The ship, which had been left to steer itself automatically while the professor was absent from the conning tower, was moving along at about half speed. The gage showed they were going at twenty miles an hour, and were three hundred feet below the surface. "Washington and I will share the first night's watch between us," said the inventor, after the supper things had been cleared away. "There will not be much to do, as the ship will steer automatically in whatever direction I set her. Still I want to see how she behaves. The rest of you might as well go to your bunks." The two boys were especially glad of a chance to go to bed, as they had had but little sleep the night before on account of the fire. So they lost no time in undressing and rolling up in the blankets, for it was quite cool so far down under the water. "Well, we've slept on the earth, above the earth and now we're under the waters," observed Jack. "There's only one place more to spend your time taking a snooze," said Mark. "Where's that?" "Inside the earth." Then they fell asleep. During the night and the next day the _Porpoise_ forged on underneath the waves. Washington relieved Mr. Henderson in the conning tower and reported the machinery to be working well. "Keep her headed due south," was the order of the inventor, and the colored man did so. It was about four o'clock one morning that Washington felt a slight jar to the submarine. "Hope we ain't goin' to hit no more battleships," he said. He glanced at the speed-indicating gage. To his surprise it stood at zero. The craft was not moving forward a foot! Yet the engines were going at half speed! In great alarm Washington shut off the power and ran to acquaint Professor Henderson with the news. "Suffin's ketched us!" cried the colored man. "Nonsense!" said the inventor, yet he seemed alarmed as he slipped on his clothes and hastened to the conning tower. He peered ahead along the path of water illuminated by the glare of the searchlight, but nothing was to be seen. Then he started the engine, increasing the speed gradually until the big screw in the shaft revolved more than one thousand times a minute. Still the _Porpoise_ never stirred. She remained in the same position, as if some giant hand grasped her. "Reverse the engine," said the professor. Washington did so. To the surprise of both of them the ship shot backward like a frightened crab. "Now forward!" exclaimed the old inventor. But this time the _Porpoise_ did not move. It was as if she was up against a stone wall. "What's the matter?" asked Mark, who had been awakened by the excitement on board. "I do not know," replied Mr. Henderson gravely. "Something mysterious has occurred. We can go no further!" CHAPTER VIII ASHORE IN THE DARK "Stop the engine," the captain commanded after he had peered through the lens in the conning tower for some time. "We must see what is the matter."