One of the greatest reasons for the increased speed of these new ships was the introduction of the compound engine. It was in 1854 that John Elder, a Briton, adapted the compound engine to marine uses. This improvement, by utilizing more thoroughly the expansive power of steam, increased at one stroke the power developed by engines without increasing the supply of steam. The principle of the compound engine is simple. Steam escaping from the single cylinder of a simple steam engine still retains a part of its pressure—that is, a part of its power to expand. As it is largely the expansion of the steam that forces the piston from one end of the cylinder to the other this means that a part of the useful force of the steam is wasted in the average single-cylinder engine. A compound engine, however, utilizes this power by leading the steam from the exhaust port of the first cylinder to the inlet port of another and much larger cylinder. Here the steam, now occupying more space, is used again to operate another piston connected to the same crankshaft. There is often still a third cylinder, and in some cases a fourth, in each of which some of the remaining power of the steam is utilized. The gradual increase of steam pressure in the better boilers that were being built also aided the development of these compound engines. In 1854, for instance, 42 pounds pressure per square inch was seldom exceeded, while in 1882, 125 pounds was a pressure occasionally reached. With the development of compound engines and boilers capable of more pressure the screw propeller became even more efficient, and gradually the paddle-wheel disappeared from the deep sea. Furthermore, the compound engine, by its more economic power, made it possible for the steamer to compete with the sailing ship in the carrying of cargoes, even on long voyages, and so began the rapid growth of the cargo steamers that now have practically driven sailing ships from the sea. And now comes a division of this subject of steamships—a division that later led to subdivision after subdivision, but which I shall treat in two major parts: steamers equipped to carry passengers, and steamers not so equipped. The passenger steamers have gone through an amazingly rapid growth since 1888, and have developed along many lines, but it was in that year that the first twinscrew steamers of large dimensions were put in service. The Inman liners _City of New York_ and _City of Paris_ were the first large ships to be so equipped. This double system of propulsion eliminated the necessity for sails on liners, and from that time on the masts of ocean liners have deteriorated to mere supports for derricks and signal spars. By this time, too, all the larger steamers were being fitted with steam steering gears. This important (and now almost universal) appliance was first installed on the Inman liner _City of Brussels_ in 1869.