Editing Pendulum clock (section)

==History==
{{multiple image
| footer   = The first pendulum clock, invented by [[Christiaan Huygens]] in 1656
| image1   = Huygens first pendulum clock - front view.png
| width1   = 120
| image2   = Huygens first pendulum clock.png
| width2   = 112
}}

The pendulum clock was invented on 25 December 1656 by [[Dutch (ethnic group and nation)|Dutch]] scientist and inventor [[Christiaan Huygens]], and patented the following year. He described it in his manuscript ''Horologium'' published in 1658.<ref name="Andrewes">Andrewes, W.J.H. ''Clocks and Watches: The leap to precision'' in {{cite book
  | first = Samuel
  | last  = Macey
  | title = Encyclopedia of Time
  | pages = 123–125
  | publisher = Taylor & Francis
  | url   = https://books.google.com/books?id=F7wNQk219KMC&pg=PA126
  | year  = 1994
  | isbn  = 978-0-8153-0615-3}}</ref> Huygens contracted the construction of his clock designs to the Dutch clockmaker [[Salomon Coster]], who actually built the clock.<ref name="Andrewes" /> Huygens was inspired by investigations of pendulums by [[Galileo Galilei]] beginning around 1602. Galileo discovered the key property that makes pendulums useful timekeepers: they are isochronic, which means that the [[Frequency|period]] of swing of a pendulum is approximately the same for different sized swings.<ref>{{cite web
|title=Huygens' Clocks
|work=Stories
|publisher=Science Museum, London, UK
|url=http://www.sciencemuseum.org.uk/onlinestuff/stories/huygens_clocks.aspx
|access-date=2007-11-14
|archive-date=2007-10-10
|archive-url=https://web.archive.org/web/20071010034250/http://www.sciencemuseum.org.uk/onlinestuff/stories/huygens_clocks.aspx
|url-status=dead
}}</ref><ref>{{cite web
|title=Pendulum Clock
|work=The Galileo Project
|publisher=Rice Univ.
|url=http://galileo.rice.edu/sci/instruments/pendulum.html
|access-date=2007-12-03}}</ref> Galileo in 1637 described to his son, [[Vincenzo Gamba|Vincenzo]], a mechanism which could keep a pendulum swinging, which has been called the first pendulum clock design ''(picture at top)''. It was partly constructed by his son in 1649, but neither lived to finish it.<ref name="Andrewes" /><ref>A modern reconstruction can be seen at {{cite web
|title=Pendulum clock designed by Galileo, Item #1883-29
|work=Time Measurement
|publisher=Science Museum, London, UK|url=http://www.sciencemuseum.org.uk/objects/time_measurement/1883-29.aspx
|access-date=2007-11-14}}</ref>   The introduction of the pendulum, the first [[harmonic oscillator]] used in timekeeping, increased the accuracy of clocks enormously, from about 15 minutes per day to 15 seconds per day<ref>{{cite web
|last=Bennet
|first=Matthew
|title=Huygens' Clocks
|year=2002
|publisher=Georgia Institute of Technology
|url=http://www.physics.gatech.edu/research/schatz/pubs/royclocks2.pdf
|access-date=2007-12-04 |archive-url = https://web.archive.org/web/20080410084732/http://www.physics.gatech.edu/research/schatz/pubs/royclocks2.pdf <!-- Bot retrieved archive --> |archive-date = 2008-04-10|display-authors=etal}}, p.3, also published in ''Proceedings of the Royal Society of London'', ''A'' '''458''', 563–579</ref> leading to their rapid spread as existing '[[verge and foliot]]' clocks were retrofitted with pendulums. By 1659 pendulum clocks were being manufactured in France by clockmaker [[Nicolaus Hanet]], and in England by [[Ahasuerus Fromanteel]].<ref name="Andrewes" />

[[Image:Edward East winged lantern clock.jpg|thumb|left|upright|A [[lantern clock]] that has been converted to use a pendulum. To accommodate the wide pendulum swings caused by the [[verge escapement]], "wings" have been added on the sides]]
[[File:Grandfather clock q.jpg|thumb|upright=0.6|Grandfather clock]]
{{multiple image
| align = right
| direction = horizontal
| header   =
| image1   = Riefler clock NIST.jpg
| width1   = 77
| image2   = Shortt Synchronome free pendulum clock.jpg
| width2   = 200
| footer   = Some of the most accurate pendulum clocks: ''(left)'' [[Riefler clock|Riefler regulator clock]], that served as the US time standard from 1909 to 1929, ''(right)'' [[Shortt-Synchronome clock]], the most accurate pendulum clock ever manufactured, which served as the time standard during the 1930s.
}}

These early clocks, due to their [[verge escapement]]s, had wide pendulum swings<ref name="Andrewes" /> of 80–100°. In his 1673 analysis of pendulums, ''[[Horologium Oscillatorium]]'', Huygens showed that wide swings made the pendulum inaccurate, causing its period, and thus the rate of the clock, to vary with unavoidable variations in the driving force provided by the [[movement (clockwork)|movement]].<ref name="Andrewes" /> Clockmakers' realization that only pendulums with small swings of a few degrees are [[isochronous (horology)|isochronous]] motivated the invention of the [[anchor escapement]] by [[Robert Hooke]] around 1658,<ref name="Andrewes" /> which reduced the pendulum's swing to 4–6°.<ref>{{cite journal
 |last        = Headrick
 |first       = Michael
 |year        = 2002
 |title       = Origin and Evolution of the Anchor Clock Escapement
 |journal     = Control Systems Magazine
 |publisher   = Inst. of Electrical and Electronic Engineers
 |volume      = 22
 |issue       = 2
 |url         = http://www.geocities.com/mvhw/anchor.html
 |access-date  = 2007-06-06
 |archive-url  = https://web.archive.org/web/20091025120920/http://geocities.com/mvhw/anchor.html
 |archive-date = October 25, 2009
 |url-status     = dead
}}</ref> The anchor became the standard escapement used in pendulum clocks. In addition to increased accuracy, the anchor's narrow pendulum swing allowed the clock's case to accommodate longer, slower pendulums, which needed less power and caused less wear on the movement. The [[seconds pendulum]] (also called the Royal pendulum), {{convert|0.994|m|in|abbr=on}} long, in which the time period is two seconds, became widely used in quality clocks. The long narrow freestanding clocks built around these pendulums, first made by William Clement around 1680, who also claimed invention of the anchor escapement,<ref name="Andrewes" /> became known as [[grandfather clock]]s. The increased accuracy resulting from these developments caused the minute hand, previously rare, to be added to clock faces beginning around 1690.<ref>Milham 1945, p. 190</ref><ref name="Andrewes" />

The 18th and 19th century wave of [[horological]] innovation that followed the invention of the pendulum brought many improvements to pendulum clocks.<ref name="Macey" />{{rp|p.624}} The [[deadbeat escapement]] invented in 1675 by [[Richard Towneley]] and popularized by [[George Graham (clockmaker)|George Graham]] around 1715 in his precision "regulator" clocks gradually replaced the anchor escapement<ref>Milham 1945, p.181, 441</ref><ref name="Andrewes" /> and is now used in most modern pendulum clocks. Observation that pendulum clocks slowed down in summer brought the realization that [[thermal expansion]] and contraction of the pendulum rod with changes in temperature was a source of error. This was solved by the invention of temperature-compensated pendulums; the [[mercury pendulum]] by Graham in 1721 and the [[gridiron pendulum]] by [[John Harrison]] in 1726.<ref>Milham 1945, pp. 193–195</ref><ref name="Andrewes" /> With these improvements, by the mid-18th century precision pendulum clocks achieved accuracies of a few seconds per week.

Until the 19th century, clocks were handmade by individual craftsmen and were very expensive.<ref name="Macey" />{{rp|p.625}} The rich ornamentation of pendulum clocks of this period indicates their value as status symbols of the wealthy. The [[clockmaker]]s of each country and region in Europe developed their own distinctive styles. By the 19th century, factory production of clock parts gradually made pendulum clocks affordable by middle-class families.

During the [[Industrial Revolution]], the faster pace of life and scheduling of shifts and public transportation like trains depended on the more accurate timekeeping made possible by the pendulum.<ref name="Macey" />{{rp|p.624}} Daily life was organized around the home pendulum clock. More accurate pendulum clocks, called ''regulators'', were installed in places of business and [[railroad station]]s and used to schedule work and set other clocks. The need for extremely accurate timekeeping in [[celestial navigation]] to determine [[longitude]] on ships during long sea voyages drove the development of the most accurate pendulum clocks, called ''astronomical regulators''. These precision instruments, installed in clock vaults in [[naval observatory|naval observatories]] and kept accurate within a fraction of a second by observation of [[star transit]]s overhead, were used to set [[marine chronometer]]s on naval and commercial vessels. Beginning in the 19th century, astronomical regulators in naval observatories served as primary standards for national [[Time signal|time distribution services]] that distributed time signals over [[telegraph]] wires.<ref>Milham 1945, p.83</ref> From 1909, US National Bureau of Standards (now [[NIST]]) based the US time standard on [[Riefler escapement|Riefler]] pendulum clocks, accurate to about 10 milliseconds per day. In 1929 it switched to the [[Shortt-Synchronome clock|Shortt-Synchronome free pendulum clock]] before phasing in [[Quartz clock|quartz]] standards in the 1930s.<ref>{{cite web
 | date=April 30, 2002
 | url=http://physics.nist.gov/GenInt/Time/revol.html
 | title=A Revolution in Timekeeping
 | publisher=Time and Frequency Services, NIST
 | access-date=2007-05-29 |archive-url = https://web.archive.org/web/20070528005441/http://physics.nist.gov/GenInt/Time/revol.html <!-- Bot retrieved archive --> |archive-date = 2007-05-28}}</ref>
<ref>{{cite conference
 |last        = Sullivan
 |first       = D.B.
 |title       = Time and frequency measurement at NIST: The first 100 years
 |year        = 2001
 |book-title   = 2001 IEEE Int'l Frequency Control Symp.
 |publisher   = National Institute of Standards and Technology
 |url         = http://tf.nist.gov/timefreq/general/pdf/1485.pdf
 |url-status     = dead
 |archive-url  = https://web.archive.org/web/20110927062444/http://tf.nist.gov/timefreq/general/pdf/1485.pdf
 |archive-date = 2011-09-27
}}</ref>  With an error of less than one second per year, the Shortt was the most accurate commercially produced pendulum clock.<ref name="Jones">{{cite book
 | last = Jones
 | first = Tony
 | title = Splitting the Second: The Story of Atomic Time
 | publisher = CRC Press
 | year = 2000
 | location = US
 | pages = 30
 | url = https://books.google.com/books?id=krZBQbnHTY0C&pg=PA30
 | isbn = 978-0-7503-0640-9}}</ref><ref>{{cite book
 | last = Milham
 | first = Willis I.
 | title = Time and Timekeepers
 | publisher = MacMillan
 | year = 1945
 | location = New York
 | pages = 615
  }}</ref><ref name="Marrison">{{cite journal
 |last        = Marrison
 |first       = Warren
 |title       = The Evolution of the Quartz Crystal Clock
 |journal     = Bell System Technical Journal
 |year        = 1948
 |volume      = 27
 |issue = 3
 |pages       = 510–588
 |url         = http://www.ieee-uffc.org/main/history.asp?file=marrison
 |doi         = 10.1002/j.1538-7305.1948.tb01343.x
 |url-status     = dead
 |archive-url  = https://web.archive.org/web/20110717061023/http://www.ieee-uffc.org/main/history.asp?file=marrison
 |archive-date = 2011-07-17
}}</ref><ref>{{cite web
 | title = The Reifler and Shortt clocks
 | publisher = JagAir Institute of Time and Technology
 | url = http://www.clockvault.com/heritage/index.htm
 | access-date = 2009-12-29}}</ref><ref name="Betts">{{cite web
 |last        = Betts
 |first       = Jonathan
 |title       = Expert's Statement, Case 6 (2008-09) William Hamilton Shortt regulator
 |work        = Export licensing hearing, Reviewing Committee on the Export of Works of Art and Objects of Cultural Interest
 |publisher   = UK Museums, Libraries, and Archives Council
 |date        = May 22, 2008
 |url         = http://www.mla.gov.uk/what/cultural/export/reviewing_cttee/~/media/Files/word/2009/RCEWA/Cases%202008-09/Case%206%202008-09%20Regulator/internet%20experts%20statement%20shortt.ashx
 |format      = DOC
 |access-date  = 2009-12-29
 |url-status     = dead
 |archive-url  = https://web.archive.org/web/20091025180404/http://www.mla.gov.uk/what/cultural/export/reviewing_cttee/~/media/Files/word/2009/RCEWA/Cases%202008-09/Case%206%202008-09%20Regulator/internet%20experts%20statement%20shortt.ashx
 |archive-date = October 25, 2009
}}</ref>

Pendulum clocks remained the world standard for accurate timekeeping for 270 years, until the invention of the [[quartz clock]] in 1927, and were used as time standards through [[World War II]]. The French Time Service included pendulum clocks in their ensemble of standard clocks until 1954.<ref>{{cite book
 | last = Audoin
 | first = Claude
  |author2=Bernard Guinot |author3=Stephen Lyle
  | title = The Measurement of Time: Time, Frequency, and the Atomic Clock
 | publisher = Cambridge Univ. Press
 | year = 2001
 | location = UK
 | pages = 83
 | url = https://books.google.com/books?id=LqdgUcm03A8C
 | isbn = 0-521-00397-0}}</ref> The home pendulum clock began to be replaced as domestic timekeeper during the 1930s and 1940s by the synchronous [[electric clock]], which kept more accurate time because it was synchronized to the oscillation of the [[electric power grid]]. {{anchor|Littlemore clock}}The most accurate experimental pendulum clock ever made<ref name="Kennedy">{{Cite news
 | last = Kennedy
 | first = Maev
 | title = Scientist's historic clock collection for sale
 | newspaper = The Guardian
 | location = London
 | publisher = Scott Trust Ltd.
 | date = May 7, 2003
 | url = https://www.theguardian.com/uk/2003/may/07/arts.science
 | access-date = March 18, 2017}}</ref><ref name="Mumford">{{cite journal
 | last1  = Mumford
 | first1 = Bryan
 | title = Some thoughts on the Littlemore clock
 | journal = Horological Science Newsletter
 | pages = 20–22
 | publisher = National Assoc. of Watch and Clock Collectors
 | date = November 2005
 | url = http://www.cleyet.org/Pendula,%20Horological%20and%20Otherwise/The%20Littlemore%20clock%202.pdf
 | access-date = March 18, 2017}}</ref> may be the Littlemore Clock built by [[Edward Thomas Hall|Edward T. Hall]] in the 1990s<ref>{{cite web
|last=Hall
|first=E.T.
|title=The Littlemore Clock
|date=June 1996
|work=Horological Science
|publisher=Nat'l Assoc. of Watch and Clock Collectors
|pages=fig. 7b
|url=http://www.hsn161.com/HSN/hsn_article.php}}</ref>
(donated in 2003 to the [[National Watch and Clock Museum]], Columbia, Pennsylvania, USA). The largest pendulum clocks, exceeding {{convert|30|m|ft|abbr=on}}, were built in [[Geneva]] (1972) and [[Gdańsk]] (2016).<ref>{{cite web
 |url=http://www.patrimoine-horloge.fr/mec-geneve.html
 |title=Genève [Geneva]
 |first=Gérard
 |last=Guilbaud
 |publisher=Patrimoine-Horloge
 |language=fr
 |access-date=February 11, 2024}}</ref><ref>{{cite press release
 |url=https://media.muzeumgdansk.pl/komunikaty/814591/rusza-konkurs-na-nowa-nazwe-dla-rekordowego-zegara-z-muzeum-nauki-gdanskiej
 |title=Rusza konkurs na nową nazwę dla rekordowego zegara z Muzeum Nauki Gdańskiej [A competition for a new name for the record clock from the Gdańsk Science Museum is starting]
 |first=Andrzej
 |last=Gierszewski
 |publisher=Gdańsk Museum
 |language=pl
 |date=June 29, 2023
 |access-date=February 11, 2024}}</ref>