"I don't know. To warm the ship by electric current, or something I suppose," said Frank listlessly. "I wonder where the engineer is? The ship seems deserted."
"I guess he's out with the rest looking over OUR treasure," said the professor bitterly.
"Ours no longer,—might is right, you know," quoted Harry miserably.
Frank had been examining the machinery with some care. Even as a prisoner he felt some interest in the completeness of the engine room of the Japanese dirigible. He bent over her twin fifty-horse-power motors with admiring appreciation and examined the other machinery with intense interest.
The purring dynamo next came in for his attention and he was puzzling over the utility of several wires that led from it through the engine room roof when a sudden thought flashed into his mind. With a cry of triumph he bent over a small lever marked "accelerator," beside which was a small gauge. He rapidly adjusted the gauge, so that it would not register any more than the pressure it recorded at that moment and then shoved the lever over to its furthest extent.
"Whatever are you doing?" demanded Harry, much mystified at these actions, at the conclusion of which he had strolled up.
"You know that the gas in the bag of this dirigible is heated by electric radiators in order to avoid condensation of the gas?" was the seemingly incoherent reply.
"Yes," was the astonished answer, "but what has that—?"
"Hold on a minute," cried Frank, raising his hand, "and that gas when expanded by heat soon becomes too buoyant for its container, and will, if allowed to continue expanding, burst its confines."
Harry nodded his head.