(Redirected from Clocks)
A 'clock' is an instrument for measuring and indicating the
time. Deriving ultimately – via
Dutch, Northern
French, and
Medieval Latin – from a
Celtic word 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' (see Baillie et al., p. 307; Palmer, p. 19; Zea & Cheney, p. 172). 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.
History
The clock is one of the oldest human
inventions. Its purpose is to quantify and label the physical process of change. As the seasons and the phases of the moon can be used to measure the passage of longer periods of change, shorter processes of measurement were desired, hence the invention of the terms, "hours" and "minutes".
Sundials and other techniques
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 doesn't work at all during the night - encouraged the use of other techniques for measuring time.
Candles 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
Main articles: Water clock
Water clocks, along with the sundials, are possibly the oldest time-measuring instruments, with the only exceptions being the
gnomon and day-counting
tally stick.
[1] Given their great antiquity, where and when they first existed are not known and perhaps unknowable. The simplest form of water clocks, the bowl-shaped outflow type, are known to have existed in
Babylon and in
Egypt around the 16th century B.C. 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.
[2]
The Greek and Roman civilizations are credited for initially advancing the water clock design to include complex gearing, which was connected to fanciful
automata and improved accuracy. These advances were passed on through
Byzantium and
Islamic times, which eventually made their way on to
Europe. Independently, China developed its own advanced water clocks, passing on their ideas 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 time, 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.
Early mechanical clocks
In 797 (or possibly 801), the
Abbasid caliph of
Baghdad,
Harun al-Rashid, presented
Charlemagne with an
Asian Elephant named Abul-Abbas together with a mechanical clock, out of which came a mechanical bird to announce the hours. This indicates that the early mechanical clocks were probably made in
Asia.
None of the first clocks survive 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. 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.
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.
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. 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.
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; its location above the
rood screen suggests that it was not a water clock. 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 technicians for two years.
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, 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 toward the end of the 14th century, is considered to be 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
A wrist watch
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
15th century, 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.
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 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 record of a second hand on a clock is 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 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.
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 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 the type of time display, as well as by the method of timekeeping.
Time display methods
Analog 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
Analog 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 often also as a scale of 60
seconds – 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 type 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).
Another type of analog 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 analog dial. There also exist clocks which use a digital display despite having an analog mechanism - these are commonly referred to as
flip clocks.
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.
Digital clocks
A digital clock outside
Kanazawa Station displays 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:
★ 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 or
LED 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.
Basic digital clock radio
Auditory clocks
Main articles: 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.
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.
★ '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 2
15 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 kilometers 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.
Purposes
Clocks are in homes and offices; smaller ones (
watches) 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 displays,
mobile phones and many
MP3 players, including
iPods.
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.
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. 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. An ideal clock should too measure time in consistent, for example decimalized time units.
A desk clock
This leads to the following definitions:
★ A clock is a recurrent
periodic 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 (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 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.
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.
Specific types of clocks
A windup, mechanical, spring-driven alarm clock
★
Alarm clock
★
Analog clock with digital display
★
Astronomical clock
★
Atomic clock
★
Balloon clock
★
Binary clock
★
Bracket clock
★
Carriage clock
★
Cartel clock
★
Chiming clock
★
Clock network
★
Clock of the Long Now
★
Countdown clock
★
Cuckoo clock
★
Data clock for
timescapes created with
time-technology
★
Digital clock
★
Doll's head clock
★
Electric clock
★
Flip clock
★
Floral clock
★
Game clock
★
Hourglass
★
Japanese clock
★
Lantern clock
★
Lighthouse Clock
★
Longcase (or "grandfather") clock
★
Mantel clock
★
Musical clock
★
Master clock
★
Paper clock
★
Pedestal clock
★
Pendulum clock
★
Projection clock
★
Quartz clock
★
Railroad chronometers
★
Reference clock
★
Rolling ball clock
★
Shelf clock
★
Sidereal clock
★
Skeleton clock
★
Slave clock
★
Speaking clock
★
Stopwatch
★
Striking clock
★
Sundial
★
Talking clock
★
Tall-case clock
★
Tide clock
★
Time ball
★
Time clock
★
Tower clock
★
Torsion pendulum clock
★
Watch
★
Water clock
★
World clock
References
★ Baillie, G.H., O. Clutton, & C.A. Ilbert. ''Britten’s Old Clocks and Watches and Their Makers'' (7th ed.). Bonanza Books (1956).
★ 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.
★ Bruton, Eric. ''The History of Clocks and Watches''. London: Black Cat (1993).
★
History of the Hour: Clocks and Modern Temporal Orders, , Gerhard, Dohrn-van Rossum, The University of Chicago Press, 1996, ISBN 0226155102
★ Edey, Winthrop. ''French Clocks''. New York: Walker & Co. (1967).
★ Kumar, Narendra "Science in Ancient India" (2004). ISBN 8126120568.
★ Kak, Subhash, Ph.D. Babylonian and Indian Astronomy: Early Connections. February 17, 2003.
★ Landes, David S. ''Revolution in Time: Clocks and the Making of the Modern World''. Cambridge: Harvard University Press (1983).
★ Lloyd, Alan H. “Mechanical Timekeepers”, ''A History of Technology,'' Vol. III. Edited by Charles Joseph Singer et al. Oxford: Clarendon Press (1957), pp. 648-675.
★ Macey, Samuel L., ''Clocks and the Cosmos: Time in Western Life and Thought'', Archon Books, Hamden, Conn. (1980).
★
Science & Civilisation in China, Vol. 4, Part 2: Mechanical Engineering, , Joseph, Needham, Cambridge University Press, 2000, ISBN 0521058031
★ North, John. ''God's Clockmaker: Richard of Wallingford and the Invention of Time''. London: Hambledon and London (2005).
★ Palmer, Brooks. ''The Book of American Clocks'', The Macmillan Co. (1979).
★ 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).
Notes
1. The Time Museum: Volume I, Time Measuring Instruments, Part 3, Water-clocks, Sand-glasses, Fire-clocks, , Anthony J., Turner, , 1984, ISBN 0-912947-01-2
2. Time and Its Measurement: From the stone age to the nuclear age, , Harrison J., Cowan, The World Publishing Company, 1958,
External links
★
United States National Association of Watch and Clock Collectors
★
American Watchmakers-Clockmakers Institute
★
British Horological Institute
★
Federation of the Swiss Watch Industry FH contains listings of links to all participating Swiss Watch Brands and related manufacturers, suppliers, associations, trade magazines, etc, as well as a wealth of related information
★
Illustrated Glossary of Clock Types
★
Science Museum - more details on early 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
★
Oparin's clock - a new way of indicating time
★
49-hour septenary clock
★
clock using colors to indicate hours
★
Personalised Clocks - Design and build your own clock
See also
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