“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.  This was quickly made up into flashlight cartridges, to be exploded at once, or in a series, by means of a high voltage storage battery.

The moving picture cameras had been put in place, Blake to work one and Joe the other, while the automatic, which was operated by clockwork, once the trigger-string was broken, also setting off the continuous flashlight, was set between the two boys, to command a good view of the dam, and of whoever should approach to blow it up.

It now lacked an hour of midnight when, so the rumors said, the attempt was to be made.  Of the nature of these rumors, and of how much truth there was in them, the boys could only guess.  They did not ask too much, knowing that there might be Government secrets it would not be wise for them to know.