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Platform clock at King's Cross railway station, London.

A clock is an instrument for measuring, indicating and maintaining the time. The word clock is derived ultimately (via Dutch, Northern French, and Medieval Latin) from the Celtic words clagan and clocca meaning "bell". For horologists and other specialists the term clock continues to mean exclusively a device with a striking mechanism for announcing intervals of time acoustically, by ringing a bell, a set of chimes, or a gong.^{[citation needed]} A silent instrument lacking such a mechanism has traditionally been known as a timepiece.^[1] In general usage today, however, a "clock" refers to any device for measuring and displaying the time which, unlike a watch, is not worn on the person. Image File history File links Question_book-3. ... Look up clock in Wiktionary, the free dictionary. ... Image File history File links Metadata Size of this preview: 800 × 600 pixelsFull resolution (3648 × 2736 pixel, file size: 3. ... Image File history File links Metadata Size of this preview: 800 × 600 pixelsFull resolution (3648 × 2736 pixel, file size: 3. ... Kings Cross station (often spelt Kings Cross on platform signs) is a railway station in the district of the same name in northeast central London. ... This article is about the capital of England and the United Kingdom. ... This article is about the concept of time. ... Medieval Latin was the form of Latin used in the Middle Ages, primarily as a medium of scholarly exchange and as the liturgical language of the medieval Roman Catholic Church, but also as a language of science, literature, law, and administration. ... The Celtic languages are the languages descended from Proto-Celtic, or Common Celtic, a branch of the greater Indo-European language family. ... Horology is the study of the science and art of timekeeping devices. ... Big Ben, the tower clock of the Palace of Westminster in London, is a famous striking clock. ... A carillon-like instrument with less than 23 bells is called a chime. ... A gong is one of a wide variety of metal percussion instruments. ... For other uses, see Watch (disambiguation). ...

Clock at the Royal Observatory, Greenwich

History

Further information: History of timekeeping devices

Replica of an ancient Chinese incense clock

The clock is one of the oldest human inventions, meeting the need to consistently measure intervals of time shorter than the natural units, the day, the lunar month, and the year. Such measurement requires devices. Devices operating on several different physical processes have been used over the millennia, culminating in the clocks of today. A replica incense alarm clock This ancient Chinese dragon shaped device was constructed with a sequence of bells tied to a horizontally mounted burning incense. ... A replica incense alarm clock This ancient Chinese dragon shaped device was constructed with a sequence of bells tied to a horizontally mounted burning incense. ... A replica of an ancient Chinese stick incense clock The incense clock (香鐘, xiāng zhong in Chinese) is a timekeeping devices invented by the Chinese during the Song Dynasty (960-1279) that spread to neighboring countries such as Japan. ... For the musical form, see Invention (music). ... Look up day in Wiktionary, the free dictionary. ... In lunar calendars, a lunar month is the time between two successive similar syzygies (new moons or full moons). ... A year (from Old English gēr) is the time between two recurrences of an event related to the orbit of the Earth around the Sun. ...

Sundials and other devices

The sundial, which measures the time of day by the direction of shadows cast by the sun, was widely used in ancient times. A well-designed sundial can measure local solar time with reasonable accuracy, and sundials continued to be used to monitor the performance of clocks until the modern era. However, its practical limitations - it requires the sun to shine and does not work at all during the night - encouraged the use of other techniques for measuring time. For other uses, see Sundial (disambiguation). ... Ancient redirects here. ... Solar time is based on the idea that when the sun reaches its highest point in the sky, it is noon. ... The Modern-Era of NASCAR is a dividing line in NASCARs history. ...

Candle clocks and sticks of incense that burn down at, approximately, predictable speeds have also been used to estimate the passing of time. In an hourglass, fine sand pours through a tiny hole at a constant rate and indicates a predetermined passage of an arbitrary period of time. A candle clock is a thin candle with consistently spaced markings (usually with numbers), that when burned, indicate the passage of periods of time. ... For other uses, see Hourglass (disambiguation). ... For other uses, see Sand (disambiguation). ...

Water clocks

Main article: Water clock

A scale model of Su Song's Astronomical Clock Tower, built in 11th century Kaifeng, China. It was driven by a large waterwheel, chain drive, and escapement mechanism.

Water clocks, also known as clepsydrae(sg: clepsydra), along with the sundials, are possibly the oldest time-measuring instruments, with the only exceptions being the vertical gnomon and the day-counting tally stick.^[2] Given their great antiquity, where and when they first existed are not known and perhaps unknowable. The bowl-shaped outflow is the simplest form of a water clock and is known to have existed in Babylon and in Egypt around the 16th century BC. Other regions of the world, including India and China, also have early evidence of water clocks, but the earliest dates are less certain. Some authors, however, write about water clocks appearing as early as 4000 BC in these regions of the world.^[3] A water clock or clepsydra is a device for measuring time by letting water regularly flow out of a container usually by a tiny aperture. ... Download high resolution version (393x640, 170 KB)Su Songs Water Clock (蘇頌鐘). ... Download high resolution version (393x640, 170 KB)Su Songs Water Clock (蘇頌鐘). ... A scale model of the Tower of London. ... Su Song 蘇頌 (1020 – 1101), style Zirong 子容, was a Chinese engineer. ... Astronomy, which etymologically means law of the stars, (from Greek: αστρονομία = άστρον + νόμος) is a science involving the observation and explanation of events occurring outside Earth and its atmosphere. ... Kaifeng (Simplified Chinese: ; Traditional Chinese: ; pinyin: KāifÄ“ng; Wade-Giles: Kai-feng), formerly known as Bianliang (汴梁; Wade-Giles: Pien-liang), is a prefecture-level city in eastern Henan province, Peoples Republic of China. ... An overshot water wheel standing 42 feet high powers the Old Mill at Berry College in Rome, Georgia A water wheel (also waterwheel, Norse mill, Persian wheel or noria) is a hydropower system; a system for extracting power from a flow of water. ... Roller chain and sprocket Mack AC delivery truck at the Petersen Automotive Museum with chain drive visible Chain drive was a popular power transmission system from the earliest days of the automobile. ... A simple escapement. ... The cantilever spar of this cable-stay bridge, the Sundial Bridge at Turtle Bay, forms the gnomon of a large garden sundial The gnomon is the part of a sundial that casts the shadow. ... Tally sticks are an ancient mnemonic device (memory aid) to record and document numbers or quantities even messages. ... For other uses, see Babylon (disambiguation). ...

The Greek and Roman civilizations are credited for initially advancing water clock design to include complex gearing, which was connected to fanciful automata and also resulted in improved accuracy. These advances were passed on through Byzantium and Islamic times, eventually making their way to Europe. Independently, the Chinese developed their own advanced water clocks, passing their ideas on to Korea and Japan. An automaton (plural: automata) is a self-operating machine. ... Byzantium (Greek: Βυζάντιον) was an ancient Greek city, which, according to legend, was founded by Greek colonists from Megara in 667 BC and named after their king Byzas or Byzantas (Βύζας or Βύζαντας in Greek). ... Islam (Arabic: ; ( ▶ (help· info)), the submission to God) is a monotheistic faith, one of the Abrahamic religions and the worlds second-largest religion. ... For other uses, see Europe (disambiguation). ... This article is about the Korean civilization. ...

Some water clock designs were developed independently and some knowledge was transferred through the spread of trade. It is important to point out that the need for the common person to 'know what time it is' largely did not exist until the Industrial Revolution, when it became important to keep track of hours worked. In the earliest of times, however, the purpose for using a water clock was for astronomical and astrological reasons. These early water clocks were calibrated with a sundial. Through the centuries, water clocks were used for timing lawyer's speeches during a trial, labors of prostitutes, night watches of guards, sermons and Masses in church, to name only a few. While never reaching the level of accuracy based on today's standards of timekeeping, the water clock was the most accurate and commonly used timekeeping device for millennia, until it was replaced by the more accurate pendulum clock in 17th century Europe. A Watt steam engine, the steam engine that propelled the Industrial Revolution in Britain and the world. ... For other uses, see Sundial (disambiguation). ... For the fish called lawyer, see Burbot. ... Prostitution is the sale of sexual services (typically manual stimulation, oral sex, sexual intercourse, or anal sex) for cash or other kind of return, generally indiscriminately with many persons. ... A pendulum clock uses a pendulum as its time base. ...

Early clocks

In 797 (or possibly 801), the Abbasid caliph of Baghdad, Harun al-Rashid, presented Janae with an Asian Elephant named Abul-Abbas together with a "particularly elaborate example" of a water ^[4] clock. Mashriq Dynasties  Maghrib Dynasties  The Abbasid Caliphate Abbasid (Arabic: , ) is the dynastic name generally given to the caliph of Baghdad, the second of the two great Sunni dynasties of the Arab Empire, that overthrew the Umayyad caliphs from all but Spain. ... For main article see: Caliphate The Caliph (pronounced khaleef in Arabic) is the head of state in a Caliphate, and the title for the leader of the Islamic Ummah, an Islamic community ruled by the Sharia. ... Baghdad (Arabic: ) is the capital of Iraq and of Baghdad Governorate. ... HārÅ«n al-RashÄ«d (Arabic: ‎ ); also spelled Harun ar-Rashid, Haroun al-Rashid or Haroon al Rasheed; English: Aaron the Upright, Aaron the Just, or Aaron the Rightly-Guided; March 17, 763 – March 24, 809) was born in Rayy near Tehran, Iran and was the fifth and most... Binomial name Linnaeus, 1758 Asian Elephant range The Asian or Asiatic Elephant (Elephas maximus), sometimes known by the name of its nominate subspecies (the Indian Elephant), is one of the three living species of elephant, and the only living species of the genus Elephas. ... The first historically recorded elephant in northern Europe was Abul-Abbas, an Asian elephant given to Emperor Charlemagne by the caliph of Baghdad, Harun al-Rashid, in 797. ...

None of the first clocks survived from 13th century Europe, but various mentions in church records reveal some of the early history of the clock.

Medieval religious institutions required clocks to measure and indicate the passing of time because, for many centuries, daily prayer and work schedules had to be strictly regulated. This was done by various types of time-telling and recording devices, such as water clocks, sundials and marked candles, probably used in combination. Important times and durations were broadcast by bells, rung either by hand or by some mechanical device such as a falling weight or rotating beater.

The word horologia (from the Greek ὡρα, hour, and λεγειν, to tell) was used to describe all these devices, but the use of this word (still used in several romance languages) for all timekeepers conceals from us the true nature of the mechanisms. For example, there is a record that in 1176 Sens Cathedral installed a ‘horologe’ but the mechanism used is unknown. According to Jocelin of Brakelond, in 1198 during a fire at the abbey of St Edmundsbury (now Bury St Edmunds), the monks 'ran to the clock' to fetch water, indicating that their water clock had a reservoir large enough to help extinguish the occasional fire ^[5]. The Romance languages (sometimes referred to as Romanic languages) are a branch of the Indo-European language family that comprises all the languages that descend from Latin, the language of the Roman Empire. ... Interior of the cathedral, by Jean-Baptiste Camille Corot, c. ... , Bury St Edmunds is a town in the county of Suffolk, England, and was formerly the county town of West Suffolk. ...

These early clocks may not have used hands or dials, but “told” the time with audible signals.

A new mechanism

The word clock (from the Latin word clocca, "bell"), which gradually supersedes "horologe", suggests that it was the sound of bells which also characterized the prototype mechanical clocks that appeared during the 13th century in Europe.

Between 1280 and 1320, there is an increase in the number of 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 their 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. Undershot water wheels on the Orontes River in Hama, Syria Saint Anthony Falls Hydropower or hydraulic power is the force or energy of moving water. ... A simple escapement. ...

Outside of Europe, the escapement mechanism had been known and used in medieval China, as the Song Dynasty horologist and engineer Su Song (1020 - 1101) incorporated it into his astronomical clock-tower of Kaifeng in 1088^[6]. However, his astronomical clock and rotating armillary sphere still relied on the use of flowing water (ie. hydraulics), while European clockworks of the following centuries shed this old habit for a more efficient driving power of weights, in addition to the escapement mechanism. For other uses, see Liu Song Dynasty. ... Su Song 蘇頌 (1020 – 1101), style Zirong 子容, was a Chinese engineer. ... Armillary sphere An armillary sphere (variations known as a spherical astrolabe, armilla, or armil) is a model of the celestial sphere, invented by the ancient Greek Eratosthenes in 255 BC. Its name comes from the Latin armilla (circle, bracelet), since it has a skeleton made of graduated metal circles linking... Table of Hydraulics and Hydrostatics, from the 1728 Cyclopaedia. ...

An elephant clock in a manuscript by Al-Jazari (1206 AD) from The Book of Knowledge of Ingenious Mechanical Devices. ^[7]

In the 13th century, clock construction and engineering entered a new phase with the advancements made by Al-Jazari, a Muslim engineer from Diyar-Bakr in South East Turkey, who is thought to be behind the birth to the concept of automatic machines^{[citation needed]}. While working for Artuqid king of Diyar-Bakr, Nasir al-Din, al-Jazari made numerous clocks of all shapes and sizes. In 1206 he was ordered by the king to document his inventions leading to the publication of an outstanding book on engineering called "The Book of Knowledge of Ingenious Mechanical Devices”^{[citation needed]}. This book became an invaluable resource for people of different engineering backgrounds as it described 50 mechanical devices in 6 categories, including water clocks. The most reputed clocks included the Elephant, the Castle and Scribe clocks, all of which were reconstructed by Muslim Heritage Consulting for Ibn Battuta Shopping Mall in Dubai (UAE), where they are fully functional. As well as telling the time, these grand clocks were symbols of status, grandeur and wealth of the Urtuq State.^[8] Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... The reproduction elephant clock in the Ibn Battuta Mall, Dubai. ... Diagram from The Book of Knowledge of Ingenious Mechanical Devices by al-Jazari. ... Diagram from The Book of Knowledge of Ingenious Mechanical Devices by al-Jazari. ... The Ortoqid dynasty was an Oghuz Turk dynasty that ruled in the Jezirah (northern Iraq) in the 11th and 12th centuries. ... Nasser-al-Din Shah Qajar (sometimes called Nassereddin) (died 1896) was the Shah of Persia from 1848 to 1896. ...

These mechanical clocks were intended for two main purposes: for signalling and notification (e.g. the timing of services and public events), and for modeling 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 philosophy 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. This article is about the Solar System. ... A 16th century astrolabe. ...

Simple clocks intended mainly for notification were installed in towers, and did not always require dials or hands. They would have announced the canonical hours or intervals between set times of prayer. Canonical hours varied in length as the times of sunrise and sunset shifted. The more sophisticated astronomical clocks would have had moving dials or hands, and would have shown the time in various time systems, including Italian hours, canonical hours, and time as measured by astronomers at the time. Both styles of clock started acquiring extravagant features such as automata. Canonical hours are ancient divisions of time, developed by the Christian Church, serving as increments between the prescribed prayers of the daily round. ... The hour (symbol: h) is a unit of time. ...

In 1283, a large clock was installed at Dunstable Priory; its location above the rood screen suggests that it was not a water clock^{[citation needed]}. In 1292, Canterbury Cathedral installed a 'great horloge'. Over the next 30 years there are brief mentions of clocks at a number of ecclesiastical institutions in England, Italy, and France. In 1322, a new clock was installed in Norwich, an expensive replacement for an earlier clock installed in 1273. This had a large (2 metre) astronomical dial with automata and bells. The costs of the installation included the full-time employment of two clockkeepers for two years^{[citation needed]}. The Dunstable Priory Church of St. ... The rood screen (also choir screen or chancel screen) is a common feature in late medieval church architecture, dividing the chancel from the nave. ... Canterbury Cathedral is one of the oldest and most famous Christian structures in England and forms part of a World Heritage Site. ... For other places with the same name, see Norwich (disambiguation). ...

Early astronomical clocks

Besides the Chinese astronomical clock of Su Song in 1088 mentioned above, in Europe there were the clocks constructed by Richard of Wallingford in St Albans by 1336, and by Giovanni de Dondi in Padua from 1348 to 1364. They no longer exist, but detailed descriptions of their design and construction survive,^{[citation needed]} while modern reproductions have been made. They illustrate how quickly the theory of the mechanical clock had been translated into practical constructions, and also that one of the many impulses to their development had been the desire of astronomers to investigate celestial phenomena. Richard of Wallingford (1292–1336) was an English mathematician active in the 14th century, who made major contributions to astronomy and horology whilst serving as the abbot of St Albans Abbey. ... Abbey gateway St Albans Abbey was an abbey at St Albans, Hertfordshire, England, dissolved in 1539 during the Dissolution of the Monasteries. ... Richard of Wallingford (1292–1336) was an English mathematician active in the 14th century, who made major contributions to astronomy and horology whilst serving as the abbot of St Albans Abbey. ... , St Albans is the main urban area of the City and District of St Albans in southern Hertfordshire, England, around 22 miles (35 km) north of central London. ... Jacopo and Giovanni deDondi (father and son) were scholars active in 14th century Padua, Italy, and are remembered today as being pioneers in the art of clock design and construction. ... Padua, Italy, (It. ...

Wallingford's clock had a large astrolabe-type dial, showing the sun, the moon's age, phase, and node, a star map, and possibly the planets. In addition, it had a wheel of fortune and an indicator of the state of the tide at London Bridge. Bells rang every hour, the number of strokes indicating the time. For other uses, see London Bridge (disambiguation). ...

Dondi's clock was a seven-sided construction, 1 metre high, with dials showing the time of day, including minutes, the motions of all the known planets, an automatic calendar of fixed and movable feasts, and an eclipse prediction hand rotating once every 18 years. For the book by Ernest Hemingway, see A Moveable Feast. ...

It is not known how accurate or reliable these clocks would have been. They were probably adjusted manually every day to compensate for errors caused by wear and imprecise manufacture.

The Salisbury Cathedral clock, built in 1386, is considered to be the world's oldest surviving mechanical clock that strikes the hours^[9]. The Salisbury Cathedral clock, a large iron-framed clock without a dial located in the aisle of Salisbury Cathedral, is almost certainly the oldest surviving mechanical clock in the world. ...

Elements of the mechanical clock

These 14th century clocks show the four key elements common to all clocks in subsequent centuries, at least up to the digital age:

• the power, supplied by a falling weight, later by a coiled spring
• the escapement, a periodic repetitive action that allows the power to escape in small bursts rather than drain away all at once
• the going train, a set of interlocking gear wheels that controls the speed of rotation of the wheels connected between the power supply and the indicators
• indicators, such as dials, hands, and bells

Later developments

Clockmakers developed their art in various ways. Building smaller clocks was a technical challenge, as was improving accuracy and reliability. Clocks could be impressive showpieces to demonstrate skilled craftsmanship, or less expensive, mass-produced items for domestic use. The escapement in particular was an important factor affecting the clock's accuracy, so many different mechanisms were tried.

Spring-driven clocks were developed during the 17th century,^[10] and this gave the clockmakers many new problems to solve, such as how to compensate for the changing power supplied as the spring unwound.

The first record of a minute hand on a clock is 1475, in the Almanus Manuscript of Brother Paul^{[citation needed]}.

During the 15th and 16th centuries, clockmaking flourished, particularly in the metalworking towns of Nuremberg and Augsburg, and in France, Blois. Some of the more basic table clocks have only one time-keeping hand, with the dial between the hour markers being divided into four equal parts making the clocks readable to the nearest 15 minutes. Other clocks were exhibitions of craftsmanship and skill, incorporating astronomical indicators and musical movements. The cross-beat escapement^{[citation needed]} was developed in 1585 by Jost Burgi, who also developed the remontoire. Burgi's accurate clocks helped Tycho Brahe to observe astronomical events with much greater precision than before. Nürnberg redirects here. ... For other meanings for Augsburg: See Augsburg (disambiguation) , Augsburg is a city in south-central Germany. ... Blois is a city in France, the préfecture (capital) city of the Loir-et-Cher département, situated on the banks of the lower river Loire between Orléans and Tours. ... Joost Bürgi, or Jobst Bürgi (February 28, 1552, Lichtensteig, Switzerland - January 31, 1632, Kassel, Hesse-Kassel) was a Swiss clockmaker and mathematician. ... In horology, a remontoire is a secondary winding mechanism that is periodically rewound from the main source of energy, such as a mainspring. ... This article is about the astronomer. ...

The first record of a second hand on a clock is about 1560, on a clock now in the Fremersdorf collection.^{[citation needed]} However, this clock could not have been accurate, and the second hand was probably for indicating that the clock was working.

French rococo bracket clocks, (Museum of Time, Besançon)

The next development in accuracy occurred after 1657 with the invention of the pendulum clock. Galileo had the idea to use a swinging bob to regulate 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,^{[citation needed]} an improvement over Huygens' crown escapement^{[citation needed]}. Within just one generation, minute hands and then second hands were added. A style of 18th century French art and interior design, Rococo style rooms were designed as total works of art with elegant and ornate furniture, small sculptures, ornamental mirrors, and tapestry complementing architecture, reliefs, and wall paintings. ... A pendulum clock uses a pendulum as its time base. ... Galileo redirects here. ... Christiaan Huygens (pronounced in English (IPA): ; in Dutch: ) (April 14, 1629 – July 8, 1698), was a Dutch mathematician, astronomer and physicist; born in The Hague as the son of Constantijn Huygens. ... William Bill H. Clement (born December 20, 1950 in Buckingham, Quebec) is a retired professional ice hockey player and a current broadcaster for Versus and NBC. Bill works as a studio host for The NHL on NBC partnered with Ray Ferraro and Ed Olczyk as well as covering mens... The anchor escapement is a type of escapement, the mechanism in a clock that maintains the swinging of a pendulum for accurate timekeeping. ... This article is about the unit of time, angle and right ascension. ... This article is about the unit of time. ...

A major stimulus to improving the accuracy and reliability of clocks was the importance of precise time-keeping for navigation. The position of a ship at sea could be determined with reasonable accuracy if a navigator could refer to a clock that lost or gained less than about 10 seconds per day. This clock could not contain a pendulum, which would be virtually useless on a rocking ship. Many European governments offered a large prize for anyone that could determine longitude accurately; for example, Great Britain offered 20,000 pounds, equivalent to millions of dollars today. The reward was eventually claimed in 1761 by John Harrison, who dedicated his life to improving the accuracy of his clocks. His H5 clock is reported to have lost less than 5 seconds over 10 days.^{[citation needed]} The longitude prize was a prize offered by the British government through an Act of Parliament in 1714 for the precise determination of a ships longitude. ... John Harrison John Harrison (March 24, 1693–March 24, 1776) was an English clockmaker, who designed and built the worlds first successful chronometer (maritime clock), one whose accuracy was great enough to allow the determination of longitude over long distances. ... John Harrison John Harrison (March 24, 1693–March 24, 1776) was an English clockmaker, who designed and built the worlds first successful chronometer (maritime clock), one whose accuracy was great enough to allow the determination of longitude over long distances. ...

The excitement over the pendulum clock had 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 is also 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 faces to utilize enamel as well as hand-painted ceramics. A longcase clock with a pine case, c. ... William Bill H. Clement (born December 20, 1950 in Buckingham, Quebec) is a retired professional ice hockey player and a current broadcaster for Versus and NBC. Bill works as a studio host for The NHL on NBC partnered with Ray Ferraro and Ed Olczyk as well as covering mens... A clock face is the part of an analog clock that tells time through the use of a fixed numbered dial or dials and moving hand or hands. ... In a discussion of art technology, enamel (or vitreous enamel, or porcelain enamel in American English) is the colorful result of fusion of powdered glass to a substrate through the process of firing, usually between 750 and 850 degrees Celsius. ...

French decimal clock from the time of the French Revolution

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. Image File history File links Horloge-republicaine1. ... Image File history File links Horloge-republicaine1. ... The French Revolution (1789–1815) was a period of political and social upheaval in the political history of France and Europe as a whole, during which the French governmental structure, previously an absolute monarchy with feudal privileges for the aristocracy and Catholic clergy, underwent radical change to forms based on... 17 November is also the name of a Marxist group in Greece, coinciding with the anniversary of the Athens Polytechnic uprising. ... 1797 (MDCCXCVII) was a common year starting on Sunday (see link for calendar) of the Gregorian calendar (or a common year starting on Wednesday of the 11-day-slower Julian calendar). ... Eli Terry senior Eli Terry Sr (April 13, 1772 – February 24, 1852) was an influential clockmaker in Connecticut, and the first inventor to receive a United States patent for a clock mechanism. ... For other uses, see Patent (disambiguation). ...

Alexander Bain, Scottish clockmaker, patented the electric clock in 1840. The electric clock's mainspring is wound either with an electric motor or with an electro-magnet and armature. In 1841, he first patented the electromagnetic pendulum. An electric clock is a clock that is powered by electrical current instead of powered by springs or weights. ... For other kinds of motors, see motor. ... An electromagnet is a type of magnet in which the magnetic field is induced by a flow of electric current. ... Electromagnetism is the physics of the electromagnetic field: a field, encompassing all of space, composed of the electric field and the magnetic field. ...

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 vibration of a tuning fork, the behaviour of quartz crystals, the decay of radioactive elements, or resonance of polycarbonates.^{[citation needed]} Even mechanical clocks have since come to be largely powered by batteries, removing the need for winding. Surface mount electronic components Electronics is the study of the flow of charge through various materials and devices such as semiconductors, resistors, inductors, capacitors, nano-structures and vacuum tubes. ... A tuning fork is a simple metal two-pronged fork with the tines formed from a U-shaped bar of elastic material (usually steel). ... For other uses, see Quartz (disambiguation). ...

Types

Clocks can be classified by the type of time display, as well as by the method of timekeeping.

Time display methods

Analogue clocks

A linear clock at London's Piccadilly Circus tube station. 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

Analogue clocks 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 hours, which can also serve as a scale of 60 minutes, and 60 seconds if the clock has a second hand. Many other styles and designs have been used throughout the years, including dials divided into 6, 8, 10, and 24 hours. The only other widely used clock face today is the 24 hour analogue dial, because of the use of 24 hour time in military organizations and timetables. 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). Image File history File linksMetadata Download high resolution version (896x600, 219 KB) Summary photo of a linear clock seen in London, Picadilly Circus tube station, taken by me in 2002 Licensing File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old... Image File history File linksMetadata Download high resolution version (896x600, 219 KB) Summary photo of a linear clock seen in London, Picadilly Circus tube station, taken by me in 2002 Licensing File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old... This article is about the capital of England and the United Kingdom. ... Categories: Piccadilly Line stations | Bakerloo Line stations | London Underground stubs ... A clock face is the part of an analog clock that tells time through the use of a fixed numbered dial or dials and moving hand or hands. ... The hour (symbol: h) is a unit of time. ... This article is about the unit of time, angle and right ascension. ... Seconds can refer to any of the following: Seconds, a film thriller directed by John Frankenheimer. ... French decimal clock from the time of the French Revolution Decimal time is the representation of the time of day using units which are decimally related. ... The French Revolution (1789–1815) was a period of political and social upheaval in the political history of France and Europe as a whole, during which the French governmental structure, previously an absolute monarchy with feudal privileges for the aristocracy and Catholic clergy, underwent radical change to forms based on... The International System of Units (symbol: SI) (for the French phrase Syst me International dUnit s) is the most widely used system of units. ...

Another type of analogue clock is the sundial, which tracks the sun continuously, registering the time by the shadow position of its gnomon. Sundials use some or part of the 24 hour analogue dial. There also exist clocks which use a digital display despite having an analogue mechanism—these are commonly referred to as flip clocks. For other uses, see Sundial (disambiguation). ... The cantilever spar of this cable-stay bridge, the Sundial Bridge at Turtle Bay, forms the gnomon of a large garden sundial The gnomon is the part of a sundial that casts the shadow. ...

Alternative systems have been proposed. For example, the TWELV clock indicates the current hour using one of twelve colors, and indicates the minute by showing a proportion of a circular disk, similar to a moon phase. Moon phase redirects here. ...

The mechanics of analogue clocks were also the subject of the Grammy Award winning Coldplay single, Clocks in which the continual ticking of the clocks mesmerises and fascinates the narrator of the song.

Digital clocks

Digital clock outside Kanazawa Station displaying the time by controlling valves on a fountain

Digital clocks display a numeric representation of time. Two numeric display formats are commonly used on digital clocks: Image File history File links Download high-resolution version (1818x1228, 971 KB)[edit] Summary Kanazawa Station -- water clock Photo taken by me in July, 2006 [edit] Licensing File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Image File history File links Download high-resolution version (1818x1228, 971 KB)[edit] Summary Kanazawa Station -- water clock Photo taken by me in July, 2006 [edit] Licensing File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... A torii-style gate at Kanazawa-Station. ... For other uses, see Digital (disambiguation). ...

• the 24-hour notation with hours ranging 00–23;
• the 12-hour notation with AM/PM indicator, with hours indicated as 12AM, followed by 1AM–11AM, followed by 12PM, followed by 1PM–11PM (a notation mostly used in the United States).

Most digital clocks use an LCD, LED, or VFD display; many other display technologies are used as well (cathode ray tubes, nixie tubes, 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 radio or Internet time servers that are tuned to national atomic clocks. Since the release of digital clocks in the mainstream, the use of analogue clocks has dropped dramatically. The 24-hour clock is a convention of time-keeping in which the day runs from midnight to midnight and is divided into 24 hours, numbered from 0 to 23 (and 24 in the day-ending midnight). ... The 12-hour clock is a timekeeping convention in which the 24 hours of the day are divided into two periods called ante meridiem (, Latin for before noon) and post meridiem (, Latin for after noon). Each period consists of 12 hours numbered 12, 1, 2, 3, 4, 5, 6, 7... LCD redirects here. ... External links LEd Category: TeX ... A full view of a typical vacuum fluorescent display used in a videocassette recorder A close-up of the VFD highlighting the multiple filaments, tensioned by the sheet metal springs at the right of the image A vacuum fluorescent display (VFD) is a type of display used commonly on consumer... Cathode ray tube employing electromagnetic focus and deflection Cutaway rendering of a color CRT: 1. ... The ten digits of a Z560M Nixie tube. ... For other uses, see Battery. ... See Capacitor (component) for a discussion of specific types. ... “Nuclear Clock” redirects here. ...

Basic digital clock radio

Image File history File linksMetadata Download high-resolution version (2500x1667, 730 KB) Digital clock of a basic design commonly found in hotels. ... Image File history File linksMetadata Download high-resolution version (2500x1667, 730 KB) Digital clock of a basic design commonly found in hotels. ...

Auditory clocks

Main article: Talking clock

For convenience, distance, telephony or blindness, auditory clocks present the time as sounds. The sound 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). Most telecommunication companies also provide a Speaking clock service as well. A talking clock (also known as a speaking clock or auditory clock) is a timekeeping device that presents the time as sounds. ... In the philosophy of language, a natural language (or ordinary language) is a language that is spoken, written, or signed by humans for general-purpose communication, as distinguished from formal languages (such as computer-programming languages or the languages used in the study of formal logic, especially mathematical logic) and... Big Ben redirects here. ... A speaking clock service is used for people who wish to know the correct and accurate time. ...

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. Oscillation is the periodic variation, typically in time, of some measure as seen, for example, in a swinging pendulum. ... Periodicity is the quality of occurring at regular intervals (e. ...

• Mechanical clocks use a pendulum as their oscillator, which controls the rotation of a system of gears that drive the clock display.
• Crystal clocks use an electronic quartz crystal oscillator and a frequency divider or counter. Most battery-powered crystal clocks use a 2¹⁵ Hz = 32.768 kHz oscillator.
• Atomic clocks use a microwave oscillator (maser) tuned by the energy transitions of elements such as caesium, rubidium or hydrogen. These are the most precise clocks available. Atomic clocks based on caesium are used as the official definition of time today.
• Mains power clocks count the 50 or 60 hertz periods of their AC power.
• Radio clocks receive time signal broadcasts from a radio transmitter (which may be hundreds of kilometres away). The clock can decode the transmission and adjust its hands or display for near perfect accuracy. The broadcast radio signals are generated by an atomic clock and typically have a data rate of 1 bit/s.
• Sundials observe the apparent rotation of the Sun around the Earth as their reference oscillation. They are observed with a solar tempometer.
  

  

  A quartz wrist watch

A quartz clock A quartz clock is a timepiece that uses an electronic oscillator which is made up by a quartz crystal to keep precise time. ... For other uses, see Quartz (disambiguation). ... A crystal oscillator is an electronic circuit that uses the mechanical resonance of a vibrating crystal of piezoelectric material to create an electrical signal with a very precise frequency. ... Please wikify (format) this article or section as suggested in the Guide to layout and the Manual of Style. ... “Nuclear Clock” redirects here. ... This article is about the type of Electromagnetic radiation. ... A hydrogen radio frequency discharge, the first element inside a hydrogen maser (see description below) A maser is a device that produces coherent electromagnetic waves through amplification due to stimulated emission. ... General Name, Symbol, Number caesium, Cs, 55 Chemical series alkali metals Group, Period, Block 1, 6, s Appearance silvery gold Standard atomic weight 132. ... General Name, Symbol, Number rubidium, Rb, 37 Chemical series alkali metals Group, Period, Block 1, 5, s Appearance grey white Standard atomic weight 85. ... This article is about the chemistry of hydrogen. ... This article is about the unit of time. ... This article is about the SI unit of frequency. ... Usually hidden from the unaided eye, the blinking of (non-incandescent) lighting powered by AC mains is revealed in this motion-blurred long exposure of city lights. ... A radio clock A radio clock is a clock that is synchronized by a time code bit stream transmitted by a radio transmitter connected to a time standard such as an atomic clock. ... In telecommunication, data signaling rate (DSR) is the aggregate rate at which data pass a point in the transmission path of a data transmission system. ... For other uses, see Sundial (disambiguation). ... 10 seconds of a Montinari Milano This image shows 10 seconds of a Montinari Milano. ... 10 seconds of a Montinari Milano This image shows 10 seconds of a Montinari Milano. ...

Purposes

Clocks are in homes, offices and many other places; smaller ones (watches) are carried on the wrist; larger ones are in public places, e.g. a train station or church. A small clock is often shown in a corner of computer displays, mobile phones and many MP3 players. For other uses, see Watch (disambiguation). ... Passengers bustle around the typical grand edifice of Londons Broad Street station in 1865. ... For the architectural structure, see Church (building). ... A computer display monitor, usually called simply a monitor, is a piece of electrical equipment which displays viewable images generated by a computer without producing a permanent record. ... A digital audio player (DAP) is a device that stores, organizes and plays digital music files. ...

The 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 VCR, or a time bomb (see: counter). However, in this context, it is more appropriate to refer to it as a timer or trigger mechanism rather than strictly as a clock. The video cassette recorder (or VCR, less popularly video tape recorder) is a type of video tape recorder that uses removable cassettes containing magnetic tape to record audio and video from a television broadcast so it can be played back later. ... This article or section does not adequately cite its references or sources. ... In general, a counter is a device which stores (and sometimes displays) the number of times a particular event or process has occurred, often in relationship to a clock signal. ... A simple digital timer. ... A US Army 45 Colt. ...

Computers depend on an accurate internal clock signal to allow synchronized processing. (A few research projects are developing CPUs based on asynchronous circuits.) 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 internal computer clock is generally kept running by a small battery. 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. This article is about the machine. ... In electronics and especially synchronous digital circuits, a clock signal is a signal used to coordinate the actions of two or more circuits. ... An asynchronous circuit is a circuit in which the parts are largely autonomous. ...

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.^{[citation needed]} 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. An ideal clock should too measure time in consistent, for example decimalized time units.

This leads to the following definitions:

• A clock is a recurrent process and a counter.
• A good clock is one which, when used to measure other recurrent processes, finds many of them to be periodic.
• An ideal clock is a clock (i.e., recurrent process) that makes the most other recurrent processes periodic.

The recurrent, periodic process (e.g. 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. Process (lat. ... In general, a counter is a device which stores (and sometimes displays) the number of times a particular event or process has occurred, often in relationship to a clock signal. ... A mechanical wind-up metronome in motion A digital metronome set to pulse at four beats per measure at a tempo of 130 BPM A metronome is any device that produces a regulated audible and/or visual pulse, usually used to establish a steady beat, or tempo, measured in beats... Oscillation is the periodic variation, typically in time, of some measure as seen, for example, in a swinging pendulum. ...

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 clocks 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. “Nuclear Clock” redirects here. ...

John Harrison's Chronometer H5

John Harrison John Harrison (March 24, 1693–March 24, 1776) was an English clockmaker, who designed and built the worlds first successful chronometer (maritime clock), one whose accuracy was great enough to allow the determination of longitude over long distances. ...

Navigation

Navigation by ships 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. This article