"I guessed as much," replied the young inventor. Then he went
closer to get a better look at the big cannon.

I say big cannon, and yet it was not the largest the government
had. In fact, Tom estimated the calibre to be less than twelve
inches, but the cannon was very long--much longer in proportion
than guns of greater muzzle diameter. Then, too, the breech, or
rear part, was very thick and heavy.

"He must be going to use a tremendous lot of powder," said Tom.

"He is," answered Captain Badger. "Some of us think he is going
to use too much, but he says it is impossible to burst his gun.
He wants to make a long-range record shot, and maybe he will."

"That's a new kind of breech block," commented Tom, as he
watched the mechanism being operated.

"Yes, that's General Waller's patent, too. They're going to
fire soon."

I might explain, briefly, for the benefit of you boys who have
never seen a big, modern cannon, that it consists of a central
core of cast steel. This is rifled, just as a small rifle is
bored, with twisted grooves throughout its length. The grooves,
or rifling, impart a twisting motion to the projectiles, and keep
them in a straighter line.

After the central core is made and rifled, thick jackets of
steel are "shrunk" on over the rear part of the gun. Sometimes