Down into the bowels of a submarine! A warm, peculiar, oily odor greeted them as they descended, but the air was not at all unpleasant and breathing was easy. Glancing about they saw confused masses of mechanism, tanks, pipes, valves, levers, wheels, clock-faced dial plates and other contrivances, all huddled together, with barely room to pass from one place to another. Electric bulbs were everywhere visible, lighting up the interior. Suddenly there was a slight tremor in the vessel, indicating that some machinery was in motion. Once at the bottom they stood there until the seaman stepped forward and opened a small door through which there was barely room to pass, and he motioned them to enter. They did so, and found themselves in a compartment which did not seem to be more than five by six feet in size, and even in this small space mechanism was noticed. The moment the door closed they were in total darkness. "This is a nice place to get into," said Ralph. "I wonder if they are going to keep us cooped up like this without a light?" said Alfred. After an interval of ten minutes a rumbling was heard, which continued, a rhythmic motion followed in unison with the sounds generated by the machinery. "That is the propeller," said the captain. Voices were heard occasionally, but words could not be distinguished. Confined as they were the air seemed to be pure and in abundance at all times, and while there was not the faintest signs of closeness, there was an eternal monotony,--an existence in which there was nothing to do but breathe and think. How long they were thus confined, without a single thing to break the stillness, they could not conceive. It seemed that hours had gone by, during which time there was nothing to disturb them, except the one steady whirr, broken occasionally by some remark by one or the other. Then came an unexpected hum of voices; the machinery seemed to stop for a moment, and when it was again continued it had a different melody. The wheels, if such they were, seemed to turn with smoothness, and they felt a sudden inclination in the seats on which they were sitting. "What do you suppose has happened?" asked Ralph. "The electric mechanism has been hitched to the propeller, and, if I am not mistaken, we are going down," said the captain. "It did feel as though the forward end dipped down a moment ago," said Alfred. Another wait for a half-hour, and then a most peculiar sound reached their ears. Simultaneously, the ship seemed to stop and go on. Again voices were heard, and the same reaction in the hull of the submarine was felt, accompanied by the dull noise, as before. "They have just fired two torpedoes," said the captain. CHAPTER IV THE TERRORS IN THE DARK ROOM OF AN UNDERSEA BOAT