STEAM ENGINE. The first actual working steam engine of which there is any record, was invented and construct ed by Captain Savery, an Englishman ; to whom a patent was granted for it, in 1693. These engines were employed to raise water by the expansion and conden sation of steam, and were only pumps. The steam engine received great im provements from the hands of Newco men, Beighton, Blakey, and others, from 1705 to 1710. Still, however, it was im perfect and rude in its construction, and was chiefly applied to -the draining of mines, or the raising of water. The steam engine was brought to its present high state of perfection, by the celebrat ed James Watt, about the year 1782. The numerous and vital improvements introduced by him, both in the combina tion of its mechanism, and in the econo my of its management, have rendered the steam engine at once the most pow erful, the most easily applied and regu lated, and, generally speaking, the least expensive of all prime movers, for im pelling machinery of every description. Steam engines vary much in magnitude, form, and proportions, as well as in the details of the machinery by which the power of the steam is applied. In short, the form of the engine, the arrangement and construction of its parts, its power, &c., depend entirely on the purpose to which it is to be applied, and may be in definitely diversified. The form of the steam engine is susceptible of an endless variety, according to the purposes to which it is to be applied ; its mechanical energy is usually estimated in horse power, (see HORSE PowEa,) and is propor tioned to the pressure of the steam, the area of the piston, and the velocity at which it moves. The stupendous effects which have resulted from the application of the power of steam in recent times, are striking attestations of the immense value of the invention. By the agency of steam, the seas are now navigated in defiance of wind and tide ; the earth is made to yield up in lavish abundance its metals and minerals ; vast marshes are drained, and land before barren rendered fruitful ; communities are brought into closer connection with communities ; fresh and inexhaustible sources of wealth and comfort are elicited ; new combina tions of human industry and ingenuity are brought into requisition ; knowledge is widely scattered abroad ; distance is lessened by velocity of locomotion; and time itself becomes more precious. Thus by infinitely enlarging the sphere of use ful action to was useful be fore, and by diffusing among millions what previously was attainable only by the few, this agent has wrought a change of aspect in kingdoms, in commerce, and in the individual relations of society, to an extent so wide, and in a time so brief, that the history of the world bears no parallel to it in influence.
The following is a description of the various forms of engines commonly in use : Double-acting Condensing Steam-En gine. This form of engine is that whichis almost invariably used as a moving pow er in almost all manufactures. It consists of a cylinder represented in section at C, in which a moveable piston P is driven upwards and downwards by the force of steam supplied by a boiler placed near the engine.
This piston gives motion to a work ing beam H f, which, by means of a heavy bar 0, called a connecting rod, moves afly-wheel and crank, from which the machinery to be worked directly re ceives its motion. Steam is supplied from the boiler to the cylinder by the steam-pipe S. The throttle-salve T in that pipe, near the cylinder, is regulated by a system of levers connected with the governor Q. This governor is an appara tus consisting of two heavy balls attach ed to the ends of rods which arc kept re volving on a vertical shaft by a cord or band, or by a train of cogged wheels con nected with the fly-wheel. The velocity with which the balls of the governor re volve is therefore always proportional to that of the fly-wheel, and of the machine ry driven by it. If, by reason of too ra pid a supply of steam, an undue speed be imparted to the fiy-wheel, the balls are whirled round with a corresponding velocity ; and by reason of their fugal force they recede from the vertical spindle round which they turn, and act ing thereby on the system of levers which connect them with the throttle valve T, they partially close the latter, check or diminish the supply of steam to the cylinder, and moderate the veloci ty of the machine. If, on the other hand, the motion of the engine be slower than is requisite, owing to a deficient supply of steam through S, then the balls, not being sufficiently affected by centri fugal force, fall towards the vertical spin dle, and acting on the system of levers in the contrary way, they turn the throt tle-valve T more fully open, and admit a more ample supply of steam to the cylin der, so as to increase the speed of the engine to a requisite limit.