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Page 25
"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 vacume,
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.
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