"Hear it!" whispered Joe.

"Yes," answered Blake. "The bra.s.s box--the box--he had!"

"Yes," whispered Joe. All the suspicions he had had--all those he had laughed at Blake for harboring, came back to him in a rush.

The bra.s.s-bound box contained clockwork. Was it an alarm after all? Certainly it had given an alarm now--a most portentous alarm!

"We've got to find it!" said Blake.

"Sure," Joe a.s.sented. "It may go off any minute now. We've got to find it. Seems to be near here."

They began looking about on the ground, as though they could see anything in that blackness. But they were trying to trace it by the sound of the ticks. And it is no easy matter, if you have ever tried to locate the clock in a dark room.

"We ought to give the alarm," said Blake.

"Before it is too late," a.s.sented Joe. "Where can it be? It seems near here, and yet we can't locate it."

"Get down on your hands and knees and crawl around," advised Blake. In this fashion they searched for the elusive tick-tick.

They could hear it, now plainly, and now faintly, but they never lost it altogether. And each of them recognized the peculiar clicking sound as the same they had heard coming from the bra.s.s-bound box Mr. Alcando had said was his new alarm clock.

"Hark!" suddenly exclaimed Blake.

Off to the left, where was planted the automatic camera, came a faint noise. It sounded like a suppressed exclamation. Then came an echo as if someone had fallen heavily.

An instant later the whole scene was lit up by a brilliant flash--a flash that rivaled the sun in brightness, and made Blake and Joe stare like owls thrust suddenly into the glare of day.

"The dynamite!" gasped Joe, unconsciously holding himself in readiness for a shock.

"The flashlight--the automatic camera!" cried Blake. There was no need for silence now.

The whole scene was brilliantly lighted, and remained so for many seconds. And in the glare of the magnesium powder the moving picture boys saw a curious sight.

Advancing toward the dam was a solitary figure, which had come to halt when the camera went off with the flashlight. It was the figure of a man who had evidently just arisen after a fall.

"Mr. Alcando!" gasped Joe.

"The Spaniard!" fairly shouted Blake.

Then, as the two chums looked on the brilliantly lighted scene, knowing that the camera was faithfully taking pictures of every move of their recent pupil, the boys saw, rushing toward Alcando, a number of the men and soldiers who had been in hiding.

"He's surrounded--as good as caught," Blake cried. "So he's the guilty one."

"Unless there's a mistake," spoke Joe.

"Mistake! Never!" shouted his chum. "Look--the bra.s.s box!"

The glare of the distant flashlight illuminated the ground at their feet, and there, directly in front of them, was the ticking box. From it trailed two wires, and, as Blake looked at them he gave a start.

The next moment he had knelt down, and with a pair of pliers he carried for adjusting the mechanism of his camera severed the wires with a quick snap. The ticking in the box still went on, but the affair was harmless now. It could not make the electrical current to discharge the deadly dynamite.

"Boys! Boys! Where are you?" cried Captain Wiltsey.

"Here!" cried Blake. "We've stopped the infernal machine!"

"And we've got the dynamiter. He's your friend--"

The rest of the words died away as the light burned itself out.

Intense blackness succeeded.

"Come on!" cried Joe. "They've got him. We won't have to work the hand cameras. The automatic did it!"

They stumbled on through the darkness. Lanterns were brought and they saw Mr. Alcando a prisoner in the midst of the Ca.n.a.l guards.

The Spaniard looked at the boys, and smiled sadly.

"Well, it--it's all over," he said. "But it isn't as bad as it seems."

"It's bad enough, as you'll find," said Captain Wiltsey grimly.

"Are you sure the wires are disconnected, boys?" he asked.

"Sure," replied Blake, holding out the bra.s.s box.

"Oh, so you found it," said the Spaniard. "Well, even if it had gone off there wouldn't have been much of an explosion."

"It's easy enough to say that--now," declared the captain.

But later, when they followed up the wires which Blake had severed, which had run from the bra.s.s-bound box to a point near the spillway of the dam, it was found that only a small charge of dynamite had been buried there--a charge so small that it could not possibly have done more than very slight damage to the structure.

"I can't understand it," said Captain Wiltsey. "They could just as well have put a ton there, and blown the place to atoms, and yet they didn't use enough to blow a boulder to bits. I don't understand it."

"But why should Mr. Alcando try to blow up the dam at all?" asked Blake, "That's what I can't understand."

But a little later they did, for the Spaniard confessed. He had to admit his part in the plot, for the moving pictures, made by the automatic camera, were proof positive that he was the guilty one.

"Yes, it was I who tried to blow up the dam," Alcando admitted, "but, as you have seen, it was only to be an attempt to damage it.

It was never intended to really destroy it. It was an apparent attempt, only."

"But what for?" he was asked.

"To cause a lack of confidence in the Ca.n.a.l," was the unexpected answer. "Those I represent would like to see it unused. It is going to ruin our railroad interests."

Then he told of the plot in detail.

Alcando was connected, as I have told you, with a Brazilian railroad. The road depended for its profits on carrying goods across South America. Once the Ca.n.a.l was established goods could be transported much more cheaply and quickly by the water route.

The railroad owners knew this and saw ruin ahead of them if the Ca.n.a.l were to be successful. Consequently they welcomed every delay, every accident, every slide in Culebra Cut that would put off the opening of the great waterway.

But the time finally came when it was finished, and a success.

Then one of the largest stockholders of the railroad, an unprincipled man, planned a plot. At first his fellow stockholders would not agree to it, but he persuaded them, painting the ruin of their railroad, and saying only slight damage would be done to the Ca.n.a.l.

His plan was to make a slight explosion, or two or more of them, near Culebra Cut or at the great dam. This, he antic.i.p.ated, would cause shippers to regard the Ca.n.a.l with fear, and refuse to send their goods through it. In that way the railroad would still hold its trade.