Carefully he scanned it.

"I should say that was written in a sort of German hand; would you not also?" he asked of Mr. Damon.

"I would, Tom."

"A German!" exclaimed General Waller.

At the mention of the word "German" Koku, the giant, who had entered the room, to be stared at in amazement by the officer, exclaimed:

"That he, Master! That he!"

"What do you mean?" inquired Tom.

"German man give me stuff for to put in your powder. I 'member now, he talk like Hans who make our garden here; and he say 'yah' just the same like. That man German sure."

"What does this mean?" inquired the officer.

Quickly Tom told of the visit of an unknown man who had prevailed on the simple-minded giant to "dope" Tom's new powder under the impression that he was doing his master a favor. Then the flight of the spy on a motor-cycle, just as the experiment failed, was related.

"We have a German gardener," went on Tom, "and Koku now recalls that our mysterious visitor had the same sort of speech. This ought to give us a clue."

"Let me see," murmured General Waller. "In the first place your test fails—you learn, then, that your powder has been tampered with—you see a man riding away in haste after having, in all likelihood, spied on your work—your giant servant recalls the visit of a mysterious man, and, when the word 'German' is pronounced in his hearing he recalls that his visitor was of that nationality. So far so good.

"I come to this vicinity for my health. That fact, as are all such regarding officers, was doubtless published in the Army and Navy Journal, so it might easily become known to almost anyone. I receive a letter which I think is from Tom Swift, asking me to attend the test. As the distance is short I go, only to find that the letter has been forged, presumably by a German.

"Question: Can the same German be the agent in both cases?"

"Bless my arithmetic! how concisely you put it!" exclaimed Mr. Damon.

"It is part of my training, I suppose," remarked the officer. "But it strikes me that if we find your German spy, Tom, we will find the man who played the joke on me. And if I do find him—well, I think I shall know how to deal with him," and General Waller assumed his characteristic haughty attitude.

"I believe you are right, General," spoke Tom. "Though why any German would want to prevent my experiments, or even damage my property, and possibly injure my friends, I cannot understand."

"Nor can I," spoke the officer.

"I am sorry you have had your trouble for nothing," went on Tom. "And, if you are in this vicinity when I conduct my next test, I shall be glad to have you come. I will send word by Mr. Damon, and then there will be no chance of a mistake."

"Thank you, Tom, I shall be glad to come I do not know how long I shall remain in this vicinity. If I knew where to look for the German I would make a careful search. As it is, I shall turn this letter over to the United States Secret Service, and see what its agents can do. And, Tom, if you are annoyed again, let me know. You are a sort of rival, so to speak, but, after all, we are both working to serve Uncle Sam. I'll do my best to protect you."

"Thank you, sir," replied Tom. "On my part, I shall keep a good lookout. It will be a bold spy who gets near my shop after this. I'm going to put up my highly-charged protecting electric wires again. We were just talking about them when you came in. Would you like to look about here, General?"

"I would, indeed, Tom. Have you made your big gun yet?"

"No, but I am working on the plans. I want first to decide on the kind of explosive I am to use, so I can make my gun strong enough to stand it."

"A wise idea. I think there is where I made my mistake. I did not figure carefully enough on the strength of material. The internal pressure of the powder I used, as well as the muzzle velocity of my projectile, were both greater than they should have been. Take a lesson from my failure. But I am going to start on another gun soon, and—Tom Swift—I am going to try to beat you!"

"All right, General," answered Tom, genially. "May the best gun win!"

"Bless my powder box!" cried Mr. Damon. "That's the way to talk."

General Waller was much interested in going about Tom's shop, and expressed his surprise at the many inventions he saw. While ordnance matters, big guns and high explosives were his hobby, nevertheless the airships were a source of wonder to him.

"How do you do it, Tom?" he asked.

"Oh, by keeping at it," was the modest answer. "Then my good friends here—Ned and Mr. Damon—help me."

"Bless my check book!" exclaimed the odd gentleman. "It is very little help I give, Tom."

General Waller soon took his departure, promising to call again, to see Tom's test if one were held. He also repeated his determination to set the Secret Service men at work to discover the mysterious German.

"I can't imagine who would want to injure you or me, Tom Swift," he said.

"Do you think they wanted to injure you, General?" asked Mr. Damon.

"It would seem so," remarked Ned. "That man doped Tom's powder, hoping to make it so powerful that it would blow up everything. Then he sends word to the General to be present. If there had been a blow-up he would have gone with it."

"Bless my gaiters, yes!" exclaimed Mr. Damon.

"Well, we'll see if we can ferret him out!" spoke the officer as he took his leave.

Tom, Ned and the others talked the matter over at some length.

"I wonder if we could trace that man who rode away on the motor-cycle?" said Ned.

"We'll try," decided Tom, energetically, and in the electric runabout, that had once performed such a service to his father's bank, the young inventor and his chum were soon traversing the road taken by the spy. They got some traces of him—that is, several persons had seen him pass—but that was all. So they had to record one failure at least.

"I wonder if the General himself could have sent that letter?" mused Ned, as they returned home.

"What! To himself?" cried Tom, in amazement.

"He might have," went on Ned, coolly. "You see, Tom, he admits that he was jealous of you. Now what is there to prevent him from hiring someone to dope your powder, and then, to divert suspicion from himself, faking up a letter and inviting himself to the blowout."

"But if he did that—which I don't believe—why would he come when there was danger, in case his trick worked, of the whole place being blown to kingdom come."

"Ah, but you notice he didn't arrive until after danger of an explosion had passed," commented Ned.

"Oh, pshaw!" cried Tom. "I don't take any stock in that theory."

"Well, maybe not," replied Ned. "But it's worth thinking about. I believe if General Waller could prevent you from inventing your big gun, he would."

The days that followed were busy ones for Tom. He worked on the powder problem from morning to night, scoring many failures and only a few successes. But he did not give up, and in the meanwhile drew tentative plans for the big gun.

One evening, after a hard day's work, he went to the library where his father was reading.

"Tom," said Mr. Swift, "do you remember that old fortune hunter, Alec Peterson, who wanted me to go into that opal mine scheme?"

"Yes, Dad. What about him? Has he found it?"

"No, he writes to say he reached the island safely, and has been working some time. He hasn't had any success yet in locating the mine; but he hopes to find it in a week or so."

"That's just like him," murmured Tom. "Well, Dad, if you lose the ten thousand dollars I guess I'll have to make it up to you, for it was on my account that you made the investment."

"Well, you're worth it, Tom," replied his father, with a smile.



CHAPTER XII

A POWERFUL BLAST

"Look out with that box, Koku! Handle it as though it contained a dozen eggs of the extinct great auk, worth about a thousand dollars apiece.

"Eradicate! Don't you dare stumble while you're carrying that tube. If you do, you'll never do it again!"

"By golly, Massa Tom! I—I's gwine t' walk on mah tiptoes all de way!"

Thus Eradicate answered the young inventor, while the giant, Koku, who was carrying a heavy case, nodded his head to show that he understood the danger of his task.

"So you think you've got the right stuff this time, Tom?" asked Ned Newton.

"I'm allowing myself to hope so, Ned."

"Bless my woodpile!" cried Mr. Damon. "I—I really think I'm getting nervous."

It was one afternoon, about two weeks after Tom had made his first test of the new powder. Now, after much hard work, and following many other tests, some of which were more or less successful, he had reached the point where he believed he was on the threshold of success. He had succeeded in making a new explosive that, in the preliminary tests, in which only a small quantity was used, gave promise of being more powerful than any Tom had ever experimented with—his own or the product of some other inventor.

And his experiments had not always been harmless. Once he came within a narrow margin of blowing up the shop and himself with it, and on another occasion some of the slow-burning powder, failing to explode, had set ablaze a shack in which he was working.

Only for the prompt action of Koku, Tom might have been seriously injured. As it was he lost some valuable patterns and papers.

But he had gone on his way, surmounting failure after failure, until now he was ready for the supreme test. This was to be the explosion of a large quantity of the powder in a specially prepared steel tube of great thickness. It was like a miniature cannon, but, unlike the first small one, where the test had failed, this one would carry a special projectile, that would be aimed at an armor plate set up on a big hill.

Tom's hope was that this big blast would show such pressure in foot-tons, and give such muzzle velocity to the projectile, and at the same time such penetrating power, that he would be justified in taking it as the basis of his explosive, and using it in the big gun he intended to make.

The preliminaries had been completed. The special steel tube had been constructed, and mounted on a heavy carriage in a distant part of the Swift grounds. A section of armor plate, a foot and a half in thickness, had been set up at the proper distance. A new projectile, with a hard, penetrating point, had been made—a sort of miniature of the one Tom hoped to use in his giant cannon.

Now the young inventor and his friends were on their way to the scene of the test, taking the powder and other necessaries, including the primers, with them. Tom, Ned and Mr. Damon had some of the gauges to register the energy expended by the improvised cannon. There were charts to be filled in, and other details to be looked after.

"So General Waller won't be here?" remarked Ned, as they walked along, Tom keeping a watchful eye on Koku.

"No," was the reply. "He has gone back to Sandy Hook. He wrote that his health was better, and that he wanted to resume work on a new type of gun."

"I guess he's afraid you'll beat him out, Tom," laughed Ned. "You take my advice, and look out for General Waller."

"Nonsense! I say, Rad! Look out with those primers!"

"I'se lookin' out, Massa Tom. Golly, I don't laik dis yeah job at all! I—I guess I'd better be gittin' at dat whitewashin', Massa Tom. Dat back fence suah needs a coat mighty bad."

"Never you mind about the whitewashing, Rad. You just stick around here for a while. I may need you to sit on the cannon to hold it down."

"Sit on a cannon, Massa Tom! Say, looky heah now! You jest take dese primary things from dish yeah coon. I—I'se got t' go!"

"Why, what's the matter, Rad? Surely you're not afraid; are you?" and Tom winked at Ned.

"No, Massa Tom, I'se not prezactly 'skeered, but I done jest 'membered dat I didn't gib mah mule Boomerang any oats t'day, an' he's suahly gwine t' be desprit mad at me fo' forgettin' dat. I—I'd better go!"

"Nonsense, Rad! I was only fooling. You can go as soon as we get to my private proving grounds, if you like. But you'll have to carry those primers, for all the rest of us have our hands full. Only be careful of 'em!"

"I—I will, Massa Tom."

They kept on, and it was noticed that Mr. Damon gave nervous glances from time to time in the direction of Koku, who was carrying the box of powder. The giant himself, however, did not seem to know the meaning of fear. He carried the box, which contained enough explosive to blow them all into fragments, with as much composure as though it contained loaves of bread.

"Now you can go, Rad," announced Tom, when they reached the lonely field where, pointing toward a big hill, was the little cannon.

"Good, Massa Tom!" cried the colored man, and from the way in which he hurried off no one would ever suspect him of having rheumatic joints.

"Say, that stuff looks just like Swiss cheese," remarked Ned, as Tom opened the box of explosive. It would be incorrect to call it powder, for it had no more the appearance of gunpowder, or any other "powder," than, as Ned said, swiss cheese.

And, indeed, the powerful stuff bore a decided resemblance to that peculiar product of the dairy. It was in thin sheets, with holes pierced through it here and there, irregularly.

"The idea is," Tom explained, "to make a quick-burning explosive. I want the concussion to be scattered through it all at once. It is set off by concussion, you see," he went on. "A sort of cartridge is buried in the middle of it, after it has been inserted in the cannon breech. The cartridge is exploded by a primer, which responds to an electric current. The thin plates, with holes corresponding to the centre hole in a big grain of the hexagonal powder, will, I hope, cause the stuff to burn quickly, and give a tremendous pressure. Now we'll put some in the steel tube, and see what happens."

Even Tom was a little nervous as he prepared for this latest test. But he was not nervous enough to drop any of those queer, cheese-like slabs. For, though he knew that a considerable percussion was needed to set them off, it would not do to take chances. High explosives do not always act alike, even under the same given conditions. What might with perfect safety be done at one time, could not be repeated at another. Tom knew this, and was very careful.

The powder, as I shall occasionally call it for the sake of convenience, though it was not such in the strict sense of the word—the powder was put in the small cannon, together with the primer. Then the wires were attached to it, and extended off for some distance.

"But we won't attach the battery until the last moment," Tom said. "I don't want a premature explosion."

The projectile was also put in, and Tom once more looked to see that the armor plate was in place. Then he adjusted the various gauges to get readings of the power and energy created by his new explosive.

"Well, I guess we're all ready," he announced to his friends. "I'll hook on the battery now, and we'll get off behind that other hill. I had Koku make a sort of cave there—a miniature bomb-proof, that will shelter us."

"Do you think the blast will be powerful enough to make it necessary?" asked Mr. Damon.

"It will, if this larger quantity of explosive acts anything like the small samples I set off," replied the young inventor.

The electric wires were carried behind the protecting hill, whither they all retired.

"Here she goes!" exclaimed Tom, after a pause.

His thumb pressed the electric button, and instantly the ground shook with the tremor of a mighty blast, while a deafening sound reared about them. The earth trembled, and there was a big sheet of flame, seen even in the powerful sunlight.

"Something happened, anyhow!" yelled Tom above the reverberating echoes.



CHAPTER XIII

CASTING THE CANNON

"Come on!" yelled Ned. "We'll see how this experiment came out!" and he started to run from beneath the shelter of the hill.

"Hold on!" shouted Tom, laying a restraining hand on his chum's shoulder.

"Why, what's the matter?" asked Ned in surprise.

"Some of that powder may not have exploded," went on the young inventor. "From the sound made I should say the gun burst, and, if it did, that gelatin is bound to be scattered about. There may be a mass of it burning loose somewhere, and it may go off. It ought not to, if my theory about it being harmless in the open is correct, but the trouble is that it's only a theory. Wait a few seconds."

Anxiously they lingered, the echoes of the blast still in their ears, and a peculiar smell in their nostrils.

"But there's no smoke," said Mr. Damon. "Bless my spyglass! I always thought there was smoke at an explosion."

"This is a sort of smokeless powder," explained Tom. "It throws off a slight vapor when it is ignited, but not much. I guess it's safe to go out now. Come on!"

He dropped the pushbutton connected with the igniting battery, and, followed by the others, raced to the scene of the experiment. A curious sight met their eyes.

A great hole had been torn in the hillside, and another where the improvised gun had stood. The gun itself seemed to have disappeared.

"Why—why—where is it?" asked Ned.

"Burst to pieces I guess," replied Tom. "I was afraid that charge was a bit too heavy."

"No, here it is!" shouted Mr. Damon, circling off to one side. "It's been torn from the carriage, and partly buried in the ground," and he indicated a third excavation in the earth.

It was as he had said. The terrific blast had sheared the gun from its temporary carriage, thrown it into the air, and it had come down to bury itself in the soft ground. The carriage had torn loose from the concrete base, and was tossed off in another direction.

"Is the gun shattered?" asked Tom, anxious to know how the weapon had fared. It was, in a sense, a sort of small model of the giant cannon he intended to have cast.

"The breech is cracked a little," answered Mr. Damon, who was examining it; "but otherwise it doesn't seem to be much damaged."

"Good," cried Tom. "Another steel jacket will remedy that defect. I guess I'm on the right road at last. But now to see what became of that armor plate."

"Dinner plate not here," spoke Koku, who could not understand how there could be two kind of plates in the world. "Dinner plate gone, but big hole here, and he indicated one in the side of the hill.

"I expect that is where the armor plate is," said Tom, trying not to laugh at the mistake of his giant servant. "Take a look in there, Koku, and, if you can get hold of it, pull it out for us. I'm afraid the piece of nickel-steel armor proved too much for my projectile. But we'll have a look."

Koku disappeared into the miniature cave that had been torn in the side of the bill. It was barely large enough to allow him to go in. But Tom knew none other of them could hope to loosen the piece of steel, imbedded as it must be in the solid earth.

Presently they heard Koku grunting and groaning. He seemed to be having quite a struggle.

"Can you get it, Koku?" asked Torn. "Or shall I send for picks and shovels."

"Me get, Master," was the muffled answer.

Then came a shout, as though in anger Koku had dared the buried plate to defy him. There was a shower of earth at the mouth of the cave, and the giant staggered out with the heavy piece of armor plate. At the sight of it Tom uttered a cry.

"Look!" he shouted. "My projectile went part way through and then carried the plate with it into the side of the hill. Talk about a powerful explosive! I've struck it, all right!"

It was as he had said. The projectile, driven with almost irresistible force, had bitten its way through the armor plate, but a projection at the base of the shell had prevented it from completely passing through. Then, with the energy almost unabated, the projectile had torn the plate loose and hurled it, together with its own body, into the solid earth of the hillside. There, as Koku held them up, they could all see the shell imbedded in the plate, the point sticking out on the other side, as a boy might spear an apple with a sharp stick.

"Bless my spectacle case!" cried Mr. Damon. "This is the greatest ever!"

"It sure is," agreed Ned. "Tom, my boy, I guess you can now make the longest shots on record."

"I can as soon as I get my giant cannon, perhaps," admitted the young inventor. "I think I have solved the problem of the explosive. Now to work on the cannon."

An examination of the gauges, which, being attached to the cannon and plate by electric wires, were not damaged when the blast came, showed that Tom's wildest hopes had been confirmed. He had the most powerful explosive ever made—or at least as far as he had any knowledge, and he had had samples of all the best makes.

Concerning Tom's powder, or explosive, I will only say that he kept the formula of it secret from all save his father. All that he would admit, when the government experts asked him about it, later, was that the base was not nitro-glycerine, but that this entered into it. He agreed, however, in case his gun was accepted by the government, to disclose the secret to the ordnance officers.

But Tom's work was only half done. It was one thing to have a powerful explosive, but there must be some means of utilizing it safely—some cannon in which it could be fired to send a projectile farther than any cannon had ever sent one. And to do this much work was necessary.

Tom figured and planned, far into the night, for many weeks after that. He had to begin all over again, working from the basis of the power of his new explosive. And he had many new problems to figure out.

But finally he had constructed—on paper—a gun that was to his liking. The most exhaustive figuring proved that it had a margin of safety that would obviate all danger of its bursting, even with an accidental over-charge.

"And the next thing is to get the gun cast," said Tom to Ned one day.

"Are you going to do it in your shops?" his chum asked.

"No; it would be out of the question for me. I haven't the facilities. I'm going to give the contract to the Universal Steel Company. We'll pay them a visit in a day or two."

But even the great facilities of the steel corporation proved almost inadequate for Tom's giant cannon. When he showed the drawings, on which he had already secured a patent, the manager balked.

"We can't cast that gun here!" he said.

"Oh, yes, you can!" declared Tom, who had inspected the plant. "I'll show you how."

"Why, we haven't a mould big enough for the central core," was another objection.

"Then we'll make one," declared Tom "We'll dig a pit in the earth, and after it is properly lined we can make the cast there."

"I never thought of that!" exclaimed the manager. "Perhaps it can be done."

"Of course it can!" cried Tom. "Do you think you can shrink on the jackets, and rifle the central tube?"

"Oh, yes, we can do that. The initial cast was what stumped me. But we'll go ahead now."

"And you can wind the breech with wire, and braze it on; can't you?" persisted Tom.

"Yes, I think so. Are you going to have a wire-wound gun?"

"That, in combination with a steel-jacketed one. I'm going to take no chances with 'Swiftite'!" laughed Tom, for so he had named his new explosive, in honor of his father, who had helped him with the formula.

"It must be mighty powerful," exclaimed the manager.

"It is," said Tom, simply.

I am not going to tire my readers with the details leading up to the casting of Tom's big cannon. Sufficient to say that the general plan, in brief, was this: A hole would be dug in the earth, in the center of the largest casting shop—a hole as deep as the gun was to be long. This was about one hundred feet, though the gun, when finished, would be somewhat shorter than this. An allowance was to be made for cutting.

In the center of this hole would be a small "core" made of asbestos and concrete mixed. Around this would be poured the molten steel from great caldrons. It would flow into the hole. The sides of earth—lined with fire-clay—would hold it in, and the middle core would make a hole throughout the length of the central part of the gun. Afterward this hole would be bored and rifled to the proper calibre.

After this central part was done, steel jackets or sleeves would be put on, red-hot, and allowed to shrink. Then would come a winding of wire, to further strengthen the tube, and then more sleeves or jackets. In this way the gun would be made very strong.

As the greatest pressure would come at the breech, or in the powder chamber there, the gun would be thickest at this point, decreasing in size to the muzzle.

It took many weary weeks to get ready for the first cast, but finally Tom received word that it was to be made, and with Ned, and Mr. Damon, he proceeded to the plant of the steel concern.

There was some delay, but finally the manager gave the word. Tom and his friends, standing on a high gallery, watched the tapping of the combined furnaces that were to let the molten steel into the caldrons. There were several of these, and their melted contents were to be poured into the mould at the same time.

Out gushed the liquid steel, giving off a myriad of sparks. The workers, as well as the visitors, had to wear violet-tinted glasses to protect their eyes from the glare.

"Hoist away!" cried the manager, and the electric cranes started off with the caldrons of liquid fire, weighing many tons.

"Pour!" came the command, and into the pit in the earth splashed the melted steel that was to form the big cannon. From each caldron there issued a stream of liquid metal of intense heat. There were numerous explosions as the air bubbles burst—explosions almost like a battery in action.

"So far so good!" exclaimed the manager, with a sigh of relief as the last of the melted stuff ran into the mould. "Now, when it cools, which won't be for some days, we'll see what we have."

"I hope it contains no flaws," spoke Tom, "That is the worst of big guns—you never can tell when a flaw will develop. But I hope—"

Tom was interrupted by the sound of a dispute at one of the outer doors of the shop.

"But I tell you I must go in—I belong here in!" a voice cried. It had a German accent, and at the sound of it Tom and Ned looked at each other.

"Who is there?" asked the manager sharply of the foreman..

"Oh, a crazy German. He belongs in one of the other shops, and I guess he's mixed up. He thinks he belongs here. I sent him about his business."

"That is right," remarked the manager. "I gave orders, at your request," he said to Tom, "that no one but the men in this part of the plant were to be present at the casting. I cant understand what that fellow wanted."

"I think I can," murmured Tom, to himself.



CHAPTER XIV

A NIGHT INTRUDER

"Tom, aren't you going to try to get a look at that German?" whispered Ned, as he and his chum came down from the elevated gallery at the conclusion of the cast. "I mean the one who tried to get in!"

"I'd like to, Ned, but I don't want to arouse any suspicion," replied Tom. "I've got to stay here a while yet, and arrange about shrinking on the jackets, after the core is rifled. I don't see how—"

"I'll slip out and see if I can get a peep at him," went on Ned. "If it's like the one Koku described, we'll know that he's still after you."

"All right, Ned. Do as you like, only be cautious."

"I will," promised Tom's chum. So, while the young inventor was busy arranging details with the steel manager, Ned slipped out of a side door of the casting shop, and looked about the yard. He saw a little group of workmen surrounding a man who appeared to be angry.

"I dell you dot is my shop!" one of the men was heard to exclaim—a man whom the others appeared to dragging away with main force.

"And I tell you, Baudermann, that you're mistaken!" insisted one, evidently a foreman. "I told you to work in the brazing department. What do you want to try to force your way into the heavy casting department for? Especially when we're doing one of the biggest jobs that we ever handled—making the new Swift cannon."

"Oh, iss dot vot vas going on in dere?" asked the man addressed as Baudermann. "Shure den, I makes a misdake. I ask your pardon, Herr Blackwell. I to mine own apartment will go. But I dinks my foreman sends me to dot place," and he indicated the casting shop from which he had just been barred.

"All right!" exclaimed the foreman. "Don't make that mistake again, or I'll dock you for lost time."

"Only just a twisted German employee, I guess," thought Ned, as he was about to turn back. "I was mistaken. He probably didn't understand where he was sent."

He passed by the group of men, who, laughing and jeering at the German, were showing him where to go. He seemed to be a new hand in the works.

But as Ned passed he got one look at the man's face. Instead of a stupid countenance, for one instant he had a glimpse of the sharpest, brightest eyes he had ever looked into. And they were hard, cruel eyes, too, with a glint of daring in them. And, as Ned glanced at his figure, he thought he detected a trace of military stiffness—none of the stoop-shouldered slouch that is always the mark of a moulder. The fellow's hands, too, though black and grimy, showed evidences of care under the dirt, and Ned was sure his uncouth language was assumed.

"I'd like to know more about you," murmured Ned, but the man, with one sharp glance at him, passed on, seemingly to his own department of the works.

"Well, what was it?" asked Tom, as his chum rejoined him.

"Nothing very definite, but I'm sure there was something back of it all, Tom. I wouldn't be surprised but what that fellow—whoever he was—whatever his object was—hoped to get in to see the casting; either to get some idea about your new gun, or to do some desperate deed to spoil it."

"Do you think that, Ned?"

"I sure do. You've got to be on your guard, Tom."

"I will. But I wonder what object anyone could have in spoiling my gun?"

"So as to make his own cannon stand in a better light."

"Still thinking of General Waller, are you?"

"I am, Tom."

There was nothing more to be done at present, and, as it would take several days for the big mass of metal to properly cool, Tom, Ned and Mr. Damon returned to Shopton.

There Tom busied himself over many things. Ned helping him, and Mr. Damon lending an occasional hand. Koku was very useful, for often his great strength did what the combined efforts of Tom and his friends could not accomplish.

As for Eradicate, he "puttered around," doing all he could, which was not much, for he was getting old. Still Tom would not think of discharging him, and it was pitiful to see the old colored man try to do things for the young inventor—tasks that were beyond his strength. But if Koku offered to help, Eradicate would draw himself up, and exclaim:

"Git away fom heah! I guess dish yeah coon ain't forgot how t' wait on Massa Tom. Go 'way, giant. I ain't so big as yo'-all, but I know de English language, which is mo' 'n yo' all does. Go on an' lemme be!"

Koku, good naturedly, gave place, for he, too, felt for Eradicate.

"Well, Ned," remarked Tom one day, after the visit of the postman, "I have a letter from the steel people. They are going to take the gun out of the mould tomorrow, and start to rifle it. We'll take a run down in the airship, and see how it looks. I must take those drawings, too, that show the new plan of shrinking on the jackets. I guess I'll keep them in my room, so I won't forget them."

Tom and Ned occupied adjoining and connecting apartments, for, of late, Ned had taken up his residence with his chum. It was shortly after midnight that Ned was awakened by hearing someone prowling about his room. At first he thought it was Tom, for the shorter way to the bath lay through Ned's apartment, but when the lad caught the flash of a pocket electric torch he knew it could not be Tom.

"Who's there?" cried Ned sharply, sitting up in bed.

Instantly the light went out, and there was silence.

"Who's there?" cried Ned again.

This time he thought he heard a stealthy footstep.

"What is it?" called Tom from his chamber.

"Someone is in here!" exclaimed Ned. "Look out, Tom!"



CHAPTER XV

READY FOR THE TEST

Tom Swift acted promptly, for he realized the necessity. The events that had hedged him about since he had begun work on his giant cannon made him suspicious. He did not quite know whom to suspect, nor the reasons for their actions, but he had been on the alert for several days, and was now ready to act.

The instant Ned answered as he did, and warned Tom, the young inventor slid his hand under his pillow and pressed an auxiliary electric switch he had concealed there. In a moment the rooms were flooded with a bright light, and the two lads had a momentary glimpse of an intruder making a dive for the window.

"There he is, Tom!" cried Ned.

"What do you want?" demanded Tom, instinctively. But the intruder did not stay to answer.

Instead, he made a dive for the casement. It was one story above the ground, but this did not cause him any hesitation. It was summer, and the window was open, though a wire mosquito net barred the aperture. This was no hindrance to the man, however.

As Ned and Tom leaped from their beds, Ned catching up the heavy, empty water pitcher as a weapon, and Tom an old Indian war club that served as one of the ornaments of his room, the fellow, with one kick, burst the screen.

Then, clambering out on the sill, he dropped from sight, the boys hearing him land with a thud on the turf below. It was no great leap, though the fall must have jarred him considerably, for the boys heard him grunt, and then groan as if in pain.

"Quick!" cried Ned. "Ring the bell for Koku, Ned. I want to capture this fellow if possible."

"Who is he?" asked Ned.

"I don't know, but we'll see if we can size him up. Signal for the giant!"

There was an electric bell from Tom's room to the apartment of his big servant, and a speaking tube as well. While Ned was pressing the button, and hastily telling the giant what had happened, urging him to get in pursuit of the intruder, Tom had taken from his bureau a powerful, portable, electric flash lamp, of the same variety as that used by the would-be thief. Only Tom's was provided with a tungsten filament, which gave a glaring white pencil of light, increased by reflectors.

And in this glare the young inventor saw, speeding away over the lawn, the form of a big man.

"There he goes, Ned!" he shouted.

"So I see. Koku will be right on the job. I told him not to dress. Can you make out who the fellow is?"

"No, his back is toward us. But he's limping, all right. I guess that jump jarred him up a bit. Where is Koku?"

"There he goes now!" exclaimed Ned, as a figure leaped from the side door of the house—a gigantic figure, scantily clad.

"Get to him, Koku!" cried Tom.

"Me git, Master!" was the reply, and the giant sped on.

"Let's go out and lend a hand!" suggested Ned, looking at the water pitcher as though wondering what he had intended to do with it.

"I'm with you," agreed Tom. "Only I want to get into something a little more substantial than my pajamas."

As the two lads hurriedly slipped on some clothing they heard the voice of Mr. Swift calling:

"What is it, Tom? Has anything happened?"

"Nothing much," was the reassuring answer. "It was a near-happening, only Ned woke up in time. Someone was in our rooms—a burglar, I guess."

"A burglar! Good land a massy!" cried Eradicate, who had also gotten up to see what the excitement was about. "Did you cotch him, Massa Tom?"

"No, Rad; but Koku is after him."

"Koku? Huh, he nebber cotch anybody. I'se got t' git out dere mahse'f! Koku? Hu! I s'pects it's dat no-'count cousin ob mine, arter mah chickens ag'in! I'll lambaste dat coon when I gits him, so I will. I'll cotch him for yo'-all, Massa Tom," and, muttering to himself, the aged colored man endeavored to assume the activity of former years.

"Hark!" exclaimed Ned, as he and Tom were about ready to take part in the chase. "What's that noise, Tom?"

"Sounds like a motor-cycle."

"It is. That fellow—"

"It's the same chap!" interrupted Tom. "No use trying to chase him on that speedy machine. He's a mile away from here by now. He must have had it in waiting, ready for use. But come on, anyhow."

"Where are you going?"

"Out to the shop. I want to see if he got in there."

"But the charged wires?"

"He may have cut them. Come on."

It was as Tom had suspected. The deadly, charged wires, that formed a protecting cordon about his shops, had been cut, and that by an experienced hand, probably by someone wearing rubber gloves, who must have come prepared for that very purpose. During the night the current was supplied to the wires from a storage battery, through an intensifying coil, so that the charge was only a little less deadly than when coming direct from a dynamo.

"This looks bad, Tom," said Ned.

"It does, but wait until we get inside and look around. I'm glad I took my gun-plans to the house with me."

But a quick survey of the shop did not reveal any damage done, nor had anything been taken, as far as Tom could tell. The office of his main shop was pretty well upset, and it looked as though the intruder had made a search for something, and, not finding it, had entered the house.

"It was the gun-plans he was after, all right," decided Tom. "And I believe it was the same fellow who has been making trouble for me right along."

"You mean General Waller?"

"No, that German—the one who was at the machine shop."

"But who is he—what is his object?"

"I don't know who he is, but he evidently wants my plans. Probably he's a disappointed inventor, who has been trying to make a gun himself, and can't. He wants some of my ideas, but he isn't going to get them. Well, we may as well get back to bed, after I connect these wires again. I must think up a plan to conceal them, so they can't be cut."

While Tom and Ned were engaged on this, Koku came back, much out of breath, to report:

"Me not git, Master. He git on bang-bang machine and go off—puff!"

"So we heard, Koku. Never mind, we'll get him yet."

"Hu! Ef I had de fust chanst at him, I'd a cotched dat coon suah!" declared Eradicate, following the giant. "Koku he done git in mah way!" and he glared indignantly at the big man.

"That's all right, Rad," consoled Tom. "You did your best. Now we'll all get to bed. I don't believe he'll come back." Nor did he.

Tom and Ned were up at the first sign of daylight, for they wanted to go to the steel works, some miles away, in time to see the cannon taken out of the mould, and preparations made for boring the rifle channels. They found the manager, anxiously waiting for them.

"Some of my men are as interested in this as you are," he said to the young inventor. "A number of them declare that the cast will be a failure, while some think it will be a success."

"I think it will be all right, if my plans were followed," said Tom. "However, we'll see. By the way, what became of that German who made such a disturbance the day we cast the core?"

"Oh, you mean Baudermann?"

"Yes."

"Why, it's rather queer about him. The foreman of the shop where he was detailed, saw that he was an experienced man, in spite of his seemingly stupid ways, and he was going to promote him, only he never came back."

"Never came back? What do you mean?"

"I mean the day after the cast of the gun was made he disappeared, and never came back."

"Oh!" exclaimed Tom. He said nothing more, but he believed that he understood the man's actions. Failing to obtain the desired information, or perhaps failing to spoil the cast, he realized that his chances were at an end for the present.

With great care the gun was hoisted from the mould. More eyes than Tom's anxiously regarded it as it came up out of the casting pit.

"Bless my buttonhook!" cried Mr. Damon, who had gone with the lads. "It's a monster; isn't it?"

"Oh, wait until you see it with the jackets on exclaimed," Ned, who had viewed the completed drawings. "Then you'll open your eyes."

The great piece of hollow steel tubing was lifted to the boring lathe. Then Tom and the manager examined it for superficial flaws.

"Not one!" cried the manager in delight.

"Not that I can see," added Tom.. "It's a success—so far."

"And that was the hardest part of the work," went on the manager of the steel plant. "I can almost guarantee you success from now on."

And, as far as the rifling was concerned, this was true. I will not weary you with the details of how the great core of Tom Swift's giant cannon was bored. Sufficient to say that, after some annoying delays, caused by breaks in the machinery, which had never before been used on such a gigantic piece of work, the rifling was done. After the jackets had been shrunk on, it would be rifled again, to make it true in case of any shrinkage.

Then came the almost Herculean task of shrinking on the great red-hot steel jackets and wire-windings, that would add strength to the great cannon. To do this the central core was set up on end, and the jackets, having been heated in an immense furnace, were hoisted by a great crane over the core, and lowered on it as one would lower his napkin ring over the rolled up napkin.

It took weeks of hard work to do this, and Tom and Ned, with Mr. Damon occasionally for company, remained almost constantly at the plant. But finally the cannon was completed, the rifling was done over again to correct any imperfections, and the manager said:

"You cannon is completed, Mr. Swift. I want to congratulate you on it. Never have we done such a stupendous piece of work. Only for your plans we could not have finished it. It was too big a problem for us. Your cannon is completed, but, of course, it will have to be mounted. What about the carriage?"

"I have plans for that," replied Tom; "but for the present I am going to put it on a temporary one. I want to test the gun now. It looks all right, but whether it will shoot accurately, and for a greater distance than any cannon has ever sent a projectile before, is yet to be seen."

"Where will you test it?"

"That is what we must decide. I don't want to take it too far from here. Perhaps you can select a place where it would be safe to fire it, say with a range of about thirty miles."

"Thirty miles! why, my dear sir—"

"Oh, I'm not altogether sure that it will go that distance," interrupted Tom, with a smile; "but I'm going to try for it, and I want to be on the safe side. Is there such a place near here?"

"Yes, I guess we can pick one out. I'll let you know."

"Then I must get back and arrange for my powder supply," went on the young inventor. "We'll soon test my giant cannon!"

"Bless my ear-drums!" cried Mr. Damon. "I hope nothing bursts. For if that goes up, Tom Swift—"

"I'm not making it to burst," put in Tom, with a smile. "Don't worry. Now, Ned, back to Shopton to get ready for the test."



CHAPTER XVI

A WARNING

"Whew, how it rains!" exclaimed Ned, as he looked out of the window.

"And it doesn't seem to show any signs of letting up," remarked Tom. "It's been at it nearly a week now, and it is likely to last a week longer."

"It's beastly," declared his chum. "How can you test your gun in this weather?"

"I can't. I've got to wait for it to clear."

"Bless my rubber boots! it's just got to stop some time," declared Mr. Damon. "Don't worry, Tom."

"But I don't like this delay. I have heard that General Waller has perfected a new gun—and it's a fine one, from all accounts. He has the proving grounds at Sandy Hook to test his on, and I'm handicapped here. He may beat me out."

"Oh, I hope not, Tom!" exclaimed Ned. "I'm going to see what the weather reports say," and he went to hunt up a paper.

It was several weeks after the completion of Tom's giant cannon. In the meanwhile the gun had been moved by the steel company to a little-inhabited part of New York State, some miles from the plant. The gun had been mounted on an improvised carriage, and now Tom and his friends were waiting anxiously for a chance to try it.

The work was not complete, for the steel company employees had been hampered by the rain. Never before, it seemed, had there been so much water coming down from the clouds. Nearly every day was misty, with gradations from mere drizzles to heavy downpours. There were occasional clear stretches, however, and during them the men worked.

A few more days of clear weather would be needed before the gun could be fastened securely to the carriage, and then Tom could fire one of the great projectiles that had been cast for it. Not until then would he know whether or not his cannon was going to be a success.

Meanwhile nothing more had been heard or seen of the spy. He appeared to have given up his attempts to steal Tom's secret, or to spoil his plans, if such was his object.

The place of the test, as I have said, was in a deserted spot. On one side of a great valley the gun was being set up. Its muzzle pointed up the valley, toward the side of a mountain, into which the gigantic projectile could plow its way without doing any damage. Tom was going to fire two kinds of cannon balls—a solid one, and one containing an explosive.

The gun was so mounted that the muzzle could be elevated or depressed, or swung from side to side. In this way the range could be varied. Tom estimated that the greatest possible range would be thirty miles. It could not be more than that, he decided, and he hoped it would not be much less. This extreme range could be attained by elevating the gun to exactly the proper pitch. Of course, any shorter range could, within certain limits, also be reached.

The gun was pointed slantingly up the valley, and there was ample room to attain the thirty-mile range without doing any damage.

At the head of the valley, some miles from where the giant cannon was mounted, was an immense dam, built recently by a water company for impounding a stream and furnishing a supply of drinking water for a distant city. At the other end of the valley was the thriving village of Preston. A railroad ran there, and it was to Preston station that Tom's big gun had been sent, to be transported afterward, on specially made trucks, drawn by powerful autos, to the place where it was now mounted.

Tom had been obliged to buy a piece of land on which to build the temporary carriage, and also contract for a large slice of the opposite mountain, as a target against which to fire his projectiles.

The valley, as I have said, was desolate. It was thickly wooded in spots, and in the centre, near the big dam, which held back the waters of an immense artificial lake, was a great hill, evidently a relic of some glacial epoch. This hill was a sort of division between two valleys.

Tom, Ned, Mr. Damon, with Koku, and some of the employees of the steel company, had hired a deserted farmhouse not far from the place where the gun was being mounted. In this they lived, while Tom directed operations.

"The paper says 'clear' tomorrow," read Ned, on his return. "'Clear, with freshening winds.'"

"That means rain, with no wind at all," declared Tom, with a sigh. "Well, it can't be helped. As Mr. Damon says, it will clear some time."

"Bless my overshoes!" exclaimed the odd gentleman. "It always has cleared; hasn't it?"

No one could deny this.

There came a slackening in the showers, and Tom and Ned, donning raincoats, went out to see how the work was progressing. They found the men from the steel concern busy at the great piece of engineering.

"How are you coming on?" asked Tom of the foreman.

"We could finish it in two days if this rain would only let up," replied the man.

"Well, let's hope that it will," observed Tom.

"If it doesn't, there's likely to be trouble up above," went on the foreman, nodding in the direction of the great dam.

"What do you mean?"

"I mean that the water is getting too high. The dam is weakening, I heard."

"Is that so? Why, I thought they had made it to stand any sort of a flood."

"They evidently didn't count on one like this. They've got the engineer who built it up there, and they're doing their best to strengthen it. I also heard that they're preparing to dynamite it to open breeches here and there in it, in case it is likely to give way suddenly."

"You don't mean it! Say, if it does go out with a rush it will wipe out the village."

"Yes, but it can't hurt us," went on the foreman. "We're too high up on the side of the hill. Even if the dam did burst, if the course of the water could be changed, to send it down that other valley, it would do no harm, for there are no settlements over there," and he pointed to the distant hill.

It was near this hill that Tom intended to direct his projectiles, and on the other side of it was another valley, running at right angles to the one crossed by the dam.

As the foreman had said, if the waters (in case the dam burst) could be turned into this transverse valley, the town could be saved.

"But it would take considerable digging to open a way through that side of the mountain, into the other valley," went on the man.

"Yes," said Tom, and then he gave the matter no further thought, for something came up that needed his attention.

"Have you your explosive here?" asked the foreman of the young inventor the next day, when the weather showed signs of clearing.

"Yes, some of it," said Tom. "I have another supply in a safe place in the village. I didn't want to bring too much here until the gun was to be fired. I can easily get it if we need it. Jove! I wish it would clear. I want to get out in my Humming Bird, but I can't if this keeps up." Tom had brought one of his speedy little airships with him to Preston.

The following day the clouds broke a little, and on the next the sun shone. Then the work on the gun went on apace. Tom and his friends were delighted.

"Well, I think we can try a shot tomorrow!" announced Tom with delight on the evening of the first clear day, when all hands had worked at double time.

"Bless my powder-horn!" exclaimed Mr. Damon. "You don't mean it!"

"Yes, the gun is all in place," went on the young inventor. "Of course, it's only a temporary carriage, and not the disappearing one I shall eventually use. But it will do. I'm going to try a shot tomorrow. Everything is in readiness."

There came a knock on the door of the room Tom had fitted up as an office in the old farmhouse.

"Who is it?" he asked.

"Me—Koku," was the answer.

"Well, what do you want, Koku?"

"Man here say him must see Master."

Tom and Ned looked at each other, suspicion in their eyes.

"Maybe it's that spy again," whispered Ned.

"If it is, we'll be ready for him," murmured his chum. "Show him in, Koku, and you come in too."

But the man who entered at once disarmed suspicion. He was evidently a workman from the dam above, and his manner was strangely excited.

"You folks had better get out of here!" he exclaimed.

"Why?" asked Tom, wondering what was going to happen.

"Why? Because our dam is going to burst within a few hours. I've been sent to warn the folks in town in time to let them take to the hills. You'd better move your outfit. The dam can't last twenty-four hours longer!"



CHAPTER XVII

THE BURSTING DAM

"Bless my fountain pen!" exclaimed Mr. Damon. "You don't mean it!"

"I sure do!" went on the man who had brought the startling news. "And the folks down below aren't going to have any more time than they need to get out of the way. They'll have to lose some of their goods, I reckon. But I thought I'd stop on my way down and warn you. You'd better be getting a hustle on."

"It's very kind of you," spoke Torn; "but I don't fancy we are in any danger."

"No danger!" cried the man. "Say, when that water begins to sweep-down here nothing on earth can stop it. That big gun of yours, heavy as it is, will be swept away like a straw, I know—I saw the Johnstown flood!"

"But we're so high up on the side of the hill, that the water won't come here," put in Ned. "We had that all figured out when we heard the dam was weak. We're not in any danger; do you think so, Tom?"

"Well, I hardly do, or I would not have set the gun where I did. Tell me," he went on to the man, "is there any way of opening the dam, to let the water out gradually?"

"There is, but the openings are not enough with such a flood as this. The engineers never counted on so much rain. It's beyond any they ever had here. You see, there was a small creek that we dammed up to make our lake. Some of the water from the spillway flows into that now, but its channel won't hold a hundredth part of the flood if the dam goes out.

"You'd better move, I tell you. The dam is slowly weakening. We've done all we can to save it, but that's out of the question. The only thing to do is to run while there's time. We've tried to make additional openings, but we daren't make any more, or the wall will be so weakened that it will go out in less than twenty-four hours.

"You've had your warning, now profit by it!" he added. "I'm going to tell those poor souls down in the valley below. It will be tough on them; but it can't be helped."

"If the dam bursts and the water could only be turned over into the transverse valley, this one would be safe," said Tom, in a low voice.

"Yes, but it can't be done!" the messenger exclaimed. "Our engineers thought of that, but it would take a week to open a channel, and there isn't time. It can't be done!"

"Maybe it can," spoke Tom, softly, but no one asked him what he meant.

"Well, I must be off," the man went on. "I've done my duty in warning you."

"Yes, you have," agreed Tom, "and if any damage comes to us it will be our own fault. But I don't believe there will."

The man hastened out, murmuring something about "rash and foolhardy people."

"What are you going to do, Tom?" asked Ned.

"Stay right here."

"But if the dam bursts?"

"It may not, but, if it does, we'll be safe. I have had a look at the water, and there's no chance for it to rise here, even if the whole dam went out at once, which is not likely. Don't worry. We'll be all right."

"Bless my checkbook!" cried Mr. Damon. "But what about those poor people in the valley?"

"They will have time to flee, and save their lives," spoke the young inventor; "but they may lose their homes. They can sue the water company for damages, though. Now don't do any more worrying, but get to bed, and be ready for the test tomorrow. And the first thing I do I'm going to have a little flight in the Humming Bird to get my nerves in trim. This long rain has gotten me in poor shape. Koku, you must be on the alert tonight. I don't want anything to happen to my gun at the last minute."

"Me watch!" exclaimed the giant, significantly, as he picked up a heavy club.

"Do you anticipate any trouble?" asked Ned, anxiously.

"No, but it's best to be on the safe side," answered Tom. "Now let's turn in."

Certainly the next day, bright and sunshiny as it broke, had in it little of impending disaster. The weather was fine after the long-continued rains, and the whole valley seemed peaceful and quiet. At the far end could be seen the great dam, with water pouring over it in a thin sheet, forming a small stream that trickled down the centre of the valley, and to the town below.

But, through great pipes that led to the drinking system, though they were unseen, thundered immense streams of solid water, reducing by as much as the engineers were able the pressure on the concrete wall.

Tom and Ned, in the Humming Bird, took a flight out to the dam shortly after breakfast, when the steel men were putting a few finishing touches to the gun carriage, ready for the test that was to take place about noon.

"It doesn't look as though it would burst," observed Ned, as the aircraft hovered over the big artificial lake.

"No," agreed Tom. "But I suppose the engineers want to be on the safe side in case of damage suits. I want to take a look at the place where the other valley comes up to this at right angles."

He steered his powerful little craft in that direction, and circled low over the spot.

"A bursting projectile, about where that big white stone is, would do the trick," murmured Tom.

"What trick?" asked Ned, curiously.

"Oh, I guess I was talking to myself," admitted Tom, with a laugh. "I may not have to do it, Ned."

"Well, you're talking in riddles today, all right, Tom. When you get ready to put me wise, please do."

"I will. Now we'll get back, and fire our first long shot. I do hope I make a record."

There was much to be done, in spite of the fact that the foreman of the steel workers assured Tom that all was in readiness. It was some time that afternoon when word was given for those who wished to retire to an improvised bomb-proof. Word had previously been sent down the valley so that no one, unless he was looking for trouble, need be in the vicinity of the gun, nor near where the shots were to land.

Through powerful glasses Tom and Ned surveyed the distant mountain that was to be the target. Several great squares of white cloth had been put at different bare spots to make the finding of the range easy.

"I guess we're ready now," announced the young inventor, a bit nervously. "Bring up the powder, Koku."

"Me bring," exclaimed the giant, calmly, as he went to the bomb-proof where the powerful explosive was kept.

The great projectile was in readiness to be slung into the breech by means of the hoisting apparatus, for it weighed close to two tons. It was carefully inserted under Tom's supervision. It carried no bursting charge, for Tom's first shot was merely to establish the extreme range that his cannon would shoot.

"Now the powder," called the young inventor. To avoid accidents Koku handled this himself, the hoisting apparatus being dispensed with. Tom figured out that five hundred pounds of his new, powerful explosive would be about the right amount to use, and this quantity, divided into several packages to make the handling easier, was quickly inserted in the breech of the gun by Koku.

"Bless my doormat!" cried Mr. Damon, who stood near, looking nervously on. "Don't drop any of that."

"Me no drop," was the answer.

Tom was busily engaged in figuring on a bit of paper, and Ned, who looked over his shoulder, saw a complicated compilation that looked to be a combination of geometry, algebra, differential calculus and other higher mathematics.

"What are you doing, Tom?" he asked.

"I'm trying to confirm my own theories by means of figures, to see if I can really reach that farthest target."

"What, not the one thirty miles away.

"That's it, Ned. I want to get a thirty-mile range if I can."

"It isn't possible, Tom."

"Bless my tape measure! I should say not!" cried Mr. Damon.

"We'll see," replied Tom, quietly. "Put in the primer, Ned; and, Koku, close the breech and slot it home."

In a few seconds the great gun was ready for firing.

"Now," said Tom, "this thing may be all right, and it may not. The only thing that can cause an accident will be a flaw in the steel. No one can guard against that. So, in order to be on the safe side, we will all go into the bomb-proof, and I will fire the gun from there. The wires are long enough."

They all agreed that this was good advice, and soon the steel men and Tom's friends were gathered in a sort of cave that had been hollowed out in the side of the hill, and at an angle from the big gun.

"If it does burst—which I hope it won't," said Tom, "the pieces will fly in straight lines, so we will be safe enough here. Ned, are you are ready at the instruments?"

"Yes, Tom."

"I want you to note the registered muzzle velocity. Mr. Damon, you will please read the pressure gauge. After I press the button I'm going to watch the landing of the projectile through the telescope."

The gun had been pointed, as I have said, at the farthest target—one thirty miles away, telescope sights on the giant cannon making this possible.

"All ready!" cried Tom.

"All ready," answered Ned.

There was a tense moment; Tom's thumb pressed home the electric button, and then came the explosion.

It seemed for a moment as if everyone was lifted from his feet. They had all stood on their tiptoes, and opened their mouths to lessen the shock, but even then it was terrific. The very ground shook—from the roof of their cave small stones and gravel rattled down on their heads. Their ear-drums were numbed from the shock. And the noise that filled the valley seemed like a thousand thunderbolts merged into one.

Tom rushed from the bombproof, dropping the electric button. He caught sight of his gun, resting undisturbed on the improvised carriage.

"Hurray!" he cried in delight. "She stood the charge all right. And look! look!" he cried, as he pointed the glasses toward the distant hillside. "There goes my projectile as straight as an arrow. There! By Caesar, Ned! It landed within three feet of the target! Oh, you beauty!" he yelled at his giant cannon. "You did all I hoped you would! Thirty miles, Ned! Think of that! A two-ton projectile being shot thirty miles!"

"It's great, Tom!" yelled his chum, clapping him on the back, and capering about. "It's the longest shot on record."

"It certainly is," declared the foreman of the steel workers, who had helped in casting many big guns. "No cannon ever made can equal it. You win, Tom Swift!"

"Bless my armor plate!" gasped Mr. Damon. "What attacking ship against the Panama Canal could float after a shot like that."

"Not one," declared Tom; "especially after I put a bursting charge into the projectile. We'll try that next."

By means of compressed air the gases and some particles of the unexploded powder were blown out of the big cannon. Then it was loaded again, the projectile this time carrying a bursting charge of another explosive that would be set off by concussion.

Once more they retired to the bombproof, and again the great gun was fired. Once more the ground shook, and they were nearly deafened by the shock.

Then, as they looked toward the distant hillside, they saw a shower of earth and great rocks rise up. It was like a sand geyser. Then, when this settled back again, there was left a gaping hole in the side of the mountain.

"That does the business!" cried Tom. "My cannon is a success!"

The last shot did not go quite as far as the first, but it was because a different kind of projectile was used. Tom was perfectly satisfied, however. Several more trials were given the gun, and each one confirmed the young inventor in his belief that he had made a wonderful weapon.

"If that doesn't fortify the Panama Canal nothing will," declared Ned.

"Well, I hope I can convince Uncle Sam of that," spoke Tom, simply.

The muzzle velocity and the pressure were equal to Tom's highest hopes. He knew, now, that he had hit on just the right mixture of powder, and that his gun was correctly proportioned. It showed not the slightest strain.

"Now we'll try another bursting shell," he said, after a rest, during which some records were made. "Then we'll call it a day's work. Koku, bring up some more powder. I'll use a little heavier charge this time."

It was while the gun was being loaded that a horseman was seen riding wildly down the valley. He was waving a red flag in his hand.

"Bless my watch chain!" cried Mr. Damon. "What's that?"

"It looks as though he was coming to give us a warning," suggested the steel foreman.

"Maybe someone has kicked about our shooting," remarked Ned.

"I hope not," murmured Tom.

He looked at the horseman anxiously. The rider came nearer and nearer, wildly waving his flag. He seemed to be shouting something, but his words could not be made out. Finally he came near enough to be heard.

"The dam! The dam!" he cried. "It's bursting. Your shots have hastened it. The cracks are widening. You'd better get away!" And he galloped on.

"Bless my toilet soap!" gasped Mr. Damon.

"I was afraid of this!" murmured Tom. "But, since our shots have hastened the disaster, maybe we can avert it."

"How?" demanded Ned.

"I'll show you. All hands come here and we'll shift this gun. I want it to point at that big white stone!" and he indicated an immense boulder, well up the valley, near the place where the two great gulches joined.



CHAPTER XVIII

THE DOPED POWDER

"What are you going to do, Tom?" cried Ned, as he, with the others, worked the hand gear that shifted the big gun. When it was permanently mounted electricity would accomplish this work. "What's your game, Tom?"

"Don't you remember, Ned? When we were talking about the chance of the dam bursting, I said if the current of suddenly released water could be turned into the other valley, the people below us would be saved."

"Yes."

"Well, that's what I'm going to do. I'm going to fire a bursting shell at the point where the two valleys come together. I'll break down the barrier of rock and stone between them."

"Bless my shovel and hoe!" cried Mr. Damon.

"If we can turn enough of the water into the other valley, where no one lives, and where it can escape into the big river there, the amount that will flow down this valley will be so small that only a little damage will be done."

"That's right!" declared the steel foreman, as he caught Tom's idea. "It's the only way it could be done, too, for there won't be time to make the necessary excavation any other way. Is the gun swung around far enough, Mr. Swift?"

"No, a little more toward me," answered Tom, as he peered through the telescope sights. "There, that will do. Now to get the proper elevation," and he began to work the other apparatus, having estimated the range as well as he could.

In a few seconds the giant cannon was properly trained on the white rock. Meanwhile the horseman, with his red flag, had continued on down the valley. In spite of his warning of the night before, it developed that a number had disregarded it, and had remained in their homes. Most of the inhabitants, however, had fled to the hills, to stay in tents, or with such neighbors as could accommodate them. Some lingered to move their household goods, while others fled with what they could carry.

It was to see that the town was deserted by these late-stayers that the messenger rode, crying his warning as did the messenger at the bursting of the Johnstown dam twenty-odd years ago.

"The projectile!" cried Tom, as he saw that all was in readiness. "Lively now! I can see the top of the dam beginning to crumble," and he laid aside the telescope he had been using.

The projectile, with a heavy charge of bursting powder, was slung into the breech of the gun.

"Now the powder, Koku!" called Tom. "Be quick; but not so fast that you drop any of it."

"Me fetch," responded the giant, as he hastened toward the small cave where the explosive was kept. As the big man brought the first lot, and Ned was about to insert it in the breech of the gun, behind the projectile, Tom exclaimed:

"Just let me have a look at that. It's some that I first made, and I want to be sure it hasn't gone stale."

Critically he looked at the powerful explosive. As he did so a change came over his face.

"Here, Koku!" the young inventor said. "Where did you get this?"

"In cave, Master."

"Is there any more left?"

"Only enough for this one shoot."

"By Jove!" muttered Tom. "There's been some trick played here!" and he set off on a run toward the bomb-proof.

"What's the matter?" cried Ned, as he noticed the agitation of his chum.

"The powder has been doped!" yelled Tom. "Something has been put in it to make it nonexplosive. It's no good. It wouldn't send that shell a thousand yards, and it's got to go five miles to do any good. My plan won't work."

"Doped the powder?" gasped Ned. "Who could have done it?"

"I don't know. There must have been some spy at work. Quick, run and ask the foreman if any of his men are missing. I'll see if there's enough of the good powder left to break down the barrier!"

Ned was away like a shot, while the others, not knowing what to make of the strange conduct of the two lads, looked on in wonder. Tom raced toward the cave where the powder was stored, Koku following him.

"Bless my shoe laces!" cried Mr. Damon. "Look at the dam now!"

They gazed to where he pointed. In several places the concrete spillway had crumbled down to a ragged edge, showing that the solid wall was giving way. The amount of water flowing over the dam was greater now. The creek was steadily rising. Down the valley the horseman with the red flag was but a speck in the distance.

"What can I do? What can I do?" murmured Tom. "If all the powder there is left has been doped, I can't save the town! What can I do? What can I do?"

Ned had reached the foreman, who, with his helpers, was standing about the big gun.

"Have any of your men left recently?" yelled Ned.

"Any of my men left? What do you mean?

"Schlichter went yesterday," said the timekeeper. "I thought he was in quite a hurry to get his money, too."

"Schlichter gone!" exclaimed the foreman. "He was no good anyhow. I think he was a sort of Anarchist; always against the government, the way he talked. So he has left; eh? But what's the matter, Ned?"

"Something wrong with the powder. Tom can't shoot the cannon and turn aside the water to save the town. Some of his enemies have been at work. Schlichter leaving at this time, and in such hurry, makes it look suspicious."

"It sure does! And, now I recall it, I saw him yesterday near your powder magazine. I called him down for it, for I knew Tom Swift had given orders that only his own party was to go near it. So the powder is doped; eh?"

"Yes! It's all off now."

He turned to see Tom approaching on the run.

"Any good powder left?" asked Ned.

"Not a pound. Did you hear anything?"

"Yes, one man has disappeared. Oh, Tom, we've got to fail after all! We can't save the town!"

"Yes, we can, Ned. If that dam will only hold for half an hour more."

"What do you mean

"I mean that I have another supply of good powder in the village. I secreted some there, you remember I told you. If I can go get that, and get back here in time, I can break down the barrier with one shot, and save Preston."

"But you never can make the trip there and back in time, with the powder, Tom. It's impossible. The dam may hold half an hour, or it may not. But, if it does, you can't do anything!"

"I can't? Well, I'm going to make a big try, Ned. You stay on the job here. Have everything ready so that when I get back with the new explosive, which I hope hasn't been tampered with, I can shove it into the breech, and set it off. Have the wires, primers and button all ready for me."

Then Tom set off on the run.

"Where are you going?" gasped his chum. "You can never run to Preston and back in time."

"I don't intend to. I'm going in my airship. Koku, never mind bringing the rest of the powder from the cave. It's no good. Run out the Humming Bird. I'm going to drive her to the limit. I've just got to get that powder here on time!"

"Bless my timetable!" gasped Mr. Damon. "That's the only way it can be done. Lucky Tom brought the airship along!"

The young inventor, pausing only to get some cans for the explosive, and some straps with which to fasten them in the monoplane, leaped into the speedy craft.

The motor was adjusted; Koku whirled the propeller blades. There was a staccato succession of explosions, a rushing, roaring sound, and then the craft rose like a bird, and Tom circled about, making a straight course for the distant town, while below him the creek rose higher and higher as the dam continued to crumble away.



CHAPTER XIX

BLOWING DOWN THE BARRIER

"Can you see anything of him, Ned?"

"Not a thing, Mr. Damon. Wait—hold on—no! It's only a bird," and the lad lowered the glasses with which he had been sweeping the sky. looking for his chum returning in his airship with the powder.

"He'd better hurry," murmured the foreman. "That dam can't last much longer. The water is rising fast. When it does go out it will go with a rush. Then good-bye to the village of Preston."

"Bless my insurance policy!" cried Mr. Damon. "Don't say such things, my friend."

"But they're true!" insisted the man. "You can see for yourself that the cracks in the dam are getting larger. It will be a big flood when it does come. And I'm not altogether sure that we're safe up here," he added, as he looked down the sides of the hill to where the creek was now rapidly becoming a raging torrent.

"Bless my hat-band!" gasped Mr. Damon. "You—you are getting on my nerves!"

"I don't want to be a calamity howler," went on the foreman; "but we've got to face this thing. We'd better get ready to vamoose if Tom Swift doesn't reach here in time to fire that shot—and he doesn't seem to be in sight."

Once more Ned swept the sky with his glasses. The roar of the water below them could be plainly heard now.

"I wish I could get hold of that rascally German," muttered the foreman. "I'd give him more than a piece of my mind. It will be his fault if the town is destroyed, for Tom's plan would have saved it. I wonder who he can be, anyhow?"

"Some spy," declared Ned. "We've been having trouble right along, you know, and this is part of the game. I have some suspicions, but Tom doesn't agree with me. Certainly the fellow, whatever his object, has made trouble enough this time."

"I should say so," agreed the foreman.

"Look, Ned!" cried Mr. Damon. "Is that a bird; or is it Tom?" and he pointed to a speck in the sky. Ned quickly focused his glasses on it.

"It's Tom!" he cried a second later. "It's Tom in the Humming Bird!"

"Thank Heaven for that!" exclaimed Mr. Damon, fervently, forgetting to bless anything on this occasion. "If only he can get here in time!"

"He's driving her to the limit!" cried Ned, still watching his chum through the glass. "He's coming!"

"He'll need to," murmured the foreman, grimly. "That dam can't last ten minutes more. Look at the people fleeing from the valley!"

He pointed to the north, and a confused mass of small black objects—men, women and children, doubtless, who had lingered in spite of the other warning—could be seen clambering up the sides of the valley.

"Is everything ready at the gun?" asked Mr. Damon.

"Everything," answered Ned, whom Tom had instructed in all the essentials. "As soon as he lands we'll jam in the powder, and fire the shot."

"I hope he doesn't land too hard, with all that explosive on board," murmured the foreman.

"Bless my checkerboard!" cried Mr. Damon. "Don't suggest such a thing."

"I guess we can trust Tom," spoke Ned.

They looked up. The distant throb of the monoplane's motor could now be heard above the roar of the swollen waters. Tom could be seen in his seat, and beside him, in the other, was a large package.

Nearer and nearer came the monoplane. It began to descend, very gently, for well Tom Swift knew the danger of hitting the ground too hard with the cargo he carried.

He described a circle in the air to check his speed. Then, gently as a bird, he made a landing not far from the gun, the craft running easily over one of the few level places on the side of the hill. Tom yanked on the brake, and the iron-shod pieces of wood dug into the ground, checking the progress of the monoplane on its bicycle wheels.

"Have you got it, Tom?" yelled Ned.

"I have," was the answer of the young inventor as he leaped from his seat.

"Is it good powder?" asked the foreman, anxiously.

"I don't know," spoke Tom. "I didn't have time to look. I just rushed up to where I had stored it, got some out and came back with the motor at full speed. Ran into an airpocket, too, and I thought it was all up with me when I began to fall. But I managed to get out of it. Say, we're going to have it nip and tuck here to save the village."

"That's what!" agreed the foreman, as he helped Koku take the cans of explosive.

"Wait until I look at it," suggested Tom, as he opened one. His trained eye and touch soon told him that this explosive had not been tampered with.

"It's all right!" he shouted. "Into the gun with it, and we'll see what happens."

It was the work of only a few moments to put in the charge. Then, once more, the breech-block was slotted home, and the trailing electric wires unreeled to lead to the bomb-proof.

Tom Swift took one last look through the telescope sights of his giant cannon. He changed the range slightly by means of the hand and worm-screw gear, and then, with the others, ran to the shelter of the cave. For, though the gun had stood the previous tests well, Tom had used a heavier charge this time, both in the firing chamber and in the projectile, and he wanted to take no chances.

"All ready?" asked the young inventor, as he looked around at his friends gathered in the cave.

"I—I guess so," answered Ned, somewhat doubtfully.

Tom hesitated a moment, then, as his fingers stiffened to press the electric button there sounded to the ears of all a dull, booming sound.

"The dam! It has given way!" cried Ned.

"That's it!" shouted the foreman. "Fire!"

Tom pressed the button. Once again was that awful tremor of the earth—the racking shake—the terrific explosion and a shock that knocked a couple of the men down.

"All right!" shouted Tom. "The gun held together. It's safe to go out. We'll see what happened!"

They all rushed from the shelter of the cave. Before them was an awe-inspiring sight. A great wall of water was coming down the valley, from a large opening in the centre of the dam. It seemed to leap forward like a race horse.

Tom declared afterward that he saw his projectile strike the barrier that separated one valley from the other, but none of the others had eyes-sight as keen as this—and perhaps Tom was in error.

But there was no doubt that they all saw what followed. They heard a distant report as the great projectile burst. Then a wall of earth seemed to rise up in front of the advancing wall of water. High into the air great stones and masses of dirt were thrown.

"A good shot!" cried the foreman. "Just in the right place, Tom Swift!"

For a moment it was as though that wall of water hesitated, not deciding whether to continue on down the populated valley, or to swing over into the other gash where it could do comparatively little harm. It was a moment of suspense.

Then, as Tom's great shot had, by means of the exploding projectile, torn down the barrier, the water chose the more direct and shorter path. With a mighty roar, like a distant Niagara, it swept into the new channel the young inventor had made. Into the transverse valley it tumbled and tossed in muddy billows of foam, and only a small portion of the flood added itself to the already swollen creek.

The village of Preston had been saved by the shot from Tom's giant cannon.



CHAPTER XX

THE GOVERNMENT ACCEPTS

"Whew! Let me sit down somewhere and get my breath!" gasped Tom, when it was all over.

"I should think you would want a bit of quiet," replied Ned. "You've been on the jump since early morning."

"Bless my dining-room table!" cried Mr. Damon. "I should say so! I'll go tell the cook to get us all a good meal—we need it," for a competent cook had been installed in the old farmhouse where Tom and his party had their headquarters.

"But you did the trick, Tom, old man!" exclaimed Ned, fervently, as he looked down the valley and saw the receding water. For, with the opening of the channel into the other valley the flood, at no time particularly dangerous near Preston, was subsiding rapidly.

"He sure did," declared the foreman. "No one else could have done it, either."

"Oh, I don't know," spoke Tom, modestly. "It just happened so. There was one minute, though, after I got to the place in Preston where I had stored the powder, that I didn't know whether I would succeed or not."

"How was that?" asked Mr. Damon.

"Why, in my hurry and excitement I forgot the key to the underground storeroom where I had put the explosive. I knew there was no time to get another, so I took a chance and burst in the door with an axe I found in the freight depot."

"I should say you did take a chance!" declared Ned, who knew how "freaky" the high explosive was, and how likely it was, at times, to be set off by the least concussion.

"But it came out all right," went on Tom. "I bundled it into the other seat of my Humming Bird, and started back."

"Had most of the folks left town?" asked the foreman.

"Nearly all," replied Tom. "The last of them were hurrying away as I left. And it shows how scared they were, they didn't pay any attention to me and my flying machine, though I'll wager some of them never saw one before."

"Well, they don't need to be scared any more," put in Mr. Damon "You saved their homes for them, Tom."

"I'd like to get hold of the fellow who doped my powder; that's what I'd like to do," murmured the young inventor. "Ned, we'll have to be doubly watchful from now on. But I must take a look at my gun. That last charge may have strained it."

But the giant cannon was as perfect as the day it was turned out of the shop. Not even the extra charge of the powerful explosive had injured it.

"That's fine!" cried Tom, as he looked at every part. "As soon as this flood is over we'll try some more practice shots. But we're all entitled to a rest now."

The great gun was covered with tarpaulins to protect it from the weather, and then all retired to the house for a bountiful meal. Late that afternoon nearly all signs of the flood had disappeared, save that along the edges of the creek was much driftwood, showing the height to which the creek had risen. But it would have gone much higher had it not been for Tom's timely shot.

The water from the impounded lake continued to pour down into the cross valley, and did some damage, but nothing like what would have followed its advent into Preston. The few inhabitants of the gulch into which the young inventor had directed the flood had had warning, and had fled in time. In Preston, some few houses nearest the banks of the rising creek were flooded, but were not carried away.

The following day some of the officers of the water company paid a visit to Tom, to thank him for what he had done. But for him they would have been responsible for great property damage, and loss of life might have followed.

They intended to rebuild the dam, they said, on a new principle, making it much stronger.

"And," said the president, "we will have an emergency outlet gate into that valley you so providentially opened for us, Mr. Swift. Then, in time of great rain, we can let the water out slowly as we need to."

Tom's chief anxiety, now, was to bring his perfected gun to the notice of the United States Government officials. To have them accept it, he knew he must give it a test before the ordnance board, and before the officers of the army and navy. Accordingly he prepared for this.

He ordered several new projectiles, some of a different type from those heretofore used, and leaving Koku and Ned in charge of the gun, went back to Shopton to superintend the manufacture of an additional supply of his explosive. He took care, too, that no spies gained access to it.

Then, with a plentiful supply of ammunition and projectiles, Tom resumed his practice in the lonely valley. He had, in the meanwhile, sent requests to the proper government officials to come and witness the tests.

At first he met with no success, and he learned, incidentally, that General Waller had built a new gun, the merits of which he was also anxious to show.

"It's a sort of rivalry between us," said Tom to Ned.

But, in a way, fortune favored our hero. For when General Waller tested his new gun, though it did not burst, it did not come up to expectations, and its range was not as great as some of the weapons already in use.

Then, too, Captain Badger acted as Tom's friend at court. He "pulled wires" to good advantage, and at last the government sent word that one of the ordnance officers would be present on a certain day to witness the tests.

"I wish the whole board had come," said Tom. "Probably they have only sent a young fellow, just out of West Point, who will turn me down.

"But I'm going to give him the surprise of his life; and if he doesn't report favorably, and insist on the whole board coming out here, I'll be much disappointed."

Tom made his preparations carefully, and certainly Captain Waydell, the young officer who came to represent Uncle Sam, was impressed. Tom sent shell after shell, heavily charged, against the side of the mountain. Great holes and gashes were torn in the earth. The gun even exceeded the range of thirty miles. And the heaviest armor plate that could be procured was to the projectiles of the giant cannon like cheese to a revolver bullet.

"It's great, Mr. Swift! Great!" declared the young captain. "I shall strongly recommend that the entire board see this test." And when Tom let him fire the gun himself the young man was more than delighted.

He was as good as his word, and a week later the entire ordnance board, from the youngest member to the grave and grizzled veterans, were present to witness the test of Tom's giant cannon.

It is needless to say that it was successful. Tom and Ned, not to mention Mr. Damon, Koku and every loyal member of the steel working gang, saw to it that there was no hitch. The solid shots were regarded with wonder, and when the explosive one was sent against the hillside, making a geyser of earth, the enthusiasm was unbounded.

"We shall certainly recommend your gun, Mr. Swift," declared the Chief of Staff. "It does just what we want it to do, and we have no doubt that Congress will appropriate the money for several with which to fortify the Panama Canal."

"The gun is most wonderful," spoke a voice with a German accent. "It is surprising!"

Tom and Ned both started. They saw an officer, evidently a foreigner, resplendent in gold trimmings, and with many medals, standing near the secretary of the ordnance board.

"Yes, General von Brunderger," agreed the chief, "it is a most timely invention. Mr. Swift, allow me to present you to General von Brunderger, of the German army, who is here learning how Uncle Sam does things."

Tom bowed and shook hands. He glanced sharply at the German, but was sure he had never seen him before. Then all the board, and General von Brunderger, who, it appeared, was present as an invited guest, examined the big cannon critically, while Tom explained the various details.