ld hope to loosen the piece of steel,
imbedded as it must be in the solid earth.

Presently they heard Koku grunting and groaning. He seemed to be having
quite a struggle.

"Can you get it, Koku?" asked Torn. "Or shall I send for picks and
shovels."

"Me get, Master," was the muffled answer.

Then came a shout, as though in anger Koku had dared the buried plate
to defy him. There was a shower of earth at the mouth of the cave, and
the giant staggered out with the heavy piece of armor plate. At the
sight of it Tom uttered a cry.

"Look!" he shouted. "My projectile went part way through and then
carried the plate with it into the side of the hill. Talk about a
powerful explosive! I've struck it, all right!"

It was as he had said. The projectile, driven with almost irresistible
force, had bitten its way through the armor plate, but a projection at
the base of the shell had prevented it from completely passing through.
Then, with the energy almost unabated, the projectile had torn the
plate loose and hurled it, together with its own body, into the solid
earth of the hillside. There, as Koku held them up, they could all see
the shell imbedded in the plate, the point sticking out on the other
side, as a boy might spear an apple with a sharp stick.

"Bless my spectacle case!" cried Mr. Damon. "This is the greatest ever!"

"It sure is," agreed Ned. "Tom, my boy, I guess you can now make the
longest shots on record."

"I can as soon as I get my giant cannon, perhaps," admitted the young
inventor. "I think I have solved the problem of the explosive. Now to
work on the cannon."

An examination of the gauges, which, being attached to the cannon and
plate by electric wires, were not damaged when the blast came, showed
that Tom's wildest hopes had been confirmed. He had the most powerful
explosive ever made--or at least as far as he had any knowledge, and he
had had samples of all the best makes.

Concerning Tom's powder, or explosive, I will only say that he kept the
formula of it secret from all save his father. All that he would admit,
when the government experts asked him about it, later, was that the
base was not nitro-glycerine, but that this entered into it. He agreed,
however, in case his gun was accepted by the government, to disclose
the secret to the ordnance officers.

But Tom's work was only half done. It was one thing to have a powerful
explosive, but there must be some means of utilizing it safely--so