The Congreve Clock

Sir William Congreve designed this novel clock in 1808. In place of a pendulum, it regulates time using a zigzag track in which a ball oscillates continuously — when the ball reaches either end of the track it trips the escapement, advancing the hands of the clock and reversing the tilt of the tray.

Unfortunately the horizontal tray tends to collect dust, which slows the ball and reduces the clock’s reliability.