Clock

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Clock A mechanism for measuring and indicating the passage of time, and for recording the duration of intervals. Its essential elements are a source of energy to drive the mechanism, and a device to maintain a regular (usually stepwise) rate of motion. The first cloclG4tork escapement was Chinese, AD 724, and water-powered clocks are noted in China from the 760s. In mediaeval and many later clocks, the drive was a falling weight; from the 16th-c, it was the coiled mainspring; and from the late 19th-c, it was electric current from batteries or mains. From c.1670 a balance wheel was used for small clocks and watches. In modern times, clocks are powered by electric symchrcynous motors maintained by the mains frequency, by a maintained tuning fork, or by the oscillation of a quartz crystal. >>

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