A machine by means of which water can be thrown to a great height for the purpose of extinguishing fires. The principle of its action is the same as that of the force-pump (q.v.); but in a force-pump the stream of water is intermittent, flowing only at each descent of the piston. This is obviated in the fire-engine by employing a strong air-vessel, into which the water is forced, the compressed air reacting on the water so as to keep up a steady flow. In the force-pump there is only one cylinder, but in the fire-engine there are two, in which the pistons are worked simultaneously, one ascending while the other descends. Fire-engines were formerly worked by hand, but now steam fire-engines are widely employed.