Information AboutClock |
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A clock (from the Latin ''cloca'', " Bell ") is an instrument for measuring Time . (Usually, for measuring time of intervals less than a day--as opposed to a Calendar .) Those used for technical purposes, of very high accuracy, are sometimes called Chronometer s. 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. History ]] The clock is one of the oldest human inventions. In principle, it requires no more than some 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 predictable rate. The historian Vitruvius reported that the Ancient Egyptian s 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. There 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. 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. The world's first self-striking clock was said to be invented by Chang Yeong-Sil, a chief enginner of Korea, in Korea during the Joseon Dynasty . It was called ''Chagyongru'', which means "self-striking clock" in Korean. [http://www.indiana.edu/~easc/resources/korea_slides/science/9-1.htm 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 time-keeping hand. The dial between the hour markers is divided into four equal parts making the clocks readable to the nearest 15 minutes. , London , England . The 5 foot 4 inch (1.63 m) person "holding on" to the six o'clock marking has been inserted into the picture at correct scale. The hour hand is 9 feet (2.7 m) long and the minute hand is 14 feet (4.3 m) long]] 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. The excitement over the pendulum clock attracted the attention of designers resulting in a proliferation of clock forms. Notably, the Longcase Clock (also known as the ''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 or 1671 . It was also at this time that clock cases began to be made of wood and Clock Face s to utilize Enamel as well as hand-painted ceramics. 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. The development of Electronics in the Twentieth Century led to clocks with no clockwork parts at all. Time in these cases is measured in several ways, such as by the behaviour of Quartz crystals, the decay of radioactive elements or resonance of polycarbonates. Even mechanical clocks have since come to be largely powered by batteries, removing the need for winding. Types Clocks can be classified by their method of time display, as well as by their method of timekeeping. Time display methods Analog clocks Analog Clock s usually indicate time using angles. The most common Clock Face uses a fixed numbered dial or dials and moving hand or hands. It usually has a circular scale of 12 Hour s, which can also serve as a scale of 60 Minute s, and often also as a scale of 60 Second s – though many other styles and designs have been used throughout the years, including dials divided into 6, 8, 10, and 24 hours. Of these alternative versions, the 24 Hour Analog Dial is the main alternative still in use today. The 10 hour clock was briefly popular during the French Revolution , when the Metric System was applied to time measurement, and an Italian 6 hour clock was developed in the 18th century, presumably to save power (a clock or watch chiming 24 times uses more power). The ultimate Analog clock is the Sundial , which tracks the sun continuously, registering the time by the shadow of its Gnomon . Sundials use some or part of the 24 Hour Analog Dial . The unusual linear clock shown here was photographed at London 's Picadilly Circus Tube station in 2002. The 24 hour band moves across the static map, keeping pace with the apparent movement of the sun above ground, and a pointer fixed on London points to the current time. Digital clocks Digital Clock s display a numeric representation of time. Two numeric display formats are commonly used on Digital clocks:
Most digital clocks use an LCD or LED display; many other display technologies are used as well ( Cathode Ray Tube s, Nixie Tube s, etc.). After a reset, battery change, or power failure, digital clocks without a backup Battery or Capacitor either start counting from 00:00, or stay at 00:00, often with blinking digits indicating that time needs to be set. Some newer clocks will actually reset themselves based on internet-time servers which in turn are tuned to national atomic clocks. Auditory clocks For convenience, distance, telephony or blindness, auditory clocks present the time as sounds. the form is either spoken Natural Language , (e.g. "The time is twelve thirty-five"), or as auditory codes (e.g. number of sequential bell rings on the hour represents the number of the hour like the clock Big Ben ). Textual clocks Textual clocks present the time visually in the form of Natural Language . For instance, in English, the time 12:35 could be represented as "Twelve thirty-five". Some versions of these clocks use a more approximate version intended to be relaxing, such as "About twelve thirty" [http://muse.jhu.edu/cgi-bin/access.cgi?uri=/journals/modernism-modernity/v006/6.1whittier-ferguson.html Project Muse] Timekeeping methods Most types of clocks are built around some form of Oscillator , an arrangement that goes through an endless sequence of Periodic state changes, designed to provide a continuous and stable reference frequency. The periods of this oscillator are then counted and converted into the desired clock display.
Purposes Clocks are in homes and offices; smaller ones ( Watch es) are carried; larger ones are in public places, e.g. a Train Station or Church . A small clock is often shown in a corner of Computer Display s or Mobile Phone s. Flavor Flav of Public Enemy wears a large clock always pointing to 12 O'Clock or 6 O'Clock. He says that this is so people "never have to ask what time it is." The main purpose of a clock is not always to ''display'' the time. It may also be used to ''control'' a device according to time, e.g. an alarm clock, a ). Though, in this context, it is more appropriate to refer to it as a Timer or Trigger Mechanism rather than strictly as a clock. Practically all Computer s depend on an accurate internal Clock Signal to allow synchronized processing. (A few research projects are developing CPUs based on Asynchronous Circuit s.) Some computers also maintain time and date for all manner of operations whether these be for alarms, event initiation, or just to display the time of day. The accuracy of the internal computer clock is generally maintained by a small battery which powers the internal clock. Memory of this kind is often referred to as "non-volatile". Many computers will still function, even if the internal clock battery is dead, but the computer clock will need to be reset each time the computer is restarted, since once power is lost, time is also lost. Ideal clocks An Ideal Clock is a scientific principle that measures the ratio of the duration of natural processes, and thus will give the time measure for use in physical theories. Therefore, to define an ideal clock in terms of any physical theory would be circular. An ideal clock is more appropriately defined in relationship to the set of all physical processes. This leads to the following definitions:
The recurrent, periodic process (a Metronome ) is an Oscillator and typically generates a ''clock signal''. Sometimes that signal alone is (confusingly) called "the clock," but sometimes "the clock" includes the counter, its indicator, and everything else supporting it. This definition can be further improved by the consideration of successive levels of smaller and smaller error tolerances. While not all physical processes can be surveyed, the definition should be based on the set of physical processes which includes all individual physical processes which are proposed for consideration. Since atoms are so numerous and since, within current measurement tolerances, they all beat in a manner such that if one is chosen as periodic then the others are all deemed to be periodic also, it follows that Atomic Clock s represent ideal clocks to within present measurement tolerances and in relation to all presently known physical processes. However, they are not so designated by fiat. Rather, they are designated as the current ideal clock because they are currently the best instantiation of the definition. 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 Chronometer in the mid-18th century. The Noon Gun in Cape Town still fires an accurate signal to allow ships to check their Chronometers . Modern clocks Quartz timepieces were invented in the 1920s . The Digital Clock was invented in 1956 . Specific types of clocks
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External links
www.Timeforclocks.nl: information on Dutch clocks Footnotes References
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