Clock

A clock (from the Latin cloca, "bell") is an instrument for measuring time. A clock is usually a physical instrument; an especially accurate one is called a chronometer. The clock in its modern form (24 hour clock) has been in use since at least the 14th century. Clock can refer to an abstract system of time measurement (see calendar for other measurements). Modern clocks define constant units of time: an hour is always sixty minutes, of sixty seconds each.

History

The clock is one of the oldest human inventions. Vitruvius reported that the ancient Egyptians used clepsydras, a time mechanism run by flowing water. 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. There is a record that in 1176 Sens Cathedral installed a ‘horologe’—the word still used in French for large clocks. It is derived from the Greek hora meaning ‘hour’ and legein meaning '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.

Related Topics:
Vitruvius - Ancient Egyptian - Clepsydras - Antikythera mechanism - 9th century AD - Escapement - 1176 - Sens Cathedral

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The earliest reasonably accurate clocks are the 13th century tower clocks probably developed for (and perhaps by) monks in Northern Italy. These were used to announce the canonical hours or intervals between set times of prayer. Canonical hours differ in length, and varied as the times of sunrise and sunset shifted.

Related Topics:
13th century - Canonical hours

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The earliest table clocks that survive in any quantity are mid-16th century ones from the metalworking towns of Nuremberg and Augsburg. These clocks have only one hand. The dial between the hour markers is divided into four equal parts making the clocks readable to the nearest 15 minutes.

Related Topics:
16th century - Nuremberg - Augsburg

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The next major development in accuracy occurred in 1657 with the invention of the pendulum clock. Galileo had the idea to use a swinging bob to propel the motion of a time telling device earlier in the 17th century. Christiaan Huygens, however, is usually credited as the inventor. He determined the mathematical formula that related pendulum length to time (99.38 cm or 39.13 inches for the one second movement) and had the first pendulum driven clock made. In 1670, the English clockmaker William Clement created the anchor escapement, an improvement over Huygens' crown escapement. Within just one generation, minute hands and then second hands were added.

Related Topics:
1657 - Pendulum clock - Galileo - 17th century - Christiaan Huygens - 1670 - William Clement - Anchor escapement - Crown escapement - Minute - Second

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The excitement over the pendulum clock attracted the attention of designers resulting in a proliferation of clock forms. Notably, the longcase clock (aka grandfather clock) was created to house the pendulum and works. The English clockmaker William Clement, inventor of the anchor escapement, is credited with developing this form in 1670. It was also at this time that clock cases began to be made of wood and clock faces to employ enamel. On November 17, 1797, Eli Terry received his first patent for a clock. Terry is known as the founder of the American clock-making industry.

Related Topics:
Grandfather clock - William Clement - Anchor escapement - 1670 - Clock face - Enamel - November 17 - 1797 - Eli Terry

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Navigation

Accurate navigation by ships beyond the sight of land depends on the ability to measure latitude and longitude. Latitude is fairly easy to determine through celestial navigation, but the measurement of longitude requires accurate measurement of time. This need was a major motivation for the development of accurate mechanical clocks. John Harrison created the first, highly accurate marine chronometers in the mid-18th century. The Noon gun in Cape Town still fires an accurate signal to allow ships to check their chronometers.

Related Topics:
Navigation - Latitude - Longitude - Celestial navigation - John Harrison - Marine chronometers - Noon gun - Cape Town

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Modern clocks

Quartz timepieces were invented in the 1920s.

Related Topics:
Quartz - 1920s

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The digital clock was invented in 1956.

Related Topics:
Digital clock - 1956

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