"I wonder what Washington is slowing down for," said the professor rising from the dinner table at which all save the colored man had been sitting. "I told him to keep right on. He must have seen something ahead. I'll take a look." The inventor went to the conning tower, where Washington was steering. "What are you stopping for?" he asked. "I'm not slowin' down," replied the colored man. "Guess another ob dem debil fishes has grabbed holt ob de ship. Dey suttinly am de most koslostrous conglomerations ob inconsequence dat I eber see." "You must keep your big words for another time," remarked Mr. Henderson, who seemed worried. "Hurry to the engine-room and see if the machinery is all right. We certainly are slowing down, from some cause or other." The _Porpoise_ was now scarcely moving, though from the vibration it was evident that the engines were working almost at top speed. Washington came back and reported that the big screw was revolving properly and that all the machinery was working well. "Then we're caught in something," said the professor. "Shut off the power, Washington, I don't want to strain things." The ship was now scarcely making a foot a minute, and, a little later, when the colored man had turned off the engine, the submarine became stationary, merely undulating with the roll and heave of the ocean. Hurrying to the cabin, Captain Henderson opened the side window shutters, turned off the electric lights and peered out. "I can't see anything," he said. "Yet I should be able to, as we are not very deep." The gage showed that the ship was submerged only thirty feet, and at that depth there should have been no difficulty in seeing, at least dimly, objects under water. But the windows showed as black as night. "Bring me one of the portable searchlights," called Mr. Henderson. Washington brought one, operated by a storage battery. Holding it so the reflector cast the beams out of the bull's-eye and into the water on the opposite side, the inventor peered forth. "I was afraid of this!" he murmured. "What is it?" asked Jack. "We are caught in the Sargasso Sea," replied Mr. Henderson. "The Sargasso Sea?" repeated Mark, in a questioning tone. "What is that?" "It is a great sea of grass," 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 grass 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 grass 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 mass. The grass winds about the propellers of steamships, and holds them as tight as in a vise.