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 be
en 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 fac
t 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.
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