View source for Semaphore

{{Short description|Mechanical apparatus used to send messages}}
{{other uses}}
{{Use dmy dates|date=September 2021}}
[[File:Coast telegraph, semaphore or signaling post at Scheveningen, 1799.jpg|thumb|right|Coastal semaphore using moving arms at [[Scheveningen]], circa 1799]]

'''Semaphore''' ({{lit|apparatus for signalling}}; {{etymology|grc|''{{wikt-lang|grc|σῆμα}}'' ({{grc-transl|σῆμα}})|mark, sign, token|el|''{{wikt-lang|el|-φόρος}}'' ({{grc-transl|-φόρος}})|bearer, carrier}})<ref>{{OEtymD|semaphore |access-date=2021-08-15}}</ref> is the use of an apparatus to create a visual [[signal]] transmitted over distance.<ref name="EB">{{Cite web|url=https://www.britannica.com/technology/semaphore|title=Semaphore &#124; communications|website=Encyclopedia Britannica}}</ref><ref name="FM">{{Cite web|url=https://www.factmonster.com/encyclopedia/science/tech/terms/semaphore|title=semaphore &#124; FactMonster|website=www.factmonster.com}}</ref>  A semaphore can be performed with devices including: fire, lights, [[flag]]s, [[sunlight]], and moving arms.<ref name="EB" /><ref name="FM" /><ref>Beauchamp, K. G. (2001). ''[https://books.google.com/books?id=k3XCkncd83AC&q=History+of+Telegraphy History of Telegraphy]''. (''Chapter 1''). The Institution of Engineering and Technology. {{ISBN|978-0852967928}}</ref> Semaphores can be used for [[telegraphy]] when arranged in [[Optical telegraph|visually connected networks]], or for traffic signalling such as in [[Railway semaphore signal|railway systems]], or [[traffic light]]s in cities.<ref>{{Cite web|title=Semaphore - Traffic Signals - Road Signs and Traffic Signals - Dating - Landscape Change Program|url=https://glcp.uvm.edu/landscape_new/dating/road_signs_and_traffic_signals/semaphore_signals.php|access-date=15 August 2021|website=glcp.uvm.edu}}</ref>

==Fire==
The [[Phryctoriae]] were a semaphore system used in [[Ancient Greece]] for the transmission of specific prearranged messages.  Towers were built on selected mountaintops, so that one tower, the ''phryctoria'', would be visible to the next tower, usually {{cvt|20|mi|km|-1|order=flip}} distant. Flames were lit on one tower, then the next tower would light a flame in succession.

The [[Byzantine beacon system]] was a semaphore developed in the 9th century during the [[Arab–Byzantine wars]].   The [[Byzantine Empire]] used a system of [[beacon]]s to transmit messages from the border with the [[Abbasid Caliphate]] across [[Asia Minor]] to the Byzantine capital, [[Constantinople]].  The main line of beacons stretched over some {{cvt|450|mi|km|-1|order=flip}} with stations placed from {{cvt|60|mi|km|-1|order=flip}} to {{cvt|35|mi|km|-1|order=flip}}. A message could be sent along the line in approximately one hour. A [[bonfire]] was set at the first beacon and transmitted down the line to Constantinople.

A [[smoke signal]] is one of the oldest forms of semaphore for long-distance communication. The smoke is used to transmit news, signal danger or gather people to a common area.

==Lights==
[[File:The Royal Navy during the Second World War A8066.jpg|thumb|left|Sailor with signal lamp]]
A [[signal lamp]] is a semaphore system using a visual signaling device, often utilizing [[Morse code]].  In the 19th century, the [[Royal Navy]] began using signal lamps. In 1867, then Captain, later Vice Admiral, [[Philip Howard Colomb]] for the first time began using dots and dashes from a signal lamp.<ref>{{cite book | editor-first = Christopher H. | editor-last = Sterling | title = Military Communications: From Ancient Times to the 21st Century | year = 2008 | location = Santa Barbara, California | publisher = ABC-CLIO, Inc. | isbn = 978-1-85109-732-6| page = 209 |url=https://books.google.com/books?id=RBC2nY1rp5MC&pg=PA209}}</ref>

The modern [[lighthouse]] is a semaphore using a tower, building, or another type of structure designed to emit light from a system of lamps and [[lens (optics)|lenses]] and to serve as a [[navigational aid]] for [[maritime pilot]]s at sea or on inland waterways.  Lighthouses mark dangerous coastlines, hazardous [[shoal]]s, [[reef]]s, rocks, and safe entries to harbors; they also assist in [[aerial navigation]].  Originally lit by open fires and later candles, the [[Argand lamp|Argand hollow wick lamp]] and [[parabolic reflector]] were introduced in the late 18th century.  The source of light is called the "lamp" and the light is concentrated, by the "lens" or "optic". [[Whale oil]] was also used with wicks as the source of light. [[Kerosene]] became popular in the 1870s and electricity and carbide ([[acetylene gas]]) began replacing kerosene around the turn of the 20th century. Carbide was promoted by the [[Dalén light]] which automatically lit the lamp at nightfall and extinguished it at dawn. The advent of electrification and [[automatic lamp changer]]s began to make lighthouse keepers obsolete.  Improvements in maritime navigation and safety with [[satellite navigation]] systems like the [[Global Positioning System]] (GPS) have led to the phasing out of non-automated lighthouses across the world.<ref>{{cite web|url=http://www.nps.gov/history/maritime/keep/keep19th.htm|title=Maritime Heritage Program – National Park Service|access-date=6 April 2017}}</ref>

==Flags==
[[File:Semaphore Signals A-Z.jpg|thumb|right|Flag [[Latin alphabet|alphabet]]]]
{{main|Flag semaphore}}
A [[flag semaphore]]<ref>{{Cite web|url=http://www.jproc.ca/rrp/rrp2/visual_semaphore_other.html|title=Visual Signalling in the RCN - Semaphore|website=www.jproc.ca}}</ref> is the [[telegraphy]] system conveying information at a distance by means of visual signals with hand-held flags, rods, disks, paddles, or occasionally bare or gloved hands. Information is encoded by the position of the flags.<ref name="HistUk">{{cite web |title=History of Semaphore |url=https://www.commsmuseum.co.uk/exhibits/imagestactical/history%20of%20semaphore.pdf |website=Royal Navy Communications Branch Museum/Library |access-date=16 May 2020 |archive-date=11 May 2021 |archive-url=https://web.archive.org/web/20210511225618/https://commsmuseum.co.uk/exhibits/imagestactical/history%20of%20semaphore.pdf |url-status=dead }}</ref> It is still used during [[underway replenishment]] at sea and is acceptable for emergency communication in daylight or using lighted wands instead of flags, at night.

==Sunlight==
[[File:A boer war reenactor, MC Heunis preparing his heliograph on top of Elandskop Hill in Petrus Steyn.jpg|thumb|right|Heliograph]]
A [[heliograph]] is a semaphore that signals by flashes of [[sunlight]] using a mirror, often in [[Morse code]].  The flashes are produced by momentarily pivoting the [[mirror]] or by interrupting the sunlight with a shutter.<ref name=Woods2008/> The heliograph was a simple but effective instrument for instantaneous optical communication over long distances during the late 19th and early 20th century.<ref name=Woods2008>{{cite book|last=Woods|first=Daniel|title=Military Communications: From Ancient Times to the 21st Century|year=2008|publisher=ABC-CLIO|isbn=978-1851097326|page=208|chapter-url=https://books.google.com/books?id=RBC2nY1rp5MC&q=heliograph&pg=PA211|chapter=Heliograph and Mirrors|editor=Sterling, Christopher}}</ref> The main uses were for the military, survey and forest protection work.  Heliographs were standard issue in the British and Australian armies until the 1960s and were used by the Pakistani army as late as 1975.<ref name="Boer">Major J. D. Harris [http://rapidttp.com/milhist/vol111jh.html WIRE AT WAR – Signals communication in the South African War 1899–1902]. Retrieved on 1 June 2008. Discussion of heliograph use in the Boer War.</ref>

==Moving arms==

=== Optical telegraph ===
{{main|Optical telegraph}}
[[File:Signaling by Napoleonic semaphore line.jpg|thumb|left|Napoleonic semaphore line]]
In 1792 [[Claude Chappe]], a clergyman from France, invented a [[Land|terrestrial]] [[Optical telegraph|semaphore telegraph]], which uses pivoted indicator arms and conveys information according to the direction the indicators point and was popular in the late eighteenth to early nineteenth centuries.<ref name="Burns2004">{{cite book |chapter-url=https://books.google.com/books?id=7eUUy8-VvwoC&pg=PA29 |chapter=Chapter 2: Semaphore Signalling |isbn=978-0-86341-327-8 |title=Communications: an international history of the formative years |first=R. W. |last=Burns |year=2004 }}</ref><ref name="EncyBrit1824">{{cite book |chapter-url=https://books.google.com/books?id=MsYnAAAAMAAJ&pg=PA645 |chapter=Telegraph |volume=10 |title=Encyclopædia Britannica |edition=6th |year=1824 |pages=645–651 }}</ref><ref name="EdEnc1832">{{cite book |chapter-url=https://books.google.com/books?id=VhEbAQAAMAAJ&pg=PA657 |chapter=Telegraph |volume=17 |title=The Edinburgh Encyclopaedia |pages=664–667 |year=1832 |editor=David Brewster }}</ref><ref name="EB" /><ref>{{Cite web|url=https://ethw.org/w/images/1/17/Dilhac.pdf|title=J-M. Dilhac, "The Telegraph of Claude Chappe: An Optical Telecommunication Network for the XVIIIrd Century."}}</ref> Relay towers were built with a [[sightline]] to each tower at separations of {{cvt|5|-|20|mi|km|-1|order=flip}}.  On the top of each tower was an apparatus, which uses pivoted indicator arms and conveys information according to the direction the indicators point.  An observer at each tower would watch the neighbouring tower through a [[telescope]] and when the semaphore arms began to move spelling out a message, they would pass the message on to the next tower.  This early form of telegraph system was much more effective and efficient than [[post riders]] for conveying a message over long distances.  The sightline between relay stations was limited by [[geography]] and weather.  In addition, the visual communication would not be able to cross large bodies of water.

An example is during the [[Napoleonic era]], stations were constructed to send and receive messages using the coined term ''Napoleonic semaphore''.<ref name="BBC">{{Cite news|date=16 June 2013|title=How Napoleon's semaphore telegraph changed the world|language=en-GB|work=BBC News|url=https://www.bbc.com/news/magazine-22909590|access-date=23 December 2020}}</ref><ref name="Shannon">{{Cite web|url=https://shannonselin.com/2020/05/chappe-semaphore-telegraph/|title=Napoleonic Telecommunications: The Chappe Semaphore Telegraph|date=15 May 2020|website=Shannon Selin}}</ref> This form of visual communication was so effective that messages that normally took days to communicate could now be transmitted in mere hours.<ref name="BBC" />

=== Railway signal ===
[[File:Signal Home Semaphore R & G.svg|thumb|right|Railway pivot arms]]
{{main|Railway semaphore signal}}
The [[railway semaphore signal]] is one of the earliest forms of fixed [[railway signal]]s.<ref>{{cite web|url=http://mysite.du.edu/~jcalvert/railway/semaphor/semhist.htm |title=The Origin of the Railway Semaphore |publisher=Mysite.du.edu |access-date=17 June 2013}}</ref> These signals display their different indications to [[Railroad engineer|train drivers]] by changing the angle of inclination of a pivoted 'arms'.<ref name="FM" />  A single arm that pivots is attached to a vertical post and can take one of three positions.  The horizontal position indicates stop, the vertical means all clear and the inclined indicates go ahead under control, but expect to stop.<ref name="FM" /> Designs have altered over the intervening years and colour light signals have replaced semaphore signals in most countries.

== Hydraulic ==
{{main|Hydraulic telegraph}}
A [[hydraulic telegraph]] can refer to either one of two different semaphore systems. The earliest one was developed in [[Ancient Greece|4th-century BC Greece]], while the other was developed in [[Victorian era|19th-century AD Britain]]. The Greek system was deployed in combination with [[Flag semaphore|semaphoric]] fires, while the latter British system was operated purely by [[hydraulic]] fluid pressure.

==Decline==
[[File:Wallace Study-Telegraph.jpg|thumb|right|Electric telegraph]]
In the early 19th century, the [[electrical telegraph]] was gradually invented allowing a message to be sent over a wire.<ref>{{Citation |last= Moss |first= Stephen |title= Final telegram to be sent. STOP |newspaper= The Guardian: International Edition |date= 10 July 2013 |url=https://www.theguardian.com/world/shortcuts/2013/jul/10/final-telegram-to-be-sent-india }}</ref><ref>Standage, Tom. (2014). ''[https://www.bloomsbury.com/us/the-victorian-internet-9781620405925/ The Victorian Internet: The Remarkable Story of the Telegraph and the Nineteenth Century's On-line Pioneers]''. Bloomsbury USA; Second Edition, Revised. {{ISBN|9781620405925}}</ref> In 1835, the American inventor [[Samuel Morse]] created a dots and dashes language system representing both letters and numbers, called the [[Morse code]], enabling text-based transmissions. In 1837, the British inventors [[William Fothergill Cooke]] and [[Charles Wheatstone]] obtained a patent for the first commercially viable [[Cooke and Wheatstone telegraph|telegraph]].<ref>Beauchamp, K. G. (2001). ''[https://books.google.com/books?id=k3XCkncd83AC&q=History+of+Telegraphy History of Telegraphy]''. (''Chapter 3''). The Institution of Engineering and Technology. {{ISBN|978-0852967928}}</ref>  By the 1840s, with the combination of the telegraph and Morse code, the semaphore system was replaced.<ref>{{Cite web|url=https://www.britannica.com/technology/telegraph|title=Telegraph - The end of the telegraph era|website=Encyclopedia Britannica}}</ref>  The telegraph continued to be used commercially for over 100 years and Morse code is still used by [[amateur radio]] enthusiasts.  Telecommunication evolved replacing the electric telegraph with the advent of [[wireless telegraphy]], [[teleprinter]], telephone, radio, television, [[satellite]], mobile phone, Internet and broadband.<ref>{{citation|title=ITU Radio Regulations|date=2012|chapter=Article 1.3|chapter-url=https://www.itu.int/dms_pub/itu-s/oth/02/02/S02020000244501PDFE.PDF|publisher=[[International Telecommunication Union]]|title-link=ITU Radio Regulations|archive-url=https://web.archive.org/web/20150319031957/https://www.itu.int/dms_pub/itu-s/oth/02/02/S02020000244501PDFE.PDF|archive-date=19 March 2015}}</ref><ref>Constitution and Convention of the International Telecommunication Union, Annex (Geneva, 1992)</ref>

==See also==
* [[Military communications]]
* [[Optical communication]]

== References ==
{{reflist}}

==Further reading==
* Burns, R.W. (2003). ''Communications: An International History of the Formative Years''. (''[https://books.google.com/books?id=7eUUy8-VvwoC&pg=PA29 Chapter 2]'') The Institution of Engineering and Technology. {{ISBN|978-0863413278}}.
* [http://spinroot.com/gerard/ Holzmann, Gerard J.] (1994). ''[http://spinroot.com/gerard/hist.html The Early History of Data Networks]''. Wiley-IEEE Computer Society Press; 1st edition. {{ISBN|978-0818667824}}.
* Pasley, C. W. (1823). ''[https://books.google.com/books?id=mWYUAAAAQAAJ&q=Description+Of+The+Universal+Telegraph+For+Day+And+Night+Signals Description of the Universal Telegraph for Day and Night Signals]''. T. Egerton Military Library. Egerton.
* Wilson, G. (1976). ''The Old Telegraphs''. Phillimore & Co. Chichester, West Sussex. {{ISBN|978-0900592799}}.

==External links==
{{Sister project links|d=no|n=no|b=no|v=no|voy=no|m=no|mw=no|s=no|wikt=yes|species=no|c=Category:Semaphore}}
* [https://www.youtube.com/watch?v=l0Sq7YueD1I&ab_channel=HistoryPod Youtube: "2nd March 1791: Claude Chappe sends the first message by semaphore machine"]
* [https://www.youtube.com/watch?v=WrNDeYjcCJA&t=6s&ab_channel=ArtoftheProblem YouTube: Information Theory part 4: Semaphores & signal fires]
* [https://www.youtube.com/watch?v=muMXPVCMI5o&ab_channel=Chrisstanger YouTube: TeleCommunication: Semaphore Systems]

{{List of writing systems}}
{{Telecommunications}}

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[[Category:Semaphore| ]]