ny of those queer, cheese-like
slabs. For, though he knew that a considerable percussion was needed to
set them off, it would not do to take chances. High explosives do not
always act alike, even under the same given conditions. What might with
perfect safety be done at one time, could not be repeated at another.
Tom knew this, and was very careful.

The powder, as I shall occasionally call it for the sake of
convenience, though it was not such in the strict sense of the
word--the powder was put in the small cannon, together with the primer.
Then the wires were attached to it, and extended off for some distance.

"But we won't attach the battery until the last moment," Tom said. "I
don't want a premature explosion."

The projectile was also put in, and Tom once more looked to see that
the armor plate was in place. Then he adjusted the various gauges to
get readings of the power and energy created by his new explosive.

"Well, I guess we're all ready," he announced to his friends. "I'll
hook on the battery now, and we'll get off behind that other hill. I
had Koku make a sort of cave there--a miniature bomb-proof, that will
shelter us."

"Do you think the blast will be powerful enough to make it necessary?"
asked Mr. Damon.

"It will, if this larger quantity of explosive acts anything like the
small samples I set off," replied the young inventor.

The electric wires were carried behind the protecting hill, whither
they all retired.

"Here she goes!" exclaimed Tom, after a pause.

His thumb pressed the electric button, and instantly the ground shook
with the tremor of a mighty blast, while a deafening sound reared about
them. The earth trembled, and there was a big sheet of flame, seen even
in the powerful sunlight.

"Something happened, anyhow!" yelled Tom above the reverberating echoes.

CHAPTER XIII

CASTING THE CANNON

"Come on!" yelled Ned. "We'll see how this experiment came out!" and he
started to run from beneath the shelter of the hill.

"Hold on!" shouted Tom, laying a restraining hand on his chum's
shoulder.

"Why, what's the matter?" asked Ned in surprise.

"Some of that powder may not have exploded," went on the young
inventor. "From the sound made I should say the gun burst, and, if it
did, that gelatin is bound to be scattered about. There may be a mass
of it burning loose somewhere, and it may go off. It ought not to, if
my theory about it being harmless in the open is correct,