"There are," answered Lieutenant Sibley, "twelve partitions, dividing the vessel into twenty-six compartments. In case of accident to the outer shell, whereby water might gain ingress, that particular compartment can instantly be closed and the flow of water confined to it. Before going down into the engine-room, I will give you some idea of this remarkable vessel. The Tracer, when fully submerged, displaces 1,000 tons of water. The shell of the vessel is of 1½-inch steel, covered externally by an aluminum armor of .3 of an inch in thickness, and weighs 570,000 pounds. The steel deck upon which we stand weighs 500,000; the steel partitions, braces, and iron-work weigh 195,000; the engines and machinery, 200,000; compressed air pipes, 125,000; the water cylinders, which you will soon see, weigh 100,000; all other parts, stores, lipthalite, etc., are allowed 50,000 pounds. Now, added to all this, is an immense aluminum-covered iron weight of 150,000 pounds attached to the bottom of the vessel, and which can instantly be freed and dropped from the ship into the sea, by simply breaking an electrical connection. This circuit is accessible from all parts of the vessel. Let us descend into the engine-rooms, and I will there explain why I have been so particular in giving you these weights." Following the Lieutenant down the narrow ladder into the depth below, Cobb, Rawolle, and Lyman were soon facing the powerful but small engines of the Tracer. The room was large, clean, warm, and brightly illuminated by electricity. Here, Mr. Lochridge, the first engineer, was introduced by Lieutenant Sibley. Cobb had seen the engines of many of the first-class vessels of his day, had noted their power and huge dimensions; but never before had he perceived such beautiful specimens of strength combined with size; nor did the finest workmanship he had ever seen approach to the perfection of the engines he saw beating and pulsating before him. Cobb looked them carefully over before venturing any remark. He noted an absence of steam and heat, the peculiar construction of the boilers, and many other, to him, new inventions. "I believe, Mr. Rawolle," he finally said, turning to him, "that you informed me last evening that no steam was used at the present day, but in its place, lipthalite?" "That is our fuel and vapor nowadays," broke in Mr. Lochridge. He led the way to two receivers, bearing some slight resemblance to the boilers of a steamer. "Here are our boilers and furnaces combined," he continued; "and these," as he laid his hand upon two very peculiarly constructed frontal additions, which had quite a number of straight pipes running into the large receiver, "are our furnaces, if you choose to call them by such a designation; we call them generators. Lipthalite is our fuel and gas developer."