can, Ned. If that dam will only hold for half an hour more."

"What do you mean

"I mean that I have another supply of good powder in the village. I
secreted some there, you remember I told you. If I can go get that, and
get back here in time, I can break down the barrier with one shot, and
save Preston."

"But you never can make the trip there and back in time, with the
powder, Tom. It's impossible. The dam may hold half an hour, or it may
not. But, if it does, you can't do anything!"

"I can't? Well, I'm going to make a big try, Ned. You stay on the job
here. Have everything ready so that when I get back with the new
explosive, which I hope hasn't been tampered with, I can shove it into
the breech, and set it off. Have the wires, primers and button all
ready for me."

Then Tom set off on the run.

"Where are you going?" gasped his chum. "You can never run to Preston
and back in time."

"I don't intend to. I'm going in my airship. Koku, never mind bringing
the rest of the powder from the cave. It's no good. Run out the Humming
Bird. I'm going to drive her to the limit. I've just got to get that
powder here on time!"

"Bless my timetable!" gasped Mr. Damon. "That's the only way it can be
done. Lucky Tom brought the airship along!"

The young inventor, pausing only to get some cans for the explosive,
and some straps with which to fasten them in the monoplane, leaped into
the speedy craft.

The motor was adjusted; Koku whirled the propeller blades. There was a
staccato succession of explosions, a rushing, roaring sound, and then
the craft rose like a bird, and Tom circled about, making a straight
course for the distant town, while below him the creek rose higher and
higher as the dam continued to crumble away.

CHAPTER XIX

BLOWING DOWN THE BARRIER

"Can you see anything of him, Ned?"

"Not a thing, Mr. Damon. Wait--hold on--no! It's only a bird," and the
lad lowered the glasses with which he had been sweeping the sky.
looking for his chum returning in his airship with the powder.

"He'd better hurry," murmured the foreman. "That dam can't last much
longer. The water is rising fast. When it does go out it will go with a
rush. Then good-bye to the village of Preston."

"Bless my insurance policy!" cried Mr. Damon. "Don't say such things,
my friend."

"But they're true!" insisted the man. "You can see for yourself that
the cracks in the dam are getting larger. It will be a big flood when
it