During the late 19th and early 20th centuries a number of French novelty clocks were made incorporating a clock movement and dial in models of steam engines, railway locomotives, warships and other such machinery. In these clocks the engines are periodically released by the clock movement and their subsequent motion is derived from a separate spring. Thus the beam-engine flywheel or the wheels of the railway locomotive begin to turn, or the guns of the warships revolve. One type was made in the form of James Nasmyth's steam hammer, the hammer of which moves up and down at each oscillation of the clock pendulum. In this case the pendulum is of U shape, swinging inside the hollow legs of the case and controlling, through a system of levers, a conventional brocot escapement. The clock is of patinated black iron and polished brass fittings, and was retailed by a London dealer about 1900.