Semaphore

For other uses, see Semaphore (disambiguation).

Coastal semaphore using moving arms at Scheveningen, circa 1799

Semaphore (Template:Lit; from Ancient Greek σῆμα (sêma) 'mark, sign, token', and Greek -φόρος (-phóros) 'bearer, carrier')<ref>Harper, Douglas. "semaphore". Online Etymology Dictionary. Retrieved 15 August 2021.</ref> is the use of an apparatus to create a visual signal transmitted over distance.<ref name="EB">"Semaphore | communications". Encyclopedia Britannica.</ref><ref name="FM">"semaphore | FactMonster". www.factmonster.com.</ref> A semaphore can be performed with devices including: fire, lights, flags, sunlight, and moving arms.<ref name="EB" /><ref name="FM" /><ref>Beauchamp, K. G. (2001). History of Telegraphy. (Chapter 1). The Institution of Engineering and Technology. ISBN 978-0852967928</ref> Semaphores can be used for telegraphy when arranged in visually connected networks, or for traffic signalling such as in railway systems, or traffic lights in cities.<ref></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 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 beacons 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 with stations placed from to . 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

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></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 lenses and to serve as a navigational aid for maritime pilots at sea or on inland waterways. Lighthouses mark dangerous coastlines, hazardous shoals, reefs, rocks, and safe entries to harbors; they also assist in aerial navigation. Originally lit by open fires and later candles, the 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 changers 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></ref>

Flags

Flag alphabet

A flag semaphore<ref></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"></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

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></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 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

Napoleonic semaphore line

In 1792 Claude Chappe, a clergyman from France, invented a terrestrial 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"></ref><ref name="EncyBrit1824"></ref><ref name="EdEnc1832"></ref><ref name="EB" /><ref></ref> Relay towers were built with a sightline to each tower at separations of . 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"></ref><ref name="Shannon"></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

Railway pivot arms

The railway semaphore signal is one of the earliest forms of fixed railway signals.<ref></ref> These signals display their different indications to 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

A hydraulic telegraph can refer to either one of two different semaphore systems. The earliest one was developed in 4th-century BC Greece, while the other was developed in 19th-century AD Britain. The Greek system was deployed in combination with semaphoric fires, while the latter British system was operated purely by hydraulic fluid pressure.

Decline

Electric telegraph

In the early 19th century, the electrical telegraph was gradually invented allowing a message to be sent over a wire.<ref></ref><ref>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. </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 telegraph.<ref>Beauchamp, K. G. (2001). History of Telegraphy. (Chapter 3). The Institution of Engineering and Technology. </ref> By the 1840s, with the combination of the telegraph and Morse code, the semaphore system was replaced.<ref></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></ref><ref>Constitution and Convention of the International Telecommunication Union, Annex (Geneva, 1992)</ref>

See also

• Military communications
• Optical communication

Further reading

• Burns, R.W. (2003). Communications: An International History of the Formative Years. (Chapter 2) The Institution of Engineering and Technology. .
• Holzmann, Gerard J. (1994). The Early History of Data Networks. Wiley-IEEE Computer Society Press; 1st edition. .
• Pasley, C. W. (1823). 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. .

External links

• Youtube: "2nd March 1791: Claude Chappe sends the first message by semaphore machine"
• YouTube: Information Theory part 4: Semaphores & signal fires
• YouTube: TeleCommunication: Semaphore Systems