e 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