A sudden change came over Tom's face. It was lighted up with a gleam of understanding.
"By Jove, Ned, old man!" he cried. "I believe you've struck it! And to think that has been under my nose, or, rather, over my head, all this while, and I never thought of it. Hurray! That will solve the problem!"
"Do you think it will?" asked Ned, glad that he had contributed something, if only an idea, to Tom's aerial warship.
"I'm almost sure it will. I'll give it a trial right away."
"What's in that door-check?" Ned asked. "I never stopped before to think what useful things they are, though at the bank, with the big, heavy doors, they are mighty useful."
"They are a combination of springs and hydrostatic valves," began Tom.
"Good-night!" laughed Ned. "Excuse the slang, Tom, but what in the world is a hydrostatic valve?"
"A valve through which liquids pass. In this door-check there may be a mixture of water, alcohol and glycerine, the alcohol to prevent freezing in cold weather, and the glycerine to give body to the mixture so it will not flow through the valves too freely."
"And do you think you can put something like that on your guns, so the recoil will be taken up?" Ned wanted to know.
"I think so," spoke Tom. "I'm going to work on it right away, and we'll soon see how it will turn out. It's mighty lucky you thought of that, for I sure was up against it, as the boys say."