HOW TIME MEASURED N ANCIENT TIME
Throughout history, time has been measured by the movement of the earth relative to the sun and stars. The earliest type of timekeeper, dating from as far back as 3500 bc, was the shadow clock, or gnomon, a vertical stick or obelisk that casts a shadow. An Egyptian shadow clock of the 8th century bc is still in existence. The first hemispherical sundial was described about the 3rd century bc by Chaldean astronomer Berossus. Ancient methods of measuring hours in the absence of sunlight included the notched candle and the Chinese practice of burning a knotted rope and noting the length of time required for the fire to travel from one knot to the next. Devices almost as old as the shadow clock and sundial include the hourglass, in which the flow of sand is used to measure time intervals, and the water clock, or clepsydra, in which the flow of water indicates passage of time. Clepsydras became more complicated, even to the inclusion of gearing in about 270 bc by Greek inventor Ctesibius of Alexandria. Eventually, a weight falling under the force of gravity was substituted for the flow of water in time devices, anticipating the mechanical clock.
THE MECHANICAL CLOCK
The historical origin of the mechanical clock is obscure. The first recorded examples are found in the 14th century. Until that time, a time-measuring instrument was known as a horologium, or hour teller. The name clock, which originally meant “bell,” was first applied in the present sense to the huge, mechanical time indicators installed in bell towers in the late Middle Ages.
Clockworks were initially heavy, cumbersome devices. A clock built in the 14th century by Henry De Vick of Württemberg for the royal palace (now the Palais de Justice) in Paris was powered by a 227-kg (500-lb) weight that descended a distance of 9.8 m (32 ft). The apparatus for controlling its rate of fall was crude and the clock inaccurate. Clocks of that period had dials with only one hand, which indicated the nearest quarter hour.
THE PENDULUM
A series of inventions in the 17th and 18th centuries increased the accuracy of clockworks and reduced the weight and bulk of the mechanisms. Galileo had described late in the 16th century the property of a pendulum, known as isochronism, stating that the period of the swing is constant. In 1657 Dutch physicist Christiaan Huygens showed how a pendulum could be used to regulate a clock. Ten years later English physicist Robert Hooke invented an escapement, which permitted the use in clocks of a pendulum with a small arc of oscillation. British clockmaker George Graham improved the escapement, and John Harrison developed a means of compensating for variations in the length of a pendulum resulting from changes in temperature.
WATCHES
Watchworks were developed when coiled springs were introduced as a source of power. This type of spring was used in Italy about 1450. About 1500 Peter Henlein, a locksmith in Nürnberg, Germany, began producing portable timepieces known popularly as Nürnberg eggs. In 1525 another artisan, Jacob Zech of Prague, invented a fusee, or spiral pulley, to equalize the uneven pull of the spring. Other improvements that increased the accuracy of watches included a spiral hairspring, invented about 1660 by Robert Hooke, for the balance wheel, and a lever escapement devised by British inventor Thomas Mudge about 1765.
Minute and second hands, and crystals to protect both the dial and hands, first appeared on 17th-century watches. Jeweled bearings to reduce friction and prolong the life of watchworks were introduced in the 18th century.
In the centuries that preceded the introduction of machine-made parts, craftsmanship of a high order was required to manufacture accurate, durable clocks and watches. Such local craft organizations as the Paris Guild of Clockmakers (1544) were organized to control the art of clockmaking and its apprenticeship. A guild known as the Clockmakers Company, founded in London in 1630, is still in existence. The Netherlands, Germany, and Switzerland also produced many fine artisans whose work was noted for beauty and a high degree of mechanical perfection.
The clock was often a decorative as well as a useful instrument. Early clocks were highly ornamented. Many bore sculptured figures, and clockworks were used in the towers of late medieval Europe to set in motion huge statues of saints or allegorical figures. Cuckoo clocks, containing carved wooden birds, which emerge and “sing” to tell the time, were made in the Black Forest of Germany as early as 1730 and are still popular. Some early English clocks were made in the form of lanterns or birdcages. The grandfather, or case, clock, which has the pendulum and weight exposed beneath a gear housing at the top of a tall cabinet, was designed before machine-cut gears were introduced, and it continues to be a popular ornamental clock.
Watches were originally shaped like drums or balls and were worn suspended from a belt or kept in a pocket. Wristwatches became popular as watchworks became smaller. Beginning in the 18th century, Switzerland became the center of a watchmaking industry, particularly in the villages of the Jura Mountains. At first a cottage industry, with families manufacturing watch parts at home to be assembled and sold by a master watchmaker, Swiss watchmaking by the 1850s had led to the development of a number of small factories and the foundation of a major industry. Some modern Swiss watchworks are tiny enough to fit into pencil ends or in earrings.
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