THROUGH THE ROOF
Tom rushed from his private office, and when he reached the outer door
he heard with more distinctness the sounds that had alarmed him. They
seemed to come from a small building given over to electrical
apparatus, and which, at the time, was not supposed to be in use. It
had been Tom's workroom, so to speak, when he was developing his
electric runabout and rifle, but of late he had not spent much time in
it.
"Somebody's in there!" reflected the young inventor, as he heard yells
coming from the open door of the place. "And if it isn't Koku and
Eradicate I miss my guess! Wonder what they can be doing there."
He crossed the yard between his private office and the electrical shop
in a few rapid strides, and, as he entered the latter place, he was
greeted with a series of wild yells.
"Good volume of sound here, at all events," mused Tom. "Almost as much
as my motor made when I was trying to talk to Mary. Hello there! What's
going on? Is any one hurt? What's the matter?" he cried, for, at first,
he could see no one in the dim light of the place. The interior was a
maze of electrical apparatus.
"Who's here?" demanded Tom, as he advanced.
"Oh, Master! Come quick! Koku 'most dead an' no can let go!" was the
cry.
"Yo' jest bet yo' cain't let go!" chimed in the voice of Eradicate. "I
done knowed yo would git into trouble ef yo' come heah, an' I'se glad
ob it! So I is!"
"What is it, Rad? What has happened to Koku?" cried Tom, running
forward, for though no very powerful current could be turned on in the
electrical shop at this period of unuse, there was enough to be very
painful. "What is it, Rad?"
"Oh, dat big foolish giant, Koku, done got his se'f into trouble!"
chuckled the colored man. "He done got holt ob one ob dem air
contraptions, Massa Tom, an' he cain't let go! Ha! Ha! Golly! Look at
him squirm!" and Rad laughed shrilly, which accounted for some of the
sounds Tom had heard.
Then came yells of rage and pain from the giant, and they were so loud
and vigorous, mingling with Eradicate's as they did, that it was no
wonder Tom was startled. The sounds were heard in the other shops, and
men came running out. But before then Tom had put an end to the trouble.
One look showed him what had happened. Just how or why Koku and
Eradicate had entered the electrical shop Tom did not then stop to
inquire. But he saw that the giant had grasped the handles of one of
the electric machines, designed for charging Leyden jars used in Tom's
experiments, and the powerful, though not dangerous, current had so
paralyzed, temporarily, the muscles of the giant's hands and arms that
he could not let go, and there he was, squirming, and not knowing how
to turn off the current, and unable to ease himself, while Eradicate
stood and laughed at him, fairly howling with delight.
"Ha! Guess yo' won't do no mo' spadin' in' Massa Tom's garden right
away, big man!" taunted Eradicate.
"Be quiet, Rad!" ordered Tom, as he reached up and pulled out the
switch, thus shutting off the current. "This isn't anything to laugh
at."
"But he done look so funny, Massa Tom!" pleaded the colored man. "He
done squirm laik--"
But Eradicate did not finish what he intended to say. Once free from
the powerful current, the giant looked at his numb hands, and then,
seeming to think that Eradicate was the cause of it all, he sprang at
the colored man with a yell. But Eradicate did not stay to see what
would happen. With a howl of terror, he raced out of the door, and, old
and rheumatic as he was, he managed to gain the stable of his mule,
Boomerang, over which he had his humble but comfortable quarters.
"Well, I guess he's safe for a while!" laughed Tom, as he saw the giant
turn away, shaking his fist at the closed door, for Koku, big as he
was, stood in mortal terror of the mule's heels.
Tom locked the door of the electrical shop and went back to his
interrupted problem. From Jackson he learned that Koku and Eradicate
had merely happened to stroll into the forbidden place, which had been
left open by accident. There, it appeared, Koku had handled some of the
machinery, ending by switching on the current of the machine the
handles of which he later unsuspectingly picked up. Then he received a
shock he long remembered, and for many days he believed Eradicate had
been responsible for it, and there was more than the usual hostile
feeling between the two. But Eradicate was innocent of that trick, at
all events.
"Though," said Tom, telling his father about it later, "Rad would have
turned on the current if he had known he could make trouble for Koku by
it. I never saw their like for having disagreements!"
"Yes, but they are both devoted to you, Tom," said the aged inventor.
"But what is this you hinted at--a silent motor you called it, I
believe? Are you really serious in trying to invent one?"
"Yes, Dad, I am. I think there's a big field for an aeroplane that
could travel along over the enemy's lines--particularly at night--and
not be heard from below. Think of the scout work that could be done.
"Well, yes, it could be done if you could get a silent motor, or
propellers that made no noise, Tom. But I don't believe it can be done."
"Well, maybe not, Dad. But I'm going to try!" and Tom, after a further
talk with his father, began work in earnest on the big problem. That it
was a big one Tom was not disposed to deny, and that it would be a
valuable invention even his somewhat skeptical father admitted.
"How are you going to start, Tom?" asked Mr. Swift, several days after
the big idea had come to the young man.
"I'm going to experiment a bit, at first. I've got a lot of old motors,
that weren't speedy enough for any of my flying machines, and I'm going
to make them over. If I spoil them the loss won't amount to anything,
and if I succeed--well, maybe I can help out Uncle Sam a bit more."
As Tom had said he would do, he began at the very foundation, and
studied the fundamental principles of sound.
"Sound," the young inventor told Ned Newton, in speaking about the
problem, "is a sensation which is peculiar to the ear, though the
vibrations caused by sound waves may be felt in many parts of the body.
But the ear is the great receiver of sound."
"You aren't going to invent a sort of muffler for the ears, are you,
Tom?" asked Ned. "That would be an easy way of solving the problem, but
I doubt if you could get the Germans to wear your ear-tabs so they
wouldn't hear the sound of the Allied aeroplanes."
"No, I'm not figuring on doing the trick that way," said Tom with a
laugh. "I've really got to cut down the sound of the motor and the
propeller blades, so a person, listening with all his ears, won't hear
any noise, unless he's within a few feet of the plane."
"Well, I can tell you, right off the reel, how to do it," said the bank
employee.
"How?" asked Tom eagerly.
"Run your engine and propellers in a vacuum," was the prompt reply.
"Hum!" said Tom, musingly. "Yes, that would be a simple way out, and
I'll do it, if you'll tell me how to breathe in a vacuum."
"Oh, I didn't agree to do that," laughed Ned.
But he had spoken the truth, as those who have studied physics well
know. There must be an atmosphere for the transmission of sound, which
is the reason all is cold and silent and still at the moon. There is no
atmosphere there. Sound implies vibration. Something, such as liquid,
gas, or solid, must be set in motion to produce sound, and for the
purpose of science the air we breathe may be considered a gas, being
composed of two.
Not only must the object, either solid, liquid, or gaseous, be in
motion to produce sound, but the air surrounding the vibrating body
must also be moving in unison with it. And lastly there must be some
medium of receiving the sound waves--the ear or some part of the body.
Totally deaf persons may be made aware of sound through the vibrations
received through their hands or feet. They receive, of course, only the
more intense, or largest, sound waves, and can not hear notes of music
nor spoken words, though they may feel the vibration when a piano is
played. And, as Ned has said, no sound is produced in a vacuum.
"But," said Tom, "since I can't run my aeroplane in a vacuum, or even
have the propellers revolve in one, it's up to me to solve the problem
some other way. The propellers don't really make noise enough to worry
about when they're high in the air. It's the exhaust from the motor,
and to get rid of that will be my first attempt."
"Can it be done?" asked Ned.
"I don't know," was Tom's frank answer.
"They do it on an automobile to a great extent," went on Ned. "Some of
'em you cant hardly hear."
"Yes, but an aeroplane engine runs many, many times faster than the
motor of an auto," said Tom, "and there are more explosions to muffle.
I doubt if the muffler of an auto would cut down the sound of an aero
engine to any appreciable extent. But, of course, I'll try along those
lines."
"They have mufflers or silencers for guns and rifles," went on Ned.
"Couldn't you make a big one of those contraptions and put it on an
aeroplane?"
"I doubt it," said Tom, shaking his head. "Of course it's the same
principle as that in an auto muffler, or on a motor boat--a series of
baffle plates arranged within a hollow cylinder. But all such devices
cut down power, and I don't want to do that. However, I'm going to
solve the problem or--bust!"
And Tom came near "busting," Ned remarked later, when he and his friend
talked over the progress of the invention.
Two weeks had passed since the start of his evolution of his new idea,
and following the visiting of the representatives of the Universal
Flying Machine Company. Since then neither Gale nor Ware had
communicated with Tom.
"But I must be on the watch against them," thought the young inventor.
"I'm pretty sure Gale heard me mention what I was going to try to
invent, and he may get ahead of me, and put a silent motor on the
market first. Not that I'm afraid of being done out of any profits, but
I simply don't want to be beaten."
The details of Tom's invention cannot be gone into, but, roughly, it
was based on the principle of not only a muffler but also of producing
less noise when the charges of gasoline exploded in the cylinders. It
is, of course, the explosion of gasoline mixed with air that causes an
internal combustion engine to operate. And it is the expulsion of the
burned gases that causes the exhaust and makes the noise that is heard.
Tom was working along the well-known line of the rate of travel of
sound, which progresses at the rate of about 1090 feet a second when
air is at the freezing point. And, roughly, with every degree increase
in the atmosphere's temperature the velocity of sound increases by one
foot. Thus at a temperature of 100 degrees Fahrenheit, or 68 degrees
above freezing, there would be added to the 1090 feet the 68 feet,
making sound travel at 100 degrees Fahrenheit about 1158 feet a second.
Tom had set up in his shop a powerful, but not very speedy, old
aeroplane engine, and had attached to it the device he hoped would help
him toward solving his problem of cutting down the noise. He had had
some success with it, and, after days and nights of labor, he invited
his father and Ned, as well as Mr. Damon, over to see what he hoped
would be a final experiment.
His visitors had assembled in the shop, and Eradicate was setting out
some refreshments which Tom had provided, the colored man being in his
element now.
"What's all this figuring, Tom?" asked Mr. Damon, as he saw a series of
calculations on some sheets of paper lying on Tom's desk.
"That's where I worked out how much faster sound traveled in hydrogen
gas than in the ordinary atmosphere," was the answer. "It goes about
four times as fast, or nearly four thousand two hundred feet a second.
You remember the rule, I suppose. 'The speed of sonorous vibrations
through gases varies inversely as the squares of the weights of equal
volumes of the gases,' or, in other words--"
"Give it to us chiefly in 'other words,' if you please, Tom!" pleaded
Ned, with a laugh. "Let that go and do some tricks. Start the engine
and let's see if we can hear it."
"Oh, you can hear it all right," said Tom, as he approached the motor,
which was mounted on a testing block. "The thing isn't perfected yet,
but I hope to have it soon. Rad! Where is that black rascal? Oh, there
you are! Come here, Rad!"
"Yaas sah, Massa Tom! Is I gwine to help yo' all in dish yeah job?"
"Yes. Just take hold of this lever, and when I say so pull it as hard
as you can."
"Dat's whut I will, Massa Tom. Golly! ef dat no 'count giant was heah
now he'd see he ain't de only one whut's got muscle. I'll pull good
an' hard, Massa Tom."
"Yes, that's what I want you to. Now I guess we're all ready. Can you
see, Dad--and Ned and Mr. Damon?"
"Yes," they answered. They stood near the side wall of the shop, while
Tom and Eradicate were at the testing block, on which the motor, with
the noise-eliminating devices attached, had been temporarily mounted.
"All ready," called the young inventor, as he turned on the gas and
threw over the electrical switch. "All ready! Pull the starting lever,
Rad, and when it's been running a little I'll throw on the silencer and
you can see the difference."
The motor began to hum, and there was a deafening roar, just as there
always is when the engine of an aeroplane starts. It was as though half
a dozen automobile engines were being run with the mufflers cut out.
"Now I'll show you the difference!" yelled Tom, though such was the
noise that not a word could be heard. "This shows you what my silencer
will do."
Tom pulled another lever. There was at once a cessation of the
deafening racket, though it was not altogether ended. Then, after a
moment or two, there suddenly came a roar as though a blast had been
let off in the shop.
Tom and Eradicate were tossed backward, head over heels, as though by
the giant hands of Koku himself, and Mr. Damon, Ned, and Tom's father
saw the motor fly from the testing block and shoot through the roof of
the building with a rending, crashing, and splintering sound that could
be heard for a mile.