Hotchkiss's atmospheric hammer; derives the force of its blow from compressed air-Hammer head, C, is attached to a piston fitted to a cylinder, B, which is connected by a rod, D, with a crank, A, on the rotary driving-shaft. As the cylinder ascends, air entering hole, e, is compressed below piston and lifts hammer. As cylinder descends, air entering hole, e, is compressed above and is stored up to produce the blow by its instant expansion after the crank and connecting-rod turn bottom center.