The valves of this engine were at first worked by hand; but a boy, Humphrey Potter, is credited with having devised an automatic system, which, later in 1718, carefully designed and constructed in a workmanlike manner by Henry Beighton, a well-known engineer of that period, became the first automatic valve-motion.
James Watt, introducing the needed improve ments in the Newcomen engine, finally produced the modern types of °reciprocating)) steam engine. His first great improvement was the separate condenser, which permitted condensa tion to be effected without the introduction of water into the working cylinder and thus re duced very greatly the waste of steam by initial condensation. Watt first enunciated the prin ciple: °Keep the cylinder, if possible, as hot as the steam that enters it." The first step was this of removing the primary cause of refriger ation. The next was to surround the cylinder with a chamber containing steam at boiler pres sure; thus introducing his second great inven tion, the "steam-jacket?' He next covered the upper end • of the cylinder, excluding the cold air and supplying the place of the atmosphere and its pressure on the upper side of the piston by steam from the boiler, completing his scheme of keeping the cylinder as far as was practi cable as hot as the entering steam.
The °double-acting engine" constituted the next and an easy step. With steam admitted at both ends of the cylinder, it was immedi ately evident that each might be utilized, alter nately, in the performance of work and Watt soon adjusted his valve-gear and connections in such manner as to permit this alternation and produce a push and a pull on the piston-rod. This compelled a rigid connection between the piston and overhead beam, on the one end, and between the outer end of the beam and its work, now become that of rotating a shaft with crank and fly-wheel. Thus one improvement led to another and Watt's steam-engine ultimately be came capable of supplying power to every im aginable kind of machine or work. The single acting engine was, for many years after Watt's death, used in raising water and the double acting engine continues to turn the shaft of mill, locomotive, steamship and factory.
Watt invented and introduced many acces sory inventions and devices, as the attachment of the governor — already a well-known ap paratus — the steam-engine aindicator,° the ex pansion of steam, the compound engine, the non-condensing engine, practically all that dis tinguishes the modern engine from that of New comen. These improvements raised the uduty*
of the pumping engine, in the course of 25 years, from about 7,000,000 foot-pounds to 30,000,000, and, in the latest forms of Cornish engines, about 1850, to twice the last figure or more, reducing cost of steam-power enormously, and at the same time adapting the steam-engine to every requirement in the industries, giving to the world, in fact, its contemporary civiliza tion. This cost in coal per horse-power-time is reduced from the 35 pounds of Smeaton's time to one pound, as a minimum to-day, and the work of the world is performed by steam engines, mainly, probably amounting to 150,000, 000 horse power and equivalent to the working power of several times the population of the globe, if employed in manual labor.
At the commencement of the 19th century, Trevethick and other able mechanics and in ventors were seeking to construct locomotives, and complete success was achieved by George Stephenson in engines built from 1814 to 1833. The steamboat had been suggested by numerous writers and engineers, and, after many attempts, was made a practical success by John Fitch in the United States about 1785, by John Stevens in 1804-09 and commercially by Fulton, 1807-15. In Great Britain, after many early failures, Mil ler and Symmington and Bell, step by step, at tained permanent success and by 1830, the date of the first transatlantic steamship voyages, those of the Cirius and the Great Western, all civilized countries were employing the steam boat. See STEAM VESSELS.
Meanwhile the elements of economy became recognized and steam-pressures rose from the two to seven pounds above the atmosphere of Watt's time to 25 or 30, about 1850, and to 100 and upward to occasionally 200 at the end of the 19th century; the ratio of expansion of the steam increasing in similar ratio. The speeds of engine-piston also gradually increased from about 100 feet per minute, at the beginning, to 600 and often to 1,000 at its end. The weights of engine and sizes for the usual powers mean time fell from 1,000 pounds or more per horse power developed at the time of Watt, 500 about 1850 and to 250 in 1900 where weights were comparatively unimportant and, in special cases, where weight and volume required to he reduced to the smallest possible figures, as for torpedo boats, to a fourth or a fifth the last-named quantity.