Creative Books

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.


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