vances, have talked and muttered against the United
States. Then, in a manner I cannot disclose, word came to us that
the discontent had culminated in a well-plotted plan to destroy
the dam, and to-night is the time set.

"Just who they are who will try the desperate work I do not know.
I fancy no one does. But we may soon know if you boys can
successfully work the cameras and flashlights."

"And we'll do our part!" exclaimed Blake. "Tell us where to set
the cameras."

"We can use that automatic camera, too; can't we?" asked Joe.

"Yes, that will be the very thing!" cried Blake. They had found,
when making views of wild animals in the jungle, as I have
explained in the book of that title, that to be successful in some
cases required them to be absent from the drinking holes, where
the beasts came nightly to slake their thirst.

So they had developed a combined automatic flashlight and camera,
that would, when set, take pictures of the animals as they came to
the watering-place. The beasts themselves would, by breaking a
thread, set the mechanism in motion.

"The flashlight powder--I wonder if we can get enough of that?"
spoke Joe. "It'll take quite a lot."

"We must get it--somehow," declared the captain. "I fancy we have
some on hand, and perhaps you can make more. There is quite a
chemical laboratory here at the dam. But we've got to hustle. The
attempt is to be made some time after midnight."

"Hustle it is!" cried Blake. "Come on, Joe."

CHAPTER XXIV

THE TICK-TICK

"Put one camera here, Joe."

"All right, Blake. And where will you have the other?"

"Take that with you. Easy now. Don't make a noise, and don't speak
above a whisper!" cautioned Blake Stewart. "You'll work one
machine, and I'll attend to the other. We'll put the automatic
between us and trust to luck that one of the three gets something
when the flash goes off."

The two boys, with Captain Wiltsey, had made their way to a
position near the spillway, below the great Gatun Dam. It was an
intensely dark night, though off to the west were distant flashes
of lightning now and then, telling of an approaching storm. In the
darkness the boys moved cautiously about, planting their cameras
and flashlight batteries to give the best results.

They had had to work quickly to get matters in shape before
midnight. Fortunately they were not delayed by lack of magnesium
powder, a large quantity having been found in one of the
laboratories.