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A portable clock is called a watch. The clock in its most common modern form (in use since at least the 14th century) displays the hours, minutes, and sometimes seconds that pass over a twelve or twenty-four-hour period.
HistoryThe clock is one of the oldest human inventions, requiring a physical process which will proceed at a known rate, and a way to gauge how long that process has been continuing. As the seasons and the phases of the moon can be used to measure the passage of longer periods of time, shorter processes could be used to measure off hours and minutes. The sundial, which measures the time of day by the direction of shadows cast by the sun, was widely known in ancient times. Candles and sticks of incense which burn down at approximately predictable speeds have also been used as clocks. In an hourglass fine sand pours through a tiny hole at a constant rate.
Water clocksThe historian Vitruvius reported that the ancient Egyptians also used a clepsydra, a time mechanism run by flowing water. Herodotus had mentioned an ancient Egyptian time-keeping device that was based on mercury. Historians disagree over the Antikythera mechanism but this is largely thought to be an early mechanical clock. By the 9th century AD a mechanical timekeeper had been developed that lacked only an escapement mechanism. The world's first self-striking water clock was said to be invented in Korea during the Joseon Dynasty by a royal engineer named Chang Yeong-Sil. It was called Chagyongru, which means "self-striking clock" in Korean. When the water reached a certain level, a trigger device released a metal ball which rolled down a chute into a metal drum to signal a new hour.
Early mechanical clocksThere is a record that in 1176 Sens Cathedral installed a ‘horologe’—the word still used in French for large clocks. (from Greek hora, hour, and legein, to tell). This word has led scholars to believe that these tower clocks did not employ hands or dials, but “told” the time with audible signals such as bells. Between 1280 and 1320 there is a sudden increase in references to clocks and horologes in church records, and this probably indicates that a new type of clock mechanism had been devised. Existing clock mechanisms that used water power were being adapted to take the driving power from falling weights. This power was controlled by some form of oscillating mechanism, probably derived from existing bell-ringing or alarm devices. This controlled release of power - the escapement - marks the beginning of the true mechanical clock. These mechanical clocks were intended for two main purposes: for signalling and notification (e.g. the timing of services and public events), and for modelling the solar system. The former purpose is administrative, the latter arises naturally given the scholarly interest in astronomy, science, astrology, and how these subjects integrated with the religious philosopy of the time. The astrolabe was used both by astronomers and astrologers, and it was natural to apply a clockwork drive to the rotating plate to produce a working model of the solar system. • [List your site here Free!]
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