proportions of
the cylinder.</p>


<div class="ph3"><h3>(173.)</h3> The quantity of power expended in working the engine
itself, independently of that required to move its load,
will be less in proportion to the degree of perfection which
<a class="refpn" id="Pg290">[Pg290]</a>
may be attained in the construction of the engine, and
to the order in which it is kept while working. Engines
vary one from another so much in these respects, that
it is scarcely possible to lay down any general rules for
the quantity of power to be allowed over and above what is
necessary to move the load. The means whereby mechanical
power is expended in working the engine may be
enumerated as follows:â€”</div>

<ol class="nomarker"><li>
<p><em>First.</em> Steam in passing from the boiler to the cylinder is
liable to lose its temperature by the radiation of the steam-pipes
and other passages through which it is conducted.
Since the steam produced in the boiler is in contact with
water, it will be common steam (<a href="#h3-94">94</a>.), and consequently
the least loss of heat will cause a partial condensation. To
whatever extent this condensation may be carried, a proportional
loss of power, in reference to the heat obtained from
the fuel, will be entailed upon the engine.</p>

<p>It has been said that the force necessary to move the
steam from the boiler to the cylinder through passages more
or less contracted, subject to the friction of the pipes and
tubes through which it moves, should be taken into account
in estimating the power, and a corresponding deduction
made. This, however, is not the case: the steam
having passed into the cylinder remains common steam, its
pressure being diminished by reason of the force expended in
thus moving it from the boiler to the cylinder. But its mechanical
efficacy at the reduced pressure is not sensibly different
from the efficacy which it had in the boiler. If at the
reduced pressure its volume were the same, then a loss of
effect would be sustained equivalent to the difference of the
pressures; but its volume being augmented in very nearly
the same proportion as its pressure is diminished, the
mechanical efficacy of a given weight of steam in the
cylinder will be sensibly the same as in the boiler.</p>
</li>
<li>
<p><em>Second.</em> The radiation of heat from the cylinder and its
appendages, will cause a partial condensation of steam, and
thereby produce a diminished mechanical effect.</p>
</li>
<li>
<p><em>Third.</em> The steam, which at each stroke of the piston fills
the passages between the steam-valves and the piston, at the
<a class="refpn" id="Pg291">[Pg291]</a>
moment the latter commences the stroke will be inefficient.
If it were possible for the piston to come into steam-tight
contact with each end of the cylinder, and that the steam-valve
should be in immediate contact with the side or top of
the piston, then the whole of the steam which would pass
through the steam-valve would be efficient; but as some
space, however small, must remain between the piston and
the ends of the cylinder, and between the side of the
cylinder and the steam-valve, there will always be a volume
of steam bearing a sensible proportion to the magnitude of
the cylinder, which at each stroke of the piston will be inefficient.
This volume of steam is called the <em>clearance</em>.</p>
</li>
<li>
<p><em>Fourth.</em> Since the piston must move in steam-tight contact
with the cylinder, it must have a definite amount of
friction with the sides of the cylinder by whatever means it
may be packed. This friction will produce a corresponding
resistance to the moving power.</p>
</li>
<li>
<p><em>Fifth.</em> The various joints of the machinery where steam
is contained are subject to leakage, and whatever amount of
steam shall thus escape must be placed to the account of
power lost.</p>
</li>
<li>
<p><em>Sixth.</em> When the eduction-valve is opened to admit the
steam to the condenser, a certain force is required to expel
the steam from the cylinder. This force reacts upon the
piston, and counteracts to a proportional extent the moving
power of the steam on the other side. Besides this the
water in the condenser cannot be conveniently reduced below
the temperature of about 100Â°, and at this temperature
steam has a pressure of about 1 lb. per square inch. This
vapour will continue to fill the cylinder, and will resist the
moving power which impels the piston.</p>
</li>
<li>
<p><em>Seventh.</em> Power must be provided for opening and closing
the valves or slides, for working the air-pump, hot-water
pump, and cold-water pump, and finally to overcome the friction
on the journals and centres of the parts of the parallel
motion, the main axle of the beam, the connecting rod, crank,
and fly-wheel axle.</p>
</li>
</ol>

<p>It will be apparent how very much these sources of
resistances must vary in different engines, and how rough
<a class="refpn" id="Pg292">[Pg292]</a>
an approximation any general estimate must be of their
gross amount.</p>


<div class="ph3">
<h3>(174.)</h3> There are many circumstances which obstruct the
practical application of any standard of engine-power: the
magnitude of furnace, and the extent of heating surface
necessary to produce any required rate of evaporation in the
boiler, are unascertained; each engine-maker has his own
rule in these matters, and all the rules are equally unsupported
by any experimental test entitled to respect. Thus
the circumstances that govern the rate of evaporation in the
boiler may be regarded as almost wholly unknown. But
supposing the rate of evaporation to be ascertained, the
amount of power absorbed by the condensation of steam on
its passage to the cylinder, the imperfect condensation of the
same steam after it has worked the piston, the friction of
the various moving parts of the machinery, and, above all,
the difference of effect of these losses of power in engines
constructed on different scales of magnitude, are absolutely
unknown. We are, therefore, not placed in a condition to
assign any thing more than a general account of what has
been the practice of engine-makers in constructing engines
which are nominally of a certain power.</div>

<p>In common low-pressure engines of the larger kind, to
which class alone we at present refer, it has been usual,
with the same fuel and under like circumstances, to allow
from 10 to 18 square feet of heating surface in the boiler
for every nominal horse-power of the engine. Within these
wide limits the practice of engine-makers has varied. It
is not, however, to be supposed, that the boiler with 18
square feet of surface per horse-power has the same evaporating
power as that which has but 10. This difference,
therefore, amounts to nothing more than different manufacturers
of steam-engines putting into circulation boilers having
powers <em>really</em> different while they are <em>nominally</em> the same.
The magnitude of the cylinder is regulated by the nominal
power of the engine, and it is usual so to regulate the evaporating
power of the boiler, that the piston shall move at
the average rate of 200 feet per minute. This being assumed,
it is customary to allow about 22 square inches of piston
<a class="refpn" id="Pg293">[Pg293]</a>
surface for every nominal horse-power of the engine. If this
power were in conformity to the standard already defined,
this amount of surface moved at 200 feet per minute
would be impelled by a pressure amounting to
<span class="fraction">7<sup>1</sup>â„<sub>2</sub></span> lbs. per
square inch. The safety-valve of the boiler of such engines
is usually loaded at from 4 to 5 lbs. per square inch, and
consequently the steam in the boiler will have a pressure of
from 19 to 20 lbs. per square inch. If, therefore, the effective
pressure on the piston be really only
<span class="fraction">7<sup>1</sup>â„<sub>2</sub></span> lbs. per square
inch, the pressure expended in overcoming the friction of
the engine, and the loss consequent on the partial condensation
of steam on one side and its imperfect condensation on
the other, would amount to from 12 to 13 lbs. per square inch,
or nearly double the assumed useful effect of the engine.</p>

<p>Messrs. Maudslay and Field are accustomed to allow an
evaporation of ten gallons, or 1Â·6 cubic feet of water per hour,
for each nominal horse-power of the engine. They also allow
about 22 square inches of piston surface per nominal horse-power,
the piston being supposed to move at the rate of 200
feet per second.<a name="FNanchor_24_24" id="FNanchor_24_24"></a><a href="#Footnote_24_24" class="fnanchor">[24]</a></p>

<p>The quantity of grate surface necessary in proportion to
the power of the engine, has been equally unascertained, and
engine-makers vary in their practice from half a square foot
to one square foot per nominal horse-power.</p>

<p>The proportion which the magnitude of the heating surface
of the boiler, and the fire surface of the grate bears to the evaporating
power of the boiler, has not been determined by
experiment, nor, so far as we are informed, by any well-ascertained
practical results.</p>

<p>The estimates or rather conjectures of engine-makers, of
the evaporation necessary to produce one horse-power, vary
from one to two cubic feet of water per hour. It has been
<a class="refpn" id="Pg294">[Pg294]</a>
already shown that the evaporation of 900 cubic inches, or
little more than half a cubic foot per hour, evolves a gross
mechanical effect representing one horse-power; from which
it appears, that if the evaporation of the boilers of steam
engines were what engineers suppose them to be, the gross
mechanical power produced in them for every nominal horse-power
of the engine varies in actual amount from the power
of two to that of four horses.</p>

<p>The above estimates must be understood as referring to
double-acting steam engines above thirty-horse power. The
circumstances attending the performance of single-acting engines
applied to the drainage of mines, have been ascertained
with much greater precision. This has been mainly owing
to a spirited system of general inspection, which has been
established in Cornwall, to which we shall hereafter more particularly
advert.</p>


<div class="ph3">
<h3>(175.)</h3> In expressing the duty of engines, it would have
been desirable that the duty of the boiler should have been
separated from that of the engine.</div>

<p>The duty of a boiler is estimated by the volume of water
evaporated by a given quantity of fuel, independently of the
time which such evaporation may take. The duty, therefore,
will be expressed by the number of cubic feet of water evaporated,
divided by the number of bushels of coal necessary
for that evaporation, supposing the bushel of coal to be the
unit of fuel. It will be observed that the <em>duty</em> of an engine
or boiler is entirely distinct from, and independent of, its
<em>power</em>. One boiler may be greater than another in power to
any extent, while it may be equal to or less than it in duty.
A bushel of coals may evaporate the same number of cubic
feet of water under two boilers, but may take twice as great
a time to produce such evaporation under one than under the
other. In such a case the power of one boiler will be double
that of the other, while their duty will be the same.</p>

<p>In like manner, a bushel of coals consumed in working two
engines may produce the same useful effect, but it may produce
that useful effect in the one in half the time it takes to
produce it in the other. In that case the <em>duty</em> of the engines
will be the same, but the <em>power</em> of the one will be double
that of the other.
<a class="refpn" id="Pg295">[Pg295]</a></p>

<p>In fine, <em>power</em> has reference to <em>time</em>,â€”<em>duty</em>, to <em>fuel</em>. The
more rapidly the engine produces its mechanical effect, the
greater its power will be, whatever may be the fuel consumed
in working it. And, on the other hand, the greater the useful
effect produced by a given weight of fuel, the greater will be
the duty, however long the time may be which the fuel may
take to produce the useful effect.</p>


<div class="ph3">
<h3>(176.)</h3> The proportion of the stroke to the diameter of the
cylinder must be determined by the velocity intended to be
given to the piston. With the same capacity of cylinder,
and the same evaporation in the boiler, the velocity of the
piston will augment as the magnitude of its diameter is
diminished.</div>

<p>The proportion of the diameter to the stroke of the cylinder
is very various. In engines used for steam-vessels the
length of the cylinder very little exceeds its diameter. In
land engines, however, the proportion of the length to the
diameter is greater. It is maintained by some that the proportion
of the diameter and length of the cylinder should be
such as to render its surface exposed to the cooling of the
external air, the smallest possible. Tredgold has maintained
that since, during the stroke, the steam is gradually exposed
to contact with the surface of the cylinder from the top to
the bottom, the mean surface exposed in contact with steam
being half that of the entire cylinder, the proportion of the
diameter to the stroke should be such that the surface of
half the length of the cylinder, added to the magnitude of
the top and bottom, shall be a minimum. If this principle
be admitted, then the best proportion of the diameter to the
stroke would be that of one to two, the length of the stroke
being twice the diameter of the cylinder; but since the whole
surface of the cylinder is constantly exposed to the cooling
effects of the air, and since in the intervals of the stroke there
is no sensible change of the temperature of the surface, the
loss of heat by cooling will in effect be the same, especially
in double-acting engines, as if the cylinder were constantly
filled with steam. If this be admitted, then the object should
be to give the cylinder such a proportion, that its entire surface,
including the top and bottom, shall be a minimum.
<a class="refpn" id="Pg296">[Pg296]</a>
The proportion given by this condition would be very nearly
that which is observed in the cylinders of marine engines,
viz. that the length of the cylinder should be equal to its
diameter.</p>

<p>If in a low-pressure engine the pressure of steam in the
cylinder be taken at 17 lbs. per square inch, then the volume
of steam will be about fifteen hundred times that of the
water which produces it. For every cubic foot of water,
therefore, in the effective evaporation of the boiler, 1500
cubic feet of steam will be passed through the cylinder.
If it be intended that the motion of the piston shall be
at the rate of 25 strokes per minute, or 1500 strokes per
hour, then the capacity of that portion of the cylinder
between the steam-valve and the piston at the end of the
stroke, must consist of half as many cubic feet as there are
cubic feet per hour evaporated in the boiler. If the steam,
therefore, be cut off at half stroke, the number of cubic feet
of space in the cylinder will be equal to the number of
cubic feet of water effectively evaporated by the boiler; and
if a cubic foot of water effectively evaporated be taken as
the measure of a horse-power, then there would be as many
cubic feet in the capacity of the cylinder as is equal to the
nominal power of the engine.</p>


<div class="ph3"><h3>(177.)</h3> The duty of engines varies according to their
form and magnitude, the circumstances under which they
are worked, and the purposes to which they are applied.
In double-acting engines working without expansion, the
coal consumed per nominal horse-power per hour varies
from 7 to 12 lbs. An examination of the steam-logs of
several government steamers made by me a few years
since, gave, as the average of consumption of fuel at that
time of the best class of marine engines, about 8 lbs. per
nominal horse-power per hour. Since, however, no account
could be obtained of the actual evaporation of water
in the boiler, nor, with the necessary degree of precision,
of the quantity and pressure of the steam which passed
through the cylinders, this estimate must be regarded as
an approximation subject to several causes of error. The
question of the duty of boilers and engines applied to the
<a class="refpn" id="Pg297">[Pg297]</a>
general purposes of manufactures and navigation, is one
which has not yet been satisfactorily investigated; and it
were much to be desired that the proprietors of such engines
should combine to establish a strict analysis of their performance
in reference to their consumption of fuel, their
evaporation of water, and their useful effects. The results
of such an investigation, if properly conducted, would perhaps
tend more to the improvement of the steam engine
than any discoveries in science, or inventions in mechanical
detail likely to be made in the present stage of the progress
of that machine.</div>


<div class="ph3">
<h3>(178.)</h3> A strict investigation of this kind has been for many
years carried on respecting the performance of the steam
engines used for the drainage of the mines in Cornwall; and
it has been attended with effects the most beneficial to the
interests of those concerned in them. The engines to which
this important inquiry has been applied being used for the
purpose of pumping, are generally single-acting engines, in
which steam is used expansively to a great extent. The
steam is produced under a very high pressure in the boiler,
and being admitted to the cylinder is cut off after a small
portion of the entire stroke has been made, the remainder
of the stroke being produced by the expansion of the steam.</div>

<p>About the year 1811, a number of the proprietors of the
principal Cornish mines agreed to establish this system of
inspection, under the management and direction of Captain
Joel Lean, and to publish monthly reports. In these
reports were stated the following particulars:â€”1. The load
per square inch on the piston; 2. The consumption of coal
in bushels; 3. The number of strokes made by the engine;
4. The length of the strokes in the pumps; 5. The load in
pounds; 6. The duty of the engine, expressed by the number
of pounds raised one foot high by the consumption of a
bushel of coals; 7. The number of strokes per minute;
8. The diameter and stroke of the cylinder, and a general description
of the engine. When these reports were commenced,
the number of engines brought under inspection was twenty-one.
In the year 1813 it increased to twenty-nine; in 1814
to thirty-two; in 1820 the number reported upon increased
<a class="refpn" id="Pg298">[Pg298]</a>
to forty; in 1828 the number was fifty-seven; and in 1836
it was sixty-one. This gradual increase in the number
of engines brought under this system of inspection, was
produced by the good effects which attended it. These
beneficial consequences were manifested, not only in the
improved performance of the same engines, but in the gradually
improved efficiency of those which were afterwards
constructed.</p>

<p>The following table taken from the statement of the duty
of Cornish engines by Thomas Lean and brother, lately published
by the British Association, will show in a striking
manner the improvement of the Cornish engines, from the
commencement of this system of inspection to the present
time. The duty is expressed by the number of pounds
raised one foot high by the consumption of a bushel of coals.</p>

<table summary="Improvement of Cornish Engines, Average Duty of the
whole, and Duty of the Best Engine">
<tr>
 <th align="center">Years.</th>
 <th align="center">No. of Engines.</th>
 <th align="center">Average Duty of the Whole.</th>
 <th align="center">Average Duty of the best Engine.</th></tr>
<tr>
 <td align="center">1812</td>
 <td align="center">21</td>
 <td align="center">19,300,000</td>
 <td align="center"></td></tr>
<tr>
 <td align="center">1813</td>
 <td align="center">29</td>
 <td align="center">19,500,000</td>
 <td align="center">26,400,000</td></tr>
<tr>
 <td align="center">1814</td>
 <td align="center">32</td>
 <td align="center">20,600,000</td>
 <td align="center">32,000,000</td></tr>
<tr>
 <td align="center">1815</td>
 <td align="center">35</td>
 <td align="center">20,500,000</td>
 <td align="center">28,700,000</td></tr>
<tr>
 <td align="center">1816</td>
 <td align="center">35</td>
 <td align="center">23,000,000</td>
 <td align="center">32,400,000</td></tr>
<tr>
 <td align="center">1817</td>
 <td align="center">35</td>
 <td align="center">26,500,000</td>
 <td align="center">41,600,000</td></tr>
<tr>
 <td align="center">1818</td>
 <td align="center">36</td>
 <td align="center">25,400,000</td>
 <td align="center">39,300,000</td></tr>
<tr>
 <td align="center">1819</td>
 <td align="center">40</td>
 <td align="center">26,300,000</td>
 <td align="center">40,000,000</td></tr>
<tr>
 <td align="center">1820</td>
 <td align="center">46</td>
 <td align="center">28,700,000</td>
 <td align="center">41,300,000</td></tr>
<tr>
 <td align="center">1821</td>
 <td align="center">45</td>
 <td align="center">28,200,000</td>
 <td align="center">42,800,000</td></tr>
<tr>
 <td align="center">1822</td>
 <td align="center">52</td>
 <td align="center">28,900,000</td>
 <td align="center">42,500,000</td></tr>
<tr>
 <td align="center">1823</td>
 <td align="center">52</td>
 <td align="center">28,200,000</td>
 <td align="center">42,100,000</td></tr>
<tr>
 <td align="center">1824</td>
 <td align="center">49</td>
 <td align="center">28,300,000</td>
 <td align="center">43,500,000</td></tr>
<tr>
 <td align="center">1825</td>
 <td align="center">56</td>
 <td align="center">32,000,000</td>
 <td align="center">45,400,000</td></tr>
<tr>
 <td align="center">1826</td>
 <td align="center">51</td>
 <td align="center">30,500,000</td>
 <td align="center">45,200,000</td></tr>
<tr>
 <td align="center">1827</td>
 <td align="center">51</td>
 <td align="center">32,100,000</td>
 <td align="center">59,700,000</td></tr>
<tr>
 <td align="center">1828</td>
 <td align="center">57</td>
 <td align="center">37,100,000</td>
 <td align="center">76,800,000</td></tr>
<tr>
 <td align="center">1829</td>
 <td align="center">53</td>
 <td align="center">41,700,000</td>
 <td align="center">77,000,000</td></tr>
<tr>
 <td align="center">1830</td>
 <td align="center">56</td>
 <td align="center">43,300,000</td>
 <td align="center">78,000,000</td></tr>
<tr>
 <td align="center">1831</td>
 <td align="center">58</td>
 <td align="center">43,400,000</td>
 <td align="center">71,100,000</td></tr>
<tr>
 <td align="center">1832</td>
 <td align="center">59</td>
 <td align="center">45,000,000</td>
 <td align="center">85,000,000</td></tr>
<tr>
 <td align="center">1833</td>
 <td align="center">56</td>
 <td align="center">46,600,000</td>
 <td align="center">84,300,000</td></tr>
<tr>
 <td align="center">1834</td>
 <td align="center">52</td>
 <td align="center">47,800,000</td>
 <td align="center">90,900,000</td></tr>
<tr>
 <td align="center">1835</td>
 <td align="center">51</td>
 <td align="center">47,800,000</td>
 <td align="center">91,700,000</td></tr>
<tr>
 <td align="center">1836</td>
 <td align="center">61</td>
 <td align="center">46,600,000</td>
 <td align="center">85,400,000</td></tr>
<tr>
 <td align="center">1837</td>
 <td align="center">58</td>
 <td align="center">47,000,000</td>
 <td align="center">87,200,000</td></tr>
<tr>
 <td align="center">1838</td>
 <td align="center">61</td>
 <td align="center">48,700,000</td>
 <td align="center">84,200,000</td></tr>
</table>

<p><a class="refpn" id="Pg299">[Pg299]</a>
 As an example of the beneficial effects produced upon the
efficiency of an individual engine by the first application of this
system of inspection, the case of the Stray Park engine may be
mentioned. This engine, constructed by Boulton and Watt,
had a sixty inch cylinder, and when first reported in 1811, its
duty amounted to 16,000,000 pounds. After having been
reported on for three years, its duty was found to have increased
to 32,000,000; this estimate being taken from the
average result of twelve months' performance. Its duty was
doubled in less than three years.</p>

<p>It will appear, by inspection of the duties registered in the
preceding table, that the augmentation of the efficiency of
the engines has not been the effect of any great or sudden
improvement, but has rather resulted from the combination
of a great number of small improvements in the details of the
operation of these machines. In these improvements more
is due to the successful application of practical experience
than to any new principles developed by scientific research.
Mr. John Taylor, in his "Records of Mining," has traced
the successive improvements on which the increased duty of
engines depends, and has connected these improvements with
their causes in the order of their dates. The following
results, abridged from his estimates, may not be uninteresting:â€”</p>

<p>In 1769, soon after the date of the earliest discoveries of
Mr. Watt, but before they had come into practical application,
Smeaton computed that the average duty of fifteen
atmospheric engines, working at Newcastle-on-Tyne, was
5,590,000. The duty of the best of these engines was
7,440,000, and that of the worst 3,220,000.</p>

<p>In 1772, Smeaton commenced his improvements on the
atmospheric engine, and raised the duty to 9,450,000.</p>

<p>In 1776, Watt obtained a duty of 21,600,000.</p>

<p>At this time Smeaton acknowledged that Watt's engines
gave a duty amounting to double that of his own.</p>

<p>In 1778-79, Watt reported a duty of 23,400,000.</p>

<p>From 1779 to 1788, Watt introduced the application of
expansion, and raised the duty to 26,600,000.
<a class="refpn" id="Pg300">[Pg300]</a></p>

<p>In 1798, an engine by Boulton and Watt, erected at Herland,
was reported as giving a duty of 27,000,000.</p>

<p>This engine, which was probably the best which at that
time had ever been erected, attracted the particular attention
of Mr. Watt, who, on visiting Cornwall, went to see it, and
had many experiments tried with it. It was under the care
of Mr. Murdock, the agent of Messrs. Boulton and Watt in
Cornwall. When Mr. Watt inspected it he pronounced it
perfect, and that further improvement could not be expected.
How singular an instance this of the impossibility, even of the
most sagacious, to foresee the results of mechanical improvement!
In twenty years afterwards the average duty of the
best engine was nearly 40,000,000, and in forty years it was
above 84,000,000.</p>

<div class="figcenter" style="width: 438px;">
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_322.png" width="438" height="393" alt="" />
<div class="caption">BOILER MANUFACTORY.</div>
</div>

<div class="footnotes"><h3>FOOTNOTES:</h3>

<div class="footnote">

<p><a name="Footnote_24_24" id="Footnote_24_24"></a><a
href="#FNanchor_24_24"><span class="label">[24]</span></a>
If 22 square inches of piston surface be allowed to represent a horse-power,
the power of an engine may always be computed by dividing the
square of the diameter of the piston expressed in inches by 28. And, on
the other hand, to find the diameter of piston which would correspond to
any given power, multiply the number of horses' power by 28, and take the
square root of the product. These rules, however, cannot be applied if the
piston be supposed to move with any other velocity; since, in that case,
the same amount of piston surface would cease to represent a horse-power,
unless the effective pressure on the piston were at the same time changed.</p></div></div>

<div class="figcenter" style="width: 387px;">
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_323.png" width="387" height="484" alt="" />
<div class="caption">WATT'S CHAPEL IN HANDSWORTH CHURCH.</div>
</div>

<h2><a name="CHAP_X" id="CHAP_X">CHAP. X.</a></h2>

<p class="right"><a class="refpn" id="Pg301">[Pg301]</a><br />
<a href="#CONTENTS"><small>TOC</small></a>&#160;&#160;<a
href="#INDEX"><small>INX</small></a></p>

<div class="chapheader">
NOTICE OF THE LIFE OF MR. WATT.â€”HIS FRIENDS AND ASSOCIATES
AT BIRMINGHAM.â€”INVENTION OF THE COPYING PRESS.â€”HEATING
BY STEAM.â€”DRYING LINEN BY STEAM.â€”THEORY OF THE COMPOSITION
OF WATER.â€”FIRST MARRIAGE OF WATT.â€”DEATH OF HIS
FIRST WIFE.â€”HIS SECOND MARRIAGE.â€”DEATH OF HIS YOUNGER
SON.â€”EXTRACTS FROM HIS LETTERS.â€”CHARACTER OF WATT BY
LORD BROUGHAM.â€”BY SIR WALTER SCOTT.â€”BY LORD JEFFREY.â€”OCCUPATION
OF HIS OLD AGE.â€”INVENTION OF MACHINE FOR COPYING
SCULPTURE.â€”HIS LAST DAYS.â€”MONUMENTS.</div>


<div class="ph3fst"><h3>(179.)</h3> Having brought this historical analysis of the invention
and application of the steam engine to the date of the
decease of the illustrious man, to the powers of whose mind
the world stands indebted for the benefits conferred upon
<a class="refpn" id="Pg302">[Pg302]</a>
mankind by that machine, it will perhaps not be deemed an
improper digression in this work, to devote some pages to a
notice of the principal labours of the same mind in other departments
of art and science, and to circumstances connected
with his personal history and the close of his life, which cannot
fail to possess general interest.</div>

<p>At the period when Watt, having connected himself in
partnership with Boulton, went to reside at Soho, near Birmingham,
a number of persons, some of whom have since attained
great celebrity by their discoveries and their works, and
all of whom were devoted to inquiries connected with the arts
and sciences, resided in that neighbourhood. Among these may
be mentioned <strong class="m1">Priestley</strong>, whose discoveries in physical science
have rendered his name immortal; <strong class="m1">Darwin</strong>, the philosopher
and poet; <strong class="m1">Withering</strong>, a distinguished physician and botanist;
<strong class="m1">Keir</strong>, a chemist, who published a translation of Macquer,
with annotations; <strong class="m1">Galton</strong>, the ornithologist; and <strong class="m1">Edgeworth</strong>,
whose investigations respecting wheeled carriages and
other subjects, have rendered him well known. A society was
formed by these and other individuals, of which Boulton and
Watt were leading members, the meetings of which were held
monthly on the evening of full moon, and which was thence
called the <em>Lunar Society</em>. At the meetings of this society, subjects
connected with the arts and sciences were discussed, and
out of those discussions occasionally arose suggestions not unattended
with important and advantageous consequences. At
one of these meetings, Darwin stated that he had discovered
a pen formed with two quills, by means of which, at a single
operation, an original and a copy of a letter might be produced.
Watt almost instantly observed that he thought he
could find a better expedient, and that he would turn it in
his mind that night. By the next morning the <strong>COPYING
PRESS</strong> was invented, for which he afterwards obtained a patent.</p>

<p>This machine, which is now so generally used in counting-houses,
consists of a rolling-press, by which a leaf of thin
paper, previously damped, is pressed upon the letter to be
copied. The writing, of which the ink is not yet quite dry,
leaves its impression upon the thin paper thus pressed upon
<a class="refpn" id="Pg303">[Pg303]</a>
it, and the copy taken in this manner is read through the
semi-transparent paper. If a letter be written with ink suitable
for this purpose, a copy may be taken at any time within
several hours after the letter is written.</p>

<p>The method of heating apartments and buildings by steam,
which has since been improved and brought into extensive
use, was likewise brought forward by Watt. Although this
contrivance had been previously pointed out by Sir Hugh
Platt about the middle of the seventeenth century, and by
Colonel Cooke in 1745, yet these suggestions remained barren.
Mr. Watt gave detailed methods of heating buildings by
steam<a name="FNanchor_25_25" id="FNanchor_25_25"></a><a href="#Footnote_25_25" class="fnanchor">[25]</a>; and also invented a machine for drying linen by
steam, a description of which he communicated to Dr.
Brewster, which was read in December, 1824, before the
Society for promoting Useful Arts in Scotland.<a name="FNanchor_26_26" id="FNanchor_26_26"></a><a href="#Footnote_26_26" class="fnanchor">[26]</a></p>

<p>But the circumstance, exclusive of those connected with
the invention of the steam engine, which is by far the most
memorable in the career of Watt, is the share which he had
in the discovery of the composition of water. As this circumstance
has recently excited much interest, and led to some
controversy, we shall here state, as distinctly as possible, the
leading facts connected with it.</p>

<p>Water, which was so long held to be a simple element, has,
in modern times, been proved to be a substance consisting of
two aeriform bodies or gases chemically combined. These two
gases are those called in chemistry <em>oxygen</em> and <em>hydrogen</em>. If
eight grains weight of oxygen be mixed with one grain weight
of hydrogen, and the mixture be submitted to such effects as
would cause the chemical combination of these two airs, it
would be converted into nine grains weight of pure water.</p>

<p>If, on the other hand, nine grains weight of pure water be
submitted to any conditions which would separate its constituent
parts, the result would be eight grains weight of oxygen
gas, and one grain weight of hydrogen gas. There are a variety
of methods in physics by which these effects would be
<a class="refpn" id="Pg304">[Pg304]</a>
produced. It will be sufficient here to state one method of
producing each of the above changes.</p>

<p>If eight grains weight of oxygen be inclosed in a strong
vessel with one grain weight of hydrogen, all other substances
being excluded, and the mixture be inflamed, an explosion
will take place, the gases will disappear, and a small quantity
of water will be the only substance remaining in the
vessel. If this water be weighed, it will be found to weigh
exactly nine grains.</p>

<p>It is known that the metals have a strong attraction for
oxygen gas, and this attraction is promoted by elevating their
temperature. If a glass tube be filled with iron wire heated
to redness, and to one end of this tube a small vessel of boiling
water be attached, the steam evolved from the water will force
its way through the spaces between the red-hot wires in the
tube, and would be expected to issue from the remote end;
but if the substance issuing from the remote end of the tube
be examined, it will be found to be not steam, but hydrogen
gas. If the quantity of this gas be ascertained by weight, and
also the quantity of weight lost by the vessel of water at the
other end of the tube, it will be found that the loss of weight
of the water by evaporation will be nine times the weight of
the hydrogen which has issued from the remote end of the
tube. If the weight of the tube with the wire contained in
it be next ascertained, it will be found to be increased by
eight times the weight of the hydrogen which has issued from
its remote end. From this it follows that the weight of the
hydrogen which has escaped from the tube, added to the increase
of weight which has been given to the wire in the tube,
makes up the whole weight of the water evaporated. If the
wire in the tube be next examined, it will be found that it
has suffered oxydation, or, in other words, that a new substance
has been formed in it called the oxyde of iron,â€”such
substance being a chemical compound formed of oxygen gas
and iron.</p>

<p>It follows, therefore, that in this process the vapour of the
water, in passing through the tube, has been decomposed, and
that, having given up to the iron its oxygen, the hydrogen
<a class="refpn" id="Pg305">[Pg305]</a>
alone escaped from the other end; and for every nine grains
weight of steam which passed through the tube, eight grains
of oxygen have been combined with the iron, and one grain
of hydrogen has escaped from the end of the tube.</p>

<p>Such are the class of effects on which the modern discovery
of the composition of water has been based. The merit of
that discovery has been shared between the celebrated English
chemist, <strong class="m1">Cavendish</strong>, and the not less celebrated French chemist,
<strong class="m1">Lavoisier</strong>, the chief merit, however, being ascribed to
the former.</p>

<p>We shall now briefly state the facts which led to this discovery,
with their dates, which will necessarily show the share
which Watt had in it.</p>

<p>When pure hydrogen gas is burned in an atmosphere of
common air, the process which takes place is now known to
be nothing more than the chemical combination of the hydrogen
with eight times its own weight of oxygen taken from
the atmosphere, and the product of the combustion is a quantity
of water nine times the weight of the hydrogen consumed.
In the year 1776, Macquer, a well-known chemist of that
day, having held a saucer of white porcelain over a flame of
hydrogen which was burning at the mouth of a bottle, observed
that no smoke was produced and no soot deposited on
the saucer. On the other hand, he found that after the lapse
of some time drops of a clear pellucid liquid were perceptible
on the saucer: this liquid he submitted to analysis, and found
it to be pure water. Macquer mentioned this fact without
comment or inference. It did not occur to him that the
water thus produced upon the saucer was a substance which
contained the hydrogen, which disappeared upon combustion
from the bottle.</p>

<p>On the 18th of April, 1781, Mr. Warltire addressed a
letter to Dr. Priestley, dated Birmingham, which letter is published
in Dr. Priestley's <cite>Experiments on Air</cite>, printed at Birmingham
in 1781, in which Warltire informs Priestley that
he had fired a mixture of hydrogen and common air in close
glass vessels, and that, although previously to firing the mixture
the vessels were clean and dry, a dewy deposit was
<a class="refpn" id="Pg306">[Pg306]</a>
observed afterwards on their sides. In fact, water was present
which was not present before.</p>

<p>The mixture was in this case fired by passing an electric
spark through the vessel; and it is now known that the
effect produced was the combination of the hydrogen, which
formed part of the mixture of airs in the vessel with the
oxygen, which also formed part of the same mixture.</p>

<p>It appears, from expressions in Warltire's letter, that the
same experiment had been previously made by Priestley,
and the same result observed by him.</p>

<p>The inference deduced from this by Warltire, and apparently
acquiesced in by Priestley, was, that whenever
hydrogen was fired in atmospheric air, the moisture, which
is always more or less sustained in the latter, was deposited;
but neither of these chemists perceived the real cause of the
production of the water.</p>

<p>In the beginning of 1783, and not later than the 21st of
April, this experiment of Warltire and Priestley was repeated
by Cavendish, with this difference, that, instead of
exploding the mixture of hydrogen and common air, Cavendish
exploded a mixture of hydrogen and oxygen. He observed
that water was present after the explosion, but <em>inferred
nothing</em>.</p>

<p>In a published paper dated April, 1783, Priestley announced
a further and most important result of his experiments.
This was, that in examining the weight of water
produced by the explosion of a mixture of oxygen and hydrogen,
<em>that weight was found to be precisely equal to the
sum of the weights of the two gases</em>, which disappeared in the
process.</p>

<p>Immediately on observing this, Priestley, being then, as
has been already stated, Watt's near neighbour, communicated
to the latter what he had observed; upon which Watt
immediately, viz. by a letter dated the 26th of the same
month, declared that the inevitable consequence which followed
from Priestley's observations was, that water was a
substance compounded of oxygen and hydrogen deprived of
<a class="refpn" id="Pg307">[Pg307]</a>
a quantity of heat which was previously latent in them.<a name="FNanchor_27_27" id="FNanchor_27_27"></a><a href="#Footnote_27_27" class="fnanchor">[27]</a>
The letter containing this inference was communicated immediately
by Priestley to Sir Joseph Banks, then President
of the Royal Society, to be laid before that body; and it is
accordingly printed with its proper date in the 74th volume
of the <cite>Philosophical Transactions</cite>.</p>

<p>About two months after the date of Mr. Watt's letter just
quoted, Lavoisier made experiments on the combustion of
oxygen and hydrogen, and read a memoir before the Academy
of Sciences in Paris, in which his views of the formation
of water by the combination of these gases were
developed. This paper, by Lavoisier, was afterwards printed
in the Memoirs of the Academy in the year 1784. The
experiments are there stated to have been made in the
month of June, 1783; and it is stated that Sir Charles
Blagden, who was present at the experiments, told Lavoisier
that Mr. Cavendish had already burned the same gases in
close vessels, and obtained a very sensible quantity of water.</p>

<p>On the 15th of January, 1784, the celebrated paper by
Cavendish, entitled "<cite>Experiments on Air</cite>," was read before
the Royal Society, and in this paper the composition of
water by the union of oxygen and hydrogen is explained.</p>

<p>In a controversy which afterwards ensued on the respective
<a class="refpn" id="Pg308">[Pg308]</a>
claims of Cavendish and Lavoisier to credit for the discovery
of the composition of water, Sir Charles Blagden stated that
he had told Lavoisier, in June, 1783, more than Lavoisier
acknowledged, that he had not only told him that water was
produced by the combustion of the gases, but that his information
embraced the whole theory of the composition of
water. This declaration of Blagden was subsequent in date
to January, 1784, and there is no evidence of any explanation
of this theory, verbal or otherwise, having been given
by Cavendish, or any other person, antecedent to April,
1783.</p>

<p>From this brief statement of the facts and dates it will
appear that the merit of the discovery of the <strong>FACT</strong>, that the
weight of water resulting from the combustion of oxygen
and hydrogen, is equal to the sum of the weights of the
oxygen and hydrogen which disappear in the combustion, is
due to Priestley; and that the merit of the <strong>INFERENCE</strong> from
that fact, that water is a compound body, whose constituents
are oxygen and hydrogen, is due to Watt.<a name="FNanchor_28_28" id="FNanchor_28_28"></a><a href="#Footnote_28_28" class="fnanchor">[28]</a> Whether those
who subsequently deduced the same inference, and promulgated
the same theory, were or were not informed of Mr.
Watt's solution of the phenomenon, or what credit may
be due to any person, however eminent, who at any time
posterior to Mr. Watt's letter to Priestley, asserted that they
had, at a time antecedently to that, made the same inference
without having published it, or communicated it in such a
manner as to establish their claim upon rational and credible
evidence, are questions which we shall not here discuss,
being contented with establishing the right of Mr. Watt to
the merit of the discovery of the <strong>THEORY</strong> which explained
the <strong>FACT</strong> discovered by Priestley.</p>

<p>Even in his declining years, after he had withdrawn from
the active pursuits of his business, the least excitement was
sufficient to call into play the slumbering powers of his inventive
genius. No object could present itself to his notice
<a class="refpn" id="Pg309">[Pg309]</a>
without receiving from that genius adaptation in form and
construction to useful purposes. As an example of this restless
activity of mind the following anecdote may be mentioned:â€”</p>

<p>A company at Glasgow had erected on the right bank of
the Clyde extensive buildings and powerful engines for supplying
water to the town. After this expense it was found
that a source of water, of very superior quality, existed on
the left bank of the river. To change the site of the establishment,
after the expense which had been incurred in its
erection could not be contemplated, and they therefore proposed
to carry across the bottom of the river a flexible suction
pipe, the mouth of which should terminate in the source
from which the pure water was to be derived. This pipe was
to be supported by a flooring constructed upon the bed of the
river; but it was soon apparent that the construction of such
a flooring on a shifting and muddy bottom, full of inequalities,
and under several feet depth of water would require a
greater expenditure of capital than could with propriety be
afforded. In this difficulty the aged mechanician, for whom
Glasgow itself had been the earliest stage of professional labour,
was applied to, and instantly solved the problem. His
attention is said to have been attracted by a lobster which had
been served at table: he set himself about to contrive how, by
mechanism, he could make an apparatus of iron with joints
which should have all the flexibility of the tail of the lobster.
He therefore proposed that an articulated suction-pipe, capable
of accommodating itself to all the inequalities and to
the possible changes of the bed of the river, should be carried
across it; that this flexible pipe should be two feet
in diameter, and one thousand feet in length. This project
the company accordingly caused to be executed after
the plans and drawings of Watt with the most complete success.<a name="FNanchor_29_29" id="FNanchor_29_29"></a><a href="#Footnote_29_29" class="fnanchor">[29]</a></p>

<p><a class="refpn" id="Pg310">[Pg310]</a>
 Among the less prominent, though not less useful services
rendered by Watt to his country, may be mentioned the introduction
of the use of chlorine in bleaching. That invention
of Berthollet was introduced into England by Watt after
his visit to Paris at the close of the year 1786. He constructed
all the necessary apparatus for it, directed its erection,
and superintended its first performances. He then left it to
his wife's father, Mr. Macgregor, to carry on the processes.</p>

<p>When the properties of the gases began to occupy the attention
of chemists, attempts were made to apply them as a
means of curing diseases of the lungs. Dr. Beddoes pursued
this inquiry with great activity, and established, through the
means of private subscription, at Clifton, an institution in
which this method of cure was carefully investigated. The
Pneumatic Institution (for so it was called) has been rendered
celebrated for having at its head Humphry Davy, just
then commencing his scientific career. Among its founders
was also numbered James Watt. Not content, however, with
affording the institution the sanction of his name, he designed
and caused to be constructed, at Soho, the apparatus used
for making the gases and administering them to the patients.</p>

<p>As the exalted powers of the mind of Watt, unfolded
in his numerous mechanical and philosophical inventions and
discoveries, have commanded the admiration and respect of
his species, the affection and love of his fellow men would
not have been less conciliated, had the qualities of his heart,
as developed in his private and personal relations, been as
well known as the products of his genius.</p>

<p>In the year 1764, Watt being then in the twenty-ninth
year of his age, married his cousin, Miss Miller. At this
time he had fallen into a state of despondency from his disappointments,
which produced a serious attack of nervous
illness. The accomplishments and superior understanding,
the mildness of temper and goodness of disposition of his
wife, soon restored him to health. Of this marriage four
children, two sons and two daughters, were the issue. Two
of these children died in infancy; another, a daughter, was
married to Mr. Miller of Glasgow; and the fourth is the
<a class="refpn" id="Pg311">[Pg311]</a>
present Mr. James Watt. In September, 1773, while her
husband was engaged in the design of the Caledonian canal
in the North of Scotland, Mrs. Watt died in child-bed of a
fifth child, who was still-born: "Would that I might here
transcribe," says M. Arago, "in all their simple beauty,
some lines of the journal in which he daily recorded his
inmost thoughts, his fears, his hopes! Would that you
could see him, after this heavy affliction, pausing on the
threshold of that home, where '<strong class="m1">His Kind Welcomer</strong>'
awaited him no more; unable to summon courage to enter
those rooms where he was never more to meet '<strong>the Comfort
of his Life</strong>!' Possibly, so faithful a picture of a
very deep sorrow might at last put to silence those obstinate
theorists, who, without being struck by the thousands of
instances to the contrary, do yet refuse qualities of the heart
to every man whose intellect has been fostered by the
fertile, sublime, and imperishable truths of the exact sciences!"</p>

<p>After the lapse of some years Watt married Miss Macgregor,
a person who is represented to have possessed qualities
of mind which rendered her a companion every way
suitable to her husband. This lady survived Watt, and died
in 1832 at an advanced age. Two children were the issue of
this second marriage.</p>

<p>In the year 1800 the extended patent right, which had
been granted to Boulton and Watt for their improved
engine, expired, and at this time Mr. Watt retired altogether
from business. He was succeeded by his two sons,
the present Mr. James Watt, and Gregory, one of the children
of his second marriage. The works at Soho continued
to be conducted by the present Mr. Boulton, the son of the
partner of Mr. Watt, and the two Messrs. Watt. In 1804
Gregory Watt died at the age of twenty-seven, of a disease
of the chest. This afflicting event was deeply felt by Mr.
Watt; but he did not sink under it into that state of despondency
in which he has been represented to have fallen
by M. Arago. On the contrary, he continued to show the
same activity of mind which had characterised his whole
<a class="refpn" id="Pg312">[Pg312]</a>
life; nor did he lose that interest which he always took in
the pursuit of literature and in society. The state of his feelings
under this affliction is shown by the following extracts
from letters written by him at that time, which have been
published by Mr. Muirhead.</p>

<div class="blockquot">

<p class="dateline">"Heathfield, January 26th, 1805.</p>

<p class="continue"><span
class="no-wrap">&#160;&#160;&#160;*&#160;&#160;&#160;*&#160;&#160;&#160;</span>
"I, perhaps, have said too much to you and Mrs. Campbell on
the state of my mind. I, therefore, think it necessary to say that <em>I am
not low spirited</em>; and were you here, you would find me as cheerful in
the company of my friends as usual; my feelings for the loss of poor
Gregory are not passion, but a deep regret that such was his and
my lot.</p>

<p>"I know that all men must die, and I submit to the decrees of nature,
I hope with due reverence to the Disposer of Events. Yet one stimulus
to exertion is taken away, and, somehow or other, I have lost my relish
for my usual avocations. Perhaps time may remedy that in some measure;
meanwhile, I do not neglect the means of amusement which are
in my power."</p>

<p class="dateline">"Heathfield, April 8th, 1805.</p>

<p class="continue"><span
class="no-wrap">&#160;&#160;&#160;*&#160;&#160;&#160;*&#160;&#160;&#160;</span>
"It is rather mortifying to see how easily the want of even the
best of us is dispensed with in the world; but it is very well it should
be so. We here, however, cannot help feeling a terrible blank in our
family. When I look at my son's books, his writings and drawings, I always
say to myself, where are the mind that conceived these things, and the
hands that executed them? In the course of nature, he should have
said so of mine; but it was otherwise ordered, and our sorrow is unavailing.
As Catullus says:â€”</p>

<div style="max-width:20em;margin:0.51em auto 0.49em auto;">

  <div>---- 'Nunc it, per iter tenebricosum,</div>
  <div>Illuc, unde negant redire quemquam.</div>
  <div>At vobis male sit, malÃ¦ tenebrÃ¦</div>
  <div>Orci, quÃ¦ omnia bella devoratis!'</div>

</div>

<p>"But Catullus was a heathen; let us hope that he (G.) is now rejoicing
in another and a better world, free from our cares, griefs, and infirmities.
Some one has said, I shall not wholly die; and Gregory's name, his
merits and virtues, will live at least as long as those do who knew him.
You are not, from this, to conceive that we give way to grief; on the
contrary, you will find us as cheerful as we ought to be, and as much
disposed to enjoy the friends we have left as ever; but we should approach
to brutes if we had no regrets."</p></div>

<p>Mr. Watt, at the date of these letters, had entered on his
seventieth year, a period after which great mental exertions
are rarely made.
<a class="refpn" id="Pg313">[Pg313]</a></p>

<p>In the summer of 1819, symptoms of indisposition manifested
themselves which soon rendered Watt aware of his
approaching dissolution. "I am very sensible," said he to his
afflicted friends, "of the attachment you show me, and I
hasten to thank you for it, as I am now come to my last illness."
He died on the 25th of August, 1819. His remains
were deposited in the church of Handsworth, near his estate
of Heathfield. His son has raised over his grave a
Gothic chapel, in the centre of which is placed a statue by
Chantrey.</p>

<p>The personal character of Watt could not fail to excite the
admiration and the love of those distinguished persons, whose
pride and happiness it was to be admitted to a share in the
friendship of the great engineer. Among these were reckoned
some of the men who will leave upon the present age
the deepest and most lasting impressions of their genius, and
such persons have bequeathed to posterity the sentiments
with which he inspired them. We cannot here do more justice
to the personal character of the subject of this notice
than by repeating the portraiture of it which has been given
by three of the most distinguished of his friends, and of the
most illustrious men of the present age.</p>

<p>At a meeting convened in 1824, for erecting a monument
to Watt, Lord Brougham pronounced a speech, from which
we extract the following observations:â€”</p>

<div class="blockquot">

<p>"I had the happiness of knowing Mr. Watt, for many years, in the
intercourse of private life; and I will take upon me to bear a testimony
in which all who had that gratification I am sure will join, that they who
only knew his public merit, prodigious as that was, knew but half his
worth. Those who were admitted to his society will readily allow that
anything more pure, more candid, more simple, more scrupulously loving
of justice, than the whole habits of his life and conversation, proved him
to be, was never known in society. One of the most astonishing circumstances
in this truly great man, was the versatility of his talents.
His accomplishments were so various, the powers of his mind were so
vast, and yet of such universal application, that it was hard to say whether
we should most admire the extraordinary grasp of his understanding,
or the accuracy of nice research with which he could bring it to bear
upon the most minute objects of investigation. I forget of whom it was
said, that his mind resembled the trunk of an elephant, which can pick up
<a class="refpn" id="Pg314">[Pg314]</a>
straws, and tear up trees by the roots. Mr. Watt, in some sort, resembled
the greatest and most celebrated of his own inventions, of which we
are at a loss whether most to wonder at the power of grappling with the
mightiest objects, or of handling the most minute; so that, while nothing
seems too large for its grasp, nothing seems too small for the delicacy of
its touch, which can cleave rocks, and pour forth rivers from the bowels
of the earth, and, with perfect exactness, though not with greater ease,
fashion the head of a pin, or strike the impress of some curious die.
Now, those who knew Mr. Watt, had to contemplate a man whose genius
could create such an engine, and indulge in the most abstruse speculations
of philosophy, and could at once pass from the most sublime researches
of geology and physical astronomy, the formation of our globe,
and the structure of the universe, to the manufacture of a needle or a nail;
who could discuss, in the same conversation, and with equal accuracy, if
not with the same consummate skill, the most forbidding details of art
and the elegances of classical literature, the most abstruse branches of
science and the niceties of verbal criticism.</p>

<p>"There was one quality in Mr. Watt which most honourably distinguished
him from too many inventors, and was worthy of all imitationâ€”he was
not only entirely free from jealousy, but he exercised a careful and scrupulous
self-denial, and was anxious not to appear, even by accident, as
appropriating to himself that which he thought belonged to others. I
have heard him refuse the honour universally ascribed to him, of being
the inventor of the steam engine, and call himself simply its improver;
though, in my mind, to doubt his right to that honour, would be as inaccurate
as to question Sir Isaac Newton's claim to his greatest discoveries,
because Descartes in mathematics, and Galileo in astronomy and mechanics,
had preceded him; or to deny the merits of his illustrious successor,
because galvanism was not his discovery, though, before his time,
it had remained as useless to science as the instrument called a steam
engine was to the arts before Mr. Watt. The only jealousy I have known
him to betray, was with respect to others, in the nice adjustment he was
fond of giving to the claims of inventors. Justly prizing scientific discovery
above all other possessions, he deemed the title to it so sacred,
that you might hear him arguing by the hour to settle disputed rights;
and if you ever perceived his temper ruffled, it was when one man's
invention was claimed by, or given to another; or when a clumsy adulation
pressed upon himself that which he knew to be not his own."</p></div>

<p>In the preface to the <cite>Monastery</cite> Sir Walter Scott speaks of
Watt in the following terms:â€”</p>

<div class="blockquot">

<p>"There were assembled about half a score of our northern lights.
<span class="no-wrap">&#160;&#160;&#160;*&#160;&#160;&#160;*&#160;&#160;&#160;</span>
Amidst this company stood Mr. Watt, the man whose genius discovered
the means of multiplying our national resources to a degree, perhaps,
even beyond his own stupendous powers of calculation and combination;
bringing the treasures of the abyss to the summit of the earthâ€”giving
the feeble arm of man the momentum of an Afriteâ€”commanding manufactures
to arise as the rod of the prophet produced water in the
desertâ€”affording the means of dispensing with that time and tide which
wait for no manâ€”and of sailing without that wind which defied the
command and threats of Xerxes himself. This potent commander of the
elementsâ€”this abridger of time and spaceâ€”this magician, whose cloudy
<a class="refpn" id="Pg315">[Pg315]</a>
machinery has produced a change on the world, the effects of which, extraordinary
as they are, are, perhaps, only now beginning to be feltâ€”was
not only the most profound man of scienceâ€”the most successful
combiner of powers, and calculator of numbers, as adapted to practical
purposesâ€”was not only one of the most generally well informed, but one
of the best and kindest of human beings.</p>

<p>"There he stood, surrounded by the little band I have mentioned of
northern literati, men not less tenacious, generally speaking, of their own
fame and their own opinions, than the national regiments are supposed
to be jealous of the high character which they have won upon service.
Methinks I yet see and hear what I shall never see or hear again. In
his eighty-second year, the alert, kind, benevolent old man, had his
attention alive to every one's question, his information at every one's
command.</p>

<p>"His talents and fancy overflowed on every subject. One gentleman
was a deep philologistâ€”he talked with him on the origin of the alphabet,
as if he had been coeval with Cadmus; another a celebrated criticâ€”you
would have said the old man had studied political economy and belles
lettres all his life. Of science it is unnecessary to speakâ€”it was his own
distinguished walk. And yet, Captain Clutterbuck, when he spoke with
your countryman, Jedediah Cleishbotham, you would have sworn he
had been coeval with Claverse and Burley, with the persecutors and persecuted,
and could number every shot the dragoons had fired at the
fugitive Covenanters. In fact, we discovered that no novel of the least
celebrity escaped his perusal, and that the gifted man of science was as
much addicted to the productions of your native country, in other words,
as shameless and obstinate a peruser of novels, as if he had been a very
milliner's apprentice of eighteen."</p></div>

<p>In the Edinburgh newspaper, called the <cite>Scotsman</cite>, of the
4th September, 1819, immediately after the decease of Watt,
the following sketch was published from the pen of Lord
Jeffrey:â€”</p>

<div class="blockquot">

<p>"This name fortunately needs no commemoration of ours; for he
that bore it survived to see it crowned with undisputed and unenvied
honours; and many generations will probably pass away before it shall
have gathered 'all its fame.' We have said that Mr. Watt was the great
<em>improver</em> of the steam engine; but, in truth, as to all that is admirable
in its structure, or vast in its utility, he should rather be described as its
<em>inventor</em>. It was by his inventions, that its action was so regulated as to
make it capable of being applied to the finest and most delicate manufactures,
and its power so increased, as to set weight and solidity at defiance.
By his admirable contrivance, it has become a thing stupendous
alike for its force and its flexibilityâ€”for the prodigious power which it
can exert, and the ease, and precision, and ductility with which it can be
varied, distributed, and applied. The trunk of an elephant, that can
pick up a pin or rend an oak, is as nothing to it. It can engrave a seal,
and crush masses of obdurate metal before itâ€”draw out, without breaking,
a thread as fine as gossamer, and lift a ship of war like a bauble in
the air. It can embroider muslin, and forge anchorsâ€”cut steel into
ribands, and impel loaded vessels against the fury of the winds and
waves.
<a class="refpn" id="Pg316">[Pg316]</a></p>

<p>"It would be difficult to estimate the value of the benefits which these
inventions have conferred upon this country. There is no branch of
industry that has not been indebted to them; and, in all the most material,
they have not only widened most magnificently the field of its
exertions, but multiplied a thousand fold the amount of its productions.
It is our improved steam engine that has fought the battles of Europe,
and exalted and sustained, through the late tremendous contest, the
political greatness of our land. It is the same great power which now
enables us to pay the interest of our debt, and to maintain the arduous
struggle in which we are still engaged (1819), with the skill and capital of
countries less oppressed with taxation. But these are poor and narrow
views of its importance. It has increased indefinitely the mass of human
comforts and enjoyments, and rendered cheap and accessible all over the
world the materials of wealth and prosperity. It has armed the feeble
hand of man, in short, with a power to which no limits can be assigned;
completed the dominion of mind over the most refractory qualities of
matter; and laid a sure foundation for all those future miracles of mechanic
power which are to aid and reward the labours of after generations.
It is to the genius of one man, too, that all this is mainly owing;
and certainly no man ever bestowed such a gift on his kind. The blessing
is not only universal, but unbounded; and the fabled inventors of
the plough and the loom, who were deified by the erring gratitude of their
rude contemporaries, conferred less important benefits on mankind than
the inventor of our present steam engine.</p>

<p>"This will be the fame of Watt with future generations; and it is
sufficient for his race and his country. But to those to whom he more
immediately belonged, who lived in his society and enjoyed his conversation,
it is not, perhaps, the character in which he will be most frequently
recalledâ€”most deeply lamentedâ€”or even most highly admired.
Independently of his great attainments in mechanics, Mr. Watt
was an extraordinary, and in many respects a wonderful man. Perhaps
no individual in his age possessed so much and such varied and
exact informationâ€”had read so much, or remembered what he had
read so accurately and well. He had infinite quickness of apprehension,
a prodigious memory, and a certain rectifying and methodising
power of understanding, which extracted something precious out of all
that was presented to it. His stores of miscellaneous knowledge were
immense; and yet less astonishing than the command he had at all times
over them. It seemed as if every subject that was casually started in
conversation with him, had been that which he had been last occupied in
studying and exhausting;â€”such was the copiousness, the precision, and
the admirable clearness of the information which he poured out upon it
without effort or hesitation. Nor was this promptitude and compass
of knowledge confined in any degree to the studies connected with his
ordinary pursuits. That he should have been minutely and extensively
skilled in chemistry and the arts, and in most of the branches of physical
science, might perhaps have been conjectured; but it could not
have been inferred from his usual occupations, and probably is not
generally known, that he was curiously learned in many branches of antiquity,
metaphysics, medicine, and etymology; and perfectly at home
in all the details of architecture, music, and law. He was well acquainted,
too, with most of the modern languages, and familiar with their
most recent literature. Nor was it at all extraordinary to hear the great
mechanician and engineer detailing and expounding, for hours together,
<a class="refpn" id="Pg317">[Pg317]</a>
the metaphysical theories of the German logicians, or criticising the
measures or the matter of the German poetry.</p>

<p>"His astonishing memory was aided, no doubt, in a great measure, by
a still higher and rarer facultyâ€”by his power of digesting, and arranging
in its proper place, all the information he received; and of
casting aside and rejecting, as it were instinctively, whatever was worthless
or immaterial. Every conception that was suggested to his mind
seemed instantly to take its place among its other rich furniture, and
to be condensed into the smallest and most convenient form. He
never appeared, therefore, to be at all incumbered or perplexed with
the <em>verbiage</em> of the dull books he perused, or to the idle talk to which
he listened; but to have at once extracted, by a kind of intellectual
alchemy, all that was worthy of attention, and to have reduced it, for
his own use, to its true value and to its simplest form. And thus it
often happened, that a great deal more was learned from his brief and
vigorous account of the theories and arguments of tedious writers, than
an ordinary student could ever have derived from the most painful study
of the originals; and that errors and absurdities became manifest from
the mere clearness and plainness of his statement of them, which might
have deluded and perplexed most of his hearers without that invaluable
assistance.</p>

<p>"It is needless to say that, with those vast resources, his conversation
was at all times rich and instructive in no ordinary degree: but it was,
if possible, still more pleasing than wise; and had all the charms of familiarity
with all the substantial treasures of knowledge. No man could
be more social in his spirit, less assuming or fastidious in his manners,
or more kind and indulgent toward all who approached him. He rather
liked to talk,â€”at least in his latter years; but though he took a considerable
share of the conversation, he rarely suggested the topics on
which it was to turn, but readily and quietly took up whatever was
presented by those around him, and astonished the idle and barren
propounders of an ordinary theme by the treasures which he drew from
the mine they had unconsciously opened. He generally seemed, indeed,
to have no choice or predilection for one subject of discourse rather
than another; but allowed his mind, like a great cyclopÃ¦dia, to be
opened at any letter his associates might choose to turn up, and only endeavoured
to select from his inexhaustible stores, what might be best
adapted to the taste of his present hearers. As to their capacity he
gave himself no trouble; and indeed such was his singular talent for
making all things plain, clear, and intelligible, that scarcely any one
could be aware of such a deficiency in his presence. His talk, too,
though overflowing with information, had no resemblance to lecturing or
solemn discoursing, but, on the contrary, was full of colloquial spirit and
pleasantry. He had a certain quiet and grave humour which ran through
most of his conversation; and a vein of temperate jocularity, which
gave infinite zest and effect to the condensed and inexhaustible information
which formed its main staple and characteristic. There was a
little air of affected testiness, and a tone of pretended rebuke and contradiction,
with which he used to address his younger friends, that was
always felt by them as an endearing mark of his kindness and familiarity;
and prized, accordingly, far beyond all the solemn compliments
that ever proceeded from the lips of authority. His voice was deep and
powerful, though he commonly spoke in a low and somewhat monotonous
tone, which harmonised admirably with the weight and brevity of
his observations, and set off to the greatest advantage the pleasant
<a class="refpn" id="Pg318">[Pg318]</a>
anecdotes, which he delivered with the same grave brow, and the same
calm smile playing soberly on his lips. There was nothing of effort,
indeed, or impatience, any more than of pride or levity, in his demeanour;
and there was a finer expression of reposing strength, and mild self-possession
in his manner, than we ever recollect to have met with in
any other person. He had in his character the utmost abhorrence for
all sorts of forwardness, parade, and pretensions; and, indeed, never
failed to put all such impostures out of countenance, by the manly
plainness and honest intrepidity of his language and deportment.</p>

<p>"In his temper and dispositions, he was not only kind and affectionate,
but generous, and considerate of the feelings of all around him; and
gave the most liberal assistance and encouragement to all young persons
who showed any indications of talent, or applied to him for patronage
or advice. His health, which was delicate from his youth upwards,
seemed to become firmer as he advanced in years; and he preserved,
up almost to the last moment of his existence, not only the full command
of his extraordinary intellect, but all the alacrity of spirit and the
social gaiety which had illumined his happiest days. His friends in this
part of the country never saw him more full of intellectual vigour and
colloquial animationâ€”never more delightful or more instructiveâ€”than
in his last visit to Scotland in autumn 1817. Indeed, it was after that
time that he applied himself, with all the ardour of early life, to the invention
of a machine for mechanically copying all sorts of sculpture
and statuary; and distributed among his friends some of its earliest
performances, as the productions of a young artist just entering on his
eighty-third year.</p>

<p>"This happy and useful life came, at last, to a gentle close. He had
suffered some inconvenience through the summer; but was not seriously
indisposed till within a few weeks of his death. He then became
perfectly aware of the event which was approaching; and with his usual
tranquillity and benevolence of nature, seemed only anxious to point out
to the friends around him, the many sources of consolation which were
afforded by the circumstances under which it was about to take place.
He expressed his sincere gratitude to Providence for the length of days
with which he had been blessed, and his exemption from most of the
infirmities of age; as well as for the calm and cheerful evening of life
that he had been permitted to enjoy, after the honourable labours of the
day had been concluded. And thus, full of years and honours, in all
calmness and tranquillity, he yielded up his soul without pang or
struggle; and passed from the bosom of his family to that of his God."</p></div>

<p>The English nation has ever shown itself insensible to the
claims of genius and high intellectual endowments, except
where the results have been brought directly to bear in statesmanship
or war. Of this inability to appreciate the highest
order of intellectual excellence Watt affords a striking example.
When it was suggested to the British government
by those better capable than that government was of appreciating
the genius of this great man, that the nation would
do itself honour by erecting a splendid monument at his own
<a class="refpn" id="Pg319">[Pg319]</a>
cost to him to whom it was so deeply indebted for the extension
of its resources and the augmentation of its power, the
reply was that such a measure could not be adopted as it
might be drawn into a precedent in like cases thereafter!
A precedent in like cases!! When will the time arrive when
the world will produce a like case? The monument which
has been erected in Westminster Abbey was in fact raised by
private subscription, the nation having thus stigmatised itself
through the act of its government with the everlasting disgrace
of refusing the honour proposed to it. The other statues
and monuments which have been erected to this great man,
have been for the most part raised by the filial piety and the
never-dying affection and veneration of the present Mr. James
Watt. A statue has been presented by him to the University
of Glasgow, and placed in one of the halls of that college.
The inhabitants of Greenock have also erected a marble statue
of Watt, for which, and for a library, a building has been
erected at the expense of about 3,500<i>l.</i> which has been defrayed
by Mr. James Watt. A colossal bronze statue has
been erected on a handsome granite pedestal, standing at one
of the corners of George Square, Glasgow. The monument
in Westminster Abbey, erected by the subscription raised at
the public meeting already alluded to, is a colossal statue of
Carrara marble, by Chantrey.</p>

<p>Watt was elected a fellow of the Royal Society of Edinburgh
in 1784; of the Royal Society of London in 1785;
a member of the Batavian Society in 1787; and a corresponding
member of the Institut of France in 1808. The
degree of Doctor of Laws was conferred upon him by the
University of Glasgow, in 1806; and in 1814, the highest
scientific honour which can be attained by a philosopher, was
conferred on him by the Academy of Sciences of the Institut
of France, who nominated him one of its eight foreign associates.</p>

<p>On the pedestal of the monument in Westminster Abbey
is engraved the following inscription from the pen of Lord
Brougham:â€”
<a class="refpn" id="Pg320">[Pg320]</a></p>

<div style="text-align:center; page-break-before:always;">
 <div><strong>NOT TO PERPETUATE A NAME<br />
 WHICH MUST ENDURE WHILE THE PEACEFUL ARTS FLOURISH,<br />
 BUT TO SHOW<br />
 THAT MANKIND HAVE LEARNED TO HONOUR THOSE<br />
 WHO BEST DESERVE THEIR GRATITUDE,<br />
 THE KING<br />
 HIS MINISTERS, AND MANY OF THE NOBLES<br />
 AND COMMONERS OF THE REALM<br />
 RAISED THIS MONUMENT TO</strong>
 </div>

 <div><strong class="m1">JAMES WATT</strong>,</div>

 <div><strong>WHO DIRECTING THE FORCE OF AN ORIGINAL GENIUS,<br />
 EARLY EXERCISED IN PHILOSOPHIC RESEARCH<br />
 TO THE IMPROVEMENT OF<br />
 THE STEAM ENGINE,<br />
 ENLARGED THE RESOURCES OF HIS COUNTRY,<br />
 INCREASED THE POWER OF MAN,<br />
 AND ROSE TO AN EMINENT PLACE<br />
 AMONG THE MOST ILLUSTRIOUS FOLLOWERS OF SCIENCE<br />
 AND THE REAL BENEFACTORS OF THE WORLD.<br />
 BORN AT GREENOCK MDCCXXXVI.<br />
 DIED AT HEATHFIELD IN STAFFORDSHIRE MDCCCXIX</strong>.
</div></div>

<div class="figcenter" style="width: 447px;">
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_342.png" width="447" height="409" alt="" />
<div class="caption">WATT'S CHAPEL IN HANDSWORTH CHURCH.</div>
</div>

<div class="footnotes"><h3>FOOTNOTES:</h3>

<div class="footnote">

<p><a name="Footnote_25_25" id="Footnote_25_25"></a><a href="#FNanchor_25_25"><span class="label">[25]</span></a> See Buchanan on the Economy of Fuel and Management of Heat,
especially as it relates to heating and drying by means of Steam.</p></div>

<div class="footnote">

<p><a name="Footnote_26_26" id="Footnote_26_26"></a><a href="#FNanchor_26_26"><span class="label">[26]</span></a> See Brewster's Edinburgh EncyclopÃ¦dia, article <strong class="m1">Steam-drying
Machine</strong>.</p></div>

<div class="footnote">

<p><a name="Footnote_27_27" id="Footnote_27_27"></a><a href="#FNanchor_27_27"><span class="label">[27]</span></a> The following are the words in which Watt makes this remarkable
announcement to Priestley:â€”
</p>
<p>
"Let us now consider what obviously happens in the deflagration of
the inflammable (hydrogen) and dephlogisticated air (oxygen). These
two kinds of air unite with violence; they become red hot, and upon
cooling, totally disappear. When the vessel is cooled, a quantity of
water is found in it equal to the weight of the air employed. This
water is then the only remaining product of the process; and water,
light, and heat are all the products.
</p>
<p>
"Are we not then authorised to conclude, that water is composed of
dephlogisticated air (oxygen) and phlogiston (hydrogen), deprived of
part of their latent or elementary heat; that dephlogisticated or pure air
(oxygen) is composed of water deprived of its phlogiston (hydrogen),
and united to elementary heat and light; and that the latter are contained
in it in a latent state, so as not to be sensible to the thermometer
or to the eye; and if light be only a modification of heat, or a circumstance
attending it, or a component part of the inflammable air (hydrogen),
then pure or dephlogisticated air (oxygen) is composed of
water deprived of its phlogiston (hydrogen), and united to elementary
heat."</p></div>

<div class="footnote">

<p><a name="Footnote_28_28" id="Footnote_28_28"></a><a
href="#FNanchor_28_28"><span class="label">[28]</span></a>
Those who desire to investigate this controversy more in detail will
find very full information on the subject in the Translation of Arago's Eloge,
with notes and appendix by J. P. Muirhead, Esq. Murray, London, 1839.</p></div>

<div class="footnote">

<p><a name="Footnote_29_29" id="Footnote_29_29"></a><a
href="#FNanchor_29_29"><span class="label">[29]</span></a>
An account of this remarkable apparatus, accompanied by an engraving
made from a drawing supplied by Watt, was communicated by Sir
John Robison to the <cite>Edinburgh Philosophical Journal</cite> in 1820. <i>See</i> vol. iii,
p. 60.</p></div></div>

<div class="figcenter" style="width: 460px;">
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_343.png" width="460" height="227" alt="locomotive" />
</div>

<h2><a name="CHAP_XI" id="CHAP_XI">CHAP. XI.</a></h2>

<p class="fsize2 center">LOCOMOTIVE ENGINES ON RAILWAYS.</p>

<p class="right"><a class="refpn" id="Pg321">[Pg321]</a><br />
<a href="#CONTENTS"><small>TOC</small></a>&#160;&#160;<a
href="#INDEX"><small>INX</small></a></p>

<div class="chapheader">
NON-CONDENSING ENGINES.â€”LEUPOLD'S ENGINE.-TREVETHICK AND
VIVIAN.â€”EFFECTS OF RAILWAY TRANSPORT.â€”HISTORY OF THE LOCOMOTIVE
ENGINE.â€”BLENKINSOP.â€”MESSRS. CHAPMAN.â€”WALKING ENGINE.â€”MR.
STEPHENSON'S ENGINES AT KILLINGWORTH.â€”LIVERPOOL
AND MANCHESTER RAILWAY.â€”EXPERIMENTAL TRIAL.â€”THE ROCKET.â€”THE
SANSPAREIL.â€”THE NOVELTY.â€”SUBSEQUENT IMPROVEMENTS
IN THE LOCOMOTIVE ENGINE.â€”LARDNER'S EXPERIMENTS IN 1832.â€”ADOPTION
OF BRASS TUBES.â€”MR. BOOTH'S REPORT.â€”DETAILED DESCRIPTION
OF THE MOST IMPROVED LOCOMOTIVE ENGINES.â€”POWER
OF LOCOMOTIVE ENGINES.â€”EVAPORATION OF BOILERS.â€”LARDNER'S
EXPERIMENTS IN 1838.â€”RESISTANCE TO RAILWAY TRAINS.â€”RESTRICTIONS
ON GRADIENTS.â€”COMPENSATING EFFECT OF GRADIENTS.â€”EXPERIMENT
WITH THE HECLA.â€”METHODS OF SURMOUNTING STEEP
INCLINATIONS.</div>


<div class="ph3fst"><h3>(180.)</h3> In the various modifications of the steam engine which
we have hitherto considered, the pressure introduced on
one side of the piston derives its efficacy either wholly or
partially from the vacuum produced by condensation on the
other side. This always requires a condensing apparatus,
and a constant and abundant supply of cold water. An
engine of this kind must therefore necessarily have considerable
dimensions and weight, and is inapplicable to uses
in which a small and light machine only is admissible. If
the condensing apparatus be dispensed with, the piston will
always be resisted by a force equal to the atmospheric
<a class="refpn" id="Pg322">[Pg322]</a>
pressure, and the only part of the steam pressure which will
be available as a moving power, is that part by which it
exceeds the pressure of the atmosphere. Hence, in engines
which do not work by condensation, steam of a much higher
pressure than that of the atmosphere is indispensably necessary,
and such engines are therefore called <em>high-pressure
engines</em>.</div>

<p>We are not, however, to understand that every engine,
in which steam is used of a pressure exceeding that of
the atmosphere, is what is meant by an <em>high-pressure engine</em>;
for in the ordinary engines in common use, constructed on
Watt's principle, the safety-valve is loaded with from 3 to
5 lbs. on the square inch; and in Woolf's engines, the steam
is produced under a pressure of 40 lbs. on the square inch.
These would therefore be more properly called <em>condensing
engines</em> than <em>low-pressure engines</em>; a term quite inapplicable to
those of Woolf. In fact, by <em>high-pressure engines</em> is meant
engines in which no vacuum is produced, and, therefore, in
which the piston works against a pressure equal to that of
the atmosphere.</p>

<p>In these engines the whole of the condensing apparatus,
viz. the cold-water cistern, condenser, air-pump, cold-water
pump, &#38;c., are dispensed with, and nothing is retained
except the boiler, cylinder, piston, and valves. Consequently,
such an engine is small, light, and cheap. It is portable
also, and may be moved, if necessary, along with its load,
and is therefore well adapted to locomotive purposes.</p>


<div class="ph3"><h3>(181.)</h3> High-pressure engines were one of the earliest
forms of the steam engine. The contrivance, which is
obscurely described in the article already quoted (<a href="#h3-7">7</a>.), from
the Century of Inventions, is a high-pressure engine; for
the power there alluded to is the elastic force of steam
working against the atmospheric pressure. Newcomen, in
1705, applied the working-beam, cylinder, and piston to the
atmospheric engine; and Leupold, about 1720, combined
the working-beam and cylinder with the high-pressure principle,
and produced the earliest high-pressure engine worked
by a cylinder and piston. The following is a description of
Leupold's engine:â€”
<a class="refpn" id="Pg323">[Pg323]</a></div>

<div class="figcenter" style="width: 301px;">
<a id="Fig082"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_345.png" width="301" height="471" alt="" />
<div class="caption figure">Fig. 82.</div>
</div>

<p><strong>A</strong> (<a href="#Fig082"><i>fig.</i> 82.</a>) is the boiler, with the furnace beneath it; <strong>C C</strong>
are two cylinders with solid pistons <strong>P Pâ€²</strong>, connected with the
working-beams <strong>B Bâ€²</strong>, to which are attached the pump-rods
<strong>R Râ€²</strong>, of two forcing pumps <strong>F Fâ€²</strong>, which communicate with a
great force-pipe <strong>S</strong>; <strong>G</strong> is a
<em>four-way cock</em> (<a href="#h3-66">66</a>.) already described.
In the position in which it stands in the figure, the
steam issues from below the piston <strong>P</strong> into the atmosphere,
and the piston is descending by its own weight; steam from
the boiler is at the same time pressing up the piston <strong>Pâ€²</strong>, with
a force equal to the difference between the pressure of the
steam and that of the atmosphere. Thus the piston <strong>R</strong> of the
forcing-pump is being drawn up, and the piston <strong>Pâ€²</strong> is forcing
the piston <strong>Râ€²</strong> down, and thereby driving water into the force-pipe
<a class="refpn" id="Pg324">[Pg324]</a>
<strong>S</strong>. On the arrival of the piston <strong>P</strong> at
the bottom of the cylinder <strong>C</strong>, and <strong>Pâ€²</strong> at the
top of the cylinder <strong>Câ€²</strong>, the position of the
cock is changed as represented in <a href="#Fig083"><i>fig.</i> 83.</a>
The steam, which has just pressed up the
piston <strong>Pâ€²</strong>, is allowed to escape into the atmosphere,
while the steam, passing from the
boiler below the piston <strong>P</strong>, presses it up,
and thus <strong>P</strong> ascends by the steam pressure, and <strong>Pâ€²</strong> descends by
its own weight. By these means the piston <strong>R</strong> is forced down,
driving before it the water in the pump-cylinder into the
force-pipe <strong>S</strong>, and the piston <strong>Râ€²</strong> is drawn up to allow the other
pump-cylinder to be re-filled; and so the process is continued.</p>

<div class="figleft" style="width: 121px;">
<a id="Fig083"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_346.png" width="121" height="149" alt="" />
<div class="caption figure">Fig. 83.</div>
</div>

<p>A valve is placed in the bottom of the force-pipes, to prevent
the water which has been driven into it from returning.
This valve opens upwards; and, consequently, the weight of
the water pressing upon it only keeps it more effectually
closed. On each descent of the piston, the pressure transmitted
to the valve acting upwards being greater than the weight
of the water resting upon it, forces it open, and an increased
quantity of water is introduced.</p>


<div class="ph3"><h3>(182.)</h3> From the date of the improvement of Watt until
the commencement of the present century, non-condensing
engines were altogether neglected in these countries. In
the year 1802, Messrs. Trevethick and Vivian constructed
the first non-condensing engine of this kind which was ever
brought into extensive practical use in this kingdom. A section
of this machine, made by a vertical plane, is represented
in <a href="#Fig084"><i>fig.</i> 84.</a></div>

<p>The boiler <strong>A B</strong> is a cylinder with flat circular ends. The
fire-place is constructed in the following manner:â€”A tube
enters the cylindrical boiler at one end; and, proceeding onwards
near the other extremity, is turned and recurved, so as
to be carried back parallel to the direction in which it entered.
It is thus conducted out of the boiler, at another part of the
same end at which it entered. One of the ends of this tube
communicates with the chimney <strong>E</strong>, which is carried upwards
as represented in the figure. The other mouth is furnished
<a class="refpn" id="Pg325">[Pg325]</a>
with a door; and in it is placed the grate, which is formed of
horizontal bars, dividing the tube into two parts; the upper
part forming the fire-place, and the lower the ash-pit. The
fuel is maintained in a state of combustion, on the bars, in
that part of the tube represented at <strong>C D</strong>; and the flame is
carried by the draught of the chimney round the curved flue,
and issues at <strong>E</strong> into the chimney. The flame is thus conducted
through the water, so as to expose the latter to as much heat
as possible.</p>

<div class="figcenter" style="width: 422px;">
<a id="Fig084"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_347.png" width="422" height="385" alt="" />
<div class="caption figure">Fig. 84.</div>
</div>

<p>A section of the cylinder is represented at <strong>F</strong>, immersed in
the boiler, except a few inches of the upper end, where the
four-way cock <strong>G</strong> is placed for regulating the admission of
the steam. A tube is represented at <strong>H</strong>, which leads from this
four-way cock into the chimney; so that the waste steam,
after working the piston, is carried off through this tube, and
passes into the chimney. The upper end of the piston-rod
is furnished with a cross-bar, which is placed in a direction
at right angles to the length of the boiler, and also to the
<a class="refpn" id="Pg326">[Pg326]</a>
piston-rod. This bar is guided in its motion by sliding on
two iron perpendicular rods fixed to the sides of the boiler,
and parallel to each other. To the ends of this cross-bar are
joined two connecting rods, the lower ends of which work
two cranks fixed on an axis extending across and beneath
the boiler, and immediately under the centre of the cylinder.
This axis is sustained in bearings formed in the legs which
support the boiler, and upon its extremity is fixed the fly-wheel
as represented at <strong>B</strong>. A large-toothed wheel is placed
on this axis; which, being turned with the cranked axle,
communicates motion to other wheels; and through them, to
any machinery which the engine may be applied to move.</p>

<div class="figleft" style="width: 82px;">
<a id="Fig085"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_348.png" width="82" height="185" alt="" />
<div class="caption figure">Fig. 85.</div>
</div>

<p>As the four-way cock is represented in the figure, the
steam passes from the boiler through the curved passage <strong>G</strong>
above the piston, while the steam below the piston is carried
off through a tube which does not appear in the figure, by
which it is conducted to the tube <strong>H</strong>, and thence to the
chimney. The steam, therefore, which passes above the
piston presses it downwards; while the pressure upwards
does not exceed that of the atmosphere. The
piston will therefore descend with a force depending
on the excess of the pressure of the
steam produced in the boiler above the atmospheric
pressure. When the piston has arrived
at the bottom of the cylinder, the cock is made
to assume the position represented in <a href="#Fig085"><i>fig.</i> 85.</a>
This effect is produced by the motion of the
piston-rod. The steam now passes from above
the piston, through the tube <strong>H</strong>, into the chimney,
while the steam from the boiler is conducted through another
tube below the piston. The pressure above the piston, in
this case, does not exceed that of the atmosphere; while the
pressure below it will be that of the steam in the boiler.
The piston will therefore ascend with the difference of these
pressures. On the arrival of the piston at the top of the
cylinder, the four-way cock is again turned to the position
represented in <a href="#Fig085"><i>fig.</i> 85.</a>, and the piston again descends; and in
the same manner the process is continued. A safety-valve is
placed on the boiler at <strong>V</strong>, loaded with a weight <strong>W</strong>, proportionate
<a class="refpn" id="Pg327">[Pg327]</a>
to the strength of the steam with which it is proposed
to work.</p>

<p>In the engines now described, this valve was frequently
loaded at the rate of from 60 to 80 lbs. on the square inch.
As the boilers of high-pressure engines were considered more
liable to accidents from bursting than those in which steam
of a lower pressure was used, greater precautions were taken
against such effects. A second safety-valve was provided,
which was not left in the power of the engine-man. By this
means he had a power to diminish the pressure of the steam,
but could not increase it beyond the limit determined by
the valve which was removed from his interference. The
greatest cause of danger, however, arose from the water in
the boiler being consumed by evaporation faster than it was
supplied; and therefore falling below the level of the tube
containing the furnace. To guard against accidents arising
from this circumstance, a hole was bored in the boiler, at
a certain depth, below which the water should not be allowed
to fall; and in this hole a plug of metal was soldered with
lead, or with some other metal, which would fuse at that
temperature which would expose the boiler to danger. Thus,
in the event of the water being exhausted, so that its level
would fall below the plug, the heat of the furnace would
immediately melt the solder, and the plug would fall out,
affording a vent for the steam, without allowing the boiler to
burst. The mercurial steam-gauge, already described, was
also used as an additional security. When the force of the
steam exceeded the length of the column of mercury which
the tube would contain, the mercury would be blown out,
and the tube would give vent to the steam. The water by
which the boiler was replenished was forced into it by a
pump worked by the engine. In order to economise the
heat, this water was contained in a tube <strong>T</strong>, which surrounded
the pipe <strong>H</strong>. As the waste steam, after working the piston,
passed off through <strong>H</strong>, it imparted a portion of its heat to
the water contained in the tube <strong>T</strong>, which was thus warmed
to a certain temperature before it was forced into the boiler
by the pump. Thus a part of the heat, which was originally
<a class="refpn" id="Pg328">[Pg328]</a>
carried from the boiler in the form of steam, was returned
again to the boiler with the water with which it was fed.</p>

<p>It is evident that engines constructed in this manner may
be applied to all the purposes to which the condensing engines
are applicable.</p>


<div class="ph3">
<h3>(183.)</h3> Two years after the date of the patent of this engine,
its inventor constructed a machine of the same kind
for the purpose of moving carriages on railroads; and applied
it successfully, in the year 1804, on the railroad at Merthyr
Tydvil, in South Wales. It was in principle the same as that
already described. The cylinder however was in a horizontal
position, the piston-rod working in the direction of the line
of road: the extremity of the piston-rod, by means of a connecting
rod, worked cranks placed on the axletree, on which
were fixed two cogged wheels: these worked in others, by
which their motion was communicated finally to cogged
wheels fixed on the axle of the hind wheels of the carriage,
by which this axle was kept in a state of revolution. The
hind wheels being fixed on the axletree, and turning with it,
were caused likewise to revolve; and so long as the weight of
the carriage did not exceed that which the friction of the road
was capable of propelling, the carriage would thus be moved
forwards. On this axle was placed a fly-wheel to continue
the rotatory motion at the termination of each stroke. The fore
wheels are described as being capable of turning like the fore
wheels of a carriage, so as to guide the vehicle. The projectors
appear to have contemplated, in the first instance, the
use of this carriage on common roads; but that notion seems
to have been abandoned, and its use was only adopted on the
railroad before mentioned. On the occasion of its first trial,
it drew after it as many carriages as contained ten tons of iron
a distance of nine miles; which stage it performed without
any fresh supply of water, and travelled at the rate of five
miles an hour.</div>


<div class="ph3"><h3>(184.)</h3> Capital and skill have of late years been directed
with extraordinary energy to the improvement of inland
transport; and this important instrument of national wealth
and civilisation has received a proportionate impulse. Effects
are now witnessed, which, had they been narrated a few years
<a class="refpn" id="Pg329">[Pg329]</a>
since, could only have been admitted into the pages of fiction
or volumes of romance. Who could have credited the possibility
of a ponderous engine of iron, loaded with some hundred
passengers, in a train of carriages of corresponding magnitude,
and a large quantity of water and coal, taking flight
from Manchester and arriving at Liverpool, a distance of above
thirty miles, in little more than an hour? And yet this is a
matter of daily and almost hourly occurrence. The rapidity
of transport thus attained is not less wonderful than the
weights transported. Its capabilities in this respect far transcend
the exigencies even of the two greatest commercial
marts in Great Britain. Loads, varying from fifty to one
hundred and fifty tons, are transported at the average rate of
fifteen miles an hour; and in one instance we have seen a loadâ€”we
should rather say a <em>cargo</em>â€”of waggons, conveying merchandise
to the amount of two hundred and thirty tons gross,
transported from Liverpool to Manchester at the average rate
of twelve miles an hour.</div>

<p>The astonishment with which such performances must be
viewed, might be qualified, if the art of transport by steam
on railways had been matured, and had attained that full state
of perfection which such an art is always capable of receiving
from long experience, aided by great scientific knowledge, and
the unbounded application of capital. But such is not the
present case. The art of constructing locomotive engines, so
far from having attained a state of maturity, has not even
emerged from its infancy. So complete was the ignorance
of its powers which prevailed, even among engineers, previous
to the opening of the Liverpool railway, that the transport of
heavy goods was regarded as the chief object of the undertaking,
and its principal source of revenue. The incredible
speed of transport, effected even in the very first experiments
in 1830, burst upon the public, and on the scientific world,
with all the effect of a new and unlooked-for phenomenon.
On the unfortunate occasion which deprived this country of
Mr. Huskisson, the wounded body of that statesman was
transported a distance of about fifteen miles in twenty-five
minutes, being at the rate of thirty-six miles an hour. The
revenue of the road arising from passengers since its opening,
<a class="refpn" id="Pg330">[Pg330]</a>
has, contrary to all that was foreseen, been nearly double that
which has been derived from merchandise. So great was the
want of experience in the construction of engines, that the
company was at first ignorant whether they should adopt large
steam engines fixed at different stations on the line, to pull
the carriages from station to station, or travelling engines to
drag the loads the entire distance. Having decided on the
latter, they have, even to the present moment, laboured under
the disadvantage of the want of that knowledge which experience
alone can give. The engines have been constantly
varied in their weight and proportions, in their magnitude
and form, as the experience of each successive month has indicated.
As defects became manifest they were remedied;
improvements suggested were adopted; and each year produced
engines of such increased power and efficiency, that
their predecessors were abandoned, not because they were
worn out, but because they had been outstripped in the rapid
march of improvement. Add to this, that only one species
of travelling engine has been effectively tried; the capabilities
of others remain still to be developed; and even that
form of engine which has received the advantage of a course
of experiments on so grand a scale to carry it towards perfection,
is far short of this point, and still has defects, many of
which, it is obvious, time and experience will remove.</p>

<p>If, then, the locomotive engine, subject thus to all the imperfections
inseparable from a novel contrivanceâ€”with the
restrictions on the free application of skill and capital, arising
from the nature of the monopolies granted to railway companiesâ€”with
the disadvantage of very limited experience,
the great parent of practical improvement, having been submitted
to experiments hitherto only on a limited scale, and
confined almost to one form of machine;â€”if, under such
disadvantages, such effects have been produced as are now
daily witnessed by the public, what may not be looked for from
this extraordinary power when the enterprise of the country
shall be more unfetteredâ€”when greater fields of experience
are openedâ€”when time, ingenuity, and capital have removed
or diminished existing imperfections, and have brought to light
new and more powerful principles? This is not mere speculation
<a class="refpn" id="Pg331">[Pg331]</a>
on abstract possibilities, but refers to what is in actual
progress. The points of greatest wealth and populationâ€”the
centres of largest capital and most active industry throughout
the countryâ€”will soon be connected by lines of railway;
and various experiments are proposed, with more or less prospect
of success, for the application of steam engines on stone
roads where the intercourse is not sufficient to render railways
profitable.</p>

<p>The important commercial and political effects attending
such increased facility and speed in the transport of persons
and goods, are too obvious to require any very extended
notice here. A part of the price (and in many cases a considerable
part) of every article of necessity or luxury, consists
of the cost of transporting it from the producer to the consumer;
and consequently every abatement or saving in this
cost must produce a corresponding reduction in the price of
every article transported; that is to say, of every thing which
is necessary for the subsistence of the poor, or for the enjoyment
of the richâ€”of every comfort, and of every luxury of
life. The benefit of this will extend, not to the consumer
only, but to the producer: by lowering the expense of transport
of the produce, whether of the soil or of the loom, a less
quantity of that produce will be spent in bringing the remainder
to market, and consequently a greater surplus will
reward the labour of the producer. The benefit of this will
be felt even more by the agriculturist than by the manufacturer;
because the proportional cost of transport of the produce
of the soil is greater than that of manufactures. If
two hundred quarters of corn be necessary to raise four hundred,
and one hundred more be required to bring the four
hundred to market, then the net surplus will be one hundred.
But if by the use of steam carriages the same quantity can
be brought to market with an expenditure of fifty quarters,
then the net surplus will be increased from one hundred to
one hundred and fifty quarters; and either the profit of the
farmer, or the rent of the landlord, must be increased by the
same amount.</p>

<p>But the agriculturist would not merely be benefited by an
increased return from the soil already under cultivation. Any
<a class="refpn" id="Pg332">[Pg332]</a>
reduction in the cost of transporting the produce to market
would call into cultivation tracts of inferior fertility, the returns
from which would not at present repay the cost of cultivation
and transport. Thus land would become productive
which is now waste, and an effect would be produced equivalent
to adding so much fertile soil to the present extent of
the country. It is well known, that land of a given degree of
fertility will yield increased produce by the increased application
of capital and labour. By a reduction in the cost
of transport, a saving will be made which may enable the
agriculturist to apply to tracts already under cultivation the
capital thus saved, and thereby increase their actual production.
Not only, therefore, would such an effect be attended
with an increased extent of cultivated land, but also with an
increased degree of cultivation in that which is already productive.</p>

<p>It has been said, that in Great Britain there are above a
million of horses engaged in various ways in the transport of
passengers and goods, and that to transport each horse requires
as much land as would, upon an average, support eight men.
If this quantity of animal power were displaced by steam
engines, and the means of transport drawn from the bowels of
the earth, instead of being raised upon its surface, then, supposing
the above calculation correct, as much land would
become available for the support of human beings as would
suffice for an additional population of eight millions; or, what
amounts to the same, would increase the means of support of
the present population by about one third of the present
available means. The land which now supports horses for
transport would then support men, or produce corn for food.</p>

<p>The objection that a quantity of land exists in the country
capable of supporting horses alone, and that such land would
be thrown out of cultivation, scarcely deserves notice here.
The existence of any considerable quantity of such land is
extremely doubtful. What is the soil which will feed a horse
and not feed oxen or sheep, or produce food for man? But
even if it be admitted that there exists in the country a small
portion of such land, that portion cannot exceed, nor indeed
equal, what would be sufficient for the number of horses
<a class="refpn" id="Pg333">[Pg333]</a>
which must after all continue to be employed for the purposes
of pleasure, and in a variety of cases where steam must
necessarily be inapplicable. It is to be remembered, also,
that the displacing of horses in one extensive occupation, by
diminishing their price must necessarily increase the demand
for them in others.</p>

<p>The reduction in the cost of transport of manufactured
articles, by lowering their price in the market, will stimulate
their consumption. This observation applies of course not
only to home but to foreign markets. In the latter we
already in many branches of manufactures command a monopoly.
The reduced price which we shall attain by cheapness
and facility of transport will still further extend and increase
our advantages. The necessary consequence will be, an increased
demand for manufacturing population; and this increased
population again reacting on the agricultural interests,
will form an increased market for that species of produce.
So interwoven and complicated are the fibres which form the
texture of the highly civilised and artificial community in
which we live, that an effect produced on any one point is
instantly transmitted to the most remote and apparently unconnected
parts of the system.</p>

<p>The two advantages of increased cheapness and speed, besides
extending the amount of existing traffic, call into existence
new objects of commercial intercourse. For the same
reason that the reduced cost of transport, as we have shown,
calls new soils into cultivation, it also calls into existence new
markets for manufactured and agricultural produce. The
great speed of transit which has been proved to be practicable,
must open a commerce between distant points in
various articles, the nature of which does not permit them to
be preserved so as to be fit for use beyond a certain time.
Such are, for example, many species of vegetable and animal
food, which at present are confined to markets at a very
limited distance from the grower or feeder. The truth of
this observation is manifested by the effects which have followed
the intercourse by steam on the Irish Channel. The
western towns of England have become markets for a prodigious
quantity of Irish produce, which it had been previously
<a class="refpn" id="Pg334">[Pg334]</a>
impossible to export. If animal food be transported alive
from the grower to the consumer, the distance of the market
is limited by the power of the animal to travel, and the cost
of its support on the road. It is only particular species of
cattle which bear to be carried to market on common roads
and by horse carriages. But the peculiar nature of a railway,
the magnitude and weight of the loads which may be transported
on it, and the prodigious speed which may be attained,
render the transport of cattle, of every species, to almost any
distance, both easy and cheap. In process of time, when the
railway system becomes extended, the metropolis and populous
towns will therefore become markets, not as at present
to districts within limited distances of them, but to the whole
country.</p>

<p>The moral and political consequences of so great a
change in the powers of transition of persons and intelligence
from place to place are not easily calculated. The concentration
of mind and exertion which a great metropolis
always exhibits, will be extended in a considerable degree to
the whole realm. The same effect will be produced as if all
distances were lessened in the proportion in which the speed
and cheapness of transit are increased. Towns at present
removed some stages from the metropolis, will become its
suburbs; others, now at a day's journey, will be removed to
its immediate vicinity; business will be carried on with as
much ease between them and the metropolis, as it is now between
distant points of the metropolis itself. Let those who
discard speculations like these as wild and improbable, recur
to the state of public opinion, at no very remote period, on
the subject of steam navigation. Within the memory of persons
who have not yet passed the meridian of life, the possibility
of traversing by the steam engine the channels and
seas that surround and intersect these islands, was regarded
as the dream of enthusiasts. Nautical men and men of science
rejected such speculations with equal incredulity, and with little
less than scorn for the understanding of those who could for
a moment entertain them. Yet we have witnessed steam engines
traversing not these channels and seas alone, but sweeping
the face of the waters round every coast in Europe. The
<a class="refpn" id="Pg335">[Pg335]</a>
seas which interpose between our Asiatic dominions and
Egypt, and those which separate our own shores from our
West Indian possessions, have offered an equally ineffectual
barrier to its powers, and the establishment of a regular
steam communication between the capitals of the Old and New
World has ceased to be a question of practicability, having
become merely one of commercial profit. If steam be not used
as the only means of connecting the most distant points of our
planet, it is not because it is inadequate to the accomplishment
of that end, but because the supply of the material, from
which at the present moment it derives its powers, is restricted
by local and accidental circumstances.<a name="FNanchor_30_30" id="FNanchor_30_30"></a><a href="#Footnote_30_30" class="fnanchor">[30]</a></p>

<p>We propose in the present chapter to lay before our
readers some account of the means whereby the effects above
referred to have been produced; of the manner and degree
in which the public have availed themselves of these means;
and of the improvements of which they seem to us to be susceptible.</p>


<div class="ph3"><h3>(185.)</h3> It is a singular fact, that in the history of this invention
considerable time and great ingenuity were vainly
expended in attempting to overcome a difficulty, which in the
end turned out to be purely imaginary. To comprehend distinctly
the manner in which a wheel carriage is propelled by
steam, suppose that a pin or handle is attached to the spoke
of the wheel at some distance from its centre, and that a force
is applied to this pin in such a manner as to make the wheel
revolve. If the tire of the wheel and the surface of the road
were absolutely smooth and free from friction, so that the face
of the tire would slide without resistance upon the road,
then the effect of the force thus applied would be merely to
cause the wheel to turn round, the carriage being stationary,
the surface of the tire slipping or sliding upon the road as
the wheel is made to revolve. But if, on the other hand, the
pressure of the face of the tire upon the road is such as to
produce between them such a degree of adhesion as will render
it impossible for the wheel to slide or slip upon the road by
<a class="refpn" id="Pg336">[Pg336]</a>
the force which is applied to it, the consequence will be, that
the wheel can only turn round in obedience to the force which
moves it by causing the carriage to advance, so that the wheel
will roll upon the road, and the carriage will be moved forward,
through a distance equal to the circumference of the
wheel, each time it performs a complete revolution.</div>

<p>It is obvious that both of these effects may be partially
produced; the adhesion of the wheel to the road may be insufficient
to prevent slipping altogether, and yet it may be sufficient
to prevent the wheel from slipping as fast as it revolves.
Under such circumstances the carriage would advance and the
wheel would slip. The progressive motion of the carriage
during one complete revolution of the wheel would be equal
to the difference between the complete circumference of the
wheel and the portion through which in one revolution it has
slipped.</p>

<p>When the construction of travelling steam engines first engaged
the attention of engineers, and for a considerable period
afterwards, a notion was impressed upon their minds that the
adhesion between the face of the wheel and the surface of the
road must necessarily be of very small amount, and that in
every practical case the wheels thus driven would either slip
altogether, and produce no advance of the carriage, or that a
considerable portion of the impelling power would be lost by
the partial slipping or sliding of the wheels. It is singular
that it should never have occurred to the many ingenious persons
who for several years were engaged in such experiments
and speculations, to ascertain by experiment the actual amount
of adhesion in any particular case between the wheels and the
road. Had they done so, we should probably now have found
locomotive engines in a more advanced state than that to which
they have attained.</p>

<p>To remedy this imaginary difficulty, Messrs. Trevethick and
Vivian proposed to make the external rims of the wheels
rough and uneven, by surrounding them with projecting heads
of nails or bolts, or by cutting transverse grooves on them.
They proposed, in cases where considerable elevations were to
be ascended, to cause claws or nails to project from the surface
during the ascent, so as to take hold of the road.
<a class="refpn" id="Pg337">[Pg337]</a></p>

<p>In seven years after the construction of the first locomotive
engine by these engineers, another locomotive engine
was constructed by Mr. Blinkensop, of Middleton Colliery,
near Leeds. He obtained a patent, in 1811, for the application
of a rack-rail. The railroad thus, instead of being
composed of smooth bars of iron, presented a line of projecting
teeth, like those of a cog-wheel, which stretched along
the entire distance to be travelled. The wheels on which
the engine rolled were furnished with corresponding teeth,
which worked in the teeth of the railroad, and, in this way,
produced a progressive motion in the carriage.</p>

<p>The next contrivance for overcoming this fictitious difficulty,
was that of Messrs. Chapman, who, in the year 1812,
obtained a patent for working a locomotive engine by a chain
extending along the middle of the line of railroad, from the
one end to the other. This chain was passed once round a
grooved wheel under the centre of the carriage; so that,
when this grooved wheel was turned by the engine, the chain
being incapable of slipping upon it, the carriage was consequently
advanced on the road. In order to prevent the
strain from acting on the whole length of the chain, its links
were made to fall upon upright forks placed at certain intervals,
which between those intervals sustained the tension
of the chain produced by the engine. Friction-rollers were
used to press the chain into the groove of the wheel, so as to
prevent it from slipping. This contrivance was soon abandoned,
for the very obvious reason that a prodigious loss of
force was incurred by the friction of the chain.</p>

<p>The following year, 1813, produced a contrivance of singular
ingenuity, for overcoming the supposed difficulty arising
from the want of adhesion between the wheels and the road.
This was no other than a pair of mechanical legs and feet,
which were made to walk and propel in a manner somewhat
resembling the feet of an animal.</p>

<div class="figcenter" style="width: 384px;">
<a id="Fig086"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_360.png" width="384" height="239" alt="" />
<div class="caption figure">Fig. 86.</div>
</div>

<p>A sketch of these propellers is given in <a href="#Fig086"><i>fig.</i> 86.</a> <strong>A</strong> is the
carriage moving on the railroad, <strong>L</strong> and <strong>Lâ€²</strong> are the legs, <strong>F</strong> and
<strong>Fâ€²</strong> the feet. The foot <strong>F</strong> has a joint at <strong>O</strong>, which corresponds
to the ankle; another joint is placed at <strong>K</strong>, which corresponds
to the knee; and a third is placed at <strong>L</strong>, which corresponds to
<a class="refpn" id="Pg338">[Pg338]</a>
the hip. Similar joints are placed at the corresponding letters
in the other leg. The knee-joint <strong>K</strong> is attached to the end
of the piston of the cylinder. When the piston, which is
horizontal, is pressed outwards, the leg <strong>L</strong> presses the foot <strong>F</strong>
against the ground, and the resistance forces the carriage <strong>A</strong>
onwards. As the carriage proceeds, the angle <strong>K</strong> at the knee
becomes larger, so that the leg and thigh take a straighter
position; and this continues until the piston has reached the
end of its stroke. At the hip <strong>L</strong> there is a short lever <strong>L M</strong>,
the extremity of which is connected by a cord or chain with
a point <strong>S</strong>, placed near the shin of the leg. When the piston
is pressed into the cylinder, the knee <strong>K</strong> is drawn towards
the engine, and the cord <strong>M S</strong> is made to lift the foot <strong>F</strong> from
the ground; to which it does not return until the piston has
arrived at the extremity of the cylinder. On the piston
being again driven out of the cylinder, the foot <strong>F</strong>, being
placed on the road, is pressed backwards by the force of the
piston-rod at <strong>K</strong>; but the friction of the ground preventing its
backward motion, the re-action causes the engine to advance:
and in the same manner this process is continued.</p>

<p>Attached to the thigh at <strong>N</strong>, above the knee, by a joint, is
a horizontal rod <strong>N R</strong>, which works a rack <strong>R</strong>. This rack has
beneath it a cog-wheel. This cog-wheel acts in another rack
below it. By these means, when the knee <strong>K</strong> is driven <em>from</em>
the engine, the rack <strong>R</strong> is moved <em>backwards</em>; but the cog-wheel
acting on the other rack beneath it, will move the latter <em>in
the contrary direction</em>. The rack <strong>R</strong> being then moved <em>in the</em>
<a class="refpn" id="Pg339">[Pg339]</a>
<em>same direction with the knee</em> <strong>K</strong>, it follows that the other rack
will always be moved <em>in a contrary direction</em>. The lower rack
is connected by another horizontal rod with the thigh of the
leg <strong>L Fâ€²</strong>, immediately above the knee at <strong>Nâ€²</strong>. When the
piston is forced <em>inwards</em>, the knee <strong>Kâ€²</strong> will thus be forced
<em>backwards</em>; and when the piston is forced <em>outwards</em>, the knee
<strong>Kâ€²</strong> will be drawn <em>forwards</em>. It therefore follows, that the
two knees <strong>K</strong> and <strong>Kâ€²</strong> are pressed <em>alternately backwards</em> and
<em>forwards</em>. The foot <strong>Fâ€²</strong>, when the knee <strong>Kâ€²</strong> is drawn forward,
is lifted by the means already described for the foot <strong>F</strong>.</p>

<p>It will be apparent, from this description, that the piece of
mechanism here exhibited is a contrivance derived from the
motion of the legs of an animal, and resembling in all respects
the fore legs of a horse. It is however to be regarded rather
as a specimen of great ingenuity than as a contrivance of
practical utility.</p>


<div class="ph3"><h3>(186.)</h3> It was about this period that the important fact was
first ascertained that the adhesion or friction of the wheels
with the rails on which they moved was amply sufficient
to propel the engine, even when dragging after it a load of
great weight; and that in such case, the progressive motion
would be effected without any slipping of the wheels. The
consequence of this fact rendered totally useless all the
contrivances for giving wheels a purchase on the road, such
as racks, chains, feet, &#38;c. The experiment by which this
was determined appears to have been first tried on the
Wylam railroad; where it was proved, that when the road
was level, and the rails clean, the adhesion of the wheels was
sufficient, in all kinds of weather, to propel considerable
loads. By manual labour it was first ascertained how much
weight the wheels of a common carriage would overcome
without slipping round on the rail, and having found the
proportion which that bore to the weight, they then ascertained
that the weight of the engine would produce sufficient
adhesion to drag after it on the railroad the requisite number
of waggons.<a name="FNanchor_31_31" id="FNanchor_31_31"></a><a href="#Footnote_31_31" class="fnanchor">[31]</a></div>

<p>In 1814, an engine was constructed at Killingworth, by
Mr. Stephenson, having two cylinders with a cylindrical
<a class="refpn" id="Pg340">[Pg340]</a>
boiler, and working two pair of wheels, by cranks placed at
right angles; so that when the one was in full operation, the
other was at its dead points. By these means the propelling
power was always in action. The cranks were maintained
in this position by an endless chain, which passed round two
cogged wheels placed under the engine, and which were fixed
on the same axles on which the wheels were placed. The
wheels in this case were fixed on the axles, and turned with
them.</p>

<div class="figcenter" style="width: 394px;">
<a id="Fig087"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_362.png" width="394" height="255" alt="" />
<div class="caption figure">Fig. 87.</div>
</div>

<p>This engine is represented in <a href="#Fig087"><i>fig.</i> 87.</a>, the sides being open,
to render the interior mechanism visible. <strong>A B</strong> is the cylindrical
boiler; <strong>C C</strong> are the working cylinders; <strong>D E</strong> are the
cogged wheels fixed on the axle of the wheels of the engine,
and surrounded by the endless chain. These wheels being
equal in magnitude, perform their revolutions in the same
time; so that, when the crank <strong>F</strong> descends to the lowest
point, the crank <strong>G</strong> rises from the lowest point to the horizontal
position <strong>D</strong>; and, again, when the crank <strong>F</strong> rises from
the lowest point to the horizontal position <strong>E</strong>, the other
crank rises to the highest point; and so on. A very beautiful
contrivance was adopted in this engine, by which it was
suspended on springs of steam. Small cylinders, represented
at <strong>H</strong>, are screwed by flanges to one side of the boiler, and
project within it a few inches; they have free communication
at the top with the water or steam of the boiler. Solid
pistons are represented at <strong>I</strong>, which move steam-tight in these
<a class="refpn" id="Pg341">[Pg341]</a>
cylinders; the cylinders are open at the bottom, and the
piston-rods are screwed on the carriage of the engine, over
the axle of each pair of wheels, the pistons being presented
upwards. As the engine is represented in the figure, it is
supported on four pistons, two at each side. The pistons
are pressed upon by the water or steam which occupies the
upper chamber of the cylinder; and the latter being elastic
in a high degree, the engine has all the advantage of spring
suspension. The defect of this method of supporting the
engine is, that when the steam loses that amount of elasticity
necessary for the support of the machine, the pistons are
forced into the cylinders, and the bottoms of the cylinders
bear upon them. All spring suspension is then lost. This
mode of suspension has consequently since been laid aside.</p>

<p>In an engine subsequently constructed by Mr. Stephenson,
for the Killingworth railroad, the mode adopted of connecting
the wheels by an endless chain and cog-wheels was
abandoned; and the same effect was produced by connecting
the two cranks by a straight rod. All such contrivances,
however, have this great defect, that, if the fore and hind
wheels be not constructed with dimensions accurately equal,
there must necessarily be a slipping or dragging on the road.
The nature of the machinery requires that each wheel
should perform its revolution exactly in the same time; and
consequently, in doing so, must pass over exactly equal
lengths of the road. If, therefore, the circumference of the
wheels be not accurately equal, that wheel which has the
lesser circumference must be dragged along so much of the
road as that by which it falls short of the circumference of
the greater wheel; or, on the other hand, the greater wheel
must be dragged in the opposite direction, to compensate
for the same difference. As no mechanism can accomplish
a perfect equality in four, much less in six, wheels, it may be
assumed that a great portion of that dragging effect is a necessary
consequence of the principle of this machine; and
even were the wheels, in the first instance, accurately constructed,
it is not possible that their wear could be so exactly
uniform as to continue equal.</p>


<div class="ph3"><h3>(187.)</h3> The next stimulus which the progress of this
<a class="refpn" id="Pg342">[Pg342]</a>
invention received, proceeded from the great national work
undertaken at Liverpool, by which that town and the extensive
commercial mart of Manchester were connected by a
double line of railway. When this project was undertaken,
it was not decided what moving power it might be most
expedient to adopt as a means of transport on the proposed
road: the choice lay between horse power, fixed steam
engines, and locomotive engines; but the first, for many
obvious reasons, was at once rejected in favour of one or
other of the last two.</div>

<p>The steam engine may be applied, by two distinct methods,
to move waggons either on a turnpike road or on a
railway. By the one method the steam engine is fixed, and
draws the carriage or train of carriages towards it by a chain
extending the whole length of road on which the engine
works. By this method the line of road over which the
transport is conducted is divided into a number of short
intervals, at the extremity of each of which an engine is
placed. The waggons or carriages, when drawn by any
engine to its own station, are detached, and connected with
the extremity of the chain worked by the next stationary
engine; and thus the journey is performed, from station to
station, by separate engines. By the other method the same
engine draws the load the whole journey, travelling with it.</p>

<p>The Directors of the Liverpool and Manchester railroad,
when that work was advanced towards its completion, employed,
in the spring of the year 1829, Messrs. Stephenson
and Lock, and Messrs. Walker and Rastrick, experienced
engineers, to visit the different railways, where practical
information respecting the comparative effects of stationary
and locomotive engines was likely to be obtained; and from
these gentlemen they received reports on the relative merits,
according to their judgment of the two methods. The particulars
of their calculations are given at large in the valuable
work of Mr. Nicholas Wood on railways; to which we
refer the reader, not only on this, but on many other subjects
connected with the locomotive steam engine, into which
it would be foreign to our object to enter. The result of
the comparison of the two systems was, that the capital
<a class="refpn" id="Pg343">[Pg343]</a>
necessary to be advanced to establish a line of stationary
engines was considerably greater than that which was necessary
to establish an equivalent power in locomotive engines;
that the annual expense by the stationary engines was likewise
greater; and that, consequently, the expense of transport
by the latter was greater, in a like proportion. The
subjoined table exhibits the results numerically:â€”</p>

<table summary="Comparitive expenses of Locomotive and Stationary Engines">
<tr>
 <th></th>
 <th>Capital,<br />Â£ <i>s.</i> <i>d.</i></th>
 <th>Annual Expense,<br />Â£ <i>s.</i> <i>d.</i></th>
 <th> Expense of taking a Ton of Goods a Mile,<br />penny</th></tr>
<tr>
 <td align="left">Locomotive engines</td>
 <td class="right">58,000 0 0</td>
 <td class="right">25,517 &#160;8 2</td>
 <td class="center">0Â·164</td></tr>
<tr>
 <td align="left">Stationary engines</td>
 <td class="right no-wrap linedn">121,496 7 0</td>
 <td class="right no-wrap linedn">42,031 16 5</td>
 <td class="center no-wrap linedn">0Â·269</td></tr>
<tr>
 <td align="left">Locomotive system less</td>
 <td class="right">63,496 7 0</td>
 <td class="right">16,514 &#160;8 3</td>
 <td class="center">0Â·105</td></tr>
</table>

<p>On the score of economy, therefore, the system of locomotive
engines was entitled to a preference; but there were
other considerations which conspired with this to decide the
choice of the Directors in its favour. An accident occurring
in any part of a road worked by stationary engines must
necessarily produce a total suspension of work along the entire
line. The most vigilant and active attention on the
part of every workman, however employed, in every part of
the line, would therefore be necessary; but, independently
of this, accidents arising from the fracture or derangement
of any of the chains, or from the suspension of the working
of any of the fixed engines, would be equally injurious, and
would effectually stop the intercourse along the line. On
the other hand, in locomotive engines an accident could only
affect the particular train of carriages drawn by the engine
to which the accident might occur; and even then the difficulty
could be remedied by having a supply of spare engines
at convenient stations along the line. It is true that the
<em>probability</em> of accident is, perhaps, less in the stationary than
in the locomotive system; but the <em>injurious consequences</em>,
when accident <em>does</em> happen, are prodigiously greater in the
former. "The one system," says Mr. Walker, "is like a
chain extending from Liverpool to Manchester, the failure
<a class="refpn" id="Pg344">[Pg344]</a>
of a single link of which would destroy the whole; while
the other is like a number of short and unconnected
chains," the destruction of any one of which does not interfere
with the effect of the others, and the loss of which
may be supplied with facility.</p>

<p>The decision of the Directors was, therefore, in favour of
locomotive engines; and their next measure was to devise
some means by which the inventive genius of the country
might be stimulated to supply them with the best possible form
of engines for this purpose. With this view, it was proposed
and carried into effect to offer a prize for the best locomotive
engine which might be produced under certain proposed conditions,
and to appoint a time for a public trial of the claims
of the candidates. A premium of five hundred pounds was
accordingly offered for the best locomotive engine to run on
the Liverpool and Manchester railway; under the condition
that it should produce no smoke; that the pressure of the
steam should be limited to fifty pounds on the inch; and that it
should draw at least three times its own weight, at the rate of
not less than ten miles an hour; that the engine should be supported
on springs, and should not exceed fifteen feet in height.
Precautions were also proposed against the consequences of
the boiler bursting; and other matters not necessary to mention
more particularly here. This proposal was announced
in the spring of 1829, and the time of trial was appointed
in the following October. The engines which underwent the
trial were, the Rocket, constructed by Mr. Stephenson; the
Sanspareil, by Hackworth; and the Novelty, by Messrs.
Braithwaite and Ericson. Of these, the Rocket obtained
the premium. A line of railway was selected for the trial, on
a level piece of road about two miles in length, near a place
called Rainhill, between Liverpool and Manchester; the distance
between the two stations was a mile and a half, and the
engine had to travel this distance backwards and forwards
ten times, which made altogether a journey of thirty miles.
The Rocket performed this journey twice: the first time in
2 hours 14 minutes and 8 seconds; and the second time
in 2 hours 6 minutes and 49 seconds. Its speed at different
parts of the journey varied: its greatest rate of motion was
<a class="refpn" id="Pg345">[Pg345]</a>
rather above 29 miles an hour; and its least, about
<span class="fraction">11<sup>1</sup>â„<sub>2</sub></span> miles
an hour. The average rate of the one journey was
<span class="fraction">13<sup>4</sup>â„<sub>10</sub></span> miles
an hour; and of the other,
<span class="fraction">14<sup>2</sup>â„<sub>20</sub></span> miles. This was the only
engine which performed the complete journey proposed, the
others having been stopped from accidents which occurred to
them in the experiment. The Sanspareil performed the distance
between the stations eight times, travelling
<span class="fraction">22<sup>1</sup>â„<sub>2</sub></span> miles
in 1 hour 37 minutes and 16 seconds. The greatest velocity
to which this engine attained was something less than 23
miles per hour. The Novelty had only passed twice between
the stations when the joints of the boiler gave way, and put
an end to the experiment.</p>


<div class="ph3">
<h3>(188.)</h3> The great object to be attained in the construction
of these engines was, to combine with sufficient lightness
the greatest possible heating power. The fire necessarily
acts on the water in two ways: first, by its radiant heat; and
second, by the current of heated air which is carried by the
draught through the flues, and finally passes into the chimney.
To accomplish this object, therefore, it is necessary to expose
to both these sources of heat the greatest possible quantity
of surface in contact with the water. These ends were attained
by the following admirable arrangement in the
Rocket:â€”</div>

<div class="figcenter" style="width: 375px;">
<a id="Fig088"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_368a.png" width="375" height="380" alt="" />
<div class="caption figure">Fig. 88.</div>
</div>

<div class="figleft" style="width: 139px;">
<a id="Fig089"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_368b.png" width="139" height="164" alt="" />
<div class="caption figure">Fig. 89.</div>
</div>

<p>This engine is represented in <a href="#Fig088"><i>fig.</i> 88.</a> It is supported on
four wheels; the principal part of the weight being thrown
on one pair, which are worked by the engine. The boiler
consists of a cylinder six feet in length, with flat ends; the
chimney issues from one end, and to the other end is attached
a square box <strong>B</strong>, the bottom of which is furnished with the
grate on which the fuel is placed. This box is composed of
two casings of iron, one contained within the other, having
between them a space about three inches in breadth; the magnitude
of the box being three feet in length, two feet in width,
and three feet in depth. The casing which surrounds the
box communicates with the lower part of the boiler by a pipe
marked <strong>C</strong>; and the same casing at the top of the box communicates
with the upper part of the boiler by another pipe
marked <strong>D</strong>. When water is admitted into the boiler, therefore,
it flows freely, through the pipe <strong>C</strong>, into the casing which
<a class="refpn" id="Pg346">[Pg346]</a>
surrounds the furnace or fire-box, and fills this casing to the
same level as that which it has in the boiler. When the
engine is at work, the boiler is kept about half filled with
water; and, consequently, the casing
surrounding the furnace is completely
filled. The steam which is generated in
the water contained in the casing finds
its exit through the pipe <strong>D</strong>, and escapes
into the upper part of the boiler. A
section of the engine, taken at right
angles to its length, is represented at
<a href="#Fig089"><i>fig.</i> 89.</a> Through the lower part of the
boiler pass a number of copper tubes of small size, which
communicate at one end with the fire-box, and at the other
with the chimney, and form a passage for the heated air from
the furnace to the chimney. The ignited fuel spread on the
grate at the bottom of the fire-box disperses its heat by radiation,
and acts in this manner on the whole surface of the casing
surrounding the fire-box; and thus raises the temperature of
the thin shell of water contained in that casing. The chief
<a class="refpn" id="Pg347">[Pg347]</a>
part of the water in the casing, being lower in its position
than the water in the boiler, acquires a tendency to ascend
when heated, and passes into the boiler; so that a constant
circulation of the heated water is maintained, and the water
in the boiler must necessarily be kept at nearly the same temperature
as the water in the casing. The air which passes
through the burning fuel, and which fills the fire-box, is
carried by the draught through the tubes which extend
through the lower part of the boiler; and as these tubes are
surrounded on every side with the water contained in the
boiler, this air transmits its heat through these tubes to the
water. It finally issues into the chimney, and rises by the
draught. The power of this furnace must necessarily depend
on the power of draught in the chimney; and to increase this,
and at the same time to dispose of the waste steam after it
has worked the piston, this steam is carried off by a pipe <strong>L</strong>,
which passes from the cylinder to the chimney, and escapes
there in a jet which is turned upwards. By the velocity with
which it issues from this jet, and by its great comparative
levity, it produces a strong current upwards in the chimney,
and thus gives force to the draught of the furnace. In <a href="#Fig089"><i>fig.</i> 89.</a>
the grate-bars are represented at the bottom of the fire-box
at <strong>F</strong>. There are two cylinders, one of which works each
wheel; one only appearing in the drawing <a href="#Fig088"><i>fig.</i> 88.</a>, the other
being concealed by the engine. The spokes which these
cylinders work are placed at right angles on the wheels; the
wheels being fixed on a common axle, with which they turn.</p>

<p>In this engine, the surface of water surrounding the fire-box,
exposed to the action of radiant heat, amounted to
twenty square feet, which received heat from the surface of
six square feet of burning fuel on the bars. The surface
exposed to the action of the heated air amounted to 118
square feet. The engine drew after it another carriage, containing
fuel and water; the fuel used was coke, for the purpose
of avoiding the production of smoke.</p>


<div class="ph3"><h3>(189.)</h3>
The Sanspareil of Mr. Hackworth is represented in
<a href="#Fig090"><i>fig.</i> 90.</a>; the horizontal section being exhibited in <a href="#Fig091"><i>fig.</i> 91.</a></div>

<div class="figcenter" style="width: 376px;">
<a id="Fig090"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_370a.png" width="376" height="440" alt="" />
<div class="caption figure">Fig. 90.</div>
</div>

<div class="figcenter" style="width: 325px;">
<a id="Fig091"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_370b.png" width="325" height="162" alt="" />
<div class="caption figure">Fig. 91.</div>
</div>

<p>The draught of the furnace is produced in the same manner
as in the Rocket, by ejecting the waste steam coming from
<a class="refpn" id="Pg348">[Pg348]</a>
the cylinder into the chimney; the boiler, however, differs
considerably from that of the Rocket. A recurved tube
passes through the boiler, somewhat similar to that already
described in the early engine of Messrs. Trevethick and
Vivian. In the horizontal section (<a href="#Fig091"><i>fig.</i> 91.</a>), <strong>D</strong> expresses
the opening of the furnace at the end of the boiler, beside
the chimney. The grate-bars appear at <strong>A</strong>, supporting the
burning fuel; and a curved tube passing through the boiler,
and terminating in the chimney, is expressed at <strong>B</strong>, the direction
<a class="refpn" id="Pg349">[Pg349]</a>
of the draught being indicated by the arrow; <strong>C</strong> is a section
of the chimney. The cylinders are placed, as in the Rocket,
on each side of the boiler; each working a separate wheel,
but acting on spokes placed at right angles to each other.
The tube in which the grate and flue are placed diminishes
in diameter as it approaches the chimney. At the mouth
where the grate was placed, its diameter was two feet; and it
was gradually reduced, so that, at the chimney, its diameter
was only fifteen inches. The grate-bars extended five feet
into the tube. The surface of water exposed to the radiant
heat of the fire was sixteen square feet; and that exposed to
the action of the heated air and flame was about seventy-five
square feet. The magnitude of the grate, or sheet of burning
fuel which radiated heat, was ten square feet.</p>


<div class="ph3"><h3>(190.)</h3> The Novelty, of Messrs. Braithwaite and Ericson,
is represented in <a href="#Fig092"><i>fig.</i> 92.</a>; and a section of the generator and
boiler is exhibited in <a href="#Fig093"><i>fig.</i> 93.</a>; the corresponding parts in the
two figures are marked by the same letters.</div>

<div class="figcenter" style="width: 384px;">
<a id="Fig092"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_371.png" width="384" height="236" alt="" />
<div class="caption figure">Fig. 92.</div>
</div>

<p><strong>A</strong> is the generator or receiver containing the steam which
works the engine; this communicates with a lower generator
<strong>B</strong>, which extends in a horizontal direction the entire length
of the carriage. Within the generator <strong>A</strong> is contained the
furnace <strong>F</strong>, which communicates in a tube <strong>C</strong>, carried up
through the generator, and terminated at the top by sliding
shutters, which exclude the air, and which are only opened
to supply fuel to the grate <strong>F</strong>. Below the grate the furnace
is not open, as usual, to the atmosphere, but communicates,
<a class="refpn" id="Pg350">[Pg350]</a>
by a tube <strong>E</strong>, with a bellows <strong>D</strong>; which is worked by the
engine, and which forces a constant stream of air, by the
tube <strong>E</strong>, through the fuel on <strong>F</strong>, so as to keep that fuel in vivid
combustion. The heated air contained in the furnace <strong>F</strong> is
driven on, by the same force, through a small curved tube
marked <i>e</i>, which circulates like a worm (as represented in
<a href="#Fig093"><i>fig.</i> 93.</a>) through the horizontal generator or receiver; and,
tapering gradually, until reduced to very small dimensions, it
finally issues into the chimney <strong>G</strong>. The air in passing along
this tube, imparts its heat to the water by which the tube is
surrounded, and is brought to a considerably reduced temperature
when discharged into the chimney. The cylinder,
which is represented at <strong>K</strong>, works one pair of wheels, by
means of a bell-crank, the other pair, when necessary, being
connected with them.</p>

<div class="figcenter" style="width: 386px;">
<a id="Fig093"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_372.png" width="386" height="201" alt="" />
<div class="caption figure">Fig. 93.</div>
</div>

<p>In this engine, the magnitude of the surface of burning
fuel on the grate-bars is less than two square feet; the surface
exposed to radiant heat is nine and a half square feet;
and the surface of water exposed to heated air is about thirty-three
square feet.</p>

<p>The superiority of the Rocket may be attributed chiefly to
the greater quantity of surface of the water which is exposed
to the action of the fire. With a less extent of grate-bars
than the Sanspareil, in the proportion of three to five, it exposes
a greater surface of water to radiant heat, in the proportion
of four to three; and a greater surface of water to
heated air, in the proportion of more than three to two. It
was found that the Rocket, compared with the Sanspareil, consumed
fuel, in the evaporation of a given quantity of water,
<a class="refpn" id="Pg351">[Pg351]</a>
in the proportion of eleven to twenty-eight. The suggestion
of using the tubes to conduct through the water the heated
air to the chimney is due to Mr. Booth, treasurer of the Liverpool
and Manchester Railway Company.</p>


<div class="ph3"><h3>(191.)</h3> The object to be effected in the boilers of these
engines is, to keep a small quantity of water at an excessive
temperature, by means of a small quantity of fuel kept in
the most active state of combustion. To accomplish this, it is
necessary, first, so to shape the boiler, furnace, and flues, that
the water shall be in contact with as extensive a surface
as possible, every part of which is acted on, either immediately,
by the heat radiating from the fire, or mediately, by
the air which has passed through the fire, and which finally
rushes into the chimney: and, secondly, that such a forcible
draught should be maintained in the furnace, that a quantity
of heat shall be extricated from the fuel, by combustion, sufficient
to maintain the water at the necessary temperature, and
to produce the steam with sufficient rapidity. To accomplish
these objects, therefore, the chamber containing the grate
should be completely surrounded by water, and should be
below the level of the water in the boiler. The magnitude
of the surface exposed to radiation should be as great as is
consistent with the whole magnitude of the machine. The
comparative advantage which the Rocket possessed in these
respects over the other engines will be evident on inspection.
In the next place, it is necessary that the heat, which is absorbed
by the air passing through the fuel, and keeping it
in a state of combustion, should be transferred to the water
before the air escapes into the chimney. Air being a bad
conductor of heat, to accomplish this it is necessary that the
air in the flues should be exposed to as great an extent of surface
in contact with the water as possible. No contrivance
can be less adapted for the attainment of this end than one or
two large tubes traversing the boiler, as in the earliest locomotive
engines: the body of air which passed through the
centre of these tubes had no contact with their surface, and,
consequently, passed into the chimney at nearly the same
temperature as that which it had when it quitted the fire.
The only portion of air which imparted its heat to the water
<a class="refpn" id="Pg352">[Pg352]</a>
was that portion which passed next to the surface of the
tube.</div>

<p>Several methods suggest themselves to increase the surface
of water in contact with a given quantity of air passing through
it. This would be accomplished by causing the air to pass
between plates placed near each other, so as to divide the
current into thin strata, having between them strata of water,
or it might be made to pass between tubes differing slightly
in diameter, the water passing through an inner tube, and
being also in contact with the external surface of the outer
tube. Such a method would be similar in principle to the
steam-jacket used in Watt's steam engines, or to the condenser
of Cartwright's engine already described. But, considering
the facility of constructing small tubes, and of placing
them in the boiler, that method, perhaps, is, on the whole,
the best in practice; although the shape of a tube, geometrically
considered, is most unfavourable for the exposure of
a fluid contained in it to its surface. The air which passes
from the fire-chamber, being subdivided as it passes through
the boiler by a great number of very small tubes, may be
made to impart all its excess of heat to the water before it
issues into the chimney. This is all which the most refined
contrivance can effect. The Rocket engine was traversed by
twenty-five tubes, each three inches in diameter; and the
principle has since been carried to a much greater extent.</p>

<p>The abstraction of a great quantity of heat from the air
before it reaches the chimney is attended with one consequence,
which, at first view, would present a difficulty apparently
insurmountable; the chimney would, in fact, lose its
power of draught. This difficulty, however, was removed by
using the waste steam, which had passed from the cylinder
after working the engine, for the purpose of producing a
draught. This steam was urged through a jet presented upwards
in the chimney, and driven out with such force in that
direction as to create a sufficient draught to work the furnace.</p>

<p>It will be observed that the principle of draught in the Novelty
is totally distinct from this: in that engine the draught
is produced by a bellows worked by the engine. The question,
as far as relates to these two methods, is, whether more power
<a class="refpn" id="Pg353">[Pg353]</a>
is lost in supplying the steam through the jet, as in the
Rocket, or in working the bellows, as in the Novelty. The
force requisite to impel the steam through the jet must be
exerted by the returning stroke of the piston, and, consequently,
must rob the working effect to an equivalent amount.
On the other hand, the power requisite to work the bellows
in the Novelty must be subducted from the available power
of the engine. The former method has been hitherto found
to be the more effectual and economical.</p>

<p>The importance of these details will be understood, when
it is considered that the only limit to the attainment of
speed by locomotive engines is the power to produce, in a
given time, a certain quantity of steam. Each stroke of the
piston causes one revolution of the wheels, and consumes
four cylinders full of steam: consequently, a cylinder of
steam corresponds to a certain number of feet of road travelled
over: hence it is that the production of a rapid and
abundant supply of heat, and the imparting of that heat
quickly and effectually to the water, is the key to the solution
of the problem to construct an engine capable of rapid motion.</p>

<p>The method of subdividing the flue into tubes was carried
much further by Mr. Stephenson after the construction of
the Rocket; and, indeed, the principle was so obvious,
it is only surprising that, in the first instance, tubes of
smaller diameter than three inches were not used. In engines
since constructed, the number of tubes vary from
ninety to one hundred and twenty, the diameter being
reduced to two inches or less; and in some instances tubes
have been introduced, even to the number of one hundred
and fifty, of one and a half inch diameter. In the Meteor,
twenty square feet are exposed to radiation, and one hundred
and thirty-nine to the contact of heated air; in the
Arrow, twenty square feet to radiation, and one hundred and
forty-five to the contact of heated air. The superior economy
of fuel gained by this means will be apparent by
inspecting the following table, which exhibits the consumption
of fuel which was requisite to convey a ton weight a
mile in each of four engines, expressing also the rate of the
motion:â€”
<a class="refpn" id="Pg354">[Pg354]</a></p>

<table summary="Speed and Fuel Economy of Four Engines">
<tr>
 <th>Engines.</th>
 <th>Average Rate of Speed in Miles per Hour.</th>
 <th>Consumption of Coke in Pounds per Ton per Mile.</th></tr>
<tr>
 <td align="left">No. 1. Rocket</td>
 <td align="center">14</td>
 <td align="center">2Â·41</td></tr>
<tr>
 <td class="left no-wrap">&#160;&#160;&#160;&#160;2. Sanspareil</td>
 <td align="center">15</td>
 <td align="center">2Â·47</td></tr>
<tr>
 <td align="left">&#160;&#160;&#160;&#160;3. PhÅ“nix</td>
 <td align="center">12</td>
 <td align="center">1Â·42</td></tr>
<tr>
 <td align="left">&#160;&#160;&#160;&#160;4. Arrow</td>
 <td align="center">12</td>
 <td align="center">1Â·25</td></tr>
</table>

<div class="ph3">
<h3>(192.)</h3> Since the period at which this railway was opened
for the actual purposes of transport, the locomotive engines
have been in a state of progressive improvement. Scarcely
a month has passed without suggesting some change in the
details, by which fuel might be economised, the production
of steam rendered more rapid, the wear of the engine rendered
slower, the proportionate strength of the different
parts improved, or some other desirable end obtained.</div>

<p>Engines constructed in the form of the Rocket, were subject
to two principal defects. The cylinders, being placed
outside the engine, were exposed to the cold of the atmosphere,
which produced a waste of heat more or less considerable
by condensation. The points at which the power of the
steam to turn the wheels was applied, being at the extremities
of the axle and on the exterior of the wheel, a considerable
strain was produced, owing to the distance of the point of application
of the power from the centre of resistance. If it
were possible that the impelling power could act in drawing
the train at all times with equal energy on both sides of
the engine, then no injurious strain would be produced; but
from the relative position of the points on the opposite wheels
to which it was necessary to attach the connecting rods, it
was inevitable that, at the moment when one of the pistons
exerts its full power in driving the wheel, the other piston
must be altogether inactive. The impelling power, therefore,
at alternate moments of time, acted on opposite wheels, and
on each of them at the greatest possible distance from the
centre of the axle.</p>

<div class="figcenter" style="width: 376px;">
<a id="Fig094"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_377.png" width="376" height="326" alt="" />
<div class="caption figure">Fig. 94.</div>
</div>

<div class="ph3"><h3>(193.)</h3> The next step in the improvement of the machine
was made with a view to remove these two defects. The cylinders
were transferred from the exterior of the engine to the
<a class="refpn" id="Pg355">[Pg355]</a>
interior of the casing called the smoke-box, <strong>B</strong>, <a href="#Fig094"><i>fig.</i> 94.</a>, which
supports the chimney, and which receives the heated air issuing
from the tubes which traverse the boiler. Thus placed,
the cylinders are always maintained as hot as the air which
issues from the flues, and all condensation of steam by their
exposure is prevented. The piston-rods are likewise brought
closer together, and nearer the centre of the engine: the
connecting rods, no longer attached to the wheels, are
made to act upon two cranks constructed upon the axle
of the wheels, and placed at right angles to each other.
From the position of these cranks, one would always be
at its dead point when the other is in full action. The
action of the steam upon them would, therefore, be generally
unequal; but this would not produce the same
strain as when the connecting rods are attached to points
upon the exterior of the wheels, owing to the cranks being
constructed on the axle at points so much nearer its centre.
By this means it was found that the working of the machine
was more even, and productive of much less strain, than in the
arrangement adopted in the Rocket, and the earlier engines.
On the other hand, a serious disadvantage was incurred by a
double-cranked axle. The weakness necessarily arising from
such a form of axle could only be removed by great thickness
<a class="refpn" id="Pg356">[Pg356]</a>
and weight of metal; and even this precaution, at first, did not
prevent their occasional fracture. The forging of them was,
however, subsequently much improved: the cranks, instead of
being formed by bending the metal when softened by heat,
were made by cutting the square of the crank out of the solid
metal; and now it rarely happens that one of these axles
fails.</div>

<p>The adoption of smaller tubes, and a greater number of
them, with a view more perfectly to extract the heat from the
air in passing to the chimney, rendered a more forcible draft
necessary. This was accomplished by the adoption of a more
contracted blast-pipe leading from the eduction-pipes of the
cylinders and presented up the chimney. A representation
of such a blast-pipe, with the two tubes leading from the cylinders
and uniting together near the point, which is presented
up the chimney, is given at <i>p p</i> in <a href="#Fig104"><i>fig.</i> 104.</a> The engine
thus improved is represented in <a href="#Fig094"><i>fig.</i> 94.</a></p>

<p><strong>A</strong> represents the cylindrical boiler, the lower half of which
is traversed by tubes, as described in the Rocket. They are
usually from eighty to one hundred in number, and about an
inch and a half in diameter; the boiler is about seven feet
in length; the fire-chamber is attached to one end of it, at <strong>F</strong>,
as in the Rocket, and similar in construction: the cylinders
are inserted in a chamber at the other end, immediately under
the chimney. The piston-rods are supported in the horizontal
position by guides; and connecting rods extend from them,
under the engine, to the two cranks placed on the axle of the
large wheels. The effects of an inequality in the road are
counteracted by springs, on which the engine rests; the
springs being below the axle of the great wheels, and above
that of the less. The steam is supplied to the cylinders, and
withdrawn, by means of the common sliding valves, which are
worked by an eccentric wheel placed on the axle of the large
wheels of the carriage. The motion is communicated from
this eccentric wheel to the valve by sliding rods. The stand
is placed for the attendant at the end of the engine, next the
fire-place <strong>F</strong>; and two levers <strong>L</strong> project from the end which
communicate with the valves by means of rods, by which the
engine is governed so as to reverse the motion.
<a class="refpn" id="Pg357">[Pg357]</a></p>

<p>The wheels of these engines have been commonly constructed
of wood with strong iron ties, furnished with flanges
adapted to the rails. But Mr. Stephenson afterward substituted,
in some instances, wheels of iron with hollow spokes.
The engine draws after it a tender carriage containing the fuel
and water; and, when carrying a light load, is capable of performing
the whole journey from Liverpool to Manchester
without a fresh supply of water. When a heavy load of merchandise
is drawn, it is usual to take in water at the middle
of the trip.</p>


<div class="ph3">
<h3>(194.)</h3> In reviewing all that has been stated, it will be perceived
that the efficiency of the locomotive engines used on
this railway is mainly owing to three circumstances: 1st, The
unlimited power of draft in the furnace, by projecting the
waste steam into the chimney; 2d, The almost unlimited abstraction
of heat from the air passing from the furnace, by
arrangement of tubes traversing the boiler; and, 3d, Keeping
the cylinders warm, by immersing them in the chamber
under the chimney. There are many minor details which
might be noticed with approbation, but these constitute the
main features of the improvements.</div>

<p>The successive introduction of improvements in the engines,
some of which we have mentioned, was accompanied
by corresponding accessions to their practical power, and to
the economy of fuel. In the spring of the year 1832, I made
several experiments on the Manchester Railway, with a view
to determine, in the actual state of the locomotive engines at
that time, their powers with respect to the amount of load
and the economy of fuel, from which I select the following
as examples:â€”</p>

<div class="blockquot">

<p class="center">I.</p>

<p>On Saturday, the 5th of May, the engine called the "Victory"
took 20 waggons of merchandise, weighing gross 92
tons 19 cwt. 1 qr., together with the tender containing fuel
and water, of the weight of which I have no account, from
Liverpool to Manchester (30 miles), in 1 h. 34 min. 45 sec.
The train stopped to take in water half-way, for 10 minutes,
<a class="refpn" id="Pg358">[Pg358]</a>
not included in the above-mentioned time. On the inclined
plane rising 1 in 96, and extending
<span class="fraction">1<sup>1</sup>â„<sub>2</sub></span> mile, the engine was
assisted by another engine called the "Samson," and the ascent
was performed in 9 minutes. At starting, the fire-place
was well filled with coke, and the coke supplied to the tender
accurately weighed. On arriving at Manchester, the fire-place
was again filled, and the coke remaining in the tender weighed.
The consumption was found to amount to 929 pounds net
weight, being at the rate of one third of a pound per ton per
mile.</p>

<p>Speed on the level was 18 miles an hour; on a fall of 4
feet in a mile,
<span class="fraction">21<sup>1</sup>â„<sub>2</sub></span>
 miles an hour; fall of 6 feet in a mile,
<span class="fraction">25<sup>1</sup>â„<sub>2</sub></span>
miles an hour; on the rise over Chatmoss, 8 feet in a
mile,
<span class="fraction">17<sup>5</sup>â„<sub>8</sub></span> miles an hour; on level ground sheltered from the
wind, 20 miles an hour. The wind was moderate, but direct
ahead. The working wheels slipped three times on Chatmoss,
and the train was retarded from 2 to 3 minutes.</p>

<p>The engine, on this occasion, was not examined before or
after the journey, but was presumed to be in good working
order.</p>

<p class="center">II.</p>

<p>On Tuesday, the 8th of May, the same engine performed
the same journey, with 20 waggons, weighing gross 90 tons
7 cwt. 2 qrs., exclusive of the unascertained weight of the
tender. The time of the journey was 1 h. 41 min. The consumption
of coke 1040 lbs. net weight, estimated as before.
Rate of speed:â€”</p>

<table summary="Locomotive Speed vs slope">
<tr>
 <td align="left">Level</td>
 <td class="left no-wrap">
<span class="fraction">17<sup>5</sup>â„<sub>8</sub></span> miles per hour.</td></tr>
<tr>
 <td class="left no-wrap">Fall of 4 feet in a mile</td>
 <td align="left">22</td></tr>
<tr>
 <td align="left">Fall of 6</td>
 <td align="left">
<span class="fraction">22<sup>1</sup>â„<sub>2</sub></span></td></tr>
<tr>
 <td align="left">Rise of 8</td>
 <td align="left">15</td></tr>
</table>

<p>On this occasion there was a high wind ahead on the quarter,
and the connecting rod worked hot, owing to having
been keyed too tight. On arriving at Manchester, I caused
the cylinders to be opened, and found that the pistons were
<a class="refpn" id="Pg359">[Pg359]</a>
so loose, that the steam blew through the cylinders with
great violence. By this cause, therefore, the machine was
robbed of a part of its power during the journey; and this
circumstance may explain the slight decrease in speed, and increase
in the consumption of fuel, with a lighter load, in this
journey, compared with that performed on the 5th of May.</p>

<p>The Victory weighs 8 tons 2 cwt., of which 5 tons 4 cwt.
rest on the drawing wheels. The cylinders are 11 inches
diameter, and 16 inches stroke, and the diameter of the drawing
wheels is 5 feet.</p>


<p class="center">III.</p>

<p>On the 29th of May, the engine called the "Samson"
(weighing 10 tons 2 cwt., with 14-inch cylinders, and 16-inch
stroke; wheels 4 feet 6 inches diameter, both pairs being
worked by the engine; steam 50 lbs. pressure, 130 tubes)
was attached to 50 waggons, laden with merchandise; net
weight about 150 tons; gross weight, including waggons,
223 tons 6 cwt. The tender weighed 7 tons, making a gross
load (including the engine) of 240 tons 8 cwt. The engine
with this load travelled from Liverpool to Manchester (30
miles) in 2 hours and 40 min., exclusive of delays upon the
road for watering, &#38;c.; being at the rate of nearly 12 miles
an hour. The speed varied according to the inclinations of
the road. Upon a level, it was 12 miles an hour; upon a
descent of 6 feet in a mile, it was 16 miles an hour; upon a
rise of 8 feet in a mile, it was about 9 miles an hour. The
weather was calm, the rails very wet; but the wheels did not
slip, even in the slowest speed, except at starting, the rails
being at that place soiled and greasy with the slime and dirt
to which they are always exposed at the stations. The coke
consumed in this journey, exclusive of what was raised in
getting up the steam, was 1762 lbs., being at the rate of a
quarter of a pound per ton per mile.</p></div>


<div class="ph3"><h3>(195.)</h3> The great original cost, and the heavy expense of
keeping the engines used on the railway in repair, have pressed
severely on the resources of the undertaking. One of the best
<a class="refpn" id="Pg360">[Pg360]</a>
constructed of the later engines costs originally 1500<i>l.</i> and
sometimes more. The original cost, however, is far from being
the principal source of expense: the wear and tear of these
machines, and the occasional fracture of those parts on which
the greatest strain has been laid, have greatly exceeded what
the directors had anticipated. Although this source of
expense must be in part attributed to the engines not having
yet attained that state of perfection, in the proportion and
adjustment of their parts, of which they are susceptible, and
to which experience alone can lead, yet there are some obvious
defects which demand attention.</div>

<p>The heads of the boilers are flat, and formed of iron,
similar to the material of the boilers themselves. The tubes
which traverse the boiler were, until recently, copper, and so
inserted into the flat head or end as to be water-tight.
When the boiler was heated, the tubes were found to expand
in a greater degree than the other parts of the boiler; which
frequently caused them either to be loosened at the extremities,
so as to cause leakage, or to bend from want of room
for expansion. The necessity of removing and refastening
the tubes caused, therefore, a constant expense.</p>

<p>It will be recollected that the fire-place is situated at one
end of the boiler, immediately below the mouths of the
tubes: a powerful draft of air, passing through the fire,
carries with it ashes and cinders, which are driven violently
through the tubes, and especially the lower ones, situated
near the fuel. These tubes are, by this means, subject to
rapid wear, the cinders continually acting upon their interior
surface. After a short time it becomes necessary to replace
single tubes, according as they are found to be worn, by new
ones; and it not unfrequently happens, when this is neglected,
that tubes burst. After a certain length of time the
engines require new tubing. This wear of the tubes
might possibly be avoided by constructing the fire-place
in a lower position, so as to be more removed from their
mouths; or, still more effectually, by interposing a casing
of metal, which might be filled with water, between the
fire-place and those tubes which are the most exposed to
the cinders and ashes. The unequal expansion of the tubes
<a class="refpn" id="Pg361">[Pg361]</a>
and boilers appears to be an incurable defect, if the present
form of the engine be retained. If the fire-place and chimney
could be placed at the same end of the boiler, so that
the tubes might be recurved, the unequal expansion would
then produce no injurious effect; but it would be difficult to
clean the tubes, if they were exposed, as they are at present,
to the cinders. The next source of expense arises from the
wear of the boiler-heads, which are exposed to the action
of the fire.</p>

<p>A considerable improvement was subsequently introduced
into the method of tubing, by substituting brass for copper
tubes. I am not aware that the cause of this improvement
has been discovered; but it is certain, whatever be the cause,
that brass tubes are subject to considerably slower wear than
copper ones.</p>


<div class="ph3">
<h3>(196.)</h3> The expense of locomotive power having so far exceeded
what was anticipated at the commencement of the undertaking,
it was thought advisable, about the beginning of the
year 1834, to institute an inquiry into the causes which produced
the discrepancy between the estimated and actual
expenses, with a view to the discovery of some practical
means by which they could be reduced. The directors of
the company, for this purpose, appointed a sub-committee of
their own body, assisted by Mr. Booth, their treasurer, to
inquire and report respecting the causes of the amount of
this item of their expenditure, and to ascertain whether any
and what measures could be devised for the attainment of
greater economy. A very able and satisfactory report was
made by this committee, or, to speak more correctly, by Mr.
Booth.</div>

<p>It appears that, previous to the establishment of the railway,
Messrs. Walker and Rastrick, engineers, were employed by the
company to visit various places where steam power was applied
on railways, for the purpose of forming an estimate of the
probable comparative expense of working the railway by locomotive
and by fixed power. These engineers recommended the
adoption of locomotive power; and their estimate was, that the
transport might be effected at the rate of Â·278 of a penny, or
very little more than a farthing per ton per mile. In the year
<a class="refpn" id="Pg362">[Pg362]</a>
1833, five years after this investigation took place, it was found
that the actual cost was Â·625 of a penny, or something more
than a halfpenny, per ton per mile, being considerably above
double the estimated rate. Mr. Booth very properly directed
his inquiries to ascertain the cause of this discrepancy, by
comparing the various circumstances assumed by Messrs.
Walker and Rastrick, in making their estimate, with those
under which the transport was actually effected. The first
point of difference which he observed was the <em>speed</em> of transport:
the estimate was founded on an assumed speed of ten
miles an hour, and it was stated that a four-fold speed would
require an addition of 50 per cent. to the power, without
taking into account wear and tear. Now, the actual speed
of transport being double the speed assumed in the statement,
Mr. Booth holds it to be necessary to add 25 per cent.
on that score.</p>

<p>The next point of difference is in the amount of the loads:
the estimate is founded upon the assumption, that every engine
shall start with its full complement of load, and that
with this it shall go the whole distance. "The facts, however,
are," says Mr. Booth, "that, instead of a <em>full load</em> of
profitable carriage <em>from</em> Manchester, about half the waggons
<em>come back empty</em>; and, instead of the tonnage being conveyed
the whole way, many thousand tons are conveyed only half
the way; also, instead of the daily work being uniform, it is
extremely fluctuating." It is further remarked, that in order
to accomplish the transport of goods from the branches and
from intermediate places, engines are despatched several times
a-day, from both ends of the line, <em>to clear the road</em>; the object
of this arrangement being rather to lay the foundation
of a beneficial intercourse in future, than with a view to any
immediate profit. Mr. Booth makes a rough estimate of the
disadvantages arising from these circumstances, by stating
them at 33 per cent. in addition to the original estimate.</p>

<p>The next point of difference is the fuel. In the original
estimate, <em>coal</em> is assumed as the fuel, and it is taken at the
price of five shillings and ten-pence per ton: now the act of
parliament forbids the use of coal which would produce smoke;
the company have, therefore, been obliged to use <em>coke</em>, at
<a class="refpn" id="Pg363">[Pg363]</a>
seventeen shillings and sixpence a ton.<a name="FNanchor_32_32" id="FNanchor_32_32"></a><a href="#Footnote_32_32" class="fnanchor">[32]</a> Taking coke, then, to
be equivalent to coal, ton for ton, this would add Â·162 to the
original estimate.</p>

<p>These several discrepancies being allowed for, and a proportional
amount being added to the original estimate, the
amount would be raised to Â·601 of a penny per ton per mile,
which is within one fortieth of a penny of the actual cost.
This difference is considered to be sufficiently accounted for
by the wear and tear produced by the very rapid motion,
more especially when it is considered that many of the engines
were constructed before the engineer was aware of the
great speed that would be required.</p>

<p>"What, then," says Mr. Booth, in the Report already alluded
to, "is the result of these opposite and mutually counteracting
circumstances? and what is the present position of
the company in respect of their moving power? Simply,
that they are still in a course of experiment, to ascertain
practically the best construction, and the most durable materials,
for engines required to transport greater weights, and
at greater velocities, than had, till very recently, been considered
possible; and which, a few years ago, it had not
entered into the imagination of the most daring and sanguine
inventor to conceive: and farther, that these experiments
have necessarily been made, not with the calm deliberation
and quiet pace which a salutary caution recommends,â€”making
good each step in the progress of discovery before advancing
another stage,â€”but amidst the bustle and responsibilities of
a large and increasing traffic; the directors being altogether
ignorant of the time each engine would last before it would
be laid up as inefficient, but compelled to have engines, whether
good or bad; being aware of various defects and imperfections,
which it was impossible at the time to remedy, yet
obliged to keep the machines in motion, under all the disadvantages
of heavy repairs, constantly going on during the
night, in order that the requisite number of engines might
be ready for the morning's work. Neither is this great experiment
yet complete; it is still going forward. But the most prominent
difficulties have been in a great measure surmounted,
<a class="refpn" id="Pg364">[Pg364]</a>
and your committee conceive that they are warranted in
expecting, that the expenditure in this department will, ere
long, be materially reduced,â€”more especially when they consider
the relative performances of the engines at the <em>present
time</em>, compared with what it was two years ago."</p>

<p>In the half year ending 31st December, 1831, the six best
engines performed as follows:â€”</p>

<table summary="performance of six best engines">
<tr>
 <th align="left"></th>
 <th align="right">Miles.</th></tr>
<tr>
 <td align="left">Planet</td>
 <td align="right">9,986</td></tr>
<tr>
 <td align="left">Mercury</td>
 <td align="right">11,040</td></tr>
<tr>
 <td align="left">Jupiter</td>
 <td align="right">11,618</td></tr>
<tr>
 <td align="left">Saturn</td>
 <td align="right">11,786</td></tr>
<tr>
 <td align="left">Venus</td>
 <td align="right">12,850</td></tr>
<tr>
 <td align="left">Etna</td>
 <td align="right" class="linedn">8,764</td></tr>
<tr>
 <td align="left" class="rghtpush3em">Making in all</td>
 <td align="right" class="linedn">66,044</td></tr>
</table>

<p>In the half year ending 31st December, 1833, the six best
engines performed as follows:â€”</p>

<table summary="performance of six best engines">
<tr>
 <th align="left"></th>
 <th align="right">Miles.</th></tr>
<tr>
 <td align="left">Jupiter</td>
 <td align="right">16,572</td></tr>
<tr>
 <td align="left">Saturn</td>
 <td align="right">18,678</td></tr>
<tr>
 <td align="left">Sun</td>
 <td align="right">14,552</td></tr>
<tr>
 <td align="left">Etna</td>
 <td align="right">17,763</td></tr>
<tr>
 <td align="left">Ajax</td>
 <td align="right">11,678</td></tr>
<tr>
 <td align="left">Firefly</td>
 <td align="right" class="linedn">15,608</td></tr>
<tr>
 <td align="left" class="rghtpush3em">Making in all</td>
 <td align="right" class="linedn">95,851</td></tr>
</table>

<div class="ph3"><h3>(197.)</h3> Since the date to which the preceding observations
refer, the locomotive engine has undergone several improvements
in detail of considerable importance; among which, the
addition of a third pair of wheels deserves to be particularly
mentioned. An engine supported on three pair of wheels has
great security in the event of the fracture of any one of the
axles,â€”the remaining axles and wheels being sufficient for the
support of the machine. Connected with this change is another,
recommended by Mr. Robert Stephenson, by which the
flanges are removed from the driving wheels, those upon the
remaining pairs of wheels being sufficient to keep the engine
in its position upon the rails. We shall now describe a locomotive
engine similar in construction to those almost
<a class="refpn" id="Pg365">[Pg365]</a>
universally used at present on railroads, as well in this kingdom
as in other countries.<a name="FNanchor_33_33" id="FNanchor_33_33"></a><a href="#Footnote_33_33" class="fnanchor">[33]</a></div>

<p>The external appearance of the engine and tender is shown
in the engraving at the head of this chapter. In <a href="#Fig097"><i>fig.</i> 97.</a> is
exhibited a vertical section of the engine made by a plane
carried through its length; and in <a href="#Fig098"><i>fig.</i> 98.</a> is exhibited a corresponding
section of its tender,â€”the tender being supposed
to be joined on to the engine at the part where the connecting
points appear to be broken in the drawing. In <a href="#Fig099"><i>fig.</i> 99.</a> is
exhibited the plan of the working machinery, including the
cylinders, pistons, eccentrics, &#38;c. which are under the boiler,
by the operation of which the engine is driven. <a href="#Fig100"><i>Fig.</i> 100.</a>
represents the tender, also taken in plan.</p>

<p>In <a href="#Fig101"><i>fig.</i> 101.</a> is represented an elevation of the hinder end of
the engine next the fire-box; and in <a href="#Fig102"><i>fig.</i> 102.</a> is represented
a cross vertical section through the fire-box, and at right
angles to the length of the engine, showing the interior of
the boiler above and beside the fire-box, the rivets and bolts
connecting the internal and external fire-boxes, the regulator,
steam funnel, and steam dome.</p>

<p>In <a href="#Fig103"><i>fig.</i> 103.</a> is represented an elevation of the front of the
engine next the smoke-box, showing the cylinder covers <strong>W</strong>,
buffers <strong>T</strong>, &#38;c.; and in <a href="#Fig104"><i>fig.</i> 104.</a> is represented a section of the
interior of the smoke-box, made by a vertical plane at right
angles to the engine, showing the tube plate forming the
foremost end of the boiler, the branches <strong>S</strong> of the steam-pipe
leading to the cylinders, the blast-pipe <i>p</i>, the cylinders <strong>H</strong>,
and the chimney <strong>G</strong>.</p>

<p>The same letters of reference are placed at corresponding
parts in the different figures.</p>

<p>The boiler, as has been explained in the engines already
described, is a cylinder placed upon its side, the section of
which is exhibited at <strong>A</strong>, <a href="#Fig097"><i>fig.</i> 97.</a> The fire-box consists of two
casings of metal, one within the other. The fire-grate is represented
at <strong>D</strong>. The tubes by which the products of combustion are
<a class="refpn" id="Pg366">[Pg366]</a>
drawn from the fire-box to the smoke-box <strong>F</strong> are represented
at <strong>E</strong>. Upon the smoke-box is erected the chimney <strong>G</strong>. In the
engine from which this drawing has been taken, and which
was used on the London and Birmingham Railway, the boiler
is a cylinder
<span class="fraction">7<sup>1</sup>â„<sub>2</sub></span> feet long, and
<span class="fraction">3<sup>1</sup>â„<sub>2</sub></span> feet in diameter. It is
formed of wrought-iron plates
<span class="fraction"><sup>5</sup>â„<sub>16</sub></span> of an inch in thickness, overlapping
each other, and bound together by iron rivets
<span class="fraction"><sup>7</sup>â„<sub>8</sub></span> of an
inch in diameter and
<span class="fraction">1<sup>3</sup>â„<sub>4</sub></span> inch apart. One of these rivets,
as it joins two plates, is represented
in <a href="#Fig095"><i>fig.</i> 95.</a> The boiler is
clothed with a boarding of
wood <i>a</i>, an inch in thickness,
and bound round by iron hoops screwed together at the bottom.
Wood being a slow conductor of heat, this covering has the
effect of keeping the boiler warm, and checking the condensation
of steam which would otherwise be produced by
the rapid motion of the engine through the cold air.</p>

<div class="figleft" style="width: 237px;">
<a id="Fig095"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_388a.png" width="237" height="74" alt="" />
<div class="caption figure">Fig. 95.</div>
</div>

<div class="figleft" style="width: 206px;">
<a id="Fig096"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_388b.png" width="206" height="190" alt="" />
<div class="caption figure">Fig. 96.</div>
</div>

<p>The external fire-box, <strong>B B</strong>, is a casing nearly square in its
plan, being four feet wide outside, and three feet seven and
a half inches long, measured in
the direction of the boiler. It is
constructed of wrought-iron plates,
similar to those of the boiler. This
box descends about two feet below
the boiler, the top being semi-cylindrical,
as seen in <a href="#Fig102"><i>fig.</i> 102.</a>,
of a somewhat greater diameter
than the boiler, and concentrical
with it. The front of the fire-box next the end of the
boiler has a circular opening equal in size to the end of the
boiler. To the edge of this opening the boiler is fastened
by angle irons, and rivets in the manner represented in
<a href="#Fig096"><i>fig.</i> 96.</a> These rivets are seen in section in <a href="#Fig097"><i>fig.</i> 97.</a></p>

<p>The internal fire-box <strong>C</strong>, <a href="#Fig097"><i>fig.</i> 97.</a>, is similar in shape to the
external, only it is flat at the top, and close every where
except at the bottom. Between it and the external fire-box
an open space of three inches and a half is left all round,
and on the side next the boiler this space is increased to four
inches. This internal fire-box is made of copper plates,
<span class="fraction"><sup>7</sup>â„<sub>16</sub></span>
<a class="refpn" id="Pg367">[Pg367]</a>
of an inch in thickness, every where except next the boiler,
where the thickness is
<span class="fraction"><sup>7</sup>â„<sub>8</sub>.</span></p>

<p>As the sides and front of the external fire-box, and all the
surfaces bounding the internal fire-box, are flat, their form is
unfavourable for the resistance of pressure. Adequate means
are, therefore, provided for strengthening them. The plates
forming the internal fire-box are bent outwards near the
bottom, until they are brought into contact with those of the
external fire-box, to which they are attached by copper rivets,
as represented at <i>f</i> in <a href="#Fig097"><i>fig.</i> 97.</a> The plates forming the bounding
surfaces of the two fire-boxes are fastened together by
stays represented at <i>k</i> in <i>figs.</i> 97. and 102. These stays, which
are of copper, have a screw cut upon them through their
whole length, and holes are made through the plates of both
fire-boxes tapped with corresponding threads. The copper
screws are then passed through them, and rivets formed on
their heads within and without, as seen in <a href="#Fig102"><i>fig.</i> 102.</a> These
screw rivets connect all parts of the plating of the two fire-boxes
which are opposed to each other: they are placed at
about four inches apart over the sides and back of the internal
fire-place and that part of the front which is below
the boiler.</p>

<div class="figcenter" style="width: 464px;">
<a id="Fig097"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_407.png" width="600" height="369" alt="" />
<div class="caption"><i>Fig. 97.</i> LONGITUDINAL VERTICAL SECTION OF A
LOCOMOTIVE ENGINE.</div>
<div class="lglink"><a href="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_407-hd.png">larger</a></div></div>

<div class="figcenter" style="width: 537px;">
<a id="Fig098"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_409.png" width="537" height="362" alt="" />
<div class="caption"><i>Fig. 98.</i>
LONGITUDINAL VERTICAL SECTION OF THE TENDER.</div></div>

<div class="figcenter" style="width: 537px;">
<a id="Fig099"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_411.png" width="600" height="248" alt="" />
<div class="caption">Fig. 99. PLAN
OF THE WORKING MACHINERY OF A LOCOMOTIVE ENGINE.</div>
<div class="lglink"><a href="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_411-hd.png">larger</a></div></div>

<div class="figcenter" style="width: 524px;">
<a id="Fig100"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_413.png" width="524" height="332" alt="" />
<div class="caption"><i>Fig. 100.</i>
PLAN OF THE TENDER.</div>
</div>

<div class="figcenter" style="width: 334px;">
<a id="Fig101"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_415.png" width="334" height="610" alt="" />
<div class="caption"><i>Fig. 101.</i>
ELEVATION OF THE HINDER END OF A LOCOMOTIVE ENGINE.</div>
</div>

<div class="figcenter" style="width: 334px;">
<a id="Fig102"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_417.png" width="334" height="603" alt="" />
<div class="caption"><i>Fig. 102.</i>
CROSS VERTICAL SECTION OF THE ENGINE THROUGH THE FIRE-BOX.</div></div>

<div class="figcenter" style="width: 334px;">
<a id="Fig103"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_419.png" width="331" height="603" alt="" />
<div class="caption"><i>Fig. 103.</i>
ELEVATION OF THE FOREMOST END OF THE ENGINE.</div></div>

<div class="figcenter" style="width: 331px;">
<a id="Fig104"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_421.png" width="330" height="589" alt="" />
<div class="caption"><i>Fig. 104.</i>
CROSS VERTICAL SECTION OF ENGINE THROUGH THE SMOKE-BOX.</div></div>

<p>As the top of the internal fire-box cannot be strengthened
by stays of this kind, ribs of wrought-iron, which are seen in
their length at <i>l</i>, in <a href="#Fig097"><i>fig.</i> 97.</a>, and of which an end view is seen in
<a href="#Fig102"><i>fig.</i> 102.</a>, are attached by bolts to it. These ribs are hollowed
out, as seen in <a href="#Fig097"><i>fig.</i> 97.</a>, between bolt and bolt, in order to
break their contact with the roof of the fire-box, and allow a
more free passage to the heat through it. If they were in
continuous contact with the fire-box, the metal composing
them would become more highly heated, and would soon
wear out, besides intercepting heat from the water. This
part of the fire-box is subject to rapid wear, unless care be
taken that the level of the water be preserved at its proper
height in the boiler. Even when the boiler is properly filled,
the depth of water above the roof of the fire-box is not considerable,
and on the least neglect the roof may be exposed to
the contact of steam, in which case it will soon be destroyed.</p>

<p>To prevent accidents arising from this cause, a leaden plug,
<a class="refpn" id="Pg368">[Pg368]</a>
represented at <i>m</i>, <i>figs.</i> 97. and 102., is inserted in the roof of
the internal fire-box. If the water be allowed to subside,
this plug will melt out before the copper is very injuriously
heated, and the steam rushing out at the aperture will cause
the fire to be extinguished.</p>

<p>Copper fire-boxes are almost universally used; but sometimes,
from the consideration of cheapness, the internal fire-box
is constructed of iron.</p>

<p>In the plating which forms the back of the external fire-box,
an oval aperture is formed, as represented in the back
view of the engine, <a href="#Fig101"><i>fig.</i> 101.</a>, for the fire-door <i>g</i>. The plating
of the internal fire-box around this aperture is bent at right
angles to meet that of the external fire-box, to which it is
fastened by a row of copper rivets. The fire-door is formed of
two plates of wrought-iron, riveted together with a space of
nine inches and a half between them. The air between these
plates being an imperfect conductor of heat, keeps the outer
plate of the fire-door at a moderate temperature.</p>

<p>In that part of the surface of the internal fire-box which
forms the end of the boiler, holes are made to receive the
extremities of the tubes, by which the air proceeding from
the fire is drawn to the smoke-box at the remote end of the
boiler. These tubes are represented in longitudinal section
at <strong>E</strong>, <a href="#Fig097"><i>fig.</i> 97.</a>, and their ends are seen in the surface of the
internal fire-box in <a href="#Fig102"><i>fig.</i> 102.</a>, and in the remote end of the
boiler where they terminate in the smoke-box in <a href="#Fig104"><i>fig.</i> 104.</a>
These tubes are formed of the best rolled brass, and their
thickness in the engine, to which we now refer, is
<span class="fraction"><sup>1</sup>â„<sub>13</sub></span> of an
inch. After the brass plating is bent into the form of a
tube, and being overlapped, is properly soldered together,
and the edges smoothed off, the tubes are made perfectly
cylindrical by being drawn through a circular steel die.</p>

<div class="figleft" style="width: 151px;">
<a id="Fig105"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_391.png" width="151" height="253" alt="" />
<div class="caption figure">Fig. 105.</div>
</div>

<p>The tube-plates (as those parts of the boiler ends in which
the tubes are inserted are called) are bored with holes in corresponding
positions, truly cylindrical, and corresponding in
magnitude to the tubes, so that the tubes, when passed into
them, will be just in contact with them. The length of the
tubes is so regulated, that when extending from end to end
of the boiler, and passing through the holes, they shall
<a class="refpn" id="Pg369">[Pg369]</a>
project at each end a little beyond the holes. The manner of
fastening them so as to be water-tight is as follows:â€”A steel
hoop or ferrule, made slightly conical,
a section of which is exhibited at <strong>C</strong>.
<a href="#Fig105"><i>fig.</i> 105.</a>, the smaller end of which is a
little less than the internal diameter of
the tube, but which increases towards
the outer end, is driven in as represented
in the figure. It acts as a wedge,
and forces the tube into close contact
with the edges of the hole in the tube-plate.</p>

<p>When particular tubes in a boiler
are worn out, and require to be replaced,
their removal is easily effected.
It is only necessary to cut the steel ferrule on the inside,
and to bend it off from contact with the tube, by which
means it can be loosened and withdrawn, and the tube removed.</p>

<p>In the engine to which this description refers there were
one hundred and twenty-four tubes, the external diameter of
which was
<span class="fraction">1<sup>5</sup>â„<sub>8</sub></span> inch. The distance between tube and tube
was
<span class="fraction"><sup>3</sup>â„<sub>4</sub></span> of an inch. The number of tubes vary in different
engines, some having so many as one hundred and fifty,
while the number in some is less than ninety. The evaporating
power of an engine greatly depends on the proper
number and magnitude of its tubes; and the experience which
engineers have had on railways have led them gradually to
increase the number of tubes, and diminish their magnitude.
In the Rocket, already mentioned as having gained the prize
on the opening of the Liverpool and Manchester Railway, the
number of tubes was twenty-four, and their diameter three
inches; but in all the engines subsequently made their number
was augmented, and their diameter diminished. The
practical inconvenience which limits the size of the tubes is
their liability to become choked by cinders and ashes, which
get wedged in them when they are too small, and thereby
obstruct the draft, and diminish the evaporating power of the
boiler. The tubes now in use, of about an inch and a
<a class="refpn" id="Pg370">[Pg370]</a>
half internal diameter, not only require to be cleared of the
ashes and cinders, which get fastened in them after each
journey, but it is necessary throughout a journey of any
length that the tubes should be picked and cleaned by opening
the fire door at convenient intervals.</p>

<p>The substitution of brass for copper tubes, which has been
already mentioned as so great an improvement in the construction
of locomotive engines, is ascribed to Mr. Dixon, who
suggested them in 1833, being then the resident engineer of
the Liverpool and Manchester Railway. They are said to
last six or eight times as long as copper tubes of the same
dimensions.</p>

<p>When tubes fail, they are usually destroyed by the pressure
of the water crushing them inwards: the water enters
through the rent made in the tube, and flowing upon the
fire extinguishes it. When a single tube thus fails upon a
journey, the engine, notwithstanding the accident, may generally
be made to work to the end of its journey by plugging
the ends of the broken tube with hard wood; the water in
contact with which will prevent the fire from burning it
away.</p>

<p>Tubes of the dimensions here referred to weigh about
sixteen pounds, and lose from six to seven pounds before they
are worn out. Their cost is about one pound each.</p>

<p>The tubes act as stays, connecting the ends of the boiler
to strengthen them. Besides these, there are rods of wrought
iron extended from end to end of the boiler above the roof of
the internal fire-place. These rods are represented at <i>o</i> in their
length in <a href="#Fig097"><i>fig.</i> 97.</a>, and an end view of them is seen in <a href="#Fig102"><i>fig.</i> 102.</a>
The smoke-box <strong>F</strong>, <a href="#Fig097"><i>fig.</i> 97.</a>
<a href="#Fig104"> 104.</a>, containing the cylinders, steam-pipe,
and blast-pipe, is four feet wide, and two feet long. It
is formed of wrought iron plates, half an inch thick on the
side next the boiler, and a quarter of an inch elsewhere. The
plates are riveted in the same manner as those of the fire-box
already described. From the top of the smoke-box, which,
like the fire-box, is semi-cylindrical, as seen in elevation in
<a href="#Fig103"><i>fig.</i> 103.</a>, and in section <a
href="#Fig104"><i>fig.</i> 104.</a>, rises the chimney <strong>G</strong>, fifteen
inches diameter, and formed of
<span class="fraction"><sup>1</sup>â„<sub>8</sub></span> inch iron plates, riveted
and bound round by hoops. It is flanged to the top of the
<a class="refpn" id="Pg371">[Pg371]</a>
smoke-box, as represented in <a href="#Fig104"><i>fig.</i> 104.</a> Near the bottom of
the smoke-box the working cylinders are placed, side by side,
in a horizontal position, with the slide valves upwards. In
the top of the external fire-box a circular aperture is formed
fifteen inches in diameter, and upon this aperture is placed
the steam-dome <strong>T</strong> (<i>figs.</i> 97. 101, 102.) two feet high, and
attached around the circular aperture by a flange and screw
secured by nuts. This steam dome is made of brass
<span class="fraction"><sup>3</sup>â„<sub>8</sub></span> inch
thick. In stationary boilers, where magnitude is not limited,
it has been already explained, that the space allowed for
steam is sufficiently large to secure the complete separation
of the vapour from the spray which is mixed with it when it
issues immediately from the water. In locomotive boilers
sufficient space cannot be allowed for this, and the separation
of the water from the steam is effected by the arrangement
here represented. A funnel-shaped tube <i>dâ€²</i> (<i>figs.</i> 97. 102.),
with its wide end upwards, rises into the steam-dome, and
reaches nearly to the top of it. This funnel bends towards
the back of the fire-box, and is attached by a flange and
screws to the great steam-pipe <strong>S</strong>, which traverses the whole
length of the boiler. The steam rising from the boiler fills
the steam-dome <strong>T</strong>, and descends in the funnel-shaped tube <i>dâ€²</i>.
The space it has thus to traverse enables the steam to disengage
itself almost completely from the priming. The wider
part of the great steam-pipe <i>a</i> is flanged and screwed at the
hinder end to a corresponding aperture in the back plate of
the fire-box. This opening is covered by a circular plate,
secured by screws, having a stuffing-box in its centre, of the
same kind as is used for the piston-rods of steam-cylinders.
Through this stuffing-box the spindle <i>aâ€³</i> of the regulator
passes, and to its end is attached a winch <i>hâ€²</i>, by which the
spindle <i>aâ€³</i> is capable of being turned. This winch is limited
in its play to a quarter of a revolution. The other end of the
spindle <i>aâ€³</i> is attached to a plate <i>eâ€²</i> seen edgeways in <a href="#Fig097"><i>fig.</i> 97.</a>,
and the face of which is seen in <a href="#Fig102"><i>fig.</i> 102.</a>: this circular plate
<i>e</i> is perforated with two apertures somewhat less than quadrants.
That part of the plate, therefore, which remains not
pierced forms two solid pieces somewhat greater than quadrants.
This plate is ground so as to move in steam-tight
<a class="refpn" id="Pg372">[Pg372]</a>
contact with a fixed plate under it, which terminates at the
wide end of the conical mouth of the steam-pipe <strong>S</strong>. This
fixed circular plate is likewise pierced with two nearly quadrantal
apertures, corresponding with those in the movable
plate <i>eâ€²</i>. When the movable plate <i>eâ€²</i> is turned round by the
winch <i>hâ€²</i>, the apertures in it may be made to correspond with
those of the fixed circular plate on which it moves, in which
position the steam-pipe <strong>S</strong> communicates with the funnel <i>dâ€²</i> by
the two quadrantal apertures thus open. If, on the other
hand, the winch <i>hâ€²</i> be moved from this position through a quarter
revolution, then the quadrantal openings in the movable
plate will be brought over the solid parts of the fixed plate on
which it moves, and these solid parts being a little more than
quadrants, while the openings are a little less, all communication
between the steam-pipe <strong>S</strong> and the funnel <i>dâ€²</i> will be
stopped, for in this case the quadrantal openings in the fixed
and movable plates respectively will be stopped by the solid
parts of these plates. It will be evident that as the winch
<i>hâ€²</i> of the regulator is moved from the former position to the
latter, in every intermediate position the aperture communicating
between the funnel <i>dâ€²</i> and the steam-pipe <strong>S</strong> will be less
in magnitude than the complete quadrant. It will in fact be
composed of two openings having the form of <em>sectors</em> of a
circle less than a quadrant, and these sectors may be made of
any magnitude, however small, until the opening is altogether
closed.</p>

<p>By such means the admission of steam from the boiler to
the steam-pipe <strong>S</strong> may be regulated by the winch <i>hâ€²</i>.</p>

<p>The steam being admitted to the steam-pipe passes through
it to the front end of the boiler, and the pipe being enclosed
within the boiler the temperature of the steam is maintained.
The steam-pipe passing through the tube-plate at the front
end of the boiler is carried to a small distance from the tube-plate
in the same direction, where it is flanged on to a cross
horizontal pipe proceeding to the right and to the left as represented
in <a href="#Fig104"><i>fig.</i> 104.</a> This cross pipe is itself flanged to two
curved steam-pipes <strong>S</strong> (<a href="#Fig104"><i>fig.</i> 104.</a>), by which the steam is conducted
to the valve-boxes <strong>V V</strong>. The lower ends of these curved
arms are flanged on to the valve-boxes of the two cylinders
<a class="refpn" id="Pg373">[Pg373]</a>
at the ends nearest to the boiler. The opening of one of these
is exhibited in the right hand cylinder in <a href="#Fig099"><i>fig.</i> 99.</a> By these
pipes the steam is conducted into the valve-boxes or steam-chests,
from which it is admitted by slide-valves to the cylinders
to work the pistons in the same manner as has been
already described in the large stationary engines.</p>

<p>On the upper sides of the cylinders are formed the steam-chests
or valve-boxes, which are exhibited at <strong>U</strong> (<i>figs.</i> 97. 99. 104.).
These are made of cast-iron half an inch thick, and
are bolted to the upper side of each cylinder. At the front end
they are also secured by bolts to the smoke-box, and at the
hinder end are attached to the tube-plate. These valve-boxes
communicate with the passages <i>m</i> and <i>n</i> <a href="#Fig099"><i>fig.</i> 99.</a> leading to the
top and bottom of the cylinder: these are called the steam-ports.
They also communicate with a passage <i>o</i> leading to
the mouth of a curved horizontal pipe <i>pâ€²</i> connecting the front
ends of the two cylinders, as seen in <i>figs.</i> 99. 104. These
curved pipes unite in a single vertical pipe <i>p</i>, called the <em>blast-pipe</em>,
seen in <i>figs.</i> 97. 104.: this vertical pipe becomes gradually
small towards the top, and terminates a little above the
base of the funnel or chimney <strong>G</strong>. In the valve-box is placed
the slide-valve <i>v</i> to which is attached the spindle <i>lâ€²</i>. This spindle
moves through a stuffing-box <i>kâ€²</i>, and is worked by gearing,
which will be described hereafter. According to the position
given to the slide, a communication may be opened between
the steam-chest, or the waste-port, and either end of the cylinders.
Thus when the slide is in the position represented
in <a href="#Fig097"><i>fig.</i> 97.</a> the steam-chest communicates with the front end
of the cylinder, while the waste-port communicates with the
hinder end. If, on the other hand, the spindle <i>lâ€²</i> being
pressed forward, move the slide to its extreme opposite
position, the steam-port <i>n</i> would communicate with the
waste-port <i>o</i>, while the steam-chest would communicate with
the steam-port <i>m</i>, steam would, therefore, be admitted to
the hinder end of the cylinder, while the foremost end would
communicate with the waste-port. It will be perceived that
this arrangement is precisely similar to that of the slide-valves
already described (<a href="#h3-133">133</a>.). The slide-valve is represented on
a larger scale in <a href="#Fig106"><i>fig.</i> 106.</a>, where <strong>A</strong> is the hinder steam-port,
<a class="refpn" id="Pg374">[Pg374]</a>
<strong>B</strong> the foremost steam-port, and <strong>C</strong> the waste-port. The surfaces
<strong>D</strong>, separating the steam-ports from the waste-ports, are
called the bars: they are planed
perfectly smooth, so that the
surfaces <strong>F</strong> and <strong>G</strong> of the slide-valve,
also planed perfectly
smooth, may move in steam-tight
contact with them. These
surfaces are kept in contact by the pressure of the steam in
the steam-chest, by which the slide-valve is always pressed
down. In its middle position, as represented by the dotted
lines in the figure, both the steam-ports are stopped by the
slide-valve, so that at that moment no steam is admitted to
either end of the cylinder. On either side of this intermediate
position the slide has an inch and a half play, which
is sufficient to open successively the two steam-ports.</p>

<div class="figleft" style="width: 205px;">
<a id="Fig106"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_396.png" width="205" height="105" alt="" />
<div class="caption figure">Fig. 106.</div>
</div>

<p>The cylinders are inserted at one end in the plate of the
smoke-box, and at the other in the tube-plate of the boiler.
They are closed at either end by cast iron covers, nearly an
inch thick, flanged on by bolts and screws. In the cover of
the cylinder attached to the tube-plate is a stuffing-box, in
which the piston rod plays. The metallic pistons used in
locomotive engines do not differ materially from those already
described, and therefore need not be here particularly
noticed. From their horizontal position they have a tendency
to wear unequally in the cylinders, their weight pressing
them on one side only; but from their small magnitude this
effect is found to be imperceptible in practice. In the engine
here described the stroke of the piston is eighteen inches,
and this is the most usual length of stroke in locomotive
engines. The piston, in its play, comes at either end within
about half an inch of the inner surface of the covers of the
cylinders, this space being allowed to prevent collision. In
the foremost cover of the cylinder is inserted a cock <i>qâ€²</i>
(<a href="#Fig097"><i>fig.</i> 97.</a> <a href="#Fig099">99.</a>),
by which any water which may collect in the cylinder
by condensation or priming may be discharged. A cock <i>râ€²</i>
(<a href="#Fig097"><i>fig.</i> 97.</a>),
communicating with a small tube proceeding from the
branches of the waste pipe <i>pâ€²</i> (<a href="#Fig104"><i>fig.</i> 104.</a>),
 is likewise provided
to discharge from that pipe any water which may be
<a class="refpn" id="Pg375">[Pg375]</a>
collected in it. After the steam has been admitted to work
the piston through the slide-valve, and has been discharged
through the waste-port by shifting that valve, it passes
through the pipe <i>pâ€²</i> into the blast-pipe <i>p</i>, from the mouth of
which it issues, with great force, up the funnel <strong>G</strong>. When
the motion of the engine is rapid, the steam from the two
cylinders proceeds in an almost uninterrupted current from
the blast-pipe, and causes a strong draft up the chimney.
The heated air which passes from the mouths of the tubes
into the smoke-box is drawn up by this current, and a corresponding
draft is produced in the fire-box.</p>

<div class="figleft" style="width: 118px;">
<a id="Fig107"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_397.png" width="118" height="516" alt="" />
<div class="caption figure">Fig. 107.</div>
</div>

<p>The piston-rods <strong>Y</strong> terminate in a fork, by which they are
attached to cross heads <strong>Z</strong>, the ends of which
are confined by guide-bars <strong>Aâ€²</strong>, in which
they are allowed to play backwards and
forwards through a space equal to the
stroke of the piston. To these cross heads
<strong>Z</strong>, between the prongs of the fork in which
the piston terminates, are attached the foremost
ends of the connecting rods <strong>Bâ€²</strong>. These
rods are, therefore, driven backwards and
forwards by the motion imparted to the
cross head <strong>Z</strong> by the piston-rods <strong>Y</strong>. The
connecting rods <strong>Bâ€²</strong> are attached at the
hinder ends to two cranks formed upon the
axles <strong>Câ€²</strong> of the driving wheels <strong>Dâ€²</strong>. These
two cranks are formed upon the axles precisely
at right angles to each other. The
left-hand crank is represented in its horizontal
position, in <a href="#Fig099"><i>fig.</i> 99.</a>, and the right-hand
crank is seen in its vertical position.
A cranked axle is represented on a larger
scale in <a href="#Fig107"><i>fig.</i> 107.</a>, and the two cranks are
seen in a position oblique to the plane of
the figure. As this axle is the instrument
by which the impelling force is conveyed
to the load, and as it has to support a
great portion of the weight of the engine, it is constructed
with great strength and precision. It is made all in one
<a class="refpn" id="Pg376">[Pg376]</a>
piece, and of the best wrought iron called Back Barrow,
or scrap iron. In the engine here described its extreme
length is six feet and a half, and its diameter is five inches.
At the centre part <strong>A</strong> it is cylindrical, and is increased to
five inches and a quarter at <strong>C</strong>, where the cranks are formed.
The sides <strong>D</strong> of the cranks are four inches thick, and the crank
pins <strong>B</strong>, which are truly cylindrical, are five inches diameter,
and three inches in length, the brasses at the extremities of
the connecting rods which play upon them having a corresponding
magnitude. The distance from the centre of the
crank-pins <strong>B</strong> to the centre of the axle <strong>A</strong> must be exactly
equal to half the stroke of the piston, and is, therefore, in
this case precisely nine inches. Upon the parts <strong>F</strong>, which are
seven inches and a half long, the great driving wheels are
firmly fastened, so as to be prevented from turning or shaking
upon the axle. The axle projects beyond the wheels at <strong>G</strong>,
where it is reduced to three inches and an eighth diameter.
These projecting parts <strong>G</strong> are five inches long, having collars
at the outer ends. Brasses are fixed at the outside frame of
the engine which rest upon these projections <strong>G</strong> of the axle,
and upon these brasses the weight of the engine is supported.
The entire axle is accurately turned in a lathe, and each of
the crank-pins <strong>B</strong> is likewise turned by suspending the axle
on centres corresponding with the centres of the crank-pins,
and made on strong cast iron arms, which are firmly fixed on
the ends of the axle, and project beyond the cranks so as to
balance the axle, and enable it to turn round on the centre
of the crank-pin. The axle is by such means made perfectly
true, and the cranks are made of exactly the proper length,
and precisely at right angles to each other. The corners of
the cranks are champered off, as shown in the figure, and the
ends of the cylindrical parts well rounded out.</p>

<p>The strength and accuracy of construction indispensable in
these cranked axles, in order to make them execute their
work, render them very expensive. Those which are here
described cost about 50<i>l.</i> each. When properly constructed,
however, they are seldom broken, but are sometimes bent
when the engine escapes from the rails.</p>

<p>The proper motion to admit and withdraw the steam from
<a class="refpn" id="Pg377">[Pg377]</a>
either end of the cylinder is imparted to the slide-valves by
eccentrics, in a manner and on a principle so similar to that
already described in large stationary engines, that it will not
be necessary here to enter into any detailed explanation of
the apparatus for communicating this motion, which is exhibited
in plan and section in <i>figs.</i> 97. 99. The eccentrics are
attached to the cranked axles at <strong>Eâ€² Eâ€³</strong>. The eccentric <strong>Eâ€²</strong>
imparts motion by a rod <i>eâ€³</i> to a lever <i>hâ€³</i>, formed on an axle
extending across the frame of the engine. This conveys
motion to another lever <i>lâ€³</i>, projecting from the same axle.
This lever <i>lâ€³</i> is jointed to horizontal links <i>mâ€³</i>, which at the
foremost ends are attached to the spindle <i>lâ€²</i>, by which the
slide is driven. By these means the motion received by the
eccentric from the great working axle conveys to the spindle <i>lâ€²</i>
an alternate movement backwards and forwards, and the
points at which it is reversed will be regulated by the position
given to the eccentric upon the great axle. The eccentric
is formed in two separate semicircles, and is keyed on to
the great axle, and consequently any position may be given
to it which may be required. The position to be given to
the eccentrics should be such that they shall be at right
angles to their respective cranks, and they should be fixed a
quarter of a revolution behind the cranks so as to move the
slides to that extent in advance of the pistons, since by the
position of the levers <i>hâ€³</i> and <i>lâ€³</i>, the motion of the eccentric
becomes reversed before it reaches the valve spindle.</p>

<p>The performance of the engine is materially affected by
the position of the eccentrics on the working axle. The
slide should begin to uncover the steam-port a little before
the commencement of the stroke of the piston, in order that
the steam impelling the piston should be shut off, and the
steam about to impel it in the contrary direction admitted
before the termination of the stroke. Through this small
space the steam, therefore, must act in opposition to the
motion of the piston. This is called the <em>lead</em> of the slide,
and the extent generally given to it is about a quarter of an
inch. This is accomplished by fixing the eccentrics not precisely
at right angles to the respective cranks, but a little in
advance of that position. The introduction of the steam to
<a class="refpn" id="Pg378">[Pg378]</a>
the piston before the termination of the stroke has the effect
of bringing it gradually to rest at the end of the stroke, and
thereby diminishing the jerk or shock produced by the rapid
change of motion. In stationary engines, where the reciprocations
of the engine are slow, the necessity for this provision
does not arise; but in locomotive engines in which the
motion of the piston is changed from four to six times in a
second, it becomes necessary. The steam admitted to the
piston before the termination of the stroke acts as a spring-cushion
to assist in changing its motion, and if it were not
applied, the piston could not be kept tight upon the piston-rod.
Another advantage which is produced by allowing
some lead to the slide is that the waste steam which has just
impelled the piston begins to make its escape through the
waste-port before the commencement of the next stroke, so
that when the impelling steam begins to produce the returning
stroke, there is less waste steam on the other side of the
piston to resist it.</p>

<p>When the motion of the engine is very rapid, the resistance
of the waste steam, as it escapes from the blast-pipe to
the piston, has been generally supposed to be very considerable,
though we are not aware of any direct experiments by
which its amount has been ascertained. In the account of
the locomotive engine which has been here described, supplied
by Mr. Stephenson for the last edition of Tredgold on
the Steam Engine, he states, that the average resisting pressure
of the waste steam throughout the stroke is 6 lbs.
per square inch, when running at the usual rate of from
25 to 28 miles an hour, and that at greater velocities this
negative pressure has been found to increase to more than
double that amount. No experiments are, however, cited
from which this inference has been drawn.</p>

<p>It has been also thought that the pressure of steam
upon the piston in the cylinder, at high velocities, is considerably
below the pressure of steam in the boiler; but this
has not been, so far as we are informed, ascertained by
any satisfactory experimental test. Mr. Stephenson likewise
states, that this loss of pressure, causes the negative
pressure or resistance of the waste steam to amount to
<a class="refpn" id="Pg379">[Pg379]</a>
from 30 to 40 per cent. of the positive pressure upon
the piston when the engine is running very fast, and that
therefore the power of the engine is diminished nearly
one half.</p>

<p>But it will be perceived that besides the uncertainty which
attends the estimate of the actual amount of pressure on the
piston compared with the pressure of steam in the boiler,
the inference here drawn does not appear to be compatible
with what has been already proved respecting the mechanical
effect of steam. No change of pressure which may
take place between the boiler and the cylinder can affect
the practical efficacy of the steam. As the steam passes
through the engine, whatever change of pressure it may be
subject to, it still remains common steam; and though its
pressure may be diminished, its volume being increased in a
nearly equal proportion, its mechanical effect will remain the
same. The power of the engine, therefore, estimated as it
ought to be, by the whole mechanical effect produced, will
not be altered otherwise than by the effect of the increased
resistance produced by the blast-pipe. What that resistance
is, we repeat, has not, so far as we know, been ascertained
by direct experiment, and there are circumstances attending
it which render it probable that, even at high velocities, it is
less in amount than Mr. Stephenson's estimate.</p>

<p>The position of the eccentrics which is necessary to make
the pistons drive the engine forward must be directly the
reverse of that which would cause them to drive the engine
backwards. To be able, therefore, to reverse the motion of
the engine, it would only be necessary to be able to reverse
the position of the eccentrics, which may be accomplished by
either of two expedients.</p>

<ol class="nomarker">
<li><em>First</em>, The eccentrics may be capable of revolving on the
great working axle, and also of sliding upon it through a
small space. Their revolution on the axle may be checked
by letting a pin attached to a collar fastened on the axle fall
into a hole on the side of the eccentric. Such a pin will
drive the eccentric round with the axle, and the position of
this pin and the hole will determine the position of the
eccentric with reference to the crank. At a short distance
<a class="refpn" id="Pg380">[Pg380]</a>
on the other side of the eccentric may be a corresponding
collar with a pin in the opposite position. By moving the
eccentric longitudinally on the axle, the former pin may be
withdrawn from the hole, and the latter allowed to fall into
the hole on the other side. Proper mechanism may be provided
by which the position of the eccentric may thus be
reversed in reference to the crank, and by such means the
motion of the engine may be reversed.</li>

<li><em>Secondly</em>, Supposing the eccentrics which drive the engine
forward to be immovably fixed upon the axle, two other eccentrics
may be provided attached to other parts of the same
axle, and having a position exactly the reverse with reference
to the cranks. Proper mechanism may be provided, by which
either or both pairs of eccentrics may be thrown in or out of
gear. Such are the means adopted in the engine which has
been already described. The eccentrics for driving the engine
backwards are placed outside the cranks at <strong>Fâ€² Fâ€³</strong>. A
hand lever <i>wâ€³</i> <a href="#Fig101"><i>fig.</i> 101.</a> is provided, by which the engine man
may throw either pair of eccentrics into or out of gear, so
as to make the engine work either backwards or forwards.</li>
</ol>

<div class="figleft" style="width: 147px;">
<a id="Fig108-109-110"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_402.png" width="147" height="189" alt="" />
<div class="caption figure">Figs. 108., 109., 110.</div>
</div>

<p>As all the moving parts of the engine require to be constantly
lubricated with oil to diminish the friction, and keep
them cool, oil-cups for this purpose are fixed upon them. In
some engines these oil-cups are attached separately to all the
moving parts: in others they are placed near each other in a
row on the boiler, and communicate by small tubes with the several
parts required to be lubricated. One of these is requisite
for each end of the connecting rods, for each of the guides of
the piston-rods, for the piston-rod itself,
the spindle of the slide-valve, and other
parts. An elevation of one of these oil-cups
is shown in <a href="#Fig108-109-110"><i>fig.</i> 108.</a>, a vertical
section in <a href="#Fig108-109-110"><i>fig.</i> 109.</a>, and horizontal plan
in <a href="#Fig108-109-110"><i>fig.</i> 110.</a> The cup <strong>A</strong> is made of brass
with a cover <strong>B</strong>. This cover has a piece
projecting from it turning upon a pin in
a socket <strong>C</strong> at the side of the cup <strong>A</strong>, and
square at the end, resting upon a small spring at the bottom of
the socket to hold it either open or shut. In the bottom of the
<a class="refpn" id="Pg381">[Pg381]</a>
cup is inserted an iron tube <strong>D</strong> extending nearly to the top.
This tube projects from the bottom of the cup, where it is
tapped for the purpose of fixing the cup on the part of the
engine which it is intended to lubricate. The hole into which
the cup is screwed communicates with the rubbing surface,
and some cotton thread is passed through the tube dipping
into the oil in the cup at the one end and touching the moving
part at the other. This thread acts as a siphon, and constantly
drops oil on the rubbing surface.</p>

<div class="figcenter" style="width: 323px;">
<a id="Fig111"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_404.png" width="323" height="351" alt="" />
<div class="caption figure">Fig. 111.</div>
</div>

<p>The tender is a carriage attached behind the engine and close
to it, carrying coke for the supply of the furnace, and water for
the boiler. The coke is contained in the space <strong>Râ€³</strong>, (<a href="#Fig098"><i>fig.</i> 98.</a>
 <a href="#Fig100">100.</a>)
surrounded by a tank <strong>Iâ€³</strong> containing water to feed the boiler.
The feed for the boiler is conducted from the tank through a
pipe descending downwards and in a curved direction, <strong>Pâ€³ Qâ€³</strong>,
<a href="#Fig098"><i>fig.</i> 98.</a>, and
connected with a horizontal pipe <strong>K</strong>, <a href="#Fig097"><i>fig.</i> 97.</a> A
cock is provided at <strong>Pâ€³</strong>, by which the supply of water to this
pipe may be cut off at pleasure. Another cock is provided at
<i>tâ€²</i>, <a href="#Fig097"><i>fig.</i> 97.</a>, where the curved pipe joins the horizontal pipe
by which the quantity of water supplied to <strong>K</strong> may be regulated
by opening the cock more or less fully. The handle of this
cock rises through the floor of the engine, so that the engineer
may regulate it at discretion. The pipe <strong>K</strong> being conducted
under the engine, as represented in <a href="#Fig097"><i>fig.</i> 97.</a>, terminates
in a vertical pipe, of greater diameter, containing two valves,
both of which open upwards, and between these valves to this
vertical pipe is attached a force-pump, by which the water is
drawn from the horizontal pipe <strong>K</strong> into the vertical pipe <strong>Kâ€²</strong>,
and from the latter is driven into a delivery-pipe by which it
is forced into the boiler. The details of the interior of this
feed-pump are represented on a larger scale in <a href="#Fig111"><i>fig.</i> 111.</a> The
extremity of the horizontal pipe <strong>Kâ€²</strong> is represented in section
at <strong>H</strong>, where it is joined on by a screw to the bottom of the
vertical pipe which is represented in <a href="#Fig097"><i>fig.</i> 97.</a> at <strong>K</strong>, and which is
here represented in section. The vertical pipe, represented
in <a href="#Fig097"><i>fig.</i> 97.</a> consists of several parts screwed together by nuts
and bolts passing through flanges. The lowest piece <strong>I</strong> is attached
by a flange to the piece <strong>L</strong>: within these is contained
the valve <strong>Q</strong> resting in a seat made conical, so that the ball
<a class="refpn" id="Pg382">[Pg382]</a>
which forms the valve shall rest in water-tight contact with
it. The ball is turned and ground to an accurate sphere, and
whatever position it assumes upon its seat its contact will be
perfect. It is guided in its upward and downward motion by
several vertical bars which confine it, and which are united at
the top, so as to limit the upward motion of the ball. A screw
<strong>Vâ€²</strong> is inserted in the bottom of the piece <strong>I</strong>, by removing which
access can be obtained to the valve. The piece <strong>L</strong> is secured
to the short pipe <strong>G</strong> by nuts and bolts passed through a flange.
The pipe <strong>G</strong> is cast upon the end of the feed-pump <strong>A</strong>. On
the foremost end of this feed-pump is constructed a stuffing-box
<strong>C</strong> of the usual form, having a gland <strong>D</strong> forced against
packing by nuts and screws <strong>E</strong>. The plunger <strong>B</strong> is turned so
as to be truly cylindrical, and moves in water-tight contact
through the gland <strong>D</strong>. The plunger not being in contact with
the inner surface of the pump-barrel <strong>A</strong>, the latter need not be
ground. The horizontal rod by which the plunger <strong>B</strong> is driven
is attached at its foremost extremity to an arm which projects
from the rod of the steam-piston, and consequently this
plunger is moved through a space equal to the stroke of the
steam-piston. In this case that space is eighteen inches. The
<a class="refpn" id="Pg383">[Pg383]</a>
upper end of the vertical tube <strong>G</strong> is attached by screws and a
flange to a piece <strong>P</strong> containing a valve <strong>R</strong> similar in all respects
to the lower valve <strong>Q</strong>, and like it opening upwards. A screw
<strong>V</strong> is introduced at the top by which access may be obtained
to this valve. This screw also presses on the crown of the
guides of the valve, so as to hold it down by regulated pressure.
At the side of this upper piece <strong>P</strong> is inserted a horizontal
tube <strong>M</strong> connected with the end of the delivery-pipe <strong>N</strong>.
This latter is continued to the boiler with which it communicates
at the fire-box. When the plunger <strong>B</strong> is drawn out of
the pump-barrel <strong>A</strong>, the spherical valve <strong>Q</strong> being relieved from
its downward pressure is raised, and water passes from the
pipe <strong>H</strong> through the valve <strong>Q</strong> into the vertical pipe <strong>G</strong>; the lower
valve <strong>Q</strong> then closes and stops the return of the water. The
plunger <strong>B</strong> returning into the pump-barrel <strong>A</strong> then forces the
water against the upper valve <strong>R</strong> and drives it through the delivery-tube
<strong>N</strong>, from which its return is prevented by the
valve <strong>R</strong>. When the delivery-tube <strong>N</strong> is filled with water
throughout its whole length, every stroke of the plunger will
evidently drive into the boiler a volume of water equal to
the magnitude of a part of the plunger eighteen inches in
length.</p>

<p>Until within the last few years, locomotive engines were
supported on only four wheels; they are, however, now almost
universally supported on six, the driving wheels being
in the middle. To give greater security to the position of
the engine between the rails it is usual to construct flanges on
the tires of all the six wheels. Mr. Stephenson, however, has
been in the practice of constructing the driving wheels without
flanges, and with tires truly cylindrical, depending on the
flanges of the two pairs of smaller wheels to maintain the
engine between the rails. The wheels of the engine here
described are constructed in this manner. The driving wheels
<strong>Dâ€²</strong> are fixed on the cranked axle <strong>Câ€²</strong>, and are five feet in diameter.
The other wheels <strong>Lâ€² Mâ€²</strong>, the one being placed immediately
behind the smoke-box, and the other immediately
behind the fire-box, are each three feet six inches in diameter,
and have a flange upon their tires, which running on the
<a class="refpn" id="Pg384">[Pg384]</a>
inside of each rail keeps the engine between the rails. Each
pair of these small wheels, like the driving-wheels, is fixed
upon their axle. The axles are
<span class="fraction">3<sup>5</sup>â„<sub>8</sub></span> inches diameter, and project
beyond the wheels, the projecting part supporting the
frame of the engine and turning in brasses. Upon these
brasses rest springs, which bear the whole weight of the
engine. These springs having nothing between them and
the road but the wheels and axles intercept and equalise
the sudden shocks produced by the rapid motion upon the
road.</p>

<p>When an engine is required for the transport of very heavy
loads, such as those of merchandise, the adhesion of one pair
of working wheels is found to be insufficient, and, in such
cases, one of the two pairs of wheels <strong>Lâ€² Mâ€²</strong> is made of the
same diameter as the wheels which are placed upon the working
axle, and a bar is attached to points on the outside of the
wheels at equal distances from their centre, connecting them
in such a manner that any force applied to make one pair of
wheels revolve must necessarily impart the same motion to
the other pair. By such means the force of the steam is made
to drive both pairs of wheels, and consequently a proportionally
increased adhesion is obtained.</p>

<p>The velocity which an engine is capable of imparting to
the load which it draws depends upon the rate at which the
pistons are capable of being moved in the cylinders. By every
motion of each piston backwards and forwards one revolution
of the driving wheels is produced, and by each revolution of
the driving wheels, supposing them not to slip upon the rails,
the load is driven through a distance upon the road equal to
their circumference. As the two cylinders work together, it
follows, that a quantity of steam sufficient to fill four cylinders
supplied by the boiler to the engine will move the train
through a distance equal to the circumference of the driving
wheels; and in accomplishing this, each piston must move
twice from end to end of the cylinder; each cylinder must be
twice filled with steam from the boiler; and that steam must
be twice discharged from the cylinder through the blast-pipe
into the chimney.</p>

<p><a class="refpn" id="Pg401">[Pg401]</a>
 If the driving wheels be five feet in diameter their circumference
will be fifteen feet seven inches. To drive a train with
a velocity of thirty miles an hour, it will be necessary that the
engine should be propelled through a space of forty-five feet
per second. To accomplish this with five-feet wheels they
must be therefore made to revolve at the rate of very nearly
three revolutions per second; and as each revolution requires
two motions of the piston in the cylinder, it follows that each
piston must move three times forwards and three times backwards
in the cylinder in a second; that steam must be admitted
six times per second from the steam-chest to each
cylinder, and discharged six times per second from each cylinder
into the blast-pipe. The motion, therefore, of each
piston, supposing it to be uniform, must divide a second into
six equal parts, and the puffs of the blast-pipe in the chimney
must divide a second into twelve equal parts. The motion of
the slides and other reciprocating parts of the machinery must
consequently correspond.</p>

<p>This motion of the reciprocating parts of the machinery
being found to be injurious to it, and to produce very rapid
wear, attempts have been made to remedy the defect, and to
obtain greater speed with an equal or diminished rate of
motion of the piston, by the adoption of driving wheels of
greater diameter, and on several of the great lines of railway
the magnitude of the wheels for the passenger-engines have
been increased to five feet and a half and six feet diameter;
but such engines have not been sufficiently long in use to
afford grounds for forming a practical estimate of their effects.
Experiments of a much bolder description have, however,
been tried on one of the great lines of railway by the adoption
of driving wheels of much greater diameter. In some
cases their magnitude has been increased even to ten feet;
but from various experiments to which these engines have been
submitted by myself and others, as well as from the experience
which appears to be obtained from the results of their
ordinary work, it does not appear that any advantages have
attended them, and they have been accordingly for the most
part abandoned.</p>

<p>The pressure of steam in the boiler is limited by two safety-valves,
<a class="refpn" id="Pg402">[Pg402]</a>
represented in <a href="#Fig097"><i>fig.</i> 97.</a> at
<strong>N</strong> and <strong>O</strong>. The valve at <strong>N</strong> is
under the control of the engineer, but the valve at <strong>O</strong> is inaccessible
to him. The structure of the safety-vale represented
at <strong>N</strong> is exhibited
on a larger scale in
<a href="#Fig112-113"><i>fig.</i> 112.</a>, which represents
its section, and
<a href="#Fig112-113"><i>fig.</i> 113.</a>, which shows
a plan of the valve-seat
with the valve removed.
The valve <strong>A</strong>, which is made of brass, is mitred round the
edge at an angle of 45Â°, and has a spindle, or stalk <strong>B</strong>, cast
upon it, projecting downwards from the middle of it. The
valve-seat <strong>C</strong> is also made of brass, and cast with a flange
at the bottom to attach it to the boiler. The mitred surface
of the valve is ground into the valve-seat, so as to rest in
steam-tight contact with it. Across the valve-seat, which
is two and a half inches in diameter, is cast a thin piece <strong>D</strong>,
seen in plan in <a href="#Fig112-113"><i>fig.</i> 113.</a>
and in section in <a href="#Fig112-113"><i>fig.</i> 112.</a> which
extends from the top to the bottom, and has a longitudinal
hole through it, in which the spindle <strong>B</strong> of the valve works:
by this hole it is guided when it rises from its seat. A
projection <strong>E</strong> is cast upon the seat of the valve, in which a
standard <strong>F</strong> is inserted. This standard is forked at the top,
and receives the end of a lever <strong>G</strong>, which turns in it upon a
centre. A rod <strong>H</strong> is jointed to this lever by another pin at
three inches from the former, and the lower end of this rod,
ground to a point, presses upon the centre of the valve <strong>A</strong>. At
the other end of the lever, which is broken off in <a href="#Fig112-113"><i>fig.</i> 112.</a>, at a
distance of three feet from the centre pin, inserted in the fork
of the pillar <strong>F</strong>, the rod of a common spring-balance
<i>w</i>, <a href="#Fig101"><i>fig.</i> 101.</a>,
is attached by a finger-nut <i>n</i>. The bottom of this spring-balance
is secured on to the fire-box. This balance is screwed
up by the finger-nut on the valve-lever until the required
pressure on the lever is produced through the medium of
the rod <strong>H</strong>, this pressure being generally fifty pounds per
square inch above the atmosphere. When the pressure of
the steam in the boiler exceeds this, the valve <strong>A</strong> is raised
from its seat, and the steam escapes.</p>

<div class="figcenter" style="width: 275px;">
<a id="Fig112-113"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_424.png" width="275" height="123" alt="" />
<div class="caption figure">Figs. 112., 113.</div>
</div>

<p>It is evident that the sliding weight by which the pressure
<a class="refpn" id="Pg403">[Pg403]</a>
of the safety-valve is sometimes regulated in stationary engines
would not be admissible in a locomotive engine, since
the motion of the engine would constantly jolt it up and
down, and cause the steam to escape. One of the disadvantages
attending the use of the spring-valve is that it cannot
be opened to let the steam escape without increasing its
force, so that the steam, when escaping, must really have a
greater pressure than that to which the valve has been previously
adjusted. The longer the lever is, the greater will
be this difference of pressure, inasmuch as a given elevation
of the pin governing the rod <strong>H</strong> would cause a proportionally
greater motion in that end of the lever attached to the
spring.</p>

<p>The second safety-valve <strong>O</strong> is enclosed in a case, so that it
is inaccessible, and its purpose is to limit the power of the
engineer to increase the pressure of steam in the boiler. This
valve is similar in construction to the former, but instead of
being held down by a lever, is pressed upon by several small
elliptical springs placed one above another over the valve,
and held down by a screw which turns in a frame <strong>Y</strong>, fixed
into the valve-seat. By this screw the pressure on the valve
can be adjusted to any required degree; and if the open
safety-valve be screwed down to a greater pressure, the steam
will begin to escape from this second valve.</p>

<p>Also in the case where the boiler produces surplus steam
faster than its escape can be effected at the valve <strong>N</strong>, the
pressure will sometimes be increased until the valve <strong>O</strong> is
opened, and its escape will take place from both valves.</p>

<p>The whole weight of the engine bears upon those parts of the
six axles <strong>Râ€²</strong>, <a href="#Fig099"><i>fig.</i> 99.</a>, which project beyond the wheels. Boxes
are formed in which these parts of the axles turn, and through
the medium of which the weight of the engine rests upon
them. Over these boxes are constructed oil or grease cups,
by means of which the axles are constantly lubricated. It is
usual to lubricate the axles of the engine itself with oil: the
axles of the tender, and other coaches and waggons, are
lubricated with a mixture of oil and tallow. In the middle
of the box in which the axle turns, and between the two oil-cups,
is cast a socket, in which the end of the spindle on
<a class="refpn" id="Pg404">[Pg404]</a>
which the spring presses rests. The springs are composed
of a number of steel-plates, laid, in the usual manner, one
above the other, increasing in length upwards. In the
engine here described, the plates forming the springs of
the driving wheels are thirteen in number, each of which
is four inches in width, and
<span class="fraction"><sup>5</sup>â„<sub>16</sub>ths</span> of an inch in thickness.
The springs upon the other wheels are three inches in width.
The springs of the driving wheels are below the axle, while
those of the smaller wheels are above it.</p>

<p>Buffers <strong>Dâ€³</strong> are placed behind the tender, which act upon a
spring <strong>C</strong> (<a href="#Fig100"><i>fig.</i> 100.</a>), to break the collision, when the waggons
or carriages strike upon the tender, and similar buffers are
attached to all passenger-coaches. Some of these buffers are
constructed with a system of springs similar to <strong>C</strong>, but more
elastic, and combined in greater number under the framing
of the carriage, so that a considerable play is allowed to
them. In some cases the rods of the buffers are made to act
upon strong spiral springs inserted in the sides of the framing
of the carriage. This arrangement gives greater play to the
buffers; and as every coach in a train has several buffers, the
combined effect of these is such, that a considerable shock
given to either end of the train may be rendered harmless
by being spent upon the elasticity of these several systems
of springs.</p>

<p>In order to give notice of the approach of a train, a steam-whistle
<strong>Zâ€²</strong>, <a href="#Fig097"><i>fig.</i> 97.</a>
 <a href="#Fig101"><i>fig.</i> 101.,</a> is placed immediately above the fire-box
at the back of the engine. This is an apparatus composed of two
small hemispheres of brass, separated one from the other by a
small space. Steam is made to pass through a hollow space
constructed in the lower hemisphere, and escapes from a very
narrow circular opening round the edge of that hemisphere,
rushing up with a force proportionate to its pressure. The
edge of the upper hemisphere presented downwards encounters
this steam, and an effect is produced similar to the
action of air in organ pipes. A shrill whistle is produced,
which can be heard at a very considerable distance, and,
differing from all ordinary sounds, it never fails to give timely
notice of the approach of a train.</p>

<p>The water tank <strong>Iâ€³</strong>, <a href="#Fig098"><i>fig.</i> 98.</a>
 <a href="#Fig100">100.</a>, which is constructed on the
tender, is formed of wrought-iron plates
<span class="fraction"><sup>1</sup>â„<sub>8</sub></span> of an inch thick,
<a class="refpn" id="Pg405">[Pg405]</a>
riveted at the corners by angle iron already described. This
tank is 9 feet long,
<span class="fraction">6<sup>3</sup>â„<sub>4</sub></span> feet wide, and
<span class="fraction">2<sup>1</sup>â„<sub>4</sub></span> feet deep. The top is
covered with a board <strong>Kâ€³</strong>, and a raised platform <strong>Nâ€³</strong> is constructed
behind, divided into three parts, covered with leads,
which open on hinges. The middle lid covers an opening to
the tank by which water is let in: the lids at either side cover
boxes in which are contained the tools necessary to be carried
with the engine. The curved pipe <strong>Pâ€³</strong>, <a href="#Fig098"><i>fig.</i> 98.</a>, leading from the
bottom of the tank to the pipe <strong>Qâ€³</strong>, is of copper. The pipe <strong>Qâ€³</strong>,
connecting the latter with the feed-pipe <strong>Kâ€²</strong>, <a href="#Fig099"><i>fig.</i> 99.</a>, is sometimes
formed of leather or India-rubber cloth, having a spiral spring
on the inside to prevent it from collapsing. It is necessary
that this pipe <strong>Qâ€³</strong> should have a power of yielding to a sufficient
degree to accommodate itself to the inequalities of
motion between the engine and tender. A metal pipe is
sometimes used, supplied with a double ball and socket, and
a telescopic joint, having sufficient play to allow for the
lateral and longitudinal inequalities of motion of the engine
and tender. The weight of an engine, such as that here
described, supplied with its proper quantity of water and
fuel, is about 12 tons: the tender, when empty, weighs about
<span class="fraction">3<sup>1</sup>â„<sub>4</sub></span> tons; and when filled with water and fuel its weight is
7 tons. The tank contains 700 gallons of water, and the
tender is capable of carrying about 800 weight of coke. This
supply is sufficient for a trip of from thirty to forty miles
with an ordinary load.</p>


<div class="ph3"><h3>(198.)</h3> It is not usual to express the power of locomotive engines
in the same manner as that of other engines by the term
horse-power. Indeed, until the actual amount of resistance
opposed to these machines, under the various circumstances
in which they are worked, shall be ascertained with some
degree of precision, it is impossible that their power or efficiency
can be estimated with any tolerable degree of approximation.
The quantity of water evaporated, and passed in
steam through the cylinders, supplies a major limit to the
power exerted; but even this necessary element for the calculation
of the efficacy of these machines has not been ascertained
by a sufficiently extensive course of observation and
experiment. Mr. Stephenson states, that the engine which
<a class="refpn" id="Pg406">[Pg406]</a>
has been here described is capable of evaporating 77 cubic
feet of water per hour, while the early locomotives could only
evaporate 16 cubic feet per hour. This evaporation, however,
is inferior to that which I have ascertained myself to be
produced by engines in regular operation on some of the
northern railways. In an experiment made in July, 1839,
with the Hecla engine, I found that the evaporation in a trip
of ninety-five miles, from Liverpool to Birmingham, was at
the rate of 93Â·2 cubic feet per hour, and in returning the
same distance it was at the rate of 85Â·7 cubic feet per hour,
giving a mean of 89 cubic feet per hour nearly. The Hecla
weighed 12 tons; and its dimensions and proportions corresponded
very nearly with those of the engine above described.</div>

<p>In a course of experiments which I made upon the engines
then in use on the Grand Junction Railway in the autumn
of 1838 I found that the ordinary evaporating power of these
engines varied from eighty to eighty-five cubic feet per hour.</p>

<p>Engines of much greater dimensions, and consequently of
greater evaporating power, are used on the Great Western
Railway. In the autumn of 1838 experiments were made
upon these engines by Mr. Nicholas Wood and myself, when
we found that the most powerful engine on that line, the
North Star, drawing a load of
<span class="fraction">110<sup>1</sup>â„<sub>2</sub></span>
tons gross, engine and
tender inclusive, at
<span class="fraction">30<sup>1</sup>â„<sub>2</sub></span>
miles an hour, evaporated 200 cubic
feet of water per hour. The same engine drawing a load of
<span class="fraction">194<sup>1</sup>â„<sub>2</sub></span>
 tons at
<span class="fraction">18<sup>1</sup>â„<sub>2</sub></span>
miles an hour evaporated 141 cubic feet per
hour, and when drawing 45 tons at
<span class="fraction">38<sup>1</sup>â„<sub>2</sub></span> miles an hour evaporated
198 cubic feet of water per hour.</p>

<p>It has been already shown that a cubic foot of water
evaporated per hour produces a gross amount of mechanical
force very little less than two-horse power, and consequently
the gross amount of mechanical power evolved in
these cases by the evaporation of the locomotive boilers will
be very nearly twice as many horse-power as there are cubic
feet of water evaporated per hour. Thus the evaporation of
the Hecla, in the experiments made in July, 1839, gave a
gross power of about one hundred and eighty horses, while
the evaporation of the North Star gave a power of about four
hundred horses. In stationary engines about half the gross
<a class="refpn" id="Pg407">[Pg407]</a>
power evolved in the evaporation is allowed for waste, friction,
and other sources of resistance not connected with the
load. What quantity should be allowed for this in locomotive
engines is not yet ascertained, and therefore it is impossible
to state what proportion of the whole evaporation is to
be taken as representing the useful horse-power.</p>


<div class="ph3">
<h3>(199.)</h3> The great uniformity of resistance produced by the
traction of carriages upon a railway is such as to render the
application of steam power to that purpose extremely advantageous.
So far as this resistance depends on mechanical
defects, it is probably rendered as uniform as is practicable,
and in proportion to the quantity of load carried is reduced to
as small an amount as it is likely to attain under any practicable
circumstances. Until a recent period this resistance
was ascribed altogether, or nearly so, to mechanical causes.
The inequalities of the road-surface, the friction of the axles
of the wheels in their bearings, and the various sources of
resistance due to the machinery of the engine, being the principal
of these resistances, were for the most part independent
of the speed with which the train was moved; and it
was accordingly assumed in all calculations respecting the
power of locomotive engines that the resistance would be
practically the same whatever might be the speed of the
train. It had been well understood that so far as the atmosphere
might offer resistance to the moving power this would
be dependent on the speed, and would increase in a very high
ratio with the speed; but it was considered that the part of
the resistance due to this cause formed a fraction of the whole
amount so insignificant that it might be fairly disregarded in
practice, or considered as a part of the actual computed resistance
taken at an average speed.</div>

<p>It has been, until a late period, accordingly assumed that
the total amount of resistance to railway trains which the locomotive
engines have had to overcome was about the two
hundred and fiftieth part of the gross weight of the load
drawn: some engineers estimated it at a two hundred and
twentieth; others at a two hundred and fiftieth; others at a
three hundred and thirtieth part of the load; and the two hundred
and fiftieth part of the gross load drawn may perhaps be
<a class="refpn" id="Pg408">[Pg408]</a>
considered as a mean between these much varying estimates.
What the experiments were, if any, on which these rough
estimates were based, has never appeared. Each engineer
formed his own valuation of this effect, but none produced
the experimental grounds of their opinion. It has been said
that the trains run down the engine, or that the drawing
chains connecting the engine slacken in descending an inclination
of sixteen feet in a mile, or
<span class="fraction"><sup>1</sup>â„<sub>330</sub>.</span> Numerous experiments,
however, made by myself, as well as the constant
experience now daily obtained on railways, show that this is
a fallacious opinion, except at velocities so low as are never
practised on railways.</p>


<div class="ph3"><h3>(200.)</h3> In the autumn of 1838 a course of experiments was
commenced at the suggestion of some of the proprietors of
the Great Western Railway Company, with a view to determine
various points connected with the structure and the
working of railways. A part of these experiments were
intended to determine the mean amount of the resisting
force opposed to the moving power, and this part was
conducted by me. After having tried various expedients
for determining the mean amount of resistance to the
moving power, I found that no method gave satisfactory
results except one founded on observing the motion of trains
by gravity down steep inclined planes. When a train of
waggons or coaches is placed upon an inclined plane so steep
that it shall descend by its gravity without any moving power,
its motion, when it proceeds from a state of rest, will be gradually
accelerated, and if the resistance to that motion was, as
it has been commonly supposed to be, uniform and independent
of the speed, the descent would be uniformly accelerated:
in other words, the increase of speed would be proportional
to the time of the motion. Whatever velocity the train
would gain in the first minute, it would acquire twice that
velocity at the end of the second minute, three times that
velocity at the end of the third minute, and so on; and this
increase of velocity would continue to follow the same law,
however extended the plane might be. That such would be
the law which the descending motion of a train would follow
had always been supposed, up to the time of the experiments
now referred to; and it was even maintained by some that
<a class="refpn" id="Pg409">[Pg409]</a>
such a law was in strict conformity with experiments made
upon railways and duly reported. The first experiments instituted
by me at the time just referred to afforded a complete
refutation of this doctrine. It was found that the acceleration
was not uniform, but that with every increase of speed
the acceleration was lessened. Thus if a certain speed were
gained by a train in one second when moving at five miles an
hour, a much less speed was gained in one second when moving
ten miles an hour, and a comparatively small speed was
gained in the same time when moving at fifteen miles an hour,
and so on. In fact, the augmentation of the rate of acceleration
appeared to diminish in a very rapid proportion as
the speed increased: this suggested to me the probability
that a sufficiently great increase of speed would destroy all
acceleration, and that the train would at length move at a
uniform velocity. In effect, since the moving power which
impels a train down an inclined plane of uniform inclination
is that fraction of the gross weight of the train which acts in
the direction of the plane, this moving power must be necessarily
invariable; and as any acceleration which is produced
must arise from the excess of this moving power over the
resistance opposed to the motion of the train, from whatever
causes that resistance may arise, whenever acceleration
ceases, the moving force must necessarily be equal to the
resistance; and therefore, when a train descends an inclined
plane with a uniform velocity, the gross resistance to the
motion of the train must be equal to the gross weight
of the train resolved in the direction of the plane; or, in
other words, it must be equal to that fraction of the
whole weight of the train which is expressed by the inclination
of the plane. Thus if it be supposed that the plane
falls at the rate of one foot in one hundred, then the force
impelling the train downwards will be equal to the hundredth
part of the weight of the train. So long as the resistance to
the motion of the train continues to be less than the hundredth
part of its weight, so long will the motion of the train
be accelerated; and the more the hundredth part of the
weight exceeds the resistance, the more rapid will the acceleration
be; and the less the hundredth part of the weight
<a class="refpn" id="Pg410">[Pg410]</a>
exceeds the resistance, the less rapid will the acceleration be.
If it be true that the amount of resistance increases with the
increase of speed, then a speed may at length be attained so
great that the amount of resistance to the motion of the train
will be equal to the hundredth part of the weight. When
that happens, the moving power of a hundredth part of the
weight of the train being exactly equal to the resistance to
the motion, there is no excess of power to produce acceleration,
and therefore the motion of the train will be uniform.</div>

<p>Founded on these principles, a vast number of experiments
were made on planes of different inclinations, and with loads
of various magnitudes; and it was found, in general, that
when a train descended an inclined plane, the rate of acceleration
gradually diminished, and at length became uniform;
that the uniform speed thus attained depended on the weight,
form, and magnitude of the train and the inclination of the
plane; that the same train on different inclined planes attained
different uniform speedsâ€”on the steeper planes a
greater speed being attained. From such experiments it followed,
contrary to all that had been previously supposed, that
the amount of resistance to railway trains had a dependence
on the speed; that this dependence was of great practical
importance, the resistance being subject to very considerable
variation at different speeds, and that this source of resistance
arises from the atmosphere which the train encounters. This
was rendered obvious by the different amount of resistance to
the motion of a train of coaches and to that of a train of low
waggons of equal weight.</p>

<p>The former editions of this work having been published
before the discovery which has resulted from these experiments,
the average amount of resistance to railway trains,
there stated, and the conclusions deduced therefrom, were
in conformity with what was then known. It was stated
that the resistance to the moving power was practically independent
of the speed, and on level rails was at the average
rate of about seven pounds and a half per ton. This amount
would be equivalent to the gravitation of a load down an
inclined plane falling
<span class="fraction"><sup>1</sup>â„<sub>300</sub>,</span> and consequently in ascending
such a plane the moving power would have to encounter twice
<a class="refpn" id="Pg411">[Pg411]</a>
the resistance opposed to it on a level. As it was generally
assumed that a locomotive-engine could not advantageously
vary its tractive power beyond this limit, it was therefore inferred
that gradients (as inclinations are called) ought not to
be constructed of greater steepness than
<span class="fraction"><sup>1</sup>â„<sub>300</sub>.</span> It was supposed
that in descending gradients more steep than this the
train would be accelerated and would require the use of the
brake to check its motion, while in ascending such planes the
engine would be required to exert more than twice the ordinary
tractive power required on level rails. As the resistance
produced by the air was not taken into consideration, no distinction
was made between heavy trains of goods presenting
a frontage and magnitude bearing a small proportion to
their gross weight and lighter trains of passenger-coaches presenting
great frontage and great magnitude in proportion to
their weight. The result of the experiments above explained
leads to inferences altogether at variance with those which
have been given in former editions of the present work, and
which were then universally admitted by railway engineers.
The tendency of the results of these experiments show that
low gradients on railways are not attended with the advantageous
effects which have been hitherto ascribed to them; that,
on the contrary, the resistance produced by steeper gradients
can be compensated by slackening the speed, so that
the power shall be relieved from as much atmospheric resistance
by the diminution of velocity as is equal to the increased
resistance produced by the gravity of the plane which is ascended.
And, on the other hand, in descending the plane
the speed may be increased until the resistance produced by
the atmosphere is increased to the same amount as that by
which the train is relieved of resistance by the declivity down
which it moves. Thus, on gradients, the inclination of which
is confined within practical limits, the resistance to the moving-power
may be preserved uniform, or nearly so, by varying
the velocity.</p>


<div class="ph3"><h3>(201.)</h3> The series of experiments which have established these
general conclusions have not yet been sufficiently extended
and varied to supply a correct practical estimate of the limit
which it would be most advantageous to impose upon the
<a class="refpn" id="Pg412">[Pg412]</a>
gradients of railways; but it is certain that railways may be
laid down, without practical disadvantage, with gradients considerably
steeper than those to which it has been hitherto the
practice to recommend as a limit.</div>

<p>The principle of compensation by varied speed being admitted,
it will follow that the time of transit between terminus
and terminus of a line of railway laid down with gradients,
varying from twenty to thirty feet a mile, will be practically
the same as it would be on a line of the same length constructed
upon a dead level; and not only will the time of transport
be equal, but the quantity of moving power expended
will not be materially different. The difference between the
circumstances of the transport in the two cases will be merely
that, on the undulating line, a varying velocity will be imparted
to the train and a varying resistance opposed to
the moving power; while on the level line the train would
be moved at a uniform speed, and the engine worked against
a uniform resistance. These conclusions have been abundantly
confirmed by the experiments made in last July with
the Hecla engine above referred to. The line of railway
between Liverpool and Birmingham on which the experiment
was made extended over a distance of ninety-five miles, and
the gradients on which the effects were observed varied from
a level to thirty feet per mile, a great portion of the line
being a dead level. The following table shows the uniform
speed with which the train ascended and descended the several
gradients, and also the mean of the ascent and descent
in each case, as well as the speed upon the level parts of the
line:â€”</p>

<table summary="Speed of Locomotive Hecla, Ascending, Descending, and Level">
<tr>
 <th class="linernd">Gradient.<br /><i>One in</i></th>
 <th colspan="2" class="linernd">Speed.</th>
 <th class="linernd">Mean.</th></tr>
<tr>
 <th></th>
 <th class="linernd">Ascending.<br /><i>Miles per hour.</i></th>
 <th class="linernd">Descending.<br /><i>Miles per hour.</i></th>
 <th></th></tr>
<tr>
 <td align="center">177</td>
 <td align="center">22Â·25</td>
 <td align="center">41Â·32</td>
 <td align="center">31Â·78</td></tr>
<tr>
 <td align="center">265</td>
 <td align="center">24Â·87</td>
 <td align="center">39Â·13</td>
 <td align="center">32Â·00</td></tr>
<tr>
 <td align="center">330</td>
 <td align="center">25Â·26</td>
 <td align="center">37Â·07</td>
 <td align="center">31Â·16</td></tr>
<tr>
 <td align="center">400</td>
 <td align="center">26Â·87</td>
 <td align="center">36Â·75</td>
 <td align="center">31Â·81</td></tr>
<tr>
 <td align="center">532</td>
 <td align="center">27Â·35</td>
 <td align="center">34Â·30</td>
 <td align="center">30Â·82</td></tr>
<tr>
 <td align="center">590</td>
 <td align="center">27Â·37</td>
 <td align="center">33Â·16</td>
 <td align="center">30Â·21</td></tr>
<tr>
 <td align="center">650</td>
 <td align="center">29Â·03</td>
 <td align="center">32Â·58</td>
 <td align="center" class="linedn">30Â·80</td></tr>
<tr>
 <td align="center">Level</td>
 <td align="center"></td>
 <td align="center"></td>
 <td align="center">30Â·93</td></tr>
</table>

<p><a class="refpn" id="Pg413">[Pg413]</a>
 From this table it is apparent that the gradients do possess
the compensating power with respect to speed already mentioned.
The discrepancies existing among the mean values
of the speed are only what may be fairly ascribed to casual
variations in the moving power. The experiment was made
under favourable circumstances: little disturbance was produced
from the atmosphere; the day was quite calm. In the
same experiment it was found that the water evaporated
varied very nearly in proportion to the varying resistance,
and the amount of that evaporation may be taken as affording
an approximation to the mean amount of resistance.
Taking the trip to and from Birmingham over the distance of
190 miles, the mean evaporation per mile was 3Â·36 cubic feet
of water. The volume of steam produced by this quantity
of water will be determined approximately by calculating
the number of revolutions of the driving wheels necessary to
move the engine one mile. The driving wheels being 5 feet
in diameter, their circumference was 15Â·7 feet, and consequently
in passing over a mile they would have revolved
336Â·3 times. Since each revolution consumes four cylinders
full of steam, the quantity of steam supplied by the boiler to
the cylinders per mile will be found by multiplying the contents
of the cylinder by four times 336Â·3, or 1345Â·2.</p>

<p>The cylinders of the Hecla were
<span class="fraction">12<sup>1</sup>â„<sub>2</sub></span> inches diameter, and
18 inches in length, and consequently their contents were
1Â·28 cubic feet for each cylinder: this being multiplied by
1345Â·2 gives 1721Â·86 or 1722 cubic feet of steam per mile. It
appears, therefore, that supposing the priming either nothing
or insignificant, which was considered to be the case in these
experiments, 3Â·36 cubic feet of water produced 1722 cubic
feet of steam, of the density worked in the cylinders. The ratio,
therefore, of the volume of this steam to that of the water producing
it, was 1722 to 3Â·36, or 512Â·5 to 1. The pressure of
steam of this density would be 54Â·5 pounds per square inch.<a name="FNanchor_34_34" id="FNanchor_34_34"></a><a href="#Footnote_34_34" class="fnanchor">[34]</a>
Such, therefore, was the limit of the average total pressure
of the steam in the cylinders. In this experiment the safety-valve
of the boiler was screwed down to 60 pounds per square
<a class="refpn" id="Pg414">[Pg414]</a>
inch above the atmospheric pressure, which was therefore the
major limit of the pressure of steam in the boiler; but as the
actual pressure in the boiler must have been less than this
amount, the difference between the pressure in the cylinder
and boiler could not be ascertained. This difference, however,
would produce no effect on the moving power of the
steam, since the pressure of steam in the cylinders obtained
by the above calculation is quite independent of the pressure
in the boiler, or of any source of error except what might arise
from priming. The pressure of 54Â·5 pounds per square inch,
calculated above, being the total pressure of the steam on the
pistons, let 14Â·5 pounds be deducted from it, to represent the
atmospheric pressure against which the piston must act, and
the remaining 40 pounds per square inch will represent the
whole available force drawing the train and overcoming all
the resistances arising from the machinery of the engine, including
that of the blast-pipe. The magnitude of a
<span class="fraction">12<sup>1</sup>â„<sub>2</sub></span> inch
piston being 122Â·7 square inches, the total area of the two
pistons would be 245Â·2 square inches, and the pressure upon
each of 40 pounds per inch would give a total force of 9816
on the two pistons. Since this force must act through a
space of three feet, while the train is impelled through a space
of 15Â·7 feet, it must be reduced in the proportion of 3 to
15Â·7, to obtain its effect at the point of contact of the
wheels upon the rails: this will give 1875 pounds as the total
force exerted in the direction of the motion of the train.
The gross weight of the train being 80 tons, including the
engine and tender, this would give a gross moving force along
the road of about 23Â·4 pounds per ton of the gross load, this
force being understood to include all the resistances due to
the engine. This resistance corresponds to the gravitation of
a plane rising at the rate of
<span class="fraction"><sup>1</sup>â„<sub>95</sub>,</span> and therefore it appears that
such would be the inclination of the plane by the gravitation
of which the gross resistance would be doubled, instead of
such inclination being about
<span class="fraction"><sup>1</sup>â„<sub>300</sub>,</span> as has been hitherto supposed.</p>

<p>Since the remarkable and unexpected results of this series
of experiments became known various circumstances were
brought to light, which were before unnoticed, and which
<a class="refpn" id="Pg415">[Pg415]</a>
abundantly confirm them. Among these may be mentioned
the fact, that in descending the Madeley plane, on the Grand
Junction Railway, which falls for above three miles at the
rate of twenty-nine feet a mile, the steam can never be entirely
cut off. But, on the other hand, to maintain the necessary
speed in descending, the power of the engine is always
necessary. As this plane greatly exceeds that which would
be sufficient to cause the free motion of the train down it,
the power of the engine expended in descending it, besides
all that part of the gravitating power of the plane which
exceeds the resistance due to friction and other mechanical
causes must be worked against the atmosphere.</p>

<p>This estimate of the resistance is also in conformity with
the results of a variety of experiments made by me with
trains of different magnitudes down inclined planes of various
inclinations.</p>


<div class="ph3">
<h3>(202.)</h3> In laying out a line of railway the disposition of the
gradients should be such as to preserve among them as uniform
a character as is practicable, for the weight and power of the
engine must necessarily be regulated by the general steepness
of the gradients. Thus if upon a railway which is
generally level, like that between Liverpool and Manchester,
one or two inclined planes of a very steep character occur, as
happens upon that line, then the engine which is constructed
to work upon the general gradients of the road is unfit to
draw the same load up those inclinations which form an
exception to the general character of the gradients. In such
cases some extraordinary means must generally be provided
for surmounting those exceptionable inclinations. Several
expedients have been proposed for this purpose, among which
the following may be mentioned:â€”</div>

<p>1. Upon arriving at the foot of the plane the load is
divided, and the engine carries it up in several successive
trips, descending the plane unloaded after each trip. The
objection to this method is the delay which it occasionsâ€”a
circumstance which is incompatible with a large transport
of passengers. From what has been stated, it would be
necessary, when the engine is fully loaded on a level, to
divide its load into two or more parts, to be successively
<a class="refpn" id="Pg416">[Pg416]</a>
carried up when the incline rises 52 feet per mile. This
method has been practised in the transport of merchandise
occasionally, when heavy loads were carried on the Liverpool
and Manchester line, upon the Rainhill incline.</p>

<p>2. A subsidiary or assistant locomotive engine may be kept
in constant readiness at the foot of each incline, for the purpose
of aiding the different trains, as they arrive, in ascending.
The objection to this method is the cost of keeping
such an engine with its boiler continually prepared, and its
steam up. It is necessary to keep its fire continually lighted,
whether employed or not; otherwise, when the train would
arrive at the foot of the incline, it should wait until the subsidiary
engine was prepared for work. In cases where trains
would start and arrive at stated times, this objection, however,
would have less force. This method is at present generally
adopted on the Liverpool and Manchester line.</p>

<p>3. A fixed steam-engine may be erected on the crest of the
incline, so as to communicate by ropes with the train at the
foot. Such an engine would be capable of drawing up one
or two trains together, with their locomotives, according as
they would arrive, and no delay need be occasioned. This
method requires that the fixed engine should be kept constantly
prepared for work, and the steam continually up in
the boiler.</p>

<p>4. In working on the level, the communication between the
boiler and the cylinder in the locomotives may be so restrained
by partially closing the throttle-valve, as to cause the
pressure upon the piston to be less in a considerable degree
than the pressure of steam in the boiler. If under such circumstances
a sufficient pressure upon the piston can be obtained
to draw the load on the level, the throttle-valve may be
opened on approaching the inclined plane, so as to throw on
the piston a pressure increased in the same proportion as the
previous pressure in the boiler was greater than that upon the
piston. If the fire be sufficiently active to keep up the supply
of steam in this manner during the ascent, and if the rise be
not greater in proportion than the power thus obtained, the
locomotive will draw the load up the incline without further
assistance. It is, however, to be observed, that in this case
<a class="refpn" id="Pg417">[Pg417]</a>
the load upon the engine must be less than the amount which
the adhesion of its working wheels with the railroad is capable
of drawing; for this adhesion must be adequate to the
traction of the same load up the incline, otherwise, whatever
increase of power might be obtained by opening the throttle-valve,
the drawing wheels would revolve without causing the
load to advance. This method has been generally practised
upon the Liverpool and Manchester line in the transport of
passengers; and, indeed, it is the only method yet discovered
which is consistent with the expedition necessary for that
species of traffic.</p>

<p>In the practice of this method considerable aid may be derived
also by suspending the supply of feeding water to the
boiler during the ascent. It will be recollected that a reservoir
of cold water is placed in the tender which follows the
engine, and that the water is driven from this reservoir into
the boiler by a forcing pump, which is worked by the engine
itself. This pump is so constructed that it will supply as
much cold water as is equal to the evaporation, so as to maintain
constantly the same quantity of water in the boiler. But
it is evident, on the other hand, that the supply of this water
has a tendency to check the rate of evaporation, since in being
raised to the temperature of the water with which it mixes
it must absorb a considerable portion of the heat supplied by
the fire. With a view to accelerate the production of steam,
therefore, in ascending the inclines, the engine man may
suspend the action of the forcing pump, and thereby stop the
supply of cold water to the boiler; the evaporation will go on
with increased rapidity, and the exhaustion of water produced
by it will be repaid by the forcing pump on the next level, or
still more effectually on the next descending incline. Indeed
the feeding pump may be made to act in descending an incline,
if necessary, when the action of the engine itself is suspended,
and when the train descends by its own gravity, in
which case it will perform the part of a brake upon the descending
train.</p>

<p>5. The mechanical connexion between the piston of the
cylinder and the points of contact of the working wheels with
the road may be so altered, upon arriving at the incline, as to
<a class="refpn" id="Pg418">[Pg418]</a>
give the piston a greater power over the working wheels.
This may be done in an infinite variety of ways, but hitherto
no method has been suggested sufficiently simple to be applicable
in practice; and even were any means suggested
which would accomplish this, unless the intensity of the impelling
power were at the same time increased, it would necessarily
follow that the speed of the motion would be diminished
in exactly the same proportion as the power of the
piston over the working wheels would be increased. Thus,
on the inclined plane, which rises fifty-five feet per mile, upon
the Liverpool line, the speed would be diminished to nearly
one fourth of its amount upon the level.</p>

<div class="figcenter" style="width: 474px;">
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_440.png" width="474" height="381" alt="" />
</div>

<div class="footnotes"><h3>FOOTNOTES:</h3>

<div class="footnote">
<p><a name="Footnote_30_30" id="Footnote_30_30"></a><a
href="#FNanchor_30_30"><span class="label">[30]</span></a>
Some of the preceding observations on inland transport, as well as
other parts of the present chapter, appeared in articles written by me in
the <cite>Edinburgh Review</cite> for October, 1832, and October, 1834.</p></div>

<div class="footnote">
<p><a name="Footnote_31_31" id="Footnote_31_31"></a><a
href="#FNanchor_31_31"><span class="label">[31]</span></a>
Wood on Railroads, 2d edit.</p></div>

<div class="footnote">
<p><a name="Footnote_32_32" id="Footnote_32_32"></a><a
href="#FNanchor_32_32"><span class="label">[32]</span></a>
The cost of coke has risen considerably since the date of this report.</p></div>
<div class="footnote">

<p><a name="Footnote_33_33" id="Footnote_33_33"></a><a
href="#FNanchor_33_33"><span class="label">[33]</span></a>
I am indebted to the enlarged edition of Tredgold on the Steam Engine,
published by Mr. Weale, for the drawings of this engine. The details
of the machine are very fully given in that work, the description of them
being supplied by Mr. Stephenson himself.</p></div>

<div class="footnote">

<p><a name="Footnote_34_34" id="Footnote_34_34"></a><a
href="#FNanchor_34_34"><span class="label">[34]</span></a>
See Table of Pressures, Temperatures, and Volumes, in appendix.</p></div></div>

<div class="figcenter" style="width: 497px;">
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_441.png" width="497" height="303" alt="" />
</div>

<h2><a name="CHAP_XII" id="CHAP_XII">CHAP. XII.</a></h2>

<p class="fsize2 center">LOCOMOTIVE ENGINES ON TURNPIKE ROADS.</p>

<p class="right"><a class="refpn" id="Pg419">[Pg419]</a><br />
<a href="#CONTENTS"><small>TOC</small></a>&#160;&#160;<a
href="#INDEX"><small>INX</small></a></p>

<div class="chapheader">
RAILWAYS AND STONE ROADS COMPARED.â€”MR. GURNEY'S STEAM ENGINE.â€”CONVENIENCE
AND SAFETY OF STEAM CARRIAGES.â€”HANCOCK'S STEAM
ENGINE.â€”OGLE'S STEAM ENGINE.â€”TREVETHICK'S INVENTION.â€”DR.
CHURCH'S STEAM ENGINE.</div>


<div class="ph3fst"><h3>(203.)</h3> We have hitherto confined our observations on steam-power,
as a means of transport by land, to its application on
railways. But modern speculation has not stopped there; various
attempts have been made, and attended with more or less
success, to work steam-carriages on common roads. The mere
practicability of this project had long been regarded as very
questionable; but enough has been done to show that the
only doubt which can attend it, is as to whether it can be profitably
resorted to, as a means of transport, and this question
<a class="refpn" id="Pg420">[Pg420]</a>
has been materially affected by the recent extension of railways.
In comparing the effect of a stone road with an iron
railway, there are two circumstances which give great superiority
and advantage to the latter: first, the resistance
opposed by a railway to the moving power, no matter what
that moving power may be, is considerably less in proportion
to the load than on a stone road. The average resistance on
a good level stone road, to the motion of carriages drawn at
the speed usually attained by the application of horse-power,
may be taken at about a thirty-sixth part of the load, while
the resistance to a load drawn upon a railway <em>at the same
speed</em> probably does not amount to a tenth part of this resistance.
Thus the moving power, whatever it may be, would
produce on a railway ten times the useful effect which it
would produce on a stone road; secondly, the resistance which
is opposed to the moving power on a level railway is much
more uniform than on a stone road, and, consequently, the
moving power is less subjected to jerks and inequalities. This
renders the application of inanimate power more easy on the
railway. Those inequalities of surface which increase the
amount of resistance on stone roads as compared with railways
also produce a jolting motion in the carriage, to counteract
which, the use of springs become necessary. These springs
render the motion of that part of the carriage which rests upon
them different from that part of the carriage which supports
them; and in the application of steam-machinery it becomes
necessary so to connect the moving power with the wheels
that the machinery may have one motion, and the wheels
which are put in mechanical connexion with that machinery,
and driven by it, shall have another motion. This, it is true,
is the case with locomotive engines on railways; but owing
to the greater smoothness and equality of the railway surface
the difference between the motion of the carriage body suspended
on springs and that of the wheels is much less than
it would be on a stone road.</div>

<p>But besides the greater smoothness of railways compared
with stone roads, the latter have another disadvantage, the
effects of which have probably been exaggerated by those who
are opposed to this application of steam-power. One of the
<a class="refpn" id="Pg421">[Pg421]</a>
laws of adhesion long since developed by experiment, and established
as a principle of practical science, is that the adhesion
is greater between surfaces of the same than between
surfaces of a different kind. Thus between two metals of
the same kind, the adhesion corresponding to any given
pressure is greater than between two metals of different
kinds; between two metals of any sort the adhesion is greater
than between metal and stone, or between metal and wood.
Hence, the wheels of steam-carriages running on a railroad
have a greater adhesion with the road, and therefore offer a
greater resistance to slip round without the advance of the
carriage, than wheels would offer on a turnpike road; for on
a railroad the iron tire of the wheel rests in contact with the
iron rail, while on a common road the iron tire rests in contact
with the surface of stone, or whatever material the road
may be composed of. Besides this, the dust and loose matter
which necessarily collect on a common road, when pressed between
the wheels and the solid base of the road, act somewhat
in the manner of rollers, and give the wheels a greater
facility to slip than if the road were swept clean, and the
wheels rested in immediate contact with its hard surface.
The truth of this observation is illustrated on the railroads
themselves, where the adhesion is found to be diminished
whenever the rails are covered with any extraneous matter,
such as dust or moist clay. Although the adhesion of the
wheels of a carriage with a common road, however, be less
than those of the wheels of a steam-carriage with a railroad,
yet still the actual adhesion on turnpike roads is greater in
amount than has been generally supposed, and is quite sufficient
to propel carriages drawing after them loads of large
amount.</p>

<p>The relative facility with which carriages are propelled on
railroads and turnpike-roads equally affects any moving
power, whether that of horses or steam engines; and whether
loads be propelled by the one power or the other, the railroad,
as compared with the turnpike-road, will always possess
the same proportionate advantage; and a given amount of
power, whether of the one kind or the other, will always perform
a quantity of work less in the same proportion on a
<a class="refpn" id="Pg422">[Pg422]</a>
turnpike-road than on a rail-road. But, on the other hand, the
expense of original construction, and of maintaining the
repairs of a rail-road, is to be placed against the certain
facility which it offers to draught.</p>

<p>In the attempts which have been made to adapt locomotive
engines to turnpike-roads, the projectors have aimed at the
accomplishment of two objects: first, the construction of
lighter and smaller engines; and, secondly, increased power.
These ends, it is plain, can only be attained, with our present
knowledge, by the production of steam of very high temperature
and pressure, so that the smallest volume of steam shall
produce the greatest possible mechanical effect. The methods
of propelling the carriage have been in general similar to
that used in the railroad engines, viz. either by cranks
placed on the axles, the wheels being fixed upon the same
axles, or by connecting the piston rods with the spokes of
the wheels. In some carriages, the boiler and moving power,
and the body of the carriage which bears the passengers, are
placed on the same wheels. In others, the engine is placed
on a separate carriage, and draws after it the carriage which
transports the passengers, as is always the case on railways.</p>

<p>The chief difference between the steam engines used on
railways, and those adapted to propel carriages on turnpike
roads, is in the structure of the boiler. In the latter it is
essential that, while the power remains undiminished, the
boiler should be lighter and smaller. The accomplishment
of this has been attempted by various contrivances for so
distributing the water as to expose a considerable quantity
of surface in contact with it to the action of the fire: spreading
it in thin layers on flat plates; inserting it between plates
of iron placed at a small distance asunder, the fire being admitted
between the intermediate plates; dividing it into small
tubes, round which the fire has play; introducing it between
the surfaces of cylinders placed one within another, the fire
being admitted between the alternate cylinders,â€”have all
been resorted to by different projectors.</p>


<div class="ph3"><h3>(204.)</h3> First and most prominent in the history of the application
of steam to the propelling of carriages on turnpike roads
stands the name of Mr. Goldsworthy Gurney, a medical
<a class="refpn" id="Pg423">[Pg423]</a>
gentleman, and scientific chemist, of Cornwall. In 1822, Mr.
Gurney succeeded Dr. Thompson as lecturer on chemistry at
the Surrey Institution; and, in consequence of the results of
some experiments on heat, his attention was directed to the
project of working steam-carriages on common roads; and he
subsequently devoted his exertions in perfecting a steam-engine
capable of attaining the end he had in view.</div>

<p>The mistake which so long prevailed in the application of
locomotives on railroads, and which, as we have shown,
materially retarded the progress of that invention, was shared
by Mr. Gurney. Without reducing the question to the test
of experiment, he took for granted, in his first attempts, that
the adhesion of the wheels with the road was too slight to
propel the carriage. He was assured, he says, by eminent
engineers, that this was a point settled by actual experiment.
It is strange, however, that a person of his quickness and
sagacity did not inquire after the particulars of these "actual
experiments." So, however, it was; and, taking for granted
the inability of the wheels to propel, he wasted much labour
and skill in the contrivance of levers and propellers, which
acted on the ground in a manner somewhat resembling the
feet of horses, to drive the carriage forward. After various
fruitless attempts of this kind, the experience acquired in
the trials to which they gave rise at last forced the truth
upon his notice, and he found that the adhesion of the wheels
was not only sufficient to propel the carriage heavily laden
on level roads, but was capable of causing it to ascend all the
hills which occur on ordinary turnpike-roads. In this manner
it ascended all the hills between London and Barnet, London
and Stanmore, Stanmore Hill, Brockley Hill, and mounted
Old Highgate Hill, the last at one point rising one foot in
nine.</p>

<div class="figcenter" style="width: 403px;">
<a id="Fig114"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_446a.png" width="403" height="364" alt="" />
<div class="caption figure">Fig. 114.</div>
</div>

<div class="figcenter" style="width: 379px;">
<a id="Fig115"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_446b.png" width="379" height="263" alt="" />
<div class="caption figure">Fig. 115.</div>
</div>

<p>The boiler of Mr. Gurney's engine is so constructed,
that there is no part of it in which metal exposed to the
action of the fire is out of contact with water. If it be considered
how rapidly the action of an intense furnace destroys
metal when water is not present to prevent the heat from
accumulating, the advantage of this circumstance will be
appreciated. In the boiler of Mr. Gurney, the grate-bars
<a class="refpn" id="Pg424">[Pg424]</a>
themselves are tubes filled with water, and form, in fact, a
part of the boiler itself. This boiler consists of three strong
metal cylinders placed in a horizontal position one above the
other. A section, made by a perpendicular or vertical plane,
is represented in <a href="#Fig114"><i>fig.</i> 114.</a> The ends of the three cylinders
just mentioned are represented at <strong>D</strong>, <strong>H</strong>, and <strong>I</strong>. In the side
of the lowest cylinder <strong>D</strong> are inserted a row of tubes, a ground
plan of which is represented in <a href="#Fig115"><i>fig.</i> 115.</a> These tubes, proceeding
from the side of the lowest cylinder <strong>D</strong>, are inclined
<a class="refpn" id="Pg425">[Pg425]</a>
slightly upwards, for a reason which I shall presently explain.
From the nature of the section, only one of these tubes is
visible in <a href="#Fig114"><i>fig.</i> 114.</a> at <strong>C</strong>. The other extremities of these tubes
at <strong>A</strong> are connected with the same number of upright tubes,
one of which is shown at <strong>E</strong>. The upper extremities <strong>G</strong> of these
upright tubes are connected with another set of tubes <strong>K</strong>, equal
in number, proceeding from <strong>G</strong>, inclining slightly upwards,
and terminating in the second cylinder <strong>H</strong>.</p>

<div class="figcenter" style="width: 273px;">
<a id="Fig116"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_447.png" width="273" height="374" alt="" />
<div class="caption figure">Fig. 116.</div>
</div>

<p>An end view of the boiler is exhibited in <a href="#Fig116"><i>fig.</i> 116.</a>, where
the three cylinders are expressed by the same letters. Between
the cylinders <strong>D</strong> and <strong>H</strong> there are two tubes of communication
<strong>B</strong>, and two similar tubes between the cylinders <strong>H</strong> and
<strong>I</strong>. From the nature of the section these appear only as a
single tube in <a href="#Fig114"><i>fig.</i> 114.</a> From the top of the cylinder <strong>I</strong> proceeds
a tube <strong>N</strong>, by which steam is conducted to the engine.</p>

<p>It will be perceived that the space <strong>F</strong> is enclosed on every
side by a grating of tubes, which have free communication
with the cylinders <strong>D</strong> and <strong>H</strong>, which cylinders have also a free
communication with each other by the tubes <strong>B</strong>. It follows,
<a class="refpn" id="Pg426">[Pg426]</a>
therefore, that if water be supplied to the cylinder <strong>I</strong>, it will
descend through the tubes, and first filling the cylinder <strong>D</strong> and
the tubes <strong>C</strong>, will gradually rise in the tubes <strong>B</strong> and <strong>E</strong>, will
next fill the tubes <strong>K</strong> and the cylinder <strong>H</strong>. The grating of
water-pipes <strong>C E K</strong> forms the furnace, the pipes <strong>C</strong> being the
fire-bars, and the pipes <strong>E</strong> and <strong>K</strong> being the back and roof of
the stove. The fire-door, for the supply of fuel, appears at
<strong>M</strong>, fig. 116. The flue issuing between the tubes <strong>F</strong> is conducted
over the tubes <strong>K</strong>, and the flame and hot air are
carried off through a chimney. That portion of the heat of
the burning fuel, which in other furnaces destroys the bars
of the grate, is here expended in heating the water contained
in the tubes <strong>C</strong>. The radiant heat of the fire acts upon the
tubes <strong>K</strong>, forming the roof of the furnace, on the tube <strong>E</strong> at
the back of it, and partially on the cylinders <strong>D</strong> and <strong>H</strong>, and
the tubes <strong>B</strong>. The draft of hot air and flame passing into
the flue at <strong>A</strong> acts upon the posterior surfaces of the tubes <strong>E</strong>,
and the upper sides of the tubes <strong>K</strong>, and finally passes into the
chimney.</p>

<p>As the water in the tubes <strong>C E K</strong> is heated, it becomes specifically
lighter than water of a less temperature, and consequently
acquires a tendency to ascend. It passes, therefore,
rapidly into <strong>H</strong>. Meanwhile the colder portions descend, and
the inclined positions of the tubes <strong>C</strong> and <strong>K</strong> give play to this
tendency of the heated water, so that a prodigiously rapid
circulation is produced, when the fire begins to act upon the
tubes. When the water acquires such a temperature that
steam is rapidly produced, steam-bubbles are constantly
formed in the tubes surrounding the fire; and if these remained
stationary in the tubes, the action of the fire would
not only decompose the steam, but render the tubes red hot,
the water not passing through them to carry off the heat.
But the inclined position of the tubes, already noticed, effectually
prevents this injurious consequence. A steam-bubble,
which is formed either in the tubes <strong>C</strong> or <strong>K</strong>, having a tendency
to ascend proportional to its lightness as compared with water,
necessarily rushes upwards; if in <strong>C</strong> towards <strong>A</strong>, and if in <strong>K</strong> towards
<strong>H</strong>. But this motion of the steam is also aided by the
rapid circulation of the water which is continually maintained
<a class="refpn" id="Pg427">[Pg427]</a>
in the tubes, otherwise it might be possible, notwithstanding
the levity of steam compared with water, that a bubble might
remain in a narrow tube without rising. To bring the matter
to the test of experiment, I have connected two cylinders, such
as <strong>D</strong> and <strong>H</strong>, by a system of glass tubes, such as represented at
<strong>C E K</strong>. The rapid and constant circulation of the water was then
made evident: bubbles of steam were formed in the tubes,
it is true; but they passed with great rapidity into the upper
cylinder, and rose to the surface, so that the glass tubes never
acquired a higher temperature than that of the water which
passed through them.</p>

<p>Every part of the boiler being cylindrical, it has the form
which, mechanically considered, is most favourable to strength,
and which, within given dimensions, contains the greatest
quantity of water. It is also free from the defects arising
from unequal expansion, which are found to be most injurious
in tubular boilers. The tubes <strong>C</strong> and <strong>K</strong> can freely
expand in the direction of their length, without being
loosened at their joints, and without straining any part of
the apparatus; the tubes <strong>E</strong>, being short, are subject to a very
slight degree of expansion; and it is obvious that the long
tubes, with which they are connected, will yield to this without
suffering a strain, and without causing any part of the
apparatus to be loosened.</p>

<p>When water is converted into steam, any foreign matter
which may be combined with it is disengaged, and is deposited
on the bottom of the vessel in which the water is
evaporated. All boilers, therefore, require occasional cleansing,
to prevent the crust thus formed from accumulating; and
this operation, for obvious reasons, is attended with peculiar
difficulty in tubular boilers. In the case before us, the crust
of deposited matter would gather and thicken in the tubes
<strong>C</strong> and <strong>K</strong>, and if not removed, would at length choke them.
But besides this, it would be attended with a still worse
effect; for, being a bad conductor, it would intercept the
heat in its transit from the fire to the water, and would cause
the metal of the tube to become unduly heated. Mr. Gurney
of course foresaw this inconvenience, and contrived an ingenious
chemical method of removing it, by occasionally injecting
<a class="refpn" id="Pg428">[Pg428]</a>
through the tubes such an acid as would combine with
the deposit, and carry it away. This method was effectual;
and although its practical application was found to be attended
with difficulty in the hands of common workmen,
Mr. Gurney was persuaded to adhere to it by the late Dr.
Wollaston, until experience proved the impossibility of
getting it effectually performed, under the circumstances in
which boilers are commonly used. Mr. Gurney then adopted
a method of removing the deposit by mechanical means.
Opposite the mouths of the tubes, and on the other side of
the cylinders <strong>D</strong> and <strong>H</strong>, are placed a number of holes, which,
when the boiler is in use, are stopped by pieces of metal
screwed into them. When the tubes require to be cleaned,
these stoppers are removed, and an iron scraper is introduced
through the holes into the tubes, which, being passed backwards
and forwards, removes the deposit.</p>

<p>In these engines the draught through the furnace was
produced by projecting the waste steam up the chimneys
as is practised in railway engines; a method so perfectly effectual,
that it is unlikely to be superseded by any other.
The objection which has been urged against it in locomotive
engines, working on turnpike-roads, is, that the noise which
it produces has a tendency to frighten horses.</p>

<p>In the engines on the Liverpool road, the steam is allowed
to pass directly from the eduction pipe of the cylinder
to the chimney, and it there escapes in puffs corresponding
with the alternate motion of the pistons, and produces a
noise, which, although attended with no inconvenience on the
railroad, would perhaps be objectionable on turnpike-roads.
In the engine used in Mr. Gurney's steam-carriage, the
steam which passes from the cylinders is conducted to a receptacle,
which he calls a blowing box. This box serves the
same purpose as the upper chamber of a smith's bellows. It
receives the steam from the cylinders in alternate puffs, but
lets it escape into the chimney in a continued stream by a
number of small jets. Regular draught is by this means
produced, and no noise is perceived. Another exit for the
steam is also provided, by which the conductor is enabled to
increase or diminish, or to suspend altogether, the draught
<a class="refpn" id="Pg429">[Pg429]</a>
in the chimney, so as to adapt the intensity of the fire to the
exigencies of the road. This is a great convenience in
practice; because on some roads a draught is scarcely required,
while on others a powerful blast is indispensable.</p>

<p>Connected with this blowing box is another apparatus of
considerable practical importance. The pipe through which
the feeding water is conducted from the tank is carried
through this blowing box, within which it is coiled in a
spiral form, so that an extensive thread of the water is exposed
to the heat of the waste steam which has escaped from
the cylinders, and which is enclosed in this blowing box. In
passing through this pipe the feeding water is raised from
the ordinary temperature of about 60Â° to the temperature of
212Â°. Fuel is thus economised and weight diminished; but
there is another still greater advantage attending this process.
The feeding water in the worm just mentioned, while it takes
up the heat from the surrounding steam in the blowing box,
condenses a part of the waste steam, which is thence conducted
to the tank, from which the feeding water is pumped.</p>

<p>When steam is generated so rapidly as is necessarily the
case in locomotive boilers, it rises with great violence in numerous
bubbles from the bottom of the boiler to the surface
of the water, and puts the liquid into a state of foaming turbulence
not unlike the sea in a storm. As the steam rushes
from the surface into the upper part of the boiler, under these
circumstances, it carries with it a spray by which water is
scattered in minute subdivision among the steam, and floats
there like the spray which rises from the base of a cascade.
If the steam be conducted immediately to the cylinder from
the boiler in this state, it will carry with it the water which
is thus suspended in it, which will pass through the cylinder,
and finally be driven into the atmosphere upon the returning
stroke of the piston. The hot water thus carried off possesses
none of the mechanical properties of steam, and is
wholly inefficient as a moving power, and is therefore an extensive
source of the waste of heat. In every boiler, some
means should be provided for the separation of the water thus
suspended in the steam, before the steam is conducted to
the cylinder. In ordinary boilers, the large space which
<a class="refpn" id="Pg430">[Pg430]</a>
remains above the surface of the water serves this purpose.
The steam being there subject to no agitation or disturbance,
the water mechanically suspended in it descends by its own
gravity, and leaves pure steam in the upper part. In the
small tubular boilers, this has been a matter, however, of
greater difficulty. The contracted space in which the ebullition
takes place causes the water to be mixed with the steam
in a greater quantity than could happen in common boilers;
and the want of the same steam-room renders the separation
of the water from the steam a matter of some difficulty.
These inconveniences have been attempted to be overcome
by various contrivances. I have already described the rapid
and regular circulation effected by the arrangement of the
tubes. By this a regularity in the currents is established,
which has a tendency to diminish the mixture of water with
the steam. In addition to this, a method of separation is
provided in the vessel <strong>I</strong>, which is a strong iron cylinder of
some magnitude, placed out of the immediate influence of
the fire. A partial separation of the steam from the water
takes place in the cylinder <strong>H</strong>; and the steam with the water
mechanically suspended in it, technically called moist steam,
rises into the <em>separator</em> <strong>I</strong>. Here, being free from all agitation
and currents, and being, in fact, quiescent, the particles of
water fall to the bottom, while the pure steam remains at the
top. This separator, therefore, serves all the purposes of
the steam-room above the surface of the water in the large
plate boilers. The dry steam is thus collected and ready for
the supply of the engine through the tube <strong>N</strong>, while the water,
which is disengaged from it, is collected at the bottom of the
separator, and is conducted through the tube <strong>T</strong> to the lowest
vessel <strong>D</strong>, to be again circulated through the boiler.</p>

<p>The pistons of the engine work on the axles of the hind
wheels of the carriage which bears the engine, by cranks, as
in the locomotives on the Manchester railway, so that the
axle is kept in a constant state of rotation while the engine
is at work. The wheels placed on this axle are not permanently
fixed or keyed upon it, as in the Manchester locomotives;
but they are capable of turning upon it in the same
manner as ordinary carriage wheels. Immediately within
<a class="refpn" id="Pg431">[Pg431]</a>
these wheels there are fixed upon the axles two projecting
spokes or levers, which revolve with the axle, and which
take the position of two opposite spokes of the wheel. These
may be occasionally attached to the wheel or detached from
it; so that they are capable of compelling the wheels to
turn with the axle, or leaving the axle free to turn independently
of the wheel, or the wheel independent of the axle, at
the pleasure of the conductor. It is by these levers that the
engine is made to propel either or both of the wheels. If
both pairs of spokes are thrown into connexion with the
wheels, the crank shaft or axle will cause both wheels to turn
with it, and in that case the operation of the carriage is precisely
the same as those of the locomotives already described
upon the Liverpool and Manchester line; but this is rarely
found to be necessary, since the adhesion of one wheel with
the road is generally sufficient to propel the carriage, and
consequently only one pair of these fixed levers are used,
and the carriage propelled by only one of the two hind
wheels. The fore wheels of the carriage turn upon a pivot
similar to those of a four-wheeled coach. The position of
these wheels is changed at pleasure by a pinion and circular
rack, which is moved by the conductor, and in this manner
the carriage is guided with precision and facility.</p>

<p>The force of traction necessary to propel a carriage upon
common roads must vary with the variable quality of the
road, and consequently the propelling power, or the pressure
upon the pistons of the engine, must be susceptible of a corresponding
variation; but a still greater variation becomes
necessary from the undulations and hills which are upon all
ordinary roads. This necessary change in the intensity of
the impelling power is obtained by restraining the steam in
the boiler by the throttle-valve, as already described in the
locomotive engines on the railroad. This principle, however,
is carried much further in the present case. The steam
in the boiler maybe at a pressure of from 100 to 200 lbs. on
the square inch; while the steam on the working piston may
not exceed 30 or 40 lbs. on the inch. Thus an immense increase
of power is always at the command of the conductor;
so that when a hill is encountered, or a rough piece of road,
<a class="refpn" id="Pg432">[Pg432]</a>
he is enabled to lay on power sufficient to meet the exigency
of the occasion.</p>

<p>The two difficulties which have been always apprehended
in the practical working of steam-carriages upon common
roads are, first, the command of sufficient power for hills and
rough pieces of road; and, secondly, the apprehended insufficiency
of the adhesion of the wheels with the road to propel
the carriage. The former of these difficulties has been met
by allowing steam of very great pressure to be constantly
maintained in the boiler with perfect safety. As to the
second, all experiments tend to show that there is no ground
for the supposition that the adhesion of the wheels is in any
case insufficient for the purposes of propulsion. Mr. Gurney
states, that he has succeeded in driving carriages thus propelled,
up considerable hills on the turnpike roads about
London. He made a journey to Barnet with only one wheel
attached to the axle, which was found sufficient to propel the
carriage up all hills upon that road. The same carriage, with
only one propelling wheel, also went to Bath, and surmounted
all the hills between Cranford Bridge and Bath, going and
returning.</p>

<p>A double stroke of the piston produces one revolution of
the propelling wheels, and causes the carriage to move through
a space equal to the circumference of those wheels. It will
therefore be obvious, that the greater the diameter of the
wheels, the better adapted the carriage is for speed; and, on
the other hand, wheels of smaller diameter are better adapted
for power. In fact, the propelling power of an engine on
the wheels will be in the inverse proportion of their diameter.
In carriages designed to carry great weights at a moderate
speed, smaller wheels will be used; while in those intended
for the transport of passengers at considerable velocities,
wheels of at least 5 feet diameter are most advantageous.</p>


<div class="ph3"><h3>(205.)</h3> Among the numerous popular prejudices to which
this new invention has given rise, one of the most mischievous
in its effects and most glaring in its falsehood, is the notion
that carriages thus propelled are more injurious to roads than
carriages drawn by horses. This error has been successfully
exposed in the evidence taken before the committee of the
<a class="refpn" id="Pg433">[Pg433]</a>
House of Commons upon steam carriages. It is there demonstrated,
not only that carriages thus propelled do not wear a
turnpike road more rapidly than those drawn by horses, but
that, on the other hand, the wear by the feet of horses is far
more rapid and destructive than any which could be produced
by the wheels of carriages. Steam carriages admit of having
the tires of the wheels broad, so as to act upon the road more
in the manner of rollers, and thereby to give consistency and
firmness to the material of which the road is composed. The
driving wheels being proved not to slip upon the road, do not
produce any effects more injurious than the ordinary rolling
wheels; consequently the wear occasioned by a steam carriage
upon a road, is not more than that produced by a carriage
drawn by horses, of an equivalent weight and the same or
equal tires; but the wear produced by the pounding and
digging of horses' feet in draught is many times greater than
that produced by the wear of any carriage. Those who still
have doubts upon this subject, if there be any such persons,
will be fully satisfied by referring to the evidence which accompanies
the report of the committee of the House of
Commons, printed in October, 1831.</div>

<p>The weight of machinery necessary for steam carriages is
sometimes urged as an objection to their practical utility.
Mr. Gurney states, that, by successive improvements in the
details of the machinery, the weight of his carriages, without
losing any of the propelling power, may be reduced to 35 cwt.,
exclusive of the load, and fuel and water: but thinks that it
is possible to reduce the weight still further.</p>

<p>A steam carriage constructed by Mr. Gurney, weighing
35 cwt., working for 8 hours, is found, according to his statement,
to do the work of about 30 horses. He calculates that
the weight of his propelling carriage, which would be capable
of drawing 18 persons, would be equal to the weight of 4
horses; and the carriage in which these persons would be
drawn would have the same weight as a common stage
coach capable of carrying the same number of persons. Thus
the weight of the wholeâ€”the propelling carriage and the
carriage for passengers taken togetherâ€”would be the same
<a class="refpn" id="Pg434">[Pg434]</a>
with the weight of a common stage coach, with 4 horses inclusive.</p>

<p>There are two methods of applying locomotives upon
common roads to the transport of passengers or goods; the
one is by causing the locomotive to carry, and the other to
draw the load; and different projectors have adopted the one
and the other method. Each is attended with its advantages
and disadvantages. If the same carriage transport the engine
and the load, the weight of the whole will be less in proportion
to the load carried; also a greater pressure may be produced
on the wheels by which the load is propelled. It is
also thought that a greater facility in turning and guiding
the vehicle, greater safety in descending the hills, and a saving
in the original cost, will be obtained. On the other hand,
when the passengers are placed in the same carriage with the
engine, they are necessarily more exposed to the noise of the
machinery and to the heat of the boiler and furnace. The
danger of explosion is so slight, that, perhaps, it scarcely
deserves to be mentioned; but still <em>the apprehension</em> of danger
on the part of the passengers, even though groundless, should
not be disregarded. This apprehension will be obviously removed
or diminished by transferring the passengers into a
carriage separate from the engine; but the greatest advantage
of keeping the engine separate from the passengers is the
facility which it affords of changing one engine for another in
case of accident or derangement on the road, in the same
manner as horses are changed at the different stages: or, if
such an accident occur in a place where a new engine cannot
be procured, the load of passengers may be carried forward
by horses, until it is brought to some station where a locomotive
may be obtained. There is also an advantage arising
from the circumstance, that when the engines are under
repair, or in process of cleaning, the carriages for passengers
are not necessarily idle. Thus the same number of carriages
for passengers will not be required when the engine is used
to draw as when it is used to carry.</p>

<p>In case of a very powerful engine being used to carry great
loads, it would be quite impracticable to place the engine
<a class="refpn" id="Pg435">[Pg435]</a>
and loads on four wheels, the pressure being such as no turnpike
road could bear. In this case it would be indispensably
necessary to place a part of the load at least upon separate
carriages to be drawn by the engine.</p>

<p>In the comparison of carriages propelled by steam with
carriages drawn by horses, there is no respect in which the
advantage of the former is so apparent as the safety afforded
to the passenger. Steam power is under the most perfect
control, and a carriage thus propelled is capable of being
guided with the most admirable precision. It is also capable
of being stopped almost suddenly, whatever be its speed: it
is capable of being turned within a space considerably less
than that which would be necessary for four-horse coaches.
In turning sharp corners, there is no danger, with the most
ordinary care on the part of the conductor. On the other
hand, horse power, as is well known, is under very imperfect
control, especially when horses are used adapted to that
speed which at present is generally considered necessary for
the purposes of travelling. "The danger of being run away
with and overturned," says Mr. Farey, in his evidence before
the House of Commons, "is greatly diminished in a steam
coach. It is very difficult to control four such horses as can
draw a heavy stage coach ten miles an hour, in case they are
frightened or choose to run away; and, for such quick travelling,
they must be kept in that state of courage that they
are always inclined to run away, particularly down hill, and
at sharp turns in the road. Steam power has very little corresponding
danger, being perfectly controllable, and capable
of having its power reversed, to retard in going down hill.
It must be carelessness that would occasion the overturning
of a steam carriage. The chance of breaking down has been
hitherto considerable, but it will not be more than in stage
coaches when the work is truly proportioned and properly
executed. The risk from explosion of the boiler is the only
new cause of danger, and that I consider not equivalent to
the danger from horses."</p>

<p>That the risk of accident from explosion is extremely slight,
may be proved by the fact that the railway between Liverpool
and Manchester has now been in operation for about ten
<a class="refpn" id="Pg436">[Pg436]</a>
years, and that other railways more extensive in length have
been worked for a considerable time, and that no instance has
ever yet occurred of an accident to passengers from the explosion
of a boiler. Generally these machines, when they
fail, are attended with no other effect than the extinction of
the fire, by the water of the boiler flowing in upon it. I am
not aware of more than one instance, in which a serious accident
has been produced by explosion; and in that instance,
the sufferers were only the engineer and stoker. In the
steam-engine of Mr. Gurney, the carriage is drawn after the
engine, as represented in <a href="#Fig117"><i>fig.</i> 117.</a></p>

<div class="figcenter" style="width: 384px;">
<a id="Fig117"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_458a.png" width="384" height="161" alt="" />
<div class="caption figure">Fig. 117.</div>
</div>

<div class="figcenter" style="width: 299px;">
<a id="Fig118"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_458b.png" width="299" height="351" alt="" />
<div class="caption figure">Fig. 118.</div>
</div>

<div class="ph3"><h3>(206.)</h3> In the boiler to be used in the steam carriage projected
by Mr. Walter Hancock, the subdivision of the water
is accomplished by dividing a case or box by a number of
<a class="refpn" id="Pg437">[Pg437]</a>
thin plates of metal, like a galvanic battery, the water being
allowed to flow between every alternate pair of plates, at <strong>E</strong>,
<a href="#Fig118"><i>fig.</i> 118.</a>, and the intermediate spaces <strong>H</strong> forming the flue
through which the flame and hot air are propelled.</div>

<p>In fact, a number of thin plates of water are exposed on
both sides to the most intense action of flame and heated air;
so that steam of a high pressure is produced in great abundance
and with considerable rapidity. The plates forming
the boiler are bolted together by strong iron ties, extending
across the boiler, at right angles to the plates, as represented
in the figure. The distance between the plates is two
inches.</p>

<p>There are ten flat chambers of this kind for water, and
intermediately between them ten flues. Under the flues is
the fire-place, or grate, containing six square feet of fuel in
vivid combustion. The chambers are all filled to about two
thirds of their depth with water, and the other third is left
for steam. The water chambers, throughout the whole
series, communicate with each other both at top and bottom,
and are held together by two large bolts. By releasing these
bolts, at any time, the chambers fall asunder; and by screwing
them up they may be all made tight again. The water
is supplied to the boiler by a forcing-pump, and the steam
issues from the centre of one of the flues at the top.</p>

<p>These boilers are constructed to bear a pressure of 400 or
500 lbs. on the square inch; but the average pressure of the
steam on the safety valve is from 60 to 100. There are 100
square feet of surface in contact with the water exposed to
the fire. The stages which such an engine performs are
eight miles, at the end of which a fresh supply of fuel and
water are taken in. It requires about two bushels of coke
for each stage.</p>

<p>The steam carriage of Mr. Hancock differs from that of
Mr. Gurney in thisâ€”that in the former the passengers and
engine are all placed on the same carriage. The boiler is
placed behind the carriage; and there is an engine-house between
the boiler and the passengers, the latter being placed
in the fore part of the vehicle; so that all the machinery is
behind them. The carriages are adapted to carry 14
<a class="refpn" id="Pg438">[Pg438]</a>
passengers, and weigh, exclusive of their load, about
<span class="fraction">3<sup>1</sup>â„<sub>2</sub></span> tons,
the tires of the wheels being about
<span class="fraction">3<sup>1</sup>â„<sub>2</sub></span> inches in breadth.
Mr. Hancock states, that the construction of his boiler is of
such a nature, that, even in the case of bursting, no danger
is to be apprehended, nor any other inconvenience than the
stoppage of the carriage. He states that, while travelling
about nine miles an hour, and working with a pressure of
about 100 lbs. on the square inch, loaded with thirteen passengers,
the carriage was suddenly stopped. At first the
cause of the accident was not apparent; but, on opening one
of the cocks of the boiler, it was found that it contained
neither steam nor water. Further examination proved that
the boiler had burst. On unscrewing the bolts, it was found
that there were several large holes in the plates of the water-chamber,
through which the water had flowed on the fire, but
neither noise nor explosion, nor any dangerous consequences,
ensued.</p>


<div class="ph3">
<h3>(207.)</h3> Mr. Nathaniel Ogle of Southampton obtained a patent
for a locomotive carriage, and worked it for some time
experimentally; but as his operations do not appear to have
been continued, I suppose he was unsuccessful in fulfilling
those conditions, without which the machine could not be
worked with economy and profit. In his evidence before a
committee of the House of Commons, he has thus described
his contrivance:â€”</div>

<p>"The base of the boiler and the summit are composed of
cross pieces, cylindrical within and square without; there are
holes bored through these cross pieces, and inserted through
the whole is an air tube. The inner hole of the lower surface,
and the under hole of the upper surface, are rather larger than
the other ones. Round the air tube is placed a small cylinder,
the collar of which fits round the larger aperture on the
inner surface of the lower frame, and the under surface of
the upper frame-work. These are both drawn together by
screws from the top; these cross pieces are united by connecting
pieces, the whole strongly bolted together; so that
we obtain, in one tenth of the space, and with one tenth of
the weight, the same heating surface and power as is now
obtained in other and low-pressure boilers, with incalculably
<a class="refpn" id="Pg439">[Pg439]</a>
greater safety. Our present experimental boiler contains
250 superficial feet of heating surface in the space of 3 feet
8 inches high, 3 feet long, and 2 feet 4 inches broad, and
weighs about 8 cwt. We supply the two cylinders with
steam, communicating by their pistons with a crank axle, to
the ends of which either one or both wheels are affixed as
may be required. One wheel is found to be sufficient,
except under very difficult circumstances, and when the
elevation is about one foot in six to impel the vehicle forward.</p>

<p>"The cylinders of which the boiler is composed are so
small as to bear a greater pressure than could be produced
by the quantity of fire beneath the boiler; and if any one of
these cylinders should be injured by violence, or any other
way, it would become merely a safety valve to the rest. We
never, with the greatest pressure, burst, rent, or injured our
boiler; and it has not once required cleaning, after having
been in use twelve months."</p>

<p>Dr. Church of Birmingham has obtained a succession of
patents for contrivances connected with a locomotive engine
for stone roads; and a company, consisting of a considerable
number of individuals, possessing sufficient capital, has been
formed in Birmingham, for carrying into effect his designs,
and working carriages on his principle. The present boiler
of Dr. Church is formed of copper. The water is contained
between two sheets of copper, united together by copper
nails, in a manner resembling the way in which the cloth
forming the top of a mattress or cushion is united with the
cloth which forms the bottom of it, except that the nails or
pins, which bind the sheets of copper, are much closer together.
The water, in fact, seems to be "quilted" or
"padded" in between two sheets of thin copper. This
double sheet of copper is formed into an oblong rectangular
box, the interior of which is the fire-place and ash-pit, and
over the end of which is the steam-chest. The great extent
of surface exposed to the immediate action of the fire causes
steam to be produced with great rapidity.</p>

<p>Various other projects for the application of steam engines
on common roads were in a state of progressive improvement,
<a class="refpn" id="Pg440">[Pg440]</a>
when the greater advantages attending railways were considered
so manifest, that considerable doubts were raised,
whether, supposing the problem of the application of the
steam engine on common roads to be successfully solved, it
could ever be attended with the same economy and effect, as
by the adoption of a railway. Among the projects which
promised a successful issue, may be mentioned the locomotive
engines contrived by Messrs. Maudslay and Field, by Colonel
Maceroni, and by Mr. Scott Russell. These and others
have, however, been abandoned, mainly, we believe, from the
impression, that wherever traffic can exist, sufficiently extensive
to render the application of steam power profitable, a
railway must always supersede a common road; and that,
even in the limited traffic to be expected on branches to the
great railways, horse power applied to railways would be
attended with more economy than steam power applied on
stone roads.</p>

<div class="figcenter" style="width: 392px;">
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_462.png" width="392" height="338" alt="" />
</div>

<div class="figcenter" style="width: 489px;">
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_463.png" width="489" height="399" alt="" />
</div>

<h2><a name="CHAP_XIII" id="CHAP_XIII">CHAP. XIII.</a></h2>

<p class="fsize2 center">STEAM NAVIGATION.</p>

<p class="right"><a class="refpn" id="Pg441">[Pg441]</a><br />
<a href="#CONTENTS"><small>TOC</small></a>&#160;&#160;<a
href="#INDEX"><small>INX</small></a></p>

<div class="chapheader">
FORM AND ARRANGEMENT OF MARINE ENGINES.â€”EFFECTS OF SEA
WATER IN BOILERS.â€”REMEDIES FOR THEM.â€”BLOWING OUT.â€”INDICATORS
OF SALTNESS.â€”SEAWARD'S INDICATOR.â€”HIS METHOD OF
BLOWING OUT.â€”FIELD'S BRINE PUMPS.â€”TUBULAR CONDENSERS
APPLIED BY MR. WATT.â€”HALL'S CONDENSERS.â€”COPPER BOILERS.â€”PROCESS
OF STOKING.â€”MARINE BOILERS.â€”MEANS OF ECONOMISING
FUEL.â€”COATING MARINE BOILERS WITH FELT.â€”NUMBER
AND ARRANGEMENT OF FURNACES AND FLUES.â€”HOWARD'S ENGINE.â€”APPLICATION
OF THE EXPANSIVE PRINCIPLE IN MARINE ENGINES.â€”RECENT
IMPROVEMENTS OF MESSRS. MAUDSLAY AND FIELD.â€”HUMPHRYS'
ENGINE.â€”COMMON PADDLE-WHEEL.â€”FEATHERING PADDLES.â€”MORGAN'S
WHEELS.â€”THE SPLIT PADDLE.â€”PROPORTION OF
POWER TO TONNAGE.â€”IMPROVED EFFICIENCY OF MARINE ENGINES.â€”IRON
STEAM-VESSELS.â€”STEAM-NAVIGATION TO INDIA.</div>


<div class="ph3fst"><h3>(208.)</h3> Among the many ways in which the steam-engine
has ministered to the advancement of civilisation and the
social progress of the human race, there is none more
<a class="refpn" id="Pg442">[Pg442]</a>
important or more interesting than its application to navigation.
Before it lent its giant powers to the propulsion of ships,
locomotion over the waters of the deep was attended with so
much danger and uncertainty that, as a common proverb, it
became the type and the representative of every thing which
was precarious and perilous. The application, however, of
steam to navigation has rescued the mariner and the voyager
from many of the dangers of wind and water; and even in
its present state, putting out of view its probable improvement,
it has rendered all voyages of moderate length as safe,
and very nearly as regular, as journeys over-land. As a means
of transport by sea, the application of this power may be
considered as established; and it is now receiving improvements
by which its extension to the longest class of ocean
voyages is a question not of practicability, but merely of profit.</div>

<p>The manner in which the steam-engine is rendered an
instrument for the propulsion of vessels must in its general
features be so familiar to every one as to require but short
explanation. A shaft is carried across the vessel, being continued
on either side beyond the timbers: to the extremities
of this shaft, on the outside of the vessel, are fixed a pair
of wheels constructed like undershot water-wheels, having
attached to their rims a number of flat boards called <em>paddle-boards</em>.
As the wheels revolve, these paddle-boards strike
the water, driving it in a direction contrary to that in which
it is intended the vessel should be propelled. The moving
force imparted to the water thus driven backwards is necessarily
accompanied by a re-action upon the vessel through the
medium of the paddle-shaft, by which the vessel is propelled
forwards. On the paddle-shaft two cranks are constructed,
similar to the cranks already described on the axle of the
driving wheels of a locomotive engine. These cranks are
placed at right angles to each other, so that when either is
in its highest or lowest position the other shall be horizontal.
They are driven by two steam-engines, which are
placed in the hull of the vessel below the paddle-shaft. In
the earlier steam-boats a single steam-engine was used, and
in that case the unequal action of the engine on the crank
was equalised by a fly-wheel. This, however, has been long
<a class="refpn" id="Pg443">[Pg443]</a>
since abandoned in European vessels, and the use of two
engines is now almost universal. By the relative position of
the cranks it will be seen, that when either crank is at its
dead points, the other will be in the positions most favourable
to its action, and in all intermediate positions the relative
efficiency of the cranks will be such as to render their combined
action very nearly uniform.</p>

<p>The steam-engines used to impel vessels may be either
condensing engines, similar to those of Watt, and such as
are used in manufactures generally, or they may be non-condensing
and high-pressure engines, similar in principle to
those used on railways. Low-pressure condensing engines
are, however, universally used for marine purposes in Europe
and to some extent in the United States. In the latter
country, however, high-pressure engines are also in pretty
general use, on rivers where lightness is a matter of importance.</p>

<p>The arrangement of the parts of a marine engine differs in
some respects from that of a land engine. The limitation of
space, which is unavoidable in a vessel, renders greater compactness
necessary. The paddle-shaft on which the cranks
to be driven by the engine are constructed being very little
below the deck of the vessel, the beam and connecting rod
could not be placed in the position in which they usually are
in land engines, without carrying the machinery to a considerable
elevation above the deck. This is done in the
steam-boat engines used on the American rivers; but it
would be inadmissible in steam-boats in general, and more
especially in sea-going steamers. The connecting rods, therefore,
instead of being presented downwards towards the
cranks which they drive, must, in steam-vessels, be presented
upwards, and the impelling force received from below. If,
under these circumstances, the beam were in the usual position
above the cylinder and piston-rod, it must necessarily
be placed between the engine and the paddle-shaft. This
would require a depth for the machinery which would be
incompatible with the magnitude of the vessel. The beam,
therefore, of marine engines, instead of being above the
cylinder and piston, is placed below them. To the top of the
<a class="refpn" id="Pg445">[Pg445]</a>
piston-rods cross pieces are attached of greater length than
the diameter of the cylinders, so that their extremities shall
project beyond the cylinders. To the ends of these cross
pieces are attached by joints the rods of a parallel motion:
these rods are carried downwards, and are connected with
the ends of two beams below the cylinder, and placed on
either side of it. The opposite ends of these beams are connected
by another cross piece, to which is attached a connecting
rod, which is continued upwards to the crank-pin, to
which it is attached, and which it drives. Thus the beam,
parallel motion, and connecting rod of a marine engine, is
similar to that of a land engine, only that it is turned upside
down; and in consequence of the impossibility of placing the
beam directly over the piston-rod, two beams and two systems
of parallel motion are provided, one on each side of the
engine, acted upon by, and acting on the piston-rod and
crank by cross pieces.</p>

<p>The proportion of the cylinders differs from that usually
observed in land engines, for like reasons. The length of
the cylinder of land engines is generally greater than its
diameter, in the proportion of about two to one. The cylinders
of marine engines are, however, commonly constructed
with a diameter very little less than their length. In proportion,
therefore, to their power their stroke is shorter,
which infers a corresponding shortness of crank and a greater
limitation of play of all the moving parts in the vertical
direction. The valves and the gearing by which they are
worked, the air-pump, the condenser, and other parts of the
marine engines, do not materially differ from those already
described in land engines.</p>

<div class="figcenter" style="width: 600px;">
<a id="Fig119"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_466.png" width="600" height="316" alt="" />
<div class="caption figure">Fig. 119.</div>
<div class="lglink"><a href="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_466-hd.png">larger</a></div>
</div>

<p>These arrangements of a marine engine will be more
clearly understood by reference to <a href="#Fig119"><i>fig.</i> 119.</a><a name="FNanchor_35_35" id="FNanchor_35_35"></a><a href="#Footnote_35_35" class="fnanchor">[35]</a>, in which is
represented a longitudinal section of a marine engine with its
boiler as placed in a steam-vessel. The sleepers of oak, supporting
the engine, are represented at <strong>X</strong>, the base of the
engine being secured to these by bolts passing through them
<a class="refpn" id="Pg446">[Pg446]</a>
and the bottom timbers of the vessel; <strong>S</strong> is the steam-pipe
leading from the steam-chest in the boiler to the slides <i>c</i>, by
which it is admitted to the top and bottom of the cylinder.
The condenser is represented at <strong>B</strong>, and the air-pump at <strong>E</strong>.
The hot well is seen at <strong>F</strong>, from which the feed is taken for
the boiler; <strong>L</strong> is the piston-rod connected by the parallel
motion <i>a</i> with the beam <strong>H</strong>, working on a centre <strong>K</strong>, near the
base of the engine. The other end of the beam <strong>I</strong> drives the
connecting rod <strong>M</strong>, which extends upwards to the crank which
it works upon the paddle-shaft <strong>O</strong>. <strong>Q R</strong> is the framing by
which the engine is supported. The beam here exhibited is
shown on dotted lines as being on the further side of the
engine. A similar beam similarly placed, and moving on the
same axis, must be understood to be at this side connected
with the cross head of the piston in like manner by a parallel
motion, and with a cross piece attached to the lower end of
the connecting rod and to the opposite beam. The eccentric
which works the slides is placed upon the paddle shaft <strong>O</strong>,
and the connecting arm which drives the slides may be easily
detached when the engine requires to be stopped. The
section of the boiler, grate, and flues, is represented at <strong>W U</strong>.
The safety-valve <i>y</i> is enclosed beneath a pipe carried up
beside the chimney, and is inaccessible to the engine-man;
<i>h</i> are the cocks for blowing the salted water from the boiler;
and <strong>I I</strong> the feed-pipe.</p>

<p>The general arrangement of the engine-room of a steam-vessel
is represented in <a href="#Fig120"><i>fig.</i> 120.</a></p>

<p>The nature of the effect required to be produced by marine
engines does not render either necessary or possible that
great regularity of action which is indispensable in a steam-engine
applied to the purposes of manufacture. The agitation
of the surface of the sea will cause the immersion of
the paddle-wheels to be subject to great variation, and the
resistance produced by the water to the engine will undergo
a corresponding change. The governor, therefore, and other
parts of the apparatus, contrived for giving to the engine
that great regularity required in manufactures, are omitted
in nautical engines, and nothing is introduced save what is
<a class="refpn" id="Pg447">[Pg447]</a>
necessary to maintain the machine in its full working efficiency.</p>

<div class="figcenter" style="width: 469px;">
<a id="Fig120"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_469a.png" width="469" height="374" alt="" />
<div class="caption figure">Fig. 120.</div>
</div>

<div class="figleft" style="width: 260px;">
<a id="Fig121"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_469b.png" width="260" height="320" alt="" />
<div class="caption figure">Fig. 121.</div>
</div>

<p>To save space, marine boilers are constructed so as to produce
the necessary quantity of steam within the smallest possible
dimensions. With
this view a more extensive
surface in proportion
to the capacity of the
boiler is exposed to the
action of the fire. The
flues, by which the flame
and heated air are conducted
to the chimney,
are so constructed that
the heat may act upon the
water on every side in thin
oblong shells or plates.
This is accomplished by
constructing the flues so
as to traverse the boiler
backwards and forwards several times before they terminate
<a class="refpn" id="Pg448">[Pg448]</a>
in the chimney. Such an arrangement renders the expense
of the boilers greater, but
their steam-producing
power is proportionally
augmented, and experiments
made by Mr. Watt,
at Birmingham, have
proved that such boilers
with the same consumption
of fuel will produce,
as compared with common
land boilers, an increased
evaporation in the proportion of about three to two.</p>

<div class="figleft" style="width: 255px;">
<a id="Fig122"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_470a.png" width="255" height="220" alt="" />
<div class="caption figure">Fig. 122.</div>
</div>

<div class="figleft" style="width: 312px;">
<a id="Fig123"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_470b.png" width="312" height="185" alt="" />
<div class="caption figure">Fig. 123.</div>
</div>

<p>The form and arrangement of the water-spaces and flues in
marine boilers may be collected from the sections of the
boilers used in some of the government steamers, exhibited
in <i>figs.</i> 121, 122, 123. A section made by a horizontal plane
passing through the flues is exhibited in <a href="#Fig121"><i>fig.</i> 121.</a> The furnaces
<strong>F</strong> communicate in pairs with the flues <strong>E</strong>, the air following the
course through the flues represented by the arrows. The flue
<strong>E</strong> passes to the back of the boiler, then returns to the front,
then to the back again, and is finally carried back to the
front, where it communicates at <strong>C</strong> with the curved flue <strong>B</strong>,
represented in the transverse vertical section, <a href="#Fig122"><i>fig.</i> 122.</a> This
curved flue <strong>B</strong> finally terminates in the chimney <strong>A</strong>. There are
in this case three independent boilers, each worked by two
furnaces communicating with the same system of flues; and
in the curved flues <strong>B</strong>, <a href="#Fig122"><i>fig.</i> 122.</a>, by which the air is finally conducted
through the chimney, are placed three independent
<a class="refpn" id="Pg449">[Pg449]</a>
dampers, by means of which the furnace of each boiler can be
regulated independently of the other, and by which each
boiler may be separately detached from communication with
the chimney. The letters of reference in the horizontal section,
<a href="#Fig121"><i>fig.</i> 121.</a>, correspond with those in the transverse vertical
section, <a href="#Fig122"><i>fig.</i> 122.</a>, <strong>E</strong> representing the commencement of the
flues, and <strong>C</strong> their termination.</p>

<div class="figcenter" style="width: 464px;">
<a id="Fig124"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_471.png" width="464" height="232" alt="" />
<div class="caption figure">Fig. 124.</div>
</div>

<p>A longitudinal section of the boiler made by a vertical
plane extending from the front to the back is given in <a href="#Fig123"><i>fig.</i> 123.</a>,
where <strong>F</strong>, as before, is the furnace, <strong>G</strong> the grate-bars sloping
downwards from the front to the back, <strong>H</strong> the fire-bridge, <strong>C</strong>
the commencement of the flues, and <strong>A</strong> the chimney. An
elevation of the front of the boiler is represented in <a href="#Fig124"><i>fig.</i> 124.</a>,
showing two of the fire-doors closed, and the other two removed,
displaying the position of the grate-bars in front.
Small openings are also provided, closed by proper doors, by
which access can be had to the under side of the flues between
the foundation timbers of the engine for the purpose
of cleaning them.</p>

<p>Each of these boilers can be worked independently of the
others. By this means, when at sea, the engine may be
worked by any two of the three boilers, while the third is
being cleaned and put in order. In all sea-going steamers
multiple boilers are at present provided for this purpose.</p>

<p>In the boilers here represented the flues are all upon the
same level, winding backwards and forwards without passing
one above the other. In other boilers, however, the flues,
<a class="refpn" id="Pg450">[Pg450]</a>
after passing backwards and forwards near the bottom of the
boiler, turn upwards and pass backwards and forwards through
a level of the water nearer its surface, finally terminating in
the chimney. More heating surface is thus obtained with
the same capacity of boiler.</p>

<p>The most formidable difficulty which has been encountered
in the application of the steam-engine to sea-voyages
has arisen from the necessity of supplying the boiler with sea-water
instead of pure fresh water. The sea-water is injected
into the condenser for the purpose of condensing the steam,
and it is thence, mixed with the condensed steam, conducted
as feeding water into the boiler.</p>


<div class="ph3"><h3>(209.)</h3> Sea-water holds, as is well known, certain alkaline
substances in solution, the principal of which is muriate of
soda, or common salt. Ten thousand grains of pure sea-water
contain two hundred and twenty grains of common salt, the
remaining ingredients being thirty-three grains of sulphate of
soda, forty-two grains of muriate of magnesia, and eight
grains of muriate of lime. The heat which converts pure
water into steam does not at the same time evaporate those
salts which the water holds in solution. As a consequence
it follows, that as the evaporation in the boiler is continued,
the salt, which was held in solution by the water which has
been evaporated, remains in the boiler, and enters into solution
with the water remaining in it. The quantity of salt
contained in sea-water being considerably less than that which
water is capable of holding in solution, the process of evaporation
for some time is attended with no other effect than
to render the water in the boiler a stronger solution of salt.
If, however, this process be continued, the quantity of salt
retained in the boiler having constantly an increasing proportion
to the quantity of water, it must at length render the
water in the boiler a saturated solutionâ€”that is, a solution
containing as much salt as at the actual temperature it is capable
of holding in solution. If, therefore, the evaporation
be continued beyond this point, the salt disengaged from the
water evaporated instead of entering into solution with the
water remaining in the boiler will be precipitated in the
form of sediment; and if the process be continued in the
<a class="refpn" id="Pg451">[Pg451]</a>
same manner, the boiler would at length become a mere
salt-pan.</div>

<p>But besides the deposition of salt sediment in a loose form,
some of the constituents of sea-water having an attraction
for the iron of the boiler, collect upon it in a scale or crust
in the same manner as earthy matters held in solution by
spring-water are observed to form and become incrusted on
the inner surface of land-boilers and of common culinary
vessels.</p>

<p>The coating of the inner surface of a boiler by incrustation
and the collection of salt sediment in its lower parts, are
attended with effects highly injurious to the materials of the
boiler. The crust and sediment thus formed within the
boiler are almost non-conductors of heat, and placed, as they
are, between the water contained in the boiler and the metallic
plates which form it, they obstruct the passage of heat
from the outer surface of the plates in contact with the fire
to the water. The heat, therefore, accumulating in the
boiler-plates so as to give them a much higher temperature
than the water within the boiler, has the effect of softening
them, and by the unequal temperature which will thus be
imparted to the lower plates which are incrusted, compared
with the higher parts which may not be so, an unequal expansion
is produced, by which the joints and seams of the
boiler are loosened and opened, and leaks produced.</p>

<p>These injurious effects can only be prevented by either of
two methods; first, by so regulating the feed of the boiler
that the water it contains shall not be suffered to reach the
point of saturation, but shall be so limited in its degree
of saltness that no injurious incrustation or deposit shall
be formed; secondly, by the adoption of some method by
which the boiler may be worked with fresh water. This
end can only be attained by condensing the steam by a jet
of fresh water, and working the boiler continually by the
same water, since a supply of fresh water sufficient for a
boiler worked in the ordinary way could never be commanded
at sea.</p>


<div class="ph3"><h3>(210.)</h3> The method by which the saltness of the water in the
boiler is most commonly prevented from exceeding a certain
<a class="refpn" id="Pg452">[Pg452]</a>
limit has been to discharge from the boiler into the sea a
certain quantity of over-salted water, and to supply its place
by sea-water introduced into the condenser through the injection-cock
for the purpose of condensing the steam, this
water being mixed with the steam so condensed, and being,
therefore, a weaker solution of salt than common sea-water.
To effect this, cocks called <em>blow-off cocks</em>, are usually placed
in the lower parts of the boiler, where the over-salted, and
therefore heavier, parts of the water collect. The pressure
of the steam and incumbent weight of the water in the boiler
force the lower strata of water out through these cocks; and
this process, called <em>blowing out</em>, is, or ought to be, practised
at such intervals as will prevent the water from becoming
over salted. When the salted water has been blown out in
this manner, the level of the water in the boiler is restored
by a feed of corresponding quantity.</div>

<p>This process of blowing out, on the due and regular observance
of which the preservation and efficiency of the boiler
mainly depend, is too often left at the discretion of the engineer,
who is, in most cases, not even supplied with the
proper means of ascertaining the extent to which the process
should be carried. It is commonly required that the engineer
should blow out a certain portion of the water in the
boiler every two hours, restoring the level by a feed of equivalent
amount; but it is evident that the sufficiency of the
process founded on such a rule must mainly depend on the
supposition that the evaporation proceeds always at the same
rate, which is far from being the case with marine boilers.
An indicator, by which the saltness of the water in the boiler
would always be exhibited, ought to be provided, and the
process of blowing out should be regulated by the indications
of that instrument. To blow out more frequently
than is necessary is attended with a waste of fuel; for hot
water is thus discharged into the sea while cold water is introduced
in its place, and consequently all the heat necessary to
produce the difference of the temperatures of the water
blown out and the feed introduced is lost. If, on the other
hand, the process of blowing out be observed less frequently
than is necessary, then more or less incrustation and deposit
<a class="refpn" id="Pg453">[Pg453]</a>
may be produced, and the injurious effects already described
ensue.</p>

<p>As the specific gravity of water holding salt in solution is
increased with every increase of the strength of the solution,
any form of hydrometer capable of exhibiting a visible indication
of the specific gravity of the water contained in the
boiler would serve the purpose of an indicator, to show when
the process of blowing out is necessary, and when it has been
carried to a sufficient extent. The application of such instruments,
however, would be attended with some practical difficulties
in the case of sea-boilers.</p>

<p>The temperature at which a solution of salt boils under a
given pressure varies considerably with the strength of the
solution; the more concentrated the solution is, the higher
will be its boiling temperature under the same pressure. A
comparison, therefore, of a steam-gauge attached to the boiler,
and a thermometer immersed in it, showing the pressure and
the temperature, would always indicate the saltness of the
water; and it would not be difficult so to graduate these
instruments as to make them at once show the degree of
saltness.</p>

<p>If the application of the thermometer be considered to be
attended with practical difficulty, the difference of pressures
under which the salt water of the boiler and fresh water of
the same temperature boil, might be taken as an indication
of the saltness of the water in the boiler, and it would not be
difficult to construct upon this principle a self-registering instrument,
which would not only indicate but record from hour
to hour the degree of saltness of the water. A small vessel of
distilled water being immersed in the water of the boiler
would always have the temperature of that water, and the
steam produced from it communicating with a steam-gauge,
the pressure of such steam would be indicated by that gauge,
while the pressure of the steam in the boiler under which
pressure the salted water boils might be indicated by another
gauge. The difference of the pressures indicated by the two
gauges would thus become a test by which the saltness of the
water in the boiler would be measured. The two pressures
might be made to act on opposite ends of the same column of
<a class="refpn" id="Pg454">[Pg454]</a>
mercury contained in a siphon tube, and the difference of the
levels of the two surfaces of the mercury would thus become
a measure of the saltness of the water in the boiler. A self-registering
instrument founded on this principle formed part
of the self-registering steam-log which I proposed to introduce
into steam-vessels some time since.</p>


<div class="ph3"><h3>(211.)</h3> The Messrs. Seaward of Limehouse have adopted, in
some of their recently constructed engines, a method of indicating
the saltness of the water, and of measuring the quantity
of salted water or brine discharged, by blowing out. A glass-gauge,
similar in form to that already described in land engines
(<a href="#h3-156">156</a>.), is provided to indicate the position of the
surface of the water in the boiler. In this gauge two hydrometer
balls are provided, the weight of which in proportion
to their magnitude is such that they would both sink
to the bottom in a solution of salt of the same strength as
common sea-water. When the quantity of salt exceeds

<span class="fraction"><sup>5</sup>â„<sub>32</sub></span> parts of the whole weight of the water, the lighter of the
two balls will float to the top; and when the strength is
further increased until the proportion of salt exceeds
<span class="fraction"><sup>6</sup>â„<sub>32</sub></span> parts
of the whole, then the heavier ball will float to the top. The
actual quantity of salt held in solution by sea-water in its ordinary
state is
<span class="fraction"><sup>1</sup>â„<sub>32</sub></span> part of its whole weight; and when by evaporation
the proportion of salt in solution has become
<span class="fraction"><sup>9</sup>â„<sub>32</sub></span>
parts of the whole, then a deposition of salt commences.
With an indicator such as that above described, the ascent
of the lighter hydrometer ball gives notice of the necessity for
blowing out, and the ascent of the heavier may be considered
as indicating the approach of an injurious state of saltness in
the boiler.</div>

<div class="figcenter" style="width: 296px;">
<a id="Fig125"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_477.png" width="296" height="392" alt="" />
<div class="caption figure">Fig. 125.</div>
</div>

<p>The ordinary method of blowing out the salted water from
a boiler is by a pipe having a cock in it leading from the
boiler through the bottom of the ship, or at a point low down
at its side. Whenever the engineer considers that the water
in the boiler has become so salted that the process of blowing
out should commence, he opens the cock communicating by
this pipe with the sea, and suffers an indefinite and uncertain
quantity of water to escape. In this way he discharges, according
to the magnitude of the boiler, from two to six tons
<a class="refpn" id="Pg455">[Pg455]</a>
of water, and repeats this at intervals of from two to four
hours, as he may consider to be sufficient. If, by observing
this process, he prevents the boiler from getting incrusted
during the voyage, he considers his duty to be effectually
discharged, forgetting that he may have blown out
many times more water than is necessary for the preservation
of the boiler, and thereby produced a corresponding
and unnecessary waste of fuel. In order to limit the quantity
of water discharged, Messrs. Seaward have adopted
the following method. In <a href="#Fig125"><i>fig.</i> 125.</a> is represented a transverse
section of a part of a steam-vessel; <strong>W</strong> is the water-line of
the boiler, <strong>B</strong> is the mouth of a blow-off pipe, placed near the
bottom of the boiler. This pipe rises to <strong>A</strong>, and turning in
the horizontal direction, <strong>A C</strong> is conducted to a tank <strong>T</strong>, which
contains exactly a ton of water. This pipe communicates
with the tank by a cock <strong>D</strong>, governed by a lever <strong>H</strong>. When
this lever is moved to <strong>Dâ€²</strong>, the cock <strong>D</strong> is open, and when it is
moved to <strong>K</strong>, the cock <strong>D</strong> is closed. From the same tank there
proceeds another pipe <strong>E</strong>, which issues from the side of the
<a class="refpn" id="Pg456">[Pg456]</a>
vessel into the sea governed by a cock <strong>F</strong>, which is likewise
put in connection with the lever <strong>H</strong>, so that it shall be opened
when the lever <strong>H</strong> is drawn to the position <strong>Fâ€²</strong>, the cock <strong>Dâ€²</strong> being
closed in all positions of the lever between <strong>K</strong> and <strong>Fâ€²</strong>. Thus, whenever
the cock <strong>F</strong> communicating with the sea is open, the cock
<strong>D</strong> communicating with the boiler is closed, and <i>vice versÃ¢</i>,
both cocks being closed when the lever is in the intermediate
position <strong>K</strong>. By this arrangement the boiler cannot, by any
neglect in blowing off, be left in communication with the sea,
nor can more than a ton of water be discharged except by
the immediate act of the engineer. The injurious consequences
are thus prevented which sometimes ensue when the
blow-off cocks are left open by any neglect on the part of the
engineer. When it is necessary to blow off, the engineer
moves the lever <strong>H</strong>, to the position <strong>Dâ€²</strong>. The pressure of the
steam in the boiler on the surface of the water <strong>W</strong> forces
the salted water or brine up the pipe <strong>B A</strong>, and through the
open cock <strong>C</strong> into the tank, and this continues until the tank
is filled: when that takes place, the lever is moved from the
position <strong>Dâ€²</strong> to the position <strong>Fâ€²</strong>, by which the cock <strong>D</strong> is closed, and
the cock <strong>F</strong> opened. The water in the tank flows through the
pipe <strong>E</strong> into the sea, air being admitted through the valve <strong>V</strong>,
placed at the top of the tank, opening inwards. A second ton
of brine is discharged by moving the lever back to the position
<strong>Dâ€²</strong>, and subsequently returning it to the position <strong>Fâ€²</strong>;
and in this way the brine is discharged ton by ton, until the
supply of water from the feed which replaces it has caused
both the balls in the indicator to sink to the bottom.</p>


<div class="ph3"><h3>(212.)</h3> A different method of preserving the requisite freshness
of the water in the boiler has been adopted by Messrs.
Maudslay and Field, and introduced with success into the Great
Western and other steam-vessels. Pumps called <em>brine-pumps</em>
are put into communication with the lower part of the boiler,
and so constructed as to draw the brine therefrom, and drive
it into the sea. These brine-pumps are worked by the engine,
and their operation is constant. The feed-pumps are
likewise worked by the engine, and they bear such a proportion
to the brine-pumps that the quantity of salt discharged
in a given time in the brine is equal to the quantity of salt
<a class="refpn" id="Pg457">[Pg457]</a>
introduced in solution by the water of the feed-pumps. By
this means the same actual quantity of salt is constantly
maintained in the boiler, and consequently the strength of
the solution remains invariable. If the brine discharged by
the brine-pumps contains
<span class="fraction"><sup>5</sup>â„<sub>32</sub></span> parts of salt while the water
introduced by the feed-pumps contains only
<span class="fraction"><sup>1</sup>â„<sub>32</sub></span> part, then
it is evident that five cubic feet of the feeding water will
contain no more salt than is contained in one cubic foot of
brine. Under such circumstances the brine-pumps would be
so constructed as to discharge
<span class="fraction"><sup>1</sup>â„<sub>5</sub></span> of the water introduced
by the feed-pumps, so that
<span class="fraction"><sup>4</sup>â„<sub>5</sub></span> of all the water introduced
into the boiler would be evaporated, and rendered available
for working the engine.</div>

<p>To save the heat of the brine, a method has been adopted
in the marine engines constructed by Messrs. Maudslay and
Field similar to one which has been long practised in steam-boilers,
and in various apparatus for the warming of buildings.
The current of heated brine is conducted from the
boiler through a tube which is contained in another, through
which the feed is introduced. The warm current of brine,
therefore, as it passes out, imparts a considerable portion of
its heat to the cold feed which comes in; and it is found
that by this expedient the brine discharged into the sea may
be reduced to a temperature of about 100Â°.</p>

<p>This expedient is so effectual that when the apparatus is
properly constructed, and kept in a state of efficiency, it may
be regarded as nearly a perfect preventive against the incrustation,
and the deposition of salt in the boilers, and is not
attended with any considerable waste of fuel.</p>


<div class="ph3"><h3>(213.)</h3> About the year 1776, Mr. Watt invented a tubular
condenser, with a view to condense the steam drawn off from
the cylinder without the process of injection. This apparatus
consisted of a number of small tubes connecting the top and
bottom of the condenser, arranged in a manner not very different
from that of the tubes which traverse the boiler of a
locomotive engine. These tubes were continually surrounded
by cold water, and the steam, as it escaped from the cylinder
passing through them, was condensed by their cold surfaces,
and collected in the form of water in a reservoir below, from
<a class="refpn" id="Pg458">[Pg458]</a>
whence it was drawn off by a pump in the same manner as
in engines which condensed by injection. One of the advantages
proposed by this expedient was, that no atmospheric
air would be introduced into the condenser, as is always the
case when condensation by injection is practised. Cold water,
which is injected, has always combined with it more or less
common air. When this water is mixed with the condensed
steam, the elevation of its temperature disengages the air
combined with it, and this air circulating to the cylinder,
vitiates the vacuum. One of the purposes for which the
air-pump in condensing steam-engines was provided, and
from which it took its name, was to draw off this air.
If, however, a tubular condenser could be made to act with
the necessary efficiency, no injection water would be introduced
for condensation, and the pump would have no other
duty except to remove the small quantity of water produced
by the condensed steam. That water being subsequently
carried back to the boiler by the feed-pumps, a constant
system of circulation would be maintained, and the boiler
would never require any fresh supply of water, except what
might be necessary to make good the waste by leakage and
other causes.</div>

<p>This contrivance has been of late years revived by Mr.
Samuel Hall of Basford, near Nottingham, with a view to
supersede in marine engines the necessity of using sea-water
in the boilers. Mr. Hall proposes to make marine boilers
with fresh water to condense the steam without injection, by
a tubulated condenser, and to provide by the distillation of
sea-water the small quantity of fresh water which would be
necessary to make good the waste. These condensers have
been introduced into several steam-vessels: in some they
have been continued, and in others abandoned, and various
opinions are entertained of their efficacy. I have not been
able to obtain the results of any satisfactory experiments on
them, and cannot therefore form a judgment of their usefulness.
Mr. Watt abandoned these condensers from finding
that the condensation of the steam was not sufficiently
sudden, and that consequently at the commencement of the
stroke the piston was subject to a resistance which
<a class="refpn" id="Pg459">[Pg459]</a>
injuriously diminished the amount of the moving power, whereas
condensation by jet was almost instantaneous, and the efficiency
of the piston throughout the entire stroke was more
uniform.</p>

<p>Mr. Watt also found that a fur collected around the tubes
of the condenser, so as to obstruct the free passage of heat
from the steam to the water of the cold cistern; and that,
consequently, the efficiency of the condenser was gradually
impaired, and could only be restored by frequent cleansing.</p>

<p>It is stated by Mr. Hall that a vacuum is preserved in his
condensers as perfect as that which is maintained in the
ordinary condensers by injection. It is objected, on the
other hand, that without the injection water and the air
which accompanies it being introduced into his condensers,
Mr. Hall uses as large and powerful an air-pump as those
which are used in engines of equal power condensing by
injection; that, consequently, the vacuum which is maintained
is produced, not as it ought to be altogether by the condensation
of steam, but by the air-pump drawing off the uncondensed
steam. To whatever extent this may be true, the
efficacy of the machine, as indicated by the barometer-gauge,
is only apparent; since as much power is necessary to pump
away any portion of uncondensed vapour as is obtained by
the vacuum produced by the absence of that vapour.</p>

<p>A tubular condenser of the form proposed by Mr. Hall is
represented in <a href="#Fig126"><i>fig.</i> 126.</a>; <i>a</i> is the upper part of the condenser
to which steam is admitted from the slide after having
worked the piston; <i>k</i> is the section of a thin plate, forming
the top of the condenser, perforated with small holes, in
which the tubes are inserted so as to be steam-tight and
water-tight. Water is admitted to flow around these tubes
between the top <i>k</i> and the bottom <i>d</i> of the condenser, so as
to keep them constantly at a low temperature. The steam
passes from <i>a</i> through the tubes to the lower chamber <i>f</i> of
the condenser, where it is reduced to water by the cold to
which it has been exposed. A supply of cold water is constantly
pumped through the condenser, so as to keep the tubes
at a low temperature. The air-pump <i>g</i> is of the usual construction,
having valves in the piston opening upwards, and
<a class="refpn" id="Pg460">[Pg460]</a>
similar valves in the cover of the pump also opening upwards.
The water formed by the condensed steam in <i>f</i> is drawn
through the foot-valve, and after passing through the piston-valves,
is discharged by the up-stroke of the piston into
the hot well. Any air, or other permanent gas, which may
be admitted by leakage through the tubes of the condenser,
or by any other means, is likewise drawn out by this pump,
and when drawn into the hot well is carried from thence to
the feeding apparatus of the boiler, to which it is transferred
by the feed-pump.</p>

<div class="figcenter" style="width: 465px;">
<a id="Fig126"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_482.png" width="465" height="395" alt="" />
<div class="caption figure">Fig. 126.</div>
</div>

<p>A provision is likewise made by which the steam escaping
at the safety-valve is condensed and carried away to the
feeding cistern.</p>

<div class="ph3"><h3>(214.)</h3> One of the remedies proposed for the evil consequences
arising from incrustation is the substitution of copper
for iron boilers. The attraction which produces the adhesion
of the calcareous matter held in solution by salt water to the
surface of iron has no existence in copper, and all the saline
and other alkaline matter precipitated in the boiling water in
<a class="refpn" id="Pg461">[Pg461]</a>
copper boilers is suspended in a loose form, and carried off
by the process of blowing out.</div>

<p>Besides the injury arising from the deposition of salt and
the incrustation on the inner surface of boilers, an evil of a formidable
kind attends the accumulation of soot mixed with salt
in the flues, which proceeds from the leaks. In the seams of the
boiler there are numerous apertures, of dimensions so small as
to be incapable of being rendered stanch by any practicable
means, through which the water within the boiler filters, and
the salt which it carries with it mixes with the soot, forming
a compound which rapidly corrodes the boilers. This process
of corrosion in the flues takes place not less in copper than in
iron boilers. In cleansing the flues of a copper boiler, the
salt and soot which was thrown out upon the iron-plates
which formed the flooring of the engine-room, having remained
there for some time, left behind it a permanent appearance
of copper on the iron flooring, arising from the
precipitation of the copper which had combined with the soot
and salt in the flues.<a name="FNanchor_36_36" id="FNanchor_36_36"></a><a href="#Footnote_36_36" class="fnanchor">[36]</a> In this case the leaks from whence
the salt proceeded were found, on careful examination, so unimportant,
that the usual means to stanch them could not
be resorted to without the risk of increasing the evil.</p>


<div class="ph3"><h3>(215.)</h3> In the application of the steam-engine to the propulsion
of vessels in voyages of great extent, the economy of fuel
acquires an importance greater than that which appertains to it
in land-engines, even in localities the most removed from coal-mines,
and where its expense is greatest. The practical limit to
steam-voyages being determined by the greatest quantity of
coals which a steam-vessel can carry, every expedient by which
the efficiency of the fuel can be increased becomes a means, not
merely of a saving of expense, but of an increased extension of
steam-power to navigation. Much attention has been bestowed
on the augmentation of the duty of engines in the mining
districts of Cornwall, where the question of their efficiency
is merely a question of economy, but far greater care should
be given to this subject when the practicability of maintaining
intercourse by steam between distant points of the globe
will perhaps depend on the effect produced by a given quantity
<a class="refpn" id="Pg462">[Pg462]</a>
of fuel. So long as steam-navigation was confined to
river and channel transport, and to coasting voyages, the
speed of the vessel was a paramount consideration, at whatever
expenditure of fuel it might be obtained; but since
steam-navigation has been extended to ocean-voyages, where
coals must be transported sufficient to keep the engine in
operation for a long period of time without a fresh relay,
greater attention has been bestowed upon the means of economising
it.</div>

<p>Much of the efficiency of fuel must depend on the management
of the fires, and therefore on the skill and care of
the stokers. Formerly the efficiency of firemen was determined
by the abundant production of steam, and so long as
the steam was evolved in superabundance, however it might
have blown off to waste, the duty of the stoker was considered
as well performed. The regulation of the fires
according to the demands of the engine were not thought of,
and whether much or little steam was wanted, the duty of
the stoker was to urge the fires to their extreme limit.</p>

<p>Since the resistance opposed by the action of the paddle-wheels
of a steam-vessel varies with the state of the weather,
the consumption of steam in the cylinders must undergo a
corresponding variation; and if the production of steam in
the boilers be not proportioned to this, the engines will
either work with less efficiency than they might do under
the actual circumstances of the weather, or more steam will
be produced in the boilers than the cylinders can consume,
and the surplus will be discharged to waste through the
safety-valves. The stokers of a marine engine, therefore,
to perform their duty with efficiency, and obtain from the
fuel the greatest possible effect, must discharge the functions
of a self-regulating furnace, such as has been already
described: they must regulate the force of the fires by the
amount of steam which the cylinders are capable of consuming,
and they must take care that no unconsumed fuel is
allowed to be carried away from the ash-pit.</p>


<div class="ph3"><h3>(216.)</h3> Until within a few years of the present time the heat
radiated from every part of the surface of the boiler was allowed
to go to waste, and to produce injurious effects on those parts
of the vessel to which it was transmitted. This evil,
<a class="refpn" id="Pg463">[Pg463]</a>
however, has been lately removed by coating the boilers, steam-pipes,
&#38;c. of steam-vessels with felt, by which the escape of
heat from the surface of the boiler is very nearly, if not altogether,
prevented. This felt is attached to the boiler-surface
by a thick covering of white and red lead. This expedient
was first applied in the year 1818 to a private steam-vessel
of Mr. Watt's called the <em>Caledonia</em>, and it was subsequently
adopted in another vessel, the machinery of which was constructed
at Soho, called the <i>James Watt</i>.</div>

<p>The economy of fuel depends in a considerable degree on
the arrangement of the furnaces, and the method of feeding
them. In general each boiler is worked by two or more furnaces
communicating with the same system of flues. While
the furnace is fed, the door being open, a stream of cold air
rushes in, passing over the burning fuel and lowering the
temperature of the flues: this is an evil to be avoided. But,
on the other hand, if the furnaces be fed at distant intervals,
then each furnace will be unduly heaped with fuel, a great
quantity of smoke will be evolved, and the combustion of the
fuel will be proportionally imperfect. The process of coking
in front of the grate, which would insure a complete combustion
of the fuel, has been already described (<a href="#h3-147">147</a>.). A
frequent supply of coals, however, laid carefully on the front
part of the grate, and gradually pushed backwards as each
fresh feed is introduced, would require the fire-door to be
frequently opened, and cold air to be admitted. It would
also require greater vigilance on the part of the stokers than
can generally be obtained in the circumstances in which they
work. In steam-vessels the furnaces are therefore fed less
frequently, fuel introduced in greater quantities, and a less
perfect combustion produced.</p>

<p>When several furnaces are constructed under the same
boiler, communicating with the same system of flues, the
process of feeding, and consequently opening one of them,
obstructs the due operation of the others, for the current of
cold air which is thus admitted into the flues checks the draft
and diminishes the efficiency of the furnaces in operation.
It was formerly the practice in vessels exceeding one hundred
horse-power, to place four furnaces under each boiler, communicating
with the same system of flues. Such an arrangement
<a class="refpn" id="Pg464">[Pg464]</a>
was found to be attended with a bad draft in the furnaces,
and therefore to require a greater quantity of heating surface
to produce the necessary evaporation. This entailed upon the
machinery the occupation of more space in the vessel in
proportion to its power; it has therefore been more recently
the practice to give a separate system of flues to each pair of
furnaces, or, at most, to every three furnaces. When three
furnaces communicate with a common flue, two will always
be in operation, while the third is being cleared out; but
if the same quantity of fire were divided among two furnaces,
then the clearing out of one would throw out of operation
half the entire quantity of fire, and during the process
the evaporation would be injuriously diminished. It is
found by experience, that the side plates of furnaces are
liable to more rapid destruction than their roofs, owing, probably,
to a greater liability to deposit. Furnaces, therefore,
should not be made narrower than a certain limit. Great
depth from front to back is also attended with practical inconvenience,
as it renders firing tools of considerable length,
and a corresponding extent of stoking room necessary. It
is recommended, by those who have had much practical experience
in steam-vessels, that furnaces six feet in depth from
front to back should not be less than three feet in width, to
afford means of firing with as little injury to the side plates
as possible, and of keeping the fires in the condition necessary
for the production of the greatest effect. The tops of
the furnaces almost never decay, and seldom are subject to
an alteration of figure, unless the level of the water be allowed
to fall below them.<a name="FNanchor_37_37" id="FNanchor_37_37"></a><a href="#Footnote_37_37" class="fnanchor">[37]</a></p>


<div class="ph3">
<h3>(217.)</h3> A form of marine engine was some years since proposed
and patented by Mr. Thomas Howard, possessing much
novelty and ingenuity, and having pretensions to a very
extraordinary economy of fuel, in addition to the advantages
claimed by Mr. Hall. In Mr. Howard's engines, the steam,
as in Mr. Hall's, is constantly reproduced from the same
water, so that pure or distilled water may be used; but
Mr. Howard dispenses altogether with the use of a boiler.</div>

<p>A quantity of mercury is placed in a shallow wrought-iron
vessel over a coke fire, by which it is maintained at a
<a class="refpn" id="Pg465">[Pg465]</a>
temperature varying from 400Â° to 500Â°. The surface exposed
to the fire was computed at three fourths of a square foot
for each horse-power. The upper surface of the mercury
was covered by a very thin plate of iron in contact with it,
and so contrived as to present about four times as much
surface as that exposed beneath the fire. Adjacent to this
a vessel of water was placed, maintained nearly at the boiling
point, and communicating by a nozzle and valve with the
chamber immediately above the mercury. At intervals corresponding
to the motion of the piston a small quantity of
water was injected from this vessel, and thrown upon the
plate of iron resting upon the hot mercury. From this it
received not only the heat necessary to convert it into
common steam, but to give it the qualities of highly superheated
steam. In fact, the steam thus produced had a temperature
considerably above that which corresponded to its
pressure, and was, therefore, capable of being deprived of
more or less of its heat without being condensed. (<a href="#h3-94">94</a>.)
The quantity of water injected into the steam-chamber was
regulated by the power at which the engine was intended to
be worked. The fire was supplied with air by a blower
subject to exact regulation. The steam thus produced was
conducted to a chamber surrounding the working cylinder,
and this chamber itself was enclosed by another space through
which the air from the furnace passed before it reached the
flue. By this contrivance the air imparted its redundant heat
to the steam, as the latter passed to the cylinder, and raised
its temperature to about 400Â°, the pressure, however, not exceeding
25 lbs. per square inch. The valves, governing the
admission of steam to the piston, were adapted for expansive
action.</p>

<p>The vacuum on the opposite side was maintained by condensation
in the following manner:â€”The condenser was a
copper vessel placed in a cistern of cold water, and the steam
was admitted to it from the cylinder by an eduction pipe in
the usual way. A jet was introduced from an adjacent vessel
filled with distilled water, and the condensing water and
condensed steam were pumped from the condenser as in
common engines. The warm water thus pumped out of the
<a class="refpn" id="Pg466">[Pg466]</a>
condenser was drawn through a copper worm, carried with
many coils through a cistern of cold water, so that when it
arrived at the end of this pipe it was reduced nearly to the
temperature of the atmosphere. The pipe was thus brought
to the vessel of distilled water already mentioned, and the
water supplied by it replaced. The water admitted to the
condenser through the condensing jet being purged of air,
a small air-pump was sufficient, since it had only to exhaust
the condenser and tubes at starting, and to remove the air
which might be admitted by leakage. Mr. Howard stated
that the condensation took place as rapidly and perfectly as
in the best engines of the common kind.</p>

<p>An engine of this construction was in the spring of 1835
placed in the government steamer called the <i>Comet</i>. It was
stated, that though the machinery was not advantageously
constructed, a part of the engine being old, and not made expressly
for a boiler of this kind, the vessel performed a
voyage from Falmouth to Lisbon, in which the consumption
of fuel did not exceed a third of her former consumption
when worked by Boulton and Watt's engines, the former consumption
of coals being about eight hundred pounds per hour,
and the consumption of Mr. Howard's engine being less than
two hundred and fifty pounds of coke per hour.</p>

<p>The advantages claimed for this contrivance were the following:
<em>first</em>, the small space and weight occupied by the
machinery, arising from the absence of a boiler; <em>second</em>, the
diminished consumption of fuel; <em>third</em>, the reduced size of
the flues; <em>fourth</em>, the removal of the injurious effects arising
from deposit and incrustation; <em>fifth</em>, the absence of smoke.</p>


<div class="ph3"><h3>(218.)</h3> The method by which the greatest quantity of practical
effect can be obtained from a given quantity of fuel must,
however, mainly depend on the extended application of the expansive
principle. This has been the means by which an extraordinary
amount of duty has been obtained from the Cornish
engines. The difficulty of the application of this principle in
marine engines has arisen from the objections entertained in
Europe to the use of steam of high pressure under the circumstances
in which the engine must be worked at sea. To apply
the expansive principle, it is necessary that the moving power at
the commencement of the stroke shall considerably exceed the
<a class="refpn" id="Pg467">[Pg467]</a>
resistance, its force being gradually attenuated till the completion
of the stroke, when it will at length become less than
the resistance. This condition may, however, be attained with
steam of limited pressure, if the engine be constructed with
a sufficient quantity of piston-surface. This method of rendering
the expansive principle available at sea, and compatible
with low-pressure steam, has recently been brought
into operation by Messrs. Maudslay and Field. Their improvement
consists in adapting two steam-cylinders in one
engine, in such a manner that the steam shall act simultaneously
on both pistons, causing them to ascend and descend
together. The piston-rods are both attached to the same
horizontal cross-head, whereby their combined action is applied
to one crank by means of a connecting rod placed
between the pistons.</div>

<div class="figcenter" style="width: 325px;">
<a id="Fig127"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_489.png" width="325" height="423" alt="" />
<div class="caption figure">Fig. 127.</div>
</div>

<p>A section of such an engine, made by a plane passing
through the two piston-rods <strong>P Pâ€²</strong> and cylinders, is represented
in <a href="#Fig127"><i>fig.</i> 127.</a> The piston-rods are attached to a cross-head <strong>C</strong>,
<a class="refpn" id="Pg468">[Pg468]</a>
which ascends and descends with them. This cross-head
drives upwards and downwards an axle <strong>D</strong>, to which the lower
end of the connecting rod <strong>E</strong> is attached. The other end of
the connecting rod drives the crank-pin <strong>F</strong>, and imparts revolution
to the paddle-shaft <strong>G</strong>. A rod <strong>H</strong> conveys motion by
means of a beam <strong>I</strong> to the rod <strong>K</strong> of the air-pump <strong>E</strong>.</p>


<div class="ph3"><h3>(219.)</h3> Connected with this, and in the same patent, another
improvement is included, consisting of the application of a hollow
wrought-iron framing carried across the vessel above the
machinery, to support the whole of the bearings of the crank-shaft.
A plan of this, including the cylinders and paddle-wheel,
is represented in <a href="#Fig128"><i>fig.</i> 128.</a> The advantages proposed
by these improvements are simplicity of construction, more
direct action on the crank, economy of space and weight of
material, combined with increased area of the piston, whereby
a given evaporating power of the boiler is rendered productive,
by extended application of the expansive principle, of a
greater moving power than in former arrangements. Consequently,
under like circumstances, greater power and economy
of fuel is obtained, with the further advantage at sea,
that when the engine is reduced in its speed, either by the
vessel being deeply laden with coal, as is the case at the commencement
of a long sea voyage, or by head winds, more
steam may be given to the cylinders, and consequently more
speed imparted to the vessel, all the steam produced in the
boiler being usefully employed.</div>


<div class="ph3"><h3>(220.)</h3> Another improvement, having the same objects, and
analogous to the preceding, has been likewise patented by
Messrs. Maudslay and Field. This consists in the adoption of
a cylinder of greater diameter, having two piston-rods <strong>P Pâ€²</strong>, as
represented in <a href="#Fig129"><i>fig.</i> 129.</a>, of considerable length, connected at
the top by a cross-head <strong>C</strong>. From this cross-head is carried
downwards the connecting rod <strong>D</strong>, which drives the crank-pin
<strong>E</strong>, and thereby works the paddle-shaft <strong>S</strong>. In this case the
paddle-shaft is extended immediately above the piston, and
the double piston-rod has sufficient length to be above the
paddle-shaft when the piston is at the bottom of its stroke.
This improvement is intended to be applied more particularly
for engines for river navigation, the advantages resulting from
<a class="refpn" id="Pg469">[Pg469]</a>
it being that a paddle-shaft placed at a given height from the
bottom of the vessel will be enabled to receive a longer stroke
of piston than by any other arrangement now in use. A more
<a class="refpn" id="Pg470">[Pg470]</a>
compact and firm connection of the cylinder with the crank-shaft
bearings is effected by it, and a cylinder of much greater
diameter may be applied by which the expansive action of
steam may be more fully brought into play; and a more direct
action of the steam-power on the crank with a less
weight of materials and a greater economy of space may be
obtained than by any of the arrangements of marine engines
hitherto used.</div>

<div class="figcenter" style="width: 465px;">
<a id="Fig128"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_491.png" width="465" height="747" alt="" />
<div class="caption figure">Fig. 128.</div>
</div>

<div class="figcenter" style="width: 306px;">
<a id="Fig129"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_492.png" width="306" height="464" alt="" />
<div class="caption figure">Fig. 129.</div>
</div>

<div class="ph3"><h3>(221.)</h3> Mr. Francis Humphrys has obtained a patent for a
form of marine engine, by which some simplification of the machinery
is attained, and the same power comprised within more
limited dimensions. In this engine there is attached to the
piston of the cylinder, instead of a piston-rod, a hollow casing
<strong>D D</strong> (<a href="#Fig130"><i>fig.</i> 130.</a>), which moves through a stuffing-box <strong>G</strong>, constructed
in a manner similar to the stuffing-box of a piston-rod.
In the figure, this casing is presented in section, but
<a class="refpn" id="Pg471">[Pg471]</a>
its form is that of a long narrow slit, or opening, rounded at
either end as exhibited in the plan (<i>fig.</i> 131) of the cylinder-cover.
The crank <strong>C</strong> is driven by the other end of the connecting
rod <strong>H</strong>, the crank-shaft being immediately
above the centre of the piston and the
connecting rod passing through the oblong
opening <strong>D</strong>, and descending into the hollow
piston-rod it is attached to an axis <strong>I</strong> at the
bottom of the piston. A box or cover <strong>K K</strong>
encloses the cross-piece or axis <strong>I</strong> with its bearings, and is
<a class="refpn" id="Pg472">[Pg472]</a>
attached so as to be steam-tight to the bottom of the piston.
A hollow space <strong>L L</strong> is cast in the bottom of the cylinder for
the reception of the box <strong>K K</strong>, when the piston is at the
bottom of the cylinder.</div>

<div class="figcenter" style="width: 478px;">
<a id="Fig130"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_493a.png" width="478" height="571" alt="" />
<div class="caption figure">Fig. 130.</div>
</div>

<div class="figleft" style="width: 108px;">
<a id="Fig131"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_493b.png" width="108" height="108" alt="" />
<div class="caption figure">Fig. 131.</div>
</div>

<p>By this arrangement the force by which the piston is driven
in its ascent and descent is communicated to the connecting
rod, not, as usual, through the intervention of a piston-rod,
but directly from the piston itself by the cross-pin <strong>I</strong>, and from
thence to the crank <strong>C</strong>, which it drives without the intervention
of beams, cross-heads, or any similar appendage.</p>

<p>The slide-valves regulating the admission and eduction of
steam are represented at <i>a</i>; the rod of the air-pump is shown
at <i>d</i>, being worked by a crank placed on the centre of the
great crank shaft.<a name="FNanchor_38_38" id="FNanchor_38_38"></a><a href="#Footnote_38_38" class="fnanchor">[38]</a></p>


<div class="ph3">
<h3>(222.)</h3> To obtain from the moving power its full amount of
mechanical effect in propelling the vessel, it would be necessary
that its force should propel, by constantly acting against
the water in a horizontal direction, and with a motion contrary
to the course of the vessel. No system of mechanical
propellers has, however, yet been contrived capable of perfectly
accomplishing this. Patents have been granted for
many ingenious mechanical combinations to impart to the
propelling surfaces such angles as appeared to the respective
contrivers most advantageous. In most of these the mechanical
complexity has formed a fatal objection. No part
of the machinery of a steam-vessel is so liable to become
deranged at sea as the paddle-wheels; and, therefore, that
simplicity of construction which is compatible with those
repairs which are possible on such emergencies is quite essential
for safe practical use.</div>

<div class="figcenter" style="width: 355px;">
<a id="Fig132"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_495.png" width="355" height="266" alt="" />
<div class="caption figure">Fig. 132.</div>
</div>

<p>The ordinary paddle-wheel, as has been already stated, is
a wheel revolving upon a shaft driven by the engine, and
carrying upon its circumference a number of flat boards,
called paddle-boards, which are secured by nuts and braces
in a fixed position; and that position is such that the planes
<a class="refpn" id="Pg473">[Pg473]</a>
of the paddle-boards diverge nearly from the centre of the
shaft on which the wheel turns. The consequence of this
arrangement is that each paddle-board can only act in that
direction which is most advantageous for the propulsion of
the vessel when it arrives near the lowest point of the wheel.
In <a href="#Fig132"><i>fig.</i> 132.</a> let O be the shaft on which the common paddle-wheel
revolves; the position of the paddle-boards are represented
at <strong>A</strong>, <strong>B</strong>, <strong>C</strong>, &#38;c.; <strong>X</strong>, <strong>Y</strong> represents the water line, the
course of the vessel being supposed to be from <strong>X</strong> to <strong>Y</strong>; the
arrows represent the direction in which the paddle-wheel
revolves. The wheel is immersed to the depth of the lowest
paddle-board, since a less degree of immersion would render
a portion of the surface of each paddle-board mechanically
useless. In the position <strong>A</strong> the whole force of the paddle-board
is efficient for propelling the vessel; but as the paddle
enters the water in the position <strong>H</strong>, its action upon the water,
not being horizontal, is only partially effective for propulsion:
a part of the force which drives the paddle is expended in
depressing the water, and the remainder in driving it contrary
to the course of the vessel, and, therefore, by its re-action
producing a certain propelling effect. The tendency, however,
of the paddle entering the water at <strong>H</strong>, is to form a
hollow or trough, which the water, by its ordinary property,
has a continual tendency to fill up. After passing the lowest
point <strong>A</strong>, as the paddle approaches the position <strong>B</strong>, where it
<a class="refpn" id="Pg474">[Pg474]</a>
emerges from the water, its action again becomes oblique,
a part only having a propelling effect, and the remainder
having a tendency to raise the water, and throw up a wave
and spray behind the paddle-wheel. It is evident that the
more deeply the paddle-wheel becomes immersed, the greater
will be the proportion of the propelling power thus wasted
in elevating and depressing the water; and if the wheel were
immersed to its axis, the whole force of the paddle-boards,
on entering and leaving the water, would be lost, no part of
it having a tendency to propel. If a still deeper immersion
take place, the paddle-boards above the axis would have a
tendency to retard the course of the vessel. When the vessel
is, therefore, in proper trim, the immersion should not exceed
nor fall short of the depth of the lowest paddle; but for
various reasons it is impossible in practice to maintain this
fixed immersion: the agitation of the surface of the sea,
causing the vessel to roll, will necessarily produce a great
variation in the immersion of the paddle-wheels, one becoming
frequently immersed to its axle, while the other is
raised altogether out of the water. Also the draught of
water of the vessel is liable to change, by the variation in her
cargo; this will necessarily happen in steamers which take
long voyages. At starting they are heavily laden with fuel,
which as they proceed is gradually consumed, whereby the
vessel is lightened.</p>


<div class="ph3"><h3>(223.)</h3> To remove this defect, and economise as much as
possible the propelling effect of the paddle-boards, it would
be necessary so to construct them that they may enter and
leave the water edgeways, or as nearly so as possible; such
an arrangement would be, in effect, equivalent to the process
called feathering, as applied to oars. Any mechanism which
would perfectly accomplish this would cause the paddles to
work in almost perfect silence, and would very nearly remove
the inconvenient and injurious vibration which is produced
by the action of the common paddles. But the construction
of feathering paddles is attended with great difficulty, under
the peculiar circumstances in which such wheels work. Any
mechanism so complex that it could not be easily repaired
when deranged, with such engineering implements and skill
<a class="refpn" id="Pg475">[Pg475]</a>
as can be obtained at sea, would be attended with great
objections; and the efficiency of its propelling action would
not compensate for the dangers which must attend upon
the helpless state of a steamer, deprived of her propelling
agents.</div>

<p>Feathering paddle-boards must necessarily have a motion
independently of the motion of the wheel, since any fixed
position which could be given to them, though it might be
most favourable to their action in one position would not be
so in their whole course through the water. Thus the paddle-board
when at the lowest point should be in a vertical position,
or so placed that its plane, if continued upwards, would
pass through the axis of the wheel. In other positions, however,
as it passes through the water, it should present its
upper edge, not towards the axle of the wheel, but towards a
point above the highest point of the wheel. The precise
point to which the edge of the paddle-board should be directed
is capable of mathematical determination. But it
will vary according to circumstances, which depend on the
motion of the vessel. The progressive motion of the vessel,
independently of the wind or current, must obviously be
slower than the motion of the paddle-boards round the axle
of the wheel; since it is by the difference of these velocities
that the re-action of the water is produced by which the
vessel is propelled. The proportion, however, between the
progressive speed of the vessel and the rotative speed of the
paddle-boards is not fixed: it will vary with the shape and
structure of the vessel, and with its depth of immersion;
nevertheless it is upon this proportion that the manner in
which the paddle-boards should shift their position must be
determined. If the progressive speed of the vessel were
nearly equal to the rotative speed of the paddle-boards, the
latter should so shift their position that their upper edges
should be presented to a point very little above the highest
point of the wheel. This is a state of things which could
only take place in the case of a steamer of a small draught of
water, shallop-shaped, and so constructed as to suffer little
resistance from the fluid. On the other hand, the greater
the depth of immersion, and the less fine the lines of the
<a class="refpn" id="Pg476">[Pg476]</a>
vessel, the greater will be the resistance in passing through
the water, and the greater will be the proportion which the
rotative speed of the paddle-boards will bear to the progressive
speed of the vessel. In this latter case the independent
motion of the paddle-boards should be such that their edges,
while in the water, shall be presented towards a point considerably
above the highest point of the paddle-wheel.</p>

<p>A vast number of ingenious mechanical contrivances have
been invented and patented for accomplishing the object just
explained. Some of these have failed from the circumstance
of their inventors not clearly understanding what precise
motion it was necessary to impart to the paddle-board: others
have failed from the complexity of the mechanism by which
the desired effect was produced.</p>


<div class="ph3">
<h3>(224.)</h3> In the year 1829 a patent was granted to Elijah Galloway
for a paddle-wheel with movable paddles, which patent
was purchased by Mr. William Morgan, who made various
alterations in the mechanism, not very materially departing
from the principle of the invention.</div>

<div class="figcenter" style="width: 514px;">
<a id="Fig133"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_499.png" width="514" height="398" alt="" />
<div class="caption figure">Fig. 133.</div>
</div>

<p>This paddle-wheel is represented in <a href="#Fig133"><i>fig.</i> 133.</a> The contrivance
may be shortly stated to consist in causing the wheel
which bears the paddles to revolve on one centre, and the
radial arms which move the paddles to revolve on another
centre. Let <strong>A B C D E F G H I K L</strong> be the polygonal circumference
of the paddle-wheel, formed of straight bars, securely
connected together at the extremities of the spokes or radii
of the wheel which turns on the shaft which is worked by the
engine; the centre of this wheel being at <strong>O</strong>. So far this
wheel is similar to the common paddle-wheel; but the paddle-boards
are not, as in the common wheel, fixed at <strong>A B C</strong>, &#38;c.,
so as to be always directed to the centre <strong>O</strong>, but are so placed
that they are capable of turning on axles which are always
horizontal, so that they can take any angle with respect to
the water which may be given to them. From the centres,
or the line joining the pivots on which these paddle-boards
turn, there proceed short arms <strong>K</strong>, firmly fixed to the paddle-boards
at an angle of about 120Â°. On a motion given to this
arm <strong>K</strong>, it will therefore give a corresponding angular motion
to the paddle-board, so as to make it turn on its pivots. At
<a class="refpn" id="Pg477">[Pg477]</a>
the extremities of the several arms marked <strong>K</strong> is a pin or pivot,
to which the extremities of the radial arms <strong>L</strong> are severally
attached, so that the angle between each radial arm <strong>L</strong> and the
short paddle-arm <strong>K</strong> is capable of being changed by any motion
imparted to <strong>L</strong>; the radial arms are connected at the other
end with a centre, round which they are capable of revolving.
Now, since the points <strong>A B C</strong>, &#38;c., which are the pivots on
which the paddle-boards turn, are moved in the circumference
of a circle, of which the centre is <strong>O</strong>, they are always at the
same distance from that point; consequently they will continually
vary their distance from the other centre <strong>P</strong>. Thus,
when a paddle-board arrives at that point of its revolution at
which the centre round which it revolves lies precisely between
it and the centre <strong>O</strong>, its distance from the former centre
is less than in any other position. As it departs from that
point, its distance from that centre gradually increases until it
arrives at the opposite point of its revolution, where the
centre <strong>O</strong> is exactly between it and the former centre; then the
distance of the paddle-board from the former centre is greatest.
<a class="refpn" id="Pg478">[Pg478]</a>
This constant change of distance between each paddle-board
and the centre <strong>P</strong> is accommodated by the variation of the angle
between the radial arm <strong>L</strong> and the short paddle-board arm <strong>K</strong>;
as the paddle-board approaches the centre <strong>P</strong> this gradually
diminishes; and as the distance of the paddle-board increases,
the angle is likewise augmented. This change in the magnitude
of the angle, which thus accommodates the varying position
of the paddle-board with respect to the centre <strong>P</strong>, will be
observed in the figure. The paddle-board <strong>D</strong> is nearest to <strong>P</strong>;
and it will be observed that the angle contained between <strong>L</strong>
and <strong>K</strong> is there very acute; at <strong>E</strong> the angle between <strong>L</strong> and <strong>K</strong>
increases, but is still acute; at <strong>G</strong> it increases to a right angle;
at <strong>H</strong> it becomes obtuse; and at <strong>K</strong>, where it is most distant
from the centre <strong>P</strong>, it becomes most obtuse. It again diminishes
at <strong>K</strong>, and becomes a right angle between <strong>A</strong> and <strong>B</strong>. Now
this continual shifting of the direction of the short arm <strong>K</strong> is
necessarily accompanied by an equivalent change of position
in the paddle-board to which it is attached; and the position
of the second centre <strong>P</strong> is, or may be, so adjusted that this
paddle-board, as it enters the water and emerges from it, shall
be such as shall be most advantageous for propelling the
vessel, and therefore attended with less of that vibration
which arises chiefly from the alternate depression and elevation
of the water, owing to the oblique action of the paddle-boards.</p>


<div class="ph3"><h3>(225.)</h3> In the year 1833, Mr. Field, of the firm of Maudslay
and Field, constructed a paddle-wheel with fixed paddle-boards,
but each board being divided into several narrow slips arranged
one a little behind the other, as represented in <i>fig.</i>
134. These divided boards he proposed to arrange in such
cycloidal curves that they must all enter the water at the
same place in immediate succession, avoiding the shock produced
by the entrance of the common board. These split
paddle-boards are as efficient in propelling when at the lowest
point as the common paddle-boards, and when they emerge
the water escapes simultaneously from each narrow board,
and is not thrown up, as is the case with common paddle-boards.<a name="FNanchor_39_39" id="FNanchor_39_39"></a><a href="#Footnote_39_39" class="fnanchor">[39]</a></div>

<div class="figcenter" style="width: 345px;">
<a id="Fig134"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_501.png" width="345" height="328" alt="" />
<div class="caption figure">Fig. 134.</div>
</div>

<p><a class="refpn" id="Pg479">[Pg479]</a>
 The theoretical effect of this wheel is the same as that of
the common wheel, and experience alone, the result of
which has not yet been obtained, can prove its efficiency.
The number of bars, or separate parts into which each
paddle-board is divided, has been very various. When
first introduced by Mr. Galloway each board was divided
into six or seven parts: this was subsequently reduced,
and in the more recent wheels of this form constructed
for the government vessels the paddle-boards consist only
of two parts, coming as near to the common wheel as is
possible, without altogether abandoning the principle of the
split paddle.</p>


<div class="ph3"><h3>(226.)</h3> To obtain an approximate estimate of the extent
to which steam-power is applicable to long sea-voyages, it
would be necessary to investigate the mutual relation which,
in the existing state of this application of steam-power,
exists between the capacity or tonnage of the vessel, the
magnitude, weight, and power, of the machinery, the available
stowage for fuel, and the average speed attainable in all
<a class="refpn" id="Pg480">[Pg480]</a>
weathers, as well as the general purposes to which the vessel
is to be appropriated, whether for the transport of goods or
merchandise, or merely for despatches and passengers, or for
both of these combined. That portion of the capacity of the
vessel which is appropriated to the moving power consists of
the space occupied by the machinery and the fuel. The
distribution of it between these must mainly depend on the
length of the voyage which the vessel must make without
receiving a fresh supply of coals. If the trips be short, and
frequent relays of fuel can be obtained, then the space
allotted to the machinery may bear a greater proportion to
that assigned to the fuel; but in proportion as each uninterrupted
stage of the voyage is increased, a greater stock of
coals will be necessary, and a proportionally less space left
for the machinery. Other things being the same, therefore,
steam-vessels intended for long sea-voyages must be less
powerful in proportion to their tonnage.</div>

<p>It will be apparent that every improvement which takes
place in the application of the steam-engine to navigation
will modify all these data on which such an investigation
must depend. Every increased efficiency of fuel, from
whatever cause it may be derived, will either increase the
useful tonnage of the vessel, or increase the length of the
voyage of which it is capable. Various improvements have
been and are still in progress, by which this efficiency has
undergone continual augmentation, and voyages may now be
accomplished with moderate economy and profit, to which a
few years since marine engines could not be applied with
permanent advantage. The average speed of steam-vessels
has also undergone a gradual increase by such improvements.
During the four years ending June, 1834, it was found that
the average rate of steaming obtained from fifty-one voyages
made by the Admiralty steamers between Falmouth and
Corfu, exclusive of stoppages, was seven miles and a quarter
an hour direct distance between port and port. The vessels
which performed this voyage varied from 350 to 700 tons
measured burden, and were provided with engines varying
from 100 to 200 horse-power, with stowage for coals varying
from 80 to 240 tons. The proportion of the power to the
<a class="refpn" id="Pg481">[Pg481]</a>
tonnage varied from one horse to three tons to one horse to
four tons. Thus the <strong class="m1">Messenger</strong> had a power of 200 horses
and measured 730 tons; the <strong class="m1">Flamer</strong> had a power of 120
horses, and measured 500 tons; the <strong class="m1">Columbia</strong> had a power
of 120 horses, and measured 360 tons. In general it may
be assumed that for the shortest class of trips, such as those
of the Channel steamers, the proportion of the power to the
tonnage should be about one horse for every two tons; but
for the longer class of voyages, the proportion of power to
tonnage should be about one horse-power to from three to
four tons measured tonnage. These data, however, must be
received as very rough approximations, subject to considerable
modifications in their application to particular vessels.
We have already stated that the nominal horse-power is
itself extremely indefinite; and if, as is now customary in
the longer class of voyages, the steam be worked expansively,
then the nominal power almost ceases to have any
definite relation to the actual performance of the vessel.
It is usual to calculate the horse-power by assuming a uniform
pressure of steam upon the piston, and, consequently,
by excluding the consideration of the effect of expansion.
The most certain test of the amount of mechanical power
exerted by the machinery would be obtained from the quantity
of water actually transmitted in the form of steam from
the boiler to the cylinder. But the effect of this would also
be influenced by the extent to which the expansive principle
has been brought into operation.</p>

<p>From the reported performances of the larger class of
steam-ships within the last few years, it would appear that
the average speed has been increased since the estimate
above mentioned, which was obtained in 1834; and on comparing
the consumption of fuel with the actual performance,
it would appear that the efficiency of fuel has also been considerably
augmented. No extensive course of accurate
experiments or observations have, however, been obtained
from which correct inferences may be drawn of the probable
limits to which steam-navigation, in its present state, is
capable of being extended. The jealousy of rival companies
has obstructed the inquiries of those who, solicitous more
<a class="refpn" id="Pg482">[Pg482]</a>
for the general advancement of the art than for the success
of individual enterprises, have directed their attention to
this question; and it is hardly to be expected that sufficiently
correct and extensive data can be obtained for this
purpose.</p>


<div class="ph3"><h3>(227.)</h3> Increased facility in the extension and application of
steam-navigation is expected to arise from the substitution of
iron for wood, in the construction of vessels. Hitherto iron
steamers have been chiefly confined to river-navigation; but
there appears no sufficient reason why their use should be
thus limited. For sea-voyages they offer many advantages;
they are not half the weight of vessels of equal tonnage constructed
of wood; and, consequently, with the same tonnage
they will have less draught of water, and therefore less resistance
to the propelling power; or, with the same draught of
water and the same resistance, they will carry a proportionally
heavier cargo. The nature of their material renders
them more stiff and unyielding than timber; and they do not
suffer that effect which is called <em>hogging</em>, which arises from a
slight alteration which takes place in the figure of a timber
vessel in rolling, accompanied by an alternate opening and
closing of the seams. Iron vessels have the further advantage
of being more proof against fracture upon rocks. If a
timber vessel strike, a plank is broken, and a chasm opened
in her many times greater than the point of rock which produces
the concussion. If an iron vessel strike, she will either
merely receive a dinge, or be pierced by a hole equal in size
to the point of rock which she encounters. Some examples
of the strength of iron vessels were given by Mr. Macgregor
Laird, in his evidence before the Committee of the Commons
on Steam Navigation, among which the following may be
mentioned:â€”An iron vessel, called the <strong class="m1">Alburkah</strong>, in one
of their experimental trials got aground, and lay upon her
anchor: in a wooden vessel the anchor would probably have
pierced her bottom; in this case, however, the bottom was
only dinged. An iron vessel, built for the Irish Inland Navigation
Company, was being towed across Lough Derg in a
gale of wind, when the towing rope broke, and she was driven
upon rocks, on which she bumped for a considerable time
<a class="refpn" id="Pg483">[Pg483]</a>
without any injury. A wooden vessel would in this case
have gone to pieces. A further advantage of iron vessels
(which in warm climates is deserving of consideration) is their
greater coolness and perfect freedom from vermin.</div>

<p>Iron steam-vessels on a very large scale are now in preparation
in the ports of Liverpool and Bristol, intended for
long sea-voyages. The largest vessel of this description
which has yet been projected is stated to be in preparation
for the voyage between Bristol and New York, by the company
who have established the steam-ship called the Great
Western, plying between these places.</p>

<p>Several projects for the extension of steam-navigation to
voyages of considerable length have lately been entertained
both by the public and by the legislature, and have imparted
to every attempt to improve steam-navigation increased interest.
A committee of the House of Commons collected evidence
and made a report in the last session in favour of an
experiment to establish a line of steam-communication between
Great Britain and India. Two routes have been suggested
by the committee, each being a continuation of the
line of Admiralty steam-packets already established to Malta
and the Ionian Isles. One of the routes proposed is through
Egypt, the Red Sea, and across the Indian Ocean to Bombay,
or some of the other presidencies; the other across the north
part of Syria to the banks of the Euphrates, by that river to
the Persian Gulf, and from thence to Bombay. Each of
these routes will be attended with peculiar difficulties, and in
both a long sea-voyage will be encountered.</p>

<p>In the route by the Red Sea it is proposed to establish
steamers between Malta and Alexandria (eight hundred and
sixty miles). A steamer of four hundred tons' burden and
one hundred horse-power would perform this voyage, upon
an average of all weathers incident to the situation, in from
five to six days, consuming ten tons of coal per day. But it
is probable that it might be found more advantageous to
establish a higher ratio between the power and the tonnage.
From Alexandria the transit might be effected by land across
the isthmus to Suezâ€”a journey of from four to five daysâ€”by
caravan and camels; or the transit might be made either
<a class="refpn" id="Pg484">[Pg484]</a>
by land or water from Alexandria to Cairo, a distance of one
hundred and seventy-three miles; and from Cairo to Suez,
ninety-three miles, across the desert, in about five days. At
Suez would be a station for steamers, and the Red Sea would
be traversed in three runs or more. If necessary, stations for
coals might be established at Cosseir, Judda, Mocha, and
finally at Aden or at Socatraâ€”an island immediately beyond
the mouth of the Red Sea, in the Indian Ocean; the run
from Suez to Cosseir would be three hundred milesâ€”somewhat
more than twice the distance from Liverpool to Dublin.
From Cosseir to Judda, four hundred and fifty miles; from
Judda to Mocha, five hundred and seventeen miles; and from
Mocha to Socatra, six hundred and thirty-two miles. It is
evident that all this would, without difficulty, in the most
unfavourable weather, fall within the present powers of
steam-navigation. If the terminus of the passage be Bombay,
the run from Socatra to Bombay will be twelve hundred
miles, which would be from six to eight days' steaming.
The whole passage from Alexandria to Bombay, allowing
three days for delay between Suez and Bombay, would be
twenty-six days: the time from Bombay to Malta would
therefore be about thirty-three days; and adding fourteen
days to this for the transit from Malta to England, we should
have a total of forty-seven days from London to Bombay, or
about seven weeks.</p>

<p>If the terminus proposed were Calcutta, the course from
Socatra would be one thousand two hundred and fifty miles
south-east to the Maldives, where a station for coals would
be established. This distance would be equal to that from
Socatra to Bombay. From the Maldives, a run of four
hundred miles would reach the southern point of Ceylon,
called the Point de Galle, which is the best harbour (Bombay
excepted) in British India: from the Point de Galle, a run
of six hundred miles will reach Madras, and from Madras to
Calcutta would be a run of about six hundred miles. The
voyage from London to Calcutta would be performed in about
sixty days.</p>

<p>At a certain season of the year there exists a powerful
physical opponent to the transit from India to Suez: from
<a class="refpn" id="Pg485">[Pg485]</a>
the middle of June until the end of September, the south-west
monsoon blows with unabated force across the Indian
Ocean, and more particularly between Socatra and Bombay.
This wind is so violent as to leave it barely possible for the
most powerful steam-packet to make head against it, and the
voyage could not be accomplished without serious wear and
tear upon the vessels during these months.</p>

<p>The attention of parliament has therefore been directed to
another line of communication, not liable to this difficulty: it
is proposed to establish a line of steamers from Bombay
through the Persian Gulf to the Euphrates.</p>

<p>The run from Bombay to a place called Muscat, on the
southern shore of the gulf, would be eight hundred and forty
miles in a north-west direction, and therefore not opposed to
the south-west monsoon. From Muscat to Bassidore, a point
upon the northern coast of the strait at the mouth of the
Persian Gulf, would be a run of two hundred and fifty-five
miles; from Bassidore to Bushire, another point on the eastern
coast of the Persian Gulf, would be a run of three hundred
miles; and from Bushire to the mouth of the Euphrates,
would be one hundred and twenty miles. It is evident that
the longest of these runs would offer no more difficulty than
the passage from Malta to Alexandria. From Bussora, near
the mouth of the Euphrates, to Bir, a town upon its left
bank near Aleppo, would be one thousand one hundred and
forty-three miles, throughout which there are no physical obstacles
to the river-navigation which may not be overcome.
Some difficulties arise from the wild and savage character of
the tribes who occupy its banks. It is, however, thought
that by proper measures, and securing the co-operation of the
pacha of Egypt, any serious obstruction from this cause may
be removed. From Bir, by Aleppo, to Scanderoon, a port
upon the Mediterranean, opposite Cyprus, is a land-journey,
said to be attended with some difficulty, but not of great
length; and from Scanderoon to Malta is about the same
distance as between the latter place and Alexandria. It is
calculated that the time from London to Bombay by the
Euphratesâ€”supposing the passage to be successfully
<a class="refpn" id="Pg486">[Pg486]</a>
establishedâ€”would be a few days shorter than by Egypt and the
Red Sea.</p>

<p>Whichever of these courses may be adopted, it is clear that
the difficulties, so far as the powers of the steam engine are
concerned, lie in the one case between Socatra and Bombay,
or between Socatra and the Maldives, and in the other case
between Bombay and Muscat. This, however, has already
been encountered and overcome on four several voyages by
the <strong class="m1">Hugh Lindsay</strong> steamer from Bombay to Suez: that
vessel encountered a still longer run on these several trips, by
going, not to Socatra, but to Aden, a point on the coast of
Arabia, near the Straits of Babel Mandeb, being a run of one
thousand six hundred and forty-one miles, which she performed
in ten days and nineteen hours. The same trip has
since been repeatedly made by other steamers; and, in the
present improved state of steam navigation, no insurmountable
obstacles are opposed to their passage.</p>

<div class="figcenter" style="width: 448px;">
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_508.png" width="448" height="350" alt="" />
</div>

<div class="footnotes"><h3>FOOTNOTES:</h3>

<div class="footnote">

<p><a name="Footnote_35_35" id="Footnote_35_35"></a><a href="#FNanchor_35_35"><span class="label">[35]</span></a> This cut is taken from the plate of the engine of the Red Rover, manufactured
by Boulton and Watt, given in the last edition of <cite>Tredgold on
the Steam Engine</cite>.</p></div>

<div class="footnote">

<p><a name="Footnote_36_36" id="Footnote_36_36"></a><a href="#FNanchor_36_36"><span class="label">[36]</span></a> Appendix I., <cite>on Marine Boilers, by J. Dinnen; Tredgold on the Steam
Engine</cite>, second edition.</p></div>

<div class="footnote">

<p><a name="Footnote_37_37" id="Footnote_37_37"></a><a href="#FNanchor_37_37"><span class="label">[37]</span></a> <cite>Tredgold on the Steam Engine</cite>, Appendix, I. p. 171.</p></div>

<div class="footnote">

<p><a name="Footnote_38_38" id="Footnote_38_38"></a><a href="#FNanchor_38_38"><span class="label">[38]</span></a> Engines on a very large scale constructed upon this principle are
said to be in process of construction for an iron steam-vessel of great tonnage,
which is in preparation for the New York passage. It is said that
the cylinders of these engines will be one hundred and twenty inches in
diameter.</p></div>

<div class="footnote">

<p><a name="Footnote_39_39" id="Footnote_39_39"></a><a href="#FNanchor_39_39"><span class="label">[39]</span></a> A patent was subsequently taken out for these by Mr. Galloway. Mr.
Field did not persevere in its use at the time he invented it. It has,
however, been more generally adopted since the date of Galloway's
patent.</p></div></div>

<div class="figcenter" style="width: 462px;">
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_509.png" width="462" height="369" alt="" />
</div>

<h2><a name="CHAP_XIV" id="CHAP_XIV">CHAP. XIV.</a></h2>

<p class="fsize2 center">AMERICAN STEAM NAVIGATION.</p>

<p class="right"><a class="refpn" id="Pg487">[Pg487]</a><br />
<a href="#CONTENTS"><small>TOC</small></a>&#160;&#160;<a
href="#INDEX"><small>INX</small></a></p>

<div class="chapheader">
STEAM NAVIGATION FIRST ESTABLISHED IN AMERICA.â€”CIRCUMSTANCES
WHICH LED TO IT.â€”FITCH AND RUMSEY.â€”STEVENS OF HOBOKEN.â€”LIVINGSTONE
AND FULTON.â€”EXPERIMENTS ON THE SEINE.â€”FULTON'S
FIRST BOAT.â€”THE HUDSON NAVIGATED BY STEAM.â€”EXTENSION
AND IMPROVEMENT OF RIVER NAVIGATION.â€”SPEED OF AMERICAN
STEAMERS.â€”DIFFERENCE BETWEEN THEM AND EUROPEAN STEAMERS.â€”SEA-GOING
AMERICAN STEAMERS.â€”AMERICAN PADDLE-WHEELS.â€”LAKE
STEAMERS.â€”THE MISSISIPPI AND ITS TRIBUTARIES.â€”STEAMERS
NAVIGATING IT.â€”THEIR STRUCTURE AND MACHINERY.â€”NEW ORLEANS
HARBOUR.â€”STEAM TUGS.</div>

<div class="ph3fst"><h3>(228.)</h3> The credit of having afforded the first practical
solution of the problem to apply the steam engine to the
propulsion of ships, undoubtedly belongs to the people of
the United States of America. The geographical character
of their vast country, not less than the sanguine and enterprising
spirit of the nation, contributed to this. A coast of
four thousand miles in extent, stretching from the Gulf of St.
Lawrence to the embouchures of the Mississippi, indented and
<a class="refpn" id="Pg488">[Pg488]</a>
serrated in every part with natural harbours and sheltered
bays, and fringed with islands forming soundsâ€”capes, and
promontories enclosing arms of the sea, in which the waters
are free from the roll of the ocean, and take the placid
character of lakes,â€”rivers of imposing magnitude, navigable
for vessels of the largest class, for many hundreds and
in some instances for many thousands of miles, affording
access to the innermost population of an empire, whose area
vastly exceeds the whole European continent,â€”chains of
lakes composed of the most extensive bodies of fresh water
in the known world,â€”and this extensive continent peopled
by races carrying with them the habits and feelings together
with much of the skill and knowledge of the most civilized
parts of the globe, endowed also with that inextinguishable
spirit of enterprise which ever belongs to an emigrant
people,â€”form a combination of circumstances more than
sufficient to account for the fact of this nation snatching
from England, the parent of the steam engine, the honour
of first bringing into practical operation one of the most
importantâ€”if indeed it be not altogether the most importantâ€”of
the many applications of that machine to the uses
of life.</div>

<p>The circumstances which rendered these extensive tracts
of inland and coast navigation eminently suited to the
application of steam power, formed so many obstructions
and difficulties to the application of other more ordinary
means of locomotion on water. The sheltered bays and
sounds which offered a smooth and undisturbed surface to
the action of the infant steamer argued the absence of that
element which gave effect to the sails and rigging of the
wind-propelled ship, and the rapid currents of the gigantic
streams formed by the drainage of this great continent,
though facilitating access to the coast, rendered the oar
powerless in the ascent.</p>


<div class="ph3"><h3>(229.)</h3> The first great discovery of Watt had scarcely
been realized in practice by the construction of the single-acting
steam-engine, when the speculative and enterprising
Americans conceived the project of applying it as a moving
power in their inland navigation. So early as the year 1783
<a class="refpn" id="Pg489">[Pg489]</a>
Fitch and Rumsey made attempts to apply the single-acting
engine to the propulsion of vessels, and their failure is said
to have arisen more from the inherent defects of that
machine in reference to this application of it, than from
any want of ingenuity or mechanical skill on their parts.
In 1791, John Stevens of Hoboken commenced his experiments
on steam navigation, which were continued for
sixteen years; during a part of this period he was assisted
by Livingstone (who was subsequently instrumental in advancing
the views of Fulton), and by Roosevelt. These
projectors had, at that time also, the assistance and advice
of Brunel, since so celebrated for the invention of the block
machinery, and the construction of the Thames Tunnel.
Their proceedings were interrupted by the appointment of
Livingstone as American Minister at Paris, under the Consular
Government.</div>

<p>At Paris, Livingstone met Fulton, who had been previously
engaged in similar speculations, and being struck with his
mechanical skill, and the soundness of his views, joined him
in causing a series of experiments to be made, which were
accordingly carried on at PlombiÃ¨res, and subsequently on a
still more extensive scale on the Seine, near Paris. Having
by this course of experiments obtained proofs of the efficiency
of Fulton's projects, sufficient to satisfy the mind of
Livingstone, he agreed to obtain for Fulton the funds necessary
to construct a steam boat on a large scale, to be worked
upon the Hudson. It was decided, in order to give the project
the best chance of success, to obtain the machinery from
Bolton and Watt. In 1803, Fulton accordingly made drawings
of the engines intended for this first steamer, which were
sent to Soho, with an order for their construction. Fulton,
meanwhile, repaired to America, to superintend the construction
of the boat. The delays incidental to these proceedings
retarded the completion of the boat and machinery
until the year 1807, when all was completed, and the first
successful experiment made at New York. The vessel
was placed, for regular work, to ply between New York and
Albany, in the beginning of 1808; and, from that time to
the present, this river has been the theatre of the most
<a class="refpn" id="Pg490">[Pg490]</a>
remarkable series of experiments on locomotion on water
which has ever been presented in the history of navigation.</p>


<div class="ph3">
<h3>(230.)</h3> The form and arrangement of this first marine
engine was, in many respects, similar to that which is still
generally used for marine purposes. The cold water cistern
was abandoned, and an increased condensing power obtained
by enlarging the condenser. It was usual to make the condenser
half the diameter of the cylinder, and half its length,
and therefore one eighth of its capacity. The condenser, however,
was now made of the same diameter as the cylinder, being
still half its length; its capacity therefore, instead of being only
an eighth, was half of the cylinder; the condensing jet was
admitted by a pipe passing through the bottom of the vessel.
As in the present marine engines, two working beams were
provided, one at either side of the cylinder; but in order to
provide against the difficulties which might arise in the
adaptation of machinery made at Birmingham to a vessel
made at New York, beams were constructed in the form of
an inverted â”», the working arms being twofold, one horizontal
and the other vertical, so that the connecting rod
might be carried from the crank, either downwards, to the
end of the horizontal arm, or horizontally, to the end of the
vertical arm. In fact there was a choice, to use either a
straight beam, or a bell-crank. The latter was that which was
adopted in this instance. The paddle-shaft, driven by the
crank, passed across the vessel, and had the paddle-wheels
keyed upon it as at present; and in order to equalise the
effect of the engine spur wheels were also placed on the
paddle-shaft, by which pinions were driven, placed upon
an axle, which carried a fly-wheel.</div>

<p>The speed attained by this steam boat, when it first began
to ply upon the river, did not exceed four miles an hour, but by
a series of improvements its rate of motion was soon increased
to six miles an hour. In the steam boats subsequently constructed
by Fulton a greater speed was attained; but in the
latest vessels built by him he did not exceed a speed of
nine miles an hour, which he considered to be the greatest that
could be advantageously obtained.</p>

<p>While Fulton was making his plans, and engaged in the
<a class="refpn" id="Pg491">[Pg491]</a>
construction of his first boat, Mr. Stevens of Hoboken,
already mentioned, was engaged in a like project, and completed
a vessel, to be propelled by a steam engine, within a
few weeks after the first successful voyage of Fulton.
Stevens was likewise completely successful; but the exclusive
privilege of navigating the Hudson by steam having been
granted to Fulton by an act of Congress, Stevens was compelled
to select another theatre for his operations, and he
accordingly sent his steam boat by sea to Philadelphia, to
navigate the Delaware, thus securing for himself the honour
of having made the first sea voyage by steam.</p>

<p>Fulton did not long retain the monopoly of the steam
navigation of the Hudson. Fortunately for the progress of
steam navigation, the act conferring upon him that privilege
was declared unconstitutional; and the navigation of that
noble river was thrown open to the spirit and enterprise of
American genius. The number of passengers conveyed upon
it became enormous beyond all precedent, and inducements
of the strongest kind were accordingly held out to the improvement
of its navigation. The distance between New York and
Albany, ascertained by a late survey to be one hundred and
twenty-five geographical miles by water, had been performed by
Fulton's boats occasionally in fifteen or sixteen hours, being at
the rate of about eight miles an hour, including stoppages. It
became a great object to increase the speed of this trip, so that
it might at all times of the year be performed between sunrise
and sunset. Robert L. Stevens, the son of the person of that
name already mentioned, immediately after the abolition of
Fulton's monopoly, placed on the river a vessel which had been
built for the Delaware, which easily performed the passage in
twelve hours, being at the rate of nearly ten and a half geographical
miles an hour. By this increase of speed the improved
boats so entirely monopolised the day work upon the river, that
the former steamers were either converted into steam tugs
to draw barges laden with goods, or used for night trips between
New York and Albany. In the night trips the saving
of one or two hours was immaterial, it being sufficient that
the vessel which left the one port at night should reach the
other in the morning.
<a class="refpn" id="Pg492">[Pg492]</a></p>

<p>The river Hudson rises near Lake Champlain, the easternmost
of the great chain of lakes or inland seas which extend
from east to west across the northern boundary of the United
States. The river follows nearly a straight course southwards
for two hundred and fifty miles, and empties itself into the sea
at New York. The influence of the tide is felt as far as Albany,
above which the stream begins to contract. Although this river
in magnitude and extent is by no means equal to several others
which intersect the States, it is nevertheless rendered an
object of great interest by reason of the importance and
extent of its trade. The produce of the state of New York
and that of the banks of the great Lakes Ontario and Erie
are transported by it to the capital; and one of the most
extensive and populous districts of the United States is supplied
with the necessary imports by its waters. A large fleet
of vessels is constantly engaged in its navigation; nor is the
tardy but picturesque sailing vessel as yet excluded by the
more rapid steamers. The current of the Hudson is said to
average nearly three miles an hour; but as the ebb and flow
of the tide are felt as far as Albany, the passage of the
steamers between that place and New York may be regarded
as equally affected by currents in both directions, or nearly
so. The passage therefore, whether in ascending or descending
the river, is made nearly in the same time.</p>


<div class="ph3"><h3>(231.)</h3> The prevalence of smooth water navigation, whether
on the surfaces of rivers or in sheltered bays and sounds, has
invested the problem of steam navigation in America with
conditions so entirely distinct and different from those under
which the same problem presents itself to the European
engineer, that any comparison of the performance of vessels,
whether with regard to speed or the absorption of power in
the two cases, must be utterly fallacious. In Europe a
steamer is almost invariably a vessel designed to encounter
the agitated surface of an open sea, and is accordingly constructed
upon principles of suitable strength and stability. It
is likewise supplied with rigging and with sails, to be used in
aid of the mechanical power, and manned and commanded by
experienced seamen; in fact, it is a combination of a nautical
and mechanical structure. In America, on the other hand,
<a class="refpn" id="Pg493">[Pg493]</a>
with the exception of the vessels which navigate the great
northern lakes, the steamers are structures exclusively mechanical,
being designed for smooth water. They require no
other strength or stability than that which is sufficient to
enable them to float and to bear a progressive motion through
the water. Their mould is conceived with an exclusive view
to speed; they are therefore slender and weak in their build,
of great length in proportion to their width, and having a
very small draught of water. In fact, they approach in their
form to that of a Thames wherry on a very large scale.</div>

<p>The position and form of the machinery is likewise
affected by these conditions. Without the necessity of being
protected from a rough sea, it is placed on the deck in an
elevated position. The cylinders of large diameter and
short stroke invariably used in Europe are unknown in
America, and the proportions are reversed, a small diameter
and stroke of great length being invariably adopted. It
is rarely that two engines are used. A single engine, placed
in the centre of the deck, with a cylinder from forty to sixty
inches' diameter, and from eight to ten foot stroke, drives
paddle-wheels from twenty-one to twenty-five feet in diameter,
producing from twenty-five to thirty revolutions per
minute. The great magnitude of the paddle-wheels and the
velocity imparted to them enable them to perform the office
of fly-wheels, and to carry the engine round its centres, not
however without a perceptible inequality of motion, which
gives to the American steamer an effect like that of a row
boat advancing by starts with each stroke of the piston.
The length of stroke adopted in these engines enables them
to apply with great effect the expansive principle, which is
almost universally used, the steam being generally cut off at
half stroke.</p>

<p>The steamers which navigate the Hudson are vessels of
considerable magnitude, splendidly fitted up for the accommodation
of passengers; they vary from one hundred and eighty
to two hundred and forty feet in length, and from twenty to
thirty feet in width of beam. In the following table is given
the particulars of nine steamers plying on this river, taken from
<a class="refpn" id="Pg494">[Pg494]</a>
the work of Mr. Stevenson, and from the paper of Mr. Renwick,
inserted in the last edition of Tredgold:â€”</p>

<table style="margin-left:-0.75em;"
 summary="Dimensions of Hudson River Steamers.">
<tr>
 <th>Names.</th>
 <th>Length of Deck.</th>
 <th>Breadth of Beam.</th>
 <th>Draft of Water.</th>
 <th>Drain of Wheel.</th></tr>
<tr>
 <th></th>
 <th>Ft.</th>
 <th>Ft.</th>
 <th>Ft.</th>
 <th>Ft.</th></tr>
<tr>
 <td align="left">Dewit Clinton</td>
 <td align="left">230</td>
 <td align="left">28</td>
 <td align="left">5Â·5</td>
 <td align="left">21</td></tr>
<tr>
 <td align="left">Champlain</td>
 <td align="left">180</td>
 <td align="left">27</td>
 <td align="left">5Â·5</td>
 <td align="left">22</td></tr>
<tr>
 <td align="left">Erie</td>
 <td align="left">180</td>
 <td align="left">27</td>
 <td align="left">5Â·5</td>
 <td align="left">22</td></tr>
<tr>
 <td align="left">North America</td>
 <td align="left">200</td>
 <td align="left">30</td>
 <td align="left">5</td>
 <td align="left">21</td></tr>
<tr>
 <td align="left">Independence</td>
 <td align="left">148</td>
 <td align="left">26</td>
 <td align="left">--</td>
 <td align="left">--</td></tr>
<tr>
 <td align="left">Albany</td>
 <td align="left">212</td>
 <td align="left">26</td>
 <td align="left">--</td>
 <td align="left">24Â·5</td></tr>
<tr>
 <td align="left">Swallow</td>
 <td align="left">233</td>
 <td align="left">22Â·5</td>
 <td align="left">3Â·75</td>
 <td align="left">24</td></tr>
<tr>
 <td align="left">Rochester</td>
 <td align="left">200</td>
 <td align="left">25</td>
 <td align="left">3Â·75</td>
 <td align="left">23Â·5</td></tr>
<tr>
 <td align="left">Utica</td>
 <td align="left">200</td>
 <td align="left">21</td>
 <td align="left">3Â·5</td>
 <td align="left">22</td></tr>
</table>

<table style="margin-left:-0.75em;"
 summary="Dimensions of Hudson River Steamers.">
<tr>
 <th>Names.</th>
 <th>Length of Paddles.</th>
 <th>Depth of Paddles.</th>
 <th>Number of Engines.</th>
 <th>Drain of Cylinder.</th></tr>
<tr>
 <th></th>
 <th>Ft.</th>
 <th>In.</th>
 <th></th>
 <th>In.</th></tr>
<tr>
 <td align="left">Dewit Clinton</td>
 <td align="left">13Â·7</td>
 <td align="left">36</td>
 <td align="left">1</td>
 <td align="left">65</td></tr>
<tr>
 <td align="left">Champlain</td>
 <td align="left">15</td>
 <td align="left">34</td>
 <td align="left">2</td>
 <td align="left">44</td></tr>
<tr>
 <td align="left">Erie</td>
 <td align="left">15</td>
 <td align="left">34</td>
 <td align="left">2</td>
 <td align="left">44</td></tr>
<tr>
 <td align="left">North America</td>
 <td align="left">13</td>
 <td align="left">30</td>
 <td align="left">2</td>
 <td align="left">44Â·5</td></tr>
<tr>
 <td align="left">Independence</td>
 <td align="left">--</td>
 <td align="left">--</td>
 <td align="left">1</td>
 <td align="left">44</td></tr>
<tr>
 <td align="left">Albany</td>
 <td align="left">14</td>
 <td align="left">30</td>
 <td align="left">1</td>
 <td align="left">65</td></tr>
<tr>
 <td align="left">Swallow</td>
 <td align="left">11</td>
 <td align="left">30</td>
 <td align="left">1</td>
 <td align="left">46</td></tr>
<tr>
 <td align="left">Rochester</td>
 <td align="left">10</td>
 <td align="left">24</td>
 <td align="left">1</td>
 <td align="left">43</td></tr>
<tr>
 <td align="left">Utica</td>
 <td align="left">&#160;9Â·5</td>
 <td align="left">24</td>
 <td align="left">1</td>
 <td align="left">39</td></tr>
</table>

<table style="margin-left:-0.75em;"
 summary="Dimensions of Hudson River Steamers.">
<tr>
 <th>Names.</th>
 <th>Length of Stroke.</th>
 <th>Number of Rev.</th>
 <th>Part of Stroke at which it is cut off.</th></tr>
<tr>
 <th></th>
 <th>Ft.</th></tr>
<tr>
 <td align="left">Dewit Clinton</td>
 <td align="left">10</td>
 <td align="left">29</td>
 <td align="center">
<span class="fraction"><sup>3</sup>â„<sub>4</sub></span></td></tr>
<tr>
 <td align="left">Champlain</td>
 <td align="left">10</td>
 <td align="left">27Â·5</td>
 <td align="center">
<span class="fraction"><sup>1</sup>â„<sub>2</sub></span></td></tr>
<tr>
 <td align="left">Erie</td>
 <td align="left">10</td>
 <td align="left">27Â·5</td>
 <td align="center">
<span class="fraction"><sup>1</sup>â„<sub>2</sub></span></td></tr>
<tr>
 <td align="left">North America</td>
 <td align="left">&#160;8</td>
 <td align="left">24</td>
 <td align="center">
<span class="fraction"><sup>1</sup>â„<sub>2</sub></span></td></tr>
<tr>
 <td align="left">Independence</td>
 <td align="left">10</td></tr>
<tr>
 <td align="left">Albany</td>
 <td align="left">--</td>
 <td align="left">19</td></tr>
<tr>
 <td align="left">Swallow</td>
 <td align="left">--</td>
 <td align="left">27</td></tr>
<tr>
 <td align="left">Rochester</td>
 <td align="left">10</td>
 <td align="left">28</td></tr>
<tr>
 <td align="left">Utica</td>
 <td align="left">10</td></tr>
</table>

<p>None of these vessels have either masts or rigging, and
consequently never derive any propelling power except
from the engines: they are neither manned nor commanded
by persons having any knowledge of navigation: the works
that are visible above their decks are the beam and framing
of the engine, and the chimneys.</p>

<p>The engines used for steamers on the Hudson, and other
great rivers and bays on the eastern coast of America, are
most commonly condensing engines, but they nevertheless
work with steam of very high pressure, being seldom less
than twenty-five pounds per square inch, and sometimes as
much as fifty. By reference to the preceding table it will
be seen, that the velocity of the piston greatly exceeds the
limit generally observed in Europe. It is customary in
European marine engines to limit the speed of the piston to
about two hundred and twenty feet per minute. Even the
piston of a locomotive engine does not much exceed the rate
of three hundred feet per minute. In the American steamers,
however, the pistons commonly move at the rate of from five
to six hundred feet per minute, while the circumference of
the paddle-wheels are driven at the rate of from twenty to
twenty-two miles an hour.
<a class="refpn" id="Pg495">[Pg495]</a></p>

<div class="figcenter" style="width: 447px;">
<a id="Fig135"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_517.png" width="447" height="140" alt="" />
<div class="caption figure">Fig. 135.</div>
</div>

<p>The hulls of these boats are formed with a perfectly flat
bottom and perpendicular sides, rounded at the angles, as
represented in <a href="#Fig135"><i>fig.</i> 135.</a> At the bow, or cutwater, they are
made very sharp, and the deck projects to a great distance
over the sides. The weight of the machinery is distributed
over an extensive surface of the bottom of this feeble structure,
by means of a frame-work of substantial carpentry to which
it is attached.</p>

<p>At the height of from four to six feet above the water-line
is placed the deck, which is a platform, having the shape of
a very elongated ellipse. The extremities of its longer axis
are supported by the sternpost and the cutwater, and its
sides expand in gentle curves on either hand to a considerable
distance beyond the limits of the hull; those parts of
the deck thus overhanging the water are called the wheel
guards.</p>

<p>Beneath the first deck is the saloon, or dining-room,
which also, as is usual in European steamers, forms the
gentlemen's sleeping-room. It usually extends from end
to end of the vessel. The middle of the first deck is occupied
by the engine, boilers, furnaces, and chimneys, of which latter
there are generally two. Between the chimneys and the
stern, above the first deck, is constructed the ladies' cabin,
which is covered by the second deck, called the promenade
deck. The great length of these boats and the elevation of
the cabins render it impossible for a steersman at the stern
to see ahead, and they are, consequently, steered from the
bow; the wheel placed there communicating with the helm
at the stern, by chains or rods carried along the sides of the
boat. Until a recent period, the wheel was connected with
the stern by ropes, but some fatal accidents, produced by fire,
<a class="refpn" id="Pg496">[Pg496]</a>
in which these ropes were burnt, and the steersman lost all
power to guide the vessel, caused metal rods or chains to
be substituted.</p>


<div class="ph3"><h3>(232.)</h3> The paddle-wheels universally used in American
steam-boats are formed, as if by the combination of two or
more common paddle-wheels, placed one outside the other, on
the same axle, but so that the paddle boards of each may have
an intermediate position between
those of the adjacent
one, as represented in
<a href="#Fig136"><i>fig.</i> 136.</a></div>

<div class="figleft" style="width: 254px;">
<a id="Fig136"></a>
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_518.png" width="254" height="299" alt="" />
<div class="caption figure">Fig. 136.</div>
</div>

<p>The spokes, which are
bolted to cast-iron flanges,
are of wood. These flanges,
to which they are so bolted,
are keyed upon the paddle
shaft. The outer extremities
of the spokes are attached
to circular bands or
hoops of iron, surrounding
the wheel; and the paddle
boards, which are formed
of hard wood, are bolted to the spokes. The wheels thus
constructed, sometimes consist of three, and not unfrequently
four, independent circles of paddle boards, placed
one beside the other, and so adjusted in their position, that
the boards of no two divisions shall correspond.</p>

<p>The great magnitude of the paddle-wheels, and the circumstance
of the navigation being carried on, for the most part,
in smooth water, have rendered unnecessary, in America, the
adoption of any of those expedients for neutralising the effects
of the oblique action of the paddles, which have been
tried, but hitherto with so little success, in Europe.</p>


<div class="ph3"><h3>(233.)</h3> Sea-going steamers are not numerous in America,
the chief of them being those which ply between New York
and Providence, and between New York and Charleston.
These vessels, however, do not resemble the sea-going
steamers of Europe as closely as might be expected; and to
those who are accustomed to the latter, the sea-going
<a class="refpn" id="Pg497">[Pg497]</a>
steamers of America can hardly be regarded as safe means
of transport.</div>

<p>In the following Table is given the dimensions of five of
these vessels, all plying between New York and Providence:â€”</p>

<table style="margin-left:-0.75em;"
 summary="Dimensions of Sea-going Steamers of America">
<tr>
 <th>Names.</th>
 <th>Length of Deck.</th>
 <th>Breadth of Beam.</th>
 <th>Draft.</th>
 <th>Diameter of Wheel.</th></tr>
<tr>
 <th></th>
 <th>Ft.</th>
 <th>Ft.</th>
 <th>Ft.</th>
 <th>Ft.</th></tr>
<tr>
 <td align="left">Providence</td>
 <td align="left">180</td>
 <td align="left">27</td>
 <td align="left">9</td>
 <td align="left">--</td></tr>
<tr>
 <td align="left">Lexington</td>
 <td align="left">207</td>
 <td align="left">21</td>
 <td align="left">--</td>
 <td align="left">23</td></tr>
<tr>
 <td align="left">Narragansett</td>
 <td align="left">210</td>
 <td align="left">26</td>
 <td align="left">5</td>
 <td align="left">25</td></tr>
<tr>
 <td align="left">Massachusetts</td>
 <td align="left">200</td>
 <td align="left">29Â·5</td>
 <td align="left">8Â·5</td>
 <td align="left">22</td></tr>
<tr>
 <td align="left">Rhode Island</td>
 <td align="left">210</td>
 <td align="left">26</td>
 <td align="left">6Â·5</td>
 <td align="left">24</td></tr>
</table>

<table style="margin-left:-0.75em;"
 summary="Dimensions of Sea-going Steamers of America">
<tr>
 <th>Names.</th>
 <th>Length of Paddles.</th>
 <th>Depth of Paddles.</th>
 <th>Number of Engines.</th>
 <th>Diameter of Cylinder.</th></tr>
<tr>
 <th></th>
 <th>Ft.</th>
 <th>In.</th>
 <th></th>
 <th>In.</th></tr>
<tr>
 <td align="left">Providence</td>
 <td align="left">--</td>
 <td align="left">--</td>
 <td align="left">1</td>
 <td align="left">10</td></tr>
<tr>
 <td align="left">Lexington</td>
 <td align="left">&#160;9</td>
 <td align="left">30</td>
 <td align="left">1</td>
 <td align="left">11</td></tr>
<tr>
 <td align="left">Narragansett</td>
 <td align="left">11</td>
 <td align="left">30</td>
 <td align="left">1</td>
 <td align="left">60</td></tr>
<tr>
 <td align="left">Massachusetts</td>
 <td align="left">10</td>
 <td align="left">28</td>
 <td align="left">2</td>
 <td align="left">44</td></tr>
<tr>
 <td align="left">Rhode Island</td>
 <td align="left">11</td>
 <td align="left">30</td>
 <td align="left">1</td>
 <td align="left">11</td></tr>
</table>

<table style="margin-left:-0.75em;"
 summary="Dimensions of Sea-going Steamers of America">
<tr>
 <th>Names.</th>
 <th>Length of Stroke.</th>
 <th>Number of Rev.</th>
 <th>Part of stroke at which stroke is cut off.</th></tr>
<tr>
 <th></th>
 <th>Ft.</th></tr>
<tr>
 <td align="left">Providence</td>
 <td align="left">65</td></tr>
<tr>
 <td align="left">Lexington</td>
 <td align="left">48</td>
 <td align="left">24</td></tr>
<tr>
 <td align="left">Narragansett</td>
 <td align="left">12</td>
 <td align="left">&#160;2</td>
 <td align="center">
<span class="fraction"><sup>1</sup>â„<sub>2</sub></span></td></tr>
<tr>
 <td align="left">Massachusetts</td>
 <td align="left">&#160;8</td>
 <td align="left">26</td></tr>
<tr>
 <td align="left">Rhode Island</td>
 <td align="left">60</td>
 <td align="left">21</td></tr>
</table>

<p>The Narragansett, the finest of these vessels, is built of
oak, strengthened by diagonal straps or ties of iron, by which
her timbers are connected; she is driven by a condensing
engine, and has two boilers, exposing about three thousand
square feet of surface to the fire. The steam is maintained
at a pressure of from twenty to twenty-five lbs. per square
inch: the cylinder is horizontal.</p>

<p>The cabins of these sea-boats are of great magnitude, and
afford excellent accommodation for passengers, containing
generally four hundred berths. In the Massachusetts the
chief cabin is one hundred and sixty feet long, twenty-two
feet wide, and twelve feet in height, its vast extent being uninterrupted
by pillars or any other obstruction. "I have
dined," says Mr. Stevenson, "with one hundred and seventy-five
persons in this cabin, and, notwithstanding this numerous
assembly, the tables, which were arranged in two parallel rows,
extending from one end of the cabin to the other, were far
from being fully occupied, the attendance was good, and
every thing was conducted with perfect regularity and order.
There are one hundred and twelve fixed berths ranged round
this cabin, and one hundred temporary berths can be erected
in the middle of the floor: besides these there are sixty
fixed berths in the ladies' cabin, and several temporary sleeping
<a class="refpn" id="Pg498">[Pg498]</a>
places can be erected in it also. The cabin of the Massachusetts
is by no means the largest in the United States.
Some steamers have cabins upwards of one hundred and
seventy-five feet in length. Those large saloons are lighted
by Argand lamps, suspended from the ceiling, and their
appearance, when brilliantly lighted up and filled with
company, is very remarkable. The passengers generally
arrange themselves in parties at the numerous small tables
into which the large tables are converted after dinner, and
engage in different amusements. The scene resembles much
more the coffee-room of some great hotel than the cabin of a
floating vessel."</p>


<div class="ph3">
<h3>(234.)</h3> Nothing has excited more surprise among engineers
and others interested in steam navigation in Europe, than the
statements which have been so generally and so confidently
made of the speed attained by American steamers. This
astonishment is due to several causes, the chief of which is
the omission of all notice of the great difference between the
structure and operation of the American steamers and the
nature of the navigation in which they are engaged, compared
with the structure and operation of, and the navigation
in which European steamers are employed: as well might
the performance of a Thames wherry, or one of the fly-boats
on the northern canals, be compared with that of the Great
Western, or the British Queen. The statements alluded to
all have reference to steamers navigating the Hudson between
New York and Albany, the form and structure of
which we have already described; and doubtless the greatest
speed ever attained on the surface of water has been exhibited
in the passages of these vessels.</div>

<p>Mr. Stevenson states, that exclusive of the time lost in
stoppages, the voyage between New York and Albany is
usually made in ten hours. Dr. Renwick, however, who has
probably more extensive opportunities of observation, states,
that the average time, exclusive of stoppages, is ten hours
and a half. The distance being 125Â·18 geographical miles,
the average rate would therefore be
<span class="fraction">11<sup>9</sup>â„<sub>10</sub></span> miles per hour.
If it be observed that the average rate of some of the best
sea-going steamers in Europe obtained from experiments
<a class="refpn" id="Pg499">[Pg499]</a>
and observations made by myself, more than three years
ago, showed a rate of steaming little less than ten geographical
miles per hour, and that since that time considerable
improvements in steam navigation have been made, and
further, that these performances were made under exposure
to all the disadvantages of an open sea, the difference between
them and the performance of the American river
steamers will cease to create astonishment.</p>

<p>Dr. Renwick states that he made, in a boat called the
"New Philadelphia," one of the most remarkable passages
ever performed. He left New York at five in the afternoon,
with the first of the flood, and landed at Catskill, distant
95Â·8 geographical miles from New York, at a quarter before
twelve. Passengers were landed and taken in at seven intermediate
points: the rate, including stoppages, was therefore
14Â·2 miles per hour; and if half an hour be allowed for stoppages,
the actual average rate of motion would be fifteen
miles and three quarters an hour. As the current, which in this
case was with the course of the vessel, did not exceed three
miles and a half an hour, the absolute velocity through the
water would have been somewhat under twelve miles an hour.
This speed is nearly the same as the speed obtained from
taking the average time of the voyages between New York
and Albany at ten hours and a half; it would therefore appear
that the great speed attained in this trip must have been
chiefly, if not altogether, owing to the effect of the current.</p>


<div class="ph3"><h3>(235.)</h3> The steamers which navigate the great northern
lakes differ so little in their construction and appearance
from the European steam-boats, that it will not be necessary
here to devote any considerable space to an account of them.
These vessels were introduced on the lakes at about the same
time that steamers were first introduced on the Clyde. These
steamers are strongly built vessels, supplied with sails and
rigging, and propelled by powerful engines. The largest
in 1837, when Mr. Stevenson visited the States, was the
<i>James Madison</i>. This vessel was one hundred and eighty-one
feet in length on the deck, thirty feet in breadth of beam,
and twelve feet six inches in depth of hold: her draught of
water was ten feet, and her measured capacity seven hundred
<a class="refpn" id="Pg500">[Pg500]</a>
tons. She plyed between Buffalo on Lake Erie and Chicago
on Lake Michigan, a distance of nine hundred and fifty
miles.</div>

<p>The severe storms and formidable sea encountered on the
lakes render necessary for the navigation, vessels in all
respects as strong and powerful as those which navigate the
open ocean.</p>


<div class="ph3"><h3>(236.)</h3> By far the most remarkable and important of all the
American rivers is the Mississippi and its tributaries. That part
of the American continent which extends from the southern
shores of the great northern lakes to the northern shores of the
Gulf of Mexico, is watered by these great streams. The main
stream of the Mississippi has its fountains in the tract of
country lying north of the Illinois and east of Lake Michigan,
in latitude forty-three degrees. At about latitude thirty-nine
degrees, a little north of St. Louis, it receives the waters
of the Missouri, and further south, at the latitude of thirty-seven
degrees, the Ohio flows into it, after traversing five
degrees of longitude and four of latitude, and winding its way
from the Alleghany range through several of the states, and
forming a navigable communication with numerous important
towns of the Union, among which may be mentioned Pittsburg,
Cincinnati, Frankfort, Lexington, and Louisville. The
main stream of the Mississippi, after receiving the waters of
the Arkansas, and numerous other minor tributaries, flows
into the Gulf of Mexico by four mouths. The main stream
of the Mississippi, independently of its tributaries, forms an
unbroken course of inland navigation for a distance of nearly
two thousand three hundred miles. Its width, through a
distance of one thousand one hundred miles from its mouth,
is not less than half a mile, and its average depth a hundred
feet. The Ohio, its chief eastern tributary, flowing into it at
a distance of about a thousand miles from its mouth, traverses
also about the same extent of country, and is navigable
throughout the whole of that extent. This river also has
several navigable tributaries of considerable extent, among
which may be mentioned the Muskingum, navigable for one
hundred and twenty miles; the Miami, navigable for seventy-five
miles; the Scioto, navigable for one hundred and twenty
<a class="refpn" id="Pg501">[Pg501]</a>
miles; the Tennessee, navigable for two hundred and fifty
miles; the Cumberland, navigable for four hundred and
forty miles; the Kentucky, navigable for one hundred and
thirty miles; and the Green River, navigable for one hundred
and fifty miles. The total length of the Ohio and its tributaries
is estimated at above seven thousand miles.</div>


<div class="ph3">
<h3>(237.)</h3> Steam-boats were introduced on the Mississippi
about the year 1812, the period of their first introduction in
Europe; and their increase has been rapid beyond all precedent.
In the year 1831 there were one hundred and ninety-eight
steamers plying on its waters; and the number in 1837
amounted to nearly four hundred. These vessels are built
chiefly on the banks of the Ohio, at the towns of Pittsburg
and Cincinnati, at distances of about two thousand miles from
the mouth of the river they are intended to navigate.</div>


<div class="ph3"><h3>(238.)</h3> These steamers, which are decidedly inferior to those
which navigate the eastern waters, are generally of a heavy
build, fitted to carry goods as well as passengers, and vary
from one hundred to seven hundred tons burthen. Their
draught of water is also greater than that of the eastern
river steamersâ€”varying from six to eight feet. The hull, at
about five feet from the water line, is covered with a deck,
under which is the hold, in which the heavy part of the cargo
is stowed. About the middle of this deck the engines are
placed, the boilers and furnaces occupying a space nearer to
the bow, near which two chimneys are placed. The fire-doors
of the furnaces are presented towards the bow, and
exposed so as to increase the draught. That part of the first
deck which extends from the machinery to the stern is the
place allotted to the crew and the deck passengers, and is
described as being filthy and inconvenient in the extreme. A
second deck is constructed, which extends from the chimneys
near the bow to the stern of the vessel. On this is formed
the great cabin or saloon, which extends from the chimneys
to within about thirty feet of the stern, where it is divided
by a partition from the ladies' cabin, which occupies the
remaining space. These principal cabins are surrounded by
a gallery about three feet in width, from which, at convenient
<a class="refpn" id="Pg502">[Pg502]</a>
places, an ascent is supplied by stairs to the highest deck,
called the hurricane or promenade deck.</div>

<div class="ph3">
<h3>(239.)</h3> The engines by which these boats are propelled are
totally different from the machinery already described as used
in the eastern steamers. They are invariably non-condensing
engines, worked by steam of extremely high pressure; the
boilers are therefore tubular, and the cylinders small in diameter,
but generally having a long stroke.</div>

<p>The pressure of steam used in these machines is such as is
never used in European engines, even when worked on railways.
A pressure of one hundred pounds per inch is here
considered extremely moderate. The captain of one of these
boats, plying between Pittsburg and St. Louis, told Mr.
Stevenson that "under ordinary circumstances his safety
valves were loaded with a pressure equal to one hundred and
thirty-eight pounds per square inch, but that the steam was
occasionally raised as high as one hundred and fifty pounds to
enable the vessel to pass parts of the river in which there is a
strong current;" and he added, by way of consolation, that
"this pressure was never exceeded except on <em>extraordinary
occasions</em>!"</p>

<p>The dimensions and power of the Mississippi steamers may
be collected from those of the St. Louis, a boat which was
plying on that river in 1837. That vessel measured two
hundred and fifty feet on deck, and had twenty-eight feet
breadth of beam. Her draught of water was eight feet, and
her measured capacity one thousand tons. She was propelled
by two engines with thirty-inch cylinders, and ten feet
stroke; the safety valve being loaded at one hundred pounds
per square inch.</p>

<p>The paddle wheels of these vessels are attached to the
paddle shaft, in such a manner as to be thrown into and out
of gear, at discretion, by the engineer, so that the paddle
shaft may revolve without driving the wheels: by this expedient
the power of the engine is used to feed the boilers
while the vessel stops at the several stations. The vessel is
therefore stopped, not, as is usually the case, by stopping the
engines, but by throwing the wheels out of connection with
the paddle shaft. The engines continue to work, but their
<a class="refpn" id="Pg503">[Pg503]</a>
power is expended in forcing water into the boiler. By
this expedient the activity of the engines may, within practical
limits, be varied with the resistance the vessel has to
encounter. In working against a strong current, the feed may
be cut off from the boilers, and the production of steam, and
consequently the power of the engines, thereby stimulated,
while this suspension of the feed may be compensated at the
next station.</p>

<p>The stoppages to take in goods and passengers, and for
relays of fuel, are frequent. "The liberty which they take
with their vessels on these occasions," says Mr. Stevenson,
"is somewhat amusing: I had a good example of this on
board a large vessel, called the Ontario. She was steered
close in shore amongst stones and stumps of trees, where she
lay for some hours to take in goods: the additional weight
increased her draught of water, and caused her to heel a
good deal; and when her engines were put in motion, she
actually <em>crawled</em> into the deep water on her paddle wheels:
the steam had been got up to an enormous pressure to enable
her to get off, and the volume of steam discharged from
the escapement pipe at every half stroke of the piston made
a sharp sound almost like the discharge of fire-arms, while
every timber in the vessel seemed to tremble, and the whole
structure actually groaned under the shocks."</p>

<p>Besides the steamers used for the navigation of the Mississippi,
innumerable steam tugs are constantly employed in
towing vessels between the port of New Orleans and the
open sea of the Gulf of Mexico. Before the invention of
steam navigation, this southern capital of the United States
laboured under the disadvantage of possessing almost the
only bad and inconvenient harbour in the vast range of coast
by which the country is bounded. New Orleans lies at a distance
of about one hundred miles from the Gulf of Mexico.
The force of the stream, the frequency of shoals, and the winding
course of the channel rendered it scarcely possible for a
sailing vessel to pass between the port and the sea with the
same wind. The anchorage was every where bad, and great
difficulty and risk attended the mooring of large vessels to
the banks. The steam engine has, however, overcome all
<a class="refpn" id="Pg504">[Pg504]</a>
these difficulties, and rendered the most objectionable harbour
of the Union a safe and good seaport, perfectly easy of
approach and of egress at all times; a small steam tug will
take in tow several large ships, and carry them with safety
and expedition to the offing, where it will dismiss them on
their voyage, and take back vessels which may have arrived.</p>

<div class="figcenter" style="width: 468px;">
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_526.png" width="468" height="407" alt="" />
<div class="caption">GREAT WESTERN OFF NEW YORK.</div>
</div>

<h2><a name="APPENDIX" id="APPENDIX">APPENDIX.</a></h2>

<p class="right"><a class="refpn" id="Pg505">[Pg505]</a><br />
<a href="#CONTENTS"><small>TOC</small></a>&#160;&#160;<a
href="#INDEX"><small>INX</small></a></p>

<p class="center">
<em>On the Relation between the Temperature, Pressure, and Density
of Common Steam.</em></p>

<div class="ph3fst">There is a fixed relation between the temperature and pressure
of common steam, which has not yet been ascertained by theory.
Various empirical formulÃ¦ have been proposed to express it,
derived from tables of temperatures and corresponding pressures
which have been founded on experiments and completed by interpolation.</div>

<p>The following formula, proposed by M. Biot, represents with
great accuracy the relation between the temperature and pressure
of common steam, throughout all that part of the thermometric
scale to which experiments have been extended.</p>

<p>Let</p>

<table class="equation" summary="M. Biot's constants for
steam properties, temperature and pressure.">
<tr>
 <td>&#160;&#160;&#160;&#160;&#160;<i>a</i>&#160; = &#160;5Â·96131330259</td></tr>
<tr>
 <td>log. <i>a</i><sub>1</sub> = &#160;0Â·82340688193 âˆ’ 1</td></tr>
<tr>
 <td>log. <i>b</i><sub>1</sub> = &#160;âˆ’Â·01309734295</td></tr>
<tr>
 <td>log. <i>a</i><sub>2</sub> = &#160;0Â·74110951837</td></tr>
<tr>
 <td>log. <i>b</i><sub>2</sub> = &#160;âˆ’Â·00212510583</td></tr>
</table>

<p>The relation between the temperature <i>t</i> with reference to the
centesimal thermometer, and the pressure <i>p</i> in millimÃ¨tres of
mercury at the temperature of melting ice, will then be expressed
by the following formula:â€”</p>

<table class="equation" summary="equation 1">
<tr>
 <td>log. <i>p</i> = <i>a</i> âˆ’
 <i>a</i><sub>1</sub><i>b</i><sub>1</sub><sup>20 + <i>t</i></sup>
 âˆ’ <i>a</i><sub>2</sub><i>b</i><sub>2</sub><sup>20 + <i>t</i></sup>.
 <span class="padl4">(1.)</span></td></tr>
</table>

<p>FormulÃ¦ have, however, been proposed, which, though not
applicable to the whole scale of temperatures, are more manageable
in their practical application than the preceding.</p>

<p>For pressures less than an atmosphere, Southern proposed the
following formula, where the pressure is intended to be expressed
<a class="refpn" id="Pg506">[Pg506]</a>
in pounds per square inch, and the temperature in reference to
Fahrenheit's thermometer,â€”</p>

<table class="equation" summary="equations 2.">
<tr>
 <td rowspan="2"><i>p</i> = 0Â·04948 + <span class="fsize200">(</span></td>
 <td class="linedn center">51Â·3 + <i>t</i></td>
 <td rowspan="2"><span class="fsize200">)</span></td>
 <td style="padding-right:7em;"><sup>5Â·13</sup></td>
 <td rowspan="3" class="linelft">.<span
 class="padl4">(2.)</span></td>
</tr>
<tr>
 <td class="center">155Â·7256</td></tr>
<tr>
<td colspan="4"><i>t</i> = 155Â·7256 {(<i>p</i> âˆ’
 0Â·04948)<sup><sup>1</sup>â„<sub>5Â·13</sub></sup> âˆ’
 51Â·3}</td></tr>
</table>

<p>The following formula was proposed by Tredgold, where <i>p</i>
expresses the pressure in inches of mercury:â€”</p>

<table class="equation" summary="equation">
<tr>
 <td rowspan="2"><i>p</i> = <span class="fsize200">(</span></td>
 <td class="linedn center">100 + <i>t</i></td>
 <td rowspan="2"><span class="fsize200">)</span></td>
 <td><sup>6</sup></td>
 <td rowspan="2">.</td>
</tr>
<tr>
 <td class="center">177</td></tr>
</table>

<p>This was afterwards modified by Mellet, and represents with
sufficient accuracy experiments from 1 to 4 atmospheres. Let <i>p</i>
represent pounds per square inch, and <i>t</i> the temperature by Fahrenheit's
thermometer,â€”</p>

<table class="equation" summary="equations 3.">
<tr>
 <td rowspan="2"><i>p</i> = <span class="fsize200">(</span></td>
 <td class="linedn center">103 + <i>t</i></td>
 <td rowspan="2"><span class="fsize200">)</span></td>
 <td style="padding-right:4em;"><sup>6</sup></td>
 <td rowspan="3" class="linelft">.<span
 class="padl4">(3.)</span></td>
</tr>
<tr>
 <td class="center">201Â·18</td></tr>
<tr>
 <td colspan="4"><i>t</i> = 201Â·18 <span class="no-wrap"><i>p</i><sup>
<sup>1</sup>â„<sub>6</sub></sup></span>
 âˆ’ 103</td></tr>
</table>

<p>M. de Pambour has proposed the following formula, also applicable
through the same limits of the scale:â€”</p>

<table class="equation" summary="equations 4.">
<tr>
 <td rowspan="2"><i>p</i> = <span class="fsize200">(</span></td>
 <td class="linedn center">98Â·806 + <i>t</i></td>
 <td rowspan="2"><span class="fsize200">)</span></td>
 <td style="padding-right:4em;"><sup>6</sup></td>
 <td rowspan="3" class="linelft">.
 <span class="padl4">(4.)</span></td>
</tr>
<tr>
 <td class="center">198Â·562</td></tr>
<tr>
 <td colspan="4"><i>t</i> = 198Â·562 <span class="no-wrap"><i>p</i><sup>
<sup>1</sup>â„<sub>6</sub></sup></span>
 âˆ’ 98Â·806</td></tr>
</table>

<p>MM. Dulong and Arago have proposed the following formula
for all pressures between 4 and 50 atmospheres:â€”</p>

<table class="equation" summary="equations 5.">
<tr>
 <td><i>p</i> = (0Â·26793 + 0Â·0067585 <i>t</i>)<sup>5</sup></td>
<td rowspan="2" class="linelft">.
 <span class="padl4">(5.)</span></td></tr>
<tr>
 <td><i>t</i> = 147Â·961 <i>p</i><sup><sup>1</sup>â„<sub>5</sub></sup>
 âˆ’ 39Â·644</td>
</tr>
</table>

<p>It was about the year 1801, that Dalton, at Manchester, and
Gay-Lussac, at Paris, instituted a series of experiments on gaseous
bodies, which conducted them to the discovery of the law mentioned
in art. (<a href="#h3-96">96</a>.), p. 171. These philosophers found that all gases
whatever, and all vapours raised from liquids by heat, as well as
all mixtures of gases and vapours, are subject to the <em>same
quantity of expansion</em> between the temperatures of melting ice
and boiling water; and by experiments subsequently made by
Dulong and Petit, this uniformity of expansion has been proved
to extend to all temperatures which can come under practical
inquiries.</p>

<p>Dalton found that 1000 cubic inches of air at the temperature
of melting ice dilated to 1325 cubic inches if raised to the temperature
of boiling water. According to Gay-Lussac, the increased
volume was 1375 cubic inches. The latter determination has been
subsequently found to be the more correct one.<a name="FNanchor_40_40" id="FNanchor_40_40"></a><a href="#Footnote_40_40" class="fnanchor">[40]</a></p>

<p class="right"><a class="refpn" id="Pg507">[Pg507]</a></p>
<p>It appears, therefore, that for an increase of temperature from
32Â° to 212Â°, amounting to 180Â°, the increase of volume is 375
parts in 1000; and since the expansion is uniform, the increase
of volume for 1Â° will be found by dividing this by 180, which
will give an increase of
<span class="fraction">208<sup>1</sup>â„<sub>3</sub></span> parts in 100,000 for each degree
of the common thermometer.</p>

<p>To reduce the expression of this important and general law to
mathematical language, let <i>v</i> be the volume of an elastic fluid at
the temperature of melting ice, and let <i>nv</i> be the increase which
that volume would receive by being raised one degree of temperature
under the same pressure. Let V be its volume at the
temperature T. Then we shall have</p>

<table class="equation" summary="equation">
<tr>
 <td>V = <i>v</i> + <i>nv</i> (T âˆ’ 32) = <i>v</i> {1 + <i>n</i> (T âˆ’ 32)}.</td></tr>
</table>

<p class="continue">If Vâ€² be its volume at any other temperature Tâ€², and under the
same pressure, we shall have, in like manner,</p>

<table class="equation" summary="equation">
<tr>
 <td>Vâ€² = <i>v</i> {1 + <i>n</i> (Tâ€² âˆ’ 32)}.</td></tr>
</table>

<p>Hence we obtain</p>

<table class="equation" summary="equation 6.">
<tr>
 <td class="linedn center">V</td>
 <td rowspan="2"> = </td>
 <td class="linedn center">1 + <i>n</i> (T âˆ’ 32)</td>
 <td rowspan="2">;<span class="padl4"><span class="padl4">(6.)</span></span></td>
</tr>
<tr>
 <td class="center">Vâ€²</td>
 <td>1 + <i>n</i> (Tâ€² âˆ’ 32)</td>
</tr>
</table>

<p class="continue">which expresses the relation between the volumes of the same gas
or vapour under the same pressure and at any two temperatures.
The co-efficient <i>n</i>, as explained in the text, has the same value
for the same gas or vapour throughout the whole thermometric
scale. But it is still more remarkable that this constant has the
same value for all gases and vapours. It is a number, therefore,
which must have some essential relation to the gaseous or elastic
state of fluid matter, independent of the peculiar qualities of any
particular gas or vapour.</p>

<p>The value of <i>n</i>, according to the experiments of Gay-Lussac, is
0Â·002083, or
<span class="fraction"><sup>1</sup>â„<sub>480</sub>.</span></p>

<p>To reduce the law of Mariotte, explained in (<a href="#h3-97">97</a>.) p. 171., to
mathematical language, let V, Vâ€² be the volumes of the same gas
or vapour under different pressures P, Pâ€², but at the same temperature.
We shall then have</p>

<table class="equation" summary="equation 7.">
<tr>
 <td>VP = Vâ€²Pâ€². <span class="padl4">(7.)</span></td></tr>
</table>

<p>If it be required to determine the relation between the volumes
of the same gas or vapour, under a change of both temperature
and pressure, let V be the volume at the temperature T and under
the pressure P, and let Vâ€² be the volume at the temperature Tâ€²
and under the pressure Pâ€². Let <i>v</i> be the volume at the temperature
T and under the pressure Pâ€².</p>

<p>By formula (7.) we have</p>

<table class="equation" summary="equation">
<tr>
 <td>VP = <i>v</i>Pâ€²;</td></tr>
</table>

<p class="right"><a class="refpn" id="Pg508">[Pg508]</a></p>
<p class="continue">and by formula (6.) we have</p>

<table class="equation" summary="equation">
<tr>
 <td class="linedn center">Vâ€²</td>
 <td rowspan="2"> = </td>
 <td class="linedn center">1 + <i>n</i>(Tâ€² âˆ’ 32)</td>
</tr>
<tr>
 <td class="center"><i>v</i></td>
 <td class="center">1 + <i>n</i>(T âˆ’ 32)</td></tr>
</table>

<p>Eliminating <i>v</i>, we shall obtain</p>

<table class="equation" summary="equation">
<tr>
 <td class="linedn center">V</td>
 <td rowspan="2"> = </td>
 <td class="linedn center">Pâ€²</td>
 <td rowspan="2"> Â· </td>
 <td class="linedn center">1 + <i>n</i>(T âˆ’ 32)</td>
 <td rowspan="2">;</td>
</tr>
<tr>
 <td class="center">Vâ€²</td>
 <td class="center">P</td>
 <td class="center">1 + <i>n</i>(Tâ€² âˆ’ 32)</td>
</tr>
</table>

<p class="continue">or,</p>

<table class="equation" summary="equation 8.">
<tr>
 <td class="linedn center">VP</td>
 <td rowspan="2"> = </td>
 <td class="linedn center">1 + <i>n</i>(T âˆ’ 32)</td>
 <td rowspan="2">;<span class="padl4">(8.)</span></td></tr>
<tr>
 <td class="center">Vâ€²Pâ€²</td>
 <td class="center">1 + <i>n</i>(Tâ€² âˆ’ 32)</td>
</tr>
</table>

<p class="continue">which is the general relation between the volumes, pressures, and
temperatures of the same gas or vapour in two different states.</p>

<p>To apply this general formula to the case of the vapour of
water, let Tâ€² = 212Â°. It is known by experiment that the corresponding
value of Pâ€², expressed in pounds per square inch, is 14Â·706;
and that Vâ€², expressed in cubic inches, the water evaporated being
taken as a cubic inch, is 1700. If, then, we take 0Â·002083 as the
value of <i>n</i>, we shall have by (8.),</p>

<table class="equation" summary="equation 9.">
<tr>
 <td rowspan="2">VP = </td>
 <td class="linedn center">1700 Ã— 14Â·706 Ã— {1 + 0Â·002083 (T âˆ’ 32)}</td>
</tr>
<tr>
 <td class="center">1 + 0Â·002083 Ã— 180</td>
</tr>
<tr>
 <td colspan="2">&#160;&#160; = 18183{1 + 0Â·002083 (T âˆ’ 32)}.</td>
 <td><span class="padl4">(9.)</span></td>
</tr>
</table>

<p>If, by means of this formula (9.), and any of the formulÃ¦ (1.),
(2.), (3.), (4.), (5.), T were eliminated, we should obtain a formula
between V and P, which would enable us to compute the enlargement
of volume which water undergoes in passing into steam
under any proposed pressure. But such a formula would not be
suitable for practical computations. By the formulÃ¦ (1.) to (5.),
a table of pressures and corresponding temperatures may be computed;
and these being known, the formula (9.) will be sufficient
for the computation of the corresponding values of V, or the
enlargement of volume which water undergoes in passing into
steam.</p>

<p>In the following table, the temperatures corresponding to pressures
from 1 to 240 lbs. per square inch are given by computation
from the formulÃ¦ (2.) to (5.), and the volumes of steam produced
by an unit of volume of water as computed from the formula (9.).</p>

<p>The mechanical effect is obtained by multiplying the pressure in
pounds by the expansion of a cubic inch of water in passing into
steam expressed in feet, and is therefore the number of pounds
which would be raised one foot by the evaporation of a cubic inch
of water under the given pressure.
<a class="refpn" id="Pg509">[Pg509]</a></p>

<table style="margin-left:-0.75em;"
 summary="Steam Table--temperature, volume,
  and mechanical effect of steam vs pressure">
<tr>
 <th>Total pressure in Pounds per Square Inch.</th>
 <th>Corresponding Temperature. </th>
 <th>Volume of the Steam compared to the Volume of the Water that has produced it.</th>
 <th>Mechanical Effect of a Cubic Inch of Water evaporated in Pounds raised One Foot.</th></tr>
<tr>
 <td align="center">1</td>
 <td align="center">102Â·9</td>
 <td align="center">20868</td>
 <td align="center">1739</td></tr>
<tr>
 <td align="center">2</td>
 <td align="center">126Â·1</td>
 <td align="center">10874</td>
 <td align="center">1812</td></tr>
<tr>
 <td align="center">3</td>
 <td align="center">141Â·0</td>
 <td align="center">7437</td>
 <td align="center">1859</td></tr>
<tr>
 <td align="center">4</td>
 <td align="center">152Â·3</td>
 <td align="center">5685</td>
 <td align="center">1895</td></tr>
<tr>
 <td align="center">5</td>
 <td align="center">161Â·4</td>
 <td align="center">4617</td>
 <td align="center">1924</td></tr>
<tr>
 <td align="center">6</td>
 <td align="center">169Â·2</td>
 <td align="center">3897</td>
 <td align="center">1948</td></tr>
<tr>
 <td align="center">7</td>
 <td align="center">175Â·9</td>
 <td align="center">3376</td>
 <td align="center">1969</td></tr>
<tr>
 <td align="center">8</td>
 <td align="center">182Â·0</td>
 <td align="center">2983</td>
 <td align="center">1989</td></tr>
<tr>
 <td align="center">9</td>
 <td align="center">187Â·4</td>
 <td align="center">2674</td>
 <td align="center">2006</td></tr>
<tr>
 <td align="center">10</td>
 <td align="center">192Â·4</td>
 <td align="center">2426</td>
 <td align="center">2022</td></tr>
<tr>
 <td align="center">11</td>
 <td align="center">197Â·0</td>
 <td align="center">2221</td>
 <td align="center">2036</td></tr>
<tr>
 <td align="center">12</td>
 <td align="center">201Â·3</td>
 <td align="center">2050</td>
 <td align="center">2050</td></tr>
<tr>
 <td align="center">13</td>
 <td align="center">205Â·3</td>
 <td align="center">1904</td>
 <td align="center">2063</td></tr>
<tr>
 <td align="center">14</td>
 <td align="center">209Â·1</td>
 <td align="center">1778</td>
 <td align="center">2074</td></tr>
<tr>
 <td align="center">15</td>
 <td align="center">212Â·8</td>
 <td align="center">1669</td>
 <td align="center">2086</td></tr>
<tr>
 <td align="center">16</td>
 <td align="center">216Â·3</td>
 <td align="center">1573</td>
 <td align="center">2097</td></tr>
<tr>
 <td align="center">17</td>
 <td align="center">219Â·6</td>
 <td align="center">1488</td>
 <td align="center">2107</td></tr>
<tr>
 <td align="center">18</td>
 <td align="center">222Â·7</td>
 <td align="center">1411</td>
 <td align="center">2117</td></tr>
<tr>
 <td align="center">19</td>
 <td align="center">225Â·6</td>
 <td align="center">1343</td>
 <td align="center">2126</td></tr>
<tr>
 <td align="center">20</td>
 <td align="center">228Â·5</td>
 <td align="center">1281</td>
 <td align="center">2135</td></tr>
<tr>
 <td align="center">21</td>
 <td align="center">231Â·2</td>
 <td align="center">1225</td>
 <td align="center">2144</td></tr>
<tr>
 <td align="center">22</td>
 <td align="center">233Â·8</td>
 <td align="center">1174</td>
 <td align="center">2152</td></tr>
<tr>
 <td align="center">23</td>
 <td align="center">236Â·3</td>
 <td align="center">1127</td>
 <td align="center">2160</td></tr>
<tr>
 <td align="center">24</td>
 <td align="center">238Â·7</td>
 <td align="center">1084</td>
 <td align="center">2168</td></tr>
<tr>
 <td align="center">25</td>
 <td align="center">241Â·0</td>
 <td align="center">1044</td>
 <td align="center">2175</td></tr>
<tr>
 <td align="center">26</td>
 <td align="center">243Â·3</td>
 <td align="center">1007</td>
 <td align="center">2182</td></tr>
<tr>
 <td align="center">27</td>
 <td align="center">245Â·5</td>
 <td align="center">973</td>
 <td align="center">2189</td></tr>
<tr>
 <td align="center">28</td>
 <td align="center">247Â·6</td>
 <td align="center">941</td>
 <td align="center">2196</td></tr>
<tr>
 <td align="center">29</td>
 <td align="center">249Â·6</td>
 <td align="center">911</td>
 <td align="center">2202</td></tr>
<tr>
 <td align="center">30</td>
 <td align="center">251Â·6</td>
 <td align="center">883</td>
 <td align="center">2209</td></tr>
<tr>
 <td align="center">31</td>
 <td align="center">253Â·6</td>
 <td align="center">857</td>
 <td align="center">2215</td></tr>
<tr>
 <td align="center">32</td>
 <td align="center">255Â·5</td>
 <td align="center">833</td>
 <td align="center">2221</td></tr>
<tr>
 <td align="center">33</td>
 <td align="center">257Â·3</td>
 <td align="center">810</td>
 <td align="center">2226</td></tr>
<tr>
 <td align="center">34</td>
 <td align="center">259Â·1</td>
 <td align="center">788</td>
 <td align="center">2232</td></tr>
<tr>
 <td align="center">35</td>
 <td align="center">260Â·9</td>
 <td align="center">767</td>
 <td align="center">2238</td></tr>
<tr>
 <td align="center">36</td>
 <td align="center">262Â·6</td>
 <td align="center">748</td>
 <td align="center">2243</td></tr>
<tr>
 <td align="center">37</td>
 <td align="center">264Â·3</td>
 <td align="center">729</td>
 <td align="center">2248</td></tr>
<tr>
 <td align="center">38</td>
 <td align="center">265Â·9</td>
 <td align="center">712</td>
 <td align="center">2253</td></tr>
<tr>
 <td align="center">39</td>
 <td align="center">267Â·5</td>
 <td align="center">695</td>
 <td align="center">2259</td></tr>
<tr>
 <td align="center">40</td>
 <td align="center">269Â·1</td>
 <td align="center">679</td>
 <td align="center">2264</td></tr>
<tr>
 <td align="center">41</td>
 <td align="center">270Â·6</td>
 <td align="center">664</td>
 <td align="center">2268</td></tr>
<tr>
 <td align="center">42</td>
 <td align="center">272Â·1</td>
 <td align="center">649</td>
 <td align="center">2273</td></tr>
<tr>
 <td align="center">43</td>
 <td align="center">273Â·6</td>
 <td align="center">635</td>
 <td align="center">2278</td></tr>
<tr>
 <td align="center">44</td>
 <td align="center">275Â·0</td>
 <td align="center">622</td>
 <td align="center">2282</td></tr>
<tr>
 <td align="center">45</td>
 <td align="center">276Â·4</td>
 <td align="center">610</td>
 <td align="center">2287</td></tr>
<tr>
 <td align="center">46</td>
 <td align="center">277Â·8</td>
 <td align="center">598</td>
 <td align="center">2291</td></tr>
<tr>
 <td align="center">47</td>
 <td align="center">279Â·2</td>
 <td align="center">586</td>
 <td align="center">2296</td></tr>
<tr>
 <td align="center">48</td>
 <td align="center">280Â·5</td>
 <td align="center">575</td>
 <td align="center">2300</td></tr>
<tr>
 <td align="center">49</td>
 <td align="center">281Â·9</td>
 <td align="center">564</td>
 <td align="center">2304</td></tr>
<tr>
 <td align="center">50</td>
 <td align="center">283Â·2</td>
 <td align="center">554</td>
 <td align="center">2308</td></tr>
<tr>
 <td align="center">51</td>
 <td align="center">284Â·4</td>
 <td align="center">544</td>
 <td align="center">2312</td></tr>
<tr>
 <td align="center">52</td>
 <td align="center">285Â·7</td>
 <td align="center">534</td>
 <td align="center">2316</td></tr>
<tr>
 <td align="center">53</td>
 <td align="center">286Â·9</td>
 <td align="center">525</td>
 <td align="center">2320</td></tr>
<tr>
 <td align="center">54</td>
 <td align="center">288Â·1</td>
 <td align="center">516</td>
 <td align="center">2324</td></tr>
<tr>
 <td align="center">55</td>
 <td align="center">289Â·3</td>
 <td align="center">508</td>
 <td align="center">2327</td></tr>
<tr>
 <td align="center">56</td>
 <td align="center">290Â·5</td>
 <td align="center">500</td>
 <td align="center">2331</td></tr>
<tr>
 <td align="center">57</td>
 <td align="center">291Â·7</td>
 <td align="center">492</td>
 <td align="center">2335</td></tr>
<tr>
 <td align="center">58</td>
 <td align="center">292Â·9</td>
 <td align="center">484</td>
 <td align="center">2339</td></tr>
<tr>
 <td align="center">59</td>
 <td align="center">294Â·2</td>
 <td align="center">477</td>
 <td align="center">2343</td></tr>
<tr>
 <td align="center">60</td>
 <td align="center">295Â·6</td>
 <td align="center">470</td>
 <td align="center">2347</td></tr>
<tr>
 <td align="center">61</td>
 <td align="center">296Â·9</td>
 <td align="center">463</td>
 <td align="center">2351</td></tr>
<tr>
 <td align="center">62</td>
 <td align="center">298Â·1</td>
 <td align="center">456</td>
 <td align="center">2355</td></tr>
<tr>
 <td align="center">63</td>
 <td align="center">299Â·2</td>
 <td align="center">449</td>
 <td align="center">2359</td></tr>
<tr>
 <td align="center">64</td>
 <td align="center">300Â·3</td>
 <td align="center">443</td>
 <td align="center">2362</td></tr>
<tr>
 <td align="center">65</td>
 <td align="center">301Â·3</td>
 <td align="center">437</td>
 <td align="center">2365</td></tr>
<tr>
 <td align="center">66</td>
 <td align="center">302Â·4</td>
 <td align="center">431</td>
 <td align="center">2369</td></tr>
<tr>
 <td align="center">67</td>
 <td align="center">303Â·4</td>
 <td align="center">425</td>
 <td align="center">2372</td></tr>
<tr>
 <td align="center">68</td>
 <td align="center">304Â·4</td>
 <td align="center">419</td>
 <td align="center">2375</td></tr>
<tr>
 <td align="center">69</td>
 <td align="center">305Â·4</td>
 <td align="center">414</td>
 <td align="center">2378</td></tr>
<tr>
 <td align="center">70</td>
 <td align="center">306Â·4</td>
 <td align="center">408</td>
 <td align="center">2382</td></tr>
<tr>
 <td align="center">71</td>
 <td align="center">307Â·4</td>
 <td align="center">403</td>
 <td align="center">2385</td></tr>
<tr>
 <td align="center">72</td>
 <td align="center">308Â·4</td>
 <td align="center">398</td>
 <td align="center">2388</td></tr>
<tr>
 <td align="center">73</td>
 <td align="center">309Â·3</td>
 <td align="center">393</td>
 <td align="center">2391</td></tr>
<tr>
 <td align="center">74</td>
 <td align="center">310Â·3</td>
 <td align="center">388</td>
 <td align="center">2394</td></tr>
<tr>
 <td align="center">75</td>
 <td align="center">311Â·2</td>
 <td align="center">383</td>
 <td align="center">2397</td></tr>
<tr>
 <td align="center">76</td>
 <td align="center">312Â·2</td>
 <td align="center">379</td>
 <td align="center">2400</td></tr>
<tr>
 <td align="center">77</td>
 <td align="center">313Â·1</td>
 <td align="center">374</td>
 <td align="center">2403</td></tr>
<tr>
 <td align="center">78</td>
 <td align="center">314Â·0</td>
 <td align="center">370</td>
 <td align="center">2405</td></tr>
<tr>
 <td align="center">79</td>
 <td align="center">314Â·9</td>
 <td align="center">366</td>
 <td align="center">2408</td></tr>
<tr>
 <td align="center">80</td>
 <td align="center">315Â·8</td>
 <td align="center">362</td>
 <td align="center">2411</td></tr>
<tr>
 <td align="center">81</td>
 <td align="center">316Â·7</td>
 <td align="center">358</td>
 <td align="center">2414</td></tr>
<tr>
 <td align="center">82</td>
 <td align="center">317Â·6</td>
 <td align="center">354</td>
 <td align="center">2417</td></tr>
<tr>
 <td align="center">83</td>
 <td align="center">318Â·4</td>
 <td align="center">350</td>
 <td align="center">2419</td></tr>
<tr>
 <td align="center">84</td>
 <td align="center">319Â·3</td>
 <td align="center">346</td>
 <td align="center">2422</td></tr>
<tr>
 <td align="center">85</td>
 <td align="center">320Â·1</td>
 <td align="center">342</td>
 <td align="center">2425</td></tr>
<tr>
 <td align="center">86</td>
 <td align="center">321Â·0</td>
 <td align="center">339</td>
 <td align="center">2427</td></tr>
<tr>
 <td align="center">87</td>
 <td align="center">321Â·8</td>
 <td align="center">335</td>
 <td align="center">2430</td></tr>
<tr>
 <td align="center">88</td>
 <td align="center">322Â·6</td>
 <td align="center">332</td>
 <td align="center">2432</td></tr>
<tr>
 <td align="center">89</td>
 <td align="center">323Â·5</td>
 <td align="center">328</td>
 <td align="center">2435</td></tr>
<tr>
 <td align="center">90</td>
 <td align="center">324Â·3</td>
 <td align="center">325</td>
 <td align="center">2438</td></tr>
<tr>
 <td align="center">91</td>
 <td align="center">325Â·1</td>
 <td align="center">322</td>
 <td align="center">2440</td></tr>
<tr>
 <td align="center">92</td>
 <td align="center">325Â·9</td>
 <td align="center">319</td>
 <td align="center">2443</td></tr>
<tr>
 <td align="center">93</td>
 <td align="center">326Â·7</td>
 <td align="center">316</td>
 <td align="center">2445</td></tr>
<tr>
 <td align="center">94</td>
 <td align="center">327Â·5</td>
 <td align="center">313</td>
 <td align="center">2448</td></tr>
<tr>
 <td align="center">95</td>
 <td align="center">328Â·2</td>
 <td align="center">310</td>
 <td align="center">2450</td></tr>
<tr>
 <td align="center">96</td>
 <td align="center">329Â·0</td>
 <td align="center">307</td>
 <td align="center">2453</td></tr>
<tr>
 <td align="center">97</td>
 <td align="center">329Â·8</td>
 <td align="center">304</td>
 <td align="center">2455</td></tr>
<tr>
 <td align="center">98</td>
 <td align="center">330Â·5</td>
 <td align="center">301</td>
 <td align="center">2457</td></tr>
<tr>
 <td align="center">99</td>
 <td align="center">331Â·3</td>
 <td align="center">298</td>
 <td align="center">2460</td></tr>
<tr>
 <td align="center">100</td>
 <td align="center">332Â·0</td>
 <td align="center">295</td>
 <td align="center">2462</td></tr>
<tr>
 <td align="center">110</td>
 <td align="center">339Â·2</td>
 <td align="center">271</td>
 <td align="center">2486</td></tr>
<tr>
 <td align="center">120</td>
 <td align="center">345Â·8</td>
 <td align="center">251</td>
 <td align="center">2507</td></tr>
<tr>
 <td align="center">130</td>
 <td align="center">352Â·1</td>
 <td align="center">233</td>
 <td align="center">2527</td></tr>
<tr>
 <td align="center">140</td>
 <td align="center">357Â·9</td>
 <td align="center">218</td>
 <td align="center">2545</td></tr>
<tr>
 <td align="center">150</td>
 <td align="center">363Â·4</td>
 <td align="center">205</td>
 <td align="center">2561</td></tr>
<tr>
 <td align="center">160</td>
 <td align="center">368Â·7</td>
 <td align="center">193</td>
 <td align="center">2577</td></tr>
<tr>
 <td align="center">170</td>
 <td align="center">373Â·6</td>
 <td align="center">183</td>
 <td align="center">2593</td></tr>
<tr>
 <td align="center">180</td>
 <td align="center">378Â·4</td>
 <td align="center">174</td>
 <td align="center">2608</td></tr>
<tr>
 <td align="center">190</td>
 <td align="center">382Â·9</td>
 <td align="center">166</td>
 <td align="center">2622</td></tr>
<tr>
 <td align="center">200</td>
 <td align="center">387Â·3</td>
 <td align="center">158</td>
 <td align="center">2636</td></tr>
<tr>
 <td align="center">210</td>
 <td align="center">391Â·5</td>
 <td align="center">151</td>
 <td align="center">2650</td></tr>
<tr>
 <td align="center">220</td>
 <td align="center">395Â·5</td>
 <td align="center">145</td>
 <td align="center">2663</td></tr>
<tr>
 <td align="center">230</td>
 <td align="center">399Â·4</td>
 <td align="center">140</td>
 <td align="center">2675</td></tr>
<tr>
 <td align="center">240</td>
 <td align="center">403Â·1</td>
 <td align="center">134</td>
 <td align="center">2687</td></tr>
</table>

<p class="right"><a class="refpn" id="Pg511">[Pg511]</a></p>
<p>In the absence of any direct method of determining the general
relation between the pressure and volume of common steam, empirical
formulÃ¦ expressing it have been proposed by different
mathematicians.</p>

<p>The late Professor Navier proposed the following:â€”Let S
express the volume of steam into which an unit of volume of water
is converted under the pressure P, this pressure being expressed in
kilogrammes per square mÃ¨tre. Then the relation between S and
P will be</p>

<table class="equation" summary="equation">
<tr>
 <td rowspan="2">S = </td>
 <td class="linedn center"><i>a</i></td>
<td rowspan="2">,</td></tr>
<tr>
 <td><i>b</i> + <i>m</i>P</td>
</tr>
</table>

<p class="center no-wrap">
where <i>a</i> = 1000,&#160;
<span class="padl4"><i>b</i> = 0Â·09, and</span>
<span class="padl4"><i>m</i> = 0Â·0000484.</span></p>

<p>This formula, however, does not agree with experiment at pressures
less than an atmosphere. M. de Pambour, therefore, proposes
the following changes in the values of its co-efficients:â€”Let
P express the pressure in pounds per square foot; and let</p>

<p class="center no-wrap">
<i>a</i> = 10000&#160;
<span class="padl4"><i>b</i> = 0Â·4227&#160;</span>
<span class="padl4"><i>m</i> = 0Â·00258,</span></p>

<p class="continue">and the formula will be accurate for all pressures. For pressures
above two atmospheres the following values give more accuracy
to the calculation:â€”</p>

<p class="center no-wrap">
<i>a</i> = 10000&#160;
<span class="padl4"><i>b</i> = 1Â·421&#160;</span>
<span class="padl4"><i>m</i> = 0Â·0023.</span></p>

<p>In these investigations I shall adopt the following modified
formula. The symbols S and P retaining their signification, we
shall have</p>

<table class="equation" summary="equation 10.">
<tr>
 <td rowspan="2">S = </td>
 <td class="linedn center"><i>a</i></td>
<td rowspan="2">,<span class="padl4">(10.)</span></td></tr>
<tr>
 <td><i>b</i> + P</td>
</tr>
</table>

<p class="continue">where</p>

<p class="center no-wrap">
<i>a</i> = 3875969 &#160;
<span class="padl4"><i>b</i> = 164.</span></p>

<p>These values of <i>a</i> and <i>b</i> will be sufficiently accurate for practical
purposes for all pressures, and may be used in reference to low-pressure
engines of every form, as well as for high-pressure engines
which work expansively.</p>

<p>When the pressure is not less than 30 pounds per square inch,
the following values of <i>a</i> and <i>b</i> will be more accurate:â€”</p>

<p class="center no-wrap">
<i>a</i> = 4347826 &#160;
<span class="padl4"><i>b</i> = 618.</span></p>

<p class="center"><em>On the Expansive Action of Steam.</em></p>

<p>The investigation of the effect of the expansion of steam which
has been given in the text, is intended to convey to those who are
not conversant with the principles and language of analysis, some
notion of the nature of that mechanical effect to which the advantages
attending the expansive principle are due. We shall now,
however, explain these effects more accurately.
<a class="refpn" id="Pg512">[Pg512]</a></p>

<p>The dynamical effect produced by any mechanical agent is
expressed by the product of the resistance overcome and the
space through which that resistance is moved.</p>

<p>Let</p>
<table class="dfnequation" summary="equation">
<tr>
 <td>P&#160;=&#160;
 the pressure of steam expressed in pounds per square foot.</td></tr>
<tr>
 <td>S&#160;=&#160;
 the number of cubic feet of steam of that pressure produced by the evaporation of a cubic foot of water.</td></tr>
<tr>
 <td>E&#160;=&#160;
 the mechanical effect produced by the evaporation of a cubic foot of water expressed in pounds raised one foot.</td></tr>
</table>

<p>Then we shall have E = PS; and if W be a volume of water
evaporated under the pressure P, the mechanical effect produced
by it will be WPS.</p>

<p>By (10.) we have</p>

<table class="equation" summary="equation">
<tr>
 <td>SP = <i>a</i> âˆ’ <i>b</i>S.</td></tr>
</table>

<p>Hence, for the mechanical effect of a cubic foot of water evaporated
under the pressure P we have</p>

<table class="equation" summary="equation 11.">
<tr>
 <td>E = <i>a</i> âˆ’ <i>b</i>S.<span class="padl4">(11.)</span></td></tr>
</table>

<p>Let a cubic foot of water be evaporated under the pressure Pâ€²,
and let it produce a volume of steam Sâ€² of that pressure. Let this
steam afterwards be allowed to expand to the increased volume S
and the diminished pressure P; and let it be required to determine
the mechanical effect produced during the expansion of the
steam from the volume Sâ€² to the volume S.</p>

<p>Let</p>

<table class="dfnequation" summary="equation">
<tr>
 <td>Eâ€²&#160;=&#160;
 the mechanical effect produced by the evaporation of the water
 under the pressure Pâ€² without expansion.</td></tr>
<tr>
 <td>Eâ€³&#160;=&#160;
 the mechanical effect
 produced during the expansion of the steam.</td></tr>
<tr>
 <td>E&#160;=&#160;
 the mechanical
 effect which would be produced by the evaporation under the pressure
 P without expansion.</td></tr>
<tr>
 <td><i>E</i>&#160;=&#160;
 the total mechanical effect produced by
 the evaporation under the pressure Pâ€² and subsequent expansion.</td></tr>
</table>

<p>Thus we have</p>

<table class="equation" summary="equation">
<tr>
 <td><i>E</i> = Eâ€² + Eâ€³.</td></tr>
</table>

<p>Let <i>s</i> be any volume of the steam during the process of expansion,
<i>p</i> the corresponding pressure, and <i>eâ€³</i> the mechanical effect
produced by the expansion of the steam. We have then by (10.)</p>

<table class="equation" summary="equations">
<tr>
 <td rowspan="2">&#160;&#160;&#160;&#160;<i>p</i> = </td>
 <td class="linedn center"><i>a</i></td>
 <td rowspan="2"> âˆ’ <i>b</i>;</td></tr>
<tr>
 <td class="center"><i>s</i></td></tr>
<tr>
 <td rowspan="2">âˆµ <i>deâ€³</i> = </td>
 <td class="linedn center"><i>ads</i></td>
 <td rowspan="2"> âˆ’ <i>bds</i>.</td></tr>
<tr><td class="center"><i>s</i></td></tr>
</table>

<p>Hence by integrating we obtain</p>

<table class="equation" summary="equation">
<tr>
 <td><i>eâ€³</i> = <i>a</i> log. <i>s</i> âˆ’ <i>bs</i> + C;</td></tr>
</table>

<p class="right"><a class="refpn" id="Pg513">[Pg513]</a></p>
<p class="continue">which, taken between the limits <i>s</i> = Sâ€² and <i>s</i> = S, becomes</p>

<table class="equation" summary="equation 12.">
<tr>
 <td rowspan="2">Eâ€³ = <i>a</i> log.</td>
 <td class="linedn center">S</td>
 <td rowspan="2"> âˆ’ <i>b</i>(S âˆ’ Sâ€²).<span
 class="padl4">(12.)</span></td>
</tr>
<tr>
 <td class="center">Sâ€²</td></tr>
</table>

<p>But by (11.) we have</p>

<table class="equation" summary="equation">
<tr>
 <td><span class="padl4">&#160;&#160;&#160;Eâ€² = <i>a</i> âˆ’ <i>b</i>Sâ€²,</span></td></tr>
<tr>
 <td><span class="padl4">&#160;&#160;&#160;E &#160;= <i>a</i> âˆ’ <i>b</i>S;</span></td>
</tr>
<tr>
 <td colspan="2" rowspan="2">âˆµ Eâ€² âˆ’ E = <i>b</i>(S âˆ’ Sâ€²);</td></tr>
</table>

<table class="equation" summary="equation">
<tr>
 <td rowspan="2">âˆµ Eâ€³ = <i>a</i> log. </td>
 <td class="linedn center">S</td>
 <td rowspan="2"> âˆ’ Eâ€² + E;</td>
</tr>
<tr>
 <td class="center">Sâ€²</td></tr>
</table>

<table class="equation" summary="equation">
<tr>
 <td rowspan="2">âˆµ <i>E</i> =  Eâ€³ + Eâ€² = <i>a</i> log. </td>
 <td class="linedn center">S</td>
 <td rowspan="2"> + E.<span class="padl4">(13.)</span></td></tr>
<tr>
 <td class="center">Sâ€²</td></tr>
</table>

<p>Or,</p>

<table class="equation" summary="equation 14.">
<tr>
 <td rowspan="2"><i>E</i> = <i>a</i> <span class="fsize200">(</span>1 + log. </td>
 <td class="linedn center">S</td>
 <td rowspan="2"><span class="fsize200">)</span> âˆ’ <i>b</i>S.<span class="padl4">(14.)</span></td>
</tr>
<tr>
 <td class="center">Sâ€²</td>
</tr>
</table>

<p>Hence it appears that the mechanical effect of a cubic foot of
water evaporated under the pressure P may be increased by the
quantity <i>a</i> log. <span class="fraction"><sup>S</sup>/<sub>Sâ€²</sub></span>,
 if it be first evaporated under the greater pressure
Pâ€², and subsequently expanded to the lesser pressure P.</p>

<p>The logarithms in these formulÃ¦ are hyperbolic.</p>

<p>To apply these principles to the actual case of a double acting
steam engine,</p>

<p>Let</p>

<table class="dfnequation" summary="definition equations">
<tr>
 <td>L&#160;=&#160;the stroke of the piston in feet.</td></tr>
<tr>
 <td>A&#160;=&#160;the area of the piston in square feet.</td></tr>
<tr>
 <td><i>n</i>&#160;=&#160;the number of strokes of the piston per minute.</td></tr>
<tr>
 <td>âˆµ&#160;2<i>n</i>AL&#160;=&#160;the number of cubic feet of space through which
the piston moves per minute.</td></tr>
</table>

<p>Let</p>

<table class="dfnequation" summary="definition equation">
<tr>
 <td><i>c</i>LA&#160;=&#160;the clearage, or the space between the steam valve
and the piston at each end of the stroke.</td></tr>
<tr><td>âˆµ The volume of steam admitted through the steam valve
at each stroke of the engine will be 2<i>n</i> AL(1 + <i>c</i>).</td></tr>
</table>

<p>Let</p>

<table class="dfnequation" summary="definition equation">
<tr><td>V = the mean speed of the piston in feet per minute,</td></tr>
<tr>
 <td>âˆµ 2<i>n</i>L = V.</td>
</tr>
</table>

<p>The volume of steam admitted to the cylinder per minute will
therefore be VA (1 + <i>c</i>), the part of it employed in working the
piston being VA.</p>

<p>Let</p>

<table class="dfnequation" summary="definition equations">
<tr>
 <td>W&#160;=&#160;the water in cubic feet admitted per minute in the form
of steam through the steam valve.</td></tr>
<tr>
 <td>S&#160;=&#160;
 the number of cubic feet of steam produced by a cubic foot of water.</td></tr>
</table>

<p class="right"><a class="refpn" id="Pg514">[Pg514]</a></p>

<p>Hence we shall have</p>

<table class="equation" summary="equation 15.">
<tr>
 <td colspan="2">WS&#160;=&#160;VA (1 + <i>c</i>);</td></tr>
<tr>
 <td rowspan="2">âˆµ S&#160;=&#160;</td>
 <td class="linedn center">VA(1 + <i>c</i>)</td>
 <td rowspan="2">.<span class="padl4">(15.)</span></td></tr>
<tr>
 <td class="center">W</td></tr>
</table>

<p>Since by (10.) we have</p>

<table class="equation" summary="equation 16.">
<tr>
 <td rowspan="2">P&#160;=&#160;</td>
 <td class="linedn center"><i>a</i></td>
 <td rowspan="2"> âˆ’ <i>b</i>;</td></tr>
<tr><td class="center">S</td></tr>
</table>
<table class="equation" summary="equation 16.">
<tr>
 <td rowspan="2">âˆµ P&#160;=&#160;</td>
 <td class="linedn center">W<i>a</i></td>
 <td rowspan="2"> âˆ’ <i>b</i>.<span class="padl4">(16.)</span></td></tr>
<tr><td class="center">VA(1 + <i>c</i>)</td></tr>
</table>

<p>By which the pressure of steam in the cylinder will be known,
when the effective evaporation, the diameter of the cylinder, and
speed of the piston, are given.</p>

<p>If it be required to express the mechanical effect produced per
minute by the action of steam on the piston, it is only necessary
to multiply the pressure on the surface of the piston by the space
per minute through which the piston moves. This will give</p>

<table class="equation" summary="equation 17.">
<tr>
 <td rowspan="2">VAP&#160;=&#160;W</td>
 <td class="linedn center"><i>a</i></td>
 <td rowspan="2"> âˆ’ VA<i>b</i>;<span class="padl4">(17.)</span></td></tr>
<tr>
 <td class="center">1 + <i>c</i></td></tr>
</table>

<p class="continue">which expresses the whole mechanical effect per minute in pounds
raised one foot.</p>

<p>If the steam be worked expansively, let it be cut off after the
piston has moved through a part of the stroke expressed by <i>e</i>.</p>

<p>The volume of steam of the undiminished pressure Pâ€² admitted
per minute through the valve would then be</p>

<table class="equation" summary="equation">
<tr>
 <td>VA (<i>e</i> + <i>c</i>);</td></tr>
</table>

<p class="continue">and the ratio of this volume to that of the water producing it
being expressed by Sâ€², we should have</p>

<table class="equation" summary="equation">
<tr>
 <td rowspan="2">Sâ€²&#160;=&#160;</td>
 <td class="linedn center">VA(<i>e</i> + <i>c</i>)</td>
 <td rowspan="2">.</td></tr>
<tr><td class="center">W</td></tr>
</table>

<p>The final volume into which this steam is subsequently expanded
being VA(1 + <i>c</i>), its ratio to that of the water will be</p>

<table class="equation" summary="equation">
<tr>
 <td rowspan="2">S&#160;=&#160;</td>
 <td class="linedn center">VA (1 + <i>c</i>)</td>
 <td rowspan="2">.</td></tr>
<tr><td class="center">W</td></tr>
</table>

<p>The pressure Pâ€², till the steam is cut off, will be</p>

<table class="equation" summary="equation 18.">
<tr>
 <td rowspan="2">Pâ€²&#160;=&#160;</td>
 <td class="linedn center">W<i>a</i></td>
 <td rowspan="2"> âˆ’ <i>b</i>.<span class="padl4">(18.)</span></td></tr>
<tr>
 <td class="center">VA(<i>e</i> + <i>c</i>)</td></tr>
</table>

<p>The mechanical effect Eâ€² produced per minute by the steam of
full pressure will be</p>

<table class="equation" summary="equation">
<tr>
 <td rowspan="2">Eâ€²&#160;=&#160;Pâ€²AV<i>e</i>&#160;=&#160;</td>
 <td class="linedn center">W<i>ae</i></td>
 <td rowspan="2"> âˆ’ AV<i>be</i>;</td></tr>
<tr>
 <td class="center"><i>e</i> + <i>c</i></td></tr>
</table>

<p class="continue">and the effect Eâ€³ per minute produced by the expansion of the
steam will by (12.) be
<a class="refpn" id="Pg515">[Pg515]</a></p>

<table class="equation" summary="equation">
<tr>
 <td rowspan="2">Eâ€³&#160;=&#160;W<i>a</i> log.</td>
 <td class="linedn center">1 + <i>c</i></td>
 <td rowspan="2"> âˆ’ <i>b</i>VA(1 âˆ’ <i>e</i>).</td></tr>
<tr>
 <td class="center"><i>e</i> + <i>c</i></td></tr>
</table>

<p>Hence the total effect per minute will be</p>

<table class="equation" summary="equation 19.">
<tr>
 <td rowspan="2">E&#160;=&#160;W<i>a</i><span
 class="fsize200">{</span></td>
 <td class="linedn center"><i>e</i></td>
 <td rowspan="2"> + log. </td>
 <td class="linedn center">1 + <i>c</i></td>
 <td rowspan="2"><span class="fsize200">}</span> âˆ’ <i>b</i>VA.<span
 class="padl4">(19.)</span></td></tr>
<tr>
 <td class="center"><i>e</i> + <i>c</i></td>
 <td class="center"><i>e</i> + <i>c</i></td></tr>
</table>

<p>If the engine work without expansion, <i>e</i>&#160;=&#160;1;</p>

<table class="equation" summary="equation 20.">
<tr>
 <td rowspan="2">âˆµ <i>Eâ€²</i>&#160;=&#160;</td>
 <td class="linedn center">W<i>a</i></td>
 <td rowspan="2"> âˆ’ <i>b</i>VA,<span class="padl4">(20.)</span></td></tr>
<tr>
 <td class="center">1 + <i>c</i></td></tr>
</table>

<p class="continue">as before; and the effect per minute gained by expansion will
therefore be</p>

<table class="equation" summary="Formula 21">
<tr>
 <td rowspan="2" class="left"><i>E</i>&#160;âˆ’&#160;<i>E</i>â€²&#160;=&#160;W<i>a</i><span
  class="fsize200">{</span></td>
 <td class="center linedn"><i>e</i></td>
 <td rowspan="2">&#160;âˆ’&#160;</td>
 <td class="center linedn">1</td>
 <td rowspan="2">&#160;+&#160;log.</td>
 <td class="center linedn">1&#160;+&#160;<i>c</i></td>
 <td rowspan="2" class="left"><span class="fsize200">}</span>;<span
  class="padl4">(21.)</span></td></tr>
<tr>
 <td class="center"><i>e</i>&#160;+&#160;<i>c</i></td>
 <td class="center">1&#160;+&#160;<i>c</i></td>
 <td class="center"><i>e</i>&#160;+&#160;<i>c</i></td>
</tr>
</table>

<p class="continue">which therefore represents the quantity of power gained by the
expansive action, with a given evaporating power.</p>

<p>In these formulÃ¦ the total effect of the steam is considered
without reference to the nature of the resistances which it has to
overcome.</p>

<p>These resistances may be enumerated as follows:â€”</p>

<ol><li>The resistance produced by the load which the engine is required
to move.</li>

<li>The resistance produced by the vapour which remains uncondensed
if the engine be a condensing engine, or of the atmospheric
pressure if the engine do not condense the steam.</li>

<li>The resistance of the engine and its machinery, consisting
of the friction of the various moving parts, the resistances of
the feed pump, the cold water pump, &#38;c. A part of these
resistances are of the same amount, whether the engine be
loaded or not, and part are increased, in some proportion
depending on the load.</li>
</ol>

<p>When the engine is maintained in a state of uniform motion,
the sum of all these resistances must always be equal to the whole
effect produced by the steam on the piston. The power expended
on the first alone is the <em>useful effect</em>.</p>

<p>Let</p>

<table class="dfnequation" summary="definitions">
<tr><td>R&#160;=&#160;the pressure per square foot of the piston surface,
which balances the resistances produced by the load.
</td></tr>

<tr><td><i>m</i>R&#160;=&#160;the pressure per square foot, which balances that part
of the friction of the engine which is proportional to the load.
</td></tr>

<tr><td><i>r</i>&#160;=&#160;the pressure per square foot, which balances the sum of all
those resistances that are not proportional to the load.</td></tr>
</table>

<p>The total resistance, therefore, being R + <i>m</i>R + <i>r</i>, which,
when the mean motion of the piston is uniform, must be equal to
the mean pressure on the piston. The total mechanical effect
<a class="refpn" id="Pg516">[Pg516]</a>
must therefore be equal to the total resistance multiplied by the
space through which that resistance is driven. Hence we shall have</p>

<table class="equation" summary="equation">
<tr>
 <td rowspan="2">{R(1 + <i>m</i>) + <i>r</i>}VA&#160;=&#160;W<i>a</i><span
   class="fsize200">{</span></td>
 <td class="linedn center"><i>e</i></td>
 <td rowspan="2"> + log. </td>
 <td class="linedn center">1 + <i>c</i></td>
 <td rowspan="2"><span
   class="fsize200">}</span> âˆ’ VA<i>b</i>;</td></tr>
<tr>
 <td class="center"><i>e</i> + <i>c</i></td>
 <td class="center"><i>e</i> + <i>c</i></td>
</tr>
</table>

<table class="equation" summary="equation">
<tr>
 <td rowspan="2">âˆµ RVA(1 + <i>m</i>)&#160;=&#160;W<i>a</i><span
   class="fsize200">{</span></td>
 <td class="linedn center"><i>e</i></td>
 <td rowspan="2"> + log. </td>
 <td class="linedn center">1 + <i>c</i></td>
 <td rowspan="2"><span
   class="fsize200">}</span> âˆ’ VA(<i>b</i> + <i>r</i>).</td></tr>
<tr>
 <td class="center"><i>e</i> + <i>c</i></td>
 <td class="center"><i>e</i> + <i>c</i></td>
</tr>
</table>

<p>For brevity, let</p>

<table class="equation" summary="equation">
<tr>
 <td rowspan="2"><i>eâ€²</i>&#160;=&#160;<i>a</i><span class="fsize200">{</span></td>
 <td class="linedn center"><i>e</i></td>
 <td rowspan="2">&#160;+&#160;log. </td>
 <td class="linedn center">1 + <i>c</i></td>
 <td rowspan="2"><span class="fsize200">}</span>;</td></tr>
<tr>
 <td class="center"><i>e</i> + <i>c</i></td>
 <td class="center"><i>e</i> + <i>c</i></td></tr>
</table>

<table class="equation" summary="equation">
<tr>
 <td>âˆµ RVA(1 + <i>m</i>)&#160;=&#160;W<i>eâ€²</i> âˆ’
 VA(<i>b</i> + <i>r</i>).<span class="padl4">(22.)</span></td>
</tr>
</table>

<p>By solving this for VA, we obtain</p>

<table class="equation" summary="equation 23.">
<tr>
 <td rowspan="2">VA&#160;=&#160;</td>
 <td class="linedn center">W<i>eâ€²</i></td>
 <td rowspan="2">;</td></tr>
<tr>
 <td class="center">R(1 + <i>m</i>) + <i>b</i> + <i>r</i></td></tr>
<tr>
 <td rowspan="2">âˆµ RVA&#160;=&#160;</td>
 <td class="linedn center">W<i>eâ€²</i>R</td>
 <td rowspan="2">.<span class="padl4">(23.)</span></td></tr>
<tr>
 <td class="center">R(1 + <i>m</i>) + <i>b</i> + <i>r</i></td></tr>
</table>

<p>This quantity RVA, being the product of the resistance RA,
of the load reduced to the surface of the piston, multiplied by the
space through which the piston is moved, will be equal to the load
itself multiplied by the space through which it is moved. This
being, in fact, the useful effect of the engine, let it be expressed by
U, and we shall have</p>

<table class="equation" summary="equation 24.">
<tr>
 <td rowspan="2">U&#160;=&#160;</td>
 <td class="linedn center">W<i>eâ€²</i>R</td>
 <td rowspan="2">.<span class="padl4">(24.)</span></td></tr>
<tr><td class="center">R(1 + <i>m</i>) + <i>b</i> + <i>r</i></td></tr>
</table>

<p class="continue">Or by (22.),</p>

<table class="equation" summary="equation 25.">
<tr>
 <td>U(1 + <i>m</i>)&#160;=&#160;W<i>eâ€²</i> âˆ’ VA(<i>b</i>
 + <i>r</i>).<span class="padl4">(25.)</span></td></tr>
</table>

<p>The value of the useful effect obtained from these formulÃ¦ will
be expressed in pounds, raised one foot per minute, W being the
effective evaporation in cubic feet per minute, A the area of the
piston in square feet, and V the space per minute through which it
is moved, in feet.</p>

<p>Since a resistance amounting to 33,000 pounds moved through
one foot per minute is called one-horse power, it is evident that
the horse power H of the engine is nothing more than the useful
effect per minute referred to a larger unit of weight or resistance;
that is to 33,000 pounds instead of one pound. Hence we shall
have</p>

<table class="equation" summary="equation 26.">
<tr>
 <td rowspan="2">H&#160;=&#160;</td>
 <td class="linedn center">U</td>
 <td rowspan="2">.<span class="padl4">(26.)</span></td></tr>
<tr><td class="center">33000</td></tr>
</table>

<p>Since the useful effect expressed in (24.) and (25.) is that due to
a number of cubic feet of water, expressed by W, we shall obtain
the effect due to one cubic foot of water, by dividing U by W.
If, therefore, Uâ€² be the effect produced by the effective evaporation
of a cubic foot of water, we shall have
<a class="refpn" id="Pg517">[Pg517]</a></p>

<table class="equation" summary="equation 27.">
<tr>
 <td rowspan="2">Uâ€²&#160;=&#160;</td>
 <td class="linedn center">U</td>
 <td rowspan="2">.<span class="padl4">(27.)</span></td></tr>
<tr><td class="center">W</td></tr>
</table>

<p>If the quantity of fuel consumed per minute be expressed by F,
the effect produced by the unit of fuel, called the <strong>DUTY</strong> of the
engine, will, for like reason, be</p>

<table class="equation" summary="equation 28.">
<tr>
 <td rowspan="2">D&#160;=&#160;</td>
 <td class="linedn center">U</td>
 <td rowspan="2">.<span class="padl4">(28.)</span></td></tr>
<tr><td class="center">F</td></tr>
</table>

<p>If the fuel be expressed in hundredweights of coal, then D will
express the number of pounds' weight raised one foot by a hundredweight
of coal.</p>

<p>By solving (24.) and (25.) for W, we obtain</p>

<table class="equation" summary="equation 29.">
<tr>
 <td rowspan="2">W&#160;=&#160;</td>
 <td class="linedn center">U{R(1 + <i>m</i>) + <i>b</i> + <i>r</i>}</td>
 <td rowspan="2">,<span class="padl4">(29.)</span></td></tr>
<tr><td class="center">R<i>eâ€²</i></td></tr>
</table>

<table class="equation" summary="equation 30.">
<tr>
 <td rowspan="2">W&#160;=&#160;</td>
 <td class="linedn center">1</td>
 <td rowspan="2">{U(1 + <i>m</i>) + VA(<i>b</i> + <i>r</i>)}.<span
 class="padl4">(30.)</span></td></tr>
<tr><td class="center"><i>eâ€²</i></td></tr>
</table>

<p>By eliminating U, by (26.), we shall have</p>

<table class="equation" summary="equation 31.">
<tr>
 <td rowspan="2">W&#160;=&#160;</td>
 <td class="linedn center">33000 H{R(1 + <i>m</i>) + <i>b</i> + <i>r</i>}</td>
 <td rowspan="2">,<span class="padl4">(31.)</span></td></tr>
<tr><td class="center">R<i>eâ€²</i></td></tr>
</table>

<table class="equation" summary="equation 32.">
<tr>
 <td rowspan="2">W&#160;=&#160;</td>
 <td class="linedn center">1</td>
 <td rowspan="2">{33000 H(1 + <i>m</i>) + VA(<i>b</i> +
 <i>r</i>)}.<span class="padl4">(32.)</span></td></tr>
<tr>
 <td class="center"><i>eâ€²</i></td></tr>
</table>

<p>The evaporation necessary per horse power per minute will be
found by putting H&#160;=&#160;1 in these formulÃ¦.<a name="FNanchor_41_41"
id="FNanchor_41_41"></a><a href="#Footnote_41_41" class="fnanchor">[41]</a></p>

<p>It will be observed that the quantities A and V, the area of
the cylinder and the speed of the piston, enter all these formulÃ¦
as factors of the same product. Other things, therefore, being the
same, the speed of the piston will be always inversely as the
area of the cylinder. In fact, VA is the volume of steam per
minute employed in working the piston, and if the piston be increased
or diminished in magnitude, its speed must be inversely
<a class="refpn" id="Pg518">[Pg518]</a>
varied by the necessity of being still moved through the same
number of cubic feet by the same volume of steam.</p>

<p>It has been already stated in the text, that no satisfactory experiments
have yet been made, by which the numerical value of
the quantity <i>r</i> can be exactly known. In engines of different magnitudes
and powers, this resistance bears very different proportions
to the whole power of the machine. In general, however, the larger
and more powerful the engine, the less that proportion will be.</p>

<p>That part of this resistance which arises from the reaction of
the uncondensed vapour on the piston is very variable, owing to
the more or less perfect action of the condensing apparatus, the
velocity of the piston, and the magnitude and form of the steam
passages. M. de Pambour states, that, by experiments made with indicators,
the mean amount of this resistance in the cylinder is
<span class="fraction">2<sup>1</sup>â„<sub>2</sub></span> lbs.
per square inch more than in the condenser, and that the pressure
in the latter being usually
<span class="fraction">1<sup>1</sup>â„<sub>2</sub></span> lb. per square inch, the mean amount
of the pressure of the condensed vapour in the cylinder is about
4 lbs. per square inch. Engineers, however, generally consider this
estimate to be above the truth in well-constructed engines, when
in good working order.</p>

<p>In condensing low pressure engines of forty horse power and
upwards, working with an average load, it is generally considered
that the resistance produced by the friction of the machine and
the force necessary to work the pumps may be taken at about
2 lbs. per square inch of piston surface.</p>

<p>Thus the whole resistance represented by <i>r</i> in the preceding formulÃ¦,
as applied to the larger class of low pressure engines, may
be considered as being under 6 lbs. per square inch, or 864 lbs.
per square foot, of the piston. It is necessary, however, to repeat,
that this estimate must be regarded as a very rough approximation;
and as representing the mean value of a quantity subject to great
variation, not only in one engine compared with another, but even
in the same engine compared with itself at different times and in
different states.</p>

<p>In the same class of engines, the magnitude of the clearage is
generally about a twentieth part of the capacity of the cylinder, so
that <i>c</i>&#160;=&#160;0Â·05.</p>

<p>That part of the resistance which is proportional to the load,
and on which the value of <i>m</i> in the preceding formulÃ¦ depends, is
still more variable, and depends so much on the form, magnitude,
and the arrangement of its parts, that no general rule can be given for
its value. It must, in fact, be determined in every particular case.</p>

<p>In the practical application of the preceding formulÃ¦ in condensing
engines we shall have
<a class="refpn" id="Pg519">[Pg519]</a></p>

<table class="equation" summary="equations">
<tr>
 <td><i>a</i>&#160;=&#160;3875969
 <span class="padl4"><i>b</i>&#160;=&#160;164</span>
 <span class="padl4"><i>c</i>&#160;=&#160;0Â·05;</span></td></tr>
</table>

<table class="equation" summary="equation">
<tr>
 <td rowspan="2"><i>eâ€²</i>&#160;=&#160;3875969<span
   class="fsize200">{</span></td>
 <td class="linedn center"><i>e</i></td>
 <td rowspan="2"> + log.</td>
 <td class="linedn center">1Â·05</td>
 <td rowspan="2"><span
   class="fsize200">}</span>.</td></tr>
<tr>
 <td class="center"><i>e</i> + 0Â·05</td>
 <td class="center"><i>e</i> + 0Â·05</td>
</tr>
</table>

<p>In engines which work without condensation, and therefore with
high pressure steam, we shall have</p>

<table class="equation" summary="equations">
<tr>
 <td><i>a</i>&#160;=&#160;4347826
 <span class="padl4"><i>b</i>&#160;=&#160;618</span>
 <span class="padl4"><i>c</i>&#160;=&#160;0Â·05;</span></td></tr>
</table>

<table class="equation" summary="equation">
<tr>
 <td rowspan="2"><i>eâ€²</i>&#160;=&#160;4347826<span
   class="fsize200">{</span></td>
 <td class="linedn center"><i>e</i></td>
 <td rowspan="2"> + log.</td>
 <td class="linedn center">1Â·05</td>
 <td rowspan="2"><span
   class="fsize200">}</span>.</td></tr>
<tr>
 <td class="center"><i>e</i> + 0Â·05</td>
 <td class="center"><i>e</i> + 0Â·05</td>
</tr>
</table>

<p>To facilitate computation, the values of <i>eâ€²</i> corresponding to all
values of <i>e</i>, from <i>e</i>&#160;=&#160;Â·10 to <i>e</i>&#160;=&#160;Â·90, are given in the following
table:â€”</p>

<table summary="values of unnamed variable eâ€² versus values of
 --the engine work without expansion, e-- from 0.10 to 0.90"
 style="margin-left:-0.75em;">
<tr>
 <th align="right"><i>e</i></th>
 <th align="right">Condensing Engines <span class="no-wrap"><i>eâ€²</i>.</span></th>
 <th align="right">Non-condensing Engines <span class="no-wrap"><i>eâ€²</i>.</span></th>
 <th align="right"><i>e</i></th>
 <th align="right">Condensing Engines <span class="no-wrap"><i>eâ€²</i></span>.</th>
 <th align="right">Non-condensing Engines <span class="no-wrap"><i>eâ€²</i>.</span></th></tr>
<tr>
 <td align="right">Â·10</td>
 <td align="right">10126265</td>
 <td align="right">11359029</td>
 <td align="right">Â·51</td>
 <td align="right">5966367</td>
 <td align="right">6692708</td></tr>
<tr>
 <td align="right">Â·11</td>
 <td align="right">9956867</td>
 <td align="right">11169008</td>
 <td align="right">Â·52</td>
 <td align="right">5903837</td>
 <td align="right">6622565</td></tr>
<tr>
 <td align="right">Â·12</td>
 <td align="right">9793136</td>
 <td align="right">10985344</td>
 <td align="right">Â·53</td>
 <td align="right">5842288</td>
 <td align="right">6553525</td></tr>
<tr>
 <td align="right">Â·13</td>
 <td align="right">9634926</td>
 <td align="right">10807875</td>
 <td align="right">Â·54</td>
 <td align="right">5781693</td>
 <td align="right">6485552</td></tr>
<tr>
 <td align="right">Â·14</td>
 <td align="right">9482029</td>
 <td align="right">10636364</td>
 <td align="right">Â·55</td>
 <td align="right">5722024</td>
 <td align="right">6418619</td></tr>
<tr>
 <td align="right">Â·15</td>
 <td align="right">9334219</td>
 <td align="right">10470560</td>
 <td align="right">Â·56</td>
 <td align="right">5663251</td>
 <td align="right">6352693</td></tr>
<tr>
 <td align="right">Â·16</td>
 <td align="right">9191251</td>
 <td align="right">10310186</td>
 <td align="right">Â·57</td>
 <td align="right">5605353</td>
 <td align="right">6287745</td></tr>
<tr>
 <td align="right">Â·17</td>
 <td align="right">9052888</td>
 <td align="right">10154978</td>
 <td align="right">Â·58</td>
 <td align="right">5548297</td>
 <td align="right">6223742</td></tr>
<tr>
 <td align="right">Â·18</td>
 <td align="right">8918896</td>
 <td align="right">10004675</td>
 <td align="right">Â·59</td>
 <td align="right">5492064</td>
 <td align="right">6160662</td></tr>
<tr>
 <td align="right">Â·19</td>
 <td align="right">8789043</td>
 <td align="right">9859014</td>
 <td align="right">Â·60</td>
 <td align="right">5436628</td>
 <td align="right">6098478</td></tr>
<tr>
 <td align="right">Â·20</td>
 <td align="right">8663120</td>
 <td align="right">9717760</td>
 <td align="right">Â·61</td>
 <td align="right">5381969</td>
 <td align="right">6037166</td></tr>
<tr>
 <td align="right">Â·21</td>
 <td align="right">8540918</td>
 <td align="right">9580682</td>
 <td align="right">Â·62</td>
 <td align="right">5328065</td>
 <td align="right">5976699</td></tr>
<tr>
 <td align="right">Â·22</td>
 <td align="right">8422242</td>
 <td align="right">9447559</td>
 <td align="right">Â·63</td>
 <td align="right">5274896</td>
 <td align="right">5917057</td></tr>
<tr>
 <td align="right">Â·23</td>
 <td align="right">8306916</td>
 <td align="right">9318193</td>
 <td align="right">Â·64</td>
 <td align="right">5222444</td>
 <td align="right">5858219</td></tr>
<tr>
 <td align="right">Â·24</td>
 <td align="right">8194770</td>
 <td align="right">9192396</td>
 <td align="right">Â·65</td>
 <td align="right">5170684</td>
 <td align="right">5800159</td></tr>
<tr>
 <td align="right">Â·25</td>
 <td align="right">8085644</td>
 <td align="right">9069984</td>
 <td align="right">Â·66</td>
 <td align="right">5119605</td>
 <td align="right">5742860</td></tr>
<tr>
 <td align="right">Â·26</td>
 <td align="right">7979392</td>
 <td align="right">8950796</td>
 <td align="right">Â·67</td>
 <td align="right">5069186</td>
 <td align="right">5686304</td></tr>
<tr>
 <td align="right">Â·27</td>
 <td align="right">7875870</td>
 <td align="right">8834674</td>
 <td align="right">Â·68</td>
 <td align="right">5019410</td>
 <td align="right">5630469</td></tr>
<tr>
 <td align="right">Â·28</td>
 <td align="right">7774952</td>
 <td align="right">8721468</td>
 <td align="right">Â·69</td>
 <td align="right">4970263</td>
 <td align="right">5575340</td></tr>
<tr>
 <td align="right">Â·29</td>
 <td align="right">7676514</td>
 <td align="right">8611048</td>
 <td align="right">Â·70</td>
 <td align="right">4921727</td>
 <td align="right">5520894</td></tr>
<tr>
 <td align="right">Â·30</td>
 <td align="right">7580447</td>
 <td align="right">8503284</td>
 <td align="right">Â·71</td>
 <td align="right">4873790</td>
 <td align="right">5467121</td></tr>
<tr>
 <td align="right">Â·31</td>
 <td align="right">7486640</td>
 <td align="right">8398056</td>
 <td align="right">Â·72</td>
 <td align="right">4826434</td>
 <td align="right">5414000</td></tr>
<tr>
 <td align="right">Â·32</td>
 <td align="right">7394990</td>
 <td align="right">8295250</td>
 <td align="right">Â·73</td>
 <td align="right">4779648</td>
 <td align="right">5361519</td></tr>
<tr>
 <td align="right">Â·33</td>
 <td align="right">7305407</td>
 <td align="right">8194760</td>
 <td align="right">Â·74</td>
 <td align="right">4733417</td>
 <td align="right">5309659</td></tr>
<tr>
 <td align="right">Â·34</td>
 <td align="right">7217807</td>
 <td align="right">8096496</td>
 <td align="right">Â·75</td>
 <td align="right">4687728</td>
 <td align="right">5258408</td></tr>
<tr>
 <td align="right">Â·35</td>
 <td align="right">7132097</td>
 <td align="right">8000352</td>
 <td align="right">Â·76</td>
 <td align="right">4642569</td>
 <td align="right">5207751</td></tr>
<tr>
 <td align="right">Â·36</td>
 <td align="right">7048206</td>
 <td align="right">7906249</td>
 <td align="right">Â·77</td>
 <td align="right">4597928</td>
 <td align="right">5157676</td></tr>
<tr>
 <td align="right">Â·37</td>
 <td align="right">6966058</td>
 <td align="right">7814100</td>
 <td align="right">Â·78</td>
 <td align="right">4553794</td>
 <td align="right">5108170</td></tr>
<tr>
 <td align="right">Â·38</td>
 <td align="right">6885585</td>
 <td align="right">7723832</td>
 <td align="right">Â·79</td>
 <td align="right">4510155</td>
 <td align="right">5059218</td></tr>
<tr>
 <td align="right">Â·39</td>
 <td align="right">6806720</td>
 <td align="right">7635365</td>
 <td align="right">Â·80</td>
 <td align="right">4466999</td>
 <td align="right">5010808</td></tr>
<tr>
 <td align="right">Â·40</td>
 <td align="right">6729408</td>
 <td align="right">7548642</td>
 <td align="right">Â·81</td>
 <td align="right">4424317</td>
 <td align="right">4962931</td></tr>
<tr>
 <td align="right">Â·41</td>
 <td align="right">6653578</td>
 <td align="right">7463580</td>
 <td align="right">Â·82</td>
 <td align="right">4382096</td>
 <td align="right">4915569</td></tr>
<tr>
 <td align="right">Â·42</td>
 <td align="right">6579187</td>
 <td align="right">7380132</td>
 <td align="right">Â·83</td>
 <td align="right">4340332</td>
 <td align="right">4868720</td></tr>
<tr>
 <td align="right">Â·43</td>
 <td align="right">6506174</td>
 <td align="right">7298230</td>
 <td align="right">Â·84</td>
 <td align="right">4299010</td>
 <td align="right">4822368</td></tr>
<tr>
 <td align="right">Â·44</td>
 <td align="right">6434491</td>
 <td align="right">7217822</td>
 <td align="right">Â·85</td>
 <td align="right">4258120</td>
 <td align="right">4776500</td></tr>
<tr>
 <td align="right">Â·45</td>
 <td align="right">6364099</td>
 <td align="right">7138858</td>
 <td align="right">Â·86</td>
 <td align="right">4217658</td>
 <td align="right">4731113</td></tr>
<tr>
 <td align="right">Â·46</td>
 <td align="right">6294944</td>
 <td align="right">7061285</td>
 <td align="right">Â·87</td>
 <td align="right">4177613</td>
 <td align="right">4686192</td></tr>
<tr>
 <td align="right">Â·47</td>
 <td align="right">6226989</td>
 <td align="right">6985058</td>
 <td align="right">Â·88</td>
 <td align="right">4137974</td>
 <td align="right">4641728</td></tr>
<tr>
 <td align="right">Â·48</td>
 <td align="right">6160190</td>
 <td align="right">6910126</td>
 <td align="right">Â·89</td>
 <td align="right">4098737</td>
 <td align="right">4597713</td></tr>
<tr>
 <td align="right">Â·49</td>
 <td align="right">6094510</td>
 <td align="right">6836450</td>
 <td align="right">Â·90</td>
 <td align="right">4059893</td>
 <td align="right">4554140</td></tr>
<tr>
 <td align="right">Â·50</td>
 <td align="right">6029916</td>
 <td align="right">6763992</td></tr>
</table>

<p class="right"><a class="refpn" id="Pg520">[Pg520]</a></p>
<p>In engines which work without expansion we have</p>

<table class="equation" summary="equation">
<tr>
 <td rowspan="2"><i>eâ€²</i>&#160;=&#160;</td>
 <td class="linedn center"><i>a</i></td>
 <td rowspan="2">.</td></tr>
<tr><td class="center">1 + <i>c</i></td></tr>
</table>

<p>For condensing engines without expansion, we shall then have</p>

<table class="equation" summary="equation 33.">
<tr>
 <td rowspan="2"><i>eâ€²</i>&#160;=&#160;</td>
 <td class="linedn center">3875969</td>
 <td rowspan="2">&#160;=&#160;3691399;<span
 class="padl4">(33.)</span></td></tr>
<tr><td class="center">1Â·05</td></tr>
</table>

<p class="continue">and for non-condensing engines,</p>

<table class="equation" summary="equation 34.">
<tr>
 <td rowspan="2"><i>eâ€²</i>&#160;=&#160;</td>
 <td class="linedn center">4347826</td>
 <td rowspan="2">&#160;=&#160;4140787.<span
 class="padl4">(34.)</span></td></tr>
<tr><td class="center">1Â·05</td></tr>
</table>

<p>As the diameters of the cylinders of engines are generally expressed
in inches, the corresponding areas of the pistons expressed
in square feet are given in the following table, so that the values of
A may be readily found:â€”</p>

<table summary="Area of cylinder vs diameter from 10 to 85 inches.">
<tr><th>Diameter.</th><th>Area.</th><th>Diameter.</th><th>Area.</th></tr>
<tr><th><i>Inches.</i></th><th><i>Sq. Feet.</i></th><th><i>Inches.</i></th><th><i>Sq. Feet.</i></th></tr>
<tr>
 <td align="right">10</td>
 <td align="right">07545</td>
 <td align="right">48</td>
 <td align="right">127566</td></tr>
<tr>
 <td align="right">11</td>
 <td align="right">07660</td>
 <td align="right">49</td>
 <td align="right">137095</td></tr>
<tr>
 <td align="right">12</td>
 <td align="right">07785</td>
 <td align="right">50</td>
 <td align="right">137635</td></tr>
<tr>
 <td align="right">13</td>
 <td align="right">07922</td>
 <td align="right">51</td>
 <td align="right">147186</td></tr>
<tr>
 <td align="right">14</td>
 <td align="right">17069</td>
 <td align="right">52</td>
 <td align="right">147748</td></tr>
<tr>
 <td align="right">15</td>
 <td align="right">17227</td>
 <td align="right">53</td>
 <td align="right">157321</td></tr>
<tr>
 <td align="right">16</td>
 <td align="right">17396</td>
 <td align="right">54</td>
 <td align="right">157904</td></tr>
<tr>
 <td align="right">17</td>
 <td align="right">17576</td>
 <td align="right">55</td>
 <td align="right">167499</td></tr>
<tr>
 <td align="right">18</td>
 <td align="right">17767</td>
 <td align="right">56</td>
 <td align="right">177104</td></tr>
<tr>
 <td align="right">19</td>
 <td align="right">17969</td>
 <td align="right">57</td>
 <td align="right">177721</td></tr>
<tr>
 <td align="right">20</td>
 <td align="right">27182</td>
 <td align="right">58</td>
 <td align="right">187348</td></tr>
<tr>
 <td align="right">21</td>
 <td align="right">27405</td>
 <td align="right">59</td>
 <td align="right">187986</td></tr>
<tr>
 <td align="right">22</td>
 <td align="right">27640</td>
 <td align="right">60</td>
 <td align="right">197635</td></tr>
<tr>
 <td align="right">23</td>
 <td align="right">27885</td>
 <td align="right">61</td>
 <td align="right">207295</td></tr>
<tr>
 <td align="right">24</td>
 <td align="right">37142</td>
 <td align="right">62</td>
 <td align="right">207966</td></tr>
<tr>
 <td align="right">25</td>
 <td align="right">37409</td>
 <td align="right">63</td>
 <td align="right">217648</td></tr>
<tr>
 <td align="right">26</td>
 <td align="right">37687</td>
 <td align="right">64</td>
 <td align="right">227340</td></tr>
<tr>
 <td align="right">27</td>
 <td align="right">37976</td>
 <td align="right">65</td>
 <td align="right">237044</td></tr>
<tr>
 <td align="right">28</td>
 <td align="right">47276</td>
 <td align="right">66</td>
 <td align="right">237758</td></tr>
<tr>
 <td align="right">29</td>
 <td align="right">47587</td>
 <td align="right">67</td>
 <td align="right">247484</td></tr>
<tr>
 <td align="right">30</td>
 <td align="right">47909</td>
 <td align="right">68</td>
 <td align="right">257220</td></tr>
<tr>
 <td align="right">31</td>
 <td align="right">57241</td>
 <td align="right">69</td>
 <td align="right">257967</td></tr>
<tr>
 <td align="right">32</td>
 <td align="right">57585</td>
 <td align="right">70</td>
 <td align="right">267725</td></tr>
<tr>
 <td align="right">33</td>
 <td align="right">57940</td>
 <td align="right">71</td>
 <td align="right">277494</td></tr>
<tr>
 <td align="right">34</td>
 <td align="right">67305</td>
 <td align="right">72</td>
 <td align="right">287274</td></tr>
<tr>
 <td align="right">35</td>
 <td align="right">67681</td>
 <td align="right">73</td>
 <td align="right">297065</td></tr>
<tr>
 <td align="right">36</td>
 <td align="right">77069</td>
 <td align="right">74</td>
 <td align="right">297867</td></tr>
<tr>
 <td align="right">37</td>
 <td align="right">77467</td>
 <td align="right">75</td>
 <td align="right">307680</td></tr>
<tr>
 <td align="right">38</td>
 <td align="right">77876</td>
 <td align="right">76</td>
 <td align="right">317503</td></tr>
<tr>
 <td align="right">39</td>
 <td align="right">87296</td>
 <td align="right">77</td>
 <td align="right">327338</td></tr>
<tr>
 <td align="right">40</td>
 <td align="right">87727</td>
 <td align="right">78</td>
 <td align="right">337183</td></tr>
<tr>
 <td align="right">41</td>
 <td align="right">97168</td>
 <td align="right">79</td>
 <td align="right">347039</td></tr>
<tr>
 <td align="right">42</td>
 <td align="right">97621</td>
 <td align="right">80</td>
 <td align="right">347907</td></tr>
<tr>
 <td align="right">43</td>
 <td align="right">107085</td>
 <td align="right">81</td>
 <td align="right">357785</td></tr>
<tr>
 <td align="right">44</td>
 <td align="right">107559</td>
 <td align="right">82</td>
 <td align="right">367674</td></tr>
<tr>
 <td align="right">45</td>
 <td align="right">117045</td>
 <td align="right">83</td>
 <td align="right">377574</td></tr>
<tr>
 <td align="right">46</td>
 <td align="right">117541</td>
 <td align="right">84</td>
 <td align="right">387485</td></tr>
<tr>
 <td align="right">47</td>
 <td align="right">127048</td>
 <td align="right">85</td>
 <td align="right">397406</td></tr>
</table>

<table summary="Area of cylinder vs diameter from 86 to 161 inches.">
<tr><th>Diameter.</th><th>Area.</th><th>Diameter.</th><th>Area.</th></tr>
<tr><th><i>Inches.</i></th><th><i>Sq. Feet.</i></th><th><i>Inches.</i></th><th><i>Sq. Feet.</i></th></tr>
<tr>
 <td align="right">86</td>
 <td align="right">407339</td>
 <td align="right">124</td>
 <td align="right">837863</td></tr>
<tr>
 <td align="right">87</td>
 <td align="right">417283</td>
 <td align="right">125</td>
 <td align="right">857221</td></tr>
<tr>
 <td align="right">88</td>
 <td align="right">427237</td>
 <td align="right">126</td>
 <td align="right">867590</td></tr>
<tr>
 <td align="right">89</td>
 <td align="right">437202</td>
 <td align="right">127</td>
 <td align="right">877970</td></tr>
<tr>
 <td align="right">90</td>
 <td align="right">447179</td>
 <td align="right">128</td>
 <td align="right">897361</td></tr>
<tr>
 <td align="right">91</td>
 <td align="right">457166</td>
 <td align="right">129</td>
 <td align="right">907763</td></tr>
<tr>
 <td align="right">92</td>
 <td align="right">467164</td>
 <td align="right">130</td>
 <td align="right">927175</td></tr>
<tr>
 <td align="right">93</td>
 <td align="right">477173</td>
 <td align="right">131</td>
 <td align="right">937599</td></tr>
<tr>
 <td align="right">94</td>
 <td align="right">487193</td>
 <td align="right">132</td>
 <td align="right">957033</td></tr>
<tr>
 <td align="right">95</td>
 <td align="right">497224</td>
 <td align="right">133</td>
 <td align="right">967479</td></tr>
<tr>
 <td align="right">96</td>
 <td align="right">507265</td>
 <td align="right">134</td>
 <td align="right">977935</td></tr>
<tr>
 <td align="right">97</td>
 <td align="right">517318</td>
 <td align="right">135</td>
 <td align="right">997402</td></tr>
<tr>
 <td align="right">98</td>
 <td align="right">527382</td>
 <td align="right">136</td>
 <td align="right">1007880</td></tr>
<tr>
 <td align="right">99</td>
 <td align="right">537456</td>
 <td align="right">137</td>
 <td align="right">1027369</td></tr>
<tr>
 <td align="right">100</td>
 <td align="right">547542</td>
 <td align="right">138</td>
 <td align="right">1037869</td></tr>
<tr>
 <td align="right">101</td>
 <td align="right">557638</td>
 <td align="right">139</td>
 <td align="right">1057380</td></tr>
<tr>
 <td align="right">102</td>
 <td align="right">567745</td>
 <td align="right">140</td>
 <td align="right">1067901</td></tr>
<tr>
 <td align="right">103</td>
 <td align="right">577863</td>
 <td align="right">141</td>
 <td align="right">1087434</td></tr>
<tr>
 <td align="right">104</td>
 <td align="right">587992</td>
 <td align="right">142</td>
 <td align="right">1097977</td></tr>
<tr>
 <td align="right">105</td>
 <td align="right">607132</td>
 <td align="right">143</td>
 <td align="right">1117532</td></tr>
<tr>
 <td align="right">106</td>
 <td align="right">617283</td>
 <td align="right">144</td>
 <td align="right">1137097</td></tr>
<tr>
 <td align="right">107</td>
 <td align="right">627445</td>
 <td align="right">145</td>
 <td align="right">1147674</td></tr>
<tr>
 <td align="right">108</td>
 <td align="right">637617</td>
 <td align="right">146</td>
 <td align="right">1167261</td></tr>
<tr>
 <td align="right">109</td>
 <td align="right">647801</td>
 <td align="right">147</td>
 <td align="right">1177859</td></tr>
<tr>
 <td align="right">110</td>
 <td align="right">657995</td>
 <td align="right">148</td>
 <td align="right">1197468</td></tr>
<tr>
 <td align="right">111</td>
 <td align="right">677201</td>
 <td align="right">149</td>
 <td align="right">1217088</td></tr>
<tr>
 <td align="right">112</td>
 <td align="right">687417</td>
 <td align="right">150</td>
 <td align="right">1227719</td></tr>
<tr>
 <td align="right">113</td>
 <td align="right">697644</td>
 <td align="right">151</td>
 <td align="right">1247361</td></tr>
<tr>
 <td align="right">114</td>
 <td align="right">707882</td>
 <td align="right">152</td>
 <td align="right">1267013</td></tr>
<tr>
 <td align="right">115</td>
 <td align="right">727131</td>
 <td align="right">153</td>
 <td align="right">1277676</td></tr>
<tr>
 <td align="right">116</td>
 <td align="right">737391</td>
 <td align="right">154</td>
 <td align="right">1297351</td></tr>
<tr>
 <td align="right">117</td>
 <td align="right">747662</td>
 <td align="right">155</td>
 <td align="right">1317036</td></tr>
<tr>
 <td align="right">118</td>
 <td align="right">757944</td>
 <td align="right">156</td>
 <td align="right">1327732</td></tr>
<tr>
 <td align="right">119</td>
 <td align="right">777236</td>
 <td align="right">157</td>
 <td align="right">1347439</td></tr>
<tr>
 <td align="right">120</td>
 <td align="right">787540</td>
 <td align="right">158</td>
 <td align="right">1367157</td></tr>
<tr>
 <td align="right">121</td>
 <td align="right">797854</td>
 <td align="right">159</td>
 <td align="right">1377886</td></tr>
<tr>
 <td align="right">122</td>
 <td align="right">817180</td>
 <td align="right">160</td>
 <td align="right">1397626</td></tr>
<tr>
 <td align="right">123</td>
 <td align="right">827516</td>
 <td align="right">161</td>
 <td align="right">1417377</td></tr>
</table>

<p class="right"><a class="refpn" id="Pg521">[Pg521]</a></p>
<p>The practical application of the preceding formulÃ¦ will be shown
by the following examples.</p>

<p class="center"><b>EXAMPLES.</b></p>

<p><em>1. A 36-inch cylinder with
<span class="fraction">5<sup>1</sup>â„<sub>2</sub></span> feet stroke
is supplied by a boiler
evaporating effectively 60 cubic feet of water per hour, and the
piston makes 20 strokes per minute without expansion;â€”what
is the power of the engine and the pressure of steam in the
cylinder?</em></p>

<p>Let it be assumed that <span class="no-wrap"><i>r</i>&#160;=&#160;6 Ã—
 144&#160;=&#160;864</span> and <span class="no-wrap"><i>m</i>&#160;=&#160;0Â·1</span>. Since
the engine is a condensing engine, we have <span class="no-wrap"><i>b</i>&#160;=&#160;164</span> and <span class="no-wrap"><i>eâ€²</i>&#160;=&#160;3691399</span>.
By the formulÃ¦ (25.) and (26.) we have</p>

<table class="equation" summary="equation">
<tr>
 <td rowspan="2">H&#160;=&#160;</td>
 <td class="linedn center">W<i>eâ€²</i> âˆ’ VA(<i>b</i> + <i>r</i>)</td>
 <td rowspan="2">;</td></tr>
<tr><td class="center">33000(1 + <i>m</i>)</td></tr>
</table>

<p class="continue">and since by the data we have</p>

<table class="equation" summary="equation">
<tr>
 <td>W&#160;=&#160;1
 <span class="padl4">A&#160;=&#160;7Â·069</span>
 <span class="padl4">V&#160;=&#160;2<i>n</i>L&#160;=&#160;40 Ã— 5Â·5&#160;=&#160;220,</span></td></tr>
</table>

<p class="continue">the formula, by these substitutions, becomes</p>

<table class="equation" summary="equation">
<tr>
 <td rowspan="2">H&#160;=&#160;</td>
 <td class="linedn center">3691399 âˆ’ 220 Ã— 1028 Ã— 7Â·069</td>
 <td rowspan="2">;</td></tr>
<tr><td class="center">33000 Ã— 1Â·1</td></tr>
<tr><td colspan="2">âˆµ H = 57Â·6.</td></tr>
</table>

<p>Since <i>e</i>&#160;=&#160;1, the pressure P of steam in the cylinder, by (18.), is</p>

<table class="equation" summary="equation">
<tr>
 <td rowspan="2">P&#160;=&#160;</td>
 <td class="linedn center">W<i>eâ€²</i></td>
 <td rowspan="2"> âˆ’ <i>b</i>.</td></tr>
<tr><td class="center">VA</td></tr>
</table>

<p>Therefore</p>

<table class="equation" summary="equation">
<tr>
 <td rowspan="2">P&#160;=&#160;</td>
 <td class="linedn center">3691399</td>
 <td rowspan="2"> âˆ’ 164&#160;=&#160;2210;</td></tr>
<tr><td class="center">1555Â·18</td></tr>
</table>

<p class="continue">which being the pressure in pounds per square foot, the pressure
per square inch will be
<span class="fraction">15<sup>1</sup>â„<sub>3</sub></span> lbs.</p>

<p><em>2. To find the effective evaporation necessary to produce a power
of 80 horses with the same engine. Also, find the pressure of
steam in the cylinder, the speed of the piston being the same.</em></p>

<p>By the formula (32.), with the above substitutions, we have</p>

<table class="equation" summary="equation">
<tr>
 <td rowspan="2">W&#160;=&#160;</td>
 <td class="linedn center">33000 Ã— 80 Ã— 1Â·1 + 220 Ã— 7069 Ã— 1028</td>
 <td rowspan="2">&#160;=&#160;1Â·22.</td></tr>
<tr><td class="center">3691399</td></tr>
</table>

<p>The evaporating power would therefore be only increased 22
per cent., while the working power of the engine would be increased
nearly 40 per cent.</p>

<p>The pressure P in the cylinder will be given, by (18.), as before.</p>

<table class="equation" summary="equation">
<tr>
 <td rowspan="2">P&#160;=&#160;</td>
 <td class="linedn center">1Â·22 Ã— 3691399</td>
 <td rowspan="2"> âˆ’ 164&#160;=&#160;2732;</td></tr>
<tr><td class="center">1555Â·18</td></tr>
</table>

<p class="continue">which is equivalent to 19 lbs. per square inch.
<a class="refpn" id="Pg522">[Pg522]</a></p>

<p><em>3. What must be the diameter of a cylinder to work with a power
of a hundred horses, supplied by a boiler evaporating effectively
70 cubic feet of water per hour, the mean speed of the piston
being 240 feet per minute, and the steam being cut off at half
stroke? Also, what will be the full pressure of steam on the
piston?</em></p>

<p>Taking, as in the former examples, <i>m</i>&#160;=&#160;0Â·1, <i>b</i>&#160;=&#160;164, and <i>r</i>&#160;=&#160;864,
we shall have</p>

<table class="equation" summary="equation">
<tr>
 <td>H&#160;=&#160;100
 <span class="padl4">W = <sup>7</sup>â„<sub>6</sub></span>
 <span class="padl4">V&#160;=&#160;240,</span></td></tr>
</table>

<p class="continue">and by the column for condensing engines, in table, p. 519, we have
<i>eâ€²</i>&#160;=&#160;6029916, where <i>e</i>&#160;=&#160;0Â·50. Making these substitutions in</p>

<table class="equation" summary="equation">
<tr>
 <td>W<i>eâ€²</i>&#160;=&#160;33000 H(1 + <i>m</i>)
 + VA(<i>b</i> + <i>r</i>),</td></tr>
</table>

<p class="continue">we shall have</p>

<table class="equation" summary="equation">
<tr>
 <td>(<sup>7</sup>â„<sub>6</sub>) Ã— 6029916&#160;=&#160;3300000
 Ã— 1Â·1 + 240 Ã— 1028 Ã— A.</td></tr>
</table>

<p class="continue">Whence we find</p>

<table class="equation" summary="equation">
<tr>
 <td>A&#160;=&#160;13Â·8;</td></tr>
</table>

<p class="continue">and by the table, p. 520, the corresponding diameter of the cylinder
will be
<span class="fraction">50<sup>1</sup>â„<sub>3</sub></span> inches.</p>

<p>If Pâ€² be the full pressure of the steam, we shall have, by (18.),</p>

<table class="equation" summary="equation">
<tr>
 <td rowspan="2">Pâ€²&#160;=&#160;</td>
 <td class="linedn center">W<i>a</i></td>
 <td rowspan="2"> âˆ’ <i>b</i>.</td></tr>
<tr><td class="center">VA(<i>e</i> + <i>c</i>)</td></tr>
</table>

<p class="continue">Making in this the proper substitutions, we have</p>

<table class="equation" summary="equation">
<tr>
 <td rowspan="2">Pâ€²&#160;=&#160;</td>
 <td class="linedn center"><sup>7</sup>â„<sub>6</sub> Ã— 3875969</td>
 <td rowspan="2"> âˆ’ 164&#160;=&#160;2318;</td></tr>
<tr><td class="center">240 Ã— 13Â·8 Ã— 0Â·55</td></tr>
</table>

<p class="continue">which being in pounds per square foot, the pressure per square
inch will be <span class="fraction">16<sup>1</sup>â„<sub>10</sub></span>
lbs.</p>


<div class="footnotes"><h3>FOOTNOTES:</h3>

<div class="footnote">
<p><a name="Footnote_40_40" id="Footnote_40_40"></a><a
 href="#FNanchor_40_40"><span class="label">[40]</span></a>
 M. de Pambour states that the increased volume is 1364 cubic
 inches.</p></div>

<div class="footnote">

<p><a name="Footnote_41_41" id="Footnote_41_41"></a><a
href="#FNanchor_41_41"><span class="label">[41]</span></a>
 FormulÃ¦ equivalent to some of the preceding are given, with numerous
others, by M. de Pambour, in his Theory of the Steam Engine. These mathematical
details contain nothing new in principle, being merely the application
of the known principles of general mechanics to this particular machine.
M. de Pambour objects against the methods of calculating the practical effects
of steam engines generally adopted by engineers in this country. Their
estimates of the loss of power by friction, imperfect condensation, and other
causes, are, as I have stated in this volume, vague, and can be regarded
at best as very rough approximations; but, subject to the restrictions under
which their methods of calculation are always applied, they are by no means so
defective as M. de Pambour supposes. He proves what he considers to be
their inaccuracy, by applying them in cases in which they are never intended to
be applied by English engineers. Those who desire to reduce to general algebraical
formulÃ¦ the effects of the different kinds of steam engines will, however,
find the volume of M. de Pambour of considerable use.</p></div></div>

<h2><a name="INDEX" id="INDEX">INDEX.</a></h2>

<p class="right"><a class="refpn" id="Pg523">[Pg523]</a><br />
<a href="#CONTENTS"><small>TOC</small></a></p>

<ul id="bookindex">
<li class="lsthdr">Air, elasticity of, <a href="#Pg028">28</a>;</li>
<li>  May be partially expelled from a vessel by the application of heat,
  <a href="#Pg044">44</a>.</li>

<li class="lstfst">America, steam navigation first established in,
  <a href="#Pg487">487</a>;</li>
<li>Circumstances which led to it,
  <a href="#Pg488">488</a>;</li>
<li>  Fitch and Rumsey, their attempts to apply the single-acting engine to the propulsion of vessels,
  <a href="#Pg489">489</a>;</li>
<li>  Stevens of Hoboken commences experiments on steam navigation,
  <a href="#Pg489">489</a>;</li>
<li>  Experiments of Livingstone and Fulton,
  <a href="#Pg489">489</a>;</li>
<li>  Fulton's first boat,
  <a href="#Pg490">490</a>;</li>
<li>  The Hudson navigated by steam,
  <a href="#Pg491">491</a>;</li>
<li>  Extension and improvement of river navigation,
  <a href="#Pg492">492</a>;</li>
<li>  American steamers,
  <a href="#Pg494">494</a>;</li>
<li>  Difference between them and European steamers,
  <a href="#Pg494">494</a>;</li>
<li>  Steamers on the Hudson,
  <a href="#Pg494">494</a>;</li>
<li>  American paddle-wheels,
  <a href="#Pg495">495</a>;</li>
<li>  Sea-going American steamers,
  <a href="#Pg496">496</a>;</li>
<li>  Speed attained by American steamers,
  <a href="#Pg497">497</a>;</li>
<li>  Lake steamers,
  <a href="#Pg499">499</a>;</li>
<li>  The Mississippi and its tributaries,
  <a href="#Pg499">499</a>;</li>
<li>  Steam-boats navigating it,
  <a href="#Pg500">500</a>;</li>
<li>  Their structure and machinery,
  <a href="#Pg500">500</a>;</li>
<li>  New Orleans Harbour,
  <a href="#Pg503">503</a>;</li>
<li>  Steam tugs,
  <a href="#Pg503">503</a>.</li>
<li class="lstfst">Atmosphere,
  <a href="#Pg038">38</a>;</li>
<li>  Weight of,
  <a href="#Pg039">39</a>.</li>

<li class="lstfst">Atmospheric air, mechanical properties of,
  <a href="#Pg038">38</a>;</li>
<li>  Composition of,
  <a href="#Pg253">253</a>.</li>

<li class="lstfst">Atmospheric engine, Thomas Newcomen the reputed inventor of,
  <a href="#Pg062">62</a>;</li>
<li>  Description of, as first constructed by Newcomen,
  <a href="#Pg067">67</a>;</li>
<li>  The operation of considered,
  <a href="#Pg069">69</a>;</li>
<li>  Not unfrequently used in preference to the modern steam engine,
  <a href="#Pg072">72</a>;</li>
<li>  Advantages which it possessed over Savery's,
  <a href="#Pg073">73</a>;</li>
<li>  Considerably improved by Beighton,
  <a href="#Pg075">75</a>;</li>
<li>  John Smeaton investigates this machine,
  <a href="#Pg076">76</a>;</li>
<li>  Brindley obtains a patent for improvements in,
  <a href="#Pg076">76</a>;</li>
<li>  Applied by Champion of Bristol to raise water,
  <a href="#Pg181">181</a>;</li>
<li>  Possessed but limited power of adaptation to a varying load,
  <a href="#Pg151">151</a>;</li>
<li>  Expedient to remedy this,
  <a href="#Pg151">151</a>;</li>
<li>  Working-beam, cylinder, and piston applied to by Newcomen,
  <a href="#Pg322">322</a>.</li>

<li class="lstfst">Atmospheric pressure rendered available as a mechanic agent by Denis Papin,
  <a href="#Pg038">38</a>;</li>
<li>  Means of measuring the force of,
  <a href="#Pg039">39</a>;</li>
<li>  The idea of using against a vacuum or partial vacuum to work a piston in a cylinder, suggested by Otto Guericke,
  <a href="#Pg073">73</a>.</li>


<li class="lsthdr">Barometer gauge,
  <a href="#Pg272">272</a>.</li>

<li class="lstfst">Barton's piston,
  <a href="#Pg248">248</a>.</li>

<li class="lstfst">Beighton, his improvement of the atmospheric engine,
  <a href="#Pg075">75</a>.</li>

<li class="lstfst">Black, Dr., his doctrine of latent heat,
  <a href="#Pg093">93</a>.</li>

<li class="lstfst">Blasco de Garay, his contrivance to propel vessels,
  <a href="#Pg016">16</a>;</li>
<li>  The contrivance of, probably identical with that of Hero,
  <a href="#Pg017">17</a>.</li>

<li class="lstfst">Blinkensop, his locomotive engine,
  <a href="#Pg337">337</a>.</li>

<li class="lstfst">Blowing-box,
  <a href="#Pg429">429</a>.</li>

<li class="lstfst">Blowing out, Seaward's method of,
  <a href="#Pg454">454</a>.</li>

<li class="lstfst">Blow-off cocks,
  <a href="#Pg452">452</a>.</li>

<li class="lstfst">Boiler, forms of, most convenient,
  <a href="#Pg255">255</a>;</li>
<li>  The waggon boiler adopted by Watt,
  <a href="#Pg255">255</a>;</li>
<li>  Furnace,
  <a href="#Pg256">256</a>;</li>
<li>  Method of feeding,
  <a href="#Pg257">257</a>;</li>
<li>  Combustion of gas in flues,
  <a href="#Pg260">260</a>;</li>
<li>  Mr. Williams's method of consuming the unburned gases which escape from the grate, and are carried through the flues,
  <a href="#Pg260">260</a>;</li>
<li>  Construction of grate and ash-pit,
  <a href="#Pg261">261</a>;</li>
<li>  Magnitude of heating surface of boiler,
  <a href="#Pg262">262</a>;</li>
<li>  Capacity of, must be proportioned to the quantity of water to be evaporated,
  <a href="#Pg263">263</a>;</li>
<li>  Water-space and steam-space in boiler,
  <a href="#Pg263">263</a>;</li>
<li>  Proportion of water-space in the boiler, how to be regulated,
  <a href="#Pg264">264</a>;</li>
<li>  Position of flues,
  <a href="#Pg264">264</a>;</li>
<li>  Method of feeding,
  <a href="#Pg265">265</a>;</li>
<li>  The magnitude of the feed should be equal to the quantity of water evaporated,
  <a href="#Pg265">265</a>;</li>
<li>  Different methods for indicating the level of the water in the boiler,
  <a href="#Pg266">266</a>;</li>
<li>  Level guages,
  <a href="#Pg266">266</a>;</li>
<li>  Self-regulating feeder,
  <a href="#Pg267">267</a>;</li>
<li>  Another method of arranging,
  <a href="#Pg269">269</a>;</li>
<li>  Steam gauge,
  <a href="#Pg270">270</a>;</li>
<li>  Thermometer gauge,
  <a href="#Pg271">271</a>;</li>
<li>  Barometer gauge,
  <a href="#Pg272">272</a>;</li>
<li>  The indicator to measure the mean efficient force of the piston invented by Watt,
  <a href="#Pg274">274</a>;</li>
<li>  The counter contrived by Watt,
  <a href="#Pg278">278</a>;</li>
<li>  Safety valve,
  <a href="#Pg279">279</a>;</li>
<li>  Fusible plugs used in high pressure boilers,
  <a href="#Pg280">280</a>;</li>
<li>  Self-regulating damper,
  <a href="#Pg281">281</a>;</li>
<li>  Self-regulating furnace invented by Brunton,
  <a href="#Pg283">283</a>;</li>
<li>  Duty of a boiler,
  <a href="#Pg294">294</a>;</li>
<li>  Boilers of locomotive engines,
  <a href="#Pg351">351</a>;</li>
<li>  Construction of the boiler of Gurney's steam carriage,
  <a href="#Pg423">423</a>;</li>
<li>  All boilers require occasional cleansing,
  <a href="#Pg427">427</a>;</li>
<li>  Gurney's method of removing crust of deposited matter in boilers,
  <a href="#Pg427">427</a>;</li>
<li>  The boiler of Dr. Church's engine formed of copper,
  <a href="#Pg439">439</a>;</li>
<li>  Boilers in marine engines,
  <a href="#Pg449">449</a>;</li>
<li>  Effects of sea-water in,
  <a href="#Pg450">450</a>;</li>
<li>  Remedies for them,
  <a href="#Pg451">451</a>;</li>
<li>  Substitution of copper for iron,
  <a href="#Pg460">460</a>;</li>
<li>  Expedient of coating boilers with felt, applied by Watt,
  <a href="#Pg463">463</a>.</li>

<li class="lstfst">Booth, Mr., his report on locomotive engines,
  <a href="#Pg361">361</a>.</li>

<li class="lstfst">Boulton and Watt's experiments on the horse power of engines,
  <a href="#Pg288">288</a>.</li>

<li class="lstfst">Branca, Giovanni, his machine for propelling a wheel by a blast of steam,
  <a href="#Pg022">22</a>.</li>

<li class="lstfst">Brindley (James) obtains a patent for improvements in atmospheric engine,
  <a href="#Pg076">76</a>;</li>
<li>  Undertook to erect an engine at Newcastle-under-Lyne,
  <a href="#Pg076">76</a>;</li>
<li>  Discouraged by the obstacles thrown in his way,
  <a href="#Pg076">76</a>.</li>

<li class="lstfst">Brougham, Lord, his sketch of Watt's character,
  <a href="#Pg313">313</a>;</li>
<li>  Inscription from the pen of, on Watt's monument in Westminster Abbey,
  <a href="#Pg320">320</a>.</li>

<li class="lstfst">Buffers,
  <a href="#Pg404">404</a>.</li>


<li class="lsthdr">Cartwright's engine to use the vapour of alcohol to work the piston,
  <a href="#Pg245">245</a>;</li>
<li>  His piston,
  <a href="#Pg247">247</a>.</li>

<li class="lstfst">Cawley and Newcomen obtain a patent for the atmospheric engine,
  <a href="#Pg064">64</a>.</li>

<li class="lstfst">Champion applies atmospheric engine to raise water,
  <a href="#Pg181">181</a>.</li>

<li class="lstfst">Chapman, Messrs., their locomotive engine,
  <a href="#Pg337">337</a>.</li>

<li class="lstfst">Chlorine introduced in bleaching by Watt,
  <a href="#Pg310">310</a>.</li>

<li class="lstfst">Church, Dr., his steam engine,
  <a href="#Pg439">439</a>;</li>
<li>  The boiler formed of copper,
  <a href="#Pg439">439</a>.</li>

<li class="lstfst">Coals, the virtues and powers which steam has conferred upon,
  <a href="#Pg006">6</a>;</li>
<li>  The amount of labour a bushel of performs by means of the steam engine, compared with horse power,
  <a href="#Pg007">7</a>;</li>
<li>  Constituents of,
  <a href="#Pg252">252</a>;</li>
<li>  Process of combustion,
  <a href="#Pg252">252</a>.</li>

<li class="lstfst">Coal mines, apprehensions as to the possibility of the exhaustion of groundless,
  <a href="#Pg008">8</a>.</li>

<li class="lstfst">Cocks, friction on,
  <a href="#Pg240">240</a>.</li>

<li class="lstfst">Cocks and valves,
  <a href="#Pg227">227</a>.</li>

<li class="lstfst">Combustion of gas in flues,
  <a href="#Pg260">260</a>.</li>

<li class="lstfst">Condensation by injection, accidental discovery of,
  <a href="#Pg069">69</a>.</li>

<li class="lstfst">Condensation in the cylinder incompatible with a due economy of fuel,
  <a href="#Pg120">120</a>.</li>

<li class="lstfst">Condensing principle, circumstance which led to Savery's discovery of,
  <a href="#Pg047">47</a>.</li>

<li class="lstfst">Condensing pipe in Savery's engine,
  <a href="#Pg052">52</a>.</li>

<li class="lstfst">Condensing out of the cylinder,
  <a href="#Pg120">120</a>.</li>

<li class="lstfst">Condensing jet,
  <a href="#Pg191">191</a>.</li>

<li class="lstfst">Conical steam valves,
  <a href="#Pg228">228</a>.</li>

<li class="lstfst">Conversion of ice into water,
  <a href="#Pg103">103</a>;</li>
<li>  Of water into steam,
  <a href="#Pg105">105</a>.</li>

<li class="lstfst">Copying press invented by Watt,
  <a href="#Pg302">302</a>.</li>

<li class="lstfst">Cornish system of inspection,
  <a href="#Pg297">297</a>.</li>

<li class="lstfst">Cornish engines, improvement of,
  <a href="#Pg298">298</a>;</li>
<li>  Historical detail of the duty of,
  <a href="#Pg299">299</a>.</li>

<li class="lstfst">Cylinders, Wilkinson's machine for accurately boring the insides of,
  <a href="#Pg149">149</a>.</li>


<li class="lsthdr">D valve,
  <a href="#Pg230">230</a>.</li>

<li class="lstfst">Dalton and Gay-Lussac, law of, relating to the pressure of elastic bodies,
  <a href="#Pg171">171</a>.</li>

<li class="lstfst">Dixon, Mr. The substitution of brass for copper tubes in locomotive engines ascribed to him,
  <a href="#Pg370">370</a>.</li>

<li class="lstfst">Double clack-valve,
  <a href="#Pg228">228</a>.</li>


<li class="lsthdr">Eccentric,
  <a href="#Pg225">225</a>;</li>
<li>  Two expedients to reverse the position of,
  <a href="#Pg379">379</a>.</li>

<li class="lstfst">Effect of an engine,
  <a href="#Pg285">285</a>.</li>

<li class="lstfst">Elastic fluids. The law according to which the pressure of, increases with their temperature, discovered by Dalton and Gay-Lussac,
  <a href="#Pg171">171</a>.</li>

<li class="lstfst">Evaporation of water and other liquids, physical and mechanical principles connected with,
  <a href="#Pg097">97</a>.</li>

<li class="lstfst">Expansion of common steam, effects of,
  <a href="#Pg173">173</a>.</li>

<li class="lstfst">Expansive action of steam,
  <a href="#Pg159">159</a>;</li>
<li>  Stated by Watt in a letter to Dr. Small,
  <a href="#Pg157">157</a>;</li>
<li>  Its principle explained,
  <a href="#Pg158">158</a>;</li>
<li>  Mechanical effect resulting from it,
  <a href="#Pg161">161</a>;</li>
<li>  Computed effect of cutting off steam at different portions of the stroke,
  <a href="#Pg162">162</a>;</li>
<li>  Involves the condition of a variation in the intensity of the moving power,
  <a href="#Pg163">163</a>;</li>
<li>  Expedients for equalising the power,
  <a href="#Pg164">164</a>;</li>
<li>  The expansive principle in the engines constructed by Boulton and Watt, limited,
  <a href="#Pg165">165</a>;</li>
<li>  Its more extensive application in the Cornish engines,
  <a href="#Pg165">165</a>;</li>
<li>  Methods of equalising,
  <a href="#Pg174">174</a>;</li>
<li>  Description of Hornblower's engine for this purpose,
  <a href="#Pg174">174</a>.</li>

<li class="lstfst">Expansive principle, application of in marine engines,
  <a href="#Pg466">466</a>.</li>


<li class="lsthdr">Farey on the steam engine, quotation from, relative to Savery's engine,
  <a href="#Pg058">58</a>;</li>
<li>  His evidence before the House of Commons,
  <a href="#Pg435">435</a>.</li>

<li class="lstfst">Field, construction of his split paddle,
  <a href="#Pg478">478</a>.</li>

<li class="lstfst">Fitch and Rumsey, their attempts to apply the single-acting engine to the propulsion of vessels,
  <a href="#Pg489">489</a>.</li>

<li class="lstfst">Flues, position of,
  <a href="#Pg264">264</a>.</li>

<li class="lstfst">Fluids, of two kinds,
  <a href="#Pg025">25</a>;</li>
<li>  Mechanical properties of,
  <a href="#Pg025">25</a>;</li>
<li>  Elastic,
  <a href="#Pg027">27</a>;</li>
<li>  Experimental proof that they press equally in all directions,
  <a href="#Pg041">41</a>.</li>

<li class="lstfst">Fly-wheel,
  <a href="#Pg205">205</a>.</li>

<li class="lstfst">Four-way cock,
  <a href="#Pg239">239</a>;</li>
<li>  Disadvantages of,
  <a href="#Pg240">240</a>.</li>

<li class="lstfst">Fuel, means of economising, in marine furnaces,
  <a href="#Pg463">463</a>.</li>

<li class="lstfst">Fulton and Livingstone, their experiments in steam navigation,
  <a href="#Pg489">489</a>.</li>

<li class="lstfst">Fulton's first boat,
  <a href="#Pg490">490</a>.</li>

<li class="lstfst">Furnace, self-regulating, invented by Brunton,
  <a href="#Pg283">283</a>.</li>

<li class="lstfst">Fusible plugs used in high-pressure boilers,
  <a href="#Pg280">280</a>.</li>


<li class="lsthdr">Galloway, his paddle-wheel described,
  <a href="#Pg476">476</a>.</li>

<li class="lstfst">Gas, elasticity of,
  <a href="#Pg028">28</a>.</li>

<li class="lstfst">Gay-Lussac and Dalton, law of, relating to the pressure of elastic bodies,
  <a href="#Pg171">171</a>.</li>

<li class="lstfst">Governor, adaptation of,
  <a href="#Pg209">209</a>.</li>

<li class="lstfst">Gradients, restrictions on,
  <a href="#Pg411">411</a>;</li>
<li>  Disposition of, should be uniform,
  <a href="#Pg415">415</a>.</li>

<li class="lstfst">Great Western Railway, Dr. Lardner's experiments on,
  <a href="#Pg408">408</a>.</li>

<li class="lstfst">Griff, proposals to drain a colliery at, mentioned by Desaguliers,
  <a href="#Pg064">64</a>.</li>

<li class="lstfst">Gurney's steam carriage,
  <a href="#Pg423">423</a>;</li>
<li>  Construction of the boiler of,
  <a href="#Pg423">423</a>;</li>
<li>  His method of removing crust of deposited matter in boilers,
  <a href="#Pg427">427</a>;</li>
<li>  His experiments on common roads,
  <a href="#Pg432">432</a>.</li>


<li class="lsthdr">Hall, his condensers described,
  <a href="#Pg458">458</a>.</li>

<li class="lstfst">Hancock, his steam carriage,
  <a href="#Pg436">436</a>;</li>
<li>  In what manner it differs from that of Gurney,
  <a href="#Pg437">437</a>.</li>

<li class="lstfst">Harris, Dr., mentions Savery's engine in his "Lexicon Technicum,"
  <a href="#Pg056">56</a>.</li>

<li class="lstfst">Heat, effects of upon water,
  <a href="#Pg029">29</a>;</li>
<li>  Waste of in atmospheric engine,
  <a href="#Pg089">89</a>;</li>
<li>  An examination of the analogous effects produced by the continued application of, to water in the liquid state,
  <a href="#Pg102">102</a>;</li>
<li>  Radiation of,
  <a href="#Pg254">254</a>.</li>

<li class="lstfst">Heating by steam brought forward by Watt,
  <a href="#Pg303">303</a>.</li>

<li>"Hecla," experiments with the,
  <a href="#Pg412">412</a>.</li>

<li class="lstfst">Hero of Alexandria, description of his machine,
  <a href="#Pg012">12</a>.</li>

<li class="lstfst">High pressure engines described,
  <a href="#Pg321">321</a>;</li>
<li>  One of the earliest forms of the steam engine,
  <a href="#Pg322">322</a>;</li>
<li>  Obscurely described in the "Century of Inventions,"
  <a href="#Pg322">322</a>;</li>
<li>  Construction of the first, by Messrs. Trevethick and Vivian,
  <a href="#Pg324">324</a>.</li>

<li class="lstfst">Hooke exposes the fallacy of Papin's project,
  <a href="#Pg064">64</a>.</li>

<li class="lstfst">Horse carriages compared with steam,
  <a href="#Pg435">435</a>.</li>

<li class="lstfst">Horse power of steam engines,
  <a href="#Pg288">288</a>;</li>
<li>  Smeaton's estimation of,
  <a href="#Pg288">288</a>;</li>
<li>  Boulton and Watt's experiments on,
  <a href="#Pg288">288</a>.</li>

<li class="lstfst">Howard's description of his marine engine,
  <a href="#Pg464">464</a>.</li>

<li class="lstfst">Hudson, the, navigated by steam,
  <a href="#Pg491">491</a>.</li>

<li class="lstfst">Hull, Jonathan, his application of the steam engine to water wheels,
  <a href="#Pg180">180</a>.</li>

<li class="lstfst">Humphrey. His marine engine described,
  <a href="#Pg470">470</a>.</li>

<li class="lstfst">Huskisson, Mr., death of,
  <a href="#Pg329">329</a>.</li>

<li class="lstfst">Hydrogen,
  <a href="#Pg253">253</a>.</li>


<li class="lsthdr">India, steam navigation to,
  <a href="#Pg483">483</a>.</li>

<li class="lstfst">Indicator invented by Watt,
  <a href="#Pg274">274</a>.</li>


<li class="lsthdr">Jeffrey, Lord; his sketch of the character of Watt,
  <a href="#Pg315">315</a>.</li>


<li class="lsthdr">Kinneal, description of Watt's experimental engine at,
  <a href="#Pg131">131</a>.</li>


<li class="lsthdr">Lake steamers,
  <a href="#Pg499">499</a>.</li>

<li class="lstfst">Lardner's, Dr., experiments on the Manchester Railway in 1832,
  <a href="#Pg357">357</a>;</li>
<li>  His experiments in 1838,
  <a href="#Pg406">406</a>;</li>
<li>  Experiments on the Great Western Railway,
  <a href="#Pg408">408</a>.</li>

<li class="lstfst">Leupold's engine, description of,
  <a href="#Pg323">323</a>.</li>

<li class="lstfst">Level gauges,
  <a href="#Pg266">266</a>.</li>

<li class="lstfst">Linen, machine for drying by steam, invented by Watt,
  <a href="#Pg303">303</a>.</li>

<li class="lstfst">Liverpool and Manchester railroad, effects of the introduction of steam transport on,
  <a href="#Pg329">329</a>;</li>
<li>  Want of experience in the construction of the engines,
  <a href="#Pg329">329</a>;</li>
<li>  Death of Mr. Huskisson,
  <a href="#Pg329">329</a>;</li>
<li>  Proceedings of the directors,
  <a href="#Pg342">342</a>;</li>
<li>  Premium offered by them for the best engine,
  <a href="#Pg344">344</a>;</li>
<li>  Experimental trial,
  <a href="#Pg344">344</a>.</li>

<li class="lstfst">Livingstone and Fulton, experiments of in steam navigation,
  <a href="#Pg489">489</a>.</li>

<li class="lstfst">Locomotive engine, history of,
  <a href="#Pg328">328</a>;</li>
<li>  Blinkensop's engine,
  <a href="#Pg337">337</a>;</li>
<li>  Chapman's engine,
  <a href="#Pg337">337</a>;</li>
<li>  Walking engine,
  <a href="#Pg337">337</a>;</li>
<li>  Mr. Stephenson's engine at Killingworth,
  <a href="#Pg339">339</a>;</li>
<li>  Defect of,
  <a href="#Pg341">341</a>;</li>
<li>  Description of the "Rocket,"
  <a href="#Pg345">345</a>;</li>
<li>  The "Sanspareil,"
  <a href="#Pg347">347</a>;</li>
<li>  The "Novelty,"
  <a href="#Pg349">349</a>;</li>
<li>  Superiority of the "Rocket,"
  <a href="#Pg350">350</a>;</li>
<li>  Subsequent improvements in the locomotive engine,
  <a href="#Pg352">352</a>;</li>
<li>  Table, showing the economy of fuel gained by subdividing the flue into tubes,
  <a href="#Pg354">354</a>;</li>
<li>  Engines constructed in the form of the "Rocket" subject to two principal defects,
  <a href="#Pg354">354</a>;</li>
<li>  These defects remedied,
  <a href="#Pg355">355</a>;</li>
<li>  Improved by the adoption of a more contracted blast pipe,
  <a href="#Pg356">356</a>;</li>
<li>  Dr. Lardner's experiments in 1832,
  <a href="#Pg357">357</a>;</li>
<li>  Adoption of brass tubes,
  <a href="#Pg361">361</a>;</li>
<li>  Mr. Booth's report,
  <a href="#Pg361">361</a>;</li>
<li>  Detailed description of the most improved locomotive engines,
  <a href="#Pg364">364</a>;</li>
<li>  Substitution of brass for copper tubes ascribed to Mr. Dixon,
  <a href="#Pg370">370</a>;</li>
<li>  Mr. Stephenson constructed the driving wheels without flanges,
  <a href="#Pg383">383</a>;</li>
<li>  Pressure of steam in the boiler limited by two safety-valves,
  <a href="#Pg402">402</a>;</li>
<li>  Buffers,
  <a href="#Pg404">404</a>;</li>
<li>  Steam whistle,
  <a href="#Pg404">404</a>;</li>
<li>  Water tank,
  <a href="#Pg404">404</a>;</li>
<li>  Power of locomotive engines,
  <a href="#Pg405">405</a>;</li>
<li>  Evaporation of boilers,
  <a href="#Pg406">406</a>;</li>
<li>  Dr. Lardner's experiments in 1838,
  <a href="#Pg406">406</a>;</li>
<li>  Resistance to railway trains,
  <a href="#Pg407">407</a>;</li>
<li>  Dr. Lardner's experiments on the Great Western Railway,
  <a href="#Pg408">408</a>;</li>
<li>  Restriction on gradients,
  <a href="#Pg411">411</a>;</li>
<li>  Experiment with the "Hecla,"
  <a href="#Pg412">412</a>;</li>
<li>  Disposition of gradients should be uniform,
  <a href="#Pg415">415</a>;</li>
<li>  Method of surmounting steep inclinations,
  <a href="#Pg415">415</a>;</li>
<li>  Steam carriages on common roads,
  <a href="#Pg419">419</a>;</li>
<li>  Difference between steam engines on railways and those used to propel carriages on turnpike roads,
  <a href="#Pg422">422</a>;</li>
<li>  Gurney's steam carriage,
  <a href="#Pg423">423</a>;</li>
<li>  Construction of the boiler of,
  <a href="#Pg423">423</a>;</li>
<li>  Escape of steam from the engines on the Liverpool road,
  <a href="#Pg428">428</a>;</li>
<li>  Blowing-box,
  <a href="#Pg429">429</a>;</li>
<li>  Separator,
  <a href="#Pg430">430</a>;</li>
<li>  Difficulties in the practical working of steam carriages upon common roads,
  <a href="#Pg432">432</a>;</li>
<li>  Gurney's experiments on common roads,
  <a href="#Pg432">432</a>;</li>
<li>  Prejudice against locomotive engines on common roads,
  <a href="#Pg432">432</a>;</li>
<li>  Not more destructive to roads than carriages drawn by horses,
  <a href="#Pg433">433</a>;</li>
<li>  Report of the committee of the House of Commons,
  <a href="#Pg433">433</a>;</li>
<li>  Weight of steam carriages,
  <a href="#Pg433">433</a>;</li>
<li>  Two methods of applying locomotives upon common roads,
  <a href="#Pg434">434</a>;</li>
<li>  Horse carriages compared with,
  <a href="#Pg435">435</a>;</li>
<li>  Farey's evidence before the House of Commons,
  <a href="#Pg435">435</a>;</li>
<li>  Risk of accident from explosion extremely slight,
  <a href="#Pg435">435</a>;</li>
<li>  Hancock's steam carriage,
  <a href="#Pg436">436</a>;</li>
<li>  In what manner it differs from that of Gurney,
  <a href="#Pg437">437</a>;</li>
<li>  Ogle's steam carriage,
  <a href="#Pg438">438</a>;</li>
<li>  His evidence before the House of Commons,
  <a href="#Pg439">439</a>;</li>
<li>  Dr. Church's steam engine,
  <a href="#Pg439">439</a>;</li>
<li>  The boiler of formed of copper,
  <a href="#Pg439">439</a>.</li>

<li class="lstfst">Lunar Society, Boulton and Watt leading members in,
  <a href="#Pg302">302</a>.</li>


<li class="lsthdr">Marine engines, form and arrangement of,
  <a href="#Pg441">441</a>;</li>
<li>  Difference between marine and land engines,
  <a href="#Pg443">443</a>;</li>
<li>  Engine-room, arrangement of,
  <a href="#Pg446">446</a>;</li>
<li>  Boilers in,
  <a href="#Pg449">449</a>;</li>
<li>  Effects of sea-water on boilers,
  <a href="#Pg450">450</a>;</li>
<li>  Remedies for them,
  <a href="#Pg451">451</a>;</li>
<li>  Blow-off cocks,
  <a href="#Pg452">452</a>;</li>
<li>  Indicators of saltness,
  <a href="#Pg452">452</a>;</li>
<li>  Seaward's indicator,
  <a href="#Pg454">454</a>;</li>
<li>  His method of blowing out,
  <a href="#Pg454">454</a>;</li>
<li>  Method of Maudslay and Field to preserve freshness of water in the boiler,
  <a href="#Pg456">456</a>;</li>
<li>  Brine pumps,
  <a href="#Pg457">457</a>;</li>
<li>  Tubular condensers applied by Mr. Watt,
  <a href="#Pg457">457</a>;</li>
<li>  Hall's condensers,
  <a href="#Pg458">458</a>;</li>
<li>  Substitution of copper for iron boilers,
  <a href="#Pg461">461</a>;</li>
<li>  Process of stoking,
  <a href="#Pg462">462</a>;</li>
<li>  Marine furnaces,
  <a href="#Pg463">463</a>;</li>
<li>  Expedient of coating boilers with felt applied by Watt,
  <a href="#Pg463">463</a>;</li>
<li>  Means of economising fuel,
  <a href="#Pg463">463</a>;</li>
<li>  Description of Howard's engine,
  <a href="#Pg464">464</a>;</li>
<li>  Application of the expansive principle in marine engines,
  <a href="#Pg466">466</a>;</li>
<li>  Recent improvements of Messrs. Maudslay and Field,
  <a href="#Pg467">467</a>;</li>
<li>  Humphrey's engine,
  <a href="#Pg470">470</a>;</li>
<li>  Common paddle-wheel,
  <a href="#Pg472">472</a>;</li>
<li>  Defect of,
  <a href="#Pg474">474</a>;</li>
<li>  Feathering paddles,
  <a href="#Pg474">474</a>;</li>
<li>  Galloway's paddle-wheel,
  <a href="#Pg476">476</a>;</li>
<li>  Field's split paddle,
  <a href="#Pg478">478</a>;</li>
<li>  Proportion of power to tonnage,
  <a href="#Pg480">480</a>;</li>
<li>  Iron steam vessels,
  <a href="#Pg482">482</a>.</li>

<li class="lstfst">Mariotte's law relating to pressure,
  <a href="#Pg171">171</a>.</li>

<li class="lstfst">Maudslay and Field, their method to preserve the requisite freshness of water in the boiler,
  <a href="#Pg456">456</a>;</li>
<li>  Brine pumps,
  <a href="#Pg457">457</a>;</li>
<li>  Recent improvements of in marine engines,
  <a href="#Pg466">466</a>.</li>

<li class="lstfst">Metallic pistons,
  <a href="#Pg244">244</a>;</li>
<li>  Cartwright's engine,
  <a href="#Pg245">245</a>;</li>
<li>  An improved form given to by Barton,
  <a href="#Pg248">248</a>.</li>

<li class="lstfst">Mill work, Stewart's application of the steam engine to,
  <a href="#Pg182">182</a>.</li>

<li class="lstfst">Mines, the drainage of, Watt endeavours to bring to perfection the application of the steam engine to,
  <a href="#Pg178">178</a>.</li>

<li class="lstfst">Mississippi and its tributaries,
  <a href="#Pg499">499</a>;</li>
<li>  Steam-boats on,
  <a href="#Pg500">500</a>;</li>
<li>  Their structure and machinery,
  <a href="#Pg500">500</a>.</li>

<li class="lstfst">Morland, Sir Samuel, his application of steam to raise water,
  <a href="#Pg034">34</a>;</li>
<li>  The reputed inventor of several ingenious contrivances,
  <a href="#Pg034">34</a>;</li>
<li>  His work in French upon the raising of water,
  <a href="#Pg035">35</a>;</li>
<li>  Extract from it,
  <a href="#Pg035">35</a>;</li>
<li>  Evelyn's account of his visit to,
  <a href="#Pg036">36</a>.</li>

<li class="lstfst">Murray's slide-valve,
  <a href="#Pg229">229</a>.</li>


<li class="lsthdr">Newcomen, Thomas, the reputed inventor of the atmospheric engine,
  <a href="#Pg062">62</a>;</li>
<li>  His acquaintance with Dr. Hooke,
  <a href="#Pg062">62</a>;</li>
<li>  Acquainted with Papin's writings,
  <a href="#Pg064">64</a>;</li>
<li>  The merits of his engine ascribed principally to its mechanism and combinations,
  <a href="#Pg073">73</a>;</li>
<li>  Obtains with Cawley a patent for the atmospheric engine,
  <a href="#Pg064">64</a>;</li>
<li>  Resumes the old method of raising water from mines by ordinary pumps,
  <a href="#Pg065">65</a>;</li>
<li>  The means proposed to effect this,
  <a href="#Pg066">66</a>;</li>
<li>  First conception of the atmospheric engine,
  <a href="#Pg066">66</a>;</li>
<li>  Description of his construction of atmospheric engine,
  <a href="#Pg067">67</a>;</li>
<li>  Suggestion of a better method of condensation than the application of cold water on the external surfaces of the cylinder,
  <a href="#Pg069">69</a>;</li>
<li>  He abandons the external cylinder,
  <a href="#Pg069">69</a>;</li>
<li>  Applied the working-beam, cylinder, and piston to the atmospheric engine,
  <a href="#Pg322">322</a>.</li>

<li class="lstfst">New Orleans Harbour,
  <a href="#Pg503">503</a>.</li>

<li class="lstfst">"Novelty," description of the, a locomotive engine,
  <a href="#Pg349">349</a>.</li>


<li class="lsthdr">Ogle, his steam carriage,
  <a href="#Pg438">438</a>;</li>
<li>  His evidence before the House of Commons,
  <a href="#Pg439">439</a>.</li>

<li class="lstfst">Otto Guericke, his suggestion relative to atmospheric pressure,
  <a href="#Pg073">73</a>.</li>

<li class="lstfst">Oxley made the first attempt to drive water-wheels by the steam engine,
  <a href="#Pg182">182</a>.</li>


<li class="lsthdr">Paddle-wheel described,
  <a href="#Pg472">472</a>;</li>
<li>  Defect of,
  <a href="#Pg474">474</a>;</li>
<li>  Feathering paddles,
  <a href="#Pg474">474</a>;</li>
<li>  Galloway's paddle-wheel,
  <a href="#Pg476">476</a>;</li>
<li>  Field's split paddle,
  <a href="#Pg478">478</a>.</li>

<li class="lstfst">Paddle-wheels of American steamers,
  <a href="#Pg495">495</a>.</li>

<li class="lstfst">Papin, Denis, conceived the idea of rendering atmospheric pressure available as a mechanical agent,
  <a href="#Pg037">37</a>;</li>
<li>  Description of his contrivance,
  <a href="#Pg037">37</a>;</li>
<li>  His discovery of condensation of steam,
  <a href="#Pg045">45</a>;</li>
<li>  Quotation from his work relative to this discovery,
  <a href="#Pg045">45</a>;</li>
<li>  Explanation of this important discovery,
  <a href="#Pg046">46</a>;</li>
<li>  Discovers the method of producing a vacuum by the condensation of steam,
  <a href="#Pg178">178</a>;</li>
<li>  His projected applications of the steam engine,
  <a href="#Pg178">178</a>;</li>
<li>  His proposition for the construction of an engine working by atmospheric pressure,
  <a href="#Pg062">62</a>;</li>
<li>  Abandons the project when informed of the principle and structure of Savery's engine,
  <a href="#Pg062">62</a>;</li>
<li>  His engine described,
  <a href="#Pg062">62</a>;</li>
<li>  This project nothing more than a reproduction of the Marquis of Worcester's engine,
  <a href="#Pg063">63</a>;</li>
<li>  The fallacy of his project exposed by Hooke,
  <a href="#Pg064">64</a>;</li>
<li>  His project for producing a vacuum under a piston by condensing the steam, published in the "ActÃ¦ Eruditorum,"
  <a href="#Pg064">64</a>.</li>

<li class="lstfst">Parallel motion,
  <a href="#Pg195">195</a>.</li>

<li class="lstfst">Physical science, the rapid progress of,
  <a href="#Pg008">8</a>.</li>

<li class="lstfst">Pistons,
  <a href="#Pg242">242</a>;</li>
<li>  The common hemp-packed,
  <a href="#Pg242">242</a>;</li>
<li>  Woolf's method of tightening the packing of, without removing the lid of the cylinder,
  <a href="#Pg244">244</a>;</li>
<li>  This method further simplified,
  <a href="#Pg244">244</a>;</li>
<li>  Metallic,
  <a href="#Pg244">244</a>;</li>
<li>  Cartwright's engine,
  <a href="#Pg245">245</a>;</li>
<li>  Cartwright's piston,
  <a href="#Pg247">247</a>;</li>
<li>  Invention of the indicator by Watt to measure the mean efficient force of,
  <a href="#Pg274">274</a>.</li>

<li class="lstfst">Piston rod and beam, methods of connecting in the double-acting engine,
  <a href="#Pg193">193</a>.</li>

<li class="lstfst">Pneumatic institution at Clifton, Watt one of the founders of,
  <a href="#Pg310">310</a>.</li>

<li class="lstfst">Potter, Humphrey, his contrivance for working the valves,
  <a href="#Pg071">71</a>;</li>
<li>  Improved by the substitution of a plug-frame,
  <a href="#Pg072">72</a>.</li>

<li class="lstfst">Power, proportion of, to tonnage in marine engines,
  <a href="#Pg480">480</a>.</li>

<li class="lstfst">Power and duty of steam engines,
  <a href="#Pg287">287</a>.</li>

<li class="lstfst">Priestley, Watt's letter to, relative to the composition of water,
  <a href="#Pg307">307</a>.</li>

<li class="lstfst">Pump, an illustration of force attained by a vacuum,
  <a href="#Pg043">43</a>.</li>

<li class="lstfst">Puppet clacks, or button valves,
  <a href="#Pg144">144</a>.</li>


<li class="lsthdr">Rack and Sector,
  <a href="#Pg194">194</a>.</li>

<li class="lstfst">Railways, speed of coaches on, compared with that of stage-coaches on a common road,
  <a href="#Pg007">7</a>.</li>

<li class="lstfst">Railway transport, effects of, <a href="#Pg328">328</a>.
  <a href="#Pg330">330</a>.</li>

<li class="lstfst">Railways and stone roads compared,
  <a href="#Pg420">420</a>.</li>

<li class="lstfst">River navigation, extension and improvement of,
  <a href="#Pg492">492</a>.</li>

<li class="lstfst">"Rocket," description of the, a locomotive engine,
  <a href="#Pg345">345</a>;</li>
<li>  Engines constructed in the form of, subject to two principal defects,
  <a href="#Pg354">354</a>;</li>
<li>  These defects remedied,
  <a href="#Pg355">355</a>;</li>
<li>  Improved by the adoption of a more contracted blast-pipe,
  <a href="#Pg356">356</a>.</li>

<li class="lstfst">Roebuck, Dr., Watt's partnership with,
  <a href="#Pg130">130</a>.</li>

<li class="lstfst">Rotatory motion, method of producing by sun and planet wheels,
  <a href="#Pg187">187</a>.</li>


<li class="lsthdr">Safety-valve not adopted by Savery,
  <a href="#Pg057">57</a>;</li>
<li>  Invented by Papin,
  <a href="#Pg057">57</a>;</li>
<li>  Description of,
  <a href="#Pg057">57</a>;</li>
<li>  First applied to Savery's engine by Desaguliers,
  <a href="#Pg058">58</a>.</li>

<li class="lstfst">"Sanspareil," description of the, a locomotive engine,
  <a href="#Pg347">347</a>.</li>

<li class="lstfst">Savery, Thomas, obtains a patent for an engine to raise water,
  <a href="#Pg047">47</a>;</li>
<li>  Circumstance which led to his discovery of the condensing principle,
  <a href="#Pg047">47</a>;</li>
<li>  An account of his engine,
  <a href="#Pg049">49</a>;</li>
<li>  Description of the working apparatus in which the steam is used as a moving power,
  <a href="#Pg051">51</a>;</li>
<li>  His engine described in a work entitled "<cite>The Miner's Friend</cite>,"
  <a href="#Pg056">56</a>;</li>
<li>  Mentioned by Dr. Harrison in his "Lexicon Technicum,"
  <a href="#Pg056">56</a>;</li>
<li>  Quotation from his address to the Royal Society,
  <a href="#Pg056">56</a>;</li>
<li>  Quotation from his address to the Miners of England,
  <a href="#Pg057">57</a>;</li>
<li>  Mentioned by Bradley in his "Improvements of Planting and Gardening,"
  <a href="#Pg057">57</a>;</li>
<li>  The safety-valve not adopted by him,
  <a href="#Pg057">57</a>;</li>
<li>  The safety-valve first applied to his engine by Desaguliers,
  <a href="#Pg058">58</a>;</li>
<li>  Farey on the steam engine quoted,
  <a href="#Pg058">58</a>;</li>
<li>  Further Improvements made by Desaguliers,
  <a href="#Pg058">58</a>;</li>
<li>  Defects of his engine,
  <a href="#Pg059">59</a>;</li>
<li>  His engine applied to the drainage of mines,
  <a href="#Pg059">59</a>;</li>
<li>  Further defects of,
  <a href="#Pg060">60</a>;</li>
<li>  The first to suggest the method of expressing the power of an engine with reference to that of horses,
  <a href="#Pg061">61</a>;</li>
<li>  Failure of his engine in the work of drainage,
  <a href="#Pg061">61</a>;</li>
<li>  The tendency of high pressure to weaken and gradually destroy the vessels,
  <a href="#Pg072">72</a>;</li>
<li>  The power of his engines restricted,
  <a href="#Pg073">73</a>;</li>
<li>  The atmospheric engine superior to,
  <a href="#Pg073">73</a>;</li>
<li>  The boiler, guage-pipes, and regulator borrowed from his engine,
  <a href="#Pg073">73</a>;</li>
<li>  Proposes to apply his engine as a prime mover for all sorts of machinery,
  <a href="#Pg180">180</a>.</li>

<li class="lstfst">Scott, Sir Walter, his sketch of the character of Watt,
  <a href="#Pg314">314</a>.</li>

<li class="lstfst">Sculpture, Watt's invention of machine for copying,
  <a href="#Pg318">318</a>.</li>

<li class="lstfst">Sea-going American steamers,
  <a href="#Pg496">496</a>.</li>

<li class="lstfst">Sea-water, effects of upon boilers,
  <a href="#Pg450">450</a>.</li>

<li class="lstfst">Seaward's slides,
  <a href="#Pg235">235</a>;</li>
<li>  Indicator of saltness,
  <a href="#Pg454">454</a>;</li>
<li>  His method of blowing out,
  <a href="#Pg454">454</a>.</li>

<li class="lstfst">Self-regulating damper,
  <a href="#Pg281">281</a>;</li>
<li>  Furnace,
  <a href="#Pg283">283</a>.</li>

<li class="lstfst">Separator,
  <a href="#Pg430">430</a>.</li>

<li class="lstfst">Single-acting engine, description of Watt's, <a href="#Pg133">133</a>.
  <a href="#Pg144">144</a>.</li>

<li class="lstfst">Single clack-valve,
  <a href="#Pg227">227</a>.</li>

<li class="lstfst">Single cock,
  <a href="#Pg238">238</a>.</li>

<li class="lstfst">Slide-valves,
  <a href="#Pg229">229</a>;</li>
<li>  That contrived by Mr. Murray,
  <a href="#Pg229">229</a>.</li>

<li class="lstfst">Smeaton, John, investigates the atmospheric engine,
  <a href="#Pg076">76</a>;</li>
<li>  Applies himself to the improvement of wind and water mills,
  <a href="#Pg181">181</a>;</li>
<li>  His estimate of the horse power of engines,
  <a href="#Pg288">288</a>.</li>

<li class="lstfst">Solomon De Caus, description of the apparatus of,
  <a href="#Pg017">17</a>;</li>
<li>  M. Arago claims for him a share of the honour of the invention of the steam engine,
  <a href="#Pg021">21</a>;</li>
<li>  Republished, with additions, the work of Isaac De Caus,
  <a href="#Pg022">22</a>.</li>

<li class="lstfst">Somerset, Edward, Marquis of Worcester. Invention of the steam engine ascribed to him,
  <a href="#Pg023">23</a>;</li>
<li>  Description of his contrivance,
  <a href="#Pg023">23</a>;</li>
<li>  His "Century of Inventions,"
  <a href="#Pg024">24</a>;</li>
<li>  Brief account of his engine described in this work,
  <a href="#Pg031">31</a>;</li>
<li>  His contrivance compared with that of De Caus,
  <a href="#Pg033">33</a>;</li>
<li>  Many of his inventions have been reproduced and brought into general use,
  <a href="#Pg034">34</a>.</li>

<li class="lstfst">Steam cannot be applied <em>immediately</em> to any useful purpose, but requires the interposition of mechanism,
  <a href="#Pg011">11</a>;</li>
<li>  Elastic force of, recognised by the ancients only in vague and general terms,
  <a href="#Pg014">14</a>;</li>
<li>  The power of, formerly made to minister to the objects of superstition, mentioned by Arago,
  <a href="#Pg015">15</a>;</li>
<li>  Anecdote showing the knowledge which the ancients had of the mechanical force of,
  <a href="#Pg015">15</a>;</li>
<li>  The discovery of the condensation of, by Papin,
  <a href="#Pg045">45</a>;</li>
<li>  Mechanical power obtained from the direct pressure of the elastic force of, suggested by De Caus and Lord Worcester,
  <a href="#Pg073">73</a>;</li>
<li>  Latent heat of,
  <a href="#Pg107">107</a>;</li>
<li>  The mechanical force of considered,
  <a href="#Pg115">115</a>;</li>
<li>  Watt's early experiments on,
  <a href="#Pg087">87</a>;</li>
<li>  Discovery of the expansive action of,
  <a href="#Pg157">157</a>;</li>
<li>  Expansive action of stated by Watt in a letter to Dr. Small,
  <a href="#Pg157">157</a>;</li>
<li>  Its principle explained,
  <a href="#Pg158">158</a>;</li>
<li>  Mechanical effect resulting from it,
  <a href="#Pg161">161</a>;</li>
<li>  Properties of,
  <a href="#Pg168">168</a>;</li>
<li>  Common and super-heated steam,
  <a href="#Pg168">168</a>;</li>
<li>  Pressure and temperature of,
  <a href="#Pg171">171</a>;</li>
<li>  Relation between the temperatures of common steam and its pressure and density,
  <a href="#Pg172">172</a>;</li>
<li>  Effects of the expansion of common steam,
  <a href="#Pg173">173</a>;</li>
<li>  Mechanical effects of,
  <a href="#Pg173">173</a>;</li>
<li>  Methods of equalising the varying force of expanding steam,
  <a href="#Pg174">174</a>;</li>
<li>  Method of producing a vacuum by the condensation of, discovered by Papin,
  <a href="#Pg178">178</a>;</li>
<li>  Applied to move machinery,
  <a href="#Pg179">179</a>;</li>
<li>  Steam guage,
  <a href="#Pg270">270</a>;</li>
<li>  Heating by steam brought forward by Watt,
  <a href="#Pg303">303</a>;</li>
<li>  A machine for drying linen by, invented by Watt,
  <a href="#Pg303">303</a>;</li>
<li>  Mode of escape of, from the engines on the Liverpool road,
  <a href="#Pg429">429</a>.</li>

<li class="lstfst">Steam case or jacket, invented by Watt,
  <a href="#Pg124">124</a>.</li>

<li class="lstfst">Steam engine, a subject of popular interest,
  <a href="#Pg003">3</a>;</li>
<li>  The effects which it has produced upon the well-being of the human race considered,
  <a href="#Pg004">4</a>;</li>
<li>  Presents peculiar claims upon the attention of the people of Great Britain,
  <a href="#Pg005">5</a>;</li>
<li>  The exclusive offspring of British genius,
  <a href="#Pg005">5</a>;</li>
<li>  The virtues and powers which it has conferred upon coals,
  <a href="#Pg006">6</a>;</li>
<li>  Water the means of calling these powers into activity,
  <a href="#Pg006">6</a>;</li>
<li>  Used in the drainage of Cornish mines,
  <a href="#Pg007">7</a>;</li>
<li>  Comparison of its power with human labour,
  <a href="#Pg008">8</a>;</li>
<li>  Investigation of the origin of,
  <a href="#Pg010">10</a>;</li>
<li>  A combination of a great variety of contrivances and the production of several inventions,
  <a href="#Pg012">12</a>;</li>
<li>  Before the discoveries of James Watt was of extremely limited power,
  <a href="#Pg012">12</a>;</li>
<li>  Invention of, ascribed to the Marquis of Worcester,
  <a href="#Pg023">23</a>;</li>
<li>  Account of Savery's,
  <a href="#Pg049">49</a>;</li>
<li>  Farey quoted,
  <a href="#Pg058">58</a>;</li>
<li>  Improvements made by Desaguliers,
  <a href="#Pg058">58</a>;</li>
<li>  Applied to the drainage of mines,
  <a href="#Pg059">59</a>;</li>
<li>  Humphrey Potter's contrivance,
  <a href="#Pg072">72</a>;</li>
<li>  Advantages of the atmospheric engine over that of Savery,
  <a href="#Pg073">73</a>;</li>
<li>  Progress of the atmospheric engine,
  <a href="#Pg075">75</a>;</li>
<li>  Description of Papin's engine,
  <a href="#Pg062">62</a>;</li>
<li>  Smeaton's improvements,
  <a href="#Pg076">76</a>;</li>
<li>  First experiments of Watt and subsequent improvements,
  <a href="#Pg083">83</a>;</li>
<li>  Watt's experiments on the force of steam at high pressure,
  <a href="#Pg083">83</a>;</li>
<li>  Watt discovers the great defects of the atmospheric engine,
  <a href="#Pg085">85</a>;</li>
<li>  Waste of heat in atmospheric engine,
  <a href="#Pg089">89</a>;</li>
<li>  Dr. Black's theory of latent heat,
  <a href="#Pg093">93</a>;</li>
<li>  Description of Watt's experimental engine at Kinneal,
  <a href="#Pg131">131</a>;</li>
<li>  Description of his single-acting engine,
  <a href="#Pg133">133</a>;</li>
<li>  Disadvantages of the atmospheric compared with the old engine,
  <a href="#Pg150">150</a>;</li>
<li>  Expedients to force the atmospheric engines into use,
  <a href="#Pg152">152</a>;</li>
<li>  Watt's exertions to improve the manufacture of, at Soho,
  <a href="#Pg155">155</a>;</li>
<li>  Efficiency of fuel in the new engines,
  <a href="#Pg156">156</a>;</li>
<li>  Hornblower's engine,
  <a href="#Pg175">175</a>;</li>
<li>  Woolf's engine,
  <a href="#Pg176">176</a>;</li>
<li>  Watt endeavours to bring to perfection the application of, to the drainage of mines,
  <a href="#Pg178">178</a>;</li>
<li>  Papin's projected application of,
  <a href="#Pg178">178</a>;</li>
<li>  Savery proposed to apply his steam engine as a prime mover for all sorts of machinery,
  <a href="#Pg180">180</a>;</li>
<li>  Jonathan Hull's application of, to water-wheels,
  <a href="#Pg180">180</a>;</li>
<li>  Steam engine used for driving water wheels,
  <a href="#Pg182">182</a>;</li>
<li>  First attempt of this kind made by Oxley,
  <a href="#Pg182">182</a>;</li>
<li>  Stewart's application of, to mill work,
  <a href="#Pg182">182</a>;</li>
<li>  Wasbrough's application of the fly-wheel and crank,
  <a href="#Pg183">183</a>;</li>
<li>  Reasons why Watt's single-acting engine was not adapted to produce continuous uniform motion of rotation,
  <a href="#Pg184">184</a>;</li>
<li>  Watt's second patent,
  <a href="#Pg186">186</a>;</li>
<li>  Valves of double-acting engine,
  <a href="#Pg189">189</a>;</li>
<li>  Condensing jet,
  <a href="#Pg191">191</a>;</li>
<li>  Methods of connecting the piston-rod and beam in the double-acting engine,
  <a href="#Pg193">193</a>;</li>
<li>  Rack and sector,
  <a href="#Pg194">194</a>;</li>
<li>  Parallel motion,
  <a href="#Pg195">195</a>;</li>
<li>  Connecting rod and crank,
  <a href="#Pg202">202</a>;</li>
<li>  Fly-wheel,
  <a href="#Pg205">205</a>;</li>
<li>  Throttle-valve,
  <a href="#Pg207">207</a>;</li>
<li>  Adaptation of the governor,
  <a href="#Pg209">209</a>;</li>
<li>  Double-acting engine considered as a whole,
  <a href="#Pg216">216</a>;</li>
<li>  Process of its operation investigated,
  <a href="#Pg217">217</a>;</li>
<li>  The eccentric,
  <a href="#Pg225">225</a>;</li>
<li>  Cocks and valves,
  <a href="#Pg227">227</a>;</li>
<li>  Single clack-valve,
  <a href="#Pg227">227</a>;</li>
<li>  Double clack-valve,
  <a href="#Pg228">228</a>;</li>
<li>  Conical steam-valves,
  <a href="#Pg228">228</a>;</li>
<li>  Slide-valves,
  <a href="#Pg229">229</a>;</li>
<li>  Murray's slide-valve,
  <a href="#Pg229">229</a>;</li>
<li>  D valve,
  <a href="#Pg230">230</a>;</li>
<li>  Seaward's slides,
  <a href="#Pg235">235</a>;</li>
<li>  Single cock,
  <a href="#Pg238">238</a>;</li>
<li>  Four-way cock,
  <a href="#Pg239">239</a>;</li>
<li>  Pistons,
  <a href="#Pg242">242</a>;</li>
<li>  Gross effect and useful effect of engines,
  <a href="#Pg285">285</a>;</li>
<li>  Power and duty of,
  <a href="#Pg287">287</a>;</li>
<li>  Horse power of,
  <a href="#Pg288">288</a>;</li>
<li>  The means whereby mechanical power is expended in working the engines enumerated,
  <a href="#Pg290">290</a>;</li>
<li>  Common rules followed by engine makers,
  <a href="#Pg292">292</a>;</li>
<li>  Duty of engines,
  <a href="#Pg294">294</a>;</li>
<li>  Duty distinguished from power,
  <a href="#Pg295">295</a>;</li>
<li>  Proportion of stroke to diameter of cylinder,
  <a href="#Pg295">295</a>;</li>
<li>  Cornish system of inspection,
  <a href="#Pg297">297</a>;</li>
<li>  Improvement of the Cornish engines,
  <a href="#Pg298">298</a>;</li>
<li>  Historical detail of the duty of Cornish engines,
  <a href="#Pg299">299</a>;</li>
<li>  High-pressure engines,
  <a href="#Pg321">321</a>;</li>
<li>  Leupold's engine described,
  <a href="#Pg323">323</a>;</li>
<li>  Construction of the first high-pressure engine by Messrs. Trevethick and Vivian,
  <a href="#Pg324">324</a>;</li>
<li>  First application of the steam engine to propel carriages on railroads,
  <a href="#Pg328">328</a>;</li>
<li>  Computation of how much corn could be saved by the substitution of steam engines for horse power,
  <a href="#Pg332">332</a>;</li>
<li>  Marine engines, form and arrangement of,
  <a href="#Pg441">441</a>;</li>
<li>  Difference between marine and land engines,
  <a href="#Pg443">443</a>;</li>
<li>  Mr. Howard's patent engine described,
  <a href="#Pg464">464</a>;</li>
<li>  Humphrey's engine described,
  <a href="#Pg470">470</a>.</li>

<li class="lstfst">Steam navigation to India,
  <a href="#Pg483">483</a>;</li>
<li>  First established in America,
  <a href="#Pg487">487</a>;</li>
<li>  Circumstances which led to it,
  <a href="#Pg488">488</a>;</li>
<li>  Attempts of Fitch and Rumsey to apply the single-acting engine to the propulsion of vessels,
  <a href="#Pg489">489</a>;</li>
<li>  Stevens of Hoboken commences experiments in,
  <a href="#Pg489">489</a>;</li>
<li>  Experiments of Livingstone and Fulton,
  <a href="#Pg489">489</a>;</li>
<li>  Fulton's first boat,
  <a href="#Pg490">490</a>;</li>
<li>  The Hudson navigated by steam,
  <a href="#Pg491">491</a>;</li>
<li>  Extension and improvement of river navigation,
  <a href="#Pg492">492</a>;</li>
<li>  American steamers,
  <a href="#Pg494">494</a>;</li>
<li>  Difference between them and European steamers,
  <a href="#Pg494">494</a>;</li>
<li>  Steamers on the Hudson,
  <a href="#Pg494">494</a>;</li>
<li>  Sea-going American steamers,
  <a href="#Pg496">496</a>;</li>
<li>  Speed attained by American steamers,
  <a href="#Pg497">497</a>;</li>
<li>  Lake steamers,
  <a href="#Pg499">499</a>;</li>
<li>  Steam-boats on the Mississippi,
  <a href="#Pg500">500</a>.</li>

<li class="lstfst">Steam tugs,
  <a href="#Pg503">503</a>.</li>

<li class="lstfst">Steep inclinations, method of surmounting,
  <a href="#Pg415">415</a>.</li>

<li class="lstfst">Stephenson, his locomotive engine at Killingworth,
  <a href="#Pg339">339</a>;</li>
<li>  Defect of,
  <a href="#Pg341">341</a>;</li>
<li>  Constructed the driving wheels without flanges,
  <a href="#Pg383">383</a>.</li>

<li class="lstfst">Stevens, of Hoboken, commences experiments on steam navigation,
  <a href="#Pg489">489</a>.</li>

<li class="lstfst">Stewart, his application of the steam engine to mill work,
  <a href="#Pg182">182</a>.</li>

<li class="lstfst">Stoking, process of,
  <a href="#Pg462">462</a>.</li>

<li class="lstfst">Stuffing-box, contrivance of,
  <a href="#Pg147">147</a>.</li>

<li class="lstfst">Sun and planet wheels, method of producing rotatory motion,
  <a href="#Pg187">187</a>.</li>


<li class="lsthdr">Thermometers, the process of filling described,
  <a href="#Pg044">44</a>;</li>
<li>  Explanation of the principle of,
  <a href="#Pg098">98</a>;</li>
<li>  Construction of mercurial thermometer,
  <a href="#Pg098">98</a>;</li>
<li>  Method of graduating,
  <a href="#Pg099">99</a>.</li>

<li class="lstfst">Thermometer gauge,
  <a href="#Pg270">270</a>.</li>

<li class="lstfst">Throttle-valve, description of,
  <a href="#Pg207">207</a>.</li>

<li class="lstfst">Tredgold, his remark relative to Newcomen's engine,
  <a href="#Pg073">73</a>.</li>

<li class="lstfst">Trevethick and Vivian's engine described,
  <a href="#Pg325">325</a>.</li>


<li class="lsthdr">Vacuum, force obtained by a,
  <a href="#Pg043">43</a>;</li>
<li>  The pump an illustration of this,
  <a href="#Pg043">43</a>.</li>

<li class="lstfst">Valves of double-acting engine,
  <a href="#Pg189">189</a>.</li>


<li class="lsthdr">Wasbrough, his application of the fly-wheel and crank,
  <a href="#Pg183">183</a>.</li>

<li class="lstfst">Water, a pint of, the mechanical force produced by its evaporation,
  <a href="#Pg006">6</a>;</li>
<li>  The alternate decomposition and recomposition of, by magnetism and electricity, analogous to vaporisation and condensation,
  <a href="#Pg008">8</a>;</li>
<li>  The fixed temperature which it assumes in boiling subject to variation,
  <a href="#Pg108">108</a>;</li>
<li>  Experiments to illustrate this,
  <a href="#Pg109">109</a>;</li>
<li>  Table to show the temperature at which it will boil under different pressures of the atmosphere,
  <a href="#Pg113">113</a>;</li>
<li>  Mechanical force of a cubic inch of, converted into steam,
  <a href="#Pg118">118</a>;</li>
<li>  Discovery of the composition of,
  <a href="#Pg303">303</a>;</li>
<li>  The merit of this discovery shared between Cavendish, Lavoisier, and Watt,
  <a href="#Pg305">305</a>;</li>
<li>  Latent heat of,
  <a href="#Pg101">101</a>;</li>
<li>  Conversion of ice into,
  <a href="#Pg103">103</a>.</li>

<li class="lstfst">Water tank,
  <a href="#Pg404">404</a>.</li>

<li class="lstfst">Water-wheels, steam engine used for turning,
  <a href="#Pg182">182</a>.</li>

<li class="lstfst">Watt (James), birth of,
  <a href="#Pg077">77</a>;</li>
<li>  His infancy,
  <a href="#Pg078">78</a>;</li>
<li>  Anecdotes respecting,
  <a href="#Pg078">78</a>;</li>
<li>  His boyhood,
  <a href="#Pg079">79</a>;</li>
<li>  Goes to London,
  <a href="#Pg080">80</a>;</li>
<li>  Returns to Glasgow,
  <a href="#Pg080">80</a>;</li>
<li>  Appointed mathematical instrument-maker to the university,
  <a href="#Pg081">81</a>;</li>
<li>  Adam Smith one of his earliest friends and patrons,
  <a href="#Pg081">81</a>;</li>
<li>  Also Black and Robert Simson,
  <a href="#Pg081">81</a>;</li>
<li>  Extract from an unpublished manuscript of Robison respecting the character of,
  <a href="#Pg082">82</a>;</li>
<li>  His first experiments on steam,
  <a href="#Pg083">83</a>;</li>
<li>  Observes defects of atmospheric engine,
  <a href="#Pg084">84</a>;</li>
<li>  His first attempt to improve it, by using a wooden instead of an iron cylinder,
  <a href="#Pg085">85</a>;</li>
<li>  His method to ascertain the temperatures at which water would boil under pressures less than that of the atmosphere,
  <a href="#Pg086">86</a>;</li>
<li>  His early experiments on steam,
  <a href="#Pg087">87</a>;</li>
<li>  His notice of the waste of heat in atmospheric engines,
  <a href="#Pg089">89</a>;</li>
<li>  His experiments to determine the extent to which water enlarged its volume when it passed into steam,
  <a href="#Pg090">90</a>;</li>
<li>  Discovers the latent heat of steam,
  <a href="#Pg091">91</a>;</li>
<li>  Learns the theory of latent heat,
  <a href="#Pg093">93</a>;</li>
<li>  His letter to Dr. Brewster, explaining the circumstances which led to the error that a large share of the merit of his discoveries were due to Black,
  <a href="#Pg093">93</a>;</li>
<li>  Finds that condensation in the cylinder is incompatible with a due economy of fuel,
  <a href="#Pg120">120</a>;</li>
<li>  Conceives the notion of condensing out of the cylinder,
  <a href="#Pg120">120</a>;</li>
<li>  Discovers separate condensation,
  <a href="#Pg121">121</a>;</li>
<li>  Invents the air-pump,
  <a href="#Pg122">122</a>;</li>
<li>  Substitutes steam pressure for atmospheric pressure,
  <a href="#Pg123">123</a>;</li>
<li>  Invents the steam case or jacket,
  <a href="#Pg124">124</a>;</li>
<li>  His first experiments to realise these inventions,
  <a href="#Pg125">125</a>;</li>
<li>  His experimental apparatus,
  <a href="#Pg126">126</a>;</li>
<li>  Difficulties of bringing the improved engines into use,
  <a href="#Pg128">128</a>;</li>
<li>  Practises as a civil engineer,
  <a href="#Pg129">129</a>;</li>
<li>  Makes a survey of the river Clyde,
  <a href="#Pg129">129</a>;</li>
<li>  His partnership with Dr. Roebuck,
  <a href="#Pg130">130</a>;</li>
<li>  His first patent,
  <a href="#Pg130">130</a>;</li>
<li>  Description of his experimental engine at Kinneal,
  <a href="#Pg131">131</a>;</li>
<li>  Removes to Soho,
  <a href="#Pg131">131</a>;</li>
<li>  Abstract of the act of parliament for the extension of his patent,
  <a href="#Pg132">132</a>;</li>
<li>  Description of his single-acting engine, <a href="#Pg133">133</a>-
  <a href="#Pg144">144</a>;</li>
<li>  His condenser worked by an injection,
  <a href="#Pg146">146</a>;</li>
<li>  Objections attending condensation by surface,
  <a href="#Pg146">146</a>;</li>
<li>  Improvements in construction of piston,
  <a href="#Pg147">147</a>;</li>
<li>  Effected by a contrivance called a stuffing-box,
  <a href="#Pg147">147</a>;</li>
<li>  Method of packing,
  <a href="#Pg148">148</a>;</li>
<li>  Improved methods of boring the cylinder,
  <a href="#Pg149">149</a>;</li>
<li>  His letter to Smeaton on this subject,
  <a href="#Pg149">149</a>;</li>
<li>  Used black-lead dust for the purpose of lubrication,
  <a href="#Pg149">149</a>;</li>
<li>  This found to wear the cylinder,
  <a href="#Pg149">149</a>;</li>
<li>  Disadvantages of the atmospheric compared with the old engines,
  <a href="#Pg150">150</a>;</li>
<li>  Greatly increased economy of fuel,
  <a href="#Pg151">151</a>;</li>
<li>  Expedients to force the atmospheric engines into use,
  <a href="#Pg152">152</a>;</li>
<li>  His correspondence with Boulton,
  <a href="#Pg153">153</a>;</li>
<li>  His correspondence with Smeaton,
  <a href="#Pg154">154</a>;</li>
<li>  Exertions to improve the manufacture of engines at Soho,
  <a href="#Pg155">155</a>;</li>
<li>  Efficiency of fuel in the new engines,
  <a href="#Pg156">156</a>;</li>
<li>  Endeavours to bring to perfection the application of the steam engine to the drainage of mines,
  <a href="#Pg178">178</a>;</li>
<li>  The reasons why his single-acting engine was not adapted to produce continuous uniform motion of rotation,
  <a href="#Pg184">184</a>;</li>
<li>  His notes upon Dr. Robison's article on the steam engine,
  <a href="#Pg184">184</a>;</li>
<li>  His second patent,
  <a href="#Pg186">186</a>;</li>
<li>  His third patent,
  <a href="#Pg189">189</a>;</li>
<li>  His application of the fly-wheel,
  <a href="#Pg205">205</a>;</li>
<li>  His application of the throttle-valve,
  <a href="#Pg207">207</a>;</li>
<li>  His adaptation of the governor,
  <a href="#Pg209">209</a>;</li>
<li>  His double-acting engine considered as a whole,
  <a href="#Pg216">216</a>;</li>
<li>  Investigation of the process of its operation,
  <a href="#Pg217">217</a>;</li>
<li>  Eccentric,
  <a href="#Pg225">225</a>;</li>
<li>  Cocks and valves,
  <a href="#Pg227">227</a>;</li>
<li>  Single clack-valve,
  <a href="#Pg227">227</a>;</li>
<li>  Double clack-valve,
  <a href="#Pg228">228</a>;</li>
<li>  Conical steam-valve,
  <a href="#Pg228">228</a>;</li>
<li>  Slide-valves,
  <a href="#Pg229">229</a>;</li>
<li>  The waggon boiler adopted by him,
  <a href="#Pg225">225</a>;</li>
<li>  Invents the indicator,
  <a href="#Pg274">274</a>;</li>
<li>  The counter contrived by him,
  <a href="#Pg278">278</a>;</li>
<li>  The Lunar Society in which Watt and Boulton were leading members,
  <a href="#Pg302">302</a>;</li>
<li>  Invents the copying press,
  <a href="#Pg302">302</a>;</li>
<li>  His friends and associates at Birmingham,
  <a href="#Pg302">302</a>;</li>
<li>  Method of heating by steam brought forward by him,
  <a href="#Pg303">303</a>;</li>
<li>  His invention of a machine for drying linen by steam,
  <a href="#Pg303">303</a>;</li>
<li>  His share in the discovery of the composition of water,
  <a href="#Pg303">303</a>;</li>
<li>  His letter to Priestley on this subject,
  <a href="#Pg307">307</a>;</li>
<li>  Anecdote of his inventive genius,
  <a href="#Pg309">309</a>;</li>
<li>  Introduces the use of chlorine in bleaching,
  <a href="#Pg310">310</a>;</li>
<li>  One of the founders of the Pneumatic institution at Clifton,
  <a href="#Pg310">310</a>;</li>
<li>  His first marriage,
  <a href="#Pg310">310</a>;</li>
<li>  Private life of,
  <a href="#Pg311">311</a>;</li>
<li>  Death of his first wife,
  <a href="#Pg311">311</a>;</li>
<li>  His second marriage,
  <a href="#Pg311">311</a>;</li>
<li>  He retires from business,
  <a href="#Pg311">311</a>;</li>
<li>  Death of his younger son,
  <a href="#Pg311">311</a>;</li>
<li>  Extracts from his letters,
  <a href="#Pg312">312</a>;</li>
<li>  His death,
  <a href="#Pg313">313</a>;</li>
<li>  Character of, by Lord Brougham,
  <a href="#Pg313">313</a>;</li>
<li>  By Sir Walter Scott,
  <a href="#Pg314">314</a>;</li>
<li>  By Lord Jeffrey,
  <a href="#Pg315">315</a>;</li>
<li>  Occupation of his old age,
  <a href="#Pg318">318</a>;</li>
<li>  Invention of machine for copying sculpture,
  <a href="#Pg318">318</a>;</li>
<li>  His last days,
  <a href="#Pg318">318</a>;</li>
<li>  Monuments,
  <a href="#Pg319">319</a>;</li>
<li>  Inscription on the monument in Westminster Abbey from the pen of Lord Brougham,
  <a href="#Pg319">319</a>;</li>
<li>  His application of tubular condensers,
  <a href="#Pg457">457</a>;</li>
<li>  His expedient for coating boilers with felt,
  <a href="#Pg463">463</a>.</li>

<li class="lstfst">Wilkinson, his machine for accurately boring the insides of cylinders,
  <a href="#Pg149">149</a>.</li>

<li class="lstfst">Williams's method of consuming the unburned gases which escape from the grate, and are carried through the flues,
  <a href="#Pg260">260</a>.</li>

<li class="lstfst">Woolf's engine,
  <a href="#Pg176">176</a>;</li>
<li>  Woolf's piston,
  <a href="#Pg243">243</a>.</li>
</ul>

<div class="figcenter" style="width: 470px;">
<img src="https://brian.carnell.com/wiki/_media/etext:j:james-watt-steam-engine-explained-i_557.png" width="470" height="323" alt="" />
<div class="caption">RICHMOND BRIDGE.</div>
</div>

<p class="center"><big>THE END.</big></p>

<div class="front">
<div class="fsize4"><strong class="m1">London:</strong></div>
<div class="fsize4">Printed by <strong class="m1">A. Spottiswoode</strong>,</div>
<div class="fsize4">New-Street-Square.</div>
</div>

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