such a vessel occupies, usually, about a year, and costs a quarter of a million dollars. [95] The steam-cylinders of the engines of steamers Bristol and Providence are 110 inches in diameter and of 12 feet stroke. [Illustration: FIG. 133.--A Mississippi Steamboat.] The non-condensing direct-acting engine is used principally on the Western rivers, driven by steam of from 100 to 150 pounds pressure, and exhausts its steam into the atmosphere. It is the simplest possible form of direct-acting engine. The valves are usually of the "poppet" variety, and are operated by cams which act at the ends of long levers having their fulcra on the opposite side of the valve, the stem of which latter is attached at an intermediate point. The engine is horizontal, and the connecting-rod directly attached to cross-head and crank-pin without intermediate mechanism. The paddle-wheel is used, sometimes as a stern-wheel, as in the plan of Jonathan Hulls of one and a half century ago, sometimes as a side-wheel, as is most usual elsewhere. One of the most noted of these steamers, plying on the Mississippi, is shown in the preceding sketch. One of the largest of these steamers was the Grand Republic,[96] a vessel 340 feet long, 56 feet beam, and 10-1/4 feet depth. The draught of water of this great craft was 3-1/2 feet forward and 4-1/2 aft. The two sets of compound engines, 28 and 56 inches diameter and of 10 feet stroke, drive wheels 38-1/2 feet in diameter and 18 feet wide. The boilers were steel. A steamer built still later on the Ohio has the following dimensions: Length, 225 feet; breadth, 35-1/2 feet; depth, 5 feet; cylinders, 17-3/8 inches in diameter, 6 feet stroke; three boilers. The hull and cabin were built at Jeffersonville, Ind. She has 40 large state-rooms. The cost of the steamer was $40,000. [96] Burned in 1877. These vessels have now opened to commerce the whole extent of the great Mississippi basin, transporting a large share of the products of a section of country measuring a million and a half square miles--an area equal to many times that of New York State, and twelve times that of the island of Great Britain--an area exceeding that of the whole of Europe, exclusive of Russia and Turkey, and capable, if as thoroughly cultivated as the Netherlands, of supporting a population of between three and four hundred millions of people. The steam-engine and propelling apparatus of the modern ocean-steamer have now become almost exclusively the compound or double-cylinder engine, driving the screw. The form and the location of the machinery in the vessel vary with the size and character of the ship which it drives. Very small boats are fitted with machinery of quite a different kind from that built for large steamers, and war-vessels have usually been supplied with engines of a design radically different from that adopted for merchant-steamers. [Illustration: FIG. 134.--Steam-Launch, New York Steam-Power Company.]