Curious as it may seem, Eradicate, the oldest and certainly not the most energetic of the party assembled in the experiment room, was the first to recover himself and arise. Tottering to his feet he gave one look at the testing block, whence the motor had torn itself. Then he looked at the prostrate figures around him, none of them hurt, but all stunned and very much startled. Then the gaze of Eradicate traveled to the hole in the roof. It was a gaping, ragged hole, for the motor was heavy and the roof of flimsy material. And then the colored man exclaimed:
"Good land ob massy! Did I do dat?"
His tone was one of such startled contrition, and so tragic, that Tom Swift, rueful as he felt over the failure of his experiment and the danger they had all been in, could not help laughing.
"I take it, hearing that from you, Tom, that we're all right," said Ned Newton, as he recovered himself and brushed some dirt off his coat. Ned was a natty dresser.
"Yes, we seem to be all right," replied Tom slowly. "I can't say what damage the flying motor has done outside, but—"
"Bless my insurance policy! but what happened?" asked Mr. Damon. "I saw Eradicate pull on that lever as you told him to, Tom, and then things all went topsy-turvy! Did he pull the wrong handle?"
"No, it wasn't Rad's fault at all," said Tom. "The trouble was, as I guess I'll find when I investigate, that I put too much power into the motor, and the muffler didn't give any chance for the accumulated exhaust gases to expand and escape. I didn't allow for that, and they simply backed up, compressed and exploded. I guess that's the whole explanation."
"I'm inclined to agree with you, Son," said Mr. Swift dryly. "Don't try to get rid of all the noise at once. Eliminate it by degrees and it will be safer."
"I guess so," agreed Tom.
By this time a score of workmen from the other shops had congregated around the one though the roof of which the motor had been blown. Tom opened the door to assure Jackson and the others that no one was hurt, and then the young inventor saw the exploded motor had buried in the dirt a short distance away from the experiment building.
"Lucky none of us were standing over it when it went up," said Tom, as he made an inspection of the broken machine. "We'd have gone through the roof with it."
"She certainly went sailing!" commented Ned. "Must have been a lot of power there, Tom."
And this was evidenced by the bent and twisted rods that had held the motor to the testing block, and by the cylinders, some of which were torn apart as though made of paper instead of heavy steel. But for the fact that all the force of the explosion was directly upward, instead of at the sides, none might have been left alive in the shop. All had escaped most fortunately, and they realized this.
"Well," queried Ned, as Tom gave orders to have the damaged machine removed and the roof repaired, "does this end the wonderful silent motor, Tom?"
"End it! What do you mean—"
"I mean are you going to experiment any further?"
"Why, of course! Just because I've had one failure doesn't mean that I'm going to give up. Especially when I know what the matter was—not leaving any vent for the escaping gases. Why this isn't anything. When I was perfecting my giant cannon I was nearly blown up more than once, and you remember how we got stuck in the submarine."
"I should say I did!" exclaimed Ned with a shudder. "I don't want any more of that. But as between being blown through a roof and held at the bottom of the sea, I don't know that there's much choice."
"Well, perhaps not," agreed Tom. "But as for ending my experiments, I wouldn't dream of such a thing! Why, I've only just begun! I'll have a silent motor yet!"
"And a non-explosive one, I hope," added Mr. Damon dryly. "Bless my shoe buttons, Tom, but if my wife knew what danger I'd been in she'd never let me come over to see you any more."
"Well, the next time I invite you to a test I'll be more careful," promised the young inventor.
"There isn't going to be any next time as far as I'm concerned!" laughed Ned. "I think it's safer to sell Liberty Bonds."
And, though they joked about it, they all realized the narrow escape they had had. As for Eradicate, once he knew he had not been the one who caused the damage, he felt rather proud of the part he had taken in the mishap, and for many days he boasted about it to Koku.
True to his determination, Tom Swift did not give up his experimental work on the silent motor. The machine that had been blown through the roof was useless now, and it was sent to the scrap heap, after as much of it as possible had been salvaged. Then Tom got another piece of apparatus out of his store room and began all over again.
He worked along the same lines as at first—providing a chamber for the escaping gases of the exhaust to expend their noise and energy in, at the same time laboring to cut down the concussion of the explosions in the cylinder without reducing their force any. And that it was no easy problem to do either of these, Tom had to admit as he progressed. All previous types of mufflers or silencers had to be discarded and a new one evolved.
"Jackson, I need some one to help me," said Tom to his chief mechanician one day. "Haven't you a good man who is used to experimental work that you can let me take from the works?"
"Why, yes," was the answer. "Let me see. Roberts is busy on the new bomb you got up, but I could take him off that—"
"No, don't!" interposed Tom. "I want that work to go on. Isn't there some one else you can let me have?"
"Well, there's a new man who came to me well recommended. I took him on last week, and he's a wonderful mechanic. Knows a lot about gas engines. I could let you have him—Bower his name is. The only thing about it, though, is that I don't like to give you a man of whom I am not dead certain, when you're working on a new device."
"Oh, that will be all right," said Tom. "There won't be any secrets he can get, if you mean you think he might be up to spy work."
"That's what I did mean, Tom. You never can tell, you know, and you have some bitter enemies."
"Yes, but I'll take care this man doesn't see the plans, or any of my drawings. I only want some one to do the heavy assembling work on the experimental muffler I'm getting up. We can let him think it's for a new kind of automobile."
"Oh, then I guess it will be all right. I'll send Bower to you."
Tom rather liked the new workman, who seemed quiet and efficient. He did not ask questions, either, about the machine on which he was engaged, but did as he was told. As Tom had said, he kept his plans and drawing under lock and key—in a safe to be exact—and he did not think they were in any danger from his new helper.
But Tom Swift held into altogether too slight regard the powers of those who were opposed to him. He did not appreciate the depths to which they would stoop to gain their ends.
He had been working hard on his new device, and had reached a point further along than when the other motor had exploded. He began to see success ahead of him, and he was jubilant. Whether this made him careless does not matter, but the fact was that he left Bower more to himself, and alone in the experimental shop several times.
And it was on one of these occasions, when Tom had been for some time in one of the other shops, where he and Jackson were in consultation over a new machine, that as he came back to the test room unexpectedly, he saw Bower move hastily away from in front of the safe. Moreover, Tom was almost certain he had heard the steel door clang shut as he approached the building.
And then, before he could ask his helper a question, Tom looked from a window and saw a stranger running hastily along the side of the building where his trial motor was being set up.
"Who's that? Who is that man? Did he come in here? Was he tampering with my safe?" cried Tom. He saw Bower hesitate and change color, and Tom knew it was time to act.
The window was open, and with one bound the young inventor was out and running after the stranger he had seen departing in such a hurry. The man was but a short distance ahead of him, and Tom saw he was stuffing some papers into his pocket.
"Here! Come back! Stop!" ordered Tom, but the man ran on the faster.
"That's a spy as sure as guns!" reflected Tom Swift. "And Bower is in with him!" he added. "I've got to catch that fellow!" and he speeded his pace as he ran after the fellow.
There was no question in the mind of Tom Swift but that the man he was running after was guilty of some wrong-doing. In the first place he was a stranger, and had no right inside the big fence that surrounded the Swift machine plant. Then, too, the very fact that he ran away was suspicious.
And this, coupled with the confusion on the part of Bower, and his proximity to the safe, made Tom fear that some of his plans had been stolen. These he was very anxious to recover if this strange man had them, and so he raced after him with all speed.
"Stop! Stop!" called Tom, but the on-racing stranger did not heed.
The cries of the young inventor soon attracted the attention of his men, and Jackson and some of the others came running from their various shops to give whatever aid was needed. But they were all too far away to give effective chase.
"Bower might have come with me if he had wanted to help," thought Tom. But a backward glance over his shoulder did not show that the new helper was engaging in the pursuit, and he could have started almost on the same terms as Tom himself.
The runaway, looking back to see how near the young inventor was to him, suddenly changed his course, and, noting this, Tom Swift thought:
"I've got him now! He'll be bogged if he runs that way," for the way led to a piece of swampy land that, after the recent rains, was a veritable bog which was dangerous for cattle at least; and more than one man had been caught there.
"He can't run across the swamp, that's sure," reflected Tom with some satisfaction. "I'll get him all right!"
But he wanted to capture the man, if possible, before he reached the bog, and, to this end, Tom increased his speed to such good end that presently, on the firm ground that bordered the swamp, Tom was almost within reaching distance of the stranger.
But the latter kept up running, and dodged and turned so that Tom could not lay hands on him. Suddenly, turning around a clump of trees the fleeing man headed straight for a veritable mud hole that lay directly in his path. It was part of the swamp—the most liquid part of the bog and a home of frogs and lizards.
Too late, the man, who was evidently unaware of the proximity of the swamp, saw his danger. His further flight was cut off by the mud hole, but it was too late to turn back. Tom Swift was at his heels now, and seeing that it was impossible to grab the man, Tom did the next best thing. He stuck out his foot and tripped him, and tripped him right on the edge of the mud hole, so that the man fell in with a big splash, the muddy water flying all around, some even over the young inventor.
For a moment the man disappeared completely beneath the surface, for the mud hole was rather deep just where Tom had thrown him. Then there was another violent agitation of the surface, and a very woebegone and muddy face was raised from the slough, followed by the rest of the figure of the man. Slowly he got to his feet, mud and water dripping from him. He cleared his face by rubbing his hands over it, not that it made his countenance clean, but it removed masses of mud from his eyes, nose, and mouth, so that he could see and speak, though his first operation was to gasp for breath.
"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."
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?
"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!"
"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, but 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.