a species of forcing pump in which the water is subjected to pressure sufficiently strong to raise it to the required height. Those of the ordinary construction consist of two forcing pumps, wrought by the reciprocating motions of two transverse levers. The water is forced into an air-vessel, by which means the inclosed air is condensed, and by its reaction it forces the water through a moveable pipe, which terminates in a conical form, and is directed upon the flame. Braithwaite's steam fire-engine is an ingenious application of the moving power of steam to the working of fire-engines. The mechanical arrangement of this machine consists of two cylinders of about six inches in diameter, one of them being the steam-cylinder, and the other the water-pump; and they are placed horizontally, so that a parallel motion is easily obtained. An engine of this kind will deliver about 9000 gallons an hour to the height of 90 feet. The time of getting the engine into action from the moment of igniting the fuel (the water being cold) is only 18 minutes. For further observations upon fire-engines, see Hydrodynamics, chap. iii., sec. 2.