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Page 26
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.
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