"Not at once," went on Mr. Henderson in a calm voice. "There is enough air in the entire ship, including that which has leaked from the tanks to last us five hours. After that——" he paused and looked at his watch.
"Well?" asked Andy. "After that?"
"There is enough stored in the small tanks of the diving suits to last another two hours, perhaps. Seven hours in all."
"Then what?" asked Mark.
"We shall smother to death," said the professor in a low tone. "That is," he went on, "unless before that time we can raise the Porpoise to the surface of the sea and get a fresh supply of air."
"Then we must work to raise the ship," put in Bill. "Let' get out and see if we can't cut through the sea weed."
"It would be useless," said Mr. Henderson. "We can only depend on the power of the ship herself. But do not be discouraged. We may escape. Come, Washington, start the engine again. By keeping it going constantly we can, perhaps, break loose from the grass. It is our only hope."
Steadily the machinery worked. It might as well have remained stationary, however, as far as any noticeable effect was made on the boat's progress. The grass of the Sargasso Sea held the Porpoise in a firm grasp.
Four hours passed. There was nothing to do but wait and see what would happen. It all depended on the engines. Silently the navigators of the realms under the ocean sat and hoped. Now and then the professor would go to the engine room to adjust the machines.
The atmosphere in the cabin was growing noticeably heavier. The boys' heads began to ring with strange noises, and there was a tightness across their chests. The lack of fresh air was beginning to tell.