“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 brass 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 Canal 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 brass box.