Wikipedia

Semaphore

For other uses, seeSemaphore (disambiguation).

Semaphore(lit. 'apparatus for signalling';fromAncient Greekσῆμα(sêma)'mark, sign, token' andGreek-φόρος(-phóros)'bearer, carrier')[1]is the use of an apparatus to create a visualsignaltransmitted over distance.[2][3]A semaphore can be performed with devices including: fire, lights,flags,sunlight,and moving arms.[2][3][4]Semaphores can be used fortelegraphywhen arranged invisually connected networks,or for traffic signalling such as inrailway systems,ortraffic lightsin cities.[5]

Coastal semaphore using moving arms atScheveningen,circa 1799

Fire

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ThePhryctoriaewere a semaphore system used inAncient Greecefor the transmission of specific prearranged messages. Towers were built on selected mountaintops, so that one tower, thephryctoria,would be visible to the next tower, usually 30 km (20 mi) distant. Flames were lit on one tower, then the next tower would light a flame in succession.

TheByzantine beacon systemwas a semaphore developed in the 9th century during theArab–Byzantine wars.TheByzantine Empireused a system ofbeaconsto transmit messages from the border with theAbbasid CaliphateacrossAsia Minorto the Byzantine capital,Constantinople.The main line of beacons stretched over some 720 km (450 mi) with stations placed from 100 km (60 mi) to 60 km (35 mi). A message could be sent along the line in approximately one hour. Abonfirewas set at the first beacon and transmitted down the line to Constantinople.

Asmoke signalis 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

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Sailor with signal lamp

Asignal lampis a semaphore system using a visual signaling device, often utilizingMorse code.In the 19th century, theRoyal Navybegan using signal lamps. In 1867, then Captain, later Vice Admiral,Philip Howard Colombfor the first time began using dots and dashes from a signal lamp.[6]

The modernlighthouseis a semaphore using a tower, building, or another type of structure designed to emit light from a system of lamps andlensesand to serve as anavigational aidformaritime pilotsat sea or on inland waterways. Lighthouses mark dangerous coastlines, hazardousshoals,reefs,rocks, and safe entries to harbors; they also assist inaerial navigation.Originally lit by open fires and later candles, theArgand hollow wick lampandparabolic reflectorwere 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 oilwas also used with wicks as the source of light.Kerosenebecame popular in the 1870s and electricity and carbide (acetylene gas) began replacing kerosene around the turn of the 20th century. Carbide was promoted by theDalén lightwhich automatically lit the lamp at nightfall and extinguished it at dawn. The advent of electrification andautomatic lamp changersbegan to make lighthouse keepers obsolete. Improvements in maritime navigation and safety withsatellite navigationsystems like theGlobal Positioning System(GPS) have led to the phasing out of non-automated lighthouses across the world.[7]

Flags

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FlagAlpha bet
Main articles:Flag semaphoreandInternational maritime signal flags

Aflag semaphore[8]is thetelegraphysystem 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.[9]It is still used duringunderway replenishmentat sea and is acceptable for emergency communication in daylight or using lighted wands instead of flags, at night.

International maritime signal flagsare a system used by ships for communication at sea, each flag representing a specific letter, numeral, or message in theinternational maritime signal code.They are brightly coloured and easily distinguishable, serving purposes such as spelling out messages, identifying letters and numbers, signalling distress or requests for assistance and communicating nautical procedures. Standardized by theInternational Maritime Organization(IMO), these flags ensure global uniformity. They allow maritime professionals a tool for effective and clear communication at sea.

Sunlight

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Heliograph

Aheliographis a semaphore that signals by flashes ofsunlightusing a mirror, often inMorse code.The flashes are produced by momentarily pivoting themirroror by interrupting the sunlight with a shutter.[10]The heliograph was a simple but effective instrument for instantaneous optical communication over long distances during the late 19th and early 20th century.[10]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.[11]

Moving arms

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Optical telegraph

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Main article:Optical telegraph
Napoleonic semaphore line

In 1792Claude Chappe,a clergyman from France, invented aterrestrialsemaphore 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.[12][13][14][2][15]Relay towers were built with asightlineto each tower at separations of 10–30 km (5–20 mi). 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 atelescopeand 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 thanpost ridersfor conveying a message over long distances. The sightline between relay stations was limited bygeographyand weather. In addition, the visual communication would not be able to cross large bodies of water.

An example is during theNapoleonic era,stations were constructed to send and receive messages using the coined termNapoleonic semaphore.[16][17]This form of visual communication was so effective that messages that normally took days to communicate could now be transmitted in mere hours.[16]

Railway signal

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Railway pivot arms
Main article:Railway semaphore signal

Therailway semaphore signalis one of the earliest forms of fixedrailway signals.[18]These signals display their different indications totrain driversby changing the angle of inclination of a pivoted 'arms'.[3]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.[3]Designs have altered over the intervening years and colour light signals have replaced semaphore signals in most countries.

Hydraulic

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Main article:Hydraulic telegraph

Ahydraulic telegraphcan refer to either one of two different semaphore systems. The earliest one was developed in4th-century BC Greece,while the other was developed in19th-century AD Britain.The Greek system was deployed in combination withsemaphoricfires, while the latter British system was operated purely byhydraulicfluid pressure.

Decline

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Electric telegraph

In the early 19th century, theelectrical telegraphwas gradually invented allowing a message to be sent over a wire.[19][20]In 1835, the American inventorSamuel Morsecreated a dots and dashes language system representing both letters and numbers, called theMorse code,enabling text-based transmissions. In 1837, the British inventorsWilliam Fothergill CookeandCharles Wheatstoneobtained a patent for the first commercially viabletelegraph.[21]By the 1840s, with the combination of the telegraph and Morse code, the semaphore system was replaced.[22]The telegraph continued to be used commercially for over 100 years and Morse code is still used byamateur radioenthusiasts. Telecommunication evolved replacing the electric telegraph with the advent ofwireless telegraphy,teleprinter,telephone, radio, television,satellite,mobile phone, Internet and broadband.[23][24]

See also

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References

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  1. ^Harper, Douglas."semaphore".Online Etymology Dictionary.Retrieved15 August2021.
  2. ^abc"Semaphore | communications".Encyclopedia Britannica.
  3. ^abcd"semaphore | FactMonster".factmonster.
  4. ^Beauchamp, K. G. (2001).History of Telegraphy.(Chapter 1). The Institution of Engineering and Technology.ISBN978-0852967928
  5. ^"Semaphore - Traffic Signals - Road Signs and Traffic Signals - Dating - Landscape Change Program".glcp.uvm.edu.Retrieved15 August2021.
  6. ^Sterling, Christopher H., ed. (2008).Military Communications: From Ancient Times to the 21st Century.Santa Barbara, California: ABC-CLIO, Inc. p. 209.ISBN978-1-85109-732-6.
  7. ^"Maritime Heritage Program – National Park Service".Retrieved6 April2017.
  8. ^"Visual Signalling in the RCN - Semaphore".jproc.ca.
  9. ^"History of Semaphore"(PDF).Royal Navy Communications Branch Museum/Library.Archived fromthe original(PDF)on 11 May 2021.Retrieved16 May2020.
  10. ^abWoods, Daniel (2008)."Heliograph and Mirrors".In Sterling, Christopher (ed.).Military Communications: From Ancient Times to the 21st Century.ABC-CLIO. p. 208.ISBN978-1851097326.
  11. ^Major J. D. HarrisWIRE AT WAR – Signals communication in the South African War 1899–1902.Retrieved on 1 June 2008. Discussion of heliograph use in the Boer War.
  12. ^Burns, R. W. (2004)."Chapter 2: Semaphore Signalling".Communications: an international history of the formative years.ISBN978-0-86341-327-8.
  13. ^"Telegraph".Encyclopædia Britannica.Vol. 10 (6th ed.). 1824. pp.645–651.
  14. ^David Brewster, ed. (1832)."Telegraph".The Edinburgh Encyclopaedia.Vol. 17. pp.664–667.
  15. ^"J-M. Dilhac," The Telegraph of Claude Chappe: An Optical Telecommunication Network for the XVIIIrd Century. ""(PDF).
  16. ^ab"How Napoleon's semaphore telegraph changed the world".BBC News.16 June 2013.Retrieved23 December2020.
  17. ^"Napoleonic Telecommunications: The Chappe Semaphore Telegraph".Shannon Selin.15 May 2020.
  18. ^"The Origin of the Railway Semaphore".Mysite.du.edu.Retrieved17 June2013.
  19. ^Moss, Stephen (10 July 2013),"Final telegram to be sent. STOP",The Guardian: International Edition
  20. ^Standage, Tom. (2014).The Victorian Internet: The Remarkable Story of the Telegraph and the Nineteenth Century's On-line Pioneers.Bloomsbury USA; Second Edition, Revised.ISBN9781620405925
  21. ^Beauchamp, K. G. (2001).History of Telegraphy.(Chapter 3). The Institution of Engineering and Technology.ISBN978-0852967928
  22. ^"Telegraph - The end of the telegraph era".Encyclopedia Britannica.
  23. ^"Article 1.3"(PDF),ITU Radio Regulations,International Telecommunication Union,2012, archived fromthe original(PDF)on 19 March 2015
  24. ^Constitution and Convention of the International Telecommunication Union, Annex (Geneva, 1992)

Further reading

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