第22章

Taking a lesson from what had happened, Tom was very much more careful in the following experiments on his new, silent motor.He made some changes in his shop, and took Jackson in to help on the new machine, thus insuring perfect secrecy as the apparatus developed.

Tom also changed the safe in which he kept his plans, for the one he had used previous to the episode in which Bower and the stranger who took the mud bath figured, was one the combination of which could easily be ascertained by an expert.The new safe was more complicated, and Tom felt that his plans, specifications, and formulae which he had worked out were in less danger.

"I can just about figure out what happened," said Ned Newton to Tom, when told of the circumstances."These Universal people were provoked because you wouldn't give them the benefit of your experience on their flying machines, and so they sent a spy to get work with you.They, perhaps, hoped to secure some of your ideas for their own, or they may have had a deeper motive.""What deeper motive could they have, Ned?" "They might have hoped to disable you, or some of your machines, so that you couldn't compete with them.They're unscrupulous, I hear, and will do anything to succeed and make money.So be on your guard against them.""I will," Tom promised."But I don't believe there's any more danger now.Anyhow, I have to take some chances.""Yes, but be as careful as you can.How is the silent motor coming on?""Pretty good.I've had a lot of failures, and the thing isn't so easy as I at first imagined it would be.Noise is a funny thing, and I'm just beginning to understand some of the laws of acoustics we learned at high school.But I think I'm on the right track with the muffler and the cutting down of the noise of the explosions in the cylinders.I'm working both ends, you see-- making a motor that doesn't cause as much racket as those now in use, and also providing means to take care of the noise that is made.It isn't possible to make a completely silent motor of an explosive gas type.The only thingthat can be done is to kill the noise after it is made." "What about the propeller blades?""Oh, they aren't giving me any trouble.The noise they make can't be heard a hundred feet in the air, but I am also working on improvements to the blades.Take it altogether, I'll have an almost silent aeroplane if my plans come out all right.""Have you said anything to the government yet?""No; I want to have it pretty well perfected before I do.Besides, I don't want any publicity about it until I'm ready.If these Universal people are after me I'll fool 'em.""That's right, Tom! Well, I must go.Another week of this Liberty Bond campaign!""I suppose you'll be glad when it's over.""Well, I don't know," said Ned slowly."It's part of my small contribution to Uncle Sam.I'm not like you--I can't invent things.""But you have an awful smooth line of talk, Ned!" laughed his chum."I believe you could sell chloride of sodium to some of the fishes in the Great Salt Lake--that is if it has fishes.""I don't know that it has, Tom.And, anyhow, I'm not posing as a salt salesman," and Ned grinned."But I must really go.Our bank hasn't reached its quota in the sale of Liberty Bonds yet, and it's up to me to see that it doesn't fall down.""Go to it, Ned! And I'll get busy on my silent motor.""Getting busy" was Tom Swift's favorite occupation, and when he was working on a new idea, as was the case now, he was seldom idle, night or day.

"I have hardly seen you for two weeks," Mary Nestor wrote him one day."Aren't you ever coming to see me any more, or take me for a ride?""Yes," Tom wrote back."I'll be over soon.And perhaps on the next ride we take I won't have to shout at you through a speaking tube because the motor makes so much noise."From this it may be gathered that Tom was on the verge of success.While not altogether satisfied with his progress, the young inventor felt that he was on the right track.There were certain changes that needed tobe made in the apparatus he was building--certain refinements that must be added, and when this should be done Tom was pretty certain that he would have what would prove to be a very quiet aeroplane, if not an absolutely silent one.

The young inventor was engaged one day with some of the last details of the experiment.The new motor, with the silencer and the changed cylinders, had been attached to one of Tom's speedy aeroplanes, and he was making some intricate calculations in relation to a new cylinder block, to be used when he started to make a completely new machine of the improved type.

Tom had set down on paper some computations regarding the cross- section of one of the cylinders, and was working out the amount of stress to which he could subject a shoulder strut, when a shadow was cast across the drawing board he had propped up in his lap.