"What—what are you doin'?" he demanded of Tom, and as the man opened his mouth to speak Tom was aware of a glitter, which disclosed the 'fact that the man had a large front tooth of gold.

"What am I doing?" repeated Tom. "I think it's up to you to answer that question, not me. What are you doing?"

"You—you tripped me into this mud hole!" declared the man.

"I did, yes; because you were trespassing on my property, and ran away instead of stopping when I told you to," went on Tom. "Who are you and what are you doing? What were you doing with Bower at my shop?"

"Nothin'! I wasn't doin' nothin'!"

"Well, we'll inquire into that. I want to see what you have in your pockets before I believe you. Come on out!"

"You haven't any right to go through my pockets!" blustered the stranger.

"Oh, haven't I? Well, I'm going to take the right. Jackson—Koku—just see that he doesn't get away. We'll take him back and search him," and Tom motioned to his chief machinist and the giant, who had reached the scene, to take charge of the man. But Koku was sufficient for this purpose, and the mud-bespattered stranger seemed to shrink as he saw the big creature approach him. There was no question of running away after that.

"Bring him along," ordered Tom, and Koku, taking a tight grip on the man by the slack of his garments behind, walked him along toward the office, the mud and water splashing and oozing from his shoes at every step.

"Now you look here!" the gold-toothed man cried, as he was forced along, "you ain't got any right to detain me. I ain't done nothin'!" And each time he spoke the bright tooth in his mouth glittered in the sun.

"I don't know whether you've done anything or not," said Tom. "I'm going to take you back and see what you and Bower have to say. He may know something about this."

"If he does I don't believe he'll tell," said Jackson.

"Why not?" asked Tom, quickly.

"Because he's gone."

"Gone! Bower gone?"

"Yes," answered Jackson. "I saw him running out of the experiment shop as we raced along to help you. I didn't think, at the time, that he was doing more than go for aid, perhaps. But I see the game now."

"Oh, you mean—him?" and Tom pointed to the dripping figure.

"Yes," said Jackson in a low voice, as Koku went on ahead with his prisoner. "If, as you say, this man was in league with Bower, the latter has smelled a rat and skipped. He has run away, and I only hope he hasn't done any damage or got hold of any of your plans."

"We'll soon know about that," said Tom. "I wonder who is at the bottom of this?"

"Maybe those men you wouldn't work for," suggested the machinist.

"You mean Gale and Ware of the Universal Flying Machine Company?"

"Yes."

"Oh, I don't believe they'd stoop to any such measures as this—sending spies around," replied Tom. "But I can't be too careful. We'll investigate."

The first result of the investigation was to disclose the fact that Bower was gone. He had taken his few possessions and left the Swift plant while Tom was racing after the stranger. A hasty examination of the safe did not reveal anything missing, as Tom's plans and papers were intact. But they showed evidences of having been looked over, for they were out of the regular order in which the young inventor kept them.

"I begin to see it," said Tom, musingly. "Bower must have managed to open the safe while I was gone, and he must have made a hasty copy of some of the drawings of the silent motor, and passed them out of the window to this gold-tooth man, who tried to make off with them. Did you find anything on him?" he asked, as one of the men who had been instructed to search the stranger came into the office just then.

"Not a thing, Mr. Swift! Not a thing!" was the answer. "We took off every bit of his clothes and wrapped him in a blanket. He's in the engine room getting dry now. But there isn't a thing in any of his pockets."

"But I saw him stuffing some papers in as he ran away from me," said Tom. "We must be sure about this. And don't let the fellow get away until I question him."

"Oh, he's safe enough," answered the man. "Koku is guarding him. He won't get away."

"Then I'll have a look at his clothes," decided Tom. "He may have a secret pocket."

But nothing like this was disclosed, and the most careful search did not reveal anything incriminating in the man's garments.

"He might have thrown away any papers Bower gave him," said Tom. "Maybe they're at the bottom of the mud hole! If they're there they're safe enough. But have a search made of the ground where this man ran."

This was done, but without result. Some of the workmen even dragged the mud hole without finding anything. Then Tom and his father had a talk with the stranger, who refused to give his name. The man was sullen and angry. He talked loudly about his innocence and of "having the law on" Tom for having tripped him into the mud.

"All right, if you want to make a complaint, go ahead," said the young inventor. "I'll make one against you for trespass. Why did you come on my grounds?"

"I was going to ask for work. I'm a. good machinist and I wanted a job."

"How did you get in? Who admitted you at the gate?"

"I—I jest walked in," said the man, but Tom knew this could not be true, as no strangers were admitted without a permit and none had been issued. The man denied knowing anything about Bower, but the latter's flight was evidence enough that something was wrong.

Not wishing to go to the trouble of having the man arrested merely as a trespasser, Tom let him go after his clothes had been dried on a boiler in one of the shops.

"Take him to the gate, and tell him if he comes back he'll get another dose of the same kind of medicine," ordered Tom to one of the guards at the plant, and when the latter had reported that this had been done, he added in an earnest tone:

"He went off talking to himself and saying he'd get even with you, Mr. Swift."

"All right," said Tom easily. "I'll be on the watch."

The young inventor made a thorough examination of his experiment shop and the test motor. No damage seemed to have been done, and Tom began to think he had been too quick for the conspirators, if such they were. His plans and drawings were intact, and though Bower might have given a copy to the stranger with the gold tooth, the latter did not take any away with him. That he had some papers he wished to conceal and escape with, seemed certain, but the splash into the mud hole had ended this.

No trace was found of Bower, and an effort Tom made to ascertain if the man was a spy in the employ of Gale and Ware came to naught. The machinist had come well recommended, and the firm where he was last employed had nothing but good to say of him.

"Well, it's a mystery," decided Tom. "However, I got out of it pretty well. Only if that gold-tooth individual shows up again he won't get off so easily."



CHAPTER XI

A NIGHT TRIP

Taking a lesson from what had happened, Tom was very much more careful in the following experiments on his new, silent motor. He made some changes in his shop, and took Jackson in to help on the new machine, thus insuring perfect secrecy as the apparatus developed.

Tom also changed the safe in which he kept his plans, for the one he had used previous to the episode in which Bower and the stranger who took the mud bath figured, was one the combination of which could easily be ascertained by an expert. The new safe was more complicated, and Tom felt that his plans, specifications, and formulae which he had worked out were in less danger.

"I can just about figure out what happened," said Ned Newton to Tom, when told of the circumstances. "These Universal people were provoked because you wouldn't give them the benefit of your experience on their flying machines, and so they sent a spy to get work with you. They, perhaps, hoped to secure some of your ideas for their own, or they may have had a deeper motive."

"What deeper motive could they have, Ned?" "They might have hoped to disable you, or some of your machines, so that you couldn't compete with them. They're unscrupulous, I hear, and will do anything to succeed and make money. So be on your guard against them."

"I will," Tom promised. "But I don't believe there's any more danger now. Anyhow, I have to take some chances."

"Yes, but be as careful as you can. How is the silent motor coming on?"

"Pretty good. I've had a lot of failures, and the thing isn't so easy as I at first imagined it would be. Noise is a funny thing, and I'm just beginning to understand some of the laws of acoustics we learned at high school. But I think I'm on the right track with the muffler and the cutting down of the noise of the explosions in the cylinders. I'm working both ends, you see—making a motor that doesn't cause as much racket as those now in use, and also providing means to take care of the noise that is made. It isn't possible to make a completely silent motor of an explosive gas type. The only thing that can be done is to kill the noise after it is made."

"What about the propeller blades?"

"Oh, they aren't giving me any trouble. The noise they make can't be heard a hundred feet in the air, but I am also working on improvements to the blades. Take it altogether, I'll have an almost silent aeroplane if my plans come out all right."

"Have you said anything to the government yet?"

"No; I want to have it pretty well perfected before I do. Besides, I don't want any publicity about it until I'm ready. If these Universal people are after me I'll fool 'em."

"That's right, Tom! Well, I must go. Another week of this Liberty Bond campaign!"

"I suppose you'll be glad when it's over."

"Well, I don't know," said Ned slowly. "It's part of my small contribution to Uncle Sam. I'm not like you—I can't invent things."

"But you have an awful smooth line of talk, Ned!" laughed his chum. "I believe you could sell chloride of sodium to some of the fishes in the Great Salt Lake—that is if it has fishes."

"I don't know that it has, Tom. And, anyhow, I'm not posing as a salt salesman," and Ned grinned. "But I must really go. Our bank hasn't reached its quota in the sale of Liberty Bonds yet, and it's up to me to see that it doesn't fall down."

"Go to it, Ned! And I'll get busy on my silent motor."

"Getting busy" was Tom Swift's favorite occupation, and when he was working on a new idea, as was the case now, he was seldom idle, night or day.

"I have hardly seen you for two weeks," Mary Nestor wrote him one day. "Aren't you ever coming to see me any more, or take me for a ride?"

"Yes," Tom wrote back. "I'll be over soon. And perhaps on the next ride we take I won't have to shout at you through a speaking tube because the motor makes so much noise."

From this it may be gathered that Tom was on the verge of success. While not altogether satisfied with his progress, the young inventor felt that he was on the right track. There were certain changes that needed to be made in the apparatus he was building—certain refinements that must be added, and when this should be done Tom was pretty certain that he would have what would prove to be a very quiet aeroplane, if not an absolutely silent one.

The young inventor was engaged one day with some of the last details of the experiment. The new motor, with the silencer and the changed cylinders, had been attached to one of Tom's speedy aeroplanes, and he was making some intricate calculations in relation to a new cylinder block, to be used when he started to make a completely new machine of the improved type.

Tom had set down on paper some computations regarding the cross-section of one of the cylinders, and was working out the amount of stress to which he could subject a shoulder strut, when a shadow was cast across the drawing board he had propped up in his lap.

In an instant Tom pulled a blank sheet over his mass of figures and looked up, a sudden fear coming over him that another spy was at hand. But a hearty voice reassured him.

"Bless my rice pudding!" cried Mr. Damon, "you shut yourself up here, Tom, like a hermit in the mountains. Why don't you come out and enjoy life?"

"Hello! Glad to see you!" cried Tom, joyfully. "You're just in time!"

"Time for what—dinner?" asked the eccentric man, with a chuckle. "If so, my reference to rice pudding was very proper."

"Why, yes, I imagine there must be a dinner in prospect somewhere, Mr. Damon," said Tom with a smile. "We'll have to see Mrs. Baggert about that. But what I meant was that you're just in time to have a ride with me, if you want to go."

"Go where?"

"Oh, up in cloudland. I have just finished my first sample of a silent motor, and I'm going to try it this evening. Would you like to come along?"

"I would!" exclaimed Mr. Damon. "Bless my onion soup, Tom, but I would! But why fly at night? Isn't it safer by daylight?"

"Oh, that doesn't make much difference. It's safe enough at any time. The reason I'm going to make my first flight after dark is that I don't want any spies about."

"Oh, I see! Are they camping on your trail?"

"Not exactly. But I can't tell where they may be. If I should start out in daylight and be forced to make a landing— Well, you know what a crowd always collects to see a stranded airship."

"That's right, Tom."

"That decided me to start off after dark. Then if we have to come down because of some sort of engine trouble or because my new attachment doesn't work right, we sha'n't have any prying eyes."

"I see! Well, Tom, I'll go with you. Fortunately I didn't tell my wife where I was going when I started out this afternoon, so she won't worry until after it's over, and then it won't hurt her. I'm ready any time you are."

"Good! Stay to dinner and I'll show you what I've made. Then we'll take a flight after dark."

This suited the eccentric man, and a little later, after he had eaten one of Mrs. Baggert's best meals, including rice pudding, of which he was very fond, Mr. Damon accompanied Tom to one of the big hangars where the new aeroplane had been set up.

"So that's the Air Scout, is it, Tom?" asked Mr. Damon, as he viewed the machine.

"Yes, that's the girl. 'Air Scout' is as good a name as any, until I see what she'll do."

"It doesn't look different from one of your regular craft of the skies, Tom."

"No, she isn't. The main difference is here," and Tom showed his friend where a peculiar apparatus had been attached to the motor. This was the silencer—the whole secret of the invention, so to speak.

To Mr. Damon it seemed to consist of an amazing collection of pipes, valves, baffle-plates, chambers, cylinders and reducers, which took the hot exhaust gases as they came from the motor and "ate them up," as he expressed it.

"The cylinders, too, and the spark plugs are differently arranged in the motor itself, if you could see them," said Tom to his friend. "But the main work of cutting down the noise is done right here," and he put his hand on the steel case attached to the motor, the case containing the apparatus already briefly described.

"Well, I'm ready when you are, Tom," said Mr. Damon.

"We'll go as soon as it's dark," was the reply. "But first I'll give you a demonstration. Start the motor, Jackson!" Tom called to his chief helper.

Mr. Damon had ridden in aeroplanes before, and had stood near when Tom started them; so he was prepared for a great rush of air as the propellers whirled about, and for deafening explosions from the engine.

The big blades, of new construction, were turned until the gas in the cylinders was sufficiently compressed. Then Jackson stepped back out of danger while Tom threw over the switch.

"Contact!" cried the young inventor.

Jackson gave the blades a quarter pull, and, a moment later, as he leaped back out of the way, they began to revolve with the swiftness of light. There was the familiar rush of air as the wooden wings cut through the atmosphere, but there was scarcely any noise. Mr. Damon could hardly believe his ears.

"I'm not running her at full speed," said Tom. "If I did she'd tear loose from the holding blocks. But you can see what little racket she makes."

"Bless my fountain pen!" cried Mr. Damon. "You are right, Tom Swift! Why, I can hear you talk almost as easily as if no engine were going. And I don't have to shout my head off, either."

This was perfectly true. Tom could converse with Mr. Damon in almost ordinary tones. The exhaust from the motor was nearly completely muffled.

"Out in the air it will seem even more quiet," said Tom. "I'll soon give you a chance to verify that statement."

He ran the engine a little longer, the aeroplane quivering with the vibrations, but remaining almost silent.

"I'm anxious to see what she'll do when in motion," said Tom, as he shut off the gas and spark.

Soon after supper, when the shades of evening were falling, he and Mr. Damon took their places in the first of the Air Scouts, to give it the preliminary test in actual flying.

Would Tom's hopes be justified or would he be disappointed?



CHAPTER XII

THE CRY FOR HELP

"All ready, Mr. Damon?" asked Tom, as he looked to see that all the levers, wheels, valves, and other controls were in working order on his Air Scout.

"As ready as I ever shall be, Tom," was the answer. "I don't know why it is, but somehow I feel that something is going to happen on this trip."

"Nonsense!" laughed Tom. "You're nervous; that's all."

"I suppose so. Don't think I'm going to back out, or anything like that, but I wish it were successfully over with, Tom Swift, I most certainly do."

"It will be in a little while," returned Tom, as he settled himself comfortably in his seat and pulled the safety strap tight. "You've gone up in this same plane before, when it didn't have the silent motor aboard."

"Yes, I know I have. Oh, I dare say it will be all right, Tom. And yet, somehow, I can't help feeling—"

But Tom Swift felt that the best way to set Mr. Damon's premonitions to rest was to start the motor, and this he gave orders to have done, Jackson and some others of the men from the shops congregating about the craft to see the beginning of the night flight. Mr. Swift was there also, and Eradicate. Mary Nestor had been invited, but her Red Cross work engaged her that evening, she said. Ned Newton was away from town on Liberty Bond business, and he could not be present at the test.

However, as Tom expected to have other trials when his motor was in even better shape, he was not exactly sorry for the absence of his friends.

"Contact!" called the young inventor, when Jackson had stepped back, indicating it was time to throw over the switch.

"Let her go!" cried Tom, and the next moment the motor was in operation, but so silently that his voice and that of Mr. Damon's could easily be heard above the machinery.

"Good, Tom! That's good!" cried Mr. Swift, and Tom easily heard his father's voice, though under other, and ordinary, circumstances this would have been impossible.

True, the hearing of Tom and Mr. Damon was muffled to a certain extent by the heavy leather and fur-lined caps they wore. But Tom had several small eyelet holes set into the flaps just over the opening of the ears, and these holes were sufficient to admit sounds, while keeping out most of the cold that obtains in the upper regions.

The aeroplane moved swiftly along the level starting ground, and away from the lighted hangars. Faster and faster it swung along as Tom headed it into the wind, and then, as the speed of the motor increased, the Air Scout suddenly left the earth and went soaring aloft as she had done before.

But there was this difference. She moved almost as silently as a great owl which swoops down out of the darkness—a bit of the velvety blackness itself. Up and up, and onward and onward, went the Air Scout. Tom Swift's improved, silent motor urged it onward, and as the young inventor listened to catch the noise of the machinery, his heart gave a bound of hope. For he could detect only very slight sounds.

"She's a success!" exulted Tom to himself. "She's a success, but she isn't perfect yet," he added. "I've got to make the muffler bigger and put in more baffle-plates. Then I think I can turn the trick."

He swung the machine out over the open country, and then, when they were up at a height and sailing along easily, he called back to Mr. Damon in the seat behind him:

"How do you like it?"

"Great!" exclaimed the eccentric man. "Bless my postage stamp, but it's great! Why, there's hardly a sound, Tom, and I can hear you quite easily."

"And I can hear you," added Tom. "I don't believe, down below there," and he nodded toward the earth, though Mr. Damon could not see this, as the airship, save for a tiny light over the instrument board, was in darkness, "they know that we're flying over their heads."

"I agree with you," was the answer. "Tom, my boy, I believe you've solved the trick! You have produced a silent aeroplane, and now it's up to the government to make use of it."

"I'm not quite ready for that yet," replied the young inventor. "I have several improvements to make. But, when they are finished, I'll let Uncle Sam know what I have. Then it's up to him."

"And you must be careful, Tom, that some of your rivals don't hear of your success and get it away from you," warned Mr. Damon, as Tom guided the Air Scout along the aerial way—an unlighted and limitless path in the silent darkness.

"Oh, they'll have to get up pretty early in the morning to do that!" boasted Tom, and afterward he was to recall those words with a bit of chagrin.

On and on they sailed, and as Tom increased the speed of the motor, and noted how silently it ran, he began to have high hopes that he had builded better than he knew. For even with the motor running at almost full speed there was not noise enough to hinder talk between himself and Mr. Damon.

Of course there was some little sound. Even the most perfect electric motor has a sort of hum which can be detected when one is close to it. But at a little distance a great dynamo in operation appears to be silence itself.

"I can go this one better, though," said Tom as he sailed along in the night. "I see where I've made a few mistakes in the baffle plate of the silencer. I'll correct that and—"

As he spoke the machine gave a lurch, and the motor, instead of remaining silent, began to cough and splutter as in the former days.

"Bless my rubber boots, Tom! what's the matter?" cried Mr. Damon.

"Something's gone wrong," Tom answered, barely able to hear and make himself heard above the sudden noise. "I'll have to shut off the power and glide down. We can make a landing in this big field," for just then the moon came out from behind a cloud, and Tom saw, below them, a great meadow, not far from the home of Mary Nestor. He had often landed in this same place.

"Something has broken in the muffler, I think, letting out some of the exhaust," he said to Mr. Damon, for, now that the motor was shut off, Tom could speak in his ordinary tones. "I'll soon have it fixed, or, if I can't, we can go back in the old style—with the machine making as much racket as it pleases."

So Tom guided the machine down. It went silently now, of course, making, with the motor shut off, no more sound than a falling leaf. Down to the soft, springy turf in the green meadow Tom guided the machine. As it came to a stop, and he and Mr. Damon got out, there was borne to their ears a wild cry:

"Help! Help!"



CHAPTER XIII

SOMETHING QUEER

"Did you hear that?" asked Tom Swift of his companion.

"Hear it? Bless my ear drums, I should say I did hear it! Some one is in trouble, Tom. Caught in a bog, most likely, the same as that spy chap who was at your place. That's it—caught in a bog!"

"There isn't any bog or swamp around here, Mr. Damon. If there was I shouldn't have tried a landing. No, it's something else besides that. Hark!"

Again the cry sounded, seeming to come from a point behind the landing place of the silent airship. It was clear and distinct:

"Help! Help! They are—"

The voice seemed to die away in a gurgle, as though the person's mouth had been covered quickly.

"He's sinking, Tom! He's sinking!" cried Mr. Damon. "I once heard a man who almost drowned cry out, and it sounded exactly like that!"

"But there isn't any water around here for any one to drown in," declared Tom. "It's a big, dry meadow. I know where we are."

"Then what is it?"

"I don't know, but we're going to find out. Some one attacked by some one else—or something, I should say," ventured the young inventor.

"Something! do you mean a wild beast, Tom?"

"No, for there aren't any of those here any more than there is water. Though it may be that some farmer's bull or a savage dog has got loose and has attacked some traveler. But, in that case I think we would hear bellows or barks, and all I heard was a cry for help."

"The same with me, Tom. Let's investigate;"

"That's what I intend doing. Come on. The airship will be all right until we come back."

"Better take a light—hadn't you? It's dark, even if the moon does show now and then," suggested Mr. Damon.

"Guess you are right," agreed Tom. Aboard his airship there were several small but powerful portable electric lights, and after securing one of these Tom and Mr. Damon started for the spot whence the call for help had come. As they walked along, their feet making no noise on the soft turf, they listened intently for a repetition of the call for aid.

"I don't hear anything," said Tom, after a bit.

"Nor I," added Mr. Damon. "We don't know exactly which way to go, Tom."

"That's right. Guess we'd better give him a hail; whoever it is."

Tom came to a halt, and raising his voice to a shout called:

"Hello there! What's the matter? We'll help you if you can tell us which way to come!"

They both listened intently, but no voice answered them. At the same time, however, they were aware of a sound as of hurrying feet, and there seemed to be muttered imprecations not far away. Tom and Mr. Damon looked in the direction of the sound, and the young inventor flashed his light. But there was a clump of bushes and trees at that point and the electrical rays did not penetrate very far.

"Some one's over there!" exclaimed Tom in a whisper. "We'd better go and see what it is."

"All right," agreed Mr. Damon, and he, too, spoke in a low voice.

Why they did this when their previous talk had been in ordinary tones, and when Tom had shouted so loudly, they did not stop to reason about or explain just then. But later they both admitted that they whispered because they thought there was something wrong on foot—because they feared a crime was being committed and they wanted to surprise the perpetrators if they could.

And it was this fact of their whispering that enabled the two to hear something that, otherwise, they might not have heard. And this was the sound of some vehicle hurrying away—an automobile, if Tom was any judge. The cries for help had been succeeded by stifled vocal sounds, and these, in turn, by the noise of wheels on the ground.

"What does it all mean?" asked Mr. Damon in a whisper.

"I don't know," answered Tom, resolutely, "but we've got to find out. Come on."

They advanced toward the dark clump of trees and low bushes. There was no need to be especially cautious in regard to being silent, as their feet made little, if any, sound on the deep grass. And, as Tom walked in advance, now and then flashing his light, Mr. Damon suddenly caught him by the coat.

"What is it?" asked the young inventor.

"Look! Just over the top of that hill, where the moon shines. Don't you see an automobile outlined?"

Tom looked quickly.

"I do," he answered. "There's a road from here, just the other side of those trees, to that hill. The auto must have gone that way. Well, there's no use in trying to follow it now. Whoever it was has gotten away."

"But they may have left some one behind, Tom. We'd better look in and around those trees."

"I suppose we had, but I don't believe we'll find anything. I can pretty nearly guess, now, what it was."

"What?" asked Mr. Damon.

"Well, some chauffeur was out for a ride in his employer's car without permission. He got here, had an accident—maybe some friends he took for a ride were hurt and they called for help. The chauffeur knew if there was any publicity he'd be blamed, and so he got away as quickly as he could. Guess the accident—if that's what it was—didn't amount to much, or they couldn't have run the car off. We've had our trouble for our pains."

"Well, maybe you're right, Tom Swift, butt all the same, I'd like to have a look among those trees," said Mr. Damon.

"Oh. we'll look, all right," assented Tom, "but I doubt if we find anything."

And he was right. They walked in and about the little grove, flashing the light at intervals, but beyond marks of auto wheels in the dust of the road, which was near the clump of maples, there was nothing to indicate what had happened.

"Though there was some sort of fracas," declared Tom. "Look where the dust is trampled down. There were several men here, perhaps skylarking, or perhaps it was a fight."

"Some one must have been hurt, or they wouldn't have cried for help," said Mr. Damon.

"Well, that's so. But perhaps it was some one not used to riding in autos, and he may have imagined the accident was worse than it was, and called for help involuntarily. There is no evidence of any serious accident having happened—no spots of blood, at any rate," and Tom laughed at his own grimness. "It was a new car, too, or at least one with new tires on."

"How do you know?" asked Mr. Damon.

"Tell by the plain marks of the rubber tread in the dust," was the answer. "Look," and Tom pointed to the wheel marks in the focus of his electric lamp. "It's a new tire, too, with square protuberances on the tread instead of the usual diamond or round ones. A new kind of tire, all right."

He and Mr. Damon remained for a few minutes looking about the place whence had come the calls for help, and then the eccentric man remarked:

"Well, as long as we can't do anything here, Tom, we might as well travel on; what do you say?"

"I agree with you. There isn't any use in staying. We'll get the Air Scout fixed up and travel back home. But this was something queer," mused Tom. "I hope it doesn't turn out later that a crime has been committed, and we didn't show enough gumption to prevent it."

"We couldn't prevent it. We heard the cries as soon as we landed."

"Yes, but if we had rushed over at once we might have caught the fellows. But I guess it was only a slight accident, and some one was more frightened than hurt. We'll have to let it go at that."

But the more he thought about it the more Tom Swift thought there was something queer in that weird cry for help on the lonely meadow in the darkness of the night.



CHAPTER XIV

THE TELEPHONE CALL

The defect in the motor which had caused Tom Swift to shut off the power and drift down to earth was soon remedied, once the young inventor began an examination of the craft. One of the oil feeds had become choked and this automatically cut down the gasoline supply, causing one or more cylinders to miss. It was a safety device Tom had installed to prevent the motor running dry, and so being damaged.

Once the clogged oil feed was cleared the motor ran as before, and just as silently, though, as Tom had said, he was not entirely satisfied with the quietness, but intended to do further work toward perfecting it.

"I'll start the propellers now, Mr. Damon," said Tom, when the trouble had been remedied. "You know how to throw the switch, don't you?"

"I guess so," was the answer. Mr. Damon and Tom had traveled so often together in gasoline craft that the young inventor had taught his friend certain fundamentals about them, and in an emergency the eccentric man could help start an aeroplane. This he now did, taking charge of the controls which could be operated from his seat as well as from Tom's. Tom whirled the propellers, and soon the motor was in motion.

Mr. Damon, once the big wooden blades were revolving, slowed down the apparatus until Tom could jump aboard, after which the latter took charge and soon speeded up the machine, sending it aloft.

As the green meadow, dimly seen in the light of the moon, seemed to drop away below them, and the clump of trees vanished from sight, both Tom and Mr. Damon wondered who it was that had called for help, and if the matter were at all serious. They were inclined to think it was not, but Tom could not rid himself of a faint suspicion that there might have been trouble.

However, thoughts of his new silent Air Scout soon drove everything else from his mind, and as he guided the comparatively silent machine on its quiet way toward his own home he was thinking how he could best improve the muffler.

"Well, here we are again, safe and sound," remarked Tom, as he brought the craft to a stop in front of the hangar, and Jackson and his helpers, who were awaiting the return, hurried out to take charge.

"Yes, everything seems to point to success, Tom," agreed Mr. Damon. "That is, unless the slight accident we had means trouble."

"Oh, no, that had nothing to do with the operation of the silencer. But I'm going to do better yet. Some day I'll take you for a ride in a silent machine which will make so little noise that you can hear a pin drop."

"Well," remarked Mr. Damon' with a laugh, "I don't know that listening to falling pins will give me any great amount of pleasure, Tom, but I appreciate your meaning."

"Everything all right?" asked Mr. Swift, as he came out to hear the details from his son. "Do you think you have solved the problem?"

"Not completely, but I'll soon be able to write Q. E. D. after it. Some refinements are all that are needed, Dad."

"Glad to hear it. I was a bit anxious."

Mr. Swift questioned his son about the technical details of the trip, asking how the motor had acted under the pressure caused by so completely muffling the exhaust, and for some minutes the two inventors, young and old, indulged in talk which was not at all interesting to Mr. Damon. They went into the house, and Tom asked to have a little lunch, which Mrs. Baggert set out for him.

"It's rather late to eat," said the young inventor, "but I always feel hungry after I test a new machine and find that it works pretty well. Will you join me in a sandwich or two, Mr. Damon?"

"Why, bless my ketchup bottle, I believe I will."

And so they ate and talked. Tom was on the point of telling his father something of the queer cry for help they had heard on the lonely meadow when Mrs. Baggert produced a letter which she said had come for Tom that afternoon, but had been mislaid by a new maid who had been engaged to help with the housework.

"She took it to the shop after you had left, and only now told me about it," explained Mrs. Baggert. "So I sent Eradicate for it."

"How long ago was that?" asked Tom, as he took the missive.

"Oh, an hour ago," answered Mrs. Baggert, with a smile. "But don't blame poor Rad for that. He wanted to deliver the letter to you personally, and so did Koku. The result was your giant kept after Rad, trying to get the letter from him, and Rad kept hiding and slinking about for a chance to see you himself until I saw what was going on, a little while ago, and took the letter myself. Else you might never have gotten it, so jealous are those two," and Mrs. Baggert laughed.

"Guess it isn't of much importance," Tom said, as he tore open the envelope. "It's from the Universal Flying Machine Company, of New York, and I imagine they're trying to get me to reconsider my refusal to link up with them."

"Yes," he went on, as he read the missive, "that's it. They've raised the amount to thirty thousand a year now, Dad, and they say they feel sure I shall regret it if I do not accept.

"This is a bit queer, though," went on the young inventor. "This letter was written three days ago, but it reached Shopton only to-day. And it says that unless they hear from me at once they will have to take steps that will cause me great inconvenience. They have nerve, at any rate, and impudence, too! I won't even bother to answer. But I wonder what they mean, and why this letter was delayed?"

"The mails are all late on account of the transportation congestion caused by moving troops to the camps," said Mr. Damon. "Some of my letters are delayed a week. But, as you say, Tom, these fellows are very impudent to threaten that way."

"It's all bluff," declared Tom. "I'm not worrying. And now, Dad, since I've almost reached the top of the hill with my Air Scout, I may be able to help you on that new electric motor you're puzzling over."

"I wish you would, Tom. I am trying to invent a new system of interchangeable brush contacts, but so far I've been unable to make them work. However, there is no great hurry about that. If you are going to offer your silent machine to the government finish that first. We need all the aircraft we can get. The battles on the other side seem to be all in favor of the Germans, so far."

"We haven't got into our stride yet," declared Mr. Damon. "Once Uncle Sam gets the boys over there in force, there'll be a different story to tell. I only wish—"

At that moment the telephone set up an insistent ringing, breaking in on Mr. Damon's remarks.

"I'll answer," said Tom, as Mrs. Baggert moved toward the instrument, which was an extension from the main one.

"Hello!" called the young inventor into the transmitter, and as he received an answer a look of pleasure came over his face.

"Yes, Mary, this is Tom," he said. He remained silent a moment, while it was evident he was listening to the voice at the other end of the wire. Then he suddenly exclaimed:

"What's that? Tell him to come home? Why, he isn't here. I just came in and—what—wait a minute!"

With a rather strange look on his face Tom covered the mouth-piece of the instrument with his hand, and, turning to his father, asked:

"Is Mr. Nestor here?"

"No," replied Mr. Swift slowly, "He was here, though. He came a little while after you and Mr. Damon started off in the Air Scout. But he didn't stay. Said he wanted to see you about something and would call again."

"Oh," remarked the young man. "I didn't know he had been there."

"I meant to tell you," said Mrs. Baggert; "but getting the lunch made me forget it, I guess."

Tom uncovered the transmitter of the telephone again, and spoke to Mary Nestor.

"Hello," he said. "I was wrong, Mary. Your father was here, but he left when he found I wasn't at home. How long ago? Wait a minute and I'll inquire.

"How long ago did Mr. Nestor leave?" asked the young inventor of the housekeeper. "Nearly an hour," he said into the instrument, after he had received the answer. Then, after listening a moment, he added: "Yes, I guess he'll be home soon now. Probably stopped down town to see some of his friends. Yes, Mr. Damon and I tried out the Air Scout. Yes, she worked pretty well, for a starter, but there is something yet to be done. Oh, yes, now I'll have time to come over to see you, and take you for a ride too. We won't have to talk through a speaking tube, either. Tell your father I am sorry I was out when he called. I'll come to see him to-morrow, if he wants me to. Yes—yes. I guess so!" and Tom laughed, it being evident that his remarks at the end of the conversation had to do with personal matters.

"A telegram has come for Mr. Nestor and they were anxious that he should get it," Tom explained to his little audience as he hung up the receiver and put aside the telephone. "I wonder what he wanted to see me about?"

"He didn't say," replied Mrs. Baggert.

Mr. Damon, Tom, and his father remained in conversation a little while longer, and the eccentric man was thinking that it was about time for him to return home, when the telephone rang again.

"Hello," answered Tom, as he was nearest the instrument. "Oh, yes, Mary, this is he. What's that? Your father hasn't reached home yet? And your mother is worried? Oh tell her there is no cause for alarm. As I said, he probably stopped on his way to see some friends."

Tom listened for perhaps half a minute to a talk that was inaudible to the others in the room, and they noticed a grave look come over his face. Then he said:

"I'll be right over, Mary. Yes, I'll come at once. And tell your mother not to worry. I'm sure nothing could have happened. I'll be with you in a jiffy!"

As Tom Swift hung up the receiver he said:

"Mr. Nestor hasn't reached home yet, and as he promised to return at once in case he didn't find me, his wife is much worried. I'll go over and see what I can do."

"I'll come along!" volunteered Mr. Damon. "It isn't late yet."

"Yes, do come," urged Tom. "But I suppose when we get there we'll find our friend has arrived safely. We'll go over in the electric runabout."



CHAPTER XV

A VAIN SEARCH

Tom Swift's speedy little electric car was soon at the door in readiness to take him and Mr. Damon to the Nestor home. The electric runabout was a machine Tom had evolved in his early inventive days, and though he had other automobiles, none was quite so fast or so simple to run as this, which well merited the name of the most rapid machine on the road. In it Tom had once won a great race, as has been related in the book bearing the title, "Tom Swift and His Electric Runabout."

"Mary didn't telephone again, did she?" Tom asked his father, as he stopped at the house to get Mr. Damon, having gone out to see about getting the electric runabout in readiness.

"No," was the answer. "The telephone hasn't rung since."

"Then, I guess, Mr. Nestor can't have arrived home," said Tom. "It's a bit queer, his delay, but I'm sure it will be explained naturally. Only Mary and her mother are alone and, very likely, they're nervous. I'll telephone to let you know everything is all right as soon as I get there," Tom promised his father and Mrs. Baggert as he drove off down the road, partly illuminated by the new moon.

Rapidly and almost as silently as his Air Scout Tom Swift drove the speedy car down the highway. It was about three miles from his home to that of Mary Nestor, and though the distance was quickly covered, to Tom, at least, the space seemed interminable. But at length he drove up to the door. There were lights in most of the rooms, which was unusual at this time of night.

The sound of the wheels had not ceased echoing on the gravel of the drive before Mary was out on the porch, which she illuminated by an overhead light.

"Oh, Tom," she cried, "he hasn't come yet, and we are so worried! Did you see anything of father as you came along?"

"No," was Tom's answer. "But we didn't look for him along the road, as we came by the turnpike, and he wouldn't travel that way. But he will be along at any moment now. You must remember it's quite a walk from my house, and—"

"But he was on his bicycle," said Mary. "We wanted him to go in the auto, but he said he wanted some exercise after supper, and he went over on his wheel. He said he'd be right back, but he hasn't come yet."

"Oh, he will!" said Tom reassuringly. "He may have had a puncture, or something like that. Bicyclists are just as liable to them as autoists," he added with a laugh.

"Well, I'm sure I hope it will be all right," sighed Mary. "I wish you could convince mother to that effect. She's as nervous as a cat. Come in and tell us what to do."

"Oh, he'll be all right," declared Mr. Damon, adding his assurances to Tom's.

They found Mrs. Nestor verging on an attack of hysteria. Though Mr. Nestor often went out during the evening, he seldom stayed late.

"And he said he'd be right back if he found you weren't at home, Tom," said Mrs. Nestor. "I'm sure I don't know what can be keeping him!"

"It's too soon to get worried yet," replied the young inventor cheerfully. "I'll wait a little while, and then, if he doesn't come, Mr. Damon and I will go back over the road and look carefully. He may have had a slight fall—sprained his ankle or something like that—and not be able to ride. We came by the turnpike, a road he probably wouldn't take on his wheel. He's all right, you may be sure of that."

Tom tried to speak reassuringly, but somehow, he did not believe himself. He was beginning to think more and more how strange it was that Mr. Nestor did not return home.

"We'll wait just a bit longer before setting out on a search," he told Mary and her mother. "But I'm sure he will be along any minute now."

They went into the library, Mary and her mother, Tom and Mr. Damon. And there they sat waiting. Tom tried to entertain Mary and Mrs. Nestor with an account of his trial trip in the Air Scout, but the two women scarcely heard what he said.

All sat watching the clock, and looking from that to the telephone, which they tried to hope would ring momentarily and transmit to them good news. Then they would listen for the sound of footsteps or bicycle wheels on the gravel walk. But they heard nothing, and as the seconds were ticked off on the clock the nervousness of Mrs. Nestor increased, until she exclaimed:

"I can stand it no longer! We must notify the police—or do something!"

"I wouldn't notify the police just yet," counseled Tom. "Mr. Damon and I will start out and look along the road. If it should happen, as will probably turn out to be the case, that Mr. Nestor has met with only a simple accident, he would not like the notoriety, or publicity, of having the police notified."

"No, I am sure he would not," agreed Mary. "Tom's way is best, Mother."

"All right, just as you say, only find my husband," and Mrs. Nestor sighed, and turned her head away.

"Even if Mr. Nestor had had a fall," reasoned Tom, "he could call for help, and get some one to telephone, unless—"

And as he reasoned thus Tom Swift gave a mental start at his own use of the word "help."

That weird cry on the lonely meadow came back to him with startling distinctness.

"Come on, Mr. Damon!" cried Tom, in a voice he tried to make cheerful. "We'll find that Mr. Nestor is probably walking along, carrying his disabled bicycle instead of having it carry him. We'll soon have him safe back to you," he called to the two women.

"I wish I could go with you, and help search," observed Mary.

"Oh, I couldn't bear to be left alone!" exclaimed her mother.

"We'll telephone as soon as we find him," called Tom to Mrs. Nestor, as he and Mr. Damon again got into the runabout and started away from the place.

"What do you think of it, Tom?" asked the eccentric man, when they were once more on the road.

"Why, nothing much—as yet," Tom said. "That is, I think nothing more than a simple accident has happened, if, indeed, it is anything more than that he has delayed to talk to some friends."

"Would he delay this long?"

"I don't know."

"And then, Tom—bless my spectacles! what of that cry we heard? Could that have been Mr. Nestor?"

There! It was out! The suspicion that Tom had been trying to keep his mind away from came to the fore. Well, he might as well race the issue now as later.

"I've been thinking of that," he told Mr. Damon. "It might have been Mary's father calling for help."

"But we looked, Tom, near the trees, and couldn't discover anything. If he had been calling for help—"

Mr. Damon did not finish.

"He may have fallen from his wheel and been hurt," said Tom, as he turned the electric runabout into the highway that Mr. Nestor would, most likely, have taken on his way from Shopton. "Then he may have called for help, and some autoists, passing, may have heard and taken him away."

"Yes, but where, Tom? Whoever called for help was taken away, that's sure. But where?"

"To some hospital, I suppose."

"Then hadn't we better inquire there? There are only two hospitals of any account around here. The one in Shopton and the one in Waterfield. My wife is on the board of Lady Managers there. We could call that hospital up and—"

"We'll look along the road first," said Tom. "If we begin to make inquiries at the hospitals there will be a lot of questions asked, and a general alarm may be sent out. Mr. Nestor wouldn't like that, if he isn't in any danger. And it may turn out that he has met an old friend, and has been talking with him all this while, forgetting all about the passage of time."

They were now driving along the highway that led from the little suburb where Mr. Nestor lived, to the main part of Shopton, just beyond which was Tom's home. This section was country-like, with very few houses and those placed at rather infrequent intervals. The road was a good one, though not the main-traveled one, and Mr. Nestor, as was known, frequently used it when he rode his bicycle, an exercise of which he was very fond.

As Tom and Mr. Damon drove along, they scanned, as best they could in the light from the young moon and the powerful lamps on the runabout, every part of the highway. They were looking for some dark blot which might indicate where a man had fallen from his wheel and was lying in some huddled heap on the road. But they saw nothing like this, much to their relief.

"Do you know, Tom," said Mr. Damon, when they were nearing the town, and their search, thus far, had been in vain, "I think we're going at this the wrong way."

"Why, so?"

"Because Mr. Nestor may have fallen, and been hurt, and have been carried into any one of a dozen houses along the road. In that case we wouldn't see him. We've passed over the most lonely part of the journey and haven't seen him. If the accident occurred near the houses his cries would have brought some one out to help him. He is well known around here, and, even if he were unconscious and couldn't tell who he was, he could be identified by papers in his pockets. Then his family would be notified by telephone."

"Perhaps you are right, Mr. Damon. We may be wasting time this way. What do you suggest?" asked Tom.

"That we don't delay any longer, but call up the hospitals at once. If he isn't in either of those he must be in some house, and in such condition that his identity cannot be established. In that event it is a case for the police. We haven't found him, and I think we had better give the alarm."

Tom Swift thought it over for a moment. Then he came to a sudden decision.

"You're right!" he told Mr. Damon. "We mustn't waste any more time. He isn't along the road he ought to have traveled in coming from my house to his home—that's sure. But before I call up the hospitals I want to try out one more idea."

"What's that, Tom?"

"I want to go to the place where we heard that cry for help."

"Do you think that could have been Mr. Nestor?"

"It may have been. We'll go and take another look around there. Some man was evidently hurt there, and was taken away. We may get a clew. The lights on the runabout will give us a better chance to look around than we had by the little pocket lamp. We'll try there, and, if we don't find anything, then I'll call up the hospitals."



CHAPTER XVI

THE LONG NIGHT

With the speedy runabout it did not take Tom Swift and Mr. Damon long to reach the place where the Air Scout had been grounded a few hours before, and where they had heard the cry for help. All was as dark and as silent as when they had been there before.

But, as Tom had said, the lights from his electric runabout would give a brilliant illumination, and these he now directed toward the clump of trees whence the cry for help had seemed to come.

"Doesn't appear to have been visited by any one since we were here," remarked Torn, as he observed the marks of the new automobile tire in the dust. "Now we'll look about more carefully."

This they did, but they were about to give up in despair and start for the nearest telephone to call up the hospitals, when Mr. Damon gave an exclamation.

"What is it?" asked Tom.

"Something bright and shining!" said his companion. "I saw it gleam in the light of the lamps. You nearly put your foot on it, Tom. Just step back a moment."

Tom did so, and the eccentric man, with another exclamation, this time of satisfaction, reached down and picked something up from the dusty road.

"It's a watch!" he exclaimed. "A gold watch! And it's been stepped on, evidently, or run over by an auto. Not much damaged, but the case is a bit bent and scratched. It's stopped, too!" he added as he held it to his ear.

"What time does it show?" asked Tom.

"Eight forty-seven," answered Mr. Damon, as he consulted the dial. "Why, Tom, that was just about when we heard the cries for help!"

"Yes, it must have been. Let me see that watch."

No sooner had the young inventor taken the timepiece into his hands than he, too, uttered a cry of amazement.

"Do you recognize it?" asked Mr. Damon, in great excitement.

"It's Mr. Nestor's watch!" cried Tom. "He must have fallen here, and been hurt. It was Mr. Nestor who cried for help, and who was taken away by the autoists. They've probably taken him to some hospital. There's been an accident all right."

Tom and Mr. Damon were of one mind now in thinking that Mr. Nestor had met with some mishap on the road—an automobile accident most likely—and that he was the person who had called for help.

"If they had only answered when we hallooed at them," said Tom, "we wouldn't be in all this stew now. We could have told the strangers who came to his aid who he was, and we might even have taken him to the hospital in the airship."

"Well, it's too late to think of that now," returned Mr. Damon. "We had better get into communication with him as soon as we can, and then send word to his wife and daughter. I hope he isn't badly hurt."

Tom hoped so, too, with all his heart.

There was nothing to do but to get back in the runabout and make all speed for the nearest telephone, and Tom Swift lost little time in doing this. They found a drug store which was open a little later than usual, and at once Tom went into the booth and called up the Shopton hospital. He was well known there, as he and his father were liberal supporters of the institution, which was a private affair. Many of Tom's men were treated at the dispensary, and, as accidents were of more or less frequent occurrence at the works, the young inventor had frequent occasions to call up the place.

"Mr. Nestor would ask to be taken there, as it's nearest his home—that is, if he was able to speak," Tom said to Mr. Damon, who agreed with him. There was a little delay in getting the hospital on the wire, but when Tom had it, and was talking to the superintendent, he was rather surprised, to tell the truth, to be told that Mr. Nestor had not been brought in.

"We haven't had any accident cases all day, nor to-night, Mr. Swift," the superintendent reported. "Was this some one special you were inquiring about?"

For Tom, determining not to give Mr. Nestor's name, except as a last resort, had merely inquired whether any recent accident cases had been brought in.

"I'll let you know later, Mr. Millard," he told the superintendent, not exactly answering the question. He hung up the receiver, and, opening the door of the booth, said to Mr. Damon: "He isn't there."

"Then try Waterfield," was the suggestion; and Tom did so, though he could not imagine why an injured man, such as Mr. Nestor might prove to be, should be taken as far as Waterfield, when the hospital at Shopton was nearer.

"Unless," he told Mr. Damon, "the people which ran down Mary's father didn't know about our hospital."

The reply from the institution in Mr. Damon's home town was just as discouraging as had been the answer from Shopton. At first, when Tom inquired, the head nurse had said there was an accident case at that moment being brought in. Tom was all excitement until she went to inquire the name and circumstances, and then he learned that it was the case of a little boy who had fallen downstairs at his home and broken a leg. There was no record of any one answering the description of Mr. Nestor having been brought in that evening.

"Hum! This is getting to be mysterious," mused Tom, as he came out of the booth. "What shall we do—go back and tell Mrs. Nestor and Mary, or communicate with the police?"

"Why not try the Alexian Hospital?" asked Mr. Damon. "That's away over in Center-fiord, to be sure, but it's more likely to be known to passing tourists than either of our institutions around here, especially if the autoists were strangers."

"That's so," agreed Tom. The Alexian Hospital was operated under the direction of the Brothers of that faith, and was well known in that part of the state. Often cases of persons who had been injured by passing automobiles had been taken there for treatment, for, as Mr. Damon had said, it was well known, and Centerford was the nearest large city.

"I can just about see how it happened," said Tom. "They ran Mr. Nestor down, and stopped to pick him up after they heard his cries for help. And the Alexian Hospital was the first one they thought of. We should have called that up first."

But once more disappointment awaited the young inventor and his friend. Word came back over the wire that no accident case, which bore any resemblance to Mary's father, had been brought in.

"Well, I'm stumped!" exclaimed Tom. "What shall we do now, Mr. Damon?"

"Much as I dislike it," said the eccentric man who was too much worried, now, to do any "blessing," which was his favorite expression, "I think we ought to communicate with Mrs. Nestor. She will be very anxious."

"I guess we'll have to," said Tom. "But wait! I'll call up my house first, and see if he has gone back there."

But Mr. Nestor had not done this, and Mrs. Baggert, who answered the telephone, said Mary had been calling frantically for Tom, as her mother was now on the verge of complete collapse.

"No help for it," said Tom, ruefully. "We've got to tell 'em we have no news, and can't find him."

And, hearing this, Mrs. Nestor did collapse, and a doctor was called in.

Thereupon Tom, who with Mr. Damon had gone back to the Nestor home, took charge of matters, sending for Mrs. Nestor's sister to come and stay with her and take charge of the house.

"You'll need some one to stay with you," he told Mary.

"Yes, I shall," she admitted, trying bravely not to give way to her emotion. "Oh, Tom, I wish you could stay, too. I'm sure something dreadful must have happened to poor father. Please stay and help us find him!"

"I will," Tom promised. "As soon as your aunt comes I'll take Mr. Damon home, and then I'll give the rest of my time to you."

And this Tom did, sending word home that he would remain at the Nestor's all night and part of the next day.

Tom got but little sleep that night. He communicated with the police and saw to it that a general alarm was sent out. He called up all hospitals within a radius of fifty miles, but could get no trace of any injured man whose description resembled that of Mr. Nestor.

"What can have happened?" asked Mary tearfully.

"Well, the way I figure it out is this," said Tom. "Your father left my house soon after Mr. Damon and I did in the Air Scout. Mr. Nestor was riding his bicycle, and he must have been run into by an automobile. That is how his watch was damaged and that was when Mr. Damon and I heard the cries for help."

"Oh, do you think he was badly hurt?" asked Mary.

"No, I don't," and Tom answered truthfully. "The voice sounded as though he was in pain, certainly, but it was strong and vigorous, and not at all as though he was dangerously hurt."

"And what do you think happened to him after he was hurt?" asked Mary.

"The autoists took him away," decided Tom. "In fact, we heard the machine go, but of course we never connected the call for help and what followed with your father. The autoists took him away."

"Where?"

"I should say to some hospital. Perhaps a private one of which we know nothing, and which may be near here. I'll get a full list from the Board of Health to-morrow. Or it may be that the autoists, seeing the damage they had done, took your father to the home of one of themselves, and summoned a doctor there."

"Why would they do that?"

"Well, they may have been so frightened they didn't realize what they were doing, or they may have thought he would get better treatment in a private house, if he were not badly injured, than if he should be taken to a hospital. It may have been that one of the persons in the auto was a physician, and wished to try his own skill on the man he had hurt."

"You make me feel more comfortable, Tom," said Mary. "But, even supposing all this, why couldn't they telephone to us that my father was all right? He always carries an identification card with him, and if he were unconscious it could be ascertained who he was."

"That's what I can't understand," said Tom frankly. "It puzzles me. But we'll find him—never fear!"

And so he kept on with his telephone inquiries, while a physician and her sister ministered to Mrs. Nestor. The night was very, very long, and no good news came in.



CHAPTER XVII

SILENT SAM

Slowly the dawn broke through the mists of darkness, and made the earth light. The sun came straggling in through cracks in the shutters in the home of Mr. Nestor, the gradually increasing gleam paling the electric lights, in the glare of which Tom Swift, Mary, and her aunt sat, waiting for some word of the missing man. But none came.

"What shall we do now?" asked Mary, as she looked at Tom.

"Oh, there's lots to do," he said, trying to make his voice sound cheerful. "We'll be busy all day. I sent word to have one of my touring cars ready to hurry to any part of the country the moment we should get word from your father."

"And do you think we shall get word, Tom?" the girl went on wistfully.

"Of course we shall!" he cried. "Word may come in at any time. Now get ready, eat a good breakfast, and then you can go with me as soon as we hear anything definite. Come, we'll have breakfast!"

"I can't eat a thing!" protested Mary.

"Oh, yes you can," said her aunt, who was a cheerful sort of person. "I'll see about getting something for you and Mr. Swift, and see that your mother is all right."

She left the room to give orders to the servant about the meal, and returned to say that Mrs. Nestor was sleeping quietly. She had been given a sedative. Mary managed to eat a little, and she gave Tom the address of several friends who were called up in the vain hope that, somehow, Mr. Nestor might have gone to see them.

"Tom, what do you really think has happened?" asked Mary again, as they sat facing one another in the library, during a respite from the telephone.

Tom Swift repeated, to the girl his theory of what had happened with an assumption of confidence he did not altogether feel.

His prediction of a speedy end to the suspense did not come true that day, nor for many days. No news was heard of Mr. Nestor. After the first day, when there was no information and when no reports came of any one of his description having been hurt in an automobile accident or having been taken to any hospital, the police started an energetic search.

The authorities in all near-by cities were notified, and all thought of keeping from the public what had happened was given over. Tom's story, of how he and Mr. Damon had heard the cry for help on the lonely meadow, was printed in the papers, though the young inventor did not say that he had been out trying his new aeroplane. That was a detail not needed in the finding of Mr. Nestor.

But Mary's father was not found. The mystery regarding his disappearance deepened, and there was no trace of him after he had left Tom's house that eventful evening. Persons living along the roads he might have taken in riding his bicycle were questioned, but they had seen nothing of him, nor were they aware of any accident. Tom's testimony and that of Mr. Damon was all the clew there was.

"I don't believe he's dead!" stoutly declared the young inventor, when this dire possibility had been hinted at. "I believe the persons who were responsible for the accident are afraid to reveal his whereabouts until he recovers from possible injuries. You'll see! Mr. Nestor will come back safe!"

And, somehow, though her mother was skeptical, Mary believed what Tom said.

The search was kept up, but without result, and Tom aided all he could. But there was not much he could do. The police and other authorities were at a total loss.

In the intervals of visiting Mary and her mother, and doing what he could for them, Tom worked on his new motor. He knew that he was on the right track and that all that was needed now was to make certain refinements and adjustments in the apparatus he had already constructed, so that it would operate more quietly.

"Absorbing the vibrations from the exhaust, caused by the exploded gases in the cylinders, does the trick," Tom told his father.

"But there is enormous pressure to overcome, Tom. You must be sure your muffler will stand the strain. Otherwise she is going to blow out a gasket some day, when you least expect it. Then the sudden resumption of pressure outside the cylinders is going to cause a change in the equilibrium, and you may turn turtle in the air."

"I've thought of that," said Tom. "At worst it can't be any more than looping the loop. But I'll make the muffler doubly strong."

"Better provide an auxiliary chamber to take care of part of the exhaust in case your main apparatus breaks," advised the older inventor, and Tom said he would. He did, too, for he valued his father's expert advice.

Meanwhile he was busy fitting one of his latest aeroplanes with the new motor. The motor he and Mr. Damon had used in their flight was one patched up from an old one. But now Tom was working on a complete new one, made after his revised model, and in which the silencer was an integral part, instead of being built on.

While giving Mary and her mother all the assistance in his power, Tom still found time to work on his new, pet scheme. He had matters now where he did not fear any tampering with his plans, for he had filed away his papers in a safe place, and was making his new machine from memory.

"But if some one got in and had a look at the inside of your silencer he could see how it is constructed, couldn't he?" asked Ned Newton.

"Yes," assented Tom, "But they're not going to get in very easily. Koku sleeps in the experiment shop now, and my machine is there."

"Oh, well that explains your confidence. I feel sorry for the burglar who makes the attempt, once Koku wakes up. Heard anything more from those Universal people?"

"No, not directly. I understand they are working hard on some new type of plane for army use, but I haven't bothered my head about them. I'm too much occupied with my own affairs and trying to help Mary."

"Very strange about Mr. Nestor, isn't it?"

"Worse than strange," said Tom. "If this keeps on, and he isn't heard from, it will be tragic pretty soon."

"He must be held a prisoner somewhere," declared Ned.

"It begins to look that way," assented Tom. "Though who would have an object in that I can't understand. He had no enemies, as far as is known, and his business affairs were in excellent shape. Unless, as I said, the persons who ran him down are, through fear, keeping him hidden until he recovers, I can't imagine what has become of him."

"Well, it certainly is a puzzle," said Ned. And Tom agreed with his chum.

It was about a week after the disappearance of Mr. Nestor that Mr. Damon came over to see Tom.

"Bless my shoe laces, Tom!" exclaimed the eccentric man, "but you are as busy as ever." For he found the young inventor in the experiment shop, surrounded by a mass of papers and all sorts of mechanical devices.

"Yes, I'm working a little," said Tom. "But you are just in time. Come on out, I want to introduce you to Silent Sam."

"'Silent Sam!'" exclaimed Mr. Damon. "Have you been taking a new trip to the Land of Wonders? Have you brought back some new kind of servant?"

"Not exactly a servant," said Tom with a laugh, "though I hope Silent Sam will serve me well."

"'Silent Sam?' What does it mean? Is that a joke?" asked the puzzled Mr. Damon.

"I hope it doesn't turn out a joke," replied Tom. "But come on, I'll introduce you to him, Mr. Damon."

He led the way to one of the big hangars where his various machines of the air were housed. On the way Mr. Damon asked about news of Mr. Nestor, but was told there was none.

Tom Swift opened the big, swinging doors and pulled aside an enveloping canvas curtain. There stood revealed a big aeroplane, of somewhat new pattern, the wings gleaming like silver from the varnish that had been applied. In shape it was not unlike the machines already in use, except that the propellers were of somewhat different design.

The engine was mounted in front, and even with his slight knowledge of mechanics Mr. Damon could tell that it was exceedingly powerful. But it was certain devices attached to the engine that attracted his attention, for they were totally different from any on any other aeroplane, though they bore some resemblance to apparatus on the plane in which Tom and the eccentric man had made the night flight.

"Is this your new machine, Tom?" asked Mr. Damon.

"Yes."

"Well, I don't see anything of that fellow you spoke of—Silent Sam."

"This is Silent Sam," returned Tom, with a laugh. "I've named my new noiseless aeroplane—my Air Scout—I've named that Silent Sam. Wait until you hear it, or rather, don't hear it, and I think you'll agree with me. Silent Sam for Uncle Sam!"

"Good!" cried Mr. Damon. "Bless my dictionary, but that's a good name! Does it sail silently, Tom?"

"I'll let you judge presently. Silent Sam is all ready for his first trial, and I'll be glad to have you with me. Now, I'll just—"

Tom suddenly ceased speaking and held up a hand to enjoin silence. Then, while Mr. Damon watched, the young inventor began moving noiselessly toward the rear of the big shed, inside which was his new machine.



CHAPTER XVIII

SUSPICIONS

"Who's there?" suddenly called Tom, and in such a sharp voice that Mr. Damon started, ready as he was for something unusual.

There was no answer and Tom suddenly switched on all the lights in the shed. Up to then there had been only a few glowing—just enough for him to show the new Air Scout to his friend.

"Who's there?" asked Tom again, sharply.

"Bless my opera glasses, Tom!" cried Mr. Damon, "but are you seeing things?"

"No; but I'm hearing them," answered Tom with a short laugh. "Did you think you heard some one moving around near the rudders of Silent Sam, Mr. Damon?"

"No, I can't say that I did. Everything seems to me to be all right."

"Well, it doesn't to me," went on Tom grimly. "I think there is an intruder in this shed, though how any one could get in when the doors have been locked all day, is more than I can figure out. But I'm going to have a look."

"I'll help you," offered Mr. Damon, and, in the bright glare from many electric lights, the two began a search of the big hangar where the new craft was kept.

But though the young inventor and his friend went around to the rear of the aeroplane, walking in opposite directions, they saw no one, nor did any one try to escape past them.

"And yet I was sure I heard some one in here," declared Tom, when a search had revealed nothing. "It sounded as if some one were scuffling softly about in rubber-soled shoes, trying to hide."

"Bless my suspenders!" cried Mr. Damon, "who do you think it could have been, Tom?"

"Who else but some spy trying to get possession of my secrets?" was the answer. "But I guess I was too quick for them. They couldn't learn much from looking at the outside of my muffler, and it hasn't been disturbed, as far as I can see."

"Who would want to gain a knowledge of it in that unlawful way?" asked Mr. Damon.

"Perhaps some of the Universal crowd. They may have been disappointed in perfecting a silent motor themselves, and think stealing my idea would be the easiest way out of it."

"Do they know you are working on such a model as this Silent Sam of yours, Tom?"

"Yes, I imagine they do. One of the firm members, as you recall, overheard something, I think, that gave them a hint as to what my plans were, though, thanks to the time I fooled the spy, they haven't any real data to go by, I believe."

"Let us hope not," said Mr. Damon.

Tom and he made a thorough search of the big shed, but found no one, nor was there any trace of an intruder. Tom notified Jackson, who, in turn, told the guards and watchmen to be on the lookout for any suspicious strangers, but none was seen in the vicinity of the Swift works.

"Well, everything seems to be all right, so we'll have the test," remarked Torn, after a further search of the premises. "Now, Mr. Damon, if all goes as I hope you will see what my new machine can do. Strain your ears for a sound, and let me know how much you hear."

His men helping him, Tom started the new motor which was tried for the first time attached to the new craft. No flight was to be made yet, the motor being tested as though on the block, though, in reality, the craft was ready for instant flight if need be.

Slowly the great propellers began to revolve, and then Tom, taking his place in the cockpit, turned on more power. The new craft—Silent Sam—was made fast so it could not progress even though the propellers revolved at high speed.

"I'm not sending her to the limit," said Tom to his friend, as the young inventor throttled down the motor. "If I did I'd tear her loose from the holding blocks."

"Her!" cried Mr. Damon. "Bless my typewriter, Tom! but I thought Silent Sam was a gentleman aeroplane.

"So he is!" laughed the young man, frankly. "I forgot about 'Silent Sam.' Guess I'll have to say 'him' instead of 'her,' though the latter sounds more natural. Anyhow what do you think?"

"I think it's wonderful!" exclaimed Mr. Damon. "There the motor is, going at almost full speed, and I can hardly hear a thing. You can the easier believe that when I say that I can hear you talk perfectly well. And I guess you hear me, don't you?"

"Yes," replied Tom. "And we don't have to shout, either. This is the best test ever! I think everything is a success."

"Are you going to take her aloft, Tom?" the eccentric man went on.

"Yes, now that I'm sure the engine is all right. Will you go for a flight with me?"

"I certainly will! I only wish we could find him, though. I'd go with a better heart."

"Oh! Mr. Nestor?"

"Yes, I can't imagine what has become of him. It is almost as if the earth had opened and swallowed him. His disappearance is a great mystery."

"It surely is," agreed Tom. "Can't seem to get any trace of him. But if we hear another cry for help, when we have to land, you can make up your mind I'll investigate more quickly than I did at first."

"I agree with you," said Mr. Damon.

It was nearly evening then, and until it was dark enough for his flight Tom spent the time tuning up the engine and seeing that all was in readiness for the latest test. He had decided not to go aloft while it was light enough for curiosity seekers to note the flight.

Tom rather wished Mary Nestor might have a sail with him in his latest improved silent Air Scout, but the girl was too much occupied at home and in trying to find some trace of her father.

Tom, his father, and Mr. Damon had helped all they could, but there were no results. A private detective had been engaged, but he had no more of a clew than the regular police.

At last it was dark enough for the flight, and Tom and Mr. Damon took their places in the machine. Once more the propellers were turned around, and when the compression had been made, and the spark switched on, around spun the big wooden blades, and the great craft moved over the grass.

On and on and up and up sailed Tom and Mr. Damon, and as they left behind them the shops and the Swift homestead, the two passengers were aware of their almost silent flight. The big aeroplane, the exhaust of which, ordinarily, would have nearly deafened them, was now as silent as a bird.

"Silent Sam for Uncle Sam!" cried Tom in delight, as he went on faster. "I'm sure the government ought to be glad to get this plane for air scout work. It's a success! A great success!"

"Yes, so it is!" agreed Mr. Damon. "You do well to speak of it so, Tom."

For, modest as the young inventor was, he felt, in justice to himself, that he must acknowledge the fact that his craft was a success. For it rose and sailed almost as silently as a bat, and a few hundred feet away no one, not seeing it, would have believed a big aeroplane was in motion.

Tom and Mr. Damon flew about twenty miles at a swift pace, and all the fault Tom had to find was that the machine was not as steady in flight as she should have been.

"But I can remedy that with the use of some of dad's gyroscope stabilizers," he told Mr. Damon.

They returned to the hangar safely, and the first trip of the new Silent Sam was an assured success.

It was the following day, when Tom was busy in the machine shop installing the gyroscopes spoken of, that Jackson came to tell him there was a visitor to see him.

"Who is it?" asked the young inventor.

"Mr. Gale of the Universal Company," was the answer.

"I don't want to see him!" declared Tom quickly. "I have nothing to say to him after his clumsy threats."

"He seems very much in earnest," said Jackson. "Better see him, if only for a minute or so."

"All right, I will," assented Tom. "Show him in."

Mr. Gale, as blusteringly bluff as ever, entered the shop. Tom had carefully put away all papers and models, as well as the finished machines, so he had no fear that his visitor might discover some secret.

"Oh, Mr. Swift!" began the president of the Universal Company, when he met the young inventor, "I wish to assure you that what has been done was entirely without our knowledge. And, though this man may have acted as our agent at one time, we repudiate any acts of his that might—"

"What are you talking about?" asked Tom in surprise. "Have I been so impolite as to sleep during part of your talk? I don't understand what you are driving at."

"Oh, I thought you did," said Gale, and he showed surprise. "I understood that the man who—"

"Do you mean there was some one here in the shed last night?" cried the young inventor suddenly, all his suspicions aroused.

"Some one here last night?" repeated Mr. Gale. "No, I don't refer to last night. But perhaps I am making a mistake. I—er—I—"

"Some one is making a mistake!" said Tom significantly.



CHAPTER XIX

ANOTHER FLIGHT

For perhaps a quarter of a minute Tom Swift and the president of the Universal Flying Machine Company of New York sat staring at one another. Mr. Gale's face wore a puzzled expression, and so did Tom's. And, after the last remark of the young inventor, the man who had called to see him said:

"Well, perhaps we are talking at cross purposes. I don't blame you for not feeling very friendly toward us, and if I had had my way that last correspondence with you would never have left our office."

"It wasn't very business-like," said Tom dryly, referring to the veiled threats when he had refused to sell his services to the rival company.

"I realize that," said Mr. Gale. "But we have some peculiar men working for us, and sometimes there is so much to do, so many possibilities of which to take advantage, that we may get a little off our balance. But what I called for was not to renew our offer to you. I understand that is definitely settled."

"As far as I am concerned, it is," said Tom, as his caller seemed to want an answer.

"Yes. Well, then, what I called to say was that if you are thinking of taking any legal action against us because of the action of that man Lydane, I wish to state that he had absolutely no authority to—"

"Excuse me!" broke in Tom, "but by Lydane do you mean the man who also posed as Bower, the spy?"

"No, I do not. Though I regret to say that Bower once worked for us. He, too, had no authority to come here and get a position. He was still in our service when he did that."

"So I have suspected," said Tom. "I realize now that he was a spy, who came here to try to find out for you some of my secrets."

"Not with my permission!" exclaimed Mr. Gale. "I was against that from the first and I came to tell you so. But Bower really did you no harm."

"No, he didn't get the chance!" chuckled Tom. "Nor did that other spy—the one with the gold tooth. I wonder how he liked our mud hole?"

"He was Lydane," said Mr. Gale. "It is about him I came."

"You might have saved yourself the trouble," returned Tom. "I don't wish to discuss him."

"But I wish to make sure," said Mr. Gale, "that what he has done will not come back on us. We repudiate him entirely. His methods we can not countenance. He is too daring—"

"Oh, don't worry!" interrupted Tom. "He hasn't done anything to me—he didn't get the chance, as I guess he's told you. You needn't apologize on his account. He did me no harm, and—"

"But I understood from him that—"

"Now I don't want to seem impolite!" broke in Tom, "nor do I want to take pattern after some of your company's acts, if not your own. But I am very busy. I have an important test to make for the government, and my time is fully occupied. I am afraid I shall have to bid you good-morning and—"

"But won't you give me a chance to—" began the president.

"Now, the less we discuss this matter the better!" interrupted Tom. "Lydane, as you call the man with the gold tooth didn't really do anything to me nor any great harm to any of my possessions, as far as I can learn. His career is a closed book—a book with muddy covers!" and the young inventor laughed.

"Oh, well, if you look at it that way, there is nothing further for me to say," said Mr. Gale stiffly. "I understood— But hasn't my partner, Mr. Ware, seen you?" he asked Tom quickly.

"No. And I don't care to see him."

"Oh, then that accounts for it," was the quick answer. "Well, if you regard the matter as closed I suppose we should also. We are not to blame for what Lydane does when he is no longer in our employ, and we repudiate anything he may do, or may have done."

This struck Tom, afterward, as being rather a queer remark, but he did not think so at the time.

The truth was that the young inventor wished very much to try out a new device on his noiseless aeroplane and wanted to get rid of Mr. Gale before doing so. So he did not pay as much attention to the remarks of the president as, otherwise, he might have done.

It was not until after Mr. Gale had taken his leave and Tom had finished the particular work on which he was engaged when the president of the rival company came in, that the young man did some hard thinking. And this thinking was done after he had received a telephone call from Mary Nestor, asking, if by any chance, he had beard anything like a clew as to the whereabouts of her father.

Tom had been obliged to tell her that he had not. Everything possible was being done to find the missing man but he had disappeared as completely as though he had ridden on his bicycle into the crater of some extinct volcano on the meadow, and had fallen to the bottom.

An effort was made to trace him through an automobile association which had a large membership. That is, the members were asked to make inquiries to ascertain, if possible, whether any one had heard of an unreported accident—one in which Mr. Nestor might have been carried away by persons who accidently ran him down.

But this came to naught, and the police and other authorities were at a loss how farther to proceed. It was a theory in some quarters that Mr. Nestor was perfectly safe, but that he was out of his mind, and was either wandering around, not knowing who he was, or was, in this condition, detained somewhere, the persons having him in charge not realizing that he was the missing man so widely sought.

This belief was a relief to Mrs. Nestor and Mary in many ways for it prevented them from giving way to the fear that Mr. Nestor was dead. That he was alive was Tom Swift's firm opinion, and he was doing all he could to prove it.

It was not until the day after the visit of Mr. Gale that Tom, having concluded some intricate calculations about the strength of cylinder valves, uttered an exclamation.

"I wonder if he could have meant that?" cried the young inventor. "I wonder if he could have meant that? I must find out at once! Queer I didn't think of that before!"

He put in a long distance call to New York, asking to speak to Mr. Gale. But when, eventually, he was connected with the office of the Universal Flying Machine Company he was told that Mr. Gale and Mr. Ware had sailed for France that day, going over as government representatives to investigate aeroplane motors. Gale's visit to Tom had been just previous to taking the boat, it was said.

"This is tough luck!" mused Tom, his suspicions doubly aroused now. "I can't let this rest here! I've got to get after it! As soon as I make this final test, and invite Uncle Sam's experts out to see how my noiseless motor works, I'll get after Gale and Ware if I have to follow them to the battlefields of France! I wonder if it was that he was hinting at all the while! I begin to believe it was!"