STEAM ENGINE 339 tain lines of road, are made with five pairs of driving wheels, and with no truek. The steam cylinders are 20|- in. in diameter, 2 ft. stroke ; grate area, 15f ft.; heating surface, 1,380 ft; weight with tank full, and full supply of wood, 112,000 Ibs.; average weight, 108,000 Ibs. Such an engine has hauled 110 tons up this grade at the speed of 5 m. an hour, the steam pressure being 145 Ibs. The adhesion was about 23 per cent, of the weight. In checking a train in motion, the inertia of the engine itself absorbs a seriously large portion of the work of the brakes. This is sometimes reduced by revers- ing the engine and allowing the steam pressure to act in aid of the brakes. To avoid injury by abrasion of the surfaces of piston, cylinder, and the valves and valve seats, M. Le Chatelier introduces a jet of steam into the exhaust pas- sages when reversing, and thus prevents the ingress of dust-laden air and the drying of the rubbing surfaces. The valve motion consists of the simplest forms of three-ported valve, moved by two eccentrics attached to a Ste- phenson link. In drawing a train weighing 150 tons at the rate of 60 m. an hour, about 800 effective horse power is required. A speed of 80 m. an hour has been attained several times. The locomotive engine has a maximum life which may be stated at about 30 years. The annual cost of repairs is from 10 to 15 per cent, of its first cost. On moderately level roads, the engine requires a pint of oil to each 25 m., and a ton of coal to each 40 or 50 m. run. (See RAILROAD.) SeeHolley, "American and European Railway Practice " (New York, 1861); Weissenborn, "American Locomotive Engineering" (26 nos. 4to, plates 2 vols. fol., New York, 1861); Vose, " Manual for Railroad Engineers " (Boston, 1872) ; and Forney, " Cat- echism of the Locomotive " (New York, 1874). STEAM EVOLVE. Hero of Alexandria (about 250 B. C.) described, in his Spiritalia or Pneumatica, several insignificant contrivances illustrating the power of steam. The first modern reference to its actual or possible use- is not definitely known. Blasco de Garay is believed by Spanish writers to have applied steam to the pro- pulsion of a ship at Barcelona, A. D. 1543. Giambattista della Porta, in his Spiritalia (1601), described his ap- paratus for raising FIG. l.-IIero's Steam Engine, water by filling a vertical tube by condensing steam within it and then forcing the water upward by pressure. Salomon de Cans, engineer and architect to Louis XIII., in Les raisons des forces mouvantes, avec diverse* machines tant utiles que plaisantes (1615), says that " water will, by the aid of fire, mount higher than its level," and describes a globe filled with water, and an attached ver- tical pipe through which the water was ele- vated by the expaDsion of steam generated by heating the vessel. Giovanni Branca pub- lished at Rome in 1629 an account of a me- chanical application of a steam jet to the im- pulsion of a wheel against the vanes of which the jet impinged, and proposed its application to many useful purposes. The marquis of Wor- cester, in his " Century of Inventions" (1663), described an apparatus consisting of steam boilers worked alternately and of pipes con- veying steam from them to a vessel in which its pressure operated to force water upward as suggested by De Caus. This was set up at Vauxhall, near London, and was the first in- stance of the application of steam to practical use. The separate boiler, was the essential feature of this invention, and this is the basis of the claim that Worcester was one of the in- ventors of the steam engine. Sir Samuel Mor- land in 1683 constructed these engines com- mercially, and with an intelligent understand- ing of their principles and of the more im- portant properties of steam. Denis Papin, of Blois, about 1690 invented an engine having a piston which separated the steam from the water in the cylinder, receiving steam from the boiler in Worcester's combination. He also invented the lever safety valve. Thomas Savery patented, July 25, 1698, a machine con- sisting of a duplicate set of boilers, steam res- ervoirs, and forcing tubes, which were worked alternately, and applied it extensively to the drainage of mines, and occasionally to raising water to turn mill wheels. , Savery recharged his reservoirs by the use of surface condensa- tion, and his apparatus was capable of working an indefinite period without stopping. Desa- guliers in 1716 improved upon it by applying the Papin safety valve, and by using jet instead of surface condensation. This engine elevated 5,000,000 Ibs. of water one foot with each hundred weight of coal consumed; it gave a " duty " therefore of 5,000,000. Thomas New- comen, John Cawley, and Savery patented in 1705 the first steam engine really deserving the name. It consisted of a cylinder containing a piston driven upward by steam from a separate boiler, and forced downward by atmospheric pressure when the steam below the piston was removed by condensation. The engine was used only for pumping, the pump rod and pis- ton rods being attached to opposite ends of a beam, as in modern engines. Steam was first condensed by the application of cold water to the exterior, as in the original Savery engine, but soon after a jet within the cylinder was used. The boiler was supplied with gauge cocks to indicate the height of water, and a safety valve. Humphrey Potter, an ingenious boy mechanic, in 1713 made the valve gear automatic by leading cords from the beam. Henry Beighton in 1718 substituted for the latter the plug rod and more substantial ap-
