"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.