In the early 19th century, an Englishman named Sir William Congreve invented an unusual clock that kept time using balls rolling down an incline. At that time, most clocks kept time through the regular swinging of a pendulum.
The Congreve rolling ball clock consists of a brass plate with a zigzag path carved on it. A small brass ball rolls down the carved track, and when it reaches the end of the track, the ball hits a lever and a spring raises the end of the plate, reversing the tilt of the plate and sending the ball rolling back the other way. The lever also advances the clock hands by the same amount of time the ball takes to run down the tracks. In most designs this is 15 seconds, but in some larger clocks it can be as long as one minute.
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