h the gun, when finished, would
be somewhat shorter than this. An allowance was to be made for cutting.

In the center of this hole would be a small "core" made of asbestos and
concrete mixed. Around this would be poured the molten steel from great
caldrons. It would flow into the hole. The sides of earth--lined with
fire-clay--would hold it in, and the middle core would make a hole
throughout the length of the central part of the gun. Afterward this
hole would be bored and rifled to the proper calibre.

After this central part was done, steel jackets or sleeves would be put
on, red-hot, and allowed to shrink. Then would come a winding of wire,
to further strengthen the tube, and then more sleeves or jackets. In
this way the gun would be made very strong.

As the greatest pressure would come at the breech, or in the powder
chamber there, the gun would be thickest at this point, decreasing in
size to the muzzle.

It took many weary weeks to get ready for the first cast, but finally
Tom received word that it was to be made, and with Ned, and Mr. Damon,
he proceeded to the plant of the steel concern.

There was some delay, but finally the manager gave the word. Tom and
his friends, standing on a high gallery, watched the tapping of the
combined furnaces that were to let the molten steel into the caldrons.
There were several of these, and their melted contents were to be
poured into the mould at the same time.

Out gushed the liquid steel, giving off a myriad of sparks. The
workers, as well as the visitors, had to wear violet-tinted glasses to
protect their eyes from the glare.

"Hoist away!" cried the manager, and the electric cranes started off
with the caldrons of liquid fire, weighing many tons.

"Pour!" came the command, and into the pit in the earth splashed the
melted steel that was to form the big cannon. From each caldron there
issued a stream of liquid metal of intense heat. There were numerous
explosions as the air bubbles burst--explosions almost like a battery
in action.

"So far so good!" exclaimed the manager, with a sigh of relief as the
last of the melted stuff ran into the mould. "Now, when it cools, which
won't be for some days, we'll see what we have."

"I hope it contains no flaws," spoke Tom, "That is the worst of big
guns--you never can tell when a flaw will develop. But I hope--"

Tom was interrupted by the sound of a dispute at one of the outer doors
of the shop.

"But I tell you I