"Sometimes a great storm may tear the mass of weed loose from the bottom of the ocean, and then the ship is free. But the Sargasso 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 cocks 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 grass. 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 grass 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."