Victor Appleton.......................................................................................................................................1

CHAPTER I. TOM IS PUZZLED ...........................................................................................................1

CHAPTER II. A FIRE ALARM ..............................................................................................................5

CHAPTER III. A DESPERATE BATTLE.............................................................................................8

CHAPTER IV. SUSPICIONS...............................................................................................................12

CHAPTER V. A QUEER STRANGER................................................................................................15

CHAPTER VI. THE AERIAL WARSHIP ............................................................................................19

CHAPTER VII. WARNINGS...............................................................................................................24

CHAPTER VIII. A SUSPECTED PLOT..............................................................................................28

CHAPTER IX. THE RECOIL CHECK................................................................................................31

CHAPTER X. THE NEW MEN ............................................................................................................34

CHAPTER XI. A DAY OFF.................................................................................................................38

CHAPTER XII. A NIGHT ALARM .....................................................................................................43

CHAPTER XIII. THE CAPTURE........................................................................................................47

CHAPTER XIV. THE FIRST FLIGHT................................................................................................50

CHAPTER XV. IN DANGER ...............................................................................................................54

CHAPTER XVI. TOM IS WORRIED..................................................................................................57

CHAPTER XVII. AN OCEAN FLIGHT..............................................................................................61

CHAPTER XVIII. IN A STORM ..........................................................................................................65

CHAPTER XIX. QUEER HAPPENINGS ............................................................................................69

CHAPTER XX. THE STOWAWAYS ..................................................................................................72

CHAPTER XXI. PRISONERS ..............................................................................................................76

CHAPTER XXII. APPREHENSIONS ..................................................................................................78

CHAPTER XXIII. ACROSS THE SEA ................................................................................................81

CHAPTER XXIV. THE LIGHTNING BOLT......................................................................................83

CHAPTER XXV. FREEDOM..............................................................................................................87

"Blue! Say, Ned, I'd turn red, green, yellow, or any other color of the rainbow, if I thought it would help

Ned Newton, the chum and companion of Tom Swift, gave vent to a whistle of surprise, as he gazed at the

young fellow sitting opposite him, near a bench covered with strangelooking tools and machinery, while

Ranged on the sides of the room were models of many queer craft, most of them flying machines of one sort

or another, while through the open door that led into a large shed could be seen the outlines of a speedy

"As bad as that, eh, Tom?" went on Ned. "I thought something was up when I first came in, but, if you'll

excuse a second mention of the color scheme, I should say it was bluedecidedly blue. You look as though

you had lost your last friend, and I want to assure you that if you do feel that way, it's dead wrong. There's

"Bless my gasoline tank!" exclaimed Tom, with a laugh, in imitation of the gentleman Ned Newton had

"And there are Eradicate, and Koku, the giant, just to mention a couple of others," went on Ned, with a smile.

"Well, what is it then? Here I go and get a halfholiday off from the bank, and just at the busiest time, too, to

come and see you, and I find you in a brown study, looking as blue as indigo, and maybe you're all yellow

"Quite a combination of colors," admitted Tom. "But it isn't what you think. It's just that I'm puzzled, Ned."

"Puzzled?" and Ned raised his eyebrows to indicate how surprised he was that anything should puzzle his

"Has anything gone wrong?" Ned asked. "No one is trying to take any of your pet inventions away from you,

"No, not exactly that, though it is about one of my inventions I am puzzled. I guess I haven't shown you my

"Well, I don't know, Tom. Time was when I could keep track of you and your inventions, but that was in your

early days, when you started with a motorcycle and were glad enough to have a motorboat. But, since you've

taken to aerial navigation and submarine work, not to mention one or two other lines of activity, I give up. I

"Well, this isn't so very new," went on the young inventor, for Tom Swift had designed and patented many

new machines of the air, earth and water. "I'm just trying to work out some new problems in aerial

"Come, now, none of that!" exclaimed Tom, with a laugh. "Why, the surface of aerial navigation has only

been scratched. The science is far from being understood, or even made safe, not to say perfected, as water

"And you're working on something new?" asked Ned, as he looked around the shop where he and Tom were

sitting. As the young bank employee had said, he had come away from the institution that afternoon to have a

little holiday with his chum, but Tom, seated in the midst of his inventions, seemed little inclined to jollity.

Through the open windows came the hum of distant machinery, for Tom Swift and his father were the heads

of a company founded to manufacture and market their many inventions, and about their home were grouped

several buildings. From a small plant the business had grown to be a great tree, under the direction of Tom

"And, Ned," he went on, "there's no reason why you shouldn't see it. I've been keeping it a bit secret, until I

had it a little further advanced, but I've got to a point now where I'm stuck, and perhaps it will do me good to

"Not to talk to me, though, I'm afraid. What I don't know about machinery, Tom, would fill a great many

"Well, perhaps you can, just the same, though you may not know a lot of technical things about machines. It

sometimes helps me just to tell my troubles to a disinterested person, and hear him ask questions. I've got dad

half distracted trying to solve the problem, so I've had to let up on him for a while. Come on out and see what

"Sure, Tom, anything to oblige. If you want me to sit in front of your phototelephone, and have my picture

taken, I'm agreeable, even if you shoot off a flashlight at my ear. Or, if you want me to see how long I can

stay under water without breathing I'll try that, too, provided you don't leave me under too long, lead the

"Oh, it isn't anything like that," Tom answered with a laugh. "I might as well give you a few hints, so you'll

"What is itair, earth or water?" asked Ned Newton, for he knew his chum's activities led along all three

"It will be dangerous, too, if I can get it to work. That's what it's intended for."

"But a warship of the air!" cried Ned. "You can't mean it. A warship carries guns, mortars, bombs, and"

"Yes, I know," interrupted Tom, "and I appreciate all that when I called my newest craft an aerial warship."

"But," objected Ned, "an aircraft that will carry big guns will be so large that"

"Then it's finished!" cried Ned eagerly, for he was much interested in his chum's inventions.

"Well, not exactly," Tom said. "But what I was going to tell you was that all guns are not necessarily large.

You can get big results with small guns and projectiles now, for highpowered explosives come in small

packages. So it isn't altogether a question of carrying a certain amount of weight. Of course, an aerial warship

will have to be big, for it will have to carry extra machinery to give it extra speed, and it will have to carry a

certain armament, and a large crew will be needed. So, as I said, it will need to be large. But that problem

"Yes, from the guns, you know. I haven't been able to overcome that, and, until I do, I'm afraid my latest

"I'm afraid I can't help you any," he said. "The only thing I know about recoils is connected with an old

"I took that once, when he didn't know it," Ned proceeded. "It was pretty heavily loaded, for the crows had

been having fun in our cornfield, and dad had been shooting at them. This time I thought I'd take a chance.

"Well, I fired the gun. But it must have had a double charge in it and been rusted at that. All I know is that

after I pulled the trigger I thought the end of the world had come. I heard a clap of thunder, and then I went

"Oh, yes," observed Ned, rubbing his shoulder in a reflective sort of way. "I always thought it was something

like that. But, at the time I put it down to an explosion, and let it go at that."

"No, it wasn't an explosion, properly speaking," said Tom. "You see, when powder explodes, in a gun, or

"You only thought so," returned Tom. "Most of the power went out in front, to force out the shot. Part of it,

of course, was exerted on the barrel of the gunthat was sidewaysbut the strength of the steel held it in.

And part of the force went backward against your shoulder. That part was the recoil, and it is the recoil of the

guns I figure on putting aboard my aerial warship that is giving me such trouble."

"That's it. I can't seem to find a way by which to take up the recoil, and the force of it, from all the guns I

"Not the guns, no. I have the warship of the air nearly done, but I've worked out on paper the problem of the

guns far enough so that I know I'm up against it. It can't be done, and an aerial warship without guns wouldn't

"Mostly. But come, take a look at my latest pet," and Tom arose to lead the way to another shed, a large one

in the distance, toward which he waved his hand to indicate to his chum that there was housed the wonderful

The two chums crossed the yard, threading their way through the various buildings, until they stood in front

"It's in here," he said. "I don't mind admitting that I'm quite proud of it, Ned; that is, proud as far as I've gone.

But the gun business sure has me worried. I'm going to talk it off on you. Hello!" cried Tom suddenly, as he

put a key in the complicated lock on the door, "someone has been in here. I wonder who it is?"

Ned was a little startled at the look on Tom s face and the sound of alarm in his chum's voice.

Tom Swift quickly opened the door of the big shed. It was built to house a dirigible balloon, or airship of

some sort. Ned could easily tell that from his knowledge of Tom's previous inventions.

"I don't know," returned Tom, and then as he looked inside the place, he breathed a sigh of relief.

"Oh, it's you, is it, Koku?" he asked, as a veritable giant of a man came forward.

"Yes, master, it is only Koku and your father," spoke the big chap, with rather a strange accent.

"Oh, is my father here?" asked Tom. "I was wondering who had opened the door of this shed."

"Yes, Tom," responded the elder Swift, coming up to them, "I had a new idea in regard to some of those side

guy wires, and I wanted to try it out. I brought Koku with me to use his strength on some of them."

"That's all right, Dad. Ned and I came out to wrestle with that recoil problem again. I want to try some guns

"You'd better not, Tom," warned his father. "It will never work, I tell you. You can't expect to take up

quickfiring guns and bombs in an airship, and have them work properly. Better give it up."

"I don't believe you will, Tom. This time you have bitten off more than you can chew, to use a homely but

"Well, Dad, we'll see," began Tom easily. "There she is, Ned," he went on. "Now, if you'll come around here

But Tom never finished that sentence, for at that moment there came running into the airship shed an elderly,

short, stout, fussy gentleman, followed by an aged colored man. Both of them seemed very much excited.

"I should say So, Massa Tom!" added the colored man. "I done did prognosticate dat some day de

"What's the matter?" interrupted Tom, jumping forward. "Speak out! Eradicate! Mr. Damon, what is it?"

"Great thunderclaps!" cried Tom. "Come on everybody on the job!" he yelled. "Koku, pull the alarm! If

Instantly the place was in confusion. Tom and Ned, looking from a window of the hangar, saw a billow of

black smoke roll across the yard. But already the private fire bell was clanging out its warning. And, while

the work of fighting the flames is under way, I will halt the progress of this story long enough to give my new

readers a little idea of who Tom Swift is, so they may read this book more intelligently. Those of you who

Tom Swift, though rather young in years, was an inventor of note. His tastes and talents were developed

along the line of machinery and locomotion. Motorcycles, automobiles, motorboats, submarine craft, and,

latest of all, craft of the air, had occupied the attention of Tom Swift and his father for some years.

Mr. Swift was a widower, and lived with Tom, his only son, in the village of Shopton, New York State. Mrs.

Baggert kept house for them, and an aged colored man, Eradicate Sampson, with his mule, Boomerang, did

Among Tom's friends was a Mr. Wakefield Damon, from a nearby village. Mr. Damon was always blessing

something, from his hat to his shoes, a harmless sort of habit that seemed to afford him much comfort. Then

there was Ned Newton, a boyhood chum of Tom's, who worked in the Shopton bank. I will just mention

Mary Nestor, a young lady of Shopton, in whom Tom was more than ordinarily interested. I have spoken of

Koku, the giant. He really was a giant of a man, of enormous strength, and was one of two whom Tom had

brought with him from a strange land where Tom was held captive for a time. You may read about it in a

Tom took Koku into his service, somewhat to the dismay of Eradicate, who was desperately jealous. But poor

Eradicate was getting old, and could not do as much as he thought he could. So, in a great measure, Koku

Tom had begun his inventive work when, some years before this story opens, he had bargained for Mr.

Damon's motorcycle, after that machine had shot its owner into a tree. Mr. Damon was, naturally, perhaps,

much disgusted, and sold the affair cheap. Tom repaired it, made some improvements, and, in the first

volume of this series, entitled "Tom Swift and His Motorcycles," you may read of his rather thrilling

From then on Tom had passed a busy life, making many machines and having some thrilling times with them.

Just previous to the opening of this story Tom had made a peculiar instrument, described in the volume

entitled "Tom Swift and His Photo Telephone." With that a person talking could not only see the features of

the person with whom he was conversing, but, by means of a selenium plate and a sort of camera, a

By means of this invention Tom had been able to make a picture that had saved a fortune. But Tom did not

stop there. With him to invent was as natural and necessary as breathing. He simply could not stop it. And so

we find him now about to show to his chum, Ned Newton, his latest patent, an aerial warship, which,

But just at present other matters than the warship were in Tom's mind. The red shed was on fire.

That mere statement might not mean anything special to the ordinary person, but to Tom, his father, and

"The red shed!" Tom cried. "We mustn't let that get the best of us! Everybody at work! Father, not you,

Even in the midst of the alarm Tom thought of his father, for the aged man had a weak heart, and had on one

occasion nearly expired, being saved just in time by the arrival of a doctor, whom Tom brought to the scene

"Now, you just take care of yourself, Father!" Tom cried. "There are enough of us to look after this fire, I

"I realize that, Dad. But it can't have much of a start yet. Is the alarm ringing, Koku?"

"Yes, Master," replied the giant, in correct but stilted English. "I have set the indicator to signal the alarm in

"Yais, sah! Heah I is!" answered the colored man. "I'll go git mah mule, Boomerang, right away, an' he"

"Don't you bring Boomerang on the scene!" Tom yelled. "When I want that shed kicked apart I can do it

better than by using a mule's heels. And you know you can't do a thing with Boomerang when he sees fire."

"No, you let Boomerang stay where he is. Come on, Ned. We'll see what we can do. Mr. Damon"

"Yes, Tom, I'm right here," answered the peculiar man, for he had come over from his home in Waterford to

pay a visit to his friends, Tom and Mr. Swift. "I'll do anything I can to help you, Tom, bless my necktie!" he

"We've got to get some of the stuff out of the place!" Tom cried. "We may be able to save it, but I can't take a

chance on putting out the fire and letting some of the things in there go up in smoke. Come on!"

Those in the shed where was housed what Tom hoped would prove to be a successful aerial warship rushed to

the open. From the other shops and buildings nearby were pouring men and boys, for the Swift plant

Above the shouts and yells, above the crackle of flames, could be heard the clanging of the alarm bell, set

ringing by Koku, who had pulled the signal in the airship shed. From there it had gone to every building in

the plant, being relayed by the telephone operator, whose duty it was to look after that.

"My, you've got a big enough firefighting force, Tom!" cried Ned in his chum's ear.

"Yes, I guess we can master it, if it hasn't gotten the best of us. Say, it's going some, though!"

Tom pointed to where a shed, painted reda sign of danger could be seen partly enveloped in smoke,

Tom had caught sight of Eradicate and the giant, Koku, unreeling from a central standpipe a long line of

"Not at this fire," was Tom's answer. "There's a lot of calcium carbide in that red shedthat's why it's

redto warn the men of danger. You know what happens when water gets on carbidethere's an explosion,

"Drop that hose!" yelled Tom in louder tones. "Drop it, Rad Koku! Do you want to kill us all!"

Tom's tones and voice were so insistent that the giant and the colored man had no choice but to obey. They

dropped the hose which, half unreeled, lay like some twisted snake in the grass. Had it been pulled out all the

way the water would have spurted from the nozzle, for it was of the automatic variety, with which Tom had

"But what are you going to do, Tom, if you don't use water?" asked Ned, wonderingly.

"I don't knowyet, but I know water is the worst thing you can put on carbide," returned Tom. For all he

spoke Slowly his brain was working fast. Already, even now, he was planning how best to give battle to the

It needed but an instant's thought on the part of Ned to make him understand that Tom was right. It would be

wellnigh fatal to use water on carbide. Those of you who have bicycle lanterns, in which that not very

pleasantsmelling chemical is used, know that if a few drops of water are allowed to drip slowly on the gray

crystals acetylene gas is generated, which makes a brilliant light. But, if the water drips too fast, the gas is

generated too quickly, and an explosion results. In lamps, of course, and in lighting plants where carbide is

used, there are automatic arrangements to prevent the water flowing too freely to the chemical. But Tom

knew if the hose were turned on the fire in the red shed a great explosion would result, for some of the tins of

Yet the fire needed to be coped with. Already the flames were coming through the roof, and the windows and

Several other employees of Tom's plant had made ready to unreel more hose, but the warning of the young

inventor, shouted to Eradicate and Koku, had had its effect. Every man dropped the line he had begun to

"Ha! Massa Tom say drop de hose, but how yo' gwine t' squirt watah on a fire wifout a hose; answer me dat?"

"Me no know," was the slow answer. "I guess Koku go pull shed down and stamp out fire."

"Huh! Maybe yo' could do dat in cannibal land, where yo' all come from," spoke Eradicate, "but yo' can't do

dat heah! 'Sides, de red shed will blow up soon. Dere's suffin' else in dere except carbide, an' dat's gwine t' go

"Maybe you get your strong manmule, Boomerang," suggested Koku. "Nothing ever hurt himexplosion

"Dat's what I wanted t' do, but Massa Tom say I cain't," explained the colored man. "Golly! Look at dat fire!"

Indeed the blaze was now assuming alarming proportions. The red shed, which was not a small structure, was

"Tom, you must do something," said Mr. Swift. "If the flames once reach that helmanite"

"I know, Father. But that explosive is in double vacuum containers, and it will be safe for some time yet.

Besides, it's in the cellar. It's the carbide I'm most worried about. We daren't use water."

"But something will have to be done!" exclaimed Mr. Damon. "Bless my red necktie, if we don't"

His words of warning had their effect, and the whole circle moved back several paces.

"I should say there was!" Tom answered. "I hoped we could get some of them out, but we can't nowuntil

"Look, Tom! The pattern shop roof is catching!" shouted Mr. Swift, pointing to where a little spurt of flame

"No, use all you like! That's the only thing to do. Come on, you with the hose!" Tom yelled. "Save the other

"But are you going to let the red shed burn?" asked Mr. Swift. "You know what it means, Tom."

"Yes, Father, I know. And I'm going to fight that fire in a new way. But we must save the other buildings,

too. Play water on all the other sheds and structures!" ordered the young inventor. "I'll tackle this one myself.

"You take charge of protecting the place where the new aerial warship is stored. Will you? I can't afford to

"Not if you don't use too much. Some of the woodwork isn't varnished yet, and I wouldn't want it to be wet.

But do the best you can. Take Koku and Eradicate with you. They can't do any good here."

"Not a bit of it, Ned. But I have another plan I want to try. Lively now! The wind's changing, and it's blowing

Tom shook his head protestingly, and Ned set off on the run, calling to the colored man and the giant to get

"I wonder what Tom is going to do?" mused Ned, as he neared the big shed he and the others had left on the

Tom, himself, seemed in no doubt as to his procedure With one look at the blazing red shed, as if to form an

opinion as to how much longer it could burn without getting entirely beyond control, Tom set off on a run

"The dirigible shed! I wonder what his game is? Surely that can't be in dangerit's too far off!"

Ned was right as to the last statement. The shed, where was housed a great dirigible balloon Tom had made,

but which he seldom used of late, was sufficiently removed from the zone of fire to be out of danger.

Meanwhile several members of the firefighting force that had been summoned from the various shops by

the alarm, had made an effort to save from the red shed some of the more valuable of the contents. There

were some machines in there, as well as explosives and chemicals, in addition to the store of carbide.

But the fire was now too hot to enable much to be done in the way of salvage. One or two small things were

carried out from a little addition to the main structure, and then the rescuers were driven back by the heat of

"That's right!" added Mr. Damon. "Bless my powderhorn! We may all be going skyhigh soon, and without

Warned by the aged inventor, the throng of men began slowly moving away from the immediate

neighborhood of the blazing shed. Though it may seem to the reader that some time has elapsed since the first

sounding of the alarm, all that I have set down took place in a very short periodhardly three minutes

elapsing since Tom and the others came rushing out of the aerial warship building.

Suddenly a cry arose from the crowd of men near the red shed. Ned, who stood ready with several lines of

hose, in charge of Koku, Eradicate and others, to turn them on the airship shed, in case of need, looked in the

The young bank clerk saw a strange sight. From the top of the dirigible balloon shed a long, black,

cigarshaped body arose, floating gradually upward. The very roof of the shed slid back out of the way, as

Tom pressed the operating lever, and the dirigible was free to riseas free as though it had been in an open

"He's going up!" cried Ned in surprise. "Making an ascent at a time like this, when he ought to stay here to

fight the fire! What's gotten into Tom, I'd like to know? I wonder if he can be"

Ned did not finish his halfformed sentence. A dreadful thought came into his mind. What if the sudden fire,

and the threatened danger, as well as the prospective loss that confronted Tom, had affected his mind?

"It certainly looks so," mused Ned, as he saw the big balloon float free from the shed. There was no doubt but

that Tom was in it. He could be seen standing within the pilothouse, operating the various wheels and levers

Koku, Eradicate and several others were attracted by the sight of the great dirigible, now a considerable

distance up in the air. Certainly it looked as though Tom Swift were running away. Yet Ned knew his chum

Then, as they watched, Ned and the others saw the direction of the balloon change. She turned around in

response to the influence of the rudders and propellers, and was headed straight for the blazing shed, but

An instant later Tom's plan was made clear to his chum. He saw Tom circling over the burning red shed, and

then the bank clerk saw what looked like fine rain dropping from the lower part of the balloon straight into

"He can't be dousing water on from up above there," reasoned Ned. "Pouring water on carbide from a height

is just as bad as spurting it on from a hose, though perhaps not so dangerous to the persons doing it. But it

"By Jove!" suddenly exclaimed Ned, as he had a better view of what was going on. "It's sand, that's what it is!

Tom is giving battle to the flames with sand from the ballast bags of the dirigible! Hurray? That's the ticket!

High up aloft, over the blazing red shed, with its dangerous contents that any moment might explode, Tom

Swift continued to hold his big dirigible balloon as near the flames as possible. And as he stood outside on

the small deck in front of the pilothouse, where were located the various controls, the young inventor pulled

the levers that emptied bag after bag of fine sand on the spouting flames that, already, were beginning to die

"Tom's done the trick!" yelled Ned, paying little attention now to the big airship shed, since he saw that the

"Dhat's what he suah hab done!" agreed Eradicate. "Mah ole mule Boomerang couldn't 'a' done any better."

"What's dat? Mah mule afraid ob fire?" cried the colored man. "Look heah, yo' great, big, overgrowed

specimen ob an equilateral quadruped, I'll hab yo' all understand dat when yo' all speaks dat way about a

"That'll do, Rad!" broke in Ned, with a laugh. He knew that when Tom's helper grew excited on the subject of

his mule there was no Stopping him, and Boomerang was a point on which Eradicate and Koku were always

"Oh, I understand!" laughed Ned. "Yes, and I hope it doesn't pay us another visit soon. Oh, look at Tom,

would you!" he cried, for the young aviator had swung his ship about over the flames, to bring another row of

Down showered more sand from the bags which Tom opened. No fire could long continue to blaze under that

treatment. The supply of air was cut off, and without that no fire can exist. Water would have been worse

than useless, because of the carbide, but the sand covered it up so that it was made perfectly harmless.

Moving slowly, the airship hovered over every part of the now slowly expiring flames, the burned opening in

the roof of the shed making it possible for the sand to reach the spots where it was most needed. The flames

died out in section after section, until no more could be seenonly clouds of black smoke.

"How is it now?" came Tom's voice, as he spoke from the deck of the balloon through a megaphone.

The eccentric man had caught up a piece of paper and, rolling it into a cone, made an improvised megaphone

"Haven't much more sand left," was Tom's comment, as he sent down a last shower. "That will have to do.

Hustle that carbide and other explosive stuff out of there now, while you have a chance."

"That's it!" cried Ned, who caught his chums meaning. "Come on, Koku. There's work for you."

The last of the sand had completely smothered the fire, and Tom, observing from aloft that his work was well

done, moved away in the dirigible, sending it to a landing space some little distance away from the shed

whence it had arisen. It was impossible to drop it back again through the roof of the hangar, as the balloon

was of such bulk that even a little breeze would deflect it so that it could not be accurately anchored. But

Tom had it under very good control, and soon it was being held down on the ground by some of his helpers.

As all the sand ballast had been allowed to run out Tom was obliged to open the gasvalves and let some of

"Come on, now!" cried the inventor, as he leaped from the deck of his sky craft. "Let's clean out the red shed.

That fire is only smothered, and there may be sparks smoldering under that sand, which will burst into flame,

"Bless my insurance policy, yes," exclaimed Mr. Damon. "That was a fine move of yours."

"It was the only way I could think of to put out the fire," Tom replied. "I knew water was out of the question,

"But I didn't know where to get any until I happened to think of the ballast bags of my dirigible. Then I knew,

if I could get above the fire, I could do the trick. I had to fly pretty high, though, as the fire was hot, and I was

"Oh, well, you have to take chances in this business," observed Tom, with a smile. "Now, then, let's finish

The sand, falling from the ballast bags of the dirigible, had so effectually quenched the fire that it was soon

cool enough to permit close approach. Koku, Tom and some of the men who best knew how to handle the

"I wish I could help you, Tom," said his aged father. "I don't seem able to do anything but stand here and look

"Never you mind, Dad!" Tom exclaimed. "We'll get along all right now. You'd better go up to the house. Mr.

"Yes, of course!" exclaimed the odd man, catching a wink from Tom, who wanted his father not to get too

excited on account of his weak heart. "Come along, Professor Swift. The danger is all over."

"And, Dad, when you haven't anything else to do," went on Tom, rather whimsically, "you might be thinking

up some plan to take up the recoil of those guns on my aerial warship. I confess I'm clean stumped on that

"Your aerial warship will never be a success," declared Mr. Swift. "You might as well give that up, Tom."

"Don't you believe it, Dad!" cried Tom, with more of a jolly air of one chum toward another than as though

the talk was between father and son. "You solve the recoil problem for me, and I'll take care of the rest, and

make the air warship sail. But we've got something else to do just now. Lively, boys."

While Mr. Swift, taking Mr. Damon's arm, walked toward the house, Tom, Ned, Koku, and some of the

workmen began carrying out the explosives which had so narrowly escaped the fire. With long hooks the men

pulled the shed apart, where the side walls had partly been burned through. Tom maintained an efficient

firefighting force at his works, and the men had the proper tools with which to work.

Soon large openings were made on three sides of the red shed, or rather, what was left of it, and through these

the dangerous chemicals and carbide, in sheetiron cans, were carried out to a place of safety. In a little while

nothing remained but a heap of hot sand, some charred embers and certain material that had been burned.

"Much loss, Tom?" asked Ned, as they surveyed the ruins. They were both black and grimy, tired and dirty,

"Well, yes, there's more lost than I like to think of," answered Tom slowly, "but it would have been a heap

sight worse if the stuff had gone up. Still, I can replace what I've lost, except a few models I kept in this

place. I really oughtn't to have stored them here, but since I've been working on my new aerial warship I have

sort of let other matters slide. I intended to make the red shed nothing but a storehouse for explosive

"Yes. It's lucky I had plenty of ballast aboard the dirigible. You see, I've been running it alone lately, and I

had to take on plenty of sand to make up for the weight of the several passengers I usually carry. So I had

plenty of stuff to shower down on the fire. I wonder how it started, anyhow? I must investigate this."

"Yes. At least they gave the alarm. Guess I'll ask Eradicate how he happened to notice. Oh, I say, Rad!" Tom

"Yais, sah, Massa Tom! I'se comin'!" the darky cried, as he finished piling up, at a safe distance from the fire,

"Why, it was jest dish yeah way, Massa Tom," began the colored man. "I had jest been feedin' mah mule,

Boomerang. He were pow'ful hungry, Boomerang were, an', when I give him some oats, wif a carrot sliced

up in 'emno, hole ondid I gib him a carrot t'day, or was it yist'day?I done fo'got. No, it were yist'day I

"Oh, never mind the carrot, or Boomerang, either, Rad!" broke in Tom, "I'm asking you about the fire."

"An' I'se tellin' yo', Massa Tom," declared Eradicate, with a rather reproachful look at his master. "But I

wanted t' do it right an' proper. I were comin' from Boomerang's stable, an' I see suffin' red spoutin' up at one

"Yes, I heard you yell," Tom said. "But what I wanted to know is, did you see anyone near the red shed at the

"I wonder if Mr. Damon did? I must ask him," went on the young inventor. "Come, on, Ned, we'll go up to

the house. Everything is all right here, I think. Whew! But that was some excitement. And I didn't show you

"That's right. Well, Koku, what is it?" for the giant had approached, holding out something in his hand.

"Koku found this in red shed," went on the giant, holding out a round, blackened object. "Maybe him powder;

"Oh, you think it's something explosive, eh?" asked Tom, as he took the object from the giant.

"Look funny! I should say it did! See here, Ned, if this isn't suspicious I'll eat my hat!" and Tom beckoned

What Tom Swift held in his hand looked like a small cannon ball, but it could not have been solid or the

young aviator would not so easily have held it out at arm's length for his friend Ned Newton to look at.

"This puts a different face on it, Ned," Tom went on, as he turned the object over.

"Is that likely to go off?" the bank clerk asked, as he came to a halt a little distance from his friend.

"Damage? It looks to me as though it had suffered the most damage itself. What is it, one of your models?

"Not exactly. I never saw this before, but it's what started the fire in the red shed all right; I'm sure of that."

"Well, if that's the case, I wouldn't leave such dangerous things around where there are explosives, Tom."

"I didn't, Ned. I wouldn't have had this within a hundred miles of my shed, if I could have had my way. It's a

fire bomb, and it was set to go off at a certain time. Only I think something went wrong, and the bomb started

"If it had worked at night, when we were all asleep, we might not have put the fire out so easily. This sure is

Tom was carefully examining the bomb, as Ned had correctly named it. The bank clerk, now that he was

assured by his chum that the, object had done all the harm it could, approached closer.

What he saw was merely a hollow shell of iron, with a small opening in it, as though intended for a place

He held the object under Ned's nose so suddenly that the young bank clerk jumped back.

"Oh, don't get nervous," laughed Tom. "It can't hurt you now. But what does that smell like?"

Ned sniffed, sniffed again, thought for a moment, and then sniffed a third time.

"Why," he said slowly, "I don't just know the name of it, but it's that funny stuff you mix up sometimes to put

in the oxygen tanks when we go up in the rarefied atmosphere in the balloon or airship."

"Manganese and potash," spoke Tom. "That and two or three other things that form a chemical combination

which goes off by itself of spontaneous combustion after a certain time. Only the person who put this bomb

together didn't get the chemical mixture just right, and it went off ahead of time; for which we have to be duly

"They not only tried it, but did it," responded Tom, more coolly than seemed natural under the circumstances.

"Only for the fact that the mixture went off before it was intended to, and found us all alert and readywell,

I don't like to think what might have happened," and Tom cast a look about at his group of buildings with

"That's exactly what I mean. Some enemy, who wanted to do me an injury, planned this thing deliberately.

He filled this steel shell with chemicals which, of themselves, after a certain time, would send out a hot

tongue of flame through this hole," and Tom pointed to the opening in the round steel shell.

"He knew the fire would be practically unquenchable by ordinary means, and he counted on its soon eating

"Why, Tom!" cried Ned. "It was just like one of those alarm clock dynamite bombsset to go off at a

"Exactly," Tom said, "only this was more delicate, and, if it had worked properly, there wouldn't have been a

vestige left to give us a clue. But the fire, thanks to the ballast sand in the dirigible, was put out in time. The

fuse burned itself out, but I can tell by the smell that chemicals were in it. That's all, Koku," he went on to the

giant who had stood waiting, not understanding all the talk between Tom and Ned. "I'll take care of this

"Bad man put it there?" asked the giant, who at least comprehended that something was wrong.

"Ha! If Koku find bad manbad for that man!" muttered the giant, as he clasped his two enormous hands

together, as though they were already on the fellow who had tried to do Tom Swift such an injury.

"I wouldn't like to be that man, if Koku catches him," observed Ned. "Have you any idea who it could be,

"Not the least. Of course I know I have enemies, Ned. Every successful inventor has persons who imagine he

has stolen their ideas, whether he has ever seen them or not. It may have been one of those persons, or some

"No; I don't believe Andy has been in this neighborhood for some time. The last lesson we gave him sickened

"How about those diamondmakers, whose secret you discovered? They wouldn't be trying to get back at

Well, it's possible, Ned. But I don't imagine so. They seem to have been pretty well broken up. No, I don't

believe it was the diamondmakers who put this fire bomb in the red shed. Their line of activities didn't

include this branch. It takes a chemist to know just how to blend the things contained in the bomb, and even a

"I don't know," and Tom spoke slowly, "I hoped I was done with all that sort of thing," he went on; "fighting

enemies whom I have never knowingly injured. But it seems they are still after me. Well, Ned, this gives us

"Well, I guess I am!" cried the bank clerk with sparkling eyes. "I wouldn't ask anything better. We've been in

things like this before, Tom, and we'll go in againand win! I'll help you all I can. Now, let's see if we can

pick up any other clues. This is like old times!" and Ned laughed, for he, like Tom, enjoyed a good "fight,"

"We sure will have our hands full," declared the young inventor. "Trying to solve the problem of carrying

"Oh, dear old dad!" exclaimed Tom affectionately. "I don't want to argue with him, but he's dead wrong!"

"I sure am, Ned! All I have to solve is the recoil proposition, and, as soon as we get straightened out from this

fire, we'll tackle that problem againyou and I. But I sure would like to know who put this in my red shed,"

"No use letting dad know about this," he went on. It would only be something else for him to worry about."

By this time nearly all evidences of the fire, except for the blackened ruins of the shed, had been cleared

away. High in the air hung a cloud of black smoke, caused by some chemicals that had burned harmlessly

The young inventor, finding his father quieted down and conversing easily with Mr. Damon, who was

blessing everything he could think of, motioned to Ned to follow him out of the house again.

"We'll leave dad here," said Tom, "and do a little investigating on our own account. We'll look for clues while

But, it must be confessed, after Tom and Ned had spent the rest of that day in and about the burned shed, they

were little wiser than when they started. They found the place where the fire bomb had evidently been placed,

right inside the main entrance to the shed. Tom knew it had been there because there were peculiar marks on

the charred wood, and a certain queer smell of chemicals that confirmed his belief.

"They put the bomb there to prevent anyone going in at the first alarm and saving anything," Tom said. "They

didn't count on the roof burning through first, giving me a chance to use the sand. I made the roof of the red

shed flimsy just on that account, so the force of the explosion if one ever came, would be mostly upward.

You know the expanding gases, caused by an explosion or by rapid combustion, always do just as electricity

does, seek the shortest and easiest route. In this case I made the roof the easiest route."

That night Tom had to confess himself beaten, as far as finding clues was concerned. The empty fire bomb

Close questioning of the workmen failed to disclose anything. Tom was particularly anxious to discover if

any mysterious strangers had been seen about the works. There was a strict rule about admitting them to the

"Well, we'll just have to lay that aside for a while," Tom said the next day, when Ned again came to pay a

visit. "Now, what do you say to tackling, with me, that recoil problem on the aerial warship?"

"I'm ready, if you are," Ned agreed, "though I know about as much of those things as a snake does about

The two friends walked out toward the shed where Tom's new craft was housed. As yet Ned had not seen it.

On the way they saw Eradicate walking along, talking to himself, as he often did.

"He suah did hab nerve, dat's what he did! De idea ob askin' me all dem questions, an' den wantin' t' know if

"Oh, it's a man I met when I were comin' back from de ash dump," Eradicate explained. One of the colored

man's duties was to cart ashes away from Tom's various shops, and dump them in a certain swampy lot. With

an old ramshackle cart, and his mule, Boomerang, Eradicate did this task to perfection.

"A manwhat sort of a man?" asked Tom, always ready to be suspicious of anything unusual.

"He were a queer man," went on the aged colored helper. "First he stopped me an' asted me fo' a ride. He was

a dressedup gen'man, too, an' I were suah s'prised at him wantin' t" set in mah ole ash cart," said Eradicate.

"But I done was polite t' him, an' fixed a blanket so's he wouldn't git too dirty. Den he asted me ef I didn't

wuk fo' yo', Massa Tom, an' of course I says as how I did. Den he asted me about de fire, an' how much

damage it done, an' how we put it out. An' he end up by sayin' he'd laik t' buy mah mule, Boomerang, an' he

"Well, a gen'man sort ob man, Massa Tom. Stranger t' me. I nebber seed him afo'. He suah was monstrous

polite t' ole black Eradicate, an' he gib me a halfdollar, too, jest fo' a little ride. But I aint' gwine t' sell

Boomerang, no indeedy, I ain't!" and Eradicate shook his gray, kinky head decidedly.

"Ned, there may be something in this!" said Tom, in an excited whisper to his chum. "I don't like the idea of a

Ned Newton looked at Tom questioningly. Then he glanced at the unsuspicious colored man, who was

"Yes, I know that much. You've said it before. But was he an Englishman, an Americanor"

"I think he were a Frenchman," spoke Eradicate. "I done didn't see him eat no frogs' laigs, but he smoked a

cigarette dat had a funny smell, and he suah was monstrous polite. He suah was a Frenchman. I think."

Tom and Ned laughed at Eradicate's description of the man, but Tom's face was soon grave again.

"Tell us more about him, Rad," he suggested. "Did he seem especially interested in the fire?"

"No, sah, Massa Tom, he seemed laik he was more special interested in mah mule, Boomerang. He done

"But every once in a while he put in some question about the fire, or about our shops, didn't he, Rad?" Tom

"Yes, sah, he done did ask about yo', and de wuks, ebery now and den," Rad confessed. "But how yo' all

knowed dat, Massa Tom, when I were atellin' yo' all about him astin' fo' mah mule, done gets medat's

"Never mind, Rad. He asked questions about the plant, that's all I want to know. But you didn't tell him much,

"Yo' all done knows me bettah dan dat, Massa Tom," the old colored man said. "Yo' all know yo' done gib

"Yes, I know I gave those orders," Tom said, with a smile, "but I want to make sure that they have been

"Then you didn't tell this queer stranger, Frenchman, or whatever he is, much about my place?"

"Dat's what I means," the colored man went on. "I done fooled him. When he asted me about de fire I said it

didn't do no damage at allin fack dat we'd rather hab de fire dan not hab it, 'case it done gib us a chance t'

"Well, he done sort ob hinted t' me ef we all knowed how de fire done start. I says as how we did, dat we

done start it ourse'ves fo' practice, an dat we done expected it all along, an' were ready fo' it. Course I knows

dat were a sort of fairy story, Massa Tom, but den dat cigarettesmokin' Frenchman didn't hab no right t'

"No, indeed, Rad. And I'm glad you didn't give him straight answers. So he's coming here later on, is he?"

"T' see ef I wants t' sell mah mule, Boomerang, yais, sah. I sort ob thought maybe you'd want t' hab a look at

dat man, so I tole him t' come on. Course I doan't want t' sell Boomerang, but ef he was t' offer me a big lot

"Of course," Tom answered. "Very well, Rad. You may go on now, and don't say anything to anyone about

"I won't, Massa Tom," promised the colored man, as he went off muttering to himself.

"Well, what do you make of it, Tom?" asked Ned of his chum, as they walked on toward the shed of the new,

"I don't know just what to think, Ned. Of course things like this have happened beforepersons trying to

"They never succeeded in getting much, I'm glad to say, but it always keeps me worried for fear something

"Well, he must be a new one. And, now I come to think of it, I did hear some of the men speaking about a

foreignera stranger being around town last week. It was just a casual reference, and I paid little attention

"Hardly. That was only talk to make Eradicate unsuspicious. The stranger, whoever he was, sized Rad up

partly right. I surmised, when Rad said he asked a lot of questions about the mule, that was only to divert

suspicion. and that he'd come back to the subject of the fire every chance he got."

"Yes, so it seems. But I don't believe the fellow will come around here. It would be too risky. All the same,

we'll be prepared for him. I'll just rig up one of my phototelephone machines, so that, if he does come to

"That's great, Tom! But do you think this fellow had anything to do with the fire?"

"I don't know. He knew about it, of course. This isn't the first fire we've had in the works, and, though we

always fight them ourselves, still news of it will leak out to the town. So he could easily have known about it.

And he might be in with those who set it, for I firmly believe the fire was set by someone who has an object

"It's too bad!" declared Ned. "Seems as though they might let you alone, if they haven't gumption enough to

"Well, don't worry. Maybe it will come out all right," returned Tom. "Now, let's go and have a look at my

aerial warship. I haven't shown it to you yet. Then we'll get ready for that mysterious Frenchman, if he

The young inventor unlocked the door of the shed where he kept his latest "pet," and at the sight which met

Ned Newton gave vent to a long whistle, and then began a detailed examination of the wonderful craft he saw

before him. That is, he made as detailed an examination as was possible under the circumstances, for it was a

long time before the young bank clerk fully appreciated all Tom Swift had accomplished in building the

Mars, which was the warlike name painted in red letters on the big gas container that tugged and swayed

"By hard work," was the modest reply. "I've been at this for a longer time than you'd suppose, working on it

at odd moments. I had a lot of help, too, or I never could have done it. And now it is nearly all finished, as far

as the ship itself is concerned. The only thing that bothers me is to provide for the recoil of the guns I want to

carry. Maybe you can help me with that. Come on, now, I'll explain how the affair works, and what I hope to

In brief Tom's aerial warship was a sort of German Zeppelin type of dirigible balloon, rising in the air by

means of a gas container, or, rather, several of them, for the section for holding the lifting gas element was

The chief difference between dirigible balloons and ordinary aeroplanes, as you all know, is that the former

are lifted from the earth by a gas, such as hydrogen, which is lighter than air, while the aeroplane lifts itself

by getting into motion, when broad, flat planes, or surfaces, hold it up, just as a flat stone is held up when you

sail it through the air. The moment the stone, or aeroplane, loses its forward motion, it begins to fall.

This is not so with a dirigible balloon. It is held in the air by means of the lifting gas, and once so in the air

Tom's aerial warship contained many new features. While it was as large as some of the wartype Zeppelins,

it differed from them materially. But the details would be of more interest to a scientific builder of such

Sufficient to say that Tom's craft consisted first of a great semirigid bag, or envelope, made of specially

prepared oiled silk and aluminum, to hold the gas, which was manufactured on board. There were a number

of gastight compartments, so that if one, or even if a number of them burst, or were shot by an enemy, the

Below the big gas bag was the ship proper, a light but strong and rigid framework about which were built

enclosed cabins. These cabins, or compartments, housed the driving machinery, the gasgenerating plant,

living, sleeping and dining quarters, and a pilothouse, whence the ship could be controlled.

Ned, making a tour of the Mars, as she swayed gently in the big shed, saw where several aluminum pedestals

"And that's exactly what they are," the young inventor replied. "I have the guns nearly ready for mounting,

but I can't seem to think of a way of providing for the recoil. And if I don't take care of that, I'm likely to find

my ship coming apart under me, after we bombard the enemy with a broadside or two."

"Well, no; not exactly personally. I was thinking of offering it to the United States Government. Foreign

nations are getting ready large fleets of aerial warships, so why shouldn't we? Matters in Europe are mighty

uncertain. There may be a great war there in which aerial craft will play a big part. I am conceited enough to

think I can build one that will measure up to the foreign ones, and I'll soon be in a position to know."

"I mean I have already communicated with our government experts, and they are soon to come and inspect

this craft. I have sent them word that it is about finished. There is only the matter of the guns, and some of the

ordnance officers may be able to help me out with a suggestion, for I admit I am stuck!" exclaimed Tom.

"Then you're going to do the same with this aerial warship as you did with your big lantern and that immense

"That's right," confirmed Tom. My former readers will know to what Ned Newton referred, and those of you

who do not may learn the details of how Tom helped Uncle Sam, by reading the previous volumes, "Tom

"Within a few days, now. But I'll have to hustle to get ready for them, as this fire has put me back. There are

quite a number of details I need to change. Well, now, let me explain about that gun recoil business. Maybe

Tom led the way from the main shed, where the aerial warship was housed, to a small private office. As Ned

entered, the door, pulled by a strong spring, swung after him. He held back his hand to prevent it from

slamming, but there was no need, for a patent arrangement took up all the force, and the door closed gently.

Ned looked around, not much surprised, for the same sort of doorcheck was in use at his bank. But a sudden

"There you are, Tom!" he cried. "Why not take up the recoil of the guns on your aerial warship by some such

For a moment or two Tom Swift did not seem to comprehend what Ned had said. He remained staring, first at

his chum, who stood pointing, and from him Tom's gaze wandered to the top of the door. It may have been,

and probably was, that Tom was thinking of other matters at that instant. But Ned said again:

"Wouldn't that do, Tom? Check the recoil of the gun with whatever stuff is in that arrangement!"

A sudden change came over Tom's face. It was lighted up with a gleam of understanding.

"By Jove, Ned, old man!" he cried. "I believe you've struck it! And to think that has been under my nose, or,

rather, over my head, all this while, and I never thought of it. Hurray! That will solve the problem!"

"Do you think it will?" asked Ned, glad that he had contributed something, if only an idea, to Tom's aerial

"What's in that doorcheck?" Ned asked. "I never stopped before to think what useful things they are, though

"Goodnight!" laughed Ned. "Excuse the slang, Tom, but what in the world is a hydrostatic valve?"

"A valve through which liquids pass. In this doorcheck there may be a mixture of water, alcohol and

glycerine, the alcohol to prevent freezing in cold weather, and the glycerine to give body to the mixture so it

"And do you think you can put something like that on your guns, so the recoil will be taken up?" Ned wanted

"I think so," spoke Tom. "I'm going to work on it right away, and we'll soon see how it will turn out It's

mighty lucky you thought of that, for I sure was up against it, as the boys say."

"If the thing works I'll give you due credit for it," promised Tom. "Now, I've got to figure out how much

force a modified hydrostatic valve check like that will take up, and how much recoil my biggest gun will

"Yes, four quickfirers, at least, two on each side, and heavier guns at the bow and stern, to throw explosive

shells in a horizontal or upward direction. For a downward direction we won't need any guns, we can simply

"Well, if it's necessary, yes. Though I guess there won't be much chance of doing that to a rival aeroplane or

dirigible. But in flying over cities or forts, explosive bombs can be dropped very nicely. For use in attacking

other air craft I am going to depend on my lateral fire, from the guns mounted on either beam, and in the bow

"You speak as though you, yourself, were going into a battle of the air," said Ned.

"No, I don't believe I'll go that far," Tom replied. "Though, if the government wants my craft, I may have to

"Please don't think that I am in favor of war, Ned," went on Tom earnestly. "I hate it, and I wish the time

would come when all nations would disarm. But if the other countries are laying themselves out to have aerial

battleships, it is time the United States did also. We must not be left behind, especially in view of what is

"Yes, all but the mounting of them on the supports aboard the Mars. I haven't dared do that yet, and fire them,

until I provided some means of taking up the recoil. Now I'm going to get right to work on that problem."

There was considerable detailed figuring and computation work ahead of Tom Swift, and I will not weary

you by going into the details of higher mathematics. Even Ned lost interest after the start of the problem,

though he was interested when Tom took down the doorcheck and began measuring the amount of force it

Once this had been done, and Tom had figured just how much force could be expected to be taken up by a

"Surely," answered Tom. "That's the only way to get at real results. I'll have the guns taken out and mounted

"Well, that may be some fun," spoke Ned, with a grin. "More fun than all these figures," and he looked at the

This was the second or third day after the fire in the red shed, and in the interim Tom had been busy making

computations. These were about finished. Meanwhile further investigation bad been made of clues leading to

A phototelephone had been installed near Eradicate's quarters, in the hope that the mysterious stranger

might keep his promise, and come to see about the mule. In that case something would have been learned

Ned was much interested in the guns, and, a little later, he helped Tom and Koku mount them in a vacant lot.

Mr. Swift strolled past, as the guns were being mounted for the preliminary test, and inquired what his son

"It will never work, Tom, never!" declared the aged inventor, when informed. "You can't take up those guns

"You wait, Dad," laughed Tom. "You haven't yet seen how the Newton hydrostatic recoil operates."

It took nearly a week to get all the guns mounted, for some of them required considerable work, and it was

also necessary to attach gauges to them to register the recoil and pressure. In the meanwhile Tom had been in

further communication with government experts who were soon to call on him to inspect the aerial warship,

"When are they coming?" asked Ned, as he and Tom went out one morning to make the first test of the guns.

"They will be here any day, now. They didn't set any definite date. I suppose they want to take us unawares,

to see that I don't 'frameup' any game on them. Well, I'll be ready any time they come. Now, Koku, bring

along those shells, and don't drop any of them, for that new powder is freakish stuff."

"Me no drop any, Master," spoke the giant, as he lifted the boxes of explosives in his strong arms.

The largest gun was loaded and aimed at a distant hill, for Tom knew that if the recoil apparatus would take

care of the excess force of his largest gun, the problem of the smaller ones would be easy to solve.

"Here, Rad, where are you going?" Tom asked, as he noticed the colored man walking away, after having

"II'se gwine t' feed mah mule, Boomerang," said the colored man slowly. "It's his eatin' time. jest now,

"Yais, sab, Massa Tom, I knows dat," said Eradicate, as he carefully edged away from the big gun, "but I'se

done changed de eatin' hours ob dat mule. He had a little touch ob indigestion de udder day, an' I'se feedin'

"Oh, well, trot along," laughed the young inventor. "I guess we won't need you. Is everything all right there,

"Now, Ned, if you'll stand here," went on Tom, "and note the extreme point to which the hand on the pressure

"Here comes someone," remarked the bank clerk, as he saw that his pencil was sharpened. He pointed to the

"It's Mr. Damon," observed Tom. "We'll wait until he arrives. He'll be interested in this."

"Bless my collar button, Tom! What's going on?" asked the eccentric man, as he came up. "Has war been

"Just practicing," replied the young inventor. "Getting ready to put the armament on my aerial warship."

There was a moment of inspection, to see that nothing had been forgotten, and then the big gun was

discharged. There was a loud report, not as heavy, though, as Ned had expected, but there was no puff of

smoke, for Tom was using smokeless powder. Only a little flash of flame was observed.

"Good! And I can build a recoil check that will take up to one hundred and twenty thousand pounds pressure.

The echoes of the first had hardly died away before the second gun was ready for the test. That, too, was

satisfactory, and then the smaller ones were operated. These were not quite so satisfactory, as the recoil

"But I can easily put a larger hydrostatic check on them," he said. "Now, we'll fire by batteries, and see what

Then began a perfect bombardment of the distant hillside, service charges being used v, and explosive shells

sent out so that dirt, stones and gravel flew in all directions. Danger signs and flags had been posted, and a

cordon of Tom's men kept spectators away from the hill, so no one would be in the danger zone.

The young inventor was busy making some calculations after the last of the firing had been completed. Koku

was packing up the unfired shells, and Mr. Damon was blessing his eardrums, and the pieces of cotton he

had stuffed in to protect them, when a tall, erect man was observed strolling over the fields in the direction of

"Yes, and a stranger, too," observed Tom. "I wonder if that can be Eradicate's Frenchman?"

But a look at the stranger's face disproved that surmise. He had a frank and pleasant countenance, obviously

"I beg your pardon," he began, addressing everyone in general, "but I am looking for Tom Swift. I was told

"Ah! Well, I am Lieutenant Marbury, with whom you had some correspondence recently about"

"Oh, yes, Lieutenant Marbury, of the United States Navy," interrupted Tom. "I'm glad to see you," he went

on, holding out his hand. "We are just completing some tests with the guns. You called, I presume, in

"Well, almost. It can be made ready in a few hours. You see, I have been delayed. There was a fire in the

"A fire!" exclaimed the officer in surprise. "How was that? We heard nothing of it in Washington."

"No, I kept it rather quiet," Tom explained. "We had reason to suspect that it was a fire purposely set, in a

"Ha!" exclaimed Lieutenant Marbury. "This fits in with what I have heard. And did you not receive

"Of foreign spies!" was the unexpected answer. "I am sorry. Some of our Secret Service men unearthed

something of a plot against you, and I presumed you had been told to watch out. If you had, the fire might not

have occurred. There must have been some error in Washington. But let me tell you now, Tom Swiftbe on

The officer's words were so filled with meaning that Tom started. Ned Newton, too, showed the effect he felt.

"Do you really mean that?" asked the young inventor, looking around to make sure his father was not present.

On account of Professor Swift's weak heart, Tom wished to spare him all possible worry.

"I certainly do mean it," insisted Lieutenant Marbury. "And, while I am rather amazed at the news of the fire,

for I did not think the plotters would be so bold as that, it is in line with what I expected, and what we

"The existence of a welllaid plot, not only against our government, but against you!"

"I might as well tell it from the beginning," the officer went on. "As long as you have not received any

official warning from Washington you had better hear the whole story. But are you sure you had no word?"

"Well, now, I won't be so sure," Tom confessed. "I have been working very hard, the last two days, making

some intricate calculations. I have rather neglected my mail, to tell you the truth.

"And, come to think of it, there were several letters received with the Washington postmark. But, I supposed

they had to do with some of my patents, and I only casually glanced over them. There was one letter, though,

"Ha! That was it!" cried the lieutenant. "It was the warning in cipher or code. I didn't think they would

"You must also have received a method of deciphering the message," the officer said. "Probably you

overlooked that. The Secret Service men sent you the warning in code, so it would not be found out by the

plotters, and, to make sure you could understand it, a method of translating the cipher was sent in a separate

"Yes, for I might have been on my guard," agreed Tom. "The red shed might not have burned, but, as it was,

"Owing to the fact that Tom put the fire out with sand ballast from his dirigible!" cried Ned. "You should

"I should have liked to be here," the lieutenant spoke. "But, if I were you, Tom Swift, I would take means to

"I shall," Tom decided. "But, if we want to talk, we had better go to my office, where we can be more private.

Now that the firing was over, a number of Tom's men from the shops had assembled around the cannon. Most

of them, the young inventor felt, could be trusted, but in so large a gathering one could never be sure.

"Did you come on from Washington yesterday?" asked Tom, as he, Ned and the officer strolled toward the

"Yes, and I spent the night in New York. I arrived in town a short time ago, and came right on out here. At

your house I was told you were over in the fields conducting experiments, so I came on here."

"Glad you did," Tom said. "I'll soon have something to show you, I hope. But I am interested in hearing the

"Perfectly sure," was the answer. "We don't know all the details yet, nor who are concerned in it, but we are

"We are convinced in Washington," went on Lieutenant Marbury, when he, Tom and Ned were seated in the

private office, "that foreign spies are at work against you and against our government."

"Because of the inventions you have perfected and turned over to Uncle Samnotably the giant cannon,

which rivals anything foreign European powers have, and the great searchlight, which proved so effective

against the border smugglers. The success of those two alone, to say nothing of your submarine, has not only

"But they won't!" interrupted the officer"They are seeking to destroy those inventions. More than once, of

"Have they really tried to damage the big gun?" asked Tom, referring to one he had built and set up at

"They have. And now this fire proves that they are taking other measuresthey are working directly against

"Either to prevent you from making further inventions, or to stop you from completing your latestthe aerial

"But I didn't know the foreign governments knew about that," Tom exclaimed. "It was a secret."

"Few secrets are safe from foreign Spies," declared Lieutenant Marbury. "They have a great ferretingout

system on the other side. We are just beginning to appreciate it. But our own men have not been idle."

"Have they really learned anything?" Tom asked. "Nothing definite enough to warrant us in acting," was the

answer of the government man. "But we know enough to let us see that the plot is farreaching."

"Tell him about Eradicate, and the man who wanted to buy the mule, Tom," suggested Ned,

Thereupon the young inventor mentioned the story told by Eradicate. He also brought out the firebomb, and

"I think you are right," said Lieutenant Marbury. "And, as regards the French, I might say they are not the

"But I thought the French and the English were friendly toward us!" Ned exclaimed.

"So they are, in a certain measure," the officer went on. "And Russia is, too. But, in all foreign countries there

"But I might add that it is neither France, England, nor Russia that we must fear. It is a certain other great

"We will talk that over," said Lieutenant Marbury. "But, before I go into details, I want to give you another

"I don't know," Tom answered. "I left orders we weren't to be disturbed unless it was something important."

"May be something has happened," suggested the navy officer, "another fire, perhaps, or a"

"It isn't a fire," Tom answered. "The automatic alarm would be ringing before this in that case."

The knock was repeated. Tom went softly to the door and opened it quickly, to disclose, standing in the

"Oh, if you please, Mn Swift," said the boy, a man has applied for work at the main office, and you know you

"Oh, so I did," Tom exclaimed. "I had forgotten about that," he went on to Lieutenant Marbury and Ned. "I

am in need of helpers to rush through the finishing touches on my aerial warship, and I left word, if any

applied, as they often do, coming here from other cities, that I wanted to see them. How many are there?"

"That's what they all say," interposed Tom, with a smile. "But, though they may be good mechanics in their

own line, they need to have special qualifications to work on airships. Tell them to wait, Rodney," Tom went

"You were about to give me another warning when that interruption came. You might complete it now."

"Yes, it was another warning," spoke the officer, "and one I hope you will heed. It concerns yourself,

"That's exactly what I do mean," was the prompt reply. "In danger of personal injury, if not something

Tom did not seem as alarmed as he might reasonably have been under the circumstances.

"That's just where I can't warn you," the officer replied. "I can only give you that hint, and beg of you to be

"No, indeed; it isn't that!" the lieutenant hastened to assure the young man. "I would gladly tell, if I knew. But

this plot, like the other one, directed against the inventions themselves, is so shrouded in mystery that I

"Our Secret Service men have been working on it for some time, not only in order to protect you, because of

what you have done for the government, but because Uncle Sam wishes to protect his own property,

especially the searchlight and the big cannon. But, though our agents have worked hard, they have not been

"So we can only warn you to be careful, and this I do in all earnestness. That was part of my errand in coming

here, though, of course, I am anxious to inspect the new aerial warship you have constructed. So watch out

"Do you really think they would do me bodily harm?" Tom asked, a trifle skeptical.

"I certainly do. These foreign spies are desperate. If they cannot secure the use of these inventions to their

own country, they are determined not to let this country have the benefit of them."

"Well, I'll be careful," Tom promised. "I'm no more anxious than anyone else to run my head into danger, and

I certainly don't want any of my shops or inventions destroyed. The fire in the red shed was as close as I want

"That's right!" agreed Ned. "And, if there's anything I can do, Tom, don't hesitate to call on me."

"All right, old man. I won't forget. And now, perhaps, you would like to see the Mars," he said to the

"I certainly would," was the ready answer. "But hadn't you better see those men who are waiting to find out

"There's no hurry about them," Tom said. "We have applicants every day, and it's earlier than the hour when I

usually see them. They can wait. Now I want your opinion on my new craft. But, you must remember that it

is not yet completed, and only recently did I begin to solve the problem of mounting the guns. So be a little

Followed by Ned and Lieutenant Marbury, Tom led the way into the big airship shed. There, Swaying about

at its moorings, was the immense aerial warship. To Ned's eyes it looked complete enough, but, when Tom

pointed out the various parts, and explained to the government officer how it was going to work, Ned

Tom showed his official guest how a new system of elevation and depressing rudders had ben adopted, how a

new type of propeller was to be used and indicated several other improvements. The lower, or cabin, part of

the aircraft could be entered by mounting a short ladder from the ground, and Tom took Ned and Lieutenant

"It certainly is most complete," the officer observed. "And when you get the guns mounted I shall be glad to

make an official test. You understand," he went on, to Tom, "that we are vitally interested in the guns, since

we now have many aircraft that can be used purely for scouting purposes. What we want is something for

"I understand," Tom answered. "And I am going to begin work on mounting the guns at once. I am going to

"Yes, he just happened to solve the problem for me!" interrupted Tom, as he told the story of the

Tom then briefly described the principle on which his aerial warship would work, explaining how the lifting

gas would raise it, with its load of crew, guns and explosives, high into the air; how it could then be sent

ahead, backward, to either side, or around in a circle, by means of the propellers and the rudders, and how it

could be raised or lowered, either by rudders or by forcing more gas into the lifting bags, or by letting some

And, while this was being done by the pilot or captain in charge, the crew could be manning the guns with

which hostile airships would be attacked, and bombs dropped on the forts or battleships of the enemy.

"It seems very complete," observed the lieutenant. "I shall be glad when I can give it an official test."

"Which ought to be in about a week," Tom said. "Meanwhile I shall be glad if you will be my guest here."

Leaving Ned and the lieutenant to entertain each other, Tom went to see the mechanics who had applied for

places. He found them satisfactory and engaged them. One of them had worked for him before. The other was

a stranger, but he had been employed in a large aeroplane factory, and brought good recommendations.

There followed busy days at the Swift plant, and work was pushed on the aerial warship. The hardest task

was the mounting of the guns, and equipping them with the recoil check, without which it would be

But finally one of the big guns, and two of the smaller ones were in place, with the apparatus designed to

"Up in the air, do you mean?" asked Ned, who was spending all his spare time with his chum.

"Well, a little way up in the air, at least," Tom answered. "I'll make a sort of captive balloon of my craft, and

see how she behaves. I don't want to take too many chances with that new recoil check, though it seems to

The day came when, for the first time, the Mars was to come out of the big shed where she had been

constructed. The craft was not completed for a flight as yet, but could be made so in a few days, with rush

work. The roof of the great shed slid back, and the big envelope containing the buoyant gas rose slowly

upward. There was a cry of surprise from the many workmen in the yard, as they saw, most of them for the

first time, the wonderful new craft. It did not go up very high, being held in place with anchor ropes.

The sun glistened on the bright brass and nickel parts, and glinted from the gleaming barrels of the

"That's enough!" Tom called to the men below, who were paying out the ropes from the windlasses. "Hold

Looking about, to see that all was in readiness, Tom gave orders to load the guns, blank charges being used,

The recoil apparatus was in place, and it now remained to see if it would do the work for which it was

"Bless my accident insurance policy!" exclaimed Mr. Damon. "I'm as ready as ever I shall be, Tom. Let 'em

"Hold fast!" cried Tom, as he prepared to press the electrical switch which would set off the guns. Ned and

Lieutenant Marbury stood near the indicators to notice how much of the recoil would be neutralized by the

"Here we go!" cried the young inventor, and, at the same moment, from down below on the ground, came a

But Eradicate had spoken too late. Tom pressed the switch; there was a deafening crash, a spurt of flame, and

then followed wild cries and confused shouts, while the echoes of the reports rolled about the hills

Thus came the cries from those aboard the captive Mars. Ned, Lieutenant Marbury and Tom had called out in

the order named. And, of course, I do not need to tell you what remark Mr. Damon made. Tom glanced

toward where Ned and the government man stood, and saw that they had made notes of the pressure recorded

on the recoil checks directly after the guns were fired. Mr. Damon, blessing innumerable objects under his

breath, was looking over the side of the rail to discover the cause of the commotion and cries of warning from

"I don't believe it was anything serious, Tom," said the odd man. "No one seems to be hurt." "Look at

They looked to where the young bank employee pointed, and saw the old colored man, seated on the seat of

his ramshackle wagon, doing his best to pull down to a walk the big galloping mule, which was dragging the

"Whoa, dere!" Eradicate was shouting, as he pulled on the lines. "Whoa, dere! Dat's jest laik yo', Boomerang,

t' run when dere ain't no call fo' it, nohow! Ef I done wanted yo' t' git a move on, yo'd lay down 'side de road

But the noise of the shots had evidently frightened the long eared animal, and he was in no mood for

stopping, now that he had once started. It was not until some of the workmen ran out from the group where

they had gathered to watch Tom's test, and got in front of Boomerang, that they succeeded in bringing him to

Eradicate climbed slowly down from the seat, and limped around until he stood in front of his pet.

"Yo'yo're a nice one, ain't yo'?" he demanded in sarcastic tones. "Yo' done enough runnin' in a few minutes

fo' a week ob Sundays, an' now I won't be able t' git a move out ob ye! I'se ashamed ob yo', dat's what I is!

Puffickly ashamed ob yo'. Go 'long, now, an' yo' won't git no oats dish yeah day! No sah!" and, highly

"I won't shoot again until you have him shut up, Rad!" laughed Tom. "I didn't know you were so close when I

"Dat's all right, Mass a Tom," was the reply. "I done called t' you t' wait, but yo' didn't heah me, I 'spects. But

it doan't mattah, now. Shoot all yo' laik, Boomerang won't run any mo' dis week. He done runned his laigs off

But Tom was not quite ready to do this. He wanted to see what effect the first shots had had on his aerial

warship, and to learn whether or not the newly devised recoil check had done what was expected of it.

"No more shooting right away," called the young inventor. "I want to see how we made out with the first

"Yes, indeed," added Lieutenant Marbury. "The recoil was hardly noticeable, though, of course, with the full

"I hope not," answered Tom. "I haven't used the full strength of the recoil check yet. I can tune it up more,

and when I do, and when I have it attached to all the guns, big and little, I think we'll do the trick. But now

The rest of that day was spent in trying out the guns, firing them with practice and service charges, though

none of the shells used contained projectiles. It would not have been possible to shoot these, with the Mars

"Well, is she a success, Tom?" asked Ned, when the experimenting was over for the time being.

"I think I can say soyes," was the answer, with a questioning look at the officer.

"Indeed it isa great success! We must give the Newton shock absorber due credit."

"Of course something may develop when you take your craft high in the air, and discharge the guns there,"

said the lieutenant. "In a rarefied atmosphere the recoil check may not be as effective as at the earth's surface.

But, in such case doubtless, you can increase the strength of the springs and the hydrostatic valves."

"Yes, I counted on that," Tom explained. "I shall have to work out that formula, though, and be ready for it.

The Mars was hauled back into the shed, and the roof slid shut over the craft. Much yet remained to do on it,

but now that Tom was sure the important item of armament was taken care of, he could devote his entire time

As his plant was working on several other pieces of machinery, some of it for the United States Government,

and some designed for his own use, Tom found himself obliged to hire several new hands. An advertisement

in a New York newspaper brought a large number of replies, and for a day or two Tom was kept busy sifting

out the least desirable, and arranging to see those whose answers showed they knew something of the

Meanwhile Lieutenant Marbury remained as Tom's guest, and was helpful in making suggestions that would

"I'd like, also, to get on the track of those spies who, I am sure, wish to do you harm," said the lieutenant, "but

"They are, indeed," agreed Tom. "I guess the way in which we handled that fire in the red shed sort of

"They're not so easily discouraged as that," he remarked. "And, with the situation in Europe growing more

acute every day, I am afraid some of those foreigners will take desperate measures to gain their ends."

"Well, I think they will either try to so injure you that you will not be able to finish this aerial warship, or

they will damage the craft itself, steal your plans, or damage some of your other inventions."

"But what object would they have in doing such a thing?" Tom wanted to know. "How would that help

"They are seeking to strike at the United States through you," was the answer. "They don't want Uncle Sam to

have such formidable weapons as your great searchlight, the giant cannon, or this new warship of the clouds."

"But why not, as long as the United States does not intend to go to war with any of the foreign nations?" Tom

"No, it is true we do not intend to go to war with any of the conflicting European nations," admitted

Lieutenant Marbury, "but you have no idea how jealous each of those foreign nations is of all the others.

Each one fears that the United States will cease to be neutral, and will aid one or the other."

"Yes, each nation, which may, at a moments notice, be drawn into a war with one or more rival nations, fears

"That's the way I believe it will work out. So you must be careful, especially since you have taken on so

"That's so," agreed the young inventor. "I have had to engage more strangers than ever before, for I am

anxious to get the Mars finished and give it a good test. And, now that you have mentioned it, there are some

"Well, not exactly; it is more their bearing, and the manner in which they go about the works. I must keep my

eye on them, for it takes only a few discontented men to spoil a whole shop full. I will be on my guard."

"And not only about your new airship and other inventions," said the officer, "but about yourself, personally.

As Tom had said, he had been obliged to hire a number of new men. Some of these were machinists who had

worked for him, or his father, on previous occasions, and, when tasks were few, had been dismissed, to go to

But there were a number of others, from New York, and other large cities, of whom Tom was not so sure.

"You have more foreigners than I ever knew you to hire before, Tom," his father said to him one day, coming

"Yes, I have quite a number," Tom admitted. "But they are all good workmen. They stood the test."

"Yes, some of them are too good," observed the older inventor. "I saw one of them making up a small motor

the other day, and he was winding the armature a new way. I spoke to him about it, and he tried to prove that

his way was an improvement on yours. Why, he'd have had it shortcircuited in no time if I hadn't stopped

"No, not yet, but I shall have to shift some there from other work I think, in order to get finished on time."

"Why, have you seen anythingdo you" began the young man, for Mr. Swift had not been told of the

"Oh, it isn't anything special," the older inventor went on. "Only I wouldn't let a man I didn't know much

"I won't, Dad. Thanks for telling me. This latest craft is sure going to be a beauty."

Tom Swift pondered long and intently over what his father had said to him. He sat for several minutes in his

private office, after the aged inventor had passed out, reviewing in his mind the talk just finished.

"I wonder," said Tom slowly, "if any of the new men could have obtained work here for the purpose of

And the more Tom thought of it, the more he was convinced that such a thing was at least possible.

"I must make a close inspection, and weed out any suspicious characters," he decided, "though I need every

man I have working now, to get the Mars finished in time. Yes, I must look into this."

Tom had reached a point in his work where he could leave much to his helpers. He had several good foremen,

and, with his father to take general supervision over more important details, the young inventor had more

time to himself. Of course he did not lay too many burdens on his father's shoulders since Mr. Swift's health

But Tom's latest idea, the aerial warship, was so well on toward completion that his presence was not needed

"When I'm not there I'll go about in the other shops, and sort of size up the situation," he decided. "I may be

Lieutenant Marbury had departed for a time, to look after some personal matters, but he was to return inside

of a week, when it was hoped to give the aerial warship its first real test in flight, and under some of the

As Tom was about to leave his office, to put into effect his new resolution to make a casual inspection of the

other shops, he met Koku, the giant, coming in. Koku's hands and face were black with oil and machine

"Well, what have you been doing?" Tom wanted to know. "Did you have an accident?" For Koku had no

knowledge of machinery, and could not even be trusted to tighten up a simple nut by himself. But if some one

stood near him, and directed him how to apply his enormous strength, Koku could do more than several

"No accident, Master," he replied. "I help man lift that hammerhammer thing that pounds so. It get stuck!"

"What, the hammer of the drop forger?" cried Tom. "Was that out of order again?"

There was an automatic triphammer in one of the shops, used for pounding out drop forgings, and this

hammer seemed to take especial delight in getting out of order. Very often it jammed, or "stuck," as Koku

described it, and if the hammer could not be forced back on the channel or upright guideplates, it meant that

it must be taken apart, and valuable time lost. Once Koku had been near when the hammer got out of order,

and while the workmen were preparing to dismantle it, the giant seized the big block of steel, and with a

"Yes, Master. Me fix hammer," Koku answered. "I get dirty, I no care. Man say I no can fix. I show him I

"Man who run hammer. Ha! I lift him by one finger! He say he no like to work on hammer. He want to work

on airship. I tell him I tell you, maybe you give him jobhe baby! Koku can work hammer. Me fix it when it

"Well, maybe you know what you're talking about, but I don't," said Tom, with a pleasant smile at his big

"Well, I'll see," half promised Tom. "If it's going to get out of gear all the while it might pay me to keep you

at it so you could get it back in place whenever it kicked up a fuss, and so save time. I'll see about it."

Koku led the way to the shop where the triphammer was installed. It was working perfectly now, as Tom

could tell by the thundering blows it struck. The man operating it looked up as Tom approached, and, at a

"Been having trouble here?" asked Tom, noting that the workman was one of the new hands he had hired.

"Yes, sir, a little," was the respectful answer. "This hammer goes on a strike every now and then, and gets

jammed. Your giant there forced it back into place, which is more than I could do with a big bar for a lever.

"Yes," agreed Tom, "he's pretty strong. But what's this you said about wanting to give up this job, and go on

"I didn't intend him to repeat that to you, Mr. Swift," he said. "I was a little put out at the way this hammer

worked. I lose so much time at it that I said I'd like to be transferred to the airship department. I've worked in

one before But I'm not making a kick," he added quickly. "Work is too scarce for that."

"I understand," said Tom. "I have been thinking of making a change. Koku seems to like this hammer, and

knows how to get it in order once it gets off the guides. You say you have had experience in airship

"Yes, I've worked on them, too, but the engineering part is my specialty. I'm a little out of my element on a

"I see. Well, perhaps I'll give you a trial. Meanwhile you might break Koku in on operating this machine. If I

"Thank you, Mr. Swift! I'll show him all I know about it. Oh, there goes the hammer again!" he exclaimed,

for, as he started it up, as Tom turned away, the big piece of steel once more jammed on the channelplates.

"Me fix!" exclaimed the giant eagerly, anxious for a chance to exhibit his great strength.

He inspected it carefully before he signaled for Koku to force the hammer back into place. But, if Tom saw

anything suspicious, he said nothing. There was, however, a queer look on his face as he turned aside, and he

"So you want to be transferred to the airship department, do you? Well, we'll see about that We'll see."

Tom had more problems to solve than those of making an aerial warship that would be acceptable to the

Ned Newton called on his chum that evening. The two talked of many things, gradually veering around to the

"You're thinking too much of that." Ned warned him. "You're as bad as the time you went for your first

"I suppose I am," admitted Tom. "But the success of the Mars means a whole lot to me. And that's something

"Sure, though I tell you that you're working too hardburning the electric light at both ends."

"But this isn't the way to the airship shed," objected the young bank clerk, as he noted in which direction Tom

"I know it isn't," Tom replied. "But I want to look at one of the triphammers in the forge shop when none of

"Trouble!" exclaimed his chum. "Has that plot Lieutenant Marbury spoke of developed?"

"Not exactly. This is something else," and Tom told of the trouble with the big hammer.

"I had an idea," the young inventor said, "that the man at the machine let it get out of order purposely, so I'd

Tom carefully inspected the hammer by the light of a powerful portable electric lamp Ned held.

"Yes. This is what's been throwing the hammer off the guides all the while," and Tom pulled out a small steel

bolt that had been slipped into an oil hole. A certain amount of vibration, he explained to Ned, would rattle

the bolt out so that it would force the hammer to one side, throwing it off the channelplates, and rendering it

"A foxy trick," commented Tom. "No wonder the machine got out of kilter so easily."

"Well, I'm not going to say. But I'm going to watch that man. He wants to be transferred to the airship

department. He put this in the hammer, perhaps, to have an excuse for a change. Well, I'll give it to him."

"You don't mean that you'd take a fellow like that and put him to work on your new aerial warship, do you,

"Yes, I think I will, Ned. You see, I look at it this way: I haven't any real proof against him now. He could

only laugh at me if I accused him. But you've heard the proverb about giving a calf rope enough and he'll

"Well, I'm going to give this fellow a little rope. I'll transfer him, as he asks, and I'll keep a close watch on

"Perhaps, but no more so than leaving him in here to work mischief. If he is hatching a plot, the sooner it's

over with the better I shall like it. I don't like a shot to hang fire. I'm warned now, and I'll be ready for him. I

have a line on whom to suspect. This is the first clue," and Tom held up the incriminating bolt.

"I think you're taking too big a risk, Tom," his chum said. "Why not discharge the man?"

"Because that might only smooth things over for a time. If this plot is being laid the sooner it comes to a

head, and breaks, the better. Have it done, short, sharp and quick, is my motto. Yes, I'll shift him in the

morning. Oh, but I wish it was all over, and the Mars was accepted by Uncle Sam!" and Tom put his hand to

"Say, old man!" exclaimed Ned, "what you want is a day off, and I'm going to see that you get it. You need a

"Then you'll have it!" cried Ned. "There's going to be a little picnic tomorrow. Why can't you go with Mary

Nestor? She'd like you to take her, I'm sure. Her cousin, Helen Randall, is on from New York, and she wants

"Because she said so," laughed Ned. "I was over to the house to call. I have met Helen before, and I

suggested that you and I would take the two girls, and have a day off. You'll come, won't you?"

"Nonsense! Give up work for one day!" urged Ned. "Come along. It'll do you goodget the cobwebs out of

The next day, having instructed his father and the foremen to look well to the various shops, and having seen

that the work on the new aerial warship was progressing favorably, Tom left for a day's outing with his chum

The picnic was held in a grove that surrounded a small lake, and after luncheon the four friends went for a

ride in a launch Tom hired. They went to the upper end of the lake, in rather a pretty but lonesome locality.

"That suits me," spoke Ned. Helen and Mary assented, and soon the four young persons were strolling

After a bit the couples became separated, and Tom found himself walking beside Mary in a woodland path.

"Oh, how nicely you say it!" she laughed. "But I know better! You're puzzling over some problem. Tell me,

Mary Nestor spoke with such earnestness, and her action in catching hold of Tom's arm to enjoin silence was

so pronounced that, though he had at first regarded the matter in the light of a joke, he soon thought

otherwise. He glanced from the girl's face to the dense underbrush on either side of the woodland path.

"I don't just know. I heard whispering, and thought it was the rustling of the leaves of the trees. Then

Distinctly then, Tom heard, from some opening in the screen of bushes, his own name spoken. "Did you hear

it?" asked Mary, barely forming the words with her lips. But Tom could read their motion.

"Yes," he nodded. Then, motioning to Mary to remain where she was, he stepped forward, taking care to

tread only on grassy places where there were no little twigs or branches to break and betray his presence. He

There was a sudden movement in the bushes, just beyond the spot Tom was making for. He halted quickly

Tom saw the forms of two men, partially concealed by bushes, walking away from him. The men took no

pains to conceal their movements, so Tom was emboldened to advance with less caution. He hurried to where

he could get a good view, and, at the sight of one of the men, he uttered an exclamation.

"What is it?" asked Mary, who was now at his side. She had seen that Tom had thrown aside caution, and she

"That manI know him!" the young inventor exclaimed. "It is Feldmanthe one who wanted to be changed

"So he is!" exclaimed Tom, in a hoarse whisper. "He must be the Frenchman that Eradicate spoke about. I

"You may know what you're talking about, but I don't, Tom," said Mary, with a smile at her companion. "Are

"Hardly," spoke the young inventor dryly. "That one, Feldman, is one of my workmen. He had charge of a

"Spare me the details, Tom!" interrupted Mary. "You know I don't understand a thing about machinery. The

"Well, a triphammer isn't as complicated as that," spoke Tom, with a laugh, as he noticed that the two men

were far enough away so they could not hear him. "What I was going to say was, that one of those men works

in our shops. The other I don't know, but I agree with you that he does look like a Frenchman, and old

Eradicate had a meeting with a man whom he described as being of that nationality."

"Then they must be enemies!" exclaimed Mary with quick intuition. "Oh, Tom, you will be careful, won't

"Of course I will, little girl," he said, a note of fondness creeping into his voice, as he covered the small hand

"Well, that may be. Probably one of them, Feldman, who works for me, was speaking to his companion about

"Well, I suppose it is all right, Tom, and I surely hope it is. But you will be careful, won't you? And you look

"Not a thing, little girl. Everything is going fine. My new aerial warship will soon make a trial flight, and I'd

"That's awfully nice of you. But you do look worried, Tom. Has anything troubled you?"

"No, not much. Everything is going all right now. We did have a little trouble at a fire in one of my

"Well, it didn't amount to muchthe only suspicious fact about it was that it seemed to have been of

Mary seemed much alarmed, and again begged Tom to be on his guard, which he promised to do. Had Mary

known the warnings uttered by Lieutenant Marbury she might have had more occasion for worry.

"Do you suppose that hammer man of yours came to these woods to meet that Frenchman and talk about you,

Tom?" asked his companion, when the two men had strolled out of sight, and the young people were on their

"Well, it's possible. I have been warned that foreign spies are trying to get hold of some of my patents, and

also to hamper the government in the use of some others I have sold. But they'll have their own troubles to

get away with anything. The works are pretty well guarded, and you forget I have the giant, Koku, who is

"Yes, but he can't be everywhere at once. Oh, you will be careful, won't you, Tom?"

"Yes, Mary, I will," promised the young inventor. "But don't say anything to Ned about what we just saw and

"Because he's been at me to hire a couple of detectives to watch over me, and this would give him another

excuse. Just don't say anything, and I'll adopt all the precautions I think are needful."

With that Mary had to be content. A little later they joined Ned and his friend, and soon they were moving

"Well, hasn't it done you good to take a day off?" Ned demanded of his chum, when they were on their

"Oh, yes, I found something new to think about," admitted the young inventor, with a quick look at Mary.

But, though Tom thus passed off lightly the little incident of the day, he gave it serious thought when he was

"Those fellows were certainly talking about me," he reasoned. "I wonder what for? And Feldman left the

shop without my knowledge. I'll have to look into that. I wonder if that Frenchy looking chap I saw was the

The last was easily disposed of, for, on reaching his shops that afternoon, Tom crossquestioned the colored

man, and obtained a most accurate description of the odd foreigner. It tallied in every detail with the man

"And now about Feldman," mused Tom, as he went to the foreman of the shop where the suspected man had

"Yes, Feldman asked for a day off," the foreman said in response to Tom's question. "He claimed his mother

was sick, and he wanted to go to see her. I knew you wouldn't object, as we were not rushed in his

"Humph!" murmured Tom. To himself he added: "Queer that he should be near Lake Loraine, in an opposite

The next day Tom made it his business to pass near the hammer that was so frequently out of order. He found

Feldman busy instructing Koku in its operation. Tom resolved on a little strategy.

"Very well, Mr. Swift. There doesn't seem to be any trouble at all, but it may happen any minute. Koku seems

"I'll see. By the way, how is your mother?" he asked quickly, looking Feldman full in the face.

"She is much better. I took a day off yesterday to go to see her," the man replied quietly enough, and without

This time Feldman could not repress a start. But he covered it admirably by stooping over to pick up a tool

"Oh," said Tom, as he turned aside to hide a smile. He was sure now he knew at least one of the plotters

But Tom was not yet ready to show his hand. He wanted better evidence than any he yet possessed. It would

Work on the aerial warship was rushed, and it seemed likely that a trial flight could be made before the date

set. Lieutenant Marbury sent word that he would be on hand when needed, and in some of the shops, where

"Well, if everything goes well, we'll take her for a trial flight tomorrow," said Tom, coming in from the

"Guns and all?" asked Ned, who had come over to pay his chum a visit. Mr. Damon was also on hand,

Ned had a little vacation from the bank, and was to stay all night, as was Mr. Damon.

What time it was, save that it must be near midnight, Tom could not tell, but he was suddenly awakened by

"Massa Tom! Massa Tom!" yelled the excited colored man. "Git up! Git up! Suffin' turrible am happenin' in

de balloon shop. Hurry! An' yo' stan' still, Boomerang, or I'll twist yo' tail, dat's what I will! Hurry, Massa

Tom Swift was something like a fireman. He had lived so long in an atmosphere of constant alarms and

danger, that he was always ready for almost any emergency. His room was equipped with the end in view that

So, when he heard Eradicate's alarm, though he wondered what the old colored man was doing out of bed at

His first care was to throw on the main switch, connected with a big storage battery, and to which were

attached the wires of the lighting system. This at once illuminated every shop in the plant, and also the

grounds themselves. Tom wanted to see what was going on. The use of a storage battery eliminated the

And once he had done this, Tom began pulling on some clothes and a pair of shoes. At the same time he

reached out with one hand and pressed a button that sounded an alarm in the sleeping quarters of Koku, the

"Killing Koku!" exclaimed Tom, as he finished his hasty dressing. "Then my giant must already be in the

"What's up, Tom?" came Ned's voice from the adjoining room. "I thought I heard a noise."

"Your thoughts do you credit, Ned!" Tom answered. "If you listen right close, you'll hear several noises."

Tom could hear his chum bound out of bed to the floor, and, at the same time, from the big shed where Tom

"Oh, Tom, what is it?" asked Mrs. Baggert, the housekeeper, looking from her room.

"I don't know. But don't let dad get excited, no matter what happens. Just put him off until I come back. I

Mr. Damon, who roomed next to Ned, came out of his own apartment partially dressed.

"Bless my suspenders!" he cried to Tom, those articles just then dangling over his hips. "What is it? What has

"I think it isn't that," Tom answered. "No alarm has rung. Koku seems to be in trouble."

"Well, he's big enough to look after himself, that's one consolation," chuckled Mr. Damon. "I'll be right with

By this time Ned had run out into the hall, and, together, he and Tom sped down the corridor. They could not

hear the shouts of Eradicate so plainly now, as he was on the other side of the house.

But when the two young men reached the front porch, they could hear the yells given with redoubled vigor.

And, in the glare of the electric lights, Tom saw Eradicate leading along Boomerang, the old mule.

From the interior of the big shed, not far from the house, Tom and Ned heard a confused jumble of shouts,

cries and pleadings, mingled with the rattle of pieces of metal, and the banging of bits of wood. And, above

all that, like the bellowing of a bull, was noted the rumbling voice of Koku, the giant.

"It's suah trouble, all right," went on Eradicate. "Mah mule, Boomerang, had a touch ob de colic, an' I got up

t' gib him some hot drops an' walk him around, when I heard de mostest terrific racketsound, and den I

"It isn't comingit's here!" called Tom, as he sped toward the big shop. Ned was but a step behind him. The

big workshop where the aerial warship was being built was, like the other buildings, brilliantly illuminated by

the lights Tom had switched on. The young inventor also saw several of his employees speeding toward the

Torn was the first to reach the small door of the shed. This was built in one of the two large main doors,

which could be swung open when it was desired to slide the Mars in from the ground, and not admit it

Ned looked over his chum's shoulder and saw the giant, Koku, struggling with four menpowerful men they

For they came at Koku from four sides, seeking to hold his hands and feet so that he could not fight them

back. On the floor near where the struggle was taking place was a coil of rope, and it was evident that it had

been the intention of the men to overcome Koku and truss him up, so that he would not interfere with what

they intended to do. But Koku was a match for even the four men, powerful as they were.

"We're here, Koku!" cried Tom. "Watch for an opening, Ned!" he called to his chum.

The sound of Tom's voice disconcerted at least two of the attackers, for they looked around quickly, and this

Though such a big man, Koku was exceptionally quick, and no sooner did he see his advantage, as two of the

Suddenly tearing loose his hands from the grip of the two men who had looked around, Koku shot out his

right and left fists, and secured good hold on the necks of two of his enemies. The other two, at his back,

So big was Koku's hands that they almost encircled the necks of his antagonists. Then happened a curious

With a shout that might have done credit to some ancient cave dweller of the stone age, Koku spread out his

mighty arms, and held apart the two men he had grasped. In vain they struggled to free themselves from that

A moment later, with a quick and sudden motion he bent his arms, bringing toward each other the two men

he held as captives. Their heads came together with a dull thud, and a second later Koku allowed two limp

"He's done for them!" Tom cried. "Knocked them unconscious. Good for you, Koku!"

The giant grunted, and then, with a quick motion, slung himself around, hoping to bring the enemies at his

As soon as the other two ruffians had seen their companions fall to the floor of the shop they turned and fled,

"Some of the other men can chase them," said the young inventor. "We'll tie up the two Koku has captured."

As he approached nearer to the unconscious captives Tom uttered a cry of surprise, for he recognized them as

He glanced toward the window through which the two men had jumped to escape, and he was just in time to

see one of them run past the open door. The face of this one was under a powerful electric light, and Tom at

once recognized the man as Feldman, the worker who had had so much trouble with the triphammer.

"This sure is a puzzle," marveled Tom. "My own men in the plot! But why did they attack Koku?"

The giant, bending over the men he had knocked unconscious by beating their heads together, seemed little

"We tie 'em up," he said grimly, as he brought over the rope that had been intended for himself.

Little time was lost in securing the two men who bad been so effectively rendered helpless by Koku's ready,

if rough, measures. One of them was showing signs of returning consciousness now, and Tom, not willing to

inflict needless pain, even on an enemy, told one of his men, summoned by the alarm, to bring water. Soon

"It must have been a thunderbolt," spoke the other dreamily. "But it didn't look like a storm."

"Oh, dere was a storm, all right," chuckled Eradicate, who, having left his mule, Boomerang outside, came

The men put their hands to their heads, and seemed to comprehend. They looked at the rope that bound their

"What does this meanRansomKurdy?" asked Tom sternly, when the men seemed able to talk. "Did you

"It looks as though he had the best of us, whether we did or not," said the man Tom knew as Kurdy. "Whew,

"What does it mean?" asked Tom sternly. "There were four of you. Feldman and one other got away."

"Oh, trust Feldman for getting away," sneered Kurdy. "He always leaves his friends in the lurch."

The two captives looked at one another, sitting bound on the floor of the shop, their backs against some

"I guess it's all up, and we might as well make a clean breast of it," admitted Kurdy.

"Perhaps it would be better," said Tom quietly. "Eradicate," he went on, to the colored man, "go to the house

"No one hurt, Massa Tom? What about dem dere fellers?" and the colored man pointed to the captives.

"Well, they're not hurt much," and Tom permitted himself a little smile. "I don't want my father to worry. Tell

"All right, Massa Tom. I'se gwine right off. I'se got t' look after mah mule, Boomerang, too. I'se gwine," and

"Who else besides Feldman got away?" asked Tom, looking alternately at the prisoners.

"All right, go ahead, we'll have to take our medicine. I might have known it would turn out this waygoing

in for this sort of thing. It's the first bit of crooked business I ever tried," the man said earnestly, "and it will

"Harrison," answered Kurdy, naming one of the most efficient of the new machinists Tom had hired during

"I'm sorry to learn that," Tom went on in a low voice. "He was an expert in his line. But what was your

"We didn't intend to attack him," explained Ransom, "but he came in when we were at work, and as he went

for us we tried to stand him off. Then your colored man heard the racket, andwell, I guess you know the

"But I don't understand why you came into this shed at night," went on Tom. "No one is allowed in here. You

"Look here!" exclaimed Kurdy, "I said we'd make a clean breast of it, and we will. We're only a couple of

tools, and we were foolish ever to go in with those fellows; or rather, in with that Frenchman, who promised

"In damaging your new aerial warship, or in getting certain parts of it so he could take them away with him."

"Yes, he's one of the foreign spies," interrupted Ransom. "You'd find it out, anyhow, if we didn't tell you.

They are after you, Tom Swift, and after your machines. They had vowed to get them by fair means or foul,

"But we were only tools in their hands. So were Feldman and Harrison, but they knew more about the details.

"Then we must try to capture them," decided Tom. "Ned, see if the chase had any results. I'll look after these

"Oh, we give in," admitted Kurdy. "We know when we've had enough," and he rubbed his head gently where

"Do you mean that you four came into this shop, at midnight, to damage the Mars?" asked Tom.

"That's about it, Mr. Swift," replied Kurdy rather shamefacedly. "We were to damage it beyond repair, set fire

to the whole place, if need be, and, at the same time, take away certain vital parts

"Harrison, Feldman, Ransom and I came in, thinking the coast was clear. But Koku must have seen us enter,

or he suspected we were here, for he came in after us, and the fight began. We couldn't stop him, and he did

for us. I'm rather glad of it, too, for I never liked the work. It was only that they tempted me with a promise of

"That FrenchmanLa Foy, he calls himself, and some other foreigners in your shops."

"Bless my chest protector!" cried Mn Damon, who had come in and had been a silent listener to this. "Can it

"That's the case," went on Kurdy. "A lot of the new men you took on are foreign spies from different

European nations. They are trying to learn all they can about your plans, Mr. Swift!"

"No; each one is trying to get ahead of the other. So far the Frenchman seems to have had the best of it. But

"That's about all we know," spoke Ransom. "We were only hired to do the rough work. Those higher up

"Then my suspicions of him were justified," thought Tom. "He evidently met La Foy in the woods to make

The two captives seemed willing enough to make a confession, but they did not know much. As they said,

they were merely tools, acting for others. And events had happened just as they had said.

The four conspirators had managed, by means of a false key, and by disconnecting the burglar alarm, to enter

the airship shed. They were about to proceed with their work of destruction when Koku came on the scene.

The giant's appearance was due to accident. He acted as a sort of night watchman, making a tour of the

buildings, but he entered the shed where the Mars was because, that day, he had left his knife in there, and

wanted to get it. Only for that he would not have gone in. When he entered he surprised the four men.

Of course he attacked them at once, and they sprang at him. Then ensued a terrific fight. Eradicate, arising to

doctor his mule, as he had said, heard the noise, and saw what was going on. He gave the alarm.

"No, they got away, Tom. I had a lot of your men out helping me search the grounds, but it wasn't of much

"I mean that the place is filled with spies, Ned! But we will sift them out in the morning. This has been a

lucky night for me. It was touch and go. Now, then, Koku, take these fellows and lock them up somewhere

The two captives were put in secure quarters, and the rest of the night passed quietly. During the fight in the

airship shed some machinery and tools had been broken, but no great amount of damage was done. Tom and

A further search was made in the morning for the two conspirators who had escaped, but no trace of them

was found. Tom then realized why Feldman was so anxious to be placed in the aeroplane departmentit was

A technical charge was made against the two prisoners, sufficient to hold them for some time. Then Tom

devoted a day to weeding out the suspected foreigners in his place. All the new men were discharged, though

"Probably I am hitting some of the innocent in punishing those who, if they had the chance, would become

guilty," Tom said to his chum, "but it cannot be helpedI can't afford to take any chances."

The Mars was being put in shape for her first flight. The guns, fitted with the recoil shock absorbers, were

mounted, and Lieutenant Marbury had returned to go aloft in the big aerial warship. He congratulated Tom on

"But there may be more," he warned the young inventor. "You are not done with them yet."

The Mars was floated out of her hangar, and made ready for an ascent. Tom, Ned, Lieutenant Marbury, Mr.

Damon, and several workmen were to be the first passengers. Tom was busy going over the various parts to

"Bless my insurance policy!" exclaimed Mr. Damon. "Now that the time comes I almost wish I wasn't

"Nonsense!" exclaimed Tom. "You're not going to back out at the last minute. All aboard! Cast off the

A moment later the Mars, the biggest airship Tom Swift had ever constructed, arose from the earth like some

"Well, Tom, we're moving!" cried Ned Newton, clapping his chum on the back, as he stood near him in the

"Well, I wasn't quite sure," Ned confessed. "You know you were so worried about"

"Not about the ship sailing," interrupted Tom. "It was only the effect the firing of the guns might have. But I

"Bless my pin cushion!" cried Mr. Damon, as he looked over the rail at the earth below. "We're moving fast,

"Yes, we can make a quicker ascent in this than in most aeroplanes," Tom said, "for they have to go up in a

"Just how fast do you think you can travel when you are in firstclass shape?" asked Lieu tenant Marbury, as

"Well, I set a limit of seventyfive miles an hour," the young inventor replied, as he shifted various levers

and handles, to change the speed of the mechanism. "But I'm afraid we won't quite equal that with all our

"That will more than satisfy the government requirements," the officer said. "But, of course, your craft will

"I'll give you every test you want," declared Tom, with a smile. "And now we'll see what the Mars can do

Up and up went the big dirigible aerial warship. Had you been fortunate enough to have seen her you would

have observed a craft not unlike, in shape, the German Zeppelins. But it differed from those war balloons in

Tom's craft was about six hundred feet long, and the diameter of the gas bag, amidships, was sixty feet,

slightly larger than the largest Zeppelin. Below the bag, which, as I have explained, was made up of a number

of gastight compartments, hung from wire cables three cabins. The forward one was a sort of pilothouse,

containing various instruments for navigating the ship of the air, observation rooms, gauges for calculating

Amidships, suspended below the great bag, were the living and sleeping quarters, where food was cooked and

served and where those who operated the craft could spend their leisure time. Extra supplies were also stored

At the stern of the big bag was the motorroom, where gas was generated to fill the balloon compartments

when necessary, where the gasoline and electrical apparatus were installed, and where the real motive power

of the craft was located. Here, also, was carried the large quantity of gasoline and oil needed for a long

voyage. The Mars could carry sufficient fuel to last for over a week, provided no accidents occurred.

There was also an arrangement in the motor compartment, so that the ship could be steered and operated from

there. This was in case the forward pilothouse should be shot away by an enemy. And, also, in the motor

All three suspended cabins were connected by a long covered runway, so that one could pass from the

At the extreme end of the big bag were the various rudders and planes, designed to keep the craft on a level

keel, automatically, and to enable it to make headway against a strong wind. The motive power consisted of

three doublebladed wooden propellers, which could be operated together or independently. A powerful

gasoline engine was the chief motive power, though there was an auxiliary storage battery, which would

operate an electrical motor and send the ship along for more than twenty four hours in case of accident to

There were many other pieces of apparatus aboard, some not completely installed, the uses of which I shall

mention from time to time, as the story progresses. The gasgenerating machine was of importance, for there

would be a leakage and shrinking of the vapor from the big bag, and some means must be provided for

"You don't seem to have forgotten anything, Tom," said Ned admiringly, as they soared upward.

"We can tell better after we've flown about a bit," observed the young inventor, with a smile. "I expect we

"Why, you're not frightened, are you?" inquired Tom. "You have been up in airships with me before."

"Oh, no, I'm not frightened!" exclaimed the odd man. "Bless my suspenders, no! But I promised my wife I'd

"We'll sail over toward Waterford," broke in Tom, "and I'll drop you down in your front yard."

"No, don't do that! Don't! I beg of you!" cried Mr. Damon. "You seeerTom, my wife doesn't like me to

make these trips. Of course, I understand there is no danger, and I like them. But it's just as well not to make

"Oh, all right," replied Tom, with a laugh. "Well, we're not going far on this trip. What I want to do, most of

all, is to test the guns, and see if the recoil check will work as well when we are aloft as it did down on the

ground. You know a balloon isn't a very stable base for a gun, even one of light caliber."

"No, it certainly is not," agreed Lieutenant Marbury, "and I am interested in seeing how you will overcome

Meanwhile the Mars, having reached a considerable height, being up so far, in fact, that the village of

Shopton could scarcely be distinguished, Tom set the signal that told the engineroom force to start the

Some of Tom's most trusted workmen formed the operating crew, the young inventor taking charge of the

"Well she seems to run all right," observed Lieutenant Marbury, as the big craft surged ahead just below a

"Yes, but not as fast as I'd like to see her go, Tom replied. "Of course the machinery is new, and it will take

They had been running for perhaps ten minutes when Tom shoved over the hand of an indicator that

communicated with the engine room from the pilothouse. At once the Mars increased her speed.

"Bless myhat! I should say so!" cried Mr. Damon, for he was standing outside the pilothouse just then, on

"There you arecaught on the fly!" cried Ned, as he put up his hand just in time to catch the article in

"Thanks! Guess I'd better tie it fast," remarked the odd man, putting his hat on tightly.

The aerial warship was put through several evolutions to test her stability, and to each one she responded

well, earning the praise of the government officer. Up and down, to one side and the other, around in big

circles, and even reversing, Tom sent his craft with a true hand and eye. In a speed test fiftyfive miles was

registered against a slight wind, and the young inventor said he knew he could do better than that as soon as

"And now suppose we get ready for the gun tests," suggested Tom, when they had been running for about an

"That's what I'm mostly interested in," said Lieutenant Marbury. "It's easy enough to get several good types

of dirigible balloons, but few of them will stand having a gun fired from them, to say nothing of several

"Well, I'm not making any rash promises," Tom went on, "but I think we can turn the trick."

The armament of the Mars was located around the center cabin. There were two large guns, fore and aft,

throwing a fourinch projectile, and two smaller calibered quickfirers on either beam. The guns were

mounted on pedestals that enabled the weapons to fire in almost any direction, save straight up, and of course

the balloon bag being above them prevented this. However, there was an arrangement whereby a small

automatic quickfirer could be sent up to a platform built on top of the gas envelope itself, and a man

But the main deck guns could be elevated to an angle of nearly fortyfive degrees, so they could take care of

"But where are the bombs I heard you speaking of?" asked Ned, as they finished looking at the guns.

"Here they are," spoke Tom, as he pointed to a space in the middle of the main cabin floor. He lifted a brass

plate, and disclosed three holes, covered with a strong wire netting that could be removed. "The bombs will

be dropped through those holes," explained the young inventor, "being released by a magnetic control when

the operator thinks he has reached a spot over the enemy's city or fortification where the most damage will be

done. I'll show you how they work a little later. Now we'll have a test of some of the guns."

Tom called for some of his men to take charge of the steering and running of the Mars while he and

Lieutenant Marbury prepared to fire the two larger weapons. This was to be one of the most important tests.

Service charges had been put in, though, of course, no projectiles would be used, since they were then flying

"We'll have to wait until we get out over the ocean to give a complete test, with a bursting shell," Tom said.

He and Lieutenant Marbury were beside a gun, and were about to fire it, when suddenly, from the stern of the

ship, came a ripping, tearing sound, and, at the same time, confused shouts came from the crew's quarters.

"One of the propellers!" was the answer. "It's split, and has torn a big hole in the gas bag!"

"Steady, all!" came in even tones from Tom Swift. Not for an instant had he lost his composure. For it was an

accident, that much was certain, and one that might endanger the lives of all on board.

Above the noise of the machinery in the motor room could be heard the thrashing and banging of the broken

or loose propeller blade. Just what its condition was, could not be told, as a bulge of the gas bag hid it from

the view of those gathered about the gun, which was about to be fired when the alarm was given.

"That's nothing," was the cool answer. "It is only for a moment. Only a few of the gas compartments can be

And so it proved. The moment the pressure of the lifting gas in the big oiled silk and aluminum container was

lowered, it started the generating machine, and enough extra gas was pumped into the uninjured

"No, and we'll soon stop falling altogether," calmly declared Tom. "Too bad this accident had to happen,

"It might have been much worse, my boy!" exclaimed the lieutenant. "That's a great arrangement of

"It's on the same principle as the air brakes of a trolley car," explained Tom, when a look at the indicators

showed that the Mars had ceased falling and remained stationary in the air. Tom had also sent a signal to the

engineroom to shut off the power, so that the two undamaged propellers, as well as the broken one, ceased

"In a trolley car, you see," Tom went on, when the excitement had calmed down, "as soon as the air pressure

in the tanks gets below a certain point, caused by using the air for a number of applications of the brakes, it

lets a magnetized bar fall, and this establishes an electrical connection, starting the air pump. The pump

forces more air into the tanks until the pressure is enough to throw the pump switch out of connection, when

"And very clever it is," said Mr. Damon. "Do you suppose the danger is all over, Tom?"

"For the time being, yes. But we must unship that damaged propeller, and go on with the two."

The necessary orders were given, and several men from the engineroom at once began the removal of the

As several spare ones were carried aboard one could be put on in place of the broken one, had this been

desired. But Tom thought the accident a good chance to see how his craft would act with only twothirds of

her motive force available, so he did not order the damaged propeller replaced. When it was lowered to the

"That's a question I can't answer," Tom replied. "There may have been a defect in the wood, but I had it all

The propeller was one of the "builtup" type, with alternate layers of ash and mahogany, but some powerful

force had torn and twisted the blades. The wood was splintered and split, and some jagged pieces, flying off

at a tangent, so great was the centrifugal force, had torn holes in the strong gas bag.

"Did something hit it; or did it hit something?" asked Ned as he saw Tom carefully examining the broken

"Hard to say. I'll have a good look at this when we get back. Just now I want to finish that gun test we didn't

"You don't mean to say you're going to keep on, and with the balloon damaged; are you?" cried Mr. Damon,

"Certainlywhy not?" Tom replied. "In warfare accidents may happen, and if the Mars can't go on, after a

little damage like this, what is going to happen when she's fired on by a hostile ship? Of course I'm going

There really was very little danger in proceeding. The Mars was just as buoyant as before, for more gas had

been automatically made, and forced into the uninjured compartments of the bag. At the same time enough

sand ballast had been allowed to run out to make the weight to be lifted less in proportion to the power

True, the speed would be less, with two propellers instead of three, and the craft would not steer as well, with

the torn ends of the gas bag floating out behind. But this made a nearer approach to war conditions, and Tom

So, after a little while, during which it was seen that the Mars was proceeding almost normally, the matter of

The weapons were all ready to fire, and when Tom had attached the pressure gauges to note how much

The two big weapons were discharged together, and for a moment after the report echoed out among the

For the big craft rolled and twisted, and seemed about to turn turtle. Her forward progress was halted,

momentarily, and a cry of fear came from several of the members of the crew, who had had only a little

"A little," admitted Tom, with a rueful look on his face. "Those recoil checks didn't work as well in practice

"Bless my watch chain!" cried Mr. Damon. "You aren't going to fire those guns again; are you, Tom?"

"Why not? We can't tell what's the matter, nor get things right without experimenting. There's no danger."

"Oh, well, if she turns over she'll right herself again," Tom said. "The center of gravity is low, you see. She

can't float in any position but right side up, though she may turn over once or twice."

"Excuse me!" said Mr. Damon firmly. "I'd rather go down, if it's all the same to you. If my wife ever knew I

"We'll go down soon," Tom promised. "But I must fire a couple of shots more. You wouldn't call the recoil

checks a success, would you?" and the young inventor appealed to the government inspector.

"No, I certainly would not," was the prompt answer. "I am sorry, too, for they seemed to be just what was

needed. Of course I understand this is not an official test, and I am not obliged to make a report of this trial.

"I realize that, and I'm not asking any favors. but I'll try it again with the recoil checks tightened up. I think

Preparations were now made for firing the fourinch guns once more. All this while the Mars had been

speeding around in space, being about two miles up in the air. Tom's craft was not designed to reach as great

an elevation as would be possible in an aeroplane, since to work havoc to an enemy's fortifications by means

In fact, experiments in Germany have shown that bombs falling from a great height are less effective than

those falling from an airship nearer the earth. For a bomb, falling from a height of two miles, acquires enough

momentum to penetrate far into the earth, so that much of the resultant explosive force is expended in a

downward direction, and little damage is done to the fortifications. A bomb dropped from a lower altitude,

On the other hand, in destroying buildings, it has been found desirable to drop a bomb from a good height so

Once more Tom made ready to fire, this time having given the recoil checks greater resistance. But though

there was less motion imparted to the airship when the guns were discharged, there was still too much for

"Well, something's wrong, that's sure," remarked Tom, in rather disappointed tones as he noted the effect of

the second shots. "If we get as much recoil from the two guns, what would happen if we fired them all at

"Don't do it! Don't do it, I beg of you!" entreated Mr. Damon. "Bless my toothbrushdon't do it!"

"I won'tjust at present," Tom said, ruefully. "I'm afraid I'll have to begin all over again, and proceed along

"Well, perhaps you will," said the lieutenant. "But you may invent something much better than anything you

"Oh, I'll get busy on it right away," Tom declared. "We'll go down now, and start right to work. I'm afraid,

"I might have known my idea wouldn't amount to anything," said the young bank clerk.

"Oh, the idea is all right," declared Tom, "but it wants modifying. There is more power to those recoils than I

figured, though our first experiments seemed to warrant us in believing that we had solved the problem."

"Yes, there can't be any recoil from that," Tom said. "I'll drop a few blank ones, and see how accurate the

While his men were getting ready for this test Tom bent over the broken propeller, looking from that to the

recoil checks, which had not come up to expectations. Then he shook his head in a worried and puzzled

Dropping bombs from an aeroplane, or a dirigible balloon, is a comparatively simple matter. Of course there

are complications that may ensue, from the danger of carrying high explosives in the limited quarters of an

airship, with its inflammable gasoline fuel, and everpresent electric spark, to the possible premature

On the other hand, while it is comparatively easy to drop a bomb from a moving aeroplane, or dirigible

balloon, it is another matter to make the bomb fall just where it will do the most damage to the enemy. It is

not easy to gauge distances, high up in the air, and then, too, allowance must be made for the speed of the

aircraft, the everincreasing velocity of a falling body, and the deflection caused by air currents.

The law of velocity governing falling bodies is well known. It varies, of course, according to the height, but

in general a body falling freely toward the earth, as all highschool boys know, is accelerated at the rate of

thirtytwo feet per second. This law has been taken advantage of by the French in the present European war.

The French drop from balloons, or aeroplanes, a steel dart about the size of a lead pencil, and sharpened in

about the same manner. Dropping from a height of a mile or so, that dart will acquire enough velocity to

But in dropping bombs from an airship the damage intended does not so much depend on velocity. It is

necessary to know how fast the bomb falls in order to know when to set the time fuse that will explode it;

At aeroplane meets there are often bombdropping contests, and balls filled with a white powder (that will

make a dustcloud on falling, and so show where they strike) are used to demonstrate the birdman's accuracy.

"We'll see how our bombrelease works," Tom went on. "But we'll have to descend a bit in order to watch

"Indeed not. Just chalkdust ones for practice. Now here is where the bombs will be placed," and he pointed

to the three openings in the floor of the amidship cabin. The wire nettings were taken out and one could look

down through the holes to the earth below, the ground being nearer now, as Tom had let out some of the

"Here is the rangefinder and the speed calculator," the young inventor went on as he indicated the various

instruments. "The operator sits here, where he can tell when is the most favorable moment for releasing the

Tom took his place before a complicated set of instruments, and began manipulating them. One of his

assistants, under the direction of Lieutenant Marbury, placed in the three openings bombs, made of light

cardboard, just the size of a regular bomb, but filled with a white powder that would, on breaking, make a

"I have first to determine where I want to drop the bomb," Tom explained, "and then I have to get my

distance from it on the rangefinder. Next I have to know how fast I am traveling, and how far up in the air I

am, to tell what the velocity of the falling bomb will attain at a certain time. This I can do by means of these

instruments. some of which I have adapted from those used by the government," he said, with a nod to the

"We will now assume that the bombs are in place in the holes in the floor of the cabin," Tom went on. "As I

sit here I have before me three buttons. They control the magnets that hold the bombs in place. If I press one

of the buttons it breaks the electrical current, the magnet no longer has any attraction, and it releases the

explosive. Now look down. I am going to try and drop a chalk bomb near that stone fence."

The Mars was then flying over a large field and a stone fence was in plain view.

"Here she goes!" cried Tom, as he made some rapid calculations from his gauge instruments. There was a

little click and the chalk bomb dropped. There was a plate glass floor in part of the cabin, and through this the

"She'll never go anywhere near the fence!" declared Ned. "You let it drop too soon, Tom!"

"Did I? You just watch. I had to allow for the momentum that would be given the bomb by the forward

Hardly had Tom spoken than a puff of white was seen on the very top of the fence.

"Yes, I thought I would. Well, that shows my gauges are correct, anyhow. Now we'll try the other two

In succession they were released from the bottom of the cabin, at other designated objects. The second one

"And I'll let the last one down near that scarecrow in the field," said Tom, pointing to a ragged figure in the

Down went the cardboard bomb, and so good was the aim of the young inventor that the white dust arose in a

And then a queer thing happened. For the figure seemed to come to life, and Ned, who was watching through

a telescope, saw a very much excited farmer looking up with an expression of the greatest wonder on his face.

He saw the balloon over his head, and shook his fist at it, evidently thinking he had had a narrow escape. But

the pasteboard bomb was so light that, had it hit him, he would not have been injured, though he might have

"Well, it proved the accuracy of your aim, at any rate," observed Lieutenant Marbury. "The bomb dropping

"And I'll have the guns fixed soon, so there will be no danger of a recoil, too," added Tom Swift, with a

"What's next?" asked Mr. Damon, looking at his watch. "I really ought to be home, Tom."

"We're going back now, and down. Are you sure you don't want me to drop you in your own front yard, or

"Bless my stovepipe, no, Tom! My wife would have hysterics. Just land me at Shopton and I'll take a car

The damaged airship seemed little the worse for the test to which she had been subjected, and made her way

at good speed in the direction of Tom's home. Several little experiments were tried on the way back. They all

worked well, and the only two problems Tom had to solve were the taking care of the recoil from the guns

A safe landing was made, and the Mars once more put away in her hangar. Mr. Damon departed for his

home, and Lieutenant Marbury again took up his residence in the Swift household.

"I was afraid so. You had better drop this line of work, and go at something else."

"No, Dad!" Tom cried. "I'm going to make this work. I never had anything stump me yet, and I'm not going

"Well, that's a good spirit to show," said the aged inventor, with a shake of his head, "but I don't believe you'll

Tom decided to begin on the problem of the propeller first, as that seemed more simple. He knew that the gun

"Just what are you trying to find out, Tom?" asked Ned, a few nights later, when he found his chum looking

"Trying to discover what made this blade break up and splinter that way. It couldn't have been centrifugal

Tom was "poking" away amid splinters, and bits of broken wood, when he suddenly uttered an exclamation,

"The thing that weakened the propeller. Look at this, and smell!" He held out a piece of wood toward Ned.

The bank employee saw where a halfround hole had been bored in what remained of the blade, and from

"That's it!" cried Tom. "Someone bored a hole in the propeller, and put in some sort of receptacle, or capsule,

containing a corrosive acid. In due time, which happened to be when we took our first flight, the acid ate

through whatever it was contained in, and then attacked the wood of the propeller blade. It weakened the

"Yes, I know we might," said Tom. "It must be the work of some of those foreign spies whose first plot we

Lieutenant Marbury agreed with Tom that someone had surreptitiously bored a small hole in the propeller

blade, and had inserted a corrosive acid that would take many hours to operate. The hole had been varnished

"And that means I've got to examine the other two blades," Tom said. "They may be doctored too."

But they did not prove to be. A careful examination showed nothing wrong. An effort was made to find out

who had tried to destroy the Mars in midair, but it came to nothing. The two men in custody declared they

Meanwhile, the torn gas bag was repaired, and Tom began working on the problem of doing away with the

gun recoil. He tried several schemes, and almost was on the point of giving up when suddenly he received a

hint by reading an account of how the recoil was taken care of on some of the German Zeppelins.

The guns there were made double, with the extra barrel filled with water or sand, that could be shot out as

was the regular charge. As both barrels were fired at the same time, and in opposite directions, with the same

amount of powder, one neutralized the other, and the recoil was canceled, the ship remaining steady after fire.

It was no easy matter to change all the guns of the Mars, and fit them with double barrels. But by working

day and night shifts Tom managed it. Meanwhile, a careful watch was kept over the shops. Several new men

applied for work, and some of them were suspicious enough in looks, but Tom took on no new hands.

Finally the new guns were made, and tried with the Mars held on the ground. They behaved perfectly, the

shooting of sand or water from the dummy barrel neutralizing the shot from the service barrel.

"And now to see how it works in practice!" cried Tom one day. "Are you with me for a long flight, Ned?"

The next evening the Mars, with a larger crew than before, and with Tom, Ned, Mr. Damon and Lieutenant

The Mars flew slowly all night, life aboard her, at about the level of the clouds, going on almost as naturally

as though the occupants of the cabins were on the earth. Excellent meals were served.

"But when are you going to try the guns?" asked Ned, as he got ready to turn in.

And, in the morning, when Ned looked down through the plate glass in the cabin floor, he uttered a cry.

"I rather thought we'd be," was the calm reply. "I told George to head straight for the Atlantic. Now we'll

Surprise, for the moment, held Mr. Damon, Ned and Lieutenant Marbury speechless. They looked from the

heaving waters of the ocean below them to the young pilot of the Mars. He smiled at their astonishment.

"Whatwhat does it mean, Tom?" asked Ned. "You never said you were going to take a trip as far as this."

"That's right," chimed in Mr. Damon. "Bless my nightcap! If I had known I was going to be brought so far

"You're not so very far from Water ford," put in Tom. "We didn't make any kind of speed coming from

"No, we just drifted along," Tom answered. "I gave orders to run the machinery slowly, as I wanted to get it

in good shape for the other tests that will come soon. But I told George, whom I left in charge when I turned

in, to head for New York. I wanted to get out over the ocean to try the guns with the new recoil arrangement."

"Well, we're over the ocean all right," spoke Ned, as he looked down at the heaving waters.

"It isn't the first time," replied Tom cheerfully. "Koku, you may serve breakfast now," for the giant had been

taken along as a sort of cook and waiter. Koku manifested no surprise or alarm when he found the airship

floating over the sea. Whatever Tom did was right to him. He had great confidence in his master.

"No, it isn't the first time we've taken a water flight," spoke Ned. "I was only surprised at the suddenness of it,

"It's my first experience so far out above the water," observed Lieutenant Marbury, "though of course I've

"About ten miles out, yes," admitted Tom. "Far enough to make it safe to test the guns with real projectiles.

"Yes, but at slow speed. The engines are in better shape now than ever before," Tom said. "Well, if you're

The meal was served by Koku with as much unconcern as though they were in the Swift homestead back in

Shopton, instead of floating near the clouds. And while it was being eaten in the main cabin, and while the

crew was having breakfast in their quarters, the aerial warship was moving along over the ocean in charge of

George Watson, one of Tom's engineers, who was stationed in the forward pilothouse.

"So you're going to give the guns a real test this time, is that it, Tom?" asked Ned, as he pushed back his

"But don't you think it's a bit risky out over the water this way. Supposing something shouldshould

"Nothing like that could happen. I'm so sure that I have solved the problem of the recoil of the guns that I'm

willing to take chances. But if any of you want to get off the Mars while the test is being made, I have a small

"No, thank you!" interrupted Mr. Damon, as he looked below. There was quite a heavy swell on, and the

ocean did not appear very attractive. They would be much more comfortable in the big Mars.

"I think you won't have any trouble," asserted Lieutenant Marbury. "I believe Tom Swift has the right idea

about the guns, and there will be so small a shock from the recoil that it will not be noticeable."

They were now well out from shore, over the Atlantic, but to make certain no ships would be endangered by

the projectiles, Tom and the others searched the waters to the horizon with powerful glasses. Nothing was

seen and the work of loading the guns was begun. The bomb tubes, in the main cabin, were also to be given a

As service charges were to be used, and as the projectiles were filled with explosives, great care was needed

"We'll try dropping bombs first," Tom suggested. "We know they will work, and that will be so much out of

To make the test a severe one, small floating targets were first dropped overboard from the Mars. Then the

aerial warship, circling about, came on toward them. Tom, seated at the range finders, pressed the button

that released the shells containing the explosives. One after another they dropped into the sea, exploding as

"That's good," responded Tom. "But the others won't be so easy. We have nothing to shoot at."

They had to fire the other guns without targets at which to aim. But, after all, it was the absence of recoil they

wanted to establish, and this could be done without shooting at any particular object.

One after another the guns were loaded. As has been explained, they were now made double, one barrel

"Are you ready?" asked Tom, when it was time to fire. Lieutenant Marbury, Ned and Mr. Damon were

The guns were to be fired simultaneously by means of an electric current, when Tom pressed a button.

There was a moment of waiting, and then came a thundering roar. The Mars trembled, but she did not shift to

either side from an even keel. From one barrel of the guns shot out the explosive projectiles, and from the

other spurted a jet of water, sent out by a charge of powder, equal in weight to that which forced out the shot.

As the projectile was fired in one direction, and the water in one directly opposite, the two discharges

Out flew the pointed steel shells, to fall harmlessly into the sea, where they exploded, sending up columns of

"Couldn't have been better," declared Lieutenant Marbury. "There wasn't the least shock of recoil. Tom Swift,

"I'm glad to hear you say so. There are one or two little things that need changing, but I really think I have

"I think we've seen the last of them," Tom declared. "Now we'll go on with the tests."

More guns were fired, singly and in batteries, and in each case the Mars stood the test perfectly. The double

For some little time longer they remained out over the sea, going through some evolutions to test the rudder

control, and then as their present object had been accomplished Tom gave orders to head back to Shopton,

"Well, Tom, how was it?" asked Mr. Swift, for though his son had said nothing to his friends about the

"That's good. I didn't think you could do it. But you did. I tell you it isn't much that can get the best of a

Swift!" exclaimed the aged man proudly. "Oh, by the way, Tom, here's a telegram that came while you were

Tom ripped it open with a single gesture, and in a flash his eyes took in the words. He read:

"Nooh, no," replied Tom, as he crumpled up the paper and thrust it into his pocket. "No bad news, Dad."

When Tom showed the message to Lieutenant Marbury, that official, after one glance at the signature, said:

"Head of the Secret Service department that has charge of this airship matter. There must be something in the

Extra precautions were taken about the shops. Strangers were not permitted to enter, and all future work on

the Mars was kept secret. Nevertheless, Tom was worried. He did not want his work to be spoiled just when it

was about to be a success. For that it was a success, Lieutenant Marbury assured him. The government man

said he would have no hesitation in recommending the purchase of Tom's aerial warship.

"In a storm. You know we can't always count on haying good weather, and I'd like to see how she behaves in

For the next week, during which finishing touches were put on the big craft, Tom anxiously waited for signs

of a storm. At last they came. Danger signals were put up all along the coast, and warnings were sent out

One dull gray morning Tom roused his friends early and announced that the Mars was going up.

"A big storm is headed this way," Tom said, "and we'll have a chance to see how she behaves in it."

And even as the flight began, the forerunning wind and rain came in a gust of fury. Into the midst of it shot

the big aerial warship, with her powerful propellers beating the moistureladen air.

It was Ned Newton who asked the question, and Tom Swift who answered it. The chums were in the

pilothouse of the dipping, swaying Mars, which was nosing her way into the storm, fighting on an upward

"Well, I mean are you sure your craft will stand all this straining, pulling and hauling?" went on Ned, as he

clung to a brass hand rail, built in the side of the pilothouse wall for the very purpose to which it was now

"If she doesn't stand it she's no good!" cried Tom, as he clung to the steering wheel, which was nearly torn

"Well, it's taking a big chance, it seems to me," went on Ned, as he peered through the rainspotted

"There's no danger," declared Tom. "I wanted to give the ship the hardest test possible before I formally

offered her to the government. If she can't stand a blow like this she isn't what I thought her, and I'll have to

build another. But I'm sure she will stand the racket, Ned. She's built strongly, and even if part of the gas bag

is carried away, as it was when our propeller shattered, we can still sail. If you think this is anything, wait

"I certainly am. We're going with the gale now, to see what is the highest rate of speed we can attain. Pretty

soon I'm going to turn her around, and see if she can make any headway in the other direction. Of course I

know she won't make much, if any speed, against the gale; but I must give her that test."

"Well, Tom, you know best, of course," admitted Ned. "But to me it seems like taking a big risk."

And indeed it did seem, not only to Ned, but to some of the experienced men of Tom's crew, that the young

inventor was taking more chances than ever before, and Tom, as my old readers well know, had, in his career,

The storm grew worse as the day progressed, until it was a veritable hurricane of wind and rain. The warnings

of the Weather Bureau had not been exaggerated. But through the fierce blow the Mars fought her way. As

Tom had said, she was going with the wind. This was comparatively easy. But what would happen when she

Mr. Damon, in the main cabin, sat and looked at Lieutenant Marbury, the eccentric man now and then

"Bless my accident insurance policy!" murmured Mr. Damon. "I wish I had stayed home. If my wife ever

In the engineroom the crew were busy over the various machines. Some of the apparatus was being strained

to keep the ship on her course in the powerful wind, and would be under a worse stress when Tom turned his

craft about. But, so far, nothing had given way, and everything was working smoothly.

As hour succeeded hour and nothing happened, the timid ones aboard began to take more courage. Tom never

for a moment lost heart. He knew what his craft could do, and he had taken her up in a terrific storm with a

definite purpose in view. He was the calmest person aboard, with the exception, perhaps, of Koku. The giant

did not seem to know what fear was. He depended entirely on Tom, and as long as his young master had

There was to be no test of the guns this time. They had worked sufficiently well, and, if need be, could have

been fired in the gale. But Tom did not want his men to take unnecessary risks, nor was he foolhardy himself.

"We'll have our hands full when we turn around and head into the wind," he said to his chum. "That will be

"I surely am. I don't want any comebacks from Uncle Sam after he accepts my aerial warship. I've guaranteed

that she'll stand up and make headway against a gale, and I'm going to prove it"

Lieutenant Marbury was told of the coming trial, and he prepared to take official note of it. While matters

were being gotten in readiness Tom turned the wheel over to his assistant pilot and went to the engineroom

to see that everything was in good shape to cope with any emergency. The rudders had been carefully

examined before the flight was made, to make sure they would not fail, for on them depended the progress of

"I rather guess those foreign spies have given up trying to do Tom an injury," remarked Ned to the lieutenant

as they sat in the main cabin, listening to the howl of the wind, and the dash of the rain.

"Well, I certainly hope so," was the answer. "But I wouldn't be too sure. The folks in Washington evidently

think something is likely to happen, or they wouldn't have sent that warning telegram."

"No, but that isn't any sign they are not getting ready to make trouble. This may be the calm before the storm.

Tom must still be on the lookout. It isn't as though his inventions alone were in danger, for they would not

"They are. But here comes Tom now. He looks as though something new was about to happen."

"Take care of yourselves now," advised the young aeroinventor, as he entered the cabin, finding it hard

"Because we are going to turn around and fight our way back against the gale. We may be turned topsyturvy

Tom went forward to the pilothouse, followed by Ned and the lieutenant. The latter wanted to take official

note of what happened. Tom relieved the man at the wheel, and gradually began to alter the direction of the

At first no change was noticeable. So strong was the force of the wind that it seemed as though the Mars was

going in the same direction. But Ned, noticing a direction compass on the wall, saw that the needle was

"Hold fast!" cried Tom suddenly. Then with a quick shift of the rudder something happened. It seemed as

though the Mars was trying to turn over, and slide along on her side, or as if she wanted to turn about and

scud before the gale, instead of facing it. But Tom held her to the reverse course.

Inch by inch he fought the big craft through the storm. Inch by inch the indicator showed the turning, until at

"Now she's headed right into it!" cried Tom in exultation. "She's nosing right into it!"

And the Mars was. There was no doubt of it. She had succeeded, under Tom's direction, in changing squarely

"But we can't expect to make much speed," Tom said, as he signaled for more power, for he had lowered it

But Tom himself scarcely had reckoned on the force of his craft, for as the propellers whirled more rapidly

the aerial warship did begin to make headway, and that in the teeth of a terrific wind.

"Well, so much the better," Tom said, trying to be calm. "If she can keep this up a little while I'll give her a

The Mars, so far, had met every test. Tom had decided on ten minutes more of galefighting, when from the

"Short circuit in the big motor," was the reply. "We've got to run on storage battery. Send Tom back here!

"Short circuit!" gasped Tom. "Run on storage battery! I'll have to see to that. Take the wheel somebody!"

"Wouldn't it be better to turn about, and run before the wind, so as not to put too great a strain on the

Ned and the government man took the wheel, while Tom hurried along the runway leading from the

The young inventor cast a hasty look about the interior of the place as he entered. He sniffed the air

"What happened?" he asked, noting that already the principal motive power was coming from the big storage

"It's hard to say," was the answer of the chief engineer. "We were running along all right, and we got your

word to switch on more power, after the turn. We did that all right, and she was running as smooth as a

sewingmachine, when, all of a sudden, she shortcircuited, and the storage battery cut in automatically."

"Couldn't have been that. The shunt box would have taken that up, and the circuitbreaker would have

worked, saving us a burn out, and that's what happeneda burnout. The motor will have to be rewound."

"Well, no use trying to fight this gale with the storage battery," Tom said, after a moment's thought. "We'll

He sent the necessary message to the pilothouse. A moment later the shift was made, and once more the

Mars was scudding before the storm. Then Tom gave his serious attention to what had happened in the engine

As he bent over the burnedout motor, looking at the big shiny connections, he saw something that startled

him. With a quick motion Tom Swift picked up a bar of copper. It was hot to the touchso hot that he

dropped it with a cry of pain, though he had let go so quickly that the burn was only momentary.

"Matter!" cried Tom. "A whole lot is the matter! That copper bar is what made the short circuit. It's hot yet

The engine room force gathered about the young inventor. No one could explain how the copper bar came to

be where it was. Certainly no one of Tom's employees had put it there, and it could not have fallen by

accident, for the motor connections were protected by a mesh of wire, and a hand would have to be thrust

under them to put the bar in place. Tom gave a quick look at his men. He knew he could trust themevery

For a moment Tom did not know what to think, and then, as the memory of that warning telegram came to

"Were any strangers in this cabin before the start was made?" he asked Mr. Mound.

But a careful search revealed no one. Yet the young inventor was sure the bar of copper, which had done the

In reality there was no danger to the craft, since there was power enough in the storage battery to run it for

several hours. But the happening showed Tom he had still to reckon with his enemies.

He looked at the height gauge on the wall of the motorroom, and noted that the Mars was going up. In

accordance with Tom's instructions they were sending her above the storm area. Once there, with no gale to

fight, they could easily beat their way back to a point above Shopton, and make the best descent possible.

And that was done while, under Tom's direction, his men took the damaged motor apart, with a view to

"What was it, Tom?" asked Ned, coming back to join his chum, after George Ventor, the assistant pilot, had

"I don't exactly know, Ned," was the answer. "But I feel certain that some of my enemies came aboard here

"Then let's make a search and find them, Tom. It must be some of those foreign spies."

But a more careful search of the craft than the one Tom had casually made revealed the presence of no one.

All the crew and helpers were accounted for, and, as they had been in Tom's service for some time, they were

beyond suspicion. Yet the fact remained that a seemingly human agency had acted to put the main motor out

"It's worse than queer," declared Tom, "it's alarming! I don't know when I'll be safe if we have ghosts

"Well, when we can't find out who put that bar in place I might as well admit it was a ghost," spoke Tom.

"Certainly, if it was done by a man, he didn't jump overboard after doing it, and he isn't here now. It sure is

In due time the Mars, having fought her way above the storm, came over Shopton, and then, the wind having

somewhat died out, she fought her way down, and, after no little trouble, was housed in the hangar.

Tom cautioned his friends and workmen to say nothing to his father about the mysterious happening on

"I'll just tell him we had a slight accident, and let it go at that," Tom decided. "No use in causing him worry."

"I'm going to keep careful watch over the aerial warship, at any rate," declared Tom. "If there's a hidden

Accordingly, a guard, under the direction of Koku, was posted about the big shed, but nothing came of it. No

stranger was observed to sneak out of the ship, after it had been deserted by the crew. The mystery seemed

It took nearly a week to repair the big motor, and, during this time, Tom put some improvements on the

He was getting it ready for the final government test, for the authorities in Washington had sent word that

they would have Captain Warner, in addition to Lieutenant Marbury, make the final inspection and write a

Meanwhile several little things occurred to annoy Tom. He was besieged with applications from new men

who wanted to work, and many of these men seemed to be foreigners. Tom was sure they were either spies of

some European nations, or the agents of spies, and they got no further than the outer gate.

But some strangers did manage to sneak into the works, though they were quickly detected and sent about

their business. Also, once or twice, small fires were discovered in outbuildings, but they were soon

"And yet, with all my precautions, they may get me, or damage something," declared Tom. "It is very

So impressed was Ned with the necessity for caution that he arranged to take his vacation at this time, so as to

The Mars was nearing completion. The repaired motor was better than ever, and everything was in shape for

the final test. Mr. Damon was persuaded to go along, and Koku was to be taken, as well as the two

The night before the trip the guards about the airship shed were doubled, and Tom made two visits to the

Consequently, when the Mars started off on her final test, it was thought that all danger from the spies was

"She certainly is a beauty," said Captain Warner, as the big craft shot upward. "I shall be interested in seeing

"Oh, she'll stand it," declared Lieutenant Marbury. The trip was to consume several days of continuous

It was after supper of the first day out, and our friends were seated in the main cabin laying out a program for

the next day, when sudden yells came from a part of the motor cabin devoted to storage. Koku, who had been

"What's up?" asked Tom, starting to his feet. He was answered almost at once by more yells.

"Oh, Master! Come quickly!" cried the giant. "There are many men here. There are stowaways aboard!"

For a moment, after hearing Koku's reply. neither Tom nor his friends spoke. Then Ned, in a dazed sort of

From the engine compartment, back of the amidship cabin, came a sound of cries and heavy blows. The yells

Then the door of the cabin where Tom Swift and his friends were was suddenly burst open, and seven or

eight men threw themselves within. They were led by a man with a small, dark mustache and a little tuft of

whiskers on his chinan imperial. He looked the typical Frenchman, and his words, snapped out, bore out

What he said was in French, as Tom understood, though he knew little of that language. Also, what the

Frenchman said produced an immediate result, for the men following him sprang at our friends with

Before Tom, Ned, Captain Warner, Mr. Damon or Lieutenant Marbury could grasp any weapon with which

Against such odds little could be done, though our friends did not give up without a struggle.

"What does this mean?" angrily demanded Tom Swift. "Who are you? What are you doing aboard my craft?

His words were lost in smothered tones, for one of his assailants put a heavy cloth over his mouth, and tied it

there, gagging him. Another man, with a quick motion, whipped a rope about Tom's hands and feet, and he

In like manner the others were treated, and, despite the struggles of Mr. Damon, the two government men and

Ned, they were soon put in a position where they could do nothinghelplessly bound, and laid on a bench in

the main cabin, staring blankly up at the ceiling. Each one was gagged so effectively that he could not utter

Of the riot of thoughts that ran through the heads of each one, I leave you to imagine.

What did it all mean? Where had the strange men come from? What did they mean by thus assaulting Tom

and his companions? And what had happened to the others of the crewKoku, Jerry Mound, the engineer,

These were only a few of the questions Tom asked himself, as he lay there, bound and helpless. Doubtless

One thing was certainwhatever the stowaways, as Koku had called them, had done, they had not neglected

the Mars, for she was running along at about the same speed, though in what direction Tom could not tell. He

strained to get a view of the compass on the forward wall of the cabin, but he could not see it.

It had been a roughandtumble fight, by which our friends were made prisoners, but no one seemed to have

been seriously, or even slightly, hurt. The invaders, under the leadership of the Frenchman, were rather

Pantingly they stood in line, surveying their captives, while the man with the mustache and imperial smiled in

a rather superior fashion at the row of bound ones. He spoke in his own tongue to the men, who, with the

exception of one, filed out, going, as Tom and the others could note, to the engineroom in the rear.

"I hope I have not had to hurt any of you," the Frenchman observed, with sarcastic politeness. "I regret the

He spoke with some accent, and Tom at once decided this was the same man who had once approached

Eradicate. He also recognized him as the man he had seen in the woods the day of the outing.

"He's one of the foreign spies," thought Tom "and he's got us and the ship, too. They were too many for us!"

Tom's anxiety to speak, to hold some converse with the captor, was so obvious that the Frenchman said:

"I am going to treat you as well as I can under the circumstances. You and your other friends, who are also

made prisoners, will be allowed to be together, and then you can talk to your hearts' content."

The other man, who had remained with the evident ringleader of the stowaways, asked a question, in French,

"Ah!" thought Tom. "This is the leader of the gang that attacked Koku in the shop that night. They have been

waiting their chance, and now they have made good. But where did they come from? Could they have

Yet, as Tom asked himself that question, he knew it could hardly have been possible. The men must have

been in hiding on his own craft, they must have been, as Koku had cried out stowawaysand have come

"If you will but have patience a little longer," went on La Foy, for that was evidently the name of the leader,

"you will all be together. We are just considering where best to put you so that you will not suffer too much.

The two Frenchmen conversed rapidly in their own language for a few minutes, and then there came into the

cabin another of the men who had helped overpower Tom and his friends. What he told La Foy seemed to

"We are going to put you all together in the largest storeroom, which is partly empty," La Foy said. "There

you will be given food and drink, and treated as well as possible under the circumstances. You will also be

unbound, and may converse among yourselves. I need hardly point out," he went on, "that calling for help

will be useless. We are a mile or so in the air, and have no intention of descending," and he smiled

"They must know how to navigate my aerial warship," thought Tom. "I wonder what their game is, anyhow?"

Night had fallen, but the cabin was aglow with electric lights. The foreigners in charge of the Mars seemed to

know their way about perfectly, and how to manage the big craft. By the vibration Tom could tell that the

A moment later several of the foreigners entered. Some of them did not look at all like Frenchmen, and Tom

"This will be your prisonfor a while," said La Foy significantly, and Tom wondered how long this would

be the case. A sharp thought came to himhow long would they be prisoners? Did not some other, and more

As La Foy spoke, he opened a storeroom door that led off from the main, or amidship, cabin. This room was

intended to contain the supplies and stores that would be taken on a long voyage. It was one of two, being the

larger, and now contained only a few odds and ends of little importance. It made a strong prison, as Tom well

One by one, beginning with Tom, the prisoners were taken up and placed in a recumbent position on the floor

of the storeroom. Then were brought in the engineer and assistant pilot, as well as Koku and a machinist

whom Tom had brought along to help him. Now the young inventor and all his friends were together. It took

"On second thought," said La Foy, as he saw Koku being placed with his friends, "I think we will keep the

big man with us. We had trouble enough to subdue him. Carry him back to the engine room."

"Now then," said La Foy to his prisoners, as he stood in the door of the room, "I will unbind one of you, and

As he spoke, he took the rope from Tom's hands, and then, quickly slipping out, locked and barred the door.

For a moment or two, after the ropes binding his hands were loosed, Tom Swift did nothing. He was not only

stunned mentally, but the bonds had been pulled so tightly about his wrists that the circulation was impeded,

But presently he felt the tingle of the coursing blood, and he found he could move his arms. He raised them to

his head, and then his first care was to remove the pad of cloth that formed a gag over his mouth. Now he

"II'll loosen you all in lust a second," he said, as he bent over to pick at the knot of the rope around his

"I don't know what it's all about, any more than you do," he went on, speaking to the others. "It's a fierce

game we're up against, and we've got to make the best of it. As soon as we can move, and talk, we'll decide

what's best to do. Whoever these fellows are, and I believe they are the foreign spies I've been warned about,

Tom found it no easy matter to loosen the bonds on his feet. The ropes were well tied, and Tom's fingers

were stiff from the lack of circulation of blood. But finally he managed to free himself. When he stood up in

the dim storeroom, that was now a prison for all save Koku, he found that he could not walk. He almost

toppled over, so weak were his legs from the tightness of the ropes. He sat down and worked his muscles

A few minutes later, weak and rather tottery, he managed to reach Mr. Damon, whom he first unbound. He

realized that Mr. Damon was the oldest of his friends, and, consequently, would suffer most. And it was

characteristic of the eccentric gentleman that, as soon as his gag was removed he burst out with:

"That's more than I can say, Mr. Damon," replied Tom, with a mournful shake of his head. "I'm very sorry it

happened, for it looks as though I hadn't taken proper care. The idea of those men stowing themselves away

on board here, and me not knowing it; and then coming out unexpectedly and getting possession of the craft!

"Oh, well, Tom, anyone might have been fooled by those plotting foreigners," said Mr. Damon. "Now, we'll

try to turn matters about and get the best of them. Oh, but it feels good to be free once more!"

He stretched his benumbed and stiffened limbs and then helped Tom free the others. They stood up, looking

"Yes," replied his assistant. "They managed to carry out the plot we tried to frustrate. It was a good trick, too,

"It looks so," observed Tom. "The attack must have started in the engineroom," he went on, with a look at

"Well, that's about the way it was," answered the engineer. "We were working away, making some

adjustments, oiling the parts and seeing that everything was running smoothly, when, all at once, I heard

Koku yell. He had gone in the oil room. At first I thought something had gone wrong with the ship, but, when

I looked at the giant, I saw he was being attacked by four strange men. And, before I, or any of the other men,

"There must have been a dozen of them, and they simply overwhelmed us. One of them hit Koku on the head

with an iron bar, and that took all the fight out of the giant, or the story might have been a different one. As it

was, we were overpowered, and that's all I know until we were carried in here, and saw you folks all tied up

"They burst in on us in the same way," Tom explained. "But where did they come from? Where were they

"In the oil and gasoline storeroom that opens out of the motor compartment," answered Mound, the engineer.

"It isn't half full, you know, and there's room for more than a dozen men in it. They must have gone in some

time last night, when the airship was in the hangar, and remained hidden among the boxes and barrels until

"That's it," decided Tom. "But I don't understand how they got in. The hangar was well guarded all night."

"Yes, that is so," admitted Tom, and, later, he learned that such had been the case. The foreign spies, for such

they were, had managed to corrupt one of Tom's trusted employees, who had looked the other way when La

Foy and his fellowconspirators sneaked into the airship shed and secreted themselves.

"Well, discussing how they got on board isn't going to do us any good now," Tom remarked ruefully. "The

"Why, get out of here, call a policeman, and have these scoundrels arrested. I'll prosecute them! I'll have my

lawyer on hand to see that they get the longest terms the statutes call for! Bless my pocketbook, but I will!"

"That's easier said than done," observed Torn Swift, quietly. "In the first place, it isn't going to be an easy

He looked around the storeroom, which was then their prison. It was illuminated by a single electric light,

"Nothing in them to help us get out," Tom went on, for he knew what the contents were.

"Oh, we'll get out," declared Ned confidently, "but I don't believe we'll find a policeman ready to take our

"That's so," agreed Mr. Damon. "I forgot that we were in an airship. But what is to he done, Tom? We really

"Yes, worse luck," returned the young inventor. "I feel foolish when I think how we let them take us

"We couldn't help it," Ned commented. "They came on us too suddenly. We didn't have a chance. And they

outnumbered us two to one. If they could take care of big Koku, what chance did we have?"

"Very little," said Engineer Mound. "They were desperate fellows. They know something about aircraft, too.

For, as soon as Koku, Ventor and I were disposed of, some of them went at the machinery as if they had been

"Oh, the foreigners are experts when it comes to craft of the air," said Captain Warner.

"Well, they seem to be running her, all right," admitted the young inventor, "and at good speed, too. They

"By several miles an hour," confirmed the assistant pilot. "Though in which direction they are heading, and

"That's so!" agreed Mr. Damon. "What is to become of us? They may heave us overboard into the ocean!"

"We must be, by this time," spoke Tom. "We were headed in that direction, and we have come almost far

A look of apprehension was on the faces of all. But Tom's face did not remain clouded long.

"We won't try to swim until we have to," he said. "Now, let's take an account of stock, and see if we have any

With one accord the hands of the captives sought their pockets. Probably the first thought of each one was a

knifea pocket knife. But blank looks succeeded their first hopeful ones, for the hands came out empty.

"Not a thing!" exclaimed Mr. Damon. "Not a blessed thing! They have even taken my keys andmy

"I guess they searched us all while they were struggling with us, tying us up," suggested Ned. "I had a knife

"And I haven't even a screwdriver, or a pocketwrench," declared the engineer, "though I had both."

"They evidently knew what they were doing," said Lieutenant Marbury. "I don't usually carry a revolver, but

"And so are all my things," went on his naval friend. "That Frenchman, La Foy, was taking no chances."

"Well," if we haven't any weapons, or means of getting out of here, we must make them," said Tom, as

hopefully as he could under the circumstances. "I don't know all the things that were put in this storeroom,

"Shall we make the try now?" asked Ned. "I'm getting thirsty, at least. Lucky we had supper before they came

"Well, there isn't any water in here, or anything to eat, of so much I am sure," went on Tom "So we will have

"At least we can shout and ask for water," said Lieutenant Marbury. "They have no excuse for being

They all agreed that this might not be a bad plan, and were preparing to raise a united shout, when there came

"Are you willing to listen to reason?" asked a voice they recognized as that of La Foy.

"What do you mean by reason?" asked Tom bitterly. "You have no right to impose any conditions on us."

"I have the right of might, and I intend exercising it," was the sharp rejoinder. "If you will listen to reason"

"Mine, in this case," snapped back the Frenchman. "What I was going to say was that I do not intend to starve

you, or cause you discomfort by thirst. I am going to open the door and put in food and water. But I warn you

"We are in sufficient force to cope with you. I think you have seen that." He spoke calmly and in perfect

English, though with a marked accent. "My men are armed, and will stand here ready to meet violence with

"I think it will be better to give in to him at least for a while," said Captain Warner in a low voice to Tom.

"We need water, and will soon need food. We can think and plan better if we are well nourished."

"Our answer isyes," spoke Tom. "We will not try to get out just yet," he added significantly.

A key was heard grating in the lock, and, a moment later, the door slid back. Through the opening could be

seen La Foy and some of his men standing armed. Others had packages of food and jugs of water. A plentiful

"Keep back from the door!" was the stern command of La Foy. "The food and drink will be passed in only if

The warning was hardly needed, for the weapons could plainly be seen. Tom had half a notion that perhaps a

concerted rush would carry the day for him and his friends, but he was forced to abandon that idea.

While the guards looked on, others of the "pirate crew," as Ned dubbed them, passed in food and water. Then

They all felt better after drinking the water, which was made cool by evaporation, for the airship was quite

high above the earth when Tom's enemies captured it, and the young inventor felt sure it had not descended

No one felt much like eating, however, so the food was put away for a time. And then, somewhat refreshed,

"Of course we might batter down the door, in time, by using some of these boxes as rams," said Tom. "But

the trouble is, that would make a noise, and they could stand outside and drive us back with guns and pistols,

"Yes, and they could turn some of your own quickfirers on us," added Captain Warner. "No, we must work

quietly, I think, and take them unawares, as they took us. That is our only plan."

"We will be better able to see what we have here by daylight," Tom said. "Suppose we wait until morning?"

That plan was deemed best, and preparations made for spending the night in their prison.

It was a most uncomfortable night for all of them. The floor was their only bed, and their only covering some

empty bags that had contained supplies. But even under these circumstances they managed to doze off

Once they were all awakened by a violent plunging of the airship. The craft seemed to be trying to stand on

her head, and then she rocked violently from side to side, nearly turning turtle. "What is it?" gasped Ned, who

"They must be trying some violent stunts," replied the young inventor, "or else we have run into a storm."

And, as the motion of the craft kept up, though less violently, this was accepted as the explanation. Through

The first gray streaks of dawn finally shone through the only window of their prison. Sore, lame and stiff,

wearied in body and disturbed in mind, the captives awoke. Tom's first move was toward the window. It was

high up, but, by standing on a box, he could look through it. He uttered an exclamation.

"What is it?" asked Ned, swaying to and fro from the violent motion ef the aerial warship.

Tom turned away from the window, to find his companions regarding him anxiously.

"It might turn into any sort," replied Tom. "All I can see now is a lot of black clouds, and the wind must be

"Bless my galvanometer!" cried Mr. Damon. "Then we are out over the ocean again, Tom?"

"Suppose I take a look?" suggested Captain Warner. "I've done quite a bit of sailing in my time."

But, when he had taken a look through the window at which Tom had been standing, the naval officer

"There isn't a landmark in sight," he announced. "We might be over the middle of the Atlantic, for all I could

"Hardly as far as that," spoke Tom. "They haven't been pushing the Mars at that speed. But we may be across

"Well, the ship is in the possession of these foreign spies," went on Tom. "All their interests are in Europe,

though it would be hard to say what nationality is in command here. I think there are even some Englishmen

among those who attacked us, as well as French, Germans, Italians and Russians."

"Yes, it seems to be a combination of European nations against us," admitted Captain Warner. "Probably,

after they have made good their seizure of Tom's aerial warship, they will portion her out among themselves,

"Undoubtedly," was the captain's answer. "It has been the object of these foreign spies, all along, not only to

prevent the United States from enjoying the benefits of these progressive inventions, but to use them for

themselves. They would stop at nothing to gain their ends. It seems we did not sufficiently appreciate their

"Well, they've got us, at any rate," observed Tom, "and they may take us and the ship to some faroff foreign

"If they don't heave us overboard halfway there," commented Ned, in rather gloomy tones

"Well, of course, there's that possibility," admitted Tom. "They are desperate characters."

"Well, we must do something," declared Lieutenant Marbury. "Come, it's daylight now, and we can see to

work better. Let's see if we can't find a way to get out of this prison. Say, but this sure is a storm!" he cried, as

"They are handling her well, though," observed Tom, as the craft came quickly to an even keel. "Either they

have a number of expert birdmen on board, or they can easily adapt themselves to a new aircraft. She is

They brought out the food which had been given to them the night before, but before they could eat this, there

came a knock on the door, and more food and fresh water was handed in, under the same precautions as

Tom and his companions indignantly demanded to be released, but their protests were only laughed at, and

But the prisoners were not the kind to sit idly down in the face of this. Under Tom's direction they set about

looking through their place of captivity for something by which they could release themselves. At first they

found nothing, and Ned even suggested trying to cut a way through the wooden walls with a fingernail file,

which he found in one of his pockets, when Tom, who had gone to the far end of the storeroom, uttered a cry.

"No, but means to that end," Tom replied. "Look, a file and a saw, left here by some of my workmen,

perhaps," and he brought out the tools. He had found them behind a barrel in the far end of the compartment.

"Hurray!" cried Ned. "That's the ticket! Now we'll soon show these fellows what's what!"

"Go easy!" cautioned Tom. "We must work carefully. It won't do to slam around and try to break down the

door with these. I think we had better select a place on the side wall, break through that, and make an opening

where we can come out unnoticed. Then, when we are ready, we can take them by surprise. We'll have to do

"Here," said Tom, indicating a place far back in the room. "We can work there in turns, sawing a hole

through the wall. It will bring us out in the passage between the aft and amidship cabins, and we can go either

While the aerial warship pitched and tossed in the storm, over some part of the Atlantic, Tom and his friends

took turns in working their way to freedom. With the sharp end of the file a small hole was made, the work

being done as slowly as a rat gnaws, so as to make no noise that would be heard by their captors. In time the

But this took many hours, and it was not until the second day of their captivity that they had the hole nearly

large enough for the passage of one person at a time. They had not been discovered, they thought.

Meanwhile they had been given food and water at intervals, but to all demands that they be released, or at

They could only guess at the fate of Koku. Probably the giant was kept bound, for once he got the chance to

The Mars continued to fly through the air. Sometimes, as Tom and his friends could tell by the motion, she

was almost stationary in the upper regions, and again she seemed to be flying at top speed. Occasionally there

"Hardly," replied Captain Warner. "The United States possesses no craft able to cope with this one in aerial

warfare, and they are hardly engaging in part of the European war yet. I think they are just trying Tom's new

The storm had either passed, or the Mars had run out of the path of it, for, after the first few hours of pitching

All the while they were secretly working to gain their freedom so they might attack and overpower their

enemies, they took occasional observations from the small window. But they could learn nothing of their

whereabouts. They could only view the heaving ocean, far below them, or see a mass of cloudmist, which

"And by the end of that time we may all be dead," spoke the young bank clerk despondently.

Indeed the hole was now almost large enough to enable them to crawl out one at a time. They could not, of

course, see how it looked from the outside, but Tom had selected a place for its cutting so that the sawdust

and the mark of the panel that was being removed, would not ordinarily be noticeable.

Their set night as the time for making the attemptlate at night, when it was hoped that most of their captors

Finally the last cut was made, and a piece of wood hung over the opening only by a shred, all ready to knock

Anxious, indeed, were those last hours of waiting. The time had almost arrived for the attempt, when Tom,

"It sure is a storm!" cried Ned, "and a heavy one, too," for there came a burst of thunder, that seemed like a

In another instant they were in the midst of a violent thunderstorm, the airship pitching and tossing in a

As Tom reached up to switch on the electric light again, there came a flash of lightning that well nigh blinded

them. And so close after it as to seem simultaneous, there came such a crash of thunder as to stun them all.

There was a tingling, as of a thousand pins and needles in the body of each of the captives, and a strong smell

For a moment there was silence, following Tom's wild cry and the noise of the thunderclap. Then, as other,

though less loud reverberations of the storm continued to sound, the captives awoke to a realization of what

"We've been struck by lightning!" Tom repeated. "I don't know whether we're all right or not."

"If the whole gas bag isn't ripped to pieces we're lucky," commented Jerry Mound.

Indeed, it was evident that the Mars was sinking rapidly. To all there came the sensation of riding in an

Then, as they stood there in the darkness, illuminated only by flashes from the lightning outside the window,

"We've stopped falling!" he cried. "The automatic gas machine is pumping. Part of the gas bag was

"If part of the gas leaked out I don't see why it wasn't all set on fire and exploded," observed Captain Warner.

"It's a nonburnable gas," Tom quickly explained. "But come on. This may be our very chance. There seems

Indeed the captives could hear confused cries and the running to and fro of many feet.

He made for the sawed panel, and, in another instant, had burst out and was through it, out into the

They looked into the rear cabin, or motor compartment, and a scene of confusion met their gaze. Two of the

foreign men who had seized the ship lay stretched out on the floor near the humming machinery, which had

been left to run itself. A look in the other direction, toward the main cabin, showed a group of the foreign

spies bending over the inert body of La Foy, the Frenchman, stretched out on a couch.

"The lightning!" exclaimed Tom. "The bolt that struck the ship has knocked out some of our enemies! Now is

The Mars seemed to have passed completely through a narrow storm belt. She was now in a quiet

atmosphere, though behind her could be seen the fitful play of lightning, and there could be heard the distant

"Come on!" cried Tom. "We must act quickly, while they are demoralized! Come on!"

His friends needed no further urging. Jerry Mound and the machinist rushed to the engineroom, to look after

any of the enemy that might be there, while Tom, Ned and the others ran into the middle cabin.

"Grab 'em! Tie 'em up!" cried Tom, for they had no weapons with which to make an attack.

But none were needed. So stunned were the foreigners by the lightning bolt, which had miraculously passed

our friends, and so unnerved by the striking down of La Foy, their leader, that they seemed like men half

asleep. Before they could offer any resistance they were bound with the same ropes that had held our friends

in bondage. That is, all but the big Frenchman himself. He seemed beyond the need of binding.

Mound, the engineer, and his assistant, came hurrying in from the motorroom, followed by Koku.

"We found him chained up," Jerry explained, as the big giant, freed from his captivity, rubbed his chafed

"Only those two knocked out by the lightning," the engineer explained. "We've made them secure. I see

"Yes," replied Tom. "And now to see where. we are, and to get back home. Whew! But this has been a time!

"They no let anything happen. I be in chains all the while," the giant answered. "Jump on me before I can do

"Well, you're out, now, and I think we'll have you stand guard over these men. The tables are turned, Koku."

The bound ones were carried to the same prison whence our friends had escaped, but their bonds were not

taken off, and Koku was put in the place with them. By this time La Foy and the two other stricken men

The young inventor and his friends, once more in possession of their airship, lost little time in planning to

return. They found that the spies were all expert aeronauts, and had kept a careful chart of their location.

They were then halfway across the Atlantic, and in a short time longer would probably have been in some

The craft had only been slightly damaged by the lightning bolt, though three of the gas bag compartments

When morning came Tom and his friends had matters running almost as smoothly as before their capture.

The prisoners had no chance to escape, and, indeed, they seemed to have been broken in spirit. La Foy was

no longer the insolent, mocking Frenchman that he had been, and the two chief foreign engineers seemed to

"But it was a mighty lucky and narrow escape for us," said Ned, as he and Tom sat in the pilothouse the

Once again they were above the earth, and, desiring to get rid as soon as possible of the presence of the spies,

a landing was made near New York City, and the government authorities communicated with. Captain

Warner and Lieutenant Marbury took charge of the prisoners, with some Secret Service men, and the

"And now what are you going to do, Tom?" asked Ned, when, once more, they had the airship to themselves.

"I'm going back to Shopton, fix up the gas bag, and give her another government trial," was the answer.

And, in due time, this was done. Tom added some improvements to the aircraft, making it better than ever,

and when she was given the test required by the government, she was an unqualified success, and the rights to

the Mars were purchased for a large sum. In sailing, and in the matter of guns and bombs, Tom's craft

"So you see I was right, after all, Dad," the young inventor said, when informed that he had succeeded. "We

Tom's aerial warship was even a bigger success than he had dared to hope. Once the government men fully

understood how to run it, in which Tom played a prominent part in giving instructions, they put the Mars to a

severe test. She was taken out over the ocean, and her guns trained on an obsolete battleship. Her bombs and

"The Mars will be the naval terror of the seas in any future war," predicted Captain Warner.

The Secret Service men succeeded in unearthing all the details of the plot against Tom. His life, at times, had

been in danger, but at the last minute the man detailed to harm him lost his nerve.

It was Tom's enemies who had set on fire the red shed, and who later tried to destroy the ship by putting a

corrosive acid in one of the propellers. That plot, though, was not wholly successful. Then came the time

when one of the spies hid on board, and dropped the copper bar on the motor, shortcircuiting it. But for the

storagebattery that scheme might have wrought fearful damage. The spy who had stowed himself away on

The foreign spies were tried and found guilty, receiving merited punishment. Of course the governments to

It came out at the trial that one of Tom's most trusted employees had proved a traitor, and had the night

before the test, allowed the foreign spies to secrete themselves on board, to rush out at an opportune time to

"Well, what are you going to tackle next, Tom?" asked Ned, one day about a month after these exciting

"I don't know," was the slow answer. "I think a selfswinging hammock, under an apple tree, with a

But it is very much to be doubted if Tom Swift, even on a vacation, could refrain from trying to invent

something, either in the line of airships, water, or land craft. And so, until he again comes to the front with