“How is the annealing done?” asked Hamilton.

“That is simple enough,” was the reply.  “All that has to be done is to heat them again all to the same degree of heat, then let the oven cool at a certain rate.  Here are the annealing ovens.”

“This is certainly a hot place,” said the boy, as he stepped into the next building.  “Whew!  I wonder any one stays in here.”

“No one does,” his conductor answered.  “We have this arranged so that all the furnaces are filled in the morning, when they are cold, and there are pyrometers to tell when the right heat is reached.  All the ovens, you see, are managed by these switches near the door.  Look here—­”

He slipped one of the switches into place, and the pyrometer needle swung around and pointed to the degree of heat in the oven which it was supposed to register.

“What are those little clocks for?”

“One for each oven,” Mr. Nebett answered; “the keeper of the furnaces sets them when an oven is up to the required heat.  Then, you see, it is easy to tell when they have been cooling long enough.”

“I should think,” said Hamilton, “that making the barrel was the most important part of a gun, because, after all, that is the only part a bullet touches, and it must have to be exact.  I’ve often thought of that, how the tiniest difference at the mouth of the barrel would at a thousand yards range cause it to be away off the mark.”

“It does have to be exact,” his guide answered, “but that is a matter of care rather than of difficulty.  In this next building we bore the rifle-barrels, just a simple boring process, as you see, but there are all sorts of precautions taken to insure absolute steadiness.  As soon as a barrel is taken from the boring machine it is put through a test, to determine whether it is correct in size to the one-half of one-thousandth of an inch in diameter.  If it is not as exact as that, it is set aside.  That is only the first of a long series of tests, too.  You would be surprised at the number of barrels that are rejected from the time of the first selection until the gun is completed.  Here, for example, is perhaps the most sensational one.”

He led the boy to a small building, standing by itself in the middle of the yard, heavily built, and looking almost like a log cabin of the old type, made of great timbers.  It was just a bit of a place, divided into two parts by a heavy timber wall.

“What in the wide world is this for?” asked the boy.

“I’ll show you in a minute, I think we’re just in time,” the official said, as he led the way in.  Hamilton followed him into the inner chamber.  A long row of gun barrels was the first thing the boy noticed, the barrels all lying in slots.  A gray-haired man was filling a heavy charge of powder behind each one.  The guns were pointing into a bank of sand.

“If you notice,” said his guide, “you’ll see that a little device, like the old percussion cap is right by each of those charges of powder.  Are you all ready, Jim?” he queried, as the old man straightened up.