TOM SWIFT AMONG THE DIAMOND MAKERS

or The Secret of Phantom Mountain

By [[Victor Appleton]]

Contents

CHAPTER I—A SUSPICIOUS JEWELER

"Well, Tom Swift, I don't believe you will make any mistake if you buy that diamond," said the jeweler to a young man who was inspecting a tray of pins, set with the sparkling stones. "It is of the first water, and without a flaw."

"It certainly seems so, Mr. Track. I don't know much about diamonds, and I'm depending on you. But this one looks to be all right."

"Is it for yourself, Tom?"

"Er—no—that is, not exactly," and Tom Swift, the young inventor of airships and submarines, blushed slightly.

"Ah, I see. It's for your housekeeper, Mrs. Baggert. Well, I think she would like a pin of this sort. True, it's rather expensive, but—"

"No, it isn't for Mrs. Baggert, Mr. Track," and Tom seemed a bit embarrassed.

"No? Well, then, Tom—of course it's none of my affair, except to sell you a good stone, But if this brooch is for a young lady, I can't recommend anything nicer. Do you think you will take this; or do you prefer to look at some others?"

"Oh, I think this will do, Mr. Track. I guess I'll take—"

Tom's words were interrupted by a sudden action on the part of the jeweler. Mr. Track ran from behind the showcase and hastened toward the front door.

"Did you see him, Tom?" he cried. "I wonder which way he went?"

"Who?" asked the lad, following the shopkeeper.

"That man. He's been walking up and down in front of my place for the last ten minutes—ever since you've been in here, in fact, and I don't like his looks."

"What did he do?"

"Nothing much, except to stare in here as if he was sizing my place up."

"Sizing it up?"

"Yes. Getting the lay of the land, so he or some confederate could commit a robbery, maybe."

"A robbery? Do you think that man was a thief?"

"I don't know that he was, Tom, and yet a jeweler has to be always on the watch, and that isn't a joke, either, Tom Swift. Swindlers and thieves are always on the alert for a chance to rob a jewelry store, and they work many games."

"I didn't notice any particular man looking in here," said Tom, who still held the diamond brooch in his hand.

"Well I did," went on the jeweler. "I happened to glance out of the window when you were looking at the pins, and I saw his eyes staring in here in a suspicious manner. He may have a confederate with him, and, when you're gone, one may come in, and pretend to want to look at some diamonds. Then, when I'm showing him some, the other man will enter, engage my attention, and the first man will slip out with a diamond ring or pin. It's often done."

"You seem to have it all worked out, Mr. Track," observed the lad, with a smile. "How do you know but what I'm in with a gang of thieves, and that I'm only pretending to want to buy a diamond pin?"

"Oh, I guess I haven't known you, Tom Swift, ever since you were big enough to toddle, not to be sure about what you're up to. But I certainly didn't like the looks of that man. However, let's forget about him. He seems to have gone down the street, and, after all, perhaps I was mistaken. Just wait until I show you a few more styles before you decide. The young lady may like one of these," and the jeweler went to another showcase and took out some more trays of brooches.

"What makes you think she's a young lady, Mr. Track?" asked the lad.

"Oh, it's easy guessing, Tom. We jewelers are good readers of character. I can size up a young fellow coming in here to buy an engagement or a wedding ring, as soon as he enters the door. I suppose you'll soon be in the market for one of those, Tom, if all the reports I hear about you are true—you and a certain Mary Nestor."

"I—er—I think I don't care for any of these pins," spoke Tom, quickly, with a blush. "I like the first lot best. I think I'll take the one I had in my hand when that man alarmed you. Ha! That's odd! What did I do with it?"

Tom looked about on the showcase, and glanced down on the floor. He had mislaid the brooch, but the jeweler, with a laugh, lifted it out of a tray a moment later.

"I saw you lay it down," he said. "We jewelers have to be on the watch. Here it is. I'll just put it in a box, and—"

With an exclamation, Mr. Track gave a hasty glance toward his big show window. Tom looked up, and saw a man's face peering in. At the sight of it, he, too, uttered a cry of surprise.

The next instant the man outside knocked on the glass, apparently with a piece of metal, making a sharp sound. As soon as he heard it, the jeweler once more sprang from behind the showcase, and leaped for the door crying:

"There's the thief! He's trying to cut a hole through my show window and reach in and get something! It's an old trick. I'll get the police! Tom, you stay here on guard!" and before the lad could utter a protest, the jeweler had opened the door, and was speeding down the street in the gathering darkness.

Tom stared about him in some bewilderment. He was left alone in charge of a very valuable stock of jewelry, the owner of which was racing after a supposed thief, crying:

"Police! Help! Thieves! Stop him, somebody!"

"This is a queer go," mused Tom. "I wonder who that man was? He looked like somebody I know, and yet I can't seem to place his face. I wonder if he was trying to rob the place? Maybe there's another one—a confederate—around here."

This thought rather alarmed Tom, so he went to the door, and looked up and down the street. He could see no suspicious characters, but in the direction in which the jeweler was running there was a little throng of people, following Mr. Track after the man who had knocked on the window.

"I wish I was there, instead of here," mused the lad. "Still I can't leave, or a thief might come in. Perhaps that was the game, and one of the gang is hanging around, hoping the store will be deserted, so he can enter and take what he likes."

Tom had read of such cases, and he at once resolved that he would not only remain in the jewelry shop, but that he would lock the door, which he at once proceeded to do. Then he breathed easier.

The town of Shopton, in the outskirts of which Tom lived with his father, and where the scene above narrated took place, was none too well lighted at night, and the lad had his doubts about the jeweler catching the oddly-acting man, especially as the latter had a good start.

"But some one may head him off," reasoned Tom. "Though if they do catch him, I don't see what they can prove against him. Hello, here I am carrying this diamond pin around. I might lose it. Guess I'll put it back on the tray."

He replaced in the proper receptacle one of the pins he had been examining when the excitement occurred.

"I wonder if Mary will like that?" he said, softly. "I hope she does. Perhaps it would be better if she could come here herself and pick out one—"

Tom's musing was suddenly interrupted by a sharp tattoo on the glass door of the jewelry shop. With a start, he looked up, to see staring in on him the face of the man who had been there before—the man of whom the jeweler was even then in chase.

"Why—why——" stammered Tom.

The man knocked again.

"Tom—Tom Swift!" he called. "Don't you know me?"

"Know you—you?" repeated the lad.

"Yes—don't you remember Earthquake Island—how we were nearly killed there—don't you remember Mr. Jenks?"

"Mr. Jenks?"

Tom was so startled that he could only repeat words after the strange man, who was talking to him from outside the glass door.

"Yes, Mr. Jenks," was the reply. "Mr. Barcoe Jenks, who makes diamonds. I saw you in the store about to buy a diamond—I wanted to tell you not to—I'll give you a better diamond than you can buy—I just arrived in this place—I must have a private talk with you—Come out—I'll share a wonderful secret with you."

A flood of memory came to Tom. He did recall the very strange man who walked around Earthquake Island—where Tom and some friends had been marooned recently—walked about with a pocketful of what he said were diamonds. Now Barcoe Jenks was here.

"I must see you privately, Tom Swift," went on Mr. Jenks, as he once more tapped on the glass. "Don't waste money buying diamonds, when you and I can make better ones. Where can I have a talk with you? I—" Mr. Jenks suddenly looked down the dimly-lighted street. "They're coming back!" he cried. "I don't want to be seen. I'll call at your house later to-night—be on the watch for me—until then—good-by!"

He waved his hand, and was gone in an instant. Tom stood staring at the glass door. He hardly knew whether to believe it or not—perhaps it was all a dream.

He pinched himself to make sure that he was awake. Very substantial flesh met his thumb and finger, and he felt the pain.

"I'm awake all right," he murmured. "But Barcoe Jenks here—and still talking that nonsense about his manufactured diamonds. I think he must be crazy. I wonder—"

Once more the lad's musing was interrupted. He heard a murmur of excited voices outside the store, on the street. Then the door of the jewelry shop was tried. Mr. Track's face was pressed against the glass.

"Open the door! Let me in, Tom!" he called. "I've caught the thief," and as the lad unlocked the portal he saw that the jeweler held by the arm a ragged lad. "Ah; you scoundrel! I've caught you!" cried the diamond merchant, shaking the small chap, while Tom looked on, more mystified than ever.

CHAPTER II—A MIDNIGHT VISIT

While Mr. Track, the jeweler, and several citizens, attracted by the chase after the supposed thief, are crowded into the store, anxious to hear explanations of the strange affair, I will take the opportunity to tell you something of Tom Swift, the lad who is to figure in this story.

Many of you have already made his acquaintance, when he has been speeding about in his airship or fast electric runabout, and to others we will state that our hero first made his bow to the public in the book called "Tom Swift and His Motor-Cycle," the initial volume of this series.

In that story there was related how Tom made the acquaintance of an odd individual, named Mr. Wakefield Damon, who was continually blessing himself, some part of his anatomy, or his possessions. Mr. Damon was riding a motor-cycle, and it started to climb a tree, to his pain and fright. Afterward Tom purchased the machine, and had many adventures on it, including a chase after a gang of men who had stolen a valuable patent model belonging to Mr. Swift.

Mr. Swift and his son were both inventors. They lived together in a fine house in the suburbs of Shopton, New York, and with them dwelt Mrs. Baggert, the housekeeper (for Tom's mother was dead), and also Garret Jackson, an expert engineer, who aided the young inventor and his father in perfecting many machines.

There was also another semi-member of the household, to wit, Eradicate Sampson, an eccentric colored man, who owned a mule called Boomerang. Eradicate did odd jobs around the place, and the mule assisted his owner—that is when the mule felt like it.

In the second volume of the series, entitled "Tom Swift and His Motor-Boat," there was related the incidents following a pursuit after a gang of unprincipled men, who sought to get possession of some of Mr. Swift's patents, and it was while in this boat that Tom, his father, and a friend, Ned Newton, rescued from Lake Carlopa a Mr. John Sharp, who fell from his burning balloon. Mr. Sharp was a skilled aeronaut, and after his recovery he joined Tom in building a big airship, called the Red Cloud. Tom's adventures in this craft are set down in detail in the third volume of the series, called "Tom Swift and His Airship." Not only did he and Mr. Sharp and Mr. Damon make a great trip, but they captured some bank robbers, and incidentally cleared themselves from the imputation of having looted the vault of seventy-five thousand dollars, which charge was fostered by a certain Mr. Foger, and his son Andy, who was Tom's enemy.

Not satisfied with having conquered the air, Tom and his father set to work to gain a victory over the ocean. They built a boat that could navigate under water, and, in the fourth book of the series, called "Tom Swift and His Submarine Boat," you will find an account of how they went under the ocean to secure a sunken treasure, and the fight they had with their enemies who sought to get it away from them. They went through many perils, not the least of which was capture by a foreign warship.

In the fifth book, entitled "Tom Swift and His Electric Runabout," there was told the story of a wonderfully speedy electric automobile the young inventor constructed, and how he made a great race in it, and saved from ruin a bank, in which his father and Mr. Damon were interested.

Tom's ability as an inventor had, by this time, become well known. One day, as related in a volume called "Tom Swift and His Wireless Message," he received a letter from a Mr. Hosmer Fenwick, of Philadelphia, asking his aid in perfecting an airship which the resident of the Quaker City had built, but which would not work. In his small monoplane, the Butterfly, Tom and Mr. Damon went to Philadelphia, as Mr. Damon was acquainted with Mr. Fenwick.

Tom carefully inspected the Whizzer which was the name of Mr. Fenwick's airship, and, after some difficulties, succeeded in getting the electric craft in shape to make a flight.

Tom, Mr. Damon and Mr. Fenwick started to make a trip to Cape May in the Whizzer, but were caught in a terrific storm, and blown out to sea. The wind became a hurricane, the airship was disabled, and wrecked in mid-air. When it fell to earth it landed on one of the small West Indian islands, but what was the terror of the three castaways to find that the island was subject to earthquake shocks.

But the earth-tremors were not the only surprise in store for Tom and his two friends, On the island they found five men and two ladies, who, by strange chance, had been stranded there when the yacht Resolute, owned by Mr. George Hosbrook, was wrecked in the same storm that disabled the airship. Mr. Hosbrook, a millionaire, was taking a party of friends to the West Indies.

When the castaways (among whom were Mr. and Mrs. Amos Nestor, parents of Mary Nestor, a girl of whom Tom was very fond) found that there was danger of the island being destroyed in an earthquake, they were in despair. There seemed no way of being rescued, as the island was out of the line of regular ship travel.

Tom, however, was resourceful. With the electrical apparatus from the wrecked airship, he built a wireless plant, and sent messages for help, broadcast over the ocean.

They were finally heard, and answered, by an operator on board the steamer Camberanian, which came on under forced draught, and rescued Tom and his friends. It was only just in time, for, no sooner had they gotten aboard the steamer in lifeboats, than the whole island was destroyed by an earthquake shock.

But Tom, the parents of Mary Nestor, Mr. Damon, Mr. Fenwick, and all the others, got safely home. Among the survivors from the yacht Resolute was a Mr. Barcoe Jenks, who now, most unexpectedly, had confronted Tom through the glass window of the jewelry store. Mr. Jenks was a peculiar man. Tom discovered this on Earthquake Island. Mr. Jenks carried with him some stones which he said were diamonds. He asserted that he had made them, but Tom did not know whether or not to believe this.

When it seemed that the castaways would not be saved Mr. Jenks offered Tom a large sum in these same diamonds for some plan whereby he might escape the earthquakes. Mr. Jenks said there was a certain secret in connection with the manufactured diamonds that he had to solve—that he had been defrauded of his rights—and that a certain Phantom Mountain figured in it. But Tom, at that time, paid little attention to Mr. Jenks' talk. The time was to come, however, when he would attach much importance to it.

When this story opens, Tom was more interested in Mr. Barcoe Jenks than in any one else, and was wondering what he wanted to see him about. The young inventor could not quite understand how Mr. Track, the jeweler, could come back with a lad he suspected of being a thief, when the person who had acted so suspiciously, and who had knocked on the glass, was the queer man, Mr. Jenks.

"Yes, Tom I caught him," the jeweler went on. "I chased after him, and nabbed him. It was hard work, too, for I'm not a good runner. Now, you little rascal, tell me why you tried to rob my store?" and the diamond merchant shook the lad roughly.

"I—I didn't try to rob your store," was the timid answer.

"Well, perhaps you didn't, exactly, but your confederates did. Why did you rap on the glass, and why were you staring in so intently?"

"I wasn't lookin' in."

"Well, if it wasn't you, it was some one just like you. But why did you run when I raced down the street?"

"I—I don't know," and the lad began to snivel. "I—I jest ran—that's all—'cause I see everybody else runnin', an' I thought there was a fire."

"Ha! That's a likely story! You ran because you are guilty! I'm going to hand you over to the police."

"Did he get anything, Mr. Track?" asked one of the men who had joined the jeweler in the chase.

"No, I can't say that he did. He didn't get a chance. Tom Swift was in here at the time. But this fellow was only waiting for a chance to steal, or else to aid his confederates."

"But, if he didn't take anything, I don't see how you can have him arrested," went on the man.

"On suspicion; that's how!" asserted Mr. Track. "Will some one get me a constable?"

"I wouldn't call a constable," said Tom, quietly.

"Why not?"

"Because that isn't the person who looked in your window."

"How do you know, Tom?"

"Because that person came back while you were out. I saw him."

"You saw him? Did he try to steal any of my diamonds, Tom?"

"No, I guess he doesn't need any."

"Why not?" There was wonder in the jeweler's tone.

"Why, he claims he can make all he wants."

"Make diamonds?"

"So he says."

"Why, he must be crazy!" and Mr. Track laughed.

"Perhaps he is," admitted Tom, "I'm only telling you what he says. He's the person who acted so suspiciously. He came back here, I'm telling you, while you were running down the street, and spoke to me."

"Oh, then you know him?" The jeweler's voice was suspicious.

"I didn't at first," admitted Tom. "But when he said he was Mr. Barcoe Jenks, I remembered that I had met him when I was cast away on Earthquake Island."

"And he says he can make diamonds?" asked Mr. Track.

"What did he want of you?" and the jeweler looked at Tom, quizzically.

"He wanted to have a talk with me," replied the lad, "and when he saw me in your store, he tried to attract my attention by knocking on the glass."

"That's a queer way to do," declared Mr. Track. "What did he want?"

"I don't know exactly," answered Tom, not caring to go into details just then. "But I'm sure, Mr. Track, that you've got the wrong person there. That lad never looked in the window, nor knocked on the glass."

"That's right—I didn't," asserted the captive.

The jeweler looked doubtful.

"Why did you run?" he asked.

"I told you, I thought there was a fire."

"That's right, I don't believe he's the fellow you want," put in another man. "I was standing on the corner, near White's grocery store, and I noticed this lad. That was before I heard you yelling, and saw you coming, and then I joined in the chase. I guess the man you were after got away, Track."

"He did," asserted Tom. "He came back here, a little while ago, and he ran away just now, as he heard you coming."

"Where did he go?" asked the jeweler, eagerly.

"I don't know," answered Tom. "Only you've got the wrong lad here."

"Well, perhaps I have," admitted the diamond merchant. "You can go, youngster, but next time, don't run if you're not guilty."

"I thought there was a fire," repeated the lad, as he hurriedly slipped through the crowd in the store, and disappeared down the dark street.

"Well, I guess the excitement's all over, and, anyhow, you weren't robbed, Track," said a stout man, as he left the store. The others soon followed, and Tom and the jeweler were once more alone in the shop.

"Can you tell me something about this man, Tom?" asked Mr. Track, eagerly. "So he really makes diamonds. Who is he?"

"I'd rather not tell—just now," replied the young inventor. "I don't take much stock in him, myself. I think he's visionary. He may think he has made diamonds, and he may have made some stones that look like them. I'm very skeptical."

"If you could bring me some, Tom, I could soon tell whether they were real or not. Can you?"

The lad shook his head.

"I don't expect to see Mr. Jenks again," he said. "He talked rather wildly about waiting to meet me, but that man is odd—crazy, perhaps—and I don't imagine I'll see him. He's harmless, but he's eccentric. Well, there was quite some excitement for a time."

"I should say there was. I thought it was a plan to rob me," and the jeweler began putting away the diamond pins. In fact, the excitement so filled the minds of himself and Tom that neither of them thought any more of the object of the lad's visit, and the young inventor departed without purchasing the pin he had come after.

It was not until he was out on the street, walking toward his home, that the matter came back to his mind.

"I declare!" he exclaimed. "I didn't get that pin for Mary, after all! Well, never mind, I have a week until her birthday, and I can get it to-morrow."

He walked rapidly toward home, for the weather looked threatening, and Tom had no umbrella. He was musing on the happenings of the evening when he reached his house. His father was out, as was Garret Jackson, the engineer; and Mrs. Baggert, the housekeeper, was entertaining a lady in the sitting-room, so, as Tom was rather tired, he went directly to his own room, and, a little later got into bed.

It was shortly after midnight when he was awakened by hearing a rattling on the window of his room. The reason he was able to fix the time so accurately was because as soon as he awakened he pressed a little electric button, and it illuminated the face of a small clock on his bureau. The hands pointed to five minutes past twelve.

"Humph! That sounds like hail!" exclaimed Tom, as he arose, and looked out of the casement. "I wonder if any of the skylights of the airship shed are open? There might be some damage. Guess I'd better go out and take a look."

He had mentally reasoned this far before he had looked out, and when he saw that the moon was brightly shining in a clear sky, he was a bit surprised.

"Why—that wasn't hail," he murmured. "It isn't even raining. I wonder what it was?"

He was answered a moment later, for a shower of fine gravel from the walk flew up and clattered against the glass. With a start, Tom looked down, and saw a dark figure standing under an apple tree.

"Hello! Who's there?" called the lad, after he had raised the sash.

"It's I—Mr. Jenks," was the surprising answer.

"Mr. Jenks?" repeated Tom.

"Yes—Barcoe Jenks, of Earthquake Island."

"You here? What do you want?"

"Can you come down?"

"What for?"

"Tom Swift, I've something very important to tell you," was the answer in a low voice, yet which carried to Tom's ears perfectly. "Do you want to make a fortune for yourself—and for me?"

"How?" Tom was beginning to think more and more that Mr. Jenks was crazy.

"How? By helping me to discover the secret of Phantom Mountain, where the diamonds are made! Will you?"

"Wait a minute—I'll come down," answered Tom, and he began to grope for his clothes in the dim light of the little electric lamp.

What was the secret of Phantom Mountain? What did Mr. Jenks really want? Could he make diamonds? Tom asked himself these questions as he hastily dressed to go down to his midnight visitor.

CHAPTER III—A STRANGE STORY

"Well, Mr. Jenks," began Tom, when he had descended to the garden, and greeted the man who had acted so strangely on Earthquake Island, "this is rather an odd time for a visit."

"I realize that, Tom Swift," was the answer, and the lad noticed that the man spoke much more calmly than he had that evening at the jewelry shop. "I realize that, but I have to be cautious in my movements."

"Why?"

"Because there are enemies on my track. If they thought I was seeking aid to discover the secret of Phantom Mountain, my life might pay the forfeit."

"Are you in earnest, Mr. Jenks?"

"I certainly am, and, while I must apologize for awakening you at this unseemly hour, and for the mysterious nature of my visit, if you will let me tell my story, you will see the need of secrecy."

"Oh, I don't mind being awakened," answered Tom, good-naturedly, "but I will be frank with you, Mr. Jenks. I hardly can believe what you have stated to me several times—that you know how diamonds can be made."

"I can prove it to you," was the quiet answer.

"Yes, I know. For centuries men have tried to discover the secret of transmuting base metals into gold, and how to make diamonds by chemical means. But they have all been failures."

"All except this process—the process used at Phantom Mountain," insisted the queer man. "Do you want to hear my story?"

"I have no objections."

"Then let me warn you," went on Mr. Jenks, "that if you do hear it, you will be so fascinated by it that I am sure you will want to cast your lot in with mine, and aid me to get my rights, and solve the mystery. And I also want to warn you that if you do, there is a certain amount of danger connected with it."

"I'm used to danger," answered Tom, quietly. "Let me hear your story. But first explain how you came to come here, and why you acted so strangely at the jewelry store."

"Willingly. I tried to attract your attention at the store, because I saw that you were going to buy a diamond, and I didn't want you to."

"Why not?"

"Because I want to present you with a beautiful stone, that will answer your purpose as well or better, than any one you could buy. That will prove my story better than any amount of words or argument. But I could not attract your attention without also attracting that of the jeweler. He became suspicious, gave chase, and I thought it best to vanish. I hope no one was made to suffer for what may have been my imprudence."

"No, the lad whom Mr. Track caught was let go. But how did you happen to come to Shopton?"

"To see you. I got your address from the owner of the yacht Resolute. I knew that if there was one person who could aid me to recover my rights, it would be you, Tom Swift. Will you help me? Will you come with me to discover the secret of Phantom Mountain? If we go, it will have to be in an airship, for in no other way, I think, can we come upon the place, as it is closely guarded. Will you come? I will pay you well."

"Perhaps I had better hear your story," said the young inventor. "But first let me suggest that we move farther away from the house. My father, or Mr. Jackson, or the housekeeper, may hear us talking, and it may disturb them. Come with me to my private shop," and Tom led the way to a small building where he did experimental work. He unlocked the door with a key he carried, turned on the lights, which were run by a storage battery, and motioned Mr. Jenks to a seat.

"Now I'll hear your story," said Tom.

"I'll make it as short as possible," went on the queer man. "To begin with, it is now several years ago since a poorly dressed stranger applied to me one night for money enough to get a meal and a bed to sleep in. I was living in New York City at the time, and this was midnight, as I was returning home from my club.

"I was touched by the man's appearance, and gave him some money. He asked for my card, saying he would repay me some day. I gave it to him, little thinking I would hear from the man again. But I did. He called at my apartments about a week later, saying he had secured work as an expert setter of diamonds, and wanted to repay me. I did not want to take his money, but the fact that such a sorry looking specimen of manhood as he had been when I aided him, was an expert handler of gems interested me. I talked with the man, and he made a curious statement.

"This man, who gave his name as Enos Folwell, said he knew a place where diamonds could be made, partly in a scientific manner, and partly by the forces of nature. I laughed at him, but he told me so many details that I began to believe him. He said he and some other friends of his, who were diamond cutters, had a plant in the midst of the Rocky Mountains, where they had succeeded in making several small, but very perfect diamonds. They had come to the end of their rope, though, so to speak, because they could not afford to buy the materials needed. Folwell said that he and his companions had temporarily separated, had left the mountain where they made diamonds, and agreed to meet there later when they had more money with which to purchase materials. They had all agreed to go out into civilization, and work for enough funds to enable them to go on with their diamond making.

"I hardly knew whether to believe the man or not, but he offered proof. He had several small, but very perfect diamonds with him, and he gave them to me, to have tested in any way I desired.

"I promised to look into the matter, and, as I was quite wealthy, as, in fact I am now, and if I found that the stones he gave me were real, I said I might invest some money in the plant."

"Were the diamonds good?" asked Tom, who was beginning to be interested.

"They were—stones of the first water, though small. An expert gem merchant, to whom I took them, said he had never seen any diamonds like them, and he wanted to know where I got them. Of course I did not tell him.

"To make a long story short, I saw Folwell again, told him to communicate with his companions, and to tell them that I would agree to supply the cash needed, if I could share in the diamond making. To this they agreed, and, after some weeks spent in preparation, a party of us set out for Phantom Mountain."

"Phantom Mountain?" interrupted Tom. "Where is it?"

"I don't know, exactly—it's somewhere in the Rockies, but the exact location is a mystery. That is why I need your help. You will soon understand the reason. Well, as I said, myself, Folwell and the others, who were not exactly prepossessing sort of men, started west. When we got to a small town, called Indian Ridge, near Leadville, Colorado, the men insisted that I must now proceed in secret, and consent to be blindfolded, as they were not yet ready to reveal the secret of the place where they made the diamonds.

"I did not want to agree to this, but they insisted, and I gave in, foolishly perhaps. At any rate I was blindfolded one night, placed in a wagon, and we drove off into the mountains. After traveling for some distance I was led, still blindfolded, up a steep trail.

"When the bandage was taken off my eyes I saw that I was in a large cave. The men were with me, and they apologized for the necessity that caused them to blindfold me. They said they were ready to proceed with the making of diamonds, but I must promise not to seek to discover the secret until they gave me permission, nor was I to attempt to leave the cave. I had to agree.

"Next they demanded that I give them a large sum, which I had promised when they showed me, conclusively, that they could make diamonds. I refused to do this until I had seen some of the precious stones, and they agreed that this was fair, but said I would have to wait a few days.

"Well, I waited, and, all that while, I was virtually a prisoner in the cave. All I could learn was that it was in the midst of a great range, near the top, and that one of the peaks was called Phantom Mountain. Why, I did not learn until later.

"At last one night, during a terrific thunder storm, the leader of the diamond makers—Folwell—announced that I could now see the stones made. The men had been preparing their chemicals for some days previous. I was taken into a small chamber of the cave, and there saw quite a complicated apparatus. Part of it was a great steel box, with a lever on it.

"We will let you make some diamonds for yourself," Folwell said to me, and he directed me to pull the lever of the box, at a certain signal. The signal came, just as a terrific crash of thunder shook the very mountain inside of which we were. The box of steel got red-hot, and when it cooled off it was opened, and was given a handful of white stones.

"Were they diamonds?" asked Tom, eagerly.

Mr. Jenks held out one hand. In the palm glittered a large stone—ostensibly a diamond. In the rays of the moon it showed all the colors of the rainbow—a beautiful gem. "That is one of the stones I made—or rather that I supposed I had made," went on Mr. Jenks. "It is one of several I have, but they have not all been cut and polished as has this one.

"Naturally I was much impressed by what I saw, and, after I had made certain tests which convinced me that the stones in the steel box were diamonds, I paid over the money as I had promised. That was my undoing."

"How?"

"As soon as the men got the cash, they had no further use for me. The next I remember is eating a rude meal, while we discussed the future of making diamonds. I knew nothing more until I found myself back in the small hotel at Indian Ridge, whence I had gone some time previous, with the men, to the cave in the mountain."

"What happened?" asked Tom, much surprised by the unexpected outcome of the affair.

"I had been tricked, that was all! As soon as the men had my money they had no further use for me. They did not want me to learn the secret of their diamond making, and they drugged me, carried me away from the cave, and left me in the hotel."

"Didn't you try to find the cave again?"

"I did, but without avail. I spent some time in the Rockies, but no one could tell where Phantom Mountain was; in fact, few had heard of it, and I was nearly lost searching for it.

"I came back East, determined to get even. I had given the men a very large sum of money, and, in exchange, they had given me several diamonds. Probably the stones are worth nearly as much as the money I invested, but I was cheated, for I was promised an equal share in the profits. These were denied me, and I was tricked. I determined to be revenged, or at least to discover the secret of making diamonds. It is my right."

"I agree with you," spoke Tom.

"But, up to the time I met you on Earthquake Island, I could form no plan for discovering Phantom Mountain, and learning the secret of the diamond makers," went on Mr. Jenks. "I carried the gems about with me, as you doubtless saw when we were on the island. But I knew I needed an airship in which to fly over the mountains, and pick out the location of the cave where the diamonds are made."

"But how can you locate it, if you were blindfolded when you were taken there, Mr. Jenks?"

"I forgot to tell you that, on our journey into the mountains, and just before I was carried into the cave, I managed to raise one corner of the bandage. I caught a glimpse of a very peculiarly shaped cliff—it is like a great head, standing out in bold relief against the moonlight, when I saw it. That head of rock is near the cave. It may be the landmark by which we can locate Phantom Mountain."

"Perhaps," admitted the young inventor.

"What I want to know is this," went on Mr. Jenks. "Will you go with me on this quest—go in your airship to discover the secret of the diamond makers? If you will, I will share with you whatever diamonds we can discover, or make; besides paying all expenses. Will you go, Tom Swift?"

The young inventor did not know what to answer. How far was Mr. Jenks to be trusted? Were the stones he had real diamonds? Was his story, fantastical as it sounded—true? Would it be safe for Tom to go?

The lad asked himself these questions. Mr. Jenks saw his hesitation.

"Here," said the strange man, "I will prove what I say. Take this diamond. I intended it for you, anyhow, for what you did for me on Earthquake Island. Take it, and—and give it to the person for whom you were about to purchase a diamond to-night. But, first of all, take it to a gem expert, and get his opinion. That will prove the truth of what I say, Tom Swift, and I feel sure that you will cast your lot in with mine, and help me to discover the secret of Phantom Mountain, and aid me to get my rights from the diamond makers!"

CHAPTER IV—ANDY FOGER GETS A FRIGHT

Tom Swift considered a few minutes. On the face of it, the proposition appealed to him. He had been home some time now after his adventures on Earthquake Island, and he was beginning to long for more excitement. The search for the mysterious mountain, and the cave of the diamond makers, might offer a new field for him. But there came to him a certain distrust of Mr. Jenks.

"I don't like to doubt your word," began Tom, slowly, "but you know, Mr. Jenks, that some of the greatest chemists have tried in vain to make diamonds; or, at best, they have made only tiny ones. To think that any man, or set of men, made real diamonds as large as the ones you have, doesn't seem—well—" and Tom hesitated.

"You mean you can hardly believe me?" asked Mr. Jenks.

"I guess that's it," assented Tom.

"I don't blame you a bit!" exclaimed the odd man. "In fact, I didn't believe it when they told me they could make diamonds. But they proved it to me. I'm ready now to prove it to you."

"I'll tell you what I'll do. Here's this one stone, cut ready for setting. Here's another, uncut," and Mr. Jenks drew from his pocket what looked like a piece of crystal. "Take them to any jeweler," he resumed—"to the one in whose place I saw you to-night. I'll abide by the verdict you get, and I'll come here to-morrow night, and hear what you have to say."

"Why do you come at night?" asked Tom, thinking there was something suspicious in that.

"Because my life might be in danger if I was seen talking to you, and showing you diamonds in the daytime—especially just now.

"Why at this particular time?"

"For the reason that the diamond makers are on my trail. As long as I remained quiet, after their shabby treatment of me, and did not try to discover their secret, they were all right. But, after I realized that I had been cheated out of my rights, and when I began to make an investigation, with a view to discovering their secret whereabouts, I received mysterious and anonymous warnings to stop."

"But I did not. I came East, and tried to get help to discover the cave of the diamond makers, but I was unsuccessful. I needed an airship, as I—said, and no person who could operate one, would agree to go with me on the quest. Again I received a warning to drop all search for the diamond makers, but I persisted, and about a week ago I found I was being shadowed."

"Shadowed; by whom?" asked Tom.

"By a man I never remember seeing, but who, I have no doubt, is one of the diamond-making gang."

"Do you think he means you harm?"

"I'm sure of it. That is the reason I have to act so in secret, and come to see you at night. I don't want those scoundrels to find out what I am about to do. On my return from Earthquake Island, I again endeavored to interest an airship man in my plan, but he evidently thought me insane. Then I thought of you, as I had done before, but I was afraid you, too, would laugh at my proposition. However, I decided to come here, and I did. It seemed almost providential that my first view of you was in a jewelry shop, looking at diamonds. I took it as a good omen. Now it remains with you. May I call here to-morrow night, and get your answer?"

Tom Swift made up his mind quickly. After all it would be easy enough to find out if the diamonds were real. If they were, he could then decide whether or not to go with Mr. Jenks on the mysterious quest. So he answered:

"I'll consider the matter, Mr. Jenks. I'll meet you here to-morrow night. In the meanwhile, for my own satisfaction, I'll let an expert look at these stones."

"Get the greatest diamond expert in the world, and he'll pronounce them perfect!" predicted the odd man. "Now I'll bid you goodnight, and be going. I'll be here at this time to-morrow."

As Mr. Jenks turned aside there was a movement among the trees in the orchard, and a shadowy figure was seen hurrying away.

"Who's that?" asked the diamond man, in a hoarse whisper. "Did you see that, Tom Swift? Some one was here—listening to what I said! Perhaps it was the man who has been shadowing me!"

"I think not. I guess it was Eradicate Sampson, a colored man who does work for us," said Tom. "Is that you, Rad?" he called.

"Yais, sah, Massa Tom, heah I is!" answered the voice of the negro, but it came from an entirely different direction than that in which the shadowy figure had been seen.

"Where are you, Rad?" called the young inventor.

"Right heah," was the reply, and the colored man came from the direction of the stable. "I were jest out seein' if mah mule Boomerang were all right. Sometimes he's restless, an' don't sleep laik he oughter."

"Then that wasn't you over in the orchard?" asked Tom, in some uneasiness.

"No, sah, I ain't been in de orchard. I were sleepin' in mah shack, till jest a few minutes ago, when I got up, an' went in t' see Boomerang. I had a dream dat some coon were tryin t' steal him, an' it sort ob 'sturbed me, laik."

"If it wasn't your man, it was some one else," said Mr. Jenks, decidedly.

"We'll have a look!" exclaimed Tom. "Here, Rad, come over and scurry among those trees. We just saw some one sneaking around."

"I'll sure do dat!" cried the colored man. "Mebby it were somebody arter Boomerang! I'll find 'em."

"I don't believe it was any one after the mule," murmured Mr. Jenks, "but it certainly was some one—more likely some one after me."

The three made a hasty search among the trees, but the intruder had vanished, leaving no trace. They went out into the road, which the moon threw into bold relief along its white stretch, but there was no figure scurrying away.

"Whoever it was, is gone," spoke Tom. "You can go back to bed, Rad," for the colored man, of late, had been sleeping in a shack on the Swift premises.

"And I guess it's time for me to go, too," added Mr. Jenks. "I'll be here to-morrow night, Tom, and I hope your answer will be favorable."

Tom did not sleep well the remainder of the night, for his fitful slumbers were disturbed by dreams of enormous caves, filled with diamonds, with dark, shadowy figures trying to put him into a red-hot steel box. Once he awakened with a start, and put his hand under his pillow to feel if the two stones Mr. Jenks had given him, were still there. They had not been disturbed.

Tom made up his mind to find out if the stones were really diamonds, before saying anything to his father about the chance of going to seek Phantom Mountain. And the young inventor wished to get the opinion of some other jeweler than Mr. Track—at least, at first.

"Though if this one proves to be a good gem, I'll have Mr. Track set it in a brooch, and give it to Mary for her birthday," decided the young inventor. "Guess I'll take a run over to Chester in the Butterfly, and see what one of the jewelers there has to say."

In addition to his big airship, Red Cloud, Tom owned a small, swift monoplane, which he called Butterfly. This had been damaged by Andy Foger just before Tom left on the trip that ended at Earthquake Island, but the monoplane had been repaired, and Andy had left town, not having returned since.

Telling his father that he was going off on a little business trip, which he often did in his aeroplane, Tom, with the aid of Mr. Jackson, the engineer, wheeled the Butterfly out of its shed.

Adjusting the mechanism, and seeing that it was in good shape, Tom took his place in one of the two seats, for the monoplane would carry two. Mr. Jackson then spun the propellers, and, with a crackle and roar the motor started. Over the ground ran the dainty, little aeroplane, until, having momentum enough, Tom tilted the wing planes and the machine sailed up into the air.

Rising about a thousand feet, and circling about several times to test the wind currents, Tom headed his craft toward Chester, a city about fifty miles from Shopton. In his pocket, snugly tucked away, were the two stones Mr. Jenks had given him.

It was not long before Tom saw, looming up in the distance the church spires and towering factory chimneys of Chester, for his machine was a speedy one, and could make ninety miles an hour when driven. But now a slower speed satisfied our hero.

"I'll just drop down outside of the city," he reasoned, "for too much of a crowd gathers when I land in the street. Besides I might frighten horses, and then, too, it's hard to get a good start from the street. I'll leave it in some barn until I want to go back."

Tom sent his craft down, in order to pick out a safe place for a landing. He was then over the suburbs of the city, and was following the line of a straight country road.

"Looks like a good place there," he murmured. "I'll shut off the motor, and vol-plane down."

Suiting the action to the word, Tom shut off his power. The little craft dipped toward the ground, but the lad threw up the forward planes, and caught a current of air that sent him skimming along horizontally.

As he got nearer to the ground, he saw the figure of a lad riding a bicycle along the country highway. Something about the figure struck Tom as being familiar, and he recognized the cyclist a moment later.

"It's Andy Foger!" said Tom, in a whisper. "I wondered where he had been keeping himself since he damaged the Butterfly. Evidently he doesn't dare venture back to Shopton. Well, here's where I give him a scare."

Tom's monoplane was making no more noise, now, than a soaring bird. He was gliding swiftly toward the earth, and, with the plan in his mind of administering some sort of punishment to the bully, he aimed the machine directly at him.

Nearer and nearer shot the monoplane, as quietly as a sheet of paper might fall. Andy pedaled on, never looking up nor behind him, A moment later, as Tom threw up his headplanes, to make his landing more easy, and just as he swooped down at one side of the cyclist, our hero let out a most alarming yell, right into Andy's ear.

"Now I've got you!" he shouted. "I'll teach you to slash my aeroplane! Come with me!"

Andy gave one look at the white bird-like apparatus that had flown up beside him so noiselessly, and, being too frightened to recognize Tom's voice, must have thought that he had been overtaken by some supernatural visitor.

Andy gave a yell like an Indian, about to do a stage scalping act, and fairly dived over the handlebars of his bicycle, sprawling in a heap on the dusty road.

"I guess that will hold you for a while," observed Tom, grimly, as he put on the ground-brake and brought his monoplane to a stop not far from the fallen rider.

CHAPTER V—A MYSTERIOUS MAN

For several minutes Andy Foger did not arise. He remained prostrate in the dust, and Tom, observing him, thought perhaps the bully might have been seriously injured. But, a little later, Andy cautiously raised his head, and inquired in a frightened voice:

"Is it—is it gone?"

"Is what gone?" asked Tom, grimly.

At the sound of his voice, Andy looked up. "Was that you, Tom Swift?" he demanded. "Did you knock me off my wheel?"

"My monoplane and I together did," was the reply; "or, rather, we didn't. It was the nervous reaction caused by your fright, and the knowledge that you had done wrong, that made you jump over the handlebars. That's the scientific explanation."

"You—you did it!" stammered Andy, getting to his feet. He wasn't hurt much, Tom thought.

"Have it your own way," resumed our hero. "Did you think it was a hob-goblin in a chariot of fire after you, Andy?"

"Huh! Never mind what I thought! I'll have you arrested for this!"

"Will you? Delighted, as the boys say. Hop in my airship and I'll take you right into town. And when I get you there I'll make a charge of malicious mischief against you, for breaking the propeller of the Butterfly and slashing her wings. I've mended her up, however, so she goes better than ever, and I can take you to the police station in jig time. Want to come, Andy?"

This was too much for the bully. He knew that Tom would have a clear case against him, and he did not dare answer. Instead he shuffled over to where his wheel lay, picked it up, and rode slowly off.

"Good riddance," murmured Tom. He looked about, and saw that he was near a house, in the rear of which was a good-sized barn. "Guess I'll ask if I can leave the Butterfly there," he murmured, and, ringing the doorbell, he was greeted by a man.

"I'll pay you if you'll let me store my machine in the barn a little while, until I go into the city, and return," spoke the lad.

"Indeed, you're welcome to leave it there without pay," was the answer. "I'm interested in airships, and, I'll consider it a favor if you'll let me look yours over while it's here."

Tom readily agreed, and a few minutes later he had caught a trolley going into the city. He was soon in one of the largest jewelry stores of Chester.

"I'd like to get an expert opinion as to whether or not those stones are diamonds," spoke Tom, to the polite clerk who came up to wait on him, and our hero handed over the two gems which Mr. Jenks had given him. "I'm willing to pay for the appraisement, of course," the young inventor added, as he saw the clerk looking rather doubtfully at him, for Tom had on a rough suit, which he always donned when he flew in his monoplane.

"I'll turn them over to our Mr. Porter, a gem expert," said the clerk. "Please be seated."

The young man disappeared into a private office with the stones, and Tom waited. He wondered if he was going to have his trouble for his pains. Presently two elderly gentlemen came from the little room, on the glass door of which appeared the word "Diamonds."

"Who brought these stones in?" asked one of the men, evidently the proprietor, from the deference paid him by the clerk. The latter motioned to Tom.

"Will you kindly step inside here?" requested the elderly man. When the door was closed, Tom found himself in a room which was mostly taken up with a bench for the display of precious stones, a few chairs, and some lights arranged peculiarly; while various scales and instruments stood on a table.

"You wished an opinion on—on these?" queried the proprietor of the place. Tom noticed at once that the word "diamonds" was not used.

"I wanted to find out if they were of any value," he said. "Are they diamonds?"

"Would you mind stating where you got them?" asked the other of the two men.

"Is that necessary?" inquired the lad. "I came by them in a legitimate manner, if that's what you mean, and I can satisfy you on that point. I am willing to pay for any information you may give me as to their value."

"Oh, it isn't that," the proprietor hastened to assure him. "But these are diamonds of such a peculiar kind, so perfect and without a flaw, that I wondered from what part of the world they came."

"Then they are diamonds?" asked Tom, eagerly.

"The finest I have ever tested!" declared the other man, evidently Mr. Porter, the gem expert. "They are a joy to look at, Mr. Roberts," he went on, turning to the proprietor. "If it is possible to get a supply of them you would be justified in asking half as much again as we charge for African or Indian diamonds. The Kimberly products are not to be compared to these," and he looked at the two stones in his hand—the one cut, and sparkling brilliantly, the other in a rough state.

"Do you care to state where these diamonds came from?" asked Mr. Roberts, looking critically at Tom.

"I had rather not," answered the lad. "It is enough for me to know that they are diamonds. How much is your charge?"

"Nothing," was the unexpected answer. "We are very glad to have had the opportunity of seeing such stones. Is there any chance of getting any more?"

"Perhaps," answered Tom, as he accepted the gems which the expert held out to him.

"Then might we speak for a supply?" went on Mr. Roberts, eagerly. "We will pay you the full market price."

"What is the value of these stones?" asked Tom.

Mr. Roberts looked at his gem expert.

"It is difficult to say," was the answer of the man who had handed Tom the gems. "They are so far superior to the usual run of diamonds, that I feel justified in saying that the cut one would bring fifteen hundred dollars, anywhere. In fact, I would offer that for it. The other is larger, though what it would lose in cutting would be hard to say. I should say it was worth two thousand dollars as it is now."

"Thirty-five hundred dollars for these two stones!" exclaimed Tom.

"They are worth every cent of it," declared Mr. Roberts. "Do you want to sell?"

Tom shook his head. He could scarcely believe the good news. Mr. Jenks had told the truth. Now the young inventor could go with him to seek the diamond makers.

"Can you get any more of these?" went on Mr. Roberts.

"I think so—that is I don't know—I am going to try," answered the lad.

"Then if you succeed I wish you would sell us some," fairly begged the proprietor of the store.

"I will," promised Tom, but he little knew what lay before him, or perhaps he would not have made that promise. He thanked the diamond merchant for his kindness, and arranged to have the cut stone set in a pin for Miss Nestor. The uncut gem Tom took away with him.

Thinking of many things, and wondering how best to start in his airship Red Cloud for the mysterious Phantom Mountain, Tom hurried back to where he had left the monoplane, wheeled it out, and was soon soaring through the air toward Shopton.

"I think I'll go with Mr. Jenks," he decided, as he prepared for a landing in the open space near his aeroplane shed. "It will be a risky trip, perhaps, but I've taken risks before. When Mr. Jenks comes to-night I'll tell him I'll help him to get his rights, and discover the secret of the diamond makers."

As Tom was wheeling the Butterfly into the shed, Eradicate came out to help him.

"Dere's a gen'man here to see yo', Massa Tom," said the colored man.

"Who is it?"

"I dunno. He keep askin' ef yo' de lad what done bust up Earthquake Island, an' send lightnin' flashes up to de sky, an' all sech questions laik dat."

"It isn't Mr. Damon; is it, Rad? He hasn't been around in some time."

"No, Massa Tom, it ain't him. I knows dat blessin' man good an' proper. I jest wish he'd bless mah mule Boomerang some day, an' take some oh de temper out ob him. No, sah, it ain't Massa Damon. De gen'man's in de airship shed waitin' fo' you."

"In the airship shed! No strangers are allowed in there, Rad."

"I knows it, Massa Tom, but he done persisted his se'f inter it, an' he wouldn't come out when I told him; an' your pa an' Mr. Jackson ain't home."

"I'll see about this," exclaimed Tom, striding to the large shed, where the Red Cloud was kept. As he entered it he saw a man looking over the wonderful craft.

"Did you want to see me?" asked Tom, sharply, for he did not like strangers prowling around.

"I did, and I apologize for entering here, but I am interested in airships, and I thought you might want to hire a pilot. I am in need of employment, and I have had considerable to do with balloons and aeroplanes, but never with an airship like this, which combines the two features. Do you wish to hire any one."

"No, I don't!" replied Tom, sharply, for he did not like the looks of the man.

"I was told that you did," was the rather surprising answer.

"Who told you?"

The man looked all around the shed, before replying, as if fearful of being overheard. Then, stepping close to Tom, he whispered:

"Mr. Jenks told me!"

"Mr. Jenks?" Tom could not conceal his astonishment.

"Yes. Mr. Barcoe Jenks. But I did not come here to merely ask you for employment. I would like to hire out to you, but the real object of my visit was to say this to you."

The man approached still closer to Tom, and, in a lower voice, and one that could scarcely be heard, he fairly hissed:

"Don't go with Barcoe Jenks to seek the diamond makers!"

Then, before Tom could put out a hand to detain him, had the lad so wished, the man turned suddenly, and fairly ran from the shed.

CHAPTER VI—MR. DAMON IS ON HAND

The young inventor stood almost spellbound for a few moments. Then recovering himself he made a dash for the door through which the mysterious man had disappeared. Tom saw him sprinting down the road, and was half-minded to take after him, but a cooler thought warned him that he had better not.

"He may be one of those men who are on Mr. Jenks' trail," reasoned Tom, in which case it might not be altogether safe to attempt to stop him, and make him explain. Or he may be a lunatic, and in that case it wouldn't be altogether healthy to interfere with him.

"I'll just let him go, and tell Mr. Jenks about him when he comes to-night. But I must warn Rad never to let him in here again. He might damage the airship."

Calling to the colored man, Tom pointed to the stranger, who was almost out of sight down the road, and said earnestly:

"Rad, do you see that fellow?"

"I sho do, Massa Tom, but I sorter has t' strain my eyes t' do it. He's goin' laik my mule Boomerang does when he's comm' home t' dinnah."

"That's right, Rad. Well, never let that man set foot inside our fence again! If he comes, and I'm home, call me. If I'm away, call dad or Mr. Jackson, and if you're here alone, drive him away, somehow."

"I will, Massa Tom!" exclaimed the colored man, earnestly, "an' if I can't do it alone, I'll get Boomerang t' help. Once let dat ar' mule git his heels on a pusson, an' dat pusson ain't goin' t' come bodderin' around any mo'—that is, not right away."

"I believe you, Rad. Well, keep a lookout for him, and don't let him in," and with that Tom entered the house to think over matters. They were beginning to assume an aspect he did not altogether like. Not that Tom was afraid of danger, but he preferred to meet it in the open, and the warning, or threat, of the mysterious man disquieted him.

When Mr. Swift came home, a little later, his son told him of the midnight interview with Mr. Jenks, for, up to this time, the aged inventor was unaware of it, and Tom also gave an account of the diamonds, speaking of their value.

"And do you propose to go to Phantom Mountain, in search of the makers of these gems, Tom?" asked Mr. Swift.

"I had about decided to do so, dad."

"And you're going in the Red Cloud?'

"Yes."

"Who are going with you?"

"Well, Mr. Jenks will go, of course, and I've no doubt but that if I mention the prospective trip to Mr. Damon, that he'll bless his skating cap, or something like that, and come along."

"I suppose so, Tom, and I'd like to have you take him. But I think you'll need some one else."

"Because, from what you have told me, you are going out to a dangerous part of the country, and you may have to deal with unscrupulous men. Three of you are hardly enough to cope with them. You ought to have at least another member of your party. If I was not busy on my invention of a new wireless motor I would go along, but I can't leave. You might take Mr. Jackson."

"No, you need him here to help you, dad."

"How about Eradicate?"

Tom smiled.

"Rad would get homesick for his mule Boomerang, and I'd have to bring him back just when we'd found the diamonds," replied the young inventor. "No, we'll have to think of some one else. I'll ask Mr. Damon, and then I'll consider matters further. I expect to see Mr. Jenks to-night, and he may have some one in mind."

"Perhaps that will be a good plan. Well, Tom, I trust you will take good care of yourself, and not run into unnecessary danger. Is the Red Cloud in good shape for the voyage?"

"It needs looking over. I'm going to get right at it."

"It's a pretty indefinite sort of a quest you're going on, Tom, my son. How do you expect to find Phantom Mountain?"

"Well, it's going to be quite a task. In the first place we'll head for Leadville, Colorado, and then we'll go to Indian Ridge and make some inquiries. We may get on the track of the place that way. If we don't, why I'll take the airship up as high as is necessary and sort of prospect until we see that big cliff that's shaped like a head. That will give us something to go by."

"Well, do the best you can. If you can discover the secret of making diamonds it will be a valuable one."

"I guess it will, dad; and Mr. Jenks is entitled to know it, for he paid his good money to that end. He has promised to go halves with me, as payment for the use of the airship, and I must say the two diamonds he gave me last night have proved very valuable."

"Two diamonds, Tom? You only showed me one, an uncut gem;" and Mr. Swift looked at his son.

"Oh, the other—er—the other is—I left it with a jeweler," and Tom blushed a trifle, as he thought of the present he contemplated making to Mary Nestor.

That afternoon, as Tom was out in the shed of the Red Cloud looking over the airship, to see what would be necessary to do to it in order to get it in shape for a long trip, he heard voices outside.

"Yes—yes, I know the way in perfectly well," he caught. "You needn't bother to come, my good fellow. Just step this way, and I'll show you something worth seeing."

"I wonder if it's that mysterious man coming back?" thought Tom. He dropped the tool he was using, and hurried to the door. As he approached it he heard the voice continue.

"Why bless my shoe laces, Mr. Parker! You'll see a wonderful airship, I promise you. Wonderful! Bless my hatband, but I hope Tom is here!"

"Mr. Damon!" exclaimed our hero, as he recognized the tones of his eccentric friend. "But who is with him?"

A moment later he caught sight of the gentleman who was always blessing himself, or something. Behind him stood another man, whose features Tom could not see plainly.

"Hello, Tom Swift!" called Mr. Damon. "Looking over the Red Cloud, eh? Does that mean you're off on another trip?"

"I guess it does," answered the lad.

"Where to this time? if I may ask."

"I'm thinking of going off to the mountains to find a band of men engaged in making diamonds," replied Tom.

"Making diamonds! Bless my finger ring! Making diamonds! A trip to the mountains! Bless my disposition! but do you know I'd like to go with you!"

"I was thinking of asking you, Mr. Damon."

"Were you? Bless my heart, I'm glad you thought of me. You don't by any possible chance want another person; do you?"

"We were thinking of having four in the party, Mr. Damon," and Tom wondered who was with his eccentric friend.

"Then bless my election ticket! This is the very chance for you, Mr. Parker!" cried Mr. Damon. "Will you go with us? It will be just what you need," and Mr. Damon stepped aside, revealing to Tom the features of Mr. Ralph Parker, the scientist who had correctly predicted the destruction of Earthquake Island.

CHAPTER VII—MR. PARKER PREDICTS

Tom Swift was a most generous lad, but when he saw that Mr. Damon had with him Mr. Parker, the gloomy scientist, who seemed to take delight in predicting disasters, our hero's spirits were not exactly of the best. He would have much preferred not to take Mr. Parker on the quest for the diamond makers, but, since Mr. Damon had mentioned it, he did not see how he could very well refuse.

"But perhaps he won't care to go," thought Tom.

He was undeceived a moment later, however, for the scientist remarked:

I am very glad to meet you once more, Mr. Swift. I have scarcely thanked you enough for what you did for us in erecting your wireless station on Earthquake Island, which, as you recall, I predicted would sink into the sea. It did, I am glad to say, not because I like to see islands destroyed, but because science has been vindicated. Now I have just heard you remark that you are about to set off to the mountains in search of some men who are making diamonds. I need hardly state that this is utterly useless, for no diamonds, commercially valuable, can be made by men. But the trip may be valuable in that it will permit me to demonstrate some scientific facts.

"Therefore, if you will permit me, I will be very glad to accompany you and Mr. Damon. I shall be delighted, in short, and I can start as soon as you are ready."

"There's no hope for it!" thought Tom, dismally. "I suppose he'll wake up every morning, and predict that before night the world will come to an end, or he'll prophesy that the airship will blow up, and vanish, when about seven miles above the clouds. Well, there's no way out of it, so here goes."

Thereupon Tom welcomed the scientist as cordially as he could, and invited him to form one of the party that would set off in the airship to search for Phantom Mountain.

"Bless my jewelry box!" exclaimed Mr. Damon, when this formality was over. "Tell me more about it, Tom."

Which our hero did, stating the need of maintaining secrecy on account of the danger to Mr. Jenks. Mr. Damon and Mr. Parker both agreed to say nothing about the matter, and then the scientist became much interested in the Red Cloud, which he closely examined. He even complimented Tom on the skill shown in making it, and, contrary to our hero's expectation, did not predict that it would blow up the next time it was used.

"How did you happen to arrive just at this time, Mr. Damon?" asked Tom.

"It was partly due to Mr. Parker," was the answer. "I had not seen him since we were rescued from the island, until a few days ago he called on me at my home. I happened to mention that you lived near here, and suggested that he might like to see some of your inventions. He agreed, and we came over in my auto. And now, bless my liver-pin! I find you about to start off on another trip."

"And have you fully decided to go with me?" asked Tom. "There may be danger, and I don't like the way that mysterious man behaved."

"Oh, bless my revolver!" cried Mr. Damon. "I'm used to danger by this time. Of course I'm going, and so is Mr. Parker. Do you know," and the man, who was always blessing something, came closer to the lad, and whispered: "Do you know, Tom, Mr. Parker is a very peculiar individual."

"I'm sure of it," answered the young inventor, looking at the gentleman in question, who was then inside the airship cabin.

"But he's all right, even if he is predicting unpleasant things," went on Mr. Damon. "I think we'll get better acquainted with him after a bit."

"I hope so," agreed Tom, but he did not realize then how close his companionship with Mr. Parker was to be, nor what dangers they were to share later.

The friends talked at considerable length of the prospective trip, and Tom, by this time, had ascertained what needed to be done to the airship to get it in shape to travel. It would take about a week, and, in the meanwhile, Mr. Damon would go home and get his affairs in order for the voyage. Tom's father was introduced to Mr. Parker, and, the former, finding that the scientist held some views in common with him, invited the gloomy predictor to remain at the Swift home until the Red Cloud was ready to sail. Tom could not repress a groan at this, but he decided he would have to make the best of it.

Mr. Damon left for home that afternoon, promising to be on hand at the time set to start for Phantom Mountain.

Tom was up waiting for Mr. Jenks at twelve o'clock that night. Shortly after the hour he saw a dark figure steal into the orchard. At first he feared lest it might be one of the spies who were, he was now convinced, on the trail of the man who was seeking to discover the secret of the diamond makers. But a whistle, which came to the lad's ear a moment later (that being a signal Mr. Jenks had agreed to sound), told Tom that it was none other than the visitor he expected.

"All right, Mr. Jenks, I'm here," called Tom, cautiously. "Come over this way," and he went out from the shadow of the house, where he had been waiting, and met the men. "We'll go into my private work-shop," the youth added, leading the way.

"Have you decided to go with me?" asked Mr. Jenks, in an anxious whisper. "Did you find the diamonds to be real ones?"

"I did; and I'm going," spoke Tom.

"Good! That relieves my mind. But we are still in danger. I was followed by my shadower to-day, and only succeeded in shaking him off just before coming here. I don't believe he knows what I am about to do."

"Oh, yes he does," said Tom.

"He does? How?"

"Because he was here, and warned me against you!"

"You don't mean it! Well, they are getting desperate! We must be on our guard. What sort of a man was he?"

Tom described the fellow, and Mr. Jenks stated that this tallied with the appearance of the person who had been shadowing him.

"But we'll fool them yet!" cried Tom, who had now fully entered into the spirit of the affair. "If they can follow us in the Red Cloud they're welcome to. I think we'll get ahead of them."

He then told of Mr. Damon and Mr. Parker, and Mr. Jenks agreed that it would add to the strength of the party to take these two gentlemen along.

"Though I can't say I care so much for Mr. Parker," he added. "But now as to ways and means. When can we start?"

Thereupon he and Tom talked over details in the seclusion of the little office, and arranged to leave Shopton in about a week. In the meanwhile the airship would be overhauled, stocked with supplies and provisions, and be made ready for a swift dash to the mountains.

"And now I must be going," said Mr. Jenks. "I have a great deal to do before I can start on this trip, and I hope I am not prevented by any of those men who seem to be trailing me."

"How could they prevent you?" Tom wanted to know.

"Oh, there are any number of ways," was the answer. "But I'm glad you found that my diamonds were real. We'll soon have plenty, if all goes well."

As Mr. Jenks left the shop, he started back, in some alarm.

"What's the matter?" asked Tom.

"Over there—I thought I saw a figure sneaking along under the trees—that man—perhaps—"

"That's Eradicate, our colored helper," replied Tom, with a laugh. "I posted him there to see that no strangers came into the orchard. Everything all right, Rad?" he asked, raising his voice.

"Yais, sah, Massa Tom. Nobody been around yeah this night."

"That's good. You can go to bed now," and Eradicate, yawning loudly, went to his shack. A little later Tom sought his own room, Mr. Jenks having hurried off to town, where he was boarding.

The next few days saw Tom busily engaged on the airship, making some changes and a few repairs that were needed. His father, Eradicate and Mr. Jackson helped him. As for Mr. Parker, the scientist, he went about the place, being much interested in the various machines which Tom or Mr. Swift had patented.

At other times the scientist would stroll about the extensive grounds, making what he said were "observations." One afternoon Tom saw him, apparently much excited, kneeling down back of a shed, with his ear to the ground.

"What is the matter?" asked the lad, thinking perhaps Mr. Parker might be ill.

"Have you ever had any earthquakes here, Tom Swift?" asked the scientist, quietly.

"Earthquakes? No. We had enough of them on the island."

"And you are going to have one here, in about two minutes!" cried Mr. Parker. "I predict that this place will be shaken by a tremendous shock very soon. We had all better get away from the vicinity of buildings."

"What makes you think there will be an earthquake?" asked Tom.

"Because I can hear the rumbling beneath the ground at this very minute. It is increasing in volume, showing that the tremors are working this way. There will soon be a great subterranean upheaval! Listen for yourself."

Tom cast himself down on the grass. Placing his ear close to the ground he did hear a series of dull thuds. He arose, not a little alarmed. There had never been any earthquakes in Shopton, yet he had great respect for Mr. Parker's scientific attainments.

Just then Eradicate Sampson came along. He saw Tom and Mr. Parker lying flat on the ground, and surprise showed on his honest, black face.

"Fo' de land sakes!" cried Eradicate. "What am de mattah now, Massa Tom?"

"Earthquake coming," answered Tom, briefly. "Better get away from the buildings, Rad. They might fall!" Tom's face showed the alarm he felt. What would happen to all of his valuable machines—to the Red Cloud?

"Earthquake?" murmured Eradicate, and he, too, cast himself down to listen. A moment later he arose with a laugh.

"What's the matter?" cried Tom.

"Why, dat ain't no earthquake!" declared the colored man.

"No. Then perhaps you know what it is," said Mr. Parker, somewhat sharply.

"Course I knows what it am," answered Eradicate, with dignity. "Dat noise am my mule Boomerang, kickin' in his stable, on account oh me not feedin' him yet. Dat's what it am. I'se gwine right now t' gib him his oats, and den yo' see dat de noise stop. Boomerang allers kick dat way when he's hungry. I show yo'!"

And, sure enough, when Eradicate had gone to the mule's stable, which was near where Mr. Parker had heard the mysterious sounds, they immediately ceased.

"Dat mule was all de earthquake dere was around here," said the colored man as he came out.

Mr. Parker walked away, saying nothing, and Tom did not make any comments—just then.

CHAPTER VIII—OFF FOR THE WEST

It was a great relief to Tom, to find that there was no danger from an earth tremor. Now that he had made up his mind to go in search of the diamond makers, he wanted nothing to interfere with it. Lest the feelings of Mr. Parker might be hurt by the mistake he had made, the young inventor cautioned Eradicate not to say anything more about the matter.

"'Deed an' I won't," the colored man promised. "I'se only too glad dere wa'n't no earthquake, dat's what I is."

As for Mr. Parker, he did not appear much put out by his error in predicting.

"I am sure that what I heard was a tremor, due to some distant earthquake shock," he said. "The mule's kicking was only a coincidence."

And Tom let him have his way about it. The week was drawing to a close, and the Red Cloud was nearly in shape for the voyage. At almost the last minute Tom found that he needed some electrical apparatus for the airship, and as he had to go to Chester for it, he decided he would make the trip in his monoplane, and, while in the city, would also get the diamond pin he was having made for Mary Nestor.

He started off early one morning, in the swift little craft Butterfly, and soon had reached Chester. The diamond brooch was ready for him.

"It is one of the most beautiful stones we have ever set," the diamond merchant told him. "Don't forget, if you find any more, Mr. Swift, to let us have a chance to bid on them."

"I may," Tom promised, rather indefinitely. Then, having purchased his electrical supplies, he made a quick trip to Shopton, stopping on the way to call on Miss Nestor.

"Why Tom, I'm delighted to see you!" cried the girl, blushing prettily. "Did you come for some apple turnovers?" and she laughed, as she referred to a call Tom had once paid, when a new cook had been engaged, and when the pastry formed a feature of the meal.

"No turnovers this time," said the young inventor. "I came to wish you many happy returns of the day."

"Oh, you remembered my birthday! How nice of you!"

"And here is something else," added our hero, rather awkwardly, as he handed her the diamond pin.

"Oh, Tom! This for me! Oh, it's too lovely—it's far too much!"

"It isn't half enough!" he declared, warmly.

"Oh, what a large diamond!" Mary cried as she saw the sparkling stone. "I never saw one so large and beautiful!"

"It's just as easy to make them large as small," explained Tom.

"Make them?" she looked the surprise she felt.

"Yes, I'm about to start for the place where diamonds are made."

"Oh, Tom! But isn't it dangerous? I mean won't you have to go to some far country—like Africa—to get to where diamonds are made?"

"Well, we are going on quite a trip, but not as far as that. And as for the danger—well, we'll have to take what comes," and he told her something of the proposed quest.

"Oh, it sounds—sounds scary!" Mary exclaimed, when she had heard of Mr. Jenks' experience. "Do be careful, Tom!"

"I will," he promised, and, somehow he was glad that she had cautioned him thus—and in such tones as she had used. For Mary Nestor was a girl that any young chap would have been glad to have manifest an interest in him.

"Well, I guess I'll have to say good-by," spoke Tom, at length. "We expect to start in a couple of days, and I may not get another chance to see you."

"Oh, I—I hope you come back safely," faltered Mary, and then she held out her hand, and Tom—well, it's none of our affair what Tom did after that, except to say that he hurried out, fairly jumped into his monoplane, and completed the trip home.

As the Red Cloud has been fully described in the volume entitled "Tom Swift and His Airship," we will not go into details about it now. Sufficient to say that it was a combination of a biplane and dirigible balloon. It could be used either as one or the other, and the gas-bag feature was of value when the wind was too great to allow the use of the planes, or when the motive power, for some reason stopped. In that event the airship could remain suspended far above the clouds if necessary. There was provision for manufacturing the gas on board.

The Red Cloud was fitted up to accommodate about ten persons, though it was seldom that this number was carried. Two persons could successfully operate the machinery. There were sleeping berths, and in the main cabin a sitting-room, a dining-room, and a kitchen. There was also the motor compartment, and a steering tower, from which the engines could be controlled.

It was in this craft that the seekers after the diamond makers proposed undertaking the trip. Mr. Damon came on from his home in Waterfield about two days before the date set to leave, and Mr. Jenks, had, three days before this, taken up his abode at the Swift home. Mr. Parker, as has been stated, was already there, and he had put in his time making a number of scientific observations, though he had made no more predictions.

Nothing more had been seen of the mysterious man who had warned Tom, and the young inventor and Mr. Jenks began to hope that they had thrown their enemies off the track.

"Though I don't imagine they'll give up altogether," said Mr. Jenks. "They're too desperate for that. We'll have trouble with them yet."

"Well, it can't be helped," decided Tom. "We'll try and be ready for it, when it comes," and then, dismissing the matter from his mind, he busied himself about the airship.

The food and supplies had all been put aboard, and they expected to start the next morning. In order to make sure that any stones which they might succeed in getting from the diamond makers were real gems, a set of testing apparatus was taken along. Mr. Parker had had some experience in this line, and, in spite of the fact that he might make direful predictions, Tom was rather glad, after all, that the scientist was going to accompany them.

"But what is worrying me," said Mr. Damon, "is what we are going to do after we get to Phantom Mountain. What are your plans, Mr. Jenks? Will you go in, and demand your share of the diamond-making business?"

"I have a right to it, as I invested a large sum in it, and I am entitled to more than a half-share. But, of course, I can't say what I'll do until I get there. We may have to act very secretly."

"I'm inclined to think we will," said Tom. "My plan would be to gain access to the cave, if possible, and watch them at work. We might be able to discover the secret of making diamonds, and, after all, that's what you want, isn't it, Mr. Jenks?"

"Yes, I paid my money for the secret, and I ought to have it. If I can get it quietly, so much the better. If not, I'll fight for my rights!" and he looked very determined.

"Bless my powder horn!" cried Mr. Damon. "That's the way to talk! And so we're to go cruising about in the air, looking for a mountain shaped like a man's head."

"That's it," agreed Mr. Jenks, "and when we find it we will be near Phantom Mountain, and the diamond makers."

The final details were completed that night. The last of the supplies had been put aboard, the larder was well stocked, the diamond testing apparatus was stored safely away, and all that remained was for the adventurers to board the Red Cloud in the morning, and soar away.

That night Tom was uneasy. Several times he got up, and looked toward the shed where the airship was stored. He could not rid himself of the idea that the men to whose interest it was that the diamond-making secret remain undiscovered, might attempt to wreck the airship before the start. Consequently both Eradicate Sampson and Engineer Jackson were on guard. Tom looked from his window, to the shed where the Red Cloud was housed. He saw nothing to cause him any uneasiness.

"I guess I'm just nervous," he mused. "But, all the same, I'll be glad when we've started."

They were all up early the next morning, Mr. Damon beginning the day by blessing the sunrise, and many other things that struck his fancy. The airship was wheeled out of the shed, and Tom gave her a final inspection.

"It's all right," he declared. "All aboard!"

"Now, do be careful," begged Mr. Swift. "Don't take too many chances, Tom."

"I'll not."

The adventurers were in the forward part of the ship, and Tom had taken his place at the wheels and levers in the pilot house. As he was about to start the motor he looked toward the road, and saw a horse and carriage. In the vehicle was a girlish figure, at the sight of which Tom blushed and smiled. He waved his hand.

"I came to wish you good luck!" cried Mary Nestor, for it was she in the carriage.

"Thanks!" cried Tom, leaning from the window of the pilot house. "It was good of you to get up so early."

"Oh. I'm always up early," she informed him.

"Look out that the motor doesn't scare your horse," Tom warned her.

"Old Dobbin doesn't mind anything," was her answer. "I'll see that he doesn't run away with me, as long as you're not on earth to rescue me. Good-by, Tom!"

"Good-by!" he called, and then he pulled the lever that set in motion the motor, and whirled the great propellers about. They whizzed around with a roar, and the Red Cloud, shivering and trembling with the vibration, rose in the air like some great bird.

"We're off for the West and Phantom Mountain!" called Tom to his companions.

As the airship soared upward, Eradicate Sampson ran forward from where he had been standing near his mule Boomerang. He waved his hands, and shouted something.

"Bless my hatband! What does he want?" asked Mr. Damon, watching him curiously.

"It sounds as if he were calling to us to come back," spoke Mr. Parker.

"It's too late now," decided Tom. "Maybe he forgot to tell us good-by," but, he felt a vague wonder at Eradicate's odd motions; for the colored man was pointing toward the stern of the airship, as if there was something wrong there. But the Red Cloud soared on.

CHAPTER IX—A WARNING BY WIRELESS

Rapidly the airship ascended, and, when it was high over the town of Shopton, Tom headed the craft due west. Looking down he tried to descry Mary Nestor, in her carriage, but the trees were in the way, their interlocking branches hiding the girl. Tom did see crowds of other persons, though, thronging the streets of Shopton, for, though the young inventor had made many flights, there was always a novelty about them, that brought out the curious.

"A good start, Tom Swift," complimented Mr. Parker. "Is it always as easy as this?"

"Starting always is," was the answer, "though, as the Irishman said, coming down isn't sometimes quite so comfortable."

"Bless my gizzard! That's so," cried the eccentric Mr. Damon. "Can we vol-plane to earth in the Red Cloud, Tom?"

"Yes, but not as easily as in the Butterfly. However I hope we will not have to. Now, Mr. Damon, if you will just take charge of the steering apparatus for a minute, I want to go aft."

"What for?"

"I wish to see if everything is all right. I can't imagine why Eradicate was making those queer motions."

Mr. Damon, who knew how to operate the Red Cloud, was soon guiding her on the course, while Tom made his way to the rear compartments, through the motor room, where the stores of supplies and food were kept. He made a careful examination, looking from an after window, and even going out on a small, open platform, but could discover nothing wrong.

"I guess Rad was just capering about without any special object," mused Tom, but it was not long after this that they learned to their dismay, that the colored man had had a method in his madness.

On his way back through the motor room Tom looked to the machinery, and adjusted some of the auxiliary oil feeders. The various pieces of apparatus were working well, though the engine had not yet been speeded up to its limit. Tom wanted it to "warm-up" first.

"Everything all right?" asked Mr. Damon, as Tom rejoined them in the pilot house, which was just forward of the living room in the main cabin.

"Yes, I can't imagine what made Rad act that way. But I'll set the automatic steering gear now, Mr. Damon, and then you will be relieved."

Mr. Jenks was gazing off toward the west—to where he hoped to discover the secret of Phantom Mountain.

"How do you like it?" asked Tom.

"It's great," replied the diamond man. "I've never been in an airship before, and it's different than what I expected; but it's great! It's the only craft that will serve our purpose among the towering mountain peaks, where the diamond makers are hidden. I hope we can find them."

In a little while the Red Cloud was skimming along at faster speed, guided by the automatic rudders, so that no one was needed in the pilot house, since there was no danger of collisions. Airships are not quite numerous enough for that, yet, though they may soon become so.

Tom and the others devoted several hours to arranging their staterooms and bunks, and getting their clothing stowed away, and when this was done Mr. Parker and Mr. Jenks sat gazing off into space.

"It's hard to realize that we are really in an airship," observed the diamond man. "At first I thought I would be frightened, but I'm not a bit. It doesn't seem as if anything could happen."

"Something is likely to happen soon," said Mr. Parker, suddenly, as he gazed at some weather instruments on the cabin wall.

"Bless my soul! Don't say that!" cried Mr. Damon. "What is it?"

"I think, from my observations, that we will soon have a hurricane," said the scientific man. "There is every indication of it;" and he seemed quite delighted at the prospect of his prediction coming true.

"A hurricane!" cried Mr. Damon. "I hope it isn't like the one that blew us to Earthquake Island."

"Oh, I think there will be no danger," spoke Tom. "If it comes on to blow we will ascend or descend out of the path of the storm. This craft is not like the ill-fated Whizzer. I can more easily handle the Red Cloud; even in a bad storm."

"I'm glad to hear that," remarked Mr. Jenks. "It would be too bad to be wrecked before we got to Phantom Mountain."

"Well, I predict that we will have a bad storm," insisted Mr. Parker, and Tom could not help wishing that the scientist would keep his gloomy forebodings to himself.

However the storm had not developed up to noon, when Tom, with Mr. Damon's help, served a fine meal in the dining-room. In the afternoon the speed of the ship was increased, and by night they had covered several hundred miles. Through the darkness the Red Cloud kept on, making good time. Tom got up, occasionally, to look to the machinery, but it was all automatically controlled, and an alarm bell would sound in his stateroom when anything went wrong.

"Bless my napkin!" exclaimed Mr. Damon the next morning, as they sat down to a breakfast of fruit, ham and eggs and fragrant coffee, "this is living as well as in a hotel, and yet we are—how far are we above the earth, Tom?" he asked, turning to the young inventor.

"About two miles now. I just sent her up, as I thought I detected that storm Mr. Parker spoke of."

"I told you it would come," declared the scientist, and there was a small hurricane below them that morning, but only the lower edge of it caught the Red Cloud, and when Tom sent her up still higher she found a comparatively quiet zone, where she slid along at good speed.

That afternoon Tom busied himself about some wires and a number of complicated pieces of apparatus which were in one corner of the main cabin.

"What are you doing now?" asked Mr. Jenks, who had been talking with Mr. Parker, and showing that scientist some of the manufactured diamonds.

"Getting our wireless apparatus in shape," answered the lad. "I should have done it before, but I had so much to do that I couldn't get at it. I'm going to send off some messages. Dad will want to know how we are doing."

As he worked away, he also made up his mind to send another message, in care of his father, for there was a receiving station in the Swift home. And to whom this message was addressed Tom did not say, but we fancy some of our readers can guess.

Finally, after several hours of work, the wireless was in shape to send and receive messages. Tom pulled over the lever, and a crackling sound was heard, as the electricity leaped from the transmitters into space. Then he clamped the receiver on his ear.

"All ready," he announced. "Has anybody any messages they wish sent?" For, with the courtesy of a true host he was ready to serve his guests before he forwarded his own wireless notes.

"Just tell my wife that I'm enjoying myself," requested Mr. Damon. "Bless my footstool! But this is great! We're off the earth yet, connected with it."

Mr. Jenks had no one to whom he wanted to send any word, but Mr. Parker wish to wire to a fellow scientist the result of some observations made in the upper air.

Tom noted all the messages down, and then, when all was in readiness he began to call his home station. He knew that either his father or Mr. Jackson, the engineer, could receive the wireless.

But, no sooner had the young inventor sent off the first few dots and dashes representing "S. I."—his home station call—than he started and a look of surprise came over his face.

"They're calling us!" he exclaimed.

"Who is?" asked Mr. Jenks.

"My house—my father. He—he's been trying to get us ever since we started, but I didn't have the wireless in shape to receive messages. Oh, I hope it's not too late!"

"Too late! Bless my soul, too late for what?" gasped Mr. Damon, somewhat alarmed by Tom's manner.

The lad did not answer at once. He was intently listening to a series of dots and dashes that clicked in the telephone receiver clamped to his left ear. On his face there was a look of worriment.

"Father has just sent me a message," he said. "It's a warning flashed through space! He's been trying to get it to me since yesterday!"

"What is it?" asked Mr. Jenks, rising from his seat.

"The mysterious man is aboard the airship—hidden away!" cried Tom. "That's what Eradicate was trying to call to our attention as we started off. Eradicate saw his face at a rear window, and tried to warn us! The mysterious man is a stowaway on board!"

CHAPTER X—DROPPING THE STOWAWAY

Tom's excited announcement startled Mr. Damon and the others as much as if the young inventor had informed them that the airship had exploded and was about to dash with them to the earth. The men leaped to their feet, and stared at the lad.

"A stowaway on board!" cried Mr. Damon. "Bless my soul! How did he—"

"Are you sure that message is straight?" asked Mr. Jenks. "Did Eradicate see the man?"

"He says he did," answered Tom. "The man is hidden away on board now—probably among the stores and supplies."

"Bless my tomato sauce!" exploded Mr. Damon. "I hope he doesn't eat them all up!"

"We must get him out at once!" declared Mr. Jenks.

"I knew something would happen on this voyage," came from Mr. Parker. "I predicted it from the first!"

Tom thought considerable, but he did not answer the scientist just then. Another communication was coming to him by wireless. He listened intently.

"Father says," the lad told his companions "that Eradicate only had a glimpse of the man at the last moment. He was looking from the rear storeroom window—he's the same man who called on me that time—Rad remembers him very well."

"Bless my shoes! What's to be done?" inquired Mr. Damon, looking around helplessly.

"We must get him out, that's all," decided Mr. Jenks; with vigor. "Get him out and drop him overboard!"

"Drop him overboard!" cried Mr. Parker, in horror.

"Not exactly, but get rid of him," proceeded the diamond seeker. "That man is one of my enemies. He has been sent by the band of diamond makers hidden among the mountains, to spy on me, and, if possible, prevent me from seeking to discover their secret. He tried to work on Tom's Swift's fears, and frighten him from using his airship on this quest. Then, when he failed, the man must have sneaked into the shed, and hidden himself in the ship. We must get rid of him, or he may wreck the Red Cloud!"

"That's so!" cried Tom. "We must try to capture him. I think we had better—" the lad paused, and again listened to the wireless message. "Father says Eradicate saw the man have a gun, so we must be careful," the young inventor translated the dots and dashes.

"Bless my powder horn!" exploded Mr. Damon.

"We shall have to proceed cautiously then," spoke Mr. Jenks. "If he is like any others in the gang he is a desperate man."

"Better sneak up on him then, if we can," proposed Mr. Parker. "There are enough of us to cope with one man, even if he is armed. You have weapons aboard, haven't you?" he inquired of Tom.

"Yes," was the hesitating answer, "but I don't want to use them if I can help it. Not only because of the danger, and a dislike of shedding blood, but because a stray bullet might pierce the gas bag and damage the ship."

"That's so," agreed Mr. Jenks. "Well, I guess if we go at it the right way we can capture him without any shooting. But we must talk more quietly—we ought to have whispered—he may have heard us."

"I don't think so," replied Tom. "The storeroom is far enough off so that he couldn't hear us. Besides, the motor makes such a racket that he couldn't distinguish what we were talking about, even if he heard our voices. So, unless he heard the wireless working, and suspects something from that, he probably doesn't know that we are aware of his presence aboard."

"But why do you think he has remained quiet all this while, Tom?" asked Mr. Damon.

"Probably he wants to wait until the ship is farther out west," suggested Mr. Jenks. "Then he will be nearer his friends, and can get help, if he needs it."

"And do you really believe he would destroy the Red Cloud?" asked Mr. Parker.

"I think that all he is waiting for is a favorable chance," declared the diamond seeker. "He would destroy the craft, and us too, if he could prevent us from discovering the secret of Phantom Mountain, I believe."

"Then we must get ahead of him," decided Tom, quietly. "I have just flashed to dad a message, telling him that we will heed his warning. Now to capture the stowaway!"

"And while we're about it, give him a good scare when we do get him," suggested Mr. Jenks.

"How?" asked Tom.

"Threaten to drop him overboard. Perhaps that will make him tell how he happened to get in our ship, and what are the plans of the gang of diamond makers. We may get valuable information that way."

"I don't believe you can scare such fellows much," was Tom's opinion, but it was agreed to try.

"How are you going to capture him?" asked Mr. Parker. "If he has a gun it won't be any too easy to go in the storeroom, and drag him out."

"We'll have to use a little strategy," decided Tom, and then they discussed several plans. The one finally adopted was that Tom and Mr. Damon should enter the storeroom, casually, as if in search of food to cook for supper. They would discuss various dishes, and Mr. Damon was to express a preference for something in the food line, the box containing which, was well back in the room. This would give the two a chance to penetrate to the far end of the apartment, without arousing the suspicions of the hidden man, who, doubtless, would be listening to the conversation.

"And as soon as we get sight of him, you and I will jump right at him, Mr. Damon," said Tom. "Jump before he has a chance to use his gun. Mr. Jenks and Mr. Parker will be waiting outside the room, to catch him if he gets away from us. I'll have some ropes ready, and we'll tie him up, and—well, we'll decide later what to do with him."

"All right. I'm ready as soon as you are, Tom," said the eccentric man. "Come ahead."

They went softly to the storeroom, and listened at the door. There was no sound heard save that made by the machinery.

"I wonder if he's really here?" whispered Mr. Damon.

"We'll soon find out," answered Tom. "Let's go in."

They entered, and, in pursuance of their plan, Tom and his friend talked of various foods.

"I think I'd like some of that canned lobster, with French dressing on," spoke the eccentric man.

"That's away in the back end of the room," said Tom, in a loud voice. "It's under a lot of boxes."

"Then I'll help you get it out! Bless my frying pan! but I am very fond of lobster!" exclaimed Mr. Damon, in as natural tones as was possible under the circumstances.

He and Tom moved cautiously back among the boxes and barrels. They were glancing about with eager eyes. Tom switched on an electric light, and, the instant he did so, he was aware of a movement in a little space formed by one box which was placed on top, of two others. The lad saw a dark figure moving, as if to get farther out of sight.

"I've got him!" cried Tom, making a dive for the shadow.

A moment later the young inventor was bowled over, as a dark figure leaped over his head.

"Catch him, Mr. Damon!" he cried.

"Bless my hatband! I—I—" Mr. Damon's voice ended in a grunt. He, too, had been knocked down by the fleeing man.

"Look out, Mr. Jenks!" cried Tom, to warn those on guard at the door of the storeroom.

There was the report of a gun, some excited shouts, and when Tom could scramble to his feet, and rush out, he beheld Mr. Parker calmly sitting on a struggling man, while Mr. Jenks held a gun, that was still smoking.

"We caught him!" cried the scientist.

"Anybody hurt?" asked Tom, anxiously.

"No, I knocked up his gun as he fired," explained Mr. Jenks. "Where are the ropes, Tom?"

The cords were produced and the man, who had now ceased to struggle, was tightly bound. He uttered not a word, but he smiled grimly when Mr. Damon remarked:

"I guess I'll go back in the storeroom, Tom, and see how much food he ate."

"Oh, I guess he didn't take much," declared the lad. "He wasn't there long enough."

"Well, Farley Munson, so it's you, is it?" asked Mr. Jenks, as he surveyed the prisoner.

"Do you know him?" asked Tom, in some surprise.

"He was in with the diamond makers," said Mr. Jenks. "He was one of those who took me to the secret cave. But it will be the last time he ever goes there. How high up are we, Tom?"

"About two miles. Why?"

"I guess that will be far enough to let him fall," went on the diamond seeker. "Come on, Mr. Damon, help me throw him overboard!"

"You—you're not going to throw me over—with the airship two miles high; are you?" gasped the man.

"Will you tell us what we want to know, if we don't?" asked Mr. Jenks.

"What do you want to know?"

"How you got aboard, and what your object was in coming."

"That's easy enough. I had been hanging around the shed for several days, watching a chance to get in. Finally I saw it, when that colored man went to feed his mule, and I slipped in, and hid in the airship. The stores were all in then, and I stowed myself away among the boxes. I had food and water, so I didn't touch any of yours," and he looked at Mr. Damon, who seemed much relieved.

"And what was your object?" demanded Mr. Jenks.

"I wanted to prevent you from going to Phantom Mountain."

"How?"

"By destroying the airship if need be. But I hoped to accomplish it by other means. I would have stopped at nothing, though, to prevent you. You must keep away from there!"

"And if we refuse?" asked Tom.

"Then you'll have to take what comes!"

"But not from you!" exclaimed Mr. Jenks. "We're going to get rid of you."

The man's face showed the alarm he felt.

"Oh, don't worry," said Mr. Jenks, quickly, "we're not going to toss you overboard. We're not as desperate as your crowd. But we're going to get rid of you, and then go on before you can send any word to your confederates. We'll put you off in the most lonesome spot we can find, and I guess you'll be some time getting back to civilization. By that time we'll have the secret of the diamonds."

"You never will!" declared the man, firmly. And he would say nothing more, though by threats and promises Mr. Jenks tried to get from him something about the men in with him, and where the cave of the diamonds was located.

Heavily bound with ropes the man was locked in a small closet, to be kept there until a favorable spot was reached for letting him go. Mr. Jenks' plan, of dropping him down in some place where he would have difficulty in sending on word to his confederates was considered a good one.

Three days later, in crossing over a lonely region, near the Nebraska National Forest, Farley Munson, which was one of the names the spy went by, was dropped off the airship, when it was sent down to within a few feet of the earth.

"It will take you some time to get to a telegraph office," said Mr. Jenks, as a package of food, and a flask of water was tossed down to the stowaway. He shook his fist at those in the airship, and shouted after them:

"You'll never discover the secret of Phantom Mountain!"

"Yes, we will," declared Tom, as he sent the Red Cloud high into the air again.

CHAPTER XI—A WEARY SEARCH

During the three days when the stowaway had been kept a prisoner, the Red Cloud had made good time on her western trip. She was now about two hundred and fifty miles from Leadville, Colorado, and Tom knew he could accomplish that distance in a short time. It was necessary, therefore, since they were so close to the place where the real search would begin, to make some more definite plans.

"We will need to replenish our supply of gasoline," said Tom, shortly after the stowaway had been dropped, and when the young inventor had made a general inspection of the airship.

"Is it all gone?" inquired Mr. Damon.

"Not all, but we will soon be in the wildest part of the Rocky Mountains, and gasoline is difficult to procure there. So I want to fill all our reserve tanks. But I would rather do that before we get far into Colorado."

"Why?" inquired Mr. Parker.

"Because airships are not so common but what the appearance of one attracts attention. Ours is sure to be talked about, and commented on. In that case, in spite of our precaution in putting Munson off in this lonely place, word of the Red Cloud being in the vicinity of Leadville may reach the diamond makers, and put them on their guard. We want to take them unawares if we can."

"That's so," agreed Mr. Jenks. "We had better get our gasoline at the first stopping place, then, and proceed with our search. Our first object ought to be to look for the landmark—the head of stone. Then we can begin to prospect about a bit."

"My idea, exactly," declared Tom. "Well, then, I'll go down at the first place we cross, where we can get gasoline, and then we'll be in a position to hover in the air for a long time, without descending."

The airship kept on her way, traveling slowly the remainder of that day, and at dusk, when there was less chance of big crowds seeing them, the Red Cloud was sent down on the outskirts of a large village. Tom and Mr. Damon went to a supply store, and arranged to have a sufficient quantity of the gasoline taken out to the airship. It was delivered after dark, and little talk was occasioned by the few who were aware of the presence of the craft. Then, once more, they went aloft, and Tom sent several wireless messages to Shopton, including one to Miss Nestor.

"Please tell my wife that I am well, and that I have a good appetite," said Mr. Damon.

Mr. Parker also sent a message to a scientific friend of his, stating that he made some observations among the mountains, of the region in which the airship then was, and that the indications were that a great landslide would soon take place.

"That won't worry us," spoke Tom, "for we'll be far above it."

"I hope we will be near enough to enable me to observe it, and make some scientific notes," came from Mr. Parker. "I am positive that one of these mountain peaks that we saw to-day will disappear in a landslide within a few days. I have an instrument somewhat like the one that records earthquakes, and it has been acting strangely of late."

Tom wondered what enjoyment Mr. Parker got out of life, when he was always looking for some calamity to happen, but the scientist seemed to take as much pleasure in his gloomy forebodings now, as he had on Earthquake Island.

They reached the vicinity of Leadville the next day, but took care to keep high above the city, so that the airship could not be observed. With powerful glasses they examined the mountainous country, looking for the little settlement of Indian Ridge.

"There it is!" exclaimed Mr. Jenks, just as dusk was settling down. "I can make out the hotel I stopped at. Now we can really begin our search. The next thing is to find the stone head, and then, I think, I will have my bearings."

"We'll begin the hunt for that landmark in the morning," said Tom.

High in the air hovered the Red Cloud. At that distance above the earth she must have looked like some great bird, and the adventurers thought it unlikely that any one in the vicinity of Leadville would observe them.

The quest for the great mountain peak, that looked like a stone head, was under way. Back and forth sailed the airship. Sometimes she was enveloped in fog, and no sight could be had of the earth below. At other times there were rain storms, which likewise prevented a view. Mr. Parker was on the lookout for his predicted mountain landslide, but it did not occur, and he was much disappointed.

"It's queer I can't pick out that landmark," said Mr. Jenks after two days of weary searching, when their eyes were strained from long peering through telescopes. "I'm sure it was around Indian Ridge, yet we've covered almost all the ground in this neighborhood, and I haven't had a glimpse of it."

"Perhaps it was destroyed in a landslide, or some cataclysm of nature," suggested Mr. Parker. "That is very possible."

"If that's the case we're going to have a hard time to locate the cave of the diamond makers," answered Mr. Jenks, "but I hope it isn't so."

They continued the search for another day, and then Tom, as they sat in the comfortable cabin of the airship that night, hovering almost motionless (for the motor had been shut down) made a proposition.

"Why not descend in some secluded place," he suggested, "and wander around on foot, making inquiries of the miners. They may know where the stone head is, or they may even know about Phantom Mountain."

"Good idea," spoke Mr. Jenks. "We'll do it."

Accordingly, the next morning, the Red Cloud was lowered in a good but lonely landing place, and securely moored. It was in a valley, well screened from observation, and the craft was not likely to be seen, but, to guard against any damage being done to it by passing hunters or miners, Mr. Parker and Mr. Damon agreed to remain on guard in it, while Tom and Mr. Jenks spent a day or two traveling around, making inquiries.

The young inventor and his companion proceeded on foot to a small settlement, where they hired horses on which to make their way about. They were to be gone two days, and in that time they hoped to get on the right trail.

CHAPTER XII—THE GREAT STONE HEAD

It was a wild and desolate country in which Tom Swift and Mr. Jenks were traveling. Villages were far apart, and they were at best but small settlements. In their journeys from place to place they met few travelers.

But of these few they made cautious inquiries as to the location of Phantom Mountain, or the landmark known as the great stone head. Prospectors, miners and hunters, whom they asked, shook their heads.

"I've heard of Phantom Mountain," said one grizzled miner, "but I couldn't say where it is. Maybe it's only a fish story—the place may not even exist."

"Oh, it does, for I've been there!" exclaimed Mr. Jenks.

"Then why don't you go back to it?" asked the miner.

"Because I can't locate it again," was the reply.

"Humph! Mighty queer if you've seen a place once, and can't get to it again," and the man looked as if he thought there was something strange about Tom and his companion. Mr. Jenks did not want to say that he had been taken to the mountain blindfolded, for that would have caused too much talk.

"I think if we spent to-night in a place where the miners congregate, listened to their talk, and put a few casual questions to them, more as if we were only asking out of idle curiosity, we might learn something," suggested Tom.

"Very well, we'll try that scheme."

Accordingly, after they had left the suspicious miner the two proceeded to a small milling town, not far from Indian Ridge. There they engaged rooms for the night at the only hotel, and, after supper they sat around the combined dance hall and gambling place.

There were wild, rough scenes, which were distasteful to Tom, and to Mr. Jenks, but they felt that this was their only chance to get on the right trail, and so they stayed. As strangers in a western mining settlement they were made roughly welcome, and in response to their inquiries about the country, they were told many tales, some of which were evidently gotten up for the benefit of the "tenderfeet."

"Is there a place around here called Phantom Mountain?" asked Tom, at length, as quietly as he could.

"Never heard of it, stranger," replied a miner who had done most of the talking. "I never heard of it, and what Bill Slatterly don't know ain't worth knowin'. I'm Bill Slatterly," he added, lest there be some doubt on that score.

"Isn't there some sort of a landmark around here shaped like a great stone head?" went on Tom, after some unimportant questions. "Seems to me I've heard of that."

"Nary a one," answered Mr. Slatterly. "No stone heads, and no Phantom Mountains—nary a one.

"Who says there ain't no Phantom Mountains?" demanded an elderly miner, who had been dozing in one corner of the room, but who was awakened by Slatterly's loud voice. "Who says so?"

"I do," answered the one who claimed to know everything.

"Then you're wrong!" Tom's heart commenced beating faster than usual.

"Do you mean to say you've seen Phantom Mountain, Jed Nugg?" demanded Slatterly.

"No, I ain't exactly seen it, an' I don't want to, but there is such a place, about sixty mile from here. Folks says it's haunted, and them sort of places I steer clear from."

"Can you tell me about it?" asked Mr. Jenks, eagerly. "I am interested in such things."

"I can't tell you much about it," was the reply, "and I wouldn't git too interested, if I was you. It might not be healthy. All I know is that one time my partner and I were in hard luck. We got grub-staked, and went out prospectin'. We strayed into a wild part of the country about sixty mile from here, and one night we camped on a mountain—a wild, desolate place it was too."

The miner stopped, and began leisurely filling his pipe.

"Well?" asked Tom, trying not to let his voice sound too eager.

"Well, that was Phantom Mountain."

The miner seemed to have finished his story.

"Is that all?" asked Mr. Jenks. "How did you know it was Phantom Mountain?"

"'Cause we seen the ghost—my partner and I—that's why!" exclaimed the man, puffing on his pipe. "As I said, we was campin' there, and 'long about midnight we seen somethin' tall and white, and all shimmerin', with a sort of yellow fire, slidin' down the side of the mountain It made straight for our camp."

"Huh! Guess you run, didn't you, Jed?" asked Bill Slatterly.

"Course we did. You'd a run too, if you seen a ghost comm' at you, an' firin' a gun."

"Ghosts can't fire guns!" declared Bill. "I guess you dreamed it, Jed."

"Ghosts can't fire guns, eh? That's all you know about it. This one did, and to prove I didn't dream it, there was a bullet hole in my hat next mornin'. I could prove it, too, only I ain't got that hat any more. But that was Phantom Mountain, strangers, an' my advice to you is to keep away from it. I was on it but I didn't exactly see it, 'cause it was dark at the time."

"Was it near a peak that looked like a stone head?" asked Tom.

"It were, stranger, but I didn't take much notice of it. Me and my partner got out of them diggin's next day, and I never went back. I ain't never said much about this place, but it's called Phantom Mountain all right, and I ain't the only one that's seen a ghost there. Other grub-stakers has had the same experience."

"Why ain't I never heard about it?" demanded Bill, suspiciously.

"'Cause as why you're allers so busy talkin' that you don't never listen to nothin' I reckon," was Jed's answer, amid laughter.

"Can you tell us what trail to take to get there?" asked Tom, of the miner.

"Yes, it's called the old silver trail, and you strike it by goin' to a place called Black Gulch, about forty mile from here. Then it's twenty mile farther on. But take my advice and don't go."

"Can it be reached by way of Indian Ridge?" asked Mr. Jenks, wondering how he had been taken to the cave of the diamond makers. He did not remember Black Gulch.

"Yes, you can git there by Indian Ridge way, but it's more dangerous. You're likely to lose your way, for that's a trail that's seldom traveled." Mr. Jenks thought that, perhaps, was the reason the gang had taken him that way. "It's easier to get to the stone head and Phantom Mountain by Black Gulch, but it ain't healthy to go there, strangers, take my advice on that," concluded the miner, as he prepared to go to sleep again.

Tom could scarcely contain the exultation he felt. At last, it seemed, they were on the trail. He motioned to Mr. Jenks, and they slipped quietly from the place, just as another dance was beginning.

"Now for Black Gulch!" cried Tom. "We must hurry back to the airship, and tell the good news.

"It's too late to-night," decided Mr. Jenks, and so they waited until morning, when they made an early start.

They found Mr. Damon and Mr. Parker anxiously awaiting their return. Mr. Damon blessed so many things that he was nearly out of breath, and Mr. Parker related something of the observations he had made.

"I think I have discovered traces of a dormant volcano," he said. "I am in hopes that it will have an eruption while we are here."

"I'm not," spoke Tom, decidedly. "We'll start for Black Gulch as soon as possible."

The airship once more rose in the air, and, following the directions the miner had given him, Tom pointed his craft for the depression in the mountains which had been given the name Black Gulch. It was reached in a short time, and then, making a turn up a long valley the airship proceeded at reduced speed.

"We ought to see that stone head soon now," spoke Tom, as he peered from the windows of the pilot house.

"It's queer we didn't notice it when we were up in the air," remarked Mr. Jenks. "We've been over this place before, I'm sure of it."

The next moment Mr. Damon uttered a cry. "Bless my watch-chain!" he exclaimed. "Look at that!"

He pointed off to the left. There, jutting out from the side of a steep mountain peak was a mass of stone—black stone—which, as the airship slowly approached, took the form and shape of a giant's head.

"That's it! That's it!" cried Tom. "The great stone head!"

"And now for Phantom Mountain and the diamonds!" shouted Mr. Jenks, as Tom let the airship slowly settle to the bottom of the valley.

CHAPTER XIII—ON PHANTOM MOUNTAIN

Out from the Red Cloud piled Tom and the others. They made a rush for the irregular mass of rock which bore so strong a resemblance to the head of some gigantic man.

"That's the one! That's the thing I saw when they were taking me along here blindfolded!" exclaimed Mr. Jenks. "I'm sure we're on the right trail, now!"

"But what gets me, though," remarked Mr. Damon, "is why we couldn't see that landmark when we were up in the air. We had a fine view, and ought to have been able to pick it out with the telescopes."

The adventurers saw the reason a few seconds later. The image was visible only from one place, and that was directly looking up the valley. If one went too far to the right or left the head disappeared from view behind jutting crags, and it was impossible to see it from overhead, because the head was almost under a great spur of a mighty mountain.

"We might have hunted for it a week in the airship, and been directly over it," said Tom, "and yet we would never have seen it."

"Yes, but we never would have gotten here in such good shape if it hadn't been for your wonderful craft," declared Mr. Jenks. "It brought us here safely and quickly, and enabled us to elude the men who tried to keep us back. We're here in spite of them. If we had traveled by train they might have interfered with us in a dozen ways."

"That's so," agreed Mr. Damon. "Well, now we're here, what's to be done? Which way do we start to reach the cave where the diamonds are manufactured, Mr. Jenks?"

"That I can't say. As you know, I only had a momentary glimpse of this stone head as they were taking me along the trail. Then one the men noticed that the bandage had slipped and he pulled it into place. So I really can't say which direction to take now, in order to discover the secret."

"How long after you saw the head before you reached the cave?" asked Tom. "In that way we may be able to tell how far away it is."

"Well, I should say it was about two or three hours after I saw the head, before we got to the halting place, and I was carried into the cave. That would make it several miles from here, for we went in a wagon."

"Yes, and they might have driven in a round-about way, in order to deceive you," suggested Mr. Damon. "At best we have but a faint idea where the diamond cave is, but we must search for it; eh, Tom?"

"Certainly. We'll start right in. And as the airship will be of but little service to us now, I suggest that we leave it in this valley. It is very much secluded, and no one will harm it, I think. We can then start off prospecting, for I have a large portable tent, and we can carry enough food with us, with what game we can shoot, to enable us to live. I have a regular camping outfit on board."

"Fine!" cried Mr. Parker, "and that will give me a chance to make some observations among the mountains, and perhaps I can predict when a landslide, or an eruption of some dormant volcano, may occur."

"Bless my stars!" cried Mr. Damon. "I don't wish you any bad luck, Mr. Parker, but I sincerely hope nothing of the sort happens! We had enough of that on Earthquake Island!"

"One can not halt the forces of nature," said the scientist, solemnly. "There are many towering peaks around here which may contain old volcanoes. And I notice the presence of iron ore all about. This must be a wonderful place in a thunder and lightning storm."

"Why?" asked Tom, curiously.

"Because lightning would be powerfully attracted here by the presence of the metal. In fact there is evidence that many of the peaks have been struck by lightning," and the scientist showed curious, livid scars on the stone faces of the peaks within sight.

"Then this is a good place to stay away from in a storm," observed Mr. Damon. "However, we won't worry about that now. If this is the landmark Mr. Jenks was searching for, then we must be in the vicinity of Phantom Mountain."

"I think we are," declared the diamond seeker. "Probably it is within sight now, but there are so many peaks, and this is such a wild and desolate part of the country that we may have trouble in locating it."

"We've got to make a beginning, anyhow," decided Tom, "and the sooner the better. Come, we'll make up our camping kits, and start out."

It was something to know that they were on the right trail, and it was a relief to be able to busy oneself, and not be aimlessly searching for a mysterious landmark. They all felt this, and soon the airship was taken to a secluded part of the valley, where it was well hidden from sight in a grove of trees.

Tom and Mr. Damon then served a good meal, and preparations were made to start on their search among the mountains—a search which they hoped would lead them to Phantom Mountain, and the cave of the diamond makers.

The tent which would afford them shelter was in sections, and could be laced together. They carried food, compressed into small packages, coffee, a few cooking utensils; and each one had a gun, Tom carrying a combination rifle and shotgun, for game.

"We can't live very high while we're on the trail," said the young inventor, "but it won't be much worse than it was on Earthquake Island. Are we all ready?"

"I guess so," answered Mr. Damon. "How long are we going to be away?"

"Until we find the diamond makers!" declared Tom, firmly.

Shouldering their packs, the adventurers started off. Tom turned for a last look at his airship, dimly seen amid the trees. Would he ever come back to the Red Cloud? Would she be there when he did return? Would their quest be successful? These questions the lad asked himself, as he followed his companions along the rocky trail.

"Perhaps we can find the road by which these men go in and out of the cave," suggested Mr. Damon, when they had gone on for several miles.

"I fancy not," replied Mr. Jenks. "They probably take great pains to hide it. I think though, that our best plan will be to go here and there, looking for the entrance to the cave. I believe I would remember the place."

"But why can't you follow the directions given by the miner who told you about Phantom Mountain?" asked Mr. Damon.

"Because his talk was too indefinite," answered Mr. Jenks. "He was so frightened by seeing what he believed to be a ghost, that he didn't take much notice of the location of the place. All he knows is that Phantom Mountain is somewhere around here."

"And we've got to hunt until we find it; is that the idea?" asked Mr. Parker.

"Or until we see the phantom," added Tom, in a low voice.

"Bless my topknot!" exclaimed Mr. Damon. "You don't mean to say you expect to see that ghost; do you Tom?"

"Perhaps," answered the young inventor, and he did not add something else of which he was thinking. For Tom had a curious theory regarding the phantom.

They tramped about the remainder of that day. Toward evening Tom shot some birds, which made a welcome addition to their supper. Then the tent was put together, some spruce and hemlock boughs were cut to make a soft bed, and on these, while the light of a campfire gleamed in on them, the adventurers slept.

Their experience the following day was similar to the first. They saw no evidence of a large cave such as Mr. Jenks had described, nor were there any traces of men having gone back and forth among the mountains, as might have been expected of the diamond makers, for, as Mr. Jenks had said, they made frequent journeys to the settlement for food, and other supplies.

"Well, I haven't begun to give up yet," announced Tom, on the third day, when their quest was still unsuccessful. "But I think we are making one mistake."

"What is that?" inquired Mr. Jenks.

"I think we should go up higher. In my opinion the cave is near the top of some peak; isn't it, Mr. Jenks?"

"I have that impression, though, as you know, I never saw the outside of it. Still, it might not be a bad idea to ascend some of these peaks."

Following this suggestion, they laid their trail more toward the sky, and that night found them encamped several thousand feet above the sea-level. It was quite cool, and the campfire was a big one about which they sat after supper, talking of many things.

Tom did not sleep well that night. He tossed from side to side on the bed of boughs, and once or twice got up to replenish the fire, which had burned low. His companions were in deep slumber.

"I wonder what time it is?" mused Tom, when he had been up the third time to throw wood on the blaze. "Must be near morning." He looked at his watch, and was somewhat startled to see that it was only a little after twelve. Somehow it seemed much later.

As he was putting the timepiece back into his pocket the lad looked around at the dark and gloomy mountains, amid which they were encamped. As his gaze wandered toward the peak of the one on the side of which the tent was pitched, he gave a start of surprise.

For, coming down a place where, that afternoon, Tom had noticed a sort of indefinite trail was a figure in white. A tall, waving figure, which swayed this way and that—a figure which halted and then came on again.

"I wonder—I wonder if that can be a wisp of fog?" mused the young inventor. He rubbed his eyes, thinking it might be a swirling of the night mist or a defect of vision. Then, as he saw more plainly, he noticed the thing in white rushing toward him.

"It's the phantom—the phantom!" cried Tom, aloud. "It's the thing the miner saw! We're on Phantom Mountain now!"

CHAPTER XIV—WARNED BACK

Tom's cries awakened the sleepers in the tent. Mr. Damon was the first to rush out.

"Bless my nightcap, Tom!" he cried. "What is it? What has happened? Are we attacked by a mountain lion?"

For answer the young inventor pointed up the mountain, to where, in the dim light from a crescent moon, there stood boldly revealed, the figure in white.

"Bless—bless my very existence!" cried the odd man. "What is it, Tom?"

"The phantom," was the quiet answer. "Watch it, and see what it does."

By this time Mr. Jenks and Mr. Parker had joined Tom and Mr. Damon. The four diamond seekers stood gazing at the apparition. And, as they looked, the thing in white, seemingly too tall for any human being, slid slowly forward, with a gliding motion. Then it raised its long, white arms, and waved them threateningly at the adventurers.

"It's motioning us to go back," said Mr. Parker in an awed whisper. "It doesn't want us to go any farther."

"Very likely," agreed Tom, coolly. "But we're not going to be frightened by anything like that; are we?"

"Not much!" exclaimed Mr. Jenks. "I expected this. A ghost can't drive me back from getting my rights from those scoundrels!"

"Suppose it uses a revolver to back up its demand?" asked the scientist.

"Wait until it does," answered Mr. Jenks. But the figure in white evidently had no such intentions. It came on a little distance farther, still waving the long arms threateningly, and then it suddenly disappeared, seeming to dissolve in the misty shadows of the night.

"Bless my suspenders!" cried Mr. Damon. "That's a very strange proceeding! Very strange! What do you make of it, Tom?"

"It is evidently some man dressed up in a sheet," declared Mr. Jenks. "I expected as much."

"The work of those diamond makers; do you think?" continued Mr. Damon.

"I believe so," answered Tom, slowly, for he was trying to think it out. "I believe they are the cause of the phantom, though I don't know that it's a man dressed in a sheet."

"Why isn't it?" demanded Mr. Jenks.

"Because it was too tall for a man, unless he's a giant."

"He may have been on stilts," suggested Mr. Parker.

"No man on stilts could walk along that way," declared Tom, confidently. "He glided along too easily. I am inclined to think it may be some sort of a light."

"A light?" queried Mr. Damon.

"Yes, the diamond makers may be hidden in some small cave near here, and they may have some sort of a magic lantern or a similar arrangement, for throwing a shadow picture. They could arrange it to move as they liked, and could cause it to disappear at will. That, I think, is the ghost we have just seen."

"But the diamond makers have only been in this mountain recently," objected Mr. Jenks, "and the phantom was here before them. In fact, that was what gave the place its name."

"That may be," admitted the lad. "There are many places that have the name of being haunted, but no one ever sees the ghost. It is always some one else, who has heard of some one who has seen it. That may have been the case here. I grant that this place may have been called 'Phantom Mountain' for a number of years, due to the superstitious tales of miners. The diamond makers came along, found the conditions just right for their work, and adopted the ghost, so to speak. As there wasn't any real spirit they made one, and they use it to scare people away. I think that's what we've just seen, though I may be wrong in my theory as to what the phantom is."

"Well, it's gone now, at any rate," said Mr. Jenks, "and I think we'd better get back inside the tent. It's cold out here."

"Aren't some of us going to stand guard?" demanded Mr. Damon.

"What for?" asked Mr. Jenks.

"Why—er—bless my key-ring! Suppose that ghost takes a notion to come down here, and use his gun, as he did on the miners?"

"I don't believe that will happen," remarked Tom. "The diamond makers, if the white thing had anything to do with them, have given us a warning, and I think they'll at least wait until morning to see how we heed it."

"We aren't going to heed it!" burst out Mr. Jenks. "I'm going to go right ahead and find that cave where they make diamonds!"

"And we're with you!" exclaimed Tom. "We'll have a good fire going the rest of the night, and that may keep intruders away. In the morning we'll begin our search, and we'll go up the trail where we saw the white figure."

A big pile of wood had been collected for the fire, and Tom now piled some logs and branches on the blaze. It would last for some time now, and the adventurers, still talking of the "ghost" went back into the tent. It was over an hour before they all got to sleep again, and Mr. Jenks and Mr. Damon took turns in getting up once or twice during the remainder of the night to replenish the fire.

Morning dawned without anything further having occurred to disturb them, and, after a hearty breakfast, to which Tom added some fish he caught in a nearby mountain stream, they set off up the trail on Phantom Mountain.

They had left their tent standing, as they proposed making that spot their headquarters until they located the cave they were seeking. What their course would be after that would depend on the circumstances.

If they had expected to have an easy task locating the cavern in which Mr. Jenks had seen diamonds made, the adventurers were disappointed. All that day they tramped up and down the mountain, looking for some secret entrance, but none was disclosed. The higher they went up the great peak, the fainter became the trail, until, at length it vanished completely.

But this was not to be wondered at, since it was on solid rock, in which no footsteps would leave an impression.

"They never brought you up here in a wagon, Mr. Jenks," decided Tom, when he saw how steep the place was.

"I'm inclined to think so myself," admitted the diamond man. "They must have reached the cave from some other way. As a matter of fact, I walked some distance after getting out of the vehicle, before we got to the cavern. But, even at that, I don't believe we came this way."

"Yet the phantom was here," persisted Tom, "and I'm convinced that the cave is in this neighborhood. It's up to us to find it!"

But they searched the remainder of that day in vain, and as night was coming on, they made their way back to the camp. As Tom, who was in the lead, approached the tent, he saw something black fastened to the entrance.

"Hello!" he cried. "Some one's been here. That wasn't on the tent when we left this morning."

"What is it?" asked Mr. Damon.

"A black piece of paper, written on with white ink," replied the lad. He was reading it, and, as he perused it a look of surprise came over his face.

"Listen to this!" called Tom. "It's evidently from the diamond makers."

Holding up the black paper, on which the white writing stood out in bold relief Tom read aloud:

"Be warned in time! Go back before it is too late! You are near to death! Go back!"

"Bless my shoelaces!" cried Mr. Damon. "This is getting serious."

CHAPTER XV—THE LANDSLIDE

Gathered about the young inventor, the three men looked at the warning. The writing was poor, and it was evident that an attempt had been made to disguise it. But there was no misspelling of words, and there were no rudely drawn daggers, or bloody hands or anything of that sort. In fact, it was a very business-like sort of warning.

"Rather odd," commented Mr. Jenks. "Black paper and white ink."

"White ink is easy enough to make," stated Mr. Parker. "I fancy they wanted it as conspicuous as possible."

"Yes," agreed Tom, "and this warning, together with the antics of the thing in white last night, shows that they are aware of our presence here, and perhaps know who we are. We will have to be on our guard."

"Do you think that fellow Munson, whom we left in the forest, could have gotten here and warned them?" asked Mr. Damon.

"It's possible," admitted Tom, "but now let's see if the person who pinned this warning on our tent took any of our things."

A hasty examination, however, showed that nothing had been disturbed, and Tom and Mr. Damon were soon getting supper ready, everyone talking, during the progress of the meal, about the events of the day, and the rather weird culmination of it.

"Well, we haven't had a great deal of success—so far," admitted Tom, as they sat about the fire, in the fast gathering dusk. "I think, perhaps, we'd better try on the other side of the mountain to-morrow. We've explored this side pretty thoroughly."

"Good idea," commented Mr. Jenks. "We'll do it, and move our camp. I only hope those fellows don't find our airship and destroy it. We'll have a hard time getting back to civilization again, if we have to walk all the way."

This contingency caused Tom some uneasiness. He did not like to think that the unscrupulous men might damage the Red Cloud, that had been built only after hard labor. But he knew he could accomplish nothing by worrying, and he tried to dismiss the matter from his mind.

They rather expected to see the thing in white again that night, but it did not appear, and morning came without anything having disturbed their heavy sleep, for they were tired from the day's tramp.

It took them the greater part of the day to make a circuit of the base of Phantom Mountain in order to get to a place where a sort of trail led upward.

"It's too late to do anything to-night," decided Tom, as they set up the tent. "We'll rest, and start the first thing in the morning."

"And the ghost isn't likely to find us here," added Mr. Damon. "Where are you going, Mr. Parker?" he asked, as he saw the scientist tramping a little way up the side of the mountain.

"I am going to make some observations," was the answer, and no one paid any more attention to him for some time. Supper was nearly ready when Mr. Parker returned. His face wore a rather serious air, and Mr. Damon, noting it, asked laughingly:

"Well, did you discover any volcanoes, that may erupt during the night, and scare us to death?"

"No," replied Mr. Parker, calmly, "but there is every indication that we will soon have a terrific electrical storm. From a high peak I caught a glimpse of one working this way across the mountains."

"Then we'd better fasten the tent well down," called Tom. "We don't want it to blow away."

"There will not be much danger from wind," was Mr. Parker's opinion.

"From what then?" asked Mr. Jenks.

"From the discharges of lightning among these mountain peaks, which contain so much iron ore. We will be in grave danger."

The fact that the scientist had not always made correct predictions was not now considered by his hearers, and Tom and the two men gazed at Mr. Parker in some alarm.

"Is there anything we can do to avoid it?" asked Mr. Jenks.

"The only thing to do would be to leave the mountain," was the answer, "and, as the iron ore extends for miles, we can not get out of the danger zone before the storm will reach us. It will be here in less than half an hour."

"Then we'd better have supper," remarked Tom, practically, "and get ready for it. Perhaps it may not be as bad as Mr. Parker fears."

"It will be bad enough," declared the gloomy scientist, and he seemed to find pleasure in his announcement.

The meal was soon over, and Tom busied himself in looking to the guy ropes of the tent, for he feared lest there might be wind with the storm. That it was coming was evident, for now low mutterings of thunder could be heard off toward the west.

Black clouds rapidly obscured the heavens, and the sound of thunder increased. Fitful flashes of lightning could be seen forking across the sky in jagged chains of purple light.

"It's going to be a heavy storm," Tom admitted to himself. "I hope lightning doesn't strike around here."

The storm came on rapidly, but there was a curious quietness in the air that was more alarming than if a wind had blown. The campfire burned steadily, and there was a certain oppressiveness in the atmosphere.

It was now quite dark, save when the fitful lightning flashes came, and they illuminated the scene brilliantly for a few seconds. Then, by contrast, it was blacker than ever.

Suddenly, as Tom was gazing up toward the peak of Phantom Mountain, he saw something that caused him to cry out in alarm. He pointed upward, and whispered hoarsely:

"The ghost again! There's our friend in white!"

The others looked, and saw the same weird figure that had menaced them when they were encamped on the other side of the peak.

"They must have followed us," said Mr. Jenks, in a low voice.

Slowly the figure advanced, It waved the long white arms, as if in warning. At times it would be only dimly visible in the blackness, then, suddenly it would stand out in bold relief as a great flash of fire split the clouds.

The thunder, meanwhile, had been growing louder and sharper, indicating the nearer approach of the storm. Each lightning flash was followed in a second or two, by a terrific clap. Still there was no wind nor rain, and the campfire burned steadily.

All at once there was a crash as if the very mountain had split asunder, and the adventurers saw a great ball of purple-bluish fire shoot down, as if from some cloud, and strike against the side of the crag, not a hundred feet from where stood the ghostly figure in white.

"That was a bad one," cried Mr. Damon, shouting so as to be heard above the echoes of the thunderclap.

Almost as he spoke there came another explosion, even louder than the one preceding. A great ball of fire, pear shaped, leaped for the same spot in the mountain.

"There's a mass of iron ore there!" yelled Mr. Parker. "The lightning is attracted to it!"

His voice was swallowed up in the terrific crash that followed, and, as there came another flash of the celestial fire, the figure in white could be seen hurrying back up the mountain trail. Evidently the electrical storm, with lightning bolts discharging so close, was too much for the "ghost."

In another instant it looked as if the whole place about where the diamond seekers stood, was a mass of fire. Great forked tongues of lightning leaped from the clouds, and seemed to lick the ground. There was a rattle and bang of thunder, like the firing of a battery of guns. Tom and the others felt themselves tingling all over, as if they had hold of an electrical battery, and there was a strong smell of sulphur in the air.

"We are in the midst of the storm!" cried Mr. Parker. "We are standing on a mass of iron ore! Any minute may be our last!"

But fate had not intended the adventurers for death by lightning. Almost as suddenly as it had begun, the discharge of the tongues of fire ceased in the immediate vicinity of our friends. They stood still—awed—not knowing what to do.

Then, once more, came a terrific clap! A great mass of fire, like some red-hot ingot from a foundry, was hurled through the air, straight at the face of the mountain, and at the spot where the figure in white had stood but a few minutes before.

Instantly the earth trembled, as it had at Earthquake Island, but it was not the same. It was over in a few seconds. Then, as the diamond seekers looked, they saw in the glare of a score of lightning flashes that followed the one great clap, the whole side of the mountain slip away, and go crashing into the valley below.

"A landslide!" cried Mr. Parker. "That is the landslide which I predicted! The lightning bolt has split Phantom Mountain!"

CHAPTER XVI—THE VAST CAVERN

For a time the roiling, slipping, sliding and tumbling of the mass of earth and stones, down the side of the mountain, effectually drowned all other sounds. Even the thunder was stilled, and though Tom and his companions called to one another in terror, their voices could not rise above that terrific tumult.

Finally, when they found that the direction of the slide was away from their tent, and that they were not likely to be engulfed, they grew more calm.

Gradually the noise subsided. The great boulders had rolled to the bottom of the valley, and now only a mass of earth and stones was sliding down. Even this stopped in about five minutes, and, as though satisfied with what it had done, the electrical storm passed. Not a drop of rain had fallen.

"Bless my shirt studs!" exclaimed Mr. Damon, who was the first to speak after the din had quieted. "Bless my soul! But that was awful!"

"It was just what I expected," said Mr. Parker, calmly. "I knew, from my observations, that we were in a region where landslides and terrific electrical storms may be expected at any time. I fully looked for this."

"Well," remarked Mr. Jenks, rather sarcastically, "I hope it came up to your expectations, Mr. Parker."

"Oh, fully," was the answer, "though I wish it could have happened in daylight, so that I could better have observed certain phenomena regarding the landslide. They are very interesting."

"At a distance," admitted Tom, with a laugh of relief. "Well, I'm glad it's over, though we'll have to wait until morning to see what damage has been done. Lucky we weren't struck by lightning. I never saw such bolts!"

"Me, either!" declared Mr. Damon. "This mountain seems to attract them."

"It is like a magnet," said Mr. Parker. "I think I shall be able to make some fine observations here."

"If we live through it," murmured Mr. Jenks.

They watched the play of lightning about a distant bank of clouds, but the storm was now far away, only a faint rumbling of thunder being heard.

"I'm wondering what happened to the phantom," said Tom, after a pause. "Seems to me he was right in that track of the storm."

"Do you think it was a 'he'?" asked Mr. Jenks.

"I think we'll find that it's some sort of a man," answered the young inventor. "We may find out very soon, now. I've changed my theory about the ghost being reflections of light."

"How's that?" Mr. Damon wanted to know.

"Well, I think we are on the side of Phantom Mountain where the diamond cave is," went on the lad. "The fact that the phantom appeared here, soon after we arrived, shows that the men kept close track of our movements. It also shows, I think, that the phantom did not have to travel far to be on the spot, whereas we had to make quite a trip to get around the base of the mountain. I think the cave is up there," and Tom pointed toward the spot where the weird figure had been last seen, before the storm drove it back.

"There may be two phantoms," suggested Mr. Jenks. "They may keep one on this side of the mountain, and one on the other, to warn intruders away.

"It's possible," admitted Tom. "Well, we'll see how things look in the morning, when we'll take up our march again, and go up the mountain. We'll reach the top, if possible, which we couldn't do from the other side, as it was too steep."

"I hope we shall be able to go forward in the morning," came from Mr. Jenks.

"What do you mean?" asked the lad, struck by a peculiar significance in the diamond man's tones.

"Why, that landslide may have opened a great gully in the side of Phantom Mountain, which will prevent us from passing. It was a terrific lot of earth and stones that slid away," answered Mr. Jenks.

"It certainly was," agreed Mr. Parker. "I would not be surprised if the mountain was half destroyed, and it may be that the diamond cave no longer exists."

"Not very cheerful, to say the least," murmured Mr. Jenks to Tom, and, as it was getting quite chilly, following the storm, they went inside the tent.

Tom could hardly wait for daylight, to get up and see what havoc the landslide had wrought. As soon as the first faint flush of dawn showed over the eastern peaks, he hurried from the tent. Mr. Damon heard him arise, and followed.

A curious scene met their eyes. All about were great rocks rent and torn by the awful power of the lightning. The fronts of the stone cliffs were scarred and burned by the electrical fire, and fantastic markings, grotesque faces, and leering animals seemed to have been drawn by some gigantic artist who used a bolt from heaven for his brush.

But the eyes of Tom and Mr. Damon took all this in at a glance, and then their gaze went forward to where the avalanche had torn away a great part of the mountain.

"Whew! I should say it was a landslide!" cried Tom.

"Bless my wishbone, yes!" agreed Mr. Damon.

Below them, in the valley, lay piled immense masses of earth and stones. Boulders were heaped up on boulders, and rocks upon rocks, being tossed about in heaps, strung about in long ridges, and swirled about in curves, as though some cyclone had toyed with them after the lightning flash had tossed them there.

"But the mountain isn't half gone," said Tom, as his eyes took in what was left of the phantom berg. "I guess it will take a few more bolts like that one, to put this hill out of business."

Though the landslide had been a great one, the larger part of the mountain still stood. An immense slice had been taken from one side, but the summit was untouched.

"And there's where the diamond cave is!" cried Tom, pointing to it.

"I think so myself," agreed Mr. Jenks, who came from the tent at that moment, and joined the lad and Mr. Damon. "I think we shall find the cave somewhere up there. We must start for it, as soon as we have eaten, and we may reach it by night."

The three stood gazing up toward the summit of the great mountain. Suddenly, as the sun rose higher in the heavens, it sent a shaft of rosy light on the face of the berg that had been scarred by the landslide. Tom Swift uttered an exclamation, and pointed at something.

"See!" he cried. "Look where the trail is—the trail down which the phantom must have come. It is on the edge of a cliff now!"

They looked, and saw that this was so. The increasing light had just revealed it to them. When the lightning bolt had torn away a great portion of the mountain it had cut sheer down for a great depth and when the earth and stones fell away they left a narrow pathway, winding around the mountain, but so near the edge of a great chasm, that there was room but for one person at a time to walk on that footway. The uncertain trail up Phantom Mountain had all but been destroyed.

"The way up to the peak is by that path, now," spoke Tom, in a low voice.

"Bless my soul!" cried Mr. Damon. "It's as much as a man's life is worth to attempt it. If he got dizzy, he'd topple over, and fall a thousand feet. Dare we risk it?"

"It's the only way to get up," went on Tom. "It's either that way, or not at all. We've tried the other side without success. We must go up this way—or turn back."

"Then we'll go up!" cried Mr. Jenks. "It may not be as dangerous as it looks from here."

But it was even more dangerous than it appeared, when they went part way up it after a hasty breakfast. The trail was a mere ledge of rock now, and in some places, to get around a projecting edge of the mountain, they had to stand with their backs to the dizzy depths at their feet, and with both arms outstretched work their way around to where the trail was wider.

"Shall we risk it?" asked Tom, when they had tried the way, and found it so dangerous. "We can't take anything with us—even our guns, for we couldn't carry them, and if we reach the mouth of the cave, and find those men there—"

He paused significantly. The adventurers looked at one another. The search for the diamond makers was becoming more and more dangerous.

"I say let's go on!" decided Mr. Damon, suddenly. "We want to locate that cave, first of all. Perhaps, when we do find it, we may see some easier way of getting to it than this. And if those diamond makers do attack us—well, I don't believe they'll shoot defenseless men, and they may listen to reason, and give Mr. Jenks his rights—tell him how to make diamonds in return for the money he gave them."

"I don't believe those scoundrels will listen to reason," replied the diamond man, "but I agree with Mr. Damon that we ought to go on. We may find some other means of reaching the cave—if we can discover it, and we'll take a chance with the men."

"Forward it is, then!" cried Tom. "I have a revolver, and I can supply one of you gentlemen with another. They may come in useful in an emergency. Let's go back to camp, take a little lunch in our pockets, and try to scale the mountain."

They were soon on their way up the dizzy path once more, and, as they advanced, they found it growing more and more dangerous. In some places they found it almost impossible to get around certain corners, where there was barely room for their feet. As Tom remarked grimly, a fat man never could have done it. Fortunately they were all comparatively thin, for their hard work, and not too abundant food, since they had left the airship, had reduced their weight.

Up and up they went, higher and higher, sometimes finding the path wide enough for two to walk abreast, and again seeing it narrow almost to a ribbon. They hardly dared look down into the chasm at their left—a chasm filled, in part, with the rocks and boulders tossed into it by the lightning bolt.

Tom was in the lead, and had just made a dangerous turn around a shoulder of rock—one of those places where he had to extend both arms, and fairly hug the cliff before he could get around.

But, when he had made it, and found himself on a broad pathway, cut in the living rock, he gave a great shout—a shout that caused his companions to hasten to his side. They found the young inventor pointing to a clump of bushes and small trees.

But it was not the shrubbery that Tom desired to call to their attention. They saw that in an instant, for, dimly seen through the leaves, was something black, and, as they looked more closely, they saw that it was a great hole in the side of the mountain—a vast cavern, opening like a tunnel.

"The cave! The cave!" cried Tom. "The diamond makers' cave!"

Hardly had he spoken than two men, each one carrying a gun, showed themselves in the mouth of the cavern, and, instant later they both ran toward the little party of adventurers.

CHAPTER XVII—THE PHANTOM CAPTURED

Surprise held Tom and his friends almost spellbound for the moment. The young inventor's hand went toward the pocket where he carried his revolver. Mr. Jenks, who had the only other weapon, sought to draw it, but he was stopped by a gesture of one of the two men with guns.

"Hold on, strangers!" the man cried. "I know what you're up to! Better not try to draw anything—it might not be healthy. Now, then, who are you, and what do you want?"

The question came rather as a surprise, at least to Tom and Mr. Jenks. They had taken it for granted that these men—if they were the diamond makers—would know Mr. Jenks, and guess at his errand in coming back to Phantom Mountain. But, it seemed, that they took them all for casual strangers.

No one answered for a moment. Tom caught the eye of Mr. Jenks, and there was a look of hope in it. If ever there was a time for strategy, it was now. Evidently Munson, the stowaway on the airship, had not yet been able to send a warning to his confederates. And neither of the two men recognized Mr. Jenks as the man who had been defrauded of his rights. It might be possible to conceal the real object of the adventurers until they had time to formulate a plan of action.

"Well," exclaimed the man with the gun, impatiently, "I ask you folks a question. What do you want?"

Fortunately, neither Mr. Damon nor Mr. Parker replied. The former because he deferred to Tom and Mr. Jenks, and the scientist because he was busy inspecting some curious rocks he picked up. As it turned out this was the luckiest thing he could have done. It lent color to what Mr. Jenks said a moment later.

"What are you doing up here?" demanded the man again. "Don't you know this is private property?"

"We—we were just looking around," answered Mr. Jenks, which was true enough; as far as it went.

"Prospecting," added Tom.

"After gold?" demanded the second man, suspiciously.

"We'd be glad to find some," retorted the lad. At that moment Mr. Parker began breaking off bits of rock with a small geologist's hammer which he carried. The men with the guns looked at him.

"So you think you'll find gold up here?" asked the one who had first spoken.

"Is there any?" inquired Tom, trying to make his voice sound eager.

"Nary a bit, strangers," was the answer, and the two men laughed heartily. "Now, we don't want to seem harsh," went on the man who seemed to be the spokesman, "but you'd better get away from here. This is private ground, and dangerous too—how'd you ever get up the trail—we heard it was destroyed."

"There is still a narrow path," said Mr. Jenks. "We came up that—the lightning and landslide haven't left much of it, though."

Mr. Parker looked quickly up from the rocks at which he was tapping with his small hammer. "You have terrific lightning up here," he said. "I am much interested in it, from a scientific standpoint. I predict that some day the entire mountain will be destroyed by a blast from the sky."

"I hope it won't be right away," spoke one of the men. "Now I guess you folks had better be leaving while there's a path left to go down by."

"Might I ask," broke in Mr. Parker, as calmly as though he was lecturing to a class of students, "might I ask if you have noticed any peculiar effect of the lightning up here on the summit of the mountain? Does it fuse and melt rocks, so to speak?"

"What's that?" cried the spokesman, with a sudden flash of anger. The two men looked at each other.

"I wanted to know, merely for scientific reasons, whether the lightning up here ever melted rocks?" repeated Mr. Jenks.

"Well, whether it's for scientific reasons or for any other, I'm not going to answer you!" snapped the man. "It's none of your affair what the lightning does up here. Now you'd all better 'vamoose'—clear out!"

"All right—we'll go," said Tom, quickly, at the same time motioning to Mr. Jenks to agree with him. The eyes of the young inventor were roving about. He saw what looked like a second trail, leading down the mountain, from the far side of the cave. He was convinced now that there was another way to get to it. Possibly they might find it. At any rate nothing more could be done now. They must go back, for the cavern was too well guarded to attempt to enter it by force—at least just yet.

"Yes, we'll go back," assented Mr. Jenks.

Mr. Parker was tapping away at the rocks. He looked toward the black mouth of the big cave. On what corresponded to the roof of it, some distance back from the entrance, he saw a slender metal rod sticking up into the air.

"May I ask if that's a lightning rod?" he inquired innocently. "If it is, I should like to ask about its action in a mountain that is so impregnated with iron ore.

"You may ask until you get tired!" cried the spokesman, again showing unreasoning anger, "but you'll get no answer from us. Now get away from here before we do something desperate. You're on private ground and you're not wanted. Clear out while you have the chance."

There was no help for it. Slowly our friends turned and began to go down the dangerous trail. They were soon out of sight of the two men who stood before the cave, with their guns ready, but neither Tom nor any of his companions spoke for some time.

When they had rounded one of the most dangerous turns the young inventor sat down to rest, an example followed by the others.

"Well," asked Tom, "do you think those are some of the diamond makers, Mr. Jenks?"

"I certainly do, though I never saw those two men before. If I could once get inside the cave, I could tell whether or not it was the one where I was practically held a prisoner. But I'm sure it is. I know some of the men used to go off every day with guns, and not come back until night. I have no doubt they were on guard, just as these two are. And, also, I think I heard them speak of a second entrance to the cavern. The one we just saw may not be the main one, through which I was taken."

"I believe we are on the right track," ventured Mr. Damon, "but we will either have to go up there after dark, which will be risky, on account of the narrow trail, or else we will have to find some other path."

"The last would be better," spoke Tom.

"That rod of metal sticking up on top of the cave interested me," said the scientist. "Did you hear anything of that when you were here before, Mr. Jenks?"

"No. Probably that is only a lightning rod, or it may be a staff for a signal flag. But what surprises me is that those men didn't suspect that we were seeking to discover their secret. They took us for ordinary prospectors."

"So much the better," remarked Tom. "We have a chance now of getting inside that cave. But we will have to go back to camp, and make other plans. And we must hurry, or it will be dark before we get there."

They hastened their steps, pausing only briefly to eat some of the lunch they had brought along, and to drink from a spring that bubbled from the side of the mountain. It was getting dusk when they got back to their tent. They found nothing disturbed.

"I wonder if we'll see that phantom again to-night?" ventured Tom, as they were sitting about the campfire a little later.

"Probably not," remarked Mr. Jenks. "I don't believe the ghost will venture down the dangerous trail after dark, and the gang may think that the warning given us by the two men on guard at the cave will be sufficient. But if we don't leave here by to-morrow I think we will have another visit from the thing in white."

It was about an hour after this when Tom was collecting some wood in a pile nearer the fire, so as to have it ready to throw on, in case there was any alarm in the night, that he happened to look up toward the summit of the mountain. A slight noise, as of loose stones rolling down, attracted his attention, and, at first, he feared lest another landslide was beginning, but a moment later he saw what caused it.

There, advancing down the steep and dangerous trail was the figure in white—the phantom. Instantly a daring plan came into Tom's head. Dropping the wood softly, he moved back out of the glare of the fire.

"Mr. Jenks!" he called in a whisper.

The diamond man, who was behind the tent, came toward Tom.

"What is it?" he asked. Then, as he saw the ghostly visitor, he added: "Oh—the phantom again! What's it up to?"

"The same thing," replied Tom, "but it won't do it long, if my plan succeeds."

"What plan is that, Tom?"

"I'm going to try to capture that—that man—or whatever it is. Will you help?"

"Surely!"

"Then let's work around behind it, while Mr. Damon and Mr. Parker come up from in front. We'll solve this part of the mystery, anyhow, if it's possible!"

The two other men were soon told of the plan. Meanwhile the thing in white had advanced slowly, until within a few hundred feet of the camp. They could see now that it was no shaft of light, but some white body, shaped like a tall, thin man, draped in a white garment. The long arms waved to and fro. There was no semblance of a head.

"You and Mr. Parker go right toward it, slowly, Mr. Damon," advised Tom. "Mr. Jenks and I will make a circle, and get in back. Then, if it's anything alive we'll have it."

The "ghost" continued to advance. Tom and the diamond man stole off to one side, their buckskin moccasins making no sound. Mr. Damon and the scientist went boldly forward.

This movement appeared to disconcert the spirit. It halted, waved the arms with greater vigor than before, and seemed to indicate to the adventurers that it was dangerous to advance. But Mr. Damon and Mr. Parker kept on. They wanted to give Tom and Mr. Jenks time enough to make the circuit.

Suddenly the stillness of the night was broken by a low whistle. It was Tom's signal that he and Mr. Jenks were ready.

"Come on! Run!" cried Mr. Damon.

The scientist and the eccentric man leaped forward.

The "ghost" heard the whistle, and heard the spoken words. The thing in white hesitated a moment, and then raised one arm. There was a flash of fire, and a loud report.

"He's firing in the air!" cried Tom. "Come on, we have him now!"

Undaunted by the display of firearms, Mr. Damon and Mr. Parker kept on. They could hear Tom and Mr. Jenks running up in back of the figure. The latter also heard this, and suddenly turned. Caught between the two forces of our friends, the "ghost" was at a loss what to do.

The next instant Tom, who had distanced Mr. Jenks, made a flying tackle for the figure in white, and caught it around the legs. Very substantial legs they were, too, Tom felt—the legs of a man.

"Wow!" yelled the "ghost," as he went down in a heap, the revolver falling from his hand.

"Come on!" cried Tom. "I have him!"

His friends rushed to his aid. There was a confused mass of dark bodies, arms and legs mingled with something tall and thin, all in white. Suddenly the moon came from behind a cloud and they could see what they had captured—for captured the phantom was.

It proved to be a rather small man, who wore upon his shoulders a framework of wood, over which some white cloth was draped. It had fallen off him when Tom made that tackle.

"Well," remarked the young inventor, as he sat on the struggling man's chest. "I guess we've got you."

"I rather guess you have, stranger," was the cool reply.

CHAPTER XVIII—BILL RENSHAW WILL HELP

They were all panting from the exertion of the run up the mountain and the contest with the phantom—a phantom no longer—though, truth to tell, the struggle was not nearly so fierce as Tom had expected. He thought the "ghost" would put up a stiff fight.

"Got any ropes to tie him with?" asked Mr. Damon, who was helping Tom hold the man down.

"Ropes? You aren't going to tie me up are you, strangers?" asked the captive.

"That's what we are!" exclaimed Mr. Jenks. "We've had trouble enough in this matter, and if I've got one of the gang, perhaps I can get some of the others, and have my rights. So tie him up, Tom, and we'll take him to camp.

"Oh, you needn't go to all that trouble, strangers," went on the man, calmly. "If one of you will get off my chest, and the other gentleman ease up on my stomach a bit, I'll walk wherever you want me, and not make any trouble. I haven't got a gun."

"Bless my gloves! But you're a cool one," commented Mr. Damon, as he complied with the man's request, and got up from his stomach. "But look out for him, Tom. He had a gun, for he fired it in the air."

"He hasn't it now," answered the young inventor. "I knocked it from his hand when I leaped for him."

"That's what you did," assented the man, as he got up, while Tom kept a tight hold of him, as did Mr. Jenks. "What kind of a grizzly bear hug do you call that, anyhow, that you gave me?"

"That was a football tackle," explained Tom.

"I allers heard that was a dangerous game!" remarked the former phantom simply. "Well, now you've got me, what are you going to do with me?"

"Take you where we can have a good look at you," replied Mr. Jenks, as he kicked aside the wooden framework, and the sheet which had made the "ghost" appear so tall. "So this is how you worked it; eh?"

"Yep. That was the 'haunt' stranger. I made it myself, and it worked all right until you folks come along. I rather suspicioned from the first, when I played the trick over on 'tother side of the mountain, that you wouldn't be so easy to fool as most prospectors are."

"Oh, so you're the only ghost then?" asked Tom.

"I'm the only one."

By this time they had reached the camp. Tom threw some light logs on the fire, which blazed up brightly. As the flames illuminated the face of their captive, Mr. Jenks looked at him, and cried out:

"Why it's Bill Renshaw!"

"That's me," admitted the man who had played the part of the phantom, "and thunder-turtles! if it ain't Mr. Jenks who was once in the diamond cave with us. Whatever happened to you? I never heard. The others said you got tired and went away."

"They took me away—defrauded me of my rights!" declared Mr. Jenks, bitterly. "But I'll get them back! To think of Bill Renshaw playing the part of a ghost!"

"They made me do it," went on the man, somewhat dejectedly. "I wanted to be at work in the cave, but they wouldn't let me."

"Is this man one of the diamond makers?" asked Tom, in great surprise.

"He is—one of the helpers, though I don't believe he knows the secret of making the gems," explained Mr. Jenks. "He was one of the men in the cave when I was there before, and he and I struck up quite a friendship; didn't we, Renshaw?"

"That's what, and there ain't no reason why we can't be friends now; that is unless you hold a grudge against me for firing at you. But I only shot in the air, to scare you away. Them's my instructions. I'm supposed to be on guard, and scare away strangers. I'm tired of the work, too, for I don't get my share, and those other fellows, in the cave, get all the money from the diamonds."

Tom Swift uttered an exclamation. A sudden plan had come to him. Quickly he whispered to Mr. Jenks:

"Make a friend of this man if possible. He evidently is dissatisfied. Offer him a sum to show us another way into the cave, and we may yet discover the secret of the diamond makers."

"I will," declared Mr. Jenks, quietly. Then, turning to Renshaw, he added:

"Bill, come over here. I want to have a talk with you. Perhaps it will be to our mutual advantage."

He led the former phantom to one side, and for some time conversed earnestly with him. Mr. Jenks told the story of how he had been deceived by Folwell and the others who were at the head of the gang of diamond makers. The rich man related how they had taken his money, and, after promising to disclose the secret process to him, had broken faith, and had drugged him, afterward taking him out of the cave.

"I want only my rights, and that for which I paid," concluded Mr. Jenks. "Now, I gather that these men haven't treated you altogether fairly, Bill."

"Indeed they haven't. I helped 'em to the best of my ability, and all I get out of it is to stay out on this lonely side of the mountain, and play ghost. They owe me money, too, and they won't pay me, either, though they have lots, for they sold some diamonds lately."

"Then they are still making diamonds?" asked Mr. Jenks, eagerly. "Have you seen them? Do you know the secret?"

"No, I don't know it, for they won't let me in on it. I'm always sent out of the cave just before they make the gems. But I know they've made some lately, and have sold 'em. I want my share."

"Look here!" exclaimed Mr. Jenks, quickly, wishing to strike while the iron was hot. "I'll make you a proposition. Show us how to get into that cave, unknown to the diamond makers, and I'll pay you twice what they agreed to. Is it a bargain?"

Bill Renshaw considered a moment. Then he thrust out his hand, clasped that of Mr. Jenks, and exclaimed:

"It is. I'll take you into the cave by an entrance that's seldom used. There are four ways to get in. The one where the two men drove you back is the rear one. The front one is on the other side of the mountain, but it's so well concealed that you'd never find it. But I can take you to one where you can get in, and those fellows will never know it. And, what's more, I'll help you if it comes to a fight!"

"Good!" exclaimed Mr. Jenks. "I think we'll discover the secret of the diamond makers this time," and he went to tell the others of the success of his talk. Bill Renshaw had been converted from an enemy into a friend, and the former phantom was now ready to lead Tom and the others into the secret cave.

"We'll start in the morning," decided Mr. Jenks, who, after many disappointments, at last saw success ahead of him.

CHAPTER XIX—IN THE SECRET CAVE

Tom Swift was up at break of day, and the others were not far behind him.

"Now for the secret cave!" cried the young inventor as he gazed up the mountain, in the interior of which the mysterious band of men were making the diamonds.

"Have you made any plans, Bill?" asked Mr. Jenks of the former phantom, who had cast his lot in with the adventurers. "What will be the best course for us to follow?"

"You just leave it to me, Mr. Jenks," was the answer. "I'll get you into the cave, and those fellows, who, I believe, are trying to do me out of my rights, as they did you out of yours, will never know a thing about it."

"Bless my finger-nails!" cried Mr. Damon. "That will be great! We can get in the cave, and watch them make the diamonds at our leisure."

"They don't make them every day," explained Renshaw. "It seems they have to wait for certain occasions. Mostly they make the diamonds when there's a big storm."

"A big storm," asked the scientist with a sudden show of interest. "Do you mean one of those electrical storms, such as we had the other night?"

"That's it, Mr. Parker, though why they wait until there's a storm is more than I can tell."

"Perhaps they know that on such occasions no one will venture up the mountain," spoke Mr. Damon.

"No, it isn't that," declared the scientist. "I think I am on the track of a great scientific discovery, and I will soon be able to make observations that will confirm it."

"Well, I'm going to make an observation right now," said Tom, with a laugh. "I'm going to see what there is for breakfast."

"And that reminds me," came from Mr. Jenks, "shall we move our camp, Bill, and take the tent with us to the cave?"

"I hardly think so," was the answer. "I think the best plan would be to conceal the tent somewhere around here, in case you might need it again. You can also store what food you have left."

"But, bless my appetite, we don't want to starve in that diamond cave!" objected Mr. Damon.

"I'll see that you don't," declared Bill Renshaw. "I'll take you in there, unbeknownst to those fellows, and I'll provide you with plenty of food and water. You see the cave is so big that there are some parts they never visit."

"And we can stay in one of those parts, and eat?" asked Tom.

"Sure," answered Bill.

"And watch the diamond makers at work?" asked Mr. Jenks.

"That's it," replied the former phantom.

"Then the sooner we get started the better," remarked Mr. Damon. Mr. Parker said nothing. He appeared to be thinking deeply, and was tapping at some rocks with his little hammer.

The advice of Bill Renshaw was followed, and the tent, and what food remained, was concealed in the bushes, with rocks piled over to keep away prowling animals. Then they started for the secret cave.

The man who played the part of a ghost picked up the framework and white cloth that had formed his disguise.

"I'll still have to use this," he explained, "for I don't want those fellows to know that I'm helping you. I'll continue to play the spirit of the mountain, but there won't be much need of it. I don't think any more people will come prospecting out here."

"Have you heard of the arrival of Farley Munson?" asked Tom, as he related the facts about the stowaway.

"He hadn't arrived up to a day or so ago," answered Bill. "I guess he's still traveling. Farley is one of the heads of the gang," he added, "and a dangerous man."

As Bill led the way toward the cave, taking a route that the adventurers had never suspected led to it, he explained that the cavern was a large one, capable of holding an army.

"But there's only a small part of it used by the diamond makers," he added. "They work in a small recess, near the summit of the mountain. The little cave, where I'm going to take you, opens off from it by a long passage. And, except that you'll be pretty much in the dark, you'll be quite comfortable. There are tables, chairs, and some bunks in the place. I can get you some lights, and plenty of food."

"But, if you are seen taking away food, won't the others suspect something?" asked Tom.

"I do pretty much as I please," said Bill. "I go and come when I like. All I'm supposed to do is to watch my two sides of the mountain, play the ghost, and give warning when any one is coming. Sometimes I leave black and white messages, like the one I put on your tent. Those fellows fix 'em up for me. I've told 'em about you, though I didn't know who you were, and they think you have gone, for the two men on guard at the rear entrance so reported. Sometimes I stay out on the mountain for a couple of days at a time, when the weather's good, and don't go back to the cave. Those times I take food with me, and so if they see me making off with some supplies they'll think I'm going to camp out."

"It doesn't look as though we'd ever get into a cave near the top of the mountain, going this way," said Tom, as they marched along. "We're going down, instead of up."

"That's the secret of this trail," explained Bill. "We go down in a sort of valley, and then go up a pretty stiff place, and then we're on a direct trail to the entrance I told you about. It's a steep road to climb, but I guess we can manage it."

And a hard climb the adventurers did find it. The road was almost as bad as the one along the edge of the chasm, but they managed to negotiate it, and finally found themselves on a fairly good trail.

"We'll soon be there," Bill assured them. "After you get in the little cave, where I'm going to hide you, I'll have to leave you for a spell, until I get my ghost rigging fixed up again. But I'll see that you have plenty of food and drink."

A little later their guide came to a sudden halt, and peered around anxiously.

"What's the matter?" asked Tom.

"I was just looking to see if any of the men were about," he answered. "But I guess not—it looks all right. The entrance is right here."

They were on a side of the mountain, near the summit. Below stretched a magnificent scene. A great valley lay at their feet, and they could look off to many distant peaks. The main trail to Leadville, and the one to the settlement of Indian Ridge, was in sight.

Suddenly Tom, who had been using a small but powerful telescope, uttered an exclamation, and focussed the instrument on a speck that seemed moving along on the trail below.

"A man—coming up the mountain," cried Tom. "And—it can't be—yet it is—it's Farley Munson—the stowaway!" he cried. "He's coming here!"

"Let me look!" begged Mr. Jenks, taking the glass from Tom. An instant later the diamond man exclaimed: "Yes, it's Munson!"

"Then in here with you—quick!" cried Renshaw. "He can't see us yet, and we'll be out of sight in another minute."

The former spirit pulled aside some thick bushes, and pointed to a hole which was disclosed.

"The entrance to the secret cave," he announced. "Slip in all of you."

Tom, after another glance at the man toiling his way up the mountain, entered the cavern. He was followed by the others. Bill was the last to enter, and he replaced the bushes over the entrance.

"At last!" exclaimed Mr. Jenks, as he gazed up at the roof of the dimly-lighted vault in which they found themselves.

"Yes, we're in the diamond makers' secret cave," added Tom. "Now to catch them at work!"

"Come on," advised Bill, in a low tone, "We're not safe yet," and he produced a lantern from some hidden recess, lighted the wick, and led the way. As the others followed they were aware of a subdued noise in the great cavern.

CHAPTER XX—MAKING THE DIAMONDS

"What's that noise?" asked Tom, as their guide flashed the lantern to show them the way.

"That's the men getting ready to make diamonds, I guess," was the answer. "You see it takes quite a while to get the stuff ready. I don't know what they use—they never tell me any of their secrets."

"Oh, I know the ingredients well enough," said Mr. Jenks, "but I don't know the secret of how they apply the terrific heat and pressure necessary to fuse the materials into diamonds."

"Well, you'll soon know," declared Bill Renshaw. "Of course it isn't always successful. I've known 'em to try half a dozen times before they got any diamonds big enough to satisfy 'em. They gave me some of the small ones when I asked for my wages.

"How did you come to get in with these men?" asked Tom, curious to understand how a person seemingly as honest as Renshaw appeared to be had cast his lot in with the men who had broken faith with Mr. Jenks.

"Oh, I've lived around these parts all my life," was the answer. "I knew of this cave before these diamond fellers came to it. In fact, I showed it to 'em. It was several years ago that a party of men who were prospecting around here came to me and asked if I knew of a small cave near the top of a high mountain, where lightning storms were frequent. I told them about Phantom Mountain, as it was called then, and also of this cave. If there's any place where they have worse lightning storms than here, I'd like to know it. They scare me, sometimes, like the night when that landslide happened, and I'm sort of used to 'em.

"Well, I took these men to the cave, and they hired me as a sort of lookout. Then they began their work, and at first I didn't know what they were up to, but finally I caught on. Then Mr. Jenks came, and disappeared mysteriously, though then I didn't know that they had played a trick on him. I was outside most of the time, pretending I was the ghost. So that's how I came to get in with 'em, and I wish I was out."

"You soon will be, I think," declared Mr. Jenks. "But won't our talking be heard by the men?"

"No danger. There is a thick wall between this part of the cave, and the part where they live and work. I'll soon have you well hid, and then you wait until I come back."

"What about Munson?" asked Tom. "He is evidently on his way here to tell his confederates about us."

"He won't know what has happened to us," said Mr. Jenks, "and he won't see anything of us. I guess we're safe enough."

Through the dark passage they followed Bill Renshaw until he came to a halt in a place that suddenly widened and broadened into a good-sized cave.

"Here's your stopping place," said the former ghost. "Now if you follow that passage, off to the left," and he pointed to it, "you'll come to the larger part of the cave where the diamond makers are. But go cautiously, and don't make any noise. I won't be responsible for what happens."

"We'll take all the risk," interrupted Tom.

"All right. Now there's a couple of lanterns around here. I'll light them, and leave you for a while until I can get some grub. I'll be back as soon as I can."

He glided away, after lighting two lanterns, by the gleams of which the adventurers could see that they were in a vaulted cavern that had evidently been fitted up as a living apartment. The sides, roof and floor were of stone. It was clean, and the air was fresh. There were some chairs, a table, and several cots, with pieces of bagging for bedding, though it was warm in the place.

"I guess we can stay here until we discover the secret," spoke Tom.

"Bless my watch! We can if we have something to eat," came from Mr. Damon, with something like a sigh. "I'm hungry!"

"And I want to make some observations," said Mr. Parker. "From what I have seen of this mountain, I would not be surprised if this cave was to be suddenly destroyed by a landslide or a lightning bolt. I will make some further investigations."

"Well, if it's going to cause you to make such gloomy prophecies as that, I'd just as soon you wouldn't look any further," spoke Tom, in a low voice. But Mr. Parker, taking one of the lanterns, set about examining the rock of which the cave consisted.

In a short time Bill Renshaw returned with enough food to last for two days. He said he was going out on the mountain once more to act the part of a lookout, and would visit the adventurers again the next day.

"In the meanwhile you can do just as you please," he said. "Nobody is likely to disturb you here, and you can sneak up and take a look at the men in the other cave whenever you're ready. Only be careful—that's all I've got to say. They're desperate men."

It was not very pleasant, eating in the gloomy cavern, but they made the best of it. They cooked on a small oil-stove they found in the place, and after some hot coffee they felt much better.

"Well," remarked Tom, after a while, "shall we take a chance, and go look at the men at work?"

"I think so," answered Mr. Jenks. "The sooner we discover this mystery, the better. Then we can go back home."

"And recover my airship," added Tom, who was a bit uneasy regarding the safety of the Red Cloud.

"Then, bless my finger-rings! let's go and see if we can find the big cave your friend the ghost told us of," suggested Mr. Damon.

Cautiously they made their way along the passage Bill had pointed out. As they went forward the subdued noise became louder, and finally they could feel the vibration of machinery.

"This is the place," whispered Mr. Jenks. "That sound we hear is one of the mixing machines, for grinding the materials—carbon and the other substances—which go to make up the diamonds. I remember hearing that when I was in the cave before."

"Then we must be near the place," observed Tom.

"Yes, but I didn't have much chance to look around when I was here before. They wouldn't let me. I never even knew of the small cave Bill took us to."

"Well, if we're close to it, we'd better go cautiously, and not talk any more than we're obliged to," suggested Mr. Parker, and they agreed that this was good advice.

They walked on softly. Suddenly Tom, who was in the lead, saw a gleam of light.

"We're here," he whispered. "I'll put out our lantern, now," which he did. Then, stealing forward he and the others beheld a curious sight. The tunnel they were in ended at a small hole which opened into a large cavern, and, fortunately, this opening was concealed from the view of those in the main place.

"The diamond makers!" whispered Tom, hoarsely, pointing to several men grouped about a number of strange machines.

"Yes—the very place where I was," answered Mr. Jenks, "and there is the apparatus—the steel box—from which the diamonds are taken—now to see how they make them."

Fascinated, the adventurers looked into the cave. The men there were unaware of the presence of our friends, and were busily engaged. Some attended to the grinding machine, the roar and clatter of which made it possible for Tom and the others to talk and move about without being overheard. Into this machine certain ingredients were put, and they were then pulverized, and taken out in powdery form.

The power to run the mixing machine was a gasoline motor, which chug-chugged away in one corner of the cave.

As the powder was taken out, other men fashioned it into small balls, which were put on pan, and into a sort of oven, that was heated by a gasoline stove.

"Is that how they make the diamonds?" asked Mr. Damon.

"That is evidently the first step," said Mr. Jenks. "Those balls of powdered chemicals are partly baked, and then they are put into the steel box. In some way terrific heat and pressure are applied, and the diamonds are made. But how the heat and pressure are obtained is what we have yet to learn."

He paused to watch the men at work. They were all busy, some attending to the machines, and others coming and going in and out of the cave. In one part a man was apparently getting ready a meal.

Suddenly there rushed into the cave a man who seemed much excited.

"Are you nearly ready with that stuff?" he cried. "There's a good storm gathering on the mountain!"

"Yes, we'll be ready in half an hour," answered one of the men at the mixing machine.

"Good. It will be flashing lightning bolts then, and we can see what luck we have. The last batch was a failure." The man hurried out again. Mr. Parker touched Tom and Mr. Jenks on their shoulders.

"What is it?" asked Tom.

"I know the secret of making the diamonds," said the scientist.

"What?" cried Mr. Jenks.

"It is by the awful power of the lightning bolts!" whispered Mr. Parker. "Everything is explained now—the reason why they make diamonds in this lonely place, near the top of the mountain. They need a place where the lightning is powerful. I can understand it now—I suspected it before. They make diamonds by lightning!"

"Are you sure?" cried Mr. Jenks.

"Positive."

"I agree with you," said Tom Swift. "I was just getting on that track myself, when I saw the electric wires running to the steel box. That explains the upright rod on the top of the mountain. The man says a storm is coming—very well; we'll stay here and watch them make diamonds!"

As he spoke there came the mutter of thunder, and the mountain vibrated slightly. The men in the cave redoubled their activity. Tom and his friends felt that the secret process they had so long sought was about to be demonstrated before their eyes.

CHAPTER XXI—FLASHING GEMS

Eagerly the adventurers looked through the opening at the end of the passage into the larger cave. The men opened the small oven in which the balls of white chemicals and carbon mixed, had been baked, and a pile of things, that looked like irregularly-shaped marbles, were placed in the steel box.

This box, which was about the size of a trunk, was of massive metal. It was placed in a recess in the solid rock, and all about were layers of asbestos and other substances that were nonconductors of heat.

"That box becomes red hot," exclaimed Mr. Jenks, in a whisper. "When things are in readiness, that lever is pulled and the diamonds are made. I pulled it once, but I did not then know the process involved. I supposed that the lightning had nothing to do with making the diamonds."

"It has—a most important part," said Mr. Parker. The hidden adventurers could talk in perfect safety now, for the men in the large cave were too excited to pay much attention to them. The muttering of the thunder grew louder, and at times a particularly loud crash told that a bolt had struck somewhere in the vicinity of the cave.

"But, bless my watch-charm!" exclaimed Mr. Damon, "I didn't know lightning made diamonds."

"It does not—always," went on the scientist. "But great heat and pressure are necessary to create the gems. In nature this was probably obtained by prehistoric volcanic fires, and by the terrific pressure of immense rocks. It is possible to make diamonds in the laboratory of the chemist, but they are so minute as to be practically valueless.

"However, these men seem to have hit upon a new plan. They utilize the terrific heat of lightning, and the pressure which is instantaneously obtained when the bolt strikes. I am anxious to see how it is done. Look, I think they are getting ready to make the gems."

Indeed there seemed to be an air of expectancy among the diamond makers. The mixing machine had now been stopped, and, as it was more quiet in the cave, our friends, in their hiding-place, had to speak in mere whispers. All the men were now gathered about the great steel box.

This receptacle had been closed by a solid metal door, which was screwed and clamped tight. Then one of the men examined a number of heavily insulated electric wires that extended from the box off into the darkness where Tom and his companions could not discern them.

"That's Folwell—the man I befriended, and who got me into this game," whispered Mr. Jenks. "He was also one of the first to turn against me. I think he's one of the leaders."

Folwell came back, after having gone into a dark part of the cave. He went over to an electrical switch on one of the stone walls.

"It's almost time," Tom heard him say to his confederates. "The storm is coming up rapidly."

"Will it be severe enough?" asked one of the helpers. "We had all our work for nothing last time. The flashes weren't heavy enough."

"These will be," asserted Folwell. "The indicator shows nearly a million volts now, and it's increasing."

"A million volts!" exclaimed Tom. "I hope it doesn't strike anywhere around here."

"Oh, it will probably be harmlessly conducted down on the heavy wires," said Mr. Parker. "We are in no danger, at present, though ultimately I expect to see the whole mountain shattered by a lightning bolt."

"Cheerful prospect," murmured Tom.

There was a terrific crash outside. The rocky floor of the cave trembled.

"Here she comes!" cried Folwell. "Get back, everybody! I'm going to throw over the switch now!"

The men retreated well away from the steel box. Folwell threw over the lever—the same one Mr. Jenks remembered pulling. Then the man ran to the electric switch on the wall, and snapped that into place, establishing a connection.

There was a moment's pause, as Folwell ran to join the others in their place of safety. Then from without there came a most nerve-racking and terrifying crash. It seemed as if the very mountain would be rent into fragments.

Watching with eager eyes, the adventurers saw sparks flash from the steel box. Instantly it became red hot, and then glowed white and incandescent. It was almost at the melting point.

Then came comparative quiet, as the echoes of the thunder died away amid the mountain peaks.

"I guess that did the trick!" cried Folwell. "It was a terrific crash all right!"

He and the others ran forward. The steel box was now a cherry red, for it was cooling. Folwell threw back the lever, and another man disconnected the switch. There was a period of waiting until the box was cool enough to open. Then the heavy door was swung back.

With a long iron rod Folwell drew something from the retort. It was the tray which had held the white balls. But they were white no longer, for they had been turned into diamonds. From their hiding-place Tom and the others could see the flashing gems, for, in spite of the fact that the diamonds were uncut, some of them sparkled most brilliantly, due to the peculiar manner in which they were made.

"We have the secret of the diamonds!" whispered Mr. Jenks. "There must be a quart of the gems there!"

The men gathered about Folwell, uttering exclamations of delight. The diamonds were too hot to handle yet.

"That's going some!" exclaimed the chief of the diamond makers. "We have a small fortune here."

The was a sudden commotion at one end of the cave. A man rushed in. At the sight of him Tom stared and uttered an exclamation.

"Munson—the stowaway!" he whispered.

"Hello!" cried Folwell, as he saw his confederate. "I thought you were East, keeping Jenks away from here."

"He got the best of me!" cried Munson, "he and that Tom Swift! I stowed away on their airship, but they found me out by a wireless message, and marooned me in the woods. I've been trying to get here ever since! Didn't you get my messages of warning?"

"No—what warnings?" cried Folwell.

"About Jenks, Tom Swift and the others. They're here—they must be on Phantom Mountain now. In fact, I shouldn't be surprised if they were in this cave. I traced them to their camp, but they're gone. They may be among us now—in some of the secret recesses!"

For an instant Folwell stared at the bearer of these tidings. Then he cried out:

"Scatter men, and find these fellows! We must get them before they discover our secret!"

"It's too late—we know it!" exulted Tom Swift. Then he whispered to the others to hurry to the part of the cave where Bill Renshaw had first hidden them.

CHAPTER XXII—PRISONERS

"Do you think there is any danger of them finding us?" asked Mr. Damon, as he hurried along beside Tom.

"I'm afraid so," was the answer. "I've been worried ever since we saw Munson heading this way. But we couldn't do any differently."

"Perhaps Bill Renshaw may be able to conceal us," suggested Mr. Jenks. "Very likely he knows that Munson is on hand. Perhaps we will be safe for a while. I want to make a few more observations as to how they manufacture the diamonds, and then, with what I already know, I'll have the secret."

"And I'd like to make some scientific tests of the sides and bottom rocks of the cave," spoke Mr. Parker. "I think it will bear out my theory that the mountain will soon be destroyed."

"Well, you were right about Earthquake Island, and you may be right about this mountain," said Tom, "but if it is going to be annihilated I hope we get far enough away from it."

"We can keep our presence here a secret for a few more days, I think that will be long enough," proceeded Mr. Jenks. "Then we will leave."

"And, in the meanwhile, they'll be searching for us," objected Mr. Damon. "I wish that ghost-chap would come back and tell us what to do. Bless my liver-pin, but we are going to be in considerable danger, I'm afraid! Those men may capture us, and decide to make diamond dust from us."

"Come on—hurry to the little cave," urged Tom. "Then we'll get ready to defend ourselves."

"The main cave is a large one," said Mr. Jenks, "and there are many hiding places in it. In fact, it is so large that it will take those fellows several days to complete a circuit of it. By that time Bill Renshaw may come back, and take us to some place in which they have already searched for us. Then we'll be comparatively safe."

This thought was some consolation to them, as they made their way through the dark passage, dimly illuminated by the lantern they had rekindled, to the place where Bill had hidden them. They found things as they had left them, and proceeded to get a meal, though Tom said it would be best not to cook anything, or even to make coffee, for fear the odors would enable the searchers to trail them.

So they ate cold food, glad to get that. Silently they sat about the dimly-lighted cavern, and discussed the situation. True they might even now retreat, going out of the entrance Bill had showed them, and so escape. But Mr. Jenks felt that his mission was not completed yet, and they all agreed to stay with him.

"For there are several points about making diamonds that are not quite clear to me," he said. "I need to know how that steel box is constructed, how the electrical switches are arranged, what kind of lightning rods they use, and how they regulate the pressure. The other things, and how to mix the ingredients, I already know."

"Then we'll do our best to help you," promised Tom. "But now I think we had better see what sort of a defense we can put up. We have our guns and revolvers, and with these chairs and tables we can build a sort of barricade behind which we can take refuge if those fellows do discover our hiding place."

This was conceded to be a good idea, and soon a rude sort of fort was made, behind which the adventurers could take their stand and fight, if necessary, though they hoped this would not come to pass.

They remained quietly in the cave the remainder of that day, and, when it was night, as they could tell by their timepieces—there was no daylight—they divided the hours into watches, taking turns standing guard.

Morning, at least in point of time, came without any disturbance, and they made a cold breakfast. They hoped that Bill Renshaw would come, but he did not appear.

After sitting in the dark cave until afternoon, Tom said:

"I think we might as well go and take another observation of the big cave. We can tell what the men are doing, then, for they don't seem to have been near us. Maybe they have given up the search for us, and we can see them at work, and Mr. Jenks can gain what further knowledge he needs."

"That will be a good plan," agreed the diamond man. "It's maddening to sit here, doing nothing."

"And it will be comparatively safe to go from here to our former post of observation," added Tom, "for there doesn't seem to be any opening along the tunnel, into the larger cave, except the place where we were."

Accordingly they started off. Cautiously they looked through the opening into the apartment where they had seen the diamonds made.

"There's not a soul here!" exclaimed Tom, in a whisper. The others looked. The place was deserted—the machinery silent. Mr. Jenks peered in for a moment, and then exclaimed:

"I'm going in! Now's my chance to find out all that I wish to know! It may never come again, and then we can soon leave Phantom Mountain!"

It was a daring plan, but it seemed to be the best one to follow. They were all tired of inactivity. Mr. Jenks managed to get through the opening, and dropped into the big cave. The others followed. Mr. Jenks hurried over to the steel box, and began an examination of it. Tom Swift was looking at the electrical switch. He saw how it was constructed. Mr. Damon and Mr. Parker were peering interestedly about.

Suddenly the sound of voices was heard, and the echo of footsteps. Mr. Jenks started.

"They're coming back!" he whispered hoarsely. "Run!"

They all turned and sped toward their hiding place. But they were too late. An instant later Folwell, Munson and the other diamond makers confronted them. Our friends made a bold rush, but were caught before they could go ten feet.

"We have them!" cried Munson. "They walked right into our hands!"

It was true. Tom Swift and the others were the prisoners of the diamond makers.

CHAPTER XXIII—BROKEN BONDS

"Well," remarked Tom Swift, in mournful tones, "this looks as if we were up against it; doesn't it?"

"Bless my umbrella, it certainly does," agreed Mr. Damon.

"And it's all my fault," said Mr. Jenks. "I shouldn't have gone into the big cave. I might have known those men would come back any time."

The above conversation took place as our friends lay securely bound in a small cave, or recess, opening from the larger cavern, where, about an hour before, they had been captured and made prisoners by the diamond makers. Despite their struggles they had been overpowered and bound, being carried to the cave, where they were laid in a row on some old bags.

"It certainly is a most unpleasant situation, to say the least," observed Mr. Parker.

"And all my fault," repeated Mr. Jenks.

"Oh, no it isn't," declared Tom Swift, quickly. "We were just as ready to follow you into that cave as you were to go. No one could tell that the men would return so soon. It's nobody's fault. It's just our bad luck."

From where he lay, tied hand and foot, the young inventor could look out into the cave where he and the others had been caught. The diamond makers were busily engaged, apparently in getting ready to manufacture another batch of the precious stones. They paid little attention to their captives, save to warn them, when they had first been taken into the little cave, that it was useless to try to escape.

"They needn't have told us that," observed Tom, as he and the others were talking over their situation in low voices. "I don't believe any one could loosen these ropes."

"They certainly are pretty tight," agreed Mr. Damon. "I've been tugging and straining at mine for the last half hour, and all I've succeeded in doing is to make the cords cut into my flesh."

"Better give it up," advised Mr. Jenks.

"We'll just have to wait."

"For what?" the scientist wanted to know.

"To see what they'll do with us. They can't keep us here forever. They'll have to let us go some time." Following their capture, Folwell and Munson, the latter the stowaway of the airship, had been in earnest conversation regarding our friends, but what conclusion they had reached the adventurers could only guess.

"And we didn't have time to examine the diamond-making machinery close enough so that we could duplicate it if necessary," complained Tom, a little later.

"No," agreed Mr. Jenks. "There are certain things about it that are not clear to me. Well, I don't believe I'll have another chance to inspect it. They'll take good care of that, though they seem to be getting ready to make more diamonds."

"Perhaps they're going to manufacture a big batch, and then leave this place," suggested Mr. Damon. "They will probably go to some other secret cave, and leave us here."

"I hope they untie us before they leave, and give us something to eat," remarked the young inventor.

For two hours longer the captives lay there, in most uncomfortable positions. Then Folwell and Munson, leaving the group of diamond makers who were grouped about the machinery, approached the captives.

"Well," remarked Munson, "we got ahead of you after all; didn't we. You thought you had our secret, but it will be a long while before you ever make diamonds."

"What are you going to do with us?" asked Tom.

"Never mind. You came where you had no right to, and you must take the consequences."

"We did have a right to come here!" exclaimed Mr. Jenks. "I am entitled to know how the diamonds are made. I paid for the information, and you tricked me. If ever it's possible I'll have the whole gang arrested for swindling."

"You'll never get the chance!" declared Folwell. "You were given some diamonds for the money you invested, and that makes us square."

"No, it doesn't!" declared Mr. Jenks. "I invested the money to learn how to make diamonds, and you know it! You tricked me, and I had a right to try to discover your secret! I nearly have it, too, and I'll get it completely before I'm done with you!"

"No, you won't!" boasted Folwell. "But we didn't come here to tell you that. We came to give you something to eat. We're not savages and we'll treat you as well as we can in spite of the fact that you are trespassers. We're going to give you some grub, but I warn you that any attempt to escape will mean that some of you will get hurt."

He signalled to some of his confederates. These men unbound the captives' arms, and stood over them while they ate some coarse food that was brought into the small cave. They were given coffee to drink, and then, when the simple meal was over, they were securely bound again, and left to themselves, while the diamond makers went back to their machinery.

It was evident that they were going to attempt a big operation, for an unusually large quantity of the white stuff was prepared. The prisoners watched them idly. They could see some but not all of the operations. In this way several hours passed.

Gloom possessed the hearts of Tom and his friends. Not only had their expedition been almost a failure so far, but the young inventor was worried lest the gang might discover and wreck his airship. This would prove a serious loss. Lying there in the semi-darkness the lad imagined all sorts of unpleasant happenings.

At times he dozed off, as did the others. They had become somewhat used to the pain caused by the bonds, for their nerves were numb from the strain and pressure.

Once, as he was lightly sleeping, Tom was awakened by hearing loud voices in the main cave. He looked out, rolling over slightly to get a better view. He saw the man who, once before had run in to give news of an approaching electrical storm.

"Are you fellows all ready?" asked this same man again.

"Yes. Is there another storm coming?"

"Yes, and it's going to be a corker!" was the reply. "It's one of the worst I've ever seen. It's sweeping right up the valley. It'll be here in an hour."

"That's good. We need a big flash to make all the material we have prepared into diamonds. It's the biggest batch we ever tried. I hope it succeeds, for we're going to leave—" The rest was in so low a tone that Tom could not catch it.

The storm messenger departed. Folwell and Munson busied themselves about the machinery. Tom dozed off again, dimly wondering what had become of Bill Renshaw, and whether the former ghost knew of their plight. The others were asleep, as the young inventor saw by the dim light of a lantern in the cave. Then, he too, shut his eyes.

Tom was suddenly awakened by feeling some one's hands moving about his clothing. At first he thought it was one of the diamond-making gang, who had sneaked in to rob him. "Here! What are you up to?" exclaimed Tom.

"Quiet!" cautioned a voice. "Are you all here?"

"All of us—yes. But who are you?"

"Easy—keep quiet, Tom Swift! I'm Bill Renshaw! I've been searching all over for you, since I got back to your cave and found it empty. Now I'm going to free you. I got in here by a secret entrance. Wait, I'll cut your ropes." There was a slight sound, and an instant later Tom was freed from his bonds.

CHAPTER XXIV—IN GREAT PERIL

The young inventor could scarcely believe the good luck that had so unexpectedly come to him and his companions. No sooner was Tom able to move freely about than Bill Renshaw performed the same service for Mr. Jenks and the others, cautioning them to be quiet as he awakened them, and cut the ropes.

"Bless my circulation!" exclaimed Mr. Damon, in a hoarse whisper. "How did you ever get here. I'd given ourselves up for lost."

"Oh, I came in off the mountain, as there's a big storm due," explained the man. "There was no need of me playing the haunt in daytime, anyhow. I went to the cave, found you and your things gone, and I surmised that you might have walked into some trap."

"We did," admitted Mr. Jenks, grimly.

"Well, I hunted around until I found you," went on Bill. "This mountain is honeycombed with caves, all opening from the large one, I know them better than these fellows do, so I could explore freely, and keep out of their sight. They didn't know that there was a second entrance to this place, but I did, and I made for it, when I couldn't find you in some of the other caves where I looked. And, sure enough, here you were."

"Well, we can't thank you enough," said Mr. Parker. "But you say there is a big storm coming?"

"One of the biggest that's been around these parts in some time," replied Bill.

"Then perhaps the mountain will be destroyed," went on the scientist, as calmly as if he had remarked that it might rain.

"I hope nothing like that happens until we get away," spoke Mr. Damon, fervently.

"What had we better do?" inquired Tom.

"Get away, unless you want to discover some more of their secrets," advised Bill. "Those fellows are planning something, but I can't find out what it is. They are suspicious of me, I think. But they are up to something, and I believe, it would be best for you to leave while you have the chance. It may not be healthy to stay. That's why I did my best to untie you."

"We appreciate what you have done," declared Mr. Jenks, "but I want my rights. I must learn a few more facts about how to make diamonds from lightning flashes, and then I will have the same secret they cheated me out of. I think if we wait a while we may be able to see the parts of the process that are not quite clear to us. What do you say, Tom Swift?"

"Well, I would like to learn the secret," replied the lad, "and if Bill thinks it's safe to stay here a while longer—"

"Oh, I guess it will be safe enough," was the reply. "Those fellows won't bother about you now that they are about to make some more diamonds. Besides, they think you're all tied up. Yes, you can stay here and watch, I reckon. I've got a couple of guns, and—"

"Then we'll stay," decided Tom. "We can put up a better fight now."

Silently, in their prison, but which they could now leave whenever they pleased, the adventurers watched the diamond makers once more. The same process they had witnessed before was gone through with. The white balls were put inside the steel box and sealed up. Then they waited for the storm to reach its height.

That this would not be long was evidenced by the mutterings of thunder which every moment grew louder. The outburst of electrical fury was likely to take place momentarily, and that it would be unusually severe was shown by the precautions taken by the diamond makers. They attached a number of extra wires, and brought out some insulated, hard rubber platforms, on which they themselves stood. Tom and Mr. Jenks were much interested in watching this detail of the work, and sought to learn how each part of the process was done.

"I almost think we can make diamonds, Tom, when we get back to civilization," whispered Mr. Jenks.

"I hope we can," answered Tom, "and we can't get back any too soon to suit me. I want to be in my airship again."

"I don't blame you. But look, they are getting ready to adjust the switch."

The adventurers ceased their whispered talk, and eagerly watched the diamond makers. Folwell and Munson were hurrying to and fro in the big cave, attending to the adjustments of the machinery.

"On your insulated plates—all of you," Folwell gave the order. "This is going to be a terrific storm. The gage shows twice the power we have ever used, and it's creeping up every minute! We'll have more diamonds than ever had before!"

"Yes, if the mountain isn't destroyed," added Mr. Parker, in a low voice. "I predict that it will be split from top to bottom!"

"Comforting," thought Tom, grimly.

"I guess we're all ready," said Folwell, in a low tone to Munson. "We'd better get insulated ourselves. I'm going to throw the switch."

He did so. A moment later the man who had before given warning of the storm came dashing in. He was very much excited.

"It's awful!" he cried. "The lightning is striking all over! Big rocks are being split like logs of wood!"

"Well, it can't do any damage in here," said Munson. "We are well protected. Get on one of the plates," and he motioned to one of the hard-rubber platforms that was not occupied. The roar and rumble of the storm outside had given place to short terrific crashes. In their small cave the adventurers could feel the solid ground shake.

A bluish light began dancing about the electrical wires. There was a smell of sulphur in the air. Crash after crash resounded outside. A flash of flame lit up the whole interior of the cave. It came from the copper switch.

"Something's wrong with the insulation!" cried Munson.

"Don't go near it!" yelled Folwell. "If you value your life, stand still!"

Hardly had he spoken than inside the cavern there sounded a report like that of a small cannon. A big ball of fire danced about the middle of the cave and then leaped on top of the steel box.

"This is a fearful storm," cried Munson.

The adventurers in the cave did not know what to say or do. They were in deadly peril.

Suddenly there came a crash louder than any that had preceded it. The whole side of the cave where the switches were was a mass of bluish flame. Then came a ripping, tearing sound, and a tangle of wires and copper connections were thrown to the floor. At the same time the steel box, containing the materials from which diamonds were made, turned blue, and flames shot from it.

"It's all up with us!" cried Munson. "Run for it, everybody! The wires are down, and this place will be an electric furnace in another minute!"

He leaped toward the exit from the cave.

"What about those fellows?" asked Folwell, indicating the place where Tom and the others had been tied.

"They'll have to do the best they can! It's every man for himself, now!" yelled Munson. There was a wild scramble from the cavern.

"Come on!" cried Tom. "We must escape! It's our only chance!"

He leaped into the big cave, followed by the others. Already long tongues of electrical fire were shooting out from the walls and roof as Tom Swift and his companions, evading them as best they could, sought safety in flight.

CHAPTER XXV—THE MOUNTAIN SHATTERED—CONCLUSION

"Can't we get some of the diamonds?" cried Mr. Damon, as he raced along behind Tom. "Now's our chance. Those fellows have all gone!" The odd man made a grab for something as he ran.

"It's as much as our lives are worth," declared the young inventor. "We dare not stop! Come on!"

"I'd like to investigate some of the machinery," spoke Mr. Jenks, "but I wouldn't stop, even for that."

"The storm is too dangerous," called Bill Renshaw. "I can show you a shorter way out than the one those fellows have taken. Follow me."

"No way can be too short," said Mr. Parker, solemnly. "This mountain will go to pieces shortly, I think!"

Tom shuddered. He remembered how narrow had been their escape when Earthquake Island sank into the sea. And that some terrific upheaval was now imminent might be judged from the awful reports that sounded more plainly as the adventurers raced toward the opening of the cave. It was like the bombardment of some doomed city.

Mr. Jenks and Tom cast one longing look behind at the complicated and expensive machinery that had been installed in the cave by the diamond makers. They had abandoned it, and in it lay the secret of making precious gems. But there was no time to stop now, and investigate.

"This way," urged Bill Renshaw. "We'll soon be out."

"But won't it be dangerous to go outside?" asked Mr. Damon. "Shan't we be struck by lightning? There is some protection in here."

"None at all," said Mr. Parker, quickly. "This mountain is a natural lightning rod. To stay here in this cave will be sure death when the storm gets directly over it. And that will be very soon. We must get on insulated ground. Is there any part of this mountain that does not contain iron ore?" the scientist asked of the former spirit.

"Yes; the way out by which we are going lands on a dirt hill."

"That's good; then we may be saved."

On they ran. They had no lanterns, but the blue light of the electricity, as it leaped from point to point inside the cave, where there were outcroppings of iron ore, made the place bright enough to see.

"Here we are!" cried Bill Renshaw at length. "Here's the way out!"

Making a sudden turn in the winding passage he showed the adventurers a small opening in the side of the crag. In an instant they had passed through, and found themselves in daylight once more. The sudden glare almost blinded them, for, though the sky was overcast by clouds, from which jagged tongues of lightning played, the outside was much lighter than the dark cave.

"I should say it was a storm!" cried Tom Swift. "See, it is striking every minute, and all around us!"

In fact, lightning bolts were falling on every side of the adventurers. Every time the balls of fire struck, they burst open great stones, or seared a livid scar on the face of some cliff. As for Tom and the others, they stood on a dry dirt hill, in which, fortunately, there was no iron ore. To this fact they undoubtedly owed their lives, though had there been rain, to moisten the ground and make the earth a good conductor of electricity, they probably would have been badly shocked. But the electrical outburst was not accompanied by rain.

Tom looked up. He saw a compact mass of cloud moving toward the summit of the mountain on the slope of which they stood. From this cloud there played shafts of reddish-green fire.

"Look!" called the young inventor to Mr. Parker. The instant the latter saw the cloud, he cried:

"We must get away from here by all means! That is the center of the storm. As soon as it gets over the mountain, where that lightning rod is, all the electrical fluid will be discharged in one bolt at the mountain, and it will be destroyed! We must run, but keep on the dirt places! Run for your lives!"

They needed no second warning. Turning, they fled down the steep side of the mountain, slipping and stumbling, but taking care not to step on any iron ore. Behind them flashed the lightning bolts.

Suddenly there was a most awful crash. It seemed as if the end of the world had come, and the ear drums of Tom and his companion almost burst with the fearful report. The concussion knocked them down, and they lay stunned for a moment.

Following the terrible report there was a low, rumbling sound. Hardly knowing whether he was dead or alive, Tom opened his eyes and looked about him. What he saw caused him to cry out in terror.

The whole mountain seemed bathed in fire. Great blue, red and green flashes played around it. Then the towering cliff seemed to melt and crumble up, and the great peak, the top of it containing the diamond makers' cave, from which they had fled but a few minutes before, the entire summit was toppled over into the valley on the other side, and in the direction opposite to that where the adventurers stood.

Then came a profound silence, and the lightning ceased. The storm was over, and only the rattle of stones and boulders, as they came to rest in the valley below, reached the ears of our friends.

"Phantom Mountain has been destroyed, just as I said it would be," spoke Mr. Parker, solemnly. Once more he had prophesied correctly.

For a few minutes the adventurers hardly knew what to say. They arose awkwardly from the ground where the shock had tossed them. Then Tom remarked, as calmly as possible:

"Well, it's all over. I guess we may as well get back to our airship."

"What became of Munson and the others?" asked Mr. Damon.

Mr. Jenks pointed to the trail, far below. The figures of some men, running madly, could be seen.

"There they go," he said; "I fancy we have seen the last of them." And they had, for some time at least.

There was little use lingering any longer on Phantom Mountain—indeed little of it was left on which to remain. Looking back toward the place where the cave had been, Tom and the others started forward again. The diamond-making machinery had all been destroyed. So, also, had the finished diamonds stored in the cavern and the large supply which had probably been made by the last terrific crash. No one would ever have them now. Tom and Mr. Jenks felt a sense of disappointment, but they were glad to have escaped with their lives. They sought their former camp, but the tent and all their food was buried under tons of earth and rocks.

Three days later, after rather severe hardships, they were near the place where they had left the Red Cloud. They had suffered cold and hunger, for they had no food supplies, and, had it not been that Bill Renshaw knew the haunts of some game, of which they managed to snare some, they would have fared badly, for they had left their guns in the cave.

"Well, there are the trees behind which I hope my airship is hidden," announced Tom, as they came to the spot. "Good old Red Cloud! Maybe we won't do some eating when we get aboard, eh?"

"Bless my appetite! but we certainly will!" cried Mr. Damon.

"There's somebody walking around the place," spoke Mr. Jenks.

"I hope it's no one who has damaged the ship," came from Tom, apprehensively. He broke into a run, and soon confronted an aged miner, who seemed to have established a rude sort of camp near the airship.

"Is anything the matter?" asked Tom, breathlessly. "Is my airship all right?"

"I guess she's all right, stranger," was the reply. "I don't know much about these contraptions, but I haven't touched her. I knowed she was an airship, for I've seen pictures of 'em, and I've been waiting until the owner came along."

"Why?" asked Tom, wonderingly.

"Because I've got a proposition to make to you," went on the miner, who said his name was Abe Abercrombie. "I've been a miner for a good many years, and I'm just back from Alaska, prospecting around here. I haven't had any luck, but I know of a gold mine in Alaska that will make us all rich. Only it needs an airship to get to it, and I've been figuring how to hire one. Then I comes along, and I sees this big one, and I makes up my mind to stay here until the owners come back. That's what I've done. Now, if I prove that I'm telling the truth, will you go to Alaska—to the valley of gold with me?"

"I don't know," answered Tom, to whom the proposition was rather sudden. "We've just had some pretty startling adventures, and we're almost starved. Wait until we get something to eat, and we'll talk. Come aboard the Red Cloud," and the lad led the way to his craft which was in as good condition as when he left it to go to the diamond cave. Later he listened to the miner's story.

Tom Swift did go to the valley of gold in Alaska, and what happened to him and his companions there will be told of in the next volume of this series, to be called "Tom Swift in the Caves of Ice; or, the Wreck of the Airship."

It did not take our friends long, after they had eaten a hearty meal, to generate some fresh gas, and start the Red Cloud on her homeward way. Tom wanted to take Bill Renshaw with him, but the old man said he would rather remain among the mountains where he had been born. So, after paying him well for his services, they said good-by to him. Abercrombie, the miner, also remained behind, but promised to call and see Tom in a few months.

"Well, we didn't make any money out of this trip," observed Mr. Jenks, rather dubiously, as they were nearing Shopton, after an uneventful trip. "I guess I owe you considerable, Tom Swift. I promised to get you a lot of diamonds, but all I have are those I had from my first visit to the cave."

"Oh, that's all right," spoke Tom, easily. "The experience was worth all the trip cost."

"Speaking of diamonds, look here!" exclaimed Mr. Damon, suddenly, and he pulled out a double handful.

"Where did you get them?" cried the others in astonishment.

"I grabbed them up, as we ran from the cave," said the eccentric man; "but, bless my gaiters! I forgot all about them until you spoke. We'll share them."

These diamonds, some of which were large, proved very valuable, though the total sum was far below what Mr. Jenks hoped to make when he started on the remarkable trip. Tom gave Mary Nestor a very fine stone, and it was set in a ring, instead of a pin, this time.

On their arrival in Shopton, where Mr. Swift, the housekeeper, Mr. Jackson and Eradicate Sampson were much alarmed for Tom's safety, an attempt was made to manufacture diamonds, using a powerful electric current instead of lightning. But it was not a success, and so Mr. Jenks concluded to give up his search for the secret which was lost on Phantom Mountain.

And now we will take leave of Tom Swift, to meet him again soon in other adventures he is destined to have in the caves of ice and the valley of gold.

THE END