by side within the frame, and immediately beneath the forward end of the boiler, or on each side and exterior to the frame. The engines are non-condensing and of the simplest possible construction. The whole machine is carried upon strong but flexible steel springs. The Fig. 41. British Express-Engine. steam-pressure is usually more than 100 pounds. The pulling-power is generally about one-fifth the weight under most favorable conditions, and becomes as low as one-tenth on wet rails. The fuel employed is wood in new countries, coke in bituminous coal districts, and anthracite coal in the eastern part of the United States. The general arrangement and the proportions of locomotives differ somewhat in different localities. In Fig. 41, a British express-engine, O is the boiler, N the fire-box, X the grate, G the smoke-box, and P the chimney. S is a spring, and H a lever safety-valve, T is the whistle, L the throttle or regulator valve, E the steam-cylinder, and W the driving-wheel. The force-pump, B C, is driven from the cross-head, D. The frame is the base of the whole system, and all other parts are firmly secured to it. The boiler is made fast at one end, and provision is made for its expansion when heated. Adhesion is secured by throwing a proper proportion of the weight upon the driving-wheel W. This is from about 6,000 pounds on standard freight-engines, having several pairs of drivers, to 10,000 pounds on passenger-engines, per axle. The peculiarities of the American type (Figs. 42, 43) are the truck or bogie supporting the forward part of the engine, the system of equalizers, or beams which distribute the weight of the machine equally over the several axles, and minor differences of detail. The cab or house protecting the engine-driver and fireman is an American device, which is gradually coming into use abroad also. The American locomotive (Fig. 43) is distinguished by its flexibility and ease of action even upon roughly-laid roads. The cost of passenger-locomotives of ordinary size is about $12,000; heavier engines sometimes cost $20,000. The locomotive is usually furnished with a tender, which carries its fuel and water. The standard passenger-engine on the Pennsylvania Railroad is quite similar in form to the Baldwin engine (Fig. 42), and has four driving-wheels (G, H), 5½ feet diameter; steam-cylinders (C, D), seventeen inches diameter and two feet stroke; grate-surface (N) 15½ square feet, and heating-surface 1,058 square feet. It weighs 63,100 pounds, of which 39,000 pounds are on the drivers and 24,100 on the truck, L K. The shell of the boiler is 49¼ inches diameter and 20 feet 2½ inches long.