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The Evolution of Mechanical Clocks
The operation of a clock depends on a stable mechanical oscillator, such as a swinging pendulum or a mass connected to a spring, by means of which the energy stored in a raised weight or coiled spring advances a pointer or other indicating device at a controlled rate. It is not definitely known when the first mechanical clocks were invented. Some authorities attribute the first weight-driven clock to Pacificus, archdeacon of Verona in the 9th cent. Gerbert, a learned monk who became Pope Sylvester II, is often credited with the invention of a mechanical clock, c.996.
Mechanical figures that struck a bell on the hour were installed in St. Paul's Cathedral, London, in 1286; a dial was added to the clock in the 14th cent. Clocks were placed in a clock tower at Westminster Hall, London, in 1288 and in the cathedral at Canterbury in 1292. In France, Rouen was especially noted for the skill of its clockmakers and watchmakers. Probably the early clock closest to the modern ones was that constructed in the 14th cent. for the tower of the palace (later the Palais de Justice) of Charles V of France by the clockmaker Henry de Vick (Vic, Wieck, Wyck) of Württemburg. Until the 17th cent. few mechanical clocks were found outside cathedral towers, monasteries, abbeys, and public squares.
The early clocks driven by hanging weights were bulky and heavy. When the coiled spring came into use (c.1500), it made possible the construction of the smaller and lighter-weight types. By applying Galileo's law of the pendulum, the Dutch scientist Christiaan Huygens invented (1656 or 1657) a pendulum clock, probably the first. Early clocks used in dwellings in the 17th cent. were variously known as lantern clocks, birdcage clocks, and sheep's-head clocks; they were of brass, sometimes ornate, with a gong bell at the top supported by a frame. Before the pendulum was introduced, they were spring-driven or weight-driven; those driven by weights had to be placed on a wall bracket to allow space for the falling weights. These clocks, probably obtained chiefly from England and Holland, were used in the Virginia and New England colonies.
Clocks with long cases to conceal the long pendulums and weights came into use after the mid-17th cent.; these were the forerunners of the grandfather clocks. With the development of the craft of cabinetmaking, more attention was concentrated on the clock case. In France the tall cabinet clocks, or grandfather clocks, were often of oak elaborately ornamented with brass and gilt. Those made in England were at first of oak and later of walnut and mahogany; simpler in style, their chief decoration was inlay work.
Electric and Other Clocks
Some Famous Clocks
See F. J. Britten, Old Clocks and Watches and Their Makers (1976); D. S. Landes, Revolution in Time: Clocks and the Making of the Modern World (1985); J. E. Barnett, Time's Pendulum: The Quest to Capture Time from Sundials to Atomic Clocks (1998); E. Bruton, Collector's Dictionary of Clocks and Watches (1999); J. Jesperson and J. Fitz-Randolph, From Sundials to Atomic Clocks: Understanding Time and Frequency (2d ed. 1999).
What does it mean when you dream about a clock?
Clocks as symbols often reflect the dreamer’s anxiety about not being on top of things, and thus behind schedule. A clock may also symbolize the biological clock that ticks away for people who want children, or those who feel that time is running out for them.
The execution times of instructions on a computer are usually measured by a number of clock cycles rather than seconds. Clock rates for various models of the computer may increase as technology improves, and it is usually the relative times one is interested in when discussing the instruction set.
clockAn internal timing device. Using a quartz crystal, the CPU clock breathes life into the microprocessor by feeding it a constant flow of pulses. For example, a 200 MHz CPU receives 200 million pulses per second from the clock. A 2 GHz CPU gets two billion pulses per second. Similarly, in a communications device, a clock is used to set the transmission speed and may also be used to synchronize the pulses between sender and receiver.
A "real-time clock," also called the "system clock," keeps track of the time of day and makes this data available to the software. A "timesharing clock" interrupts the CPU at regular intervals and allows the operating system to divide its time between active users and/or applications. See per clock, clockless computing and Hertz.
|The CPU Clock|
|The quartz crystal generates continuous waves, which are converted into digital pulses.|