Hot Air Engine

—An engine which utilizes the expansive force of heated air. Hot-air engines may be grouped under two heads; those in which the air is heated through a metallic body, and those in which the air is heated in a fire, pa ing with the products of combustion into a cylinder. The principle upon which a hot air engine works consists in the altemate heating and cooling of the air employed. The lower part of the vertical cylinder is exposed to the source of heat in sueh a manner that the internal air becomes rapidly heated and expands, doing work upon a power piston. The heated air exhausts through a regenerator or interchanger, where it parts with some of its heat to incoming air and pa es into the compre ion cylinder, where it is rapidly cooled, by means of a water jacket, etc., and is then sent back by another piston through the regenerator to perform the same cycle once more.