The history of timekeeping studies natural and mechanical inventions to track time. 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  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. None of the first European clocks survived from 13th century Europe, but various mentions in church records reveal some of the early history of the clock.
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 . These early clocks may not have used hands or dials, but “told” the time with audible signals.
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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 '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. A silent instrument lacking such a mechanism has traditionally been known as a timepiece. 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.
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.
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.
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. 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.
Water clock designs including complex gearing, which was connected to fanciful automata and also resulted in improved accuracy, was advanced in Islamic times, eventually making their way to Europe. The Chinese developed their own advanced water clocks, passing their ideas on to Korea and Japan.
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.
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. 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.
The first mechanical clocks to be driven by weights and gears were invented by medieval Muslim engineers. The first geared mechanical clock was invented by the 11th-century Arab engineer Ibn Khalaf al-Muradi in Islamic Spain; the first weight-driven mechanical clocks, employing a mercury escapement mechanism and a clock face similar to an astrolabe dial, were also invented by Muslim engineers in the 11th century. A similar weight-driven mechanical clock later appeared in a Spanish language work compiled from earlier Arabic sources for Alfonso X in 1277. The knowledge of weight-driven mechanical clocks produced by Muslim engineers in Spain was transmitted to other parts of Europe through Latin translations of Arabic and Spanish texts on Muslim mechanical technology.
In the early 11th century, Ibn al-Haytham's Maqala fi al-Binkam described a mechanical water clock that, for the first time in history, accurately measures time in hours and minutes. According to engineering historian Salim Al-Hassani: "In his description, Ibn al-Haytham gives details of the water clock. He describes it as a new invention in that it gives hours and minutes, which no other clock gave before his time." To represent the hours and minutes, Ibn al-Haytham invented a clock face. It featured a 24-hour analog dial, including a large marker for each hour and a small marker for each minute, along with medium-sized markers to indicate half-hours and quarter-hours.
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. 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”. 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 clock, Castle clock, and Scribe clock, 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.
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.
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.
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.
In 1283, a large clock was installed at Dunstable Priory. 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.
Early astronomical clocks
The Chinese astronomical clock of Su Song mentioned above was built in 1088.
The most sophisticated water-powered astronomical clock was Al-Jazari's castle clock, considered to be an early example of a programmable analog computer, in 1206. It was a complex device that was about 3,3 meters high (11 feet), and had multiple functions alongside timekeeping. It included a display of the zodiac and the solar and lunar orbits, and a pointer in the shape of the crescent moon which travelled across the top of a gateway, moved by a hidden cart and causing automatic doors to open, each revealing a mannequin, every hour.,
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 descriptions of their design and construction survive, 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.
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.
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.
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.
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 appeared during the 1400s, although they are often erroneously credited to Nürnberg watchmaker Peter Henlein (or Henle, or Hele) around 1511. The earliest existing spring driven clock is the chamber clock given to Peter the Good, Duke of Burgundy, around 1430, now in the Germanisches Nationalmuseum. Spring power presented clockmakers with a new problem; how to keep the clock movement running at a constant rate as the spring ran down. This resulted in the invention of the stackfreed and the fusee in the 1400s, and many other innovations, down to the invention of the modern going barrel in 1760.
The first record of a minute hand on a European mechanical clock is 1475, in the Almanus Manuscript of Brother Paul.
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 was possibly 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.
The first mechanical alarm clock was invented by the Ottoman engineer Taqi al-Din. He described the alarm clock in his book, The Brightest Stars for the Construction of Mechanical Clocks (Al-Kawākib al-durriyya fī wadh' al-bankāmat al-dawriyya), published in 1556-1559. His alarm clock was capable of sounding at a specified time, achieved by placing a peg on the dial wheel. At the requested time, the peg activated a ringing device. In the same treatise, he described a mechanical astronomical clock called the "observational clock", which was the first to measure time in minutes. He made use of his mathematical knowledge to design three dials which showed the hours, degrees and minutes. He later improved the design of his observational clock to measure time in seconds in an astronomical treatise written at his Istanbul observatory of al-Din (1577-1580). He described his observational clock as "a mechanical clock with three dials which show the hours, the minutes, and the seconds." This was an important innovation in 16th-century practical astronomy, as previous clocks were not accurate enough to be used for astronomical purposes. He further improved the observational clock, using only one dial to represent the hours, minutes and seconds, describing it as "a mechanical clock with a dial showing the hours, minutes and seconds and we divided every minute into five seconds."
Another early record of a second hand on a clock dates back to about 1560, on a clock now in the Fremersdorf collection. However, this clock could not have been accurate, and the second hand was probably for indicating that the clock was working.
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 possibly created the anchor escapement, an improvement over Huygens' crown escapement. Within just one generation, minute hands and then second hands were added.
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.
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.
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.
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.
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 resonance of polycarbonates, or the quantum vibrations of atoms. Even mechanical clocks have since come to be largely powered by batteries, removing the need for winding.
How clocks work
The invention of the mechanical clock in the Middle Ages started a change in timekeeping methods from continuous processes, such as the motion of the gnomon's shadow on a sundial or the flow of liquid in a water clock, to repetitive oscillatory processes, like the swing of a pendulum or the vibration of a quartz crystal, which were more accurate. All modern clocks use oscillation.
Although the methods they use vary, all oscillating clocks, mechanical and digital and atomic, work similarly and can be divided into analogous parts. They consist of an object that repeats the same motion over and over again, an oscillator, with a precisely constant time interval between each repetition, or 'beat'. Attached to the oscillator is a controller device, which sustains the oscillator's motion by replacing the energy it loses to friction, and converts its oscillations into a series of pulses. The pulses are then added up in a chain of some type of counters to express the time in convenient units, usually seconds, minutes, hours, etc. Then finally some kind of indicator displays the result in a human-readable form.
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- Bolter, David J. Turing's Man: Western Culture in the Computer Age. The University of North Carolina Press, Chapel Hill, N.C. (1984). ISBN 0-8078-4108-0 pbk. Very good, readable summary of the role of "the clock" in its setting the direction of philosophic movement for the "Western World". Cf. picture on p. 25 showing the verge and foliot. Bolton derived the picture from Macey, p. 20.
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- Robinson, Tom. The Longcase Clock. Suffolk, England: Antique Collector’s Club (1981).
- Smith, Alan. The International Dictionary of Clocks. London: Chancellor Press (1996).
- Tardy. French Clocks the World Over. Part I and II. Translated with the assistance of Alexander Ballantyne. Paris: Tardy (1981).
- Yoder, Joella Gerstmeyer. Unrolling Time: Christiaan Huygens and the Mathematization of Nature. New York: Cambridge University Press (1988).
- Zea, Philip, & Robert Cheney. Clock Making in New England – 1725-1825. Old Sturbridge Village (1992).
|Wikimedia Commons has media related to: Clocks|
- Article, by a key figure in the development of quartz crystal clocks, on the history of timekeeping up to the late 1940s from The Bell System Technical Journal, Vol. XXVII, pp. 510-588, 1948
- Information on Dutch clocks
- Science Museum - Time Measurement
- Tyranny of the Clock - Brief analysis and history of the clock within the context of the industrial revolution