"We are caught in the Sarga.s.so Sea," replied Mr. Henderson.

"The Sarga.s.so Sea?" repeated Mark, in a questioning tone. "What is that?"

"It is a great sea of gra.s.s," replied the captain. "An immense ocean of sea weed, that sometimes floats on the surface and sometimes a little below. The stalks or blades of the gra.s.s are very long and closely matted together."

"Is there any danger?" asked Andy in some alarm.

"Very much," answered the professor quietly. "A ship, once fairly entangled in the gra.s.s or sea weed, seldom gets out. If it is a sailing ship the weed clings to the rudder, making steerage impossible, and even in a strong wind the ship cannot get free of the ma.s.s. The gra.s.s winds about the propellers of steamships, and holds them as tight as in a vise.

"Sometimes a great storm may tear the ma.s.s of weed loose from the bottom of the ocean, and then the ship is free. But the Sarga.s.so Sea is the graveyard of many a fine vessel."

The pumps were set going. Anxiously everyone watched the gage. The pointer never moved, but remained at thirty feet. The _Porpoise_ was caught.

"Well, since we can't go up, let us see if we can go down," said the inventor. "Perhaps we can dive under the sea weed."

The c.o.c.ks of the tanks were opened and the water rushed in. Under the weight of it the ship should have sunk to the bottom. Instead it remained just where it was, thirty feet below the surface.

"Try the screw again," suggested Andy, "Maybe we can back out."

The big propeller in the tube was started going in a reverse direction, but the _Porpoise_ only moved a few feet and then stopped. To go forward was equally impossible.

The submarine was held fast in the grip of the long, sinuous, snake-like fingers of the terrible sea gra.s.s. Weak as one strand was, the thousands combined served to fasten the ship as securely as wire cables would have done. The weeds had entangled themselves all around the craft and refused to let go.

"Well," remarked Mr. Henderson when all efforts had failed. "We must think of a new plan."

He spoke cheerfully, for he did not want the boys and other members of the crew to know how worried he was. This was a danger he had never counted on when he planned to go to the south pole.

"There is no great hurry," Mr. Henderson went on in a few minutes. "We can stay here for several days if need be, and by that time a storm may tear the gra.s.s loose."

"If we had our old hay sythes here," spoke Bill, "me an' Tom could put on divin' suits an' go out an' cut the sea weed."

"I'm afraid that wouldn't work," answered Mr. Henderson. "I'll think up some plan, soon."

He started toward the engine room to look over the machinery. He was met by Washington, who seemed much alarmed.

"What's the matter?" asked the inventor.

"De air tank hab busted an' all de air is escapin' out!" cried the colored man. "We'll all smothercate!"

CHAPTER XII

FIRE ON BOARD

The professor jumped past Washington and hurried into the room where the tanks were kept, carrying the reserve supply of air for breathing when the ship was under water. A loud hissing told that the leak was a large one.

"Quick! Bring me some tools and a steel plug," shouted the captain.

Mark hurried in with the things the professor wanted. But before the plug could be put in the hole the air stopped hissing.

"The leak is fixed!" cried Jack.

"No," said the professor in a strange voice.

"But the air no longer rushes out."

"For a good reason, there is no longer any air to rush out. It is all gone!"

"Do you mean to say that all the reserve stock has been lost?" exclaimed Andy.

"I fear so. The leak must have been a bad one. The air was stored in tanks under pressure, and, as you know, we released it as we needed it.

Now it is all gone."

"All? Then we shall smother," said Jack, and his voice trembled.

"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 gra.s.s. 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 gra.s.s of the Sarga.s.so Sea held the _Porpoise_ in a firm grasp.

Four hours pa.s.sed. 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.

"We might as well use that in the diving suit reservoirs," remarked the professor. "We will feel better, at least for a little while."

The helmets of the suits were brought in, and the vapor released from the small tanks. A change was at once noticed. The old stale air in the cabin was forced out of the exhaust pipes, and the fresh took its place.

Every one felt better.

Faster and faster revolved the big screw. The ship vibrated more and more. Yet it did not move, nor did it rise. The crew were still prisoners beneath the water.