that doesn't fortify the Panama Canal nothing will," declared Ned.

"Well, I hope I can convince Uncle Sam of that," spoke Tom, simply.

The muzzle velocity and the pressure were equal to Tom's highest hopes.
He knew, now, that he had hit on just the right mixture of powder, and
that his gun was correctly proportioned. It showed not the slightest
strain.

"Now we'll try another bursting shell," he said, after a rest, during
which some records were made. "Then we'll call it a day's work. Koku,
bring up some more powder. I'll use a little heavier charge this time."

It was while the gun was being loaded that a horseman was seen riding
wildly down the valley. He was waving a red flag in his hand.

"Bless my watch chain!" cried Mr. Damon. "What's that?"

"It looks as though he was coming to give us a warning," suggested the
steel foreman.

"Maybe someone has kicked about our shooting," remarked Ned.

"I hope not," murmured Tom.

He looked at the horseman anxiously. The rider came nearer and nearer,
wildly waving his flag. He seemed to be shouting something, but his
words could not be made out. Finally he came near enough to be heard.

"The dam! The dam!" he cried. "It's bursting. Your shots have hastened
it. The cracks are widening. You'd better get away!" And he galloped on.

"Bless my toilet soap!" gasped Mr. Damon.

"I was afraid of this!" murmured Tom. "But, since our shots have
hastened the disaster, maybe we can avert it."

"How?" demanded Ned.

"I'll show you. All hands come here and we'll shift this gun. I want it
to point at that big white stone!" and he indicated an immense boulder,
well up the valley, near the place where the two great gulches joined.

CHAPTER XVIII

THE DOPED POWDER

"What are you going to do, Tom?" cried Ned, as he, with the others,
worked the hand gear that shifted the big gun. When it was permanently
mounted electricity would accomplish this work. "What's your game,
Tom?"

"Don't you remember, Ned? When we were talking about the chance of the
dam bursting, I said if the current of suddenly released water could be
turned into the other valley, the people below us would be saved."

"Yes."

"Well, that's what I'm going to do. I'm going to fire a bursting shell
at the point where the two valleys come together. I'll break down the
barrier of rock and stone between them."

"Bless my shovel and hoe!" cried Mr. Damon.

"If we can turn enough of the water into th