STEAM-ENGINE

A machine in which the mechanical power developed in the evaporation of water is rendered available as a moving power. Steam engines vary much in magnitude, form, and proportions, as well as in the de tails of the machinery by which the power of the steam is adapted as a prime mover. We shall first explain those forms of steam-engine most generally used in the arts and manufactures, and shall afterwards give a succinct account of the history of the invention and progre ive improvement of this machine. The forms of engine, and the mode of its application to transport by land and water, have been consigned to separate articles. See Locomotive Engine, Railways, and Steam Navigation. Double-acting Condensing Steam Engine. — This form of engine is that which is almost invariably used as a moving power in all manufactures in this country. 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. Sea Steam Boiler. This piston gives motion to a working beam H/, which, by means of a heavy bar O, called a connecting rod, moves a fly wheel and crank, from which the Machinery Is bt worked directly receives its motion. Stenm is supplied from the boiler to the cylinder by the steam pi]>e S. Tha throttle-valve T in that pipe, near the cylinder, is regulated by a system of levers connected with the governor Q. Thit governor is an apparatus consisting of two heavy balls at tached to the ends of rods which are kept revolving on a vertical shaft by a cord or bnnd, or by a train of cocgerf wheels connected with the fly wheel. The velocity with which the balls of the governor revolve is therefore always [s. 1182]