"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.