“Yes, I know,” interrupted Tom, “and I appreciate all that when I called my newest craft an aerial warship.”

“But,” objected Ned, “an aircraft that will carry big guns will be so large that—­”

“Oh, mine is large enough,” Tom broke in.

“Then it’s finished!” cried Ned eagerly, for he was much interested in his chum’s inventions.

“Well, not exactly,” Tom said.  “But what I was going to tell you was that all guns are not necessarily large.  You can get big results with small guns and projectiles now, for high-powered explosives come in small packages.  So it isn’t altogether a question of carrying a certain amount of weight.  Of course, an aerial warship will have to be big, for it will have to carry extra machinery to give it extra speed, and it will have to carry a certain armament, and a large crew will be needed.  So, as I said, it will need to be large.  But that problem isn’t worrying me.”

“Well, what is it, then?” asked Ned.

“It’s the recoil,” said Tom, with a gesture of despair.

“The recoil?” questioned Ned, wonderingly.

“Yes, from the guns, you know.  I haven’t been able to overcome that, and, until I do, I’m afraid my latest invention will be a failure.”

Ned shook his head.

“I’m afraid I can’t help you any,” he said.  “The only thing I know about recoils is connected with an old shotgun my father used to own.

“I took that once, when he didn’t know it,” Ned proceeded.  “It was pretty heavily loaded, for the crows had been having fun in our cornfield, and dad had been shooting at them.  This time I thought I’d take a chance.

“Well, I fired the gun.  But it must have had a double charge in it and been rusted at that.  All I know is that after I pulled the trigger I thought the end of the world had come.  I heard a clap of thunder, and then I went flying over backward into a blackberry patch.”

“That was the recoil,” said Tom.

“The what?” asked Ned.

“The recoil.  The recoil of the gun knocked you over.”

“Oh, yes,” observed Ned, rubbing his shoulder in a reflective sort of way.  “I always thought it was something like that.  But, at the time I put it down to an explosion, and let it go at that.”

“No, it wasn’t an explosion, properly speaking,” said Tom.  “You see, when powder explodes, in a gun, or otherwise, its force is exerted in all directions, up, down and every way.”

“This went mostly backward—­in my direction,” said Ned ruefully.

“You only thought so,” returned Tom.  “Most of the power went out in front, to force out the shot.  Part of it, of course, was exerted on the barrel of the gun—­that was sideways—­but the strength of the steel held it in.  And part of the force went backward against your shoulder.  That part was the recoil, and it is the recoil of the guns I figure on putting aboard my aerial warship that is giving me such trouble.”