310 STEAM ENGINE paratus still known to engineers. The im- proved Newcomen engine came into use du- ring the 18th century throughout Europe. Brindley and John Smeaton devised some improvements in detail and proportion, and the latter built large engines of this type, attaining a duty of 0,500,000. Smeaton says that he had seen engines with cylinders 75 in. in diameter. His largest was 72 in., and its power that of 150 horses "acting together." James Watt, an instrument maker at the uni- versity of Glasgow, when repairing a model Newcomen engine (fig. 2) in 1763, began a series of improvements which finally rendered the steam engine universally applicable. To avoid losses of -heat in the steam cylinder, which he estimated to amount to three fourths of all supplied, he attached (1765) the sepa- rate condenser, thus saving also three fourths of the injection water needed in the Newco- men engine. He first tried surface condensa- Fio. 2. Newcomen Engine Model. tion, but soon adopted the jet condenser and air pump. The piston had previously been kept from leaking by flooding it from above with water. Watt substituted oil and tallow. He closed the top with a cylinder head, pass- ing the piston rod through a " stuffing box " to prevent leakage about it, and admitting steam above the piston, instead of air, during the down stroke, thus avoiding the c.ooling effect of the atmosphere. He then protected the cylinder by non-conducting coverings to intercept the heat previously lost by radiation from its ex- terior, and applied the "steam jacket," intro- ducing a space intermediate between the cyl- inder and the external covering, in which space steam was retained. He thus converted the atmospheric steam engine of Newcomen into the type known as the engine of Watt. The firm of Boulton and Watt began building these engines at Soho, near Birmingham, in 1775. Watt proposed to secure economy of steam by its expansion in 1769, and in 1776 he adopted a form of cut-off which was patented in 1782. His" later pumping engines attained a duty of 20,000,000. The crank and fly wheel were patented by Wasborough in 1781, and Watt adopted the "sun and planet wheels" as the next best expedient for obtaining rotary mo- tion, and applied them in his double-acting engine patented July 4, 1782. This engine is shown in fig. 3, with the parallel motion, gov- ernor, and other details patented in 1784. Ad- mitting steam and condensing on both sides of the piston, the power of the engine was doubled. Jonathan Hornblower in 1781 pat- ented a compound or double cylinder engine, in which the steam used at high pressure in one cylinder was exhausted into a second, whence, after acting expansively and with re- duced pressure, it was discharged. Woolf in 1804 patented the combination of this engine with the Watt condenser, and a few such en- gines were built. Oliver Evans devised in 1779 the high-pressure non-condensing steam en- gine. He introduced it into saw and grain mills, and applied it to the propulsion of vessels and locomotives. It still remains the most com- monly used of all forms of the steam engine. Trevithick and Vivian introduced engines built on Evans's plan into Great Britain in 1802, which carried occasionally 60 to 80 Ibs. of steam pressure. Col. John Stevens of Hoboken, N. J., built the direct- acting, high-pressure, and con- densing engine, with a sectional steam boiler, in 1804. Joseph Dixon coupled two engines with cranks at right angles in 1823. The de- tachable, adjustable, or drop cut-off valve gear was patented by Frederick E. Sickels of New York in 1842, and the application of the gov- ernor to determine the point of cut-off was made by Zachariah Allen and George H. Corliss of Rhode Island, and patented by the latter in 1849. This completed the growth in general design of the now distinctive American expan- sive steam engine. Recently the revival of the double cylinder engine, with high steam, considerable expansion, and rapid motion of piston, which have proved economically suc- cessful, has been the only marked feature of this branch of engineering progress. It is es- timated that the total steam power of the world is about 15,000,000 horse power, and that were horses actually employed to do the work which these engines would be capable of doing were they kept constantly in operation, the number required would exceed 60,000,000. Form of the Steam Engine. In all engines the principal organs of the machine are present, but their forms and proportions, and their arrangement, differ greatly in different classes. In general, the piston, P, fig. 3, is accurately fitted into a steam cylinder, 0, within which it moves from end to end with slight friction, and without permitting the escape of steam past its edges. The piston rod is attached at one end to this piston, and, passing through the cylinder head,
