第17章

"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 gasesthat 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.

"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 asyou 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.