Editing Optical communication (section)

=== Semaphore line ===
{{Main|Optical telegraph}}
[[File:OptischerTelegraf.jpg|thumb|left|upright|A replica of a [[Chappe telegraph]] tower (18th century)]]
A 'semaphore telegraph', also called a 'semaphore line', 'optical telegraph', 'shutter telegraph chain', '[[Chappe telegraph]]', or 'Napoleonic semaphore', is a system used for conveying information by means of visual signals, using towers with pivoting arms or shutters, also known as blades or paddles. Information is encoded by the position of the mechanical elements; it is read when the shutter is in a fixed position.<ref name="EncyBrit1824"/><ref name="EdEnc1832">[https://books.google.com/books?id=VhEbAQAAMAAJ&pg=PA657 Telegraph], Volume 17 of The Edinburgh encyclopaedia, pp. 664–667, 1832 David Brewster, ed.</ref>

Semaphore lines were a precursor of the [[electrical telegraph]]. They were far faster than [[post rider]]s for conveying a message over long distances, but far more expensive and less private than the electrical telegraph lines which would later replace them. The maximum distance that a pair of semaphore telegraph stations can bridge is limited by geography, weather and the availability of light; thus, in practical use, most optical telegraphs used lines of relay stations to bridge longer distances. Each relay station would also require its complement of skilled operator-observers to convey messages back and forth across the line.

The modern design of semaphores was first foreseen by the British [[polymath]] [[Robert Hooke]], who first gave a vivid and comprehensive outline of visual telegraphy in a 1684 submission to the [[Royal Society]]. His proposal (which was motivated by military concerns following the [[Battle of Vienna]] the preceding year) was not put into practice during his lifetime.<ref>Calvert, J.B. [https://web.archive.org/web/20120208081932/http://mysite.du.edu/~jcalvert/railway/semaphor/semhist.htm The Origin of the Railway Semaphore<!-- Bot generated title -->], [[Boston University]], 15 April 2000, Revised 4 May 2007.</ref><ref>McVeigh, Daniel P. [http://www.ilt.columbia.edu/projects/bluetelephone/html/part2.html An Early History of the Telephone: 1664-1865, Part 2<!-- Bot generated title -->] {{Webarchive|url=https://web.archive.org/web/20121128120005/http://www.ilt.columbia.edu/projects/bluetelephone/html/part2.html |date=2012-11-28 }}, [[Columbia University|Columbia University in The City of New York]], Institute For Learning Technologies, 2000.</ref>

The first operational optical semaphore line arrived in 1792, created by the French engineer [[Claude Chappe]] and his brothers, who succeeded in covering [[France]] with a network of 556 stations stretching a total distance of {{convert|4,800|km}}. It was used for military and national communications until the 1850s.

Many national services adopted signaling systems different from the Chappe system. For example, [[UK|Britain]] and [[Sweden]] adopted systems of shuttered panels (in contradiction to the Chappe brothers' contention that angled rods are more visible). In [[Spain]], the engineer [[Agustín de Betancourt]] developed his own system which was adopted by that state. This system was considered by many experts in Europe better than Chappe's, even in France.{{cn|date=August 2023}}

These systems were popular in the late 18th to early 19th century but could not compete with the electrical telegraph, and went completely out of service by 1880.<ref name="Burns2004"/>