Semaphore line

Semaphore line
For the now closed railway in Adelaide, Australia, see Semaphore railway line, Adelaide.
A Chappe telegraph at Louvre, France

A semaphore telegraph, optical telegraph, shutter telegraph chain, Chappe telegraph, or Napoleonic semaphore is a system of conveying information by means of visual signals, using towers with pivoting 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. These systems were popular in the late 18th to early 19th century.[1][2][3] In modern usage, "semaphore line" and "optical telegraph" may refer to a relay system using flag semaphore, and "optical telegraph" may refer to a heliograph (optical telegraphy using mirror-directed sunlight reflections).

Semaphore lines were a precursor of the electrical telegraph. They were far faster than post riders for bringing a message over long distances, but far more expensive and less private than the electrical telegraph lines which would replace them. The distance that an optical telegraph can bridge is limited by geography and weather; thus, in practical use, most optical telegraphs used lines of relay stations to bridge longer distances.



Optical telegraphy dates from ancient times, in the form of hydraulic telegraphs, torches (as used by ancient Greeks) and smoke signals.

Modern design of semaphores was first foreseen by the English scientist Robert Hooke, who first gave a vivid and comprehensive outline of visual telegraphy to the Royal Society in a submission dated 1684 in which he outlined many practical details. The system (motivated by military concerns, following the recent Battle of Vienna in 1683) was never put into practice.[4][5]

The first achieved optical telegraph arrived only in 1792 from the French engineer Claude Chappe and his brothers, who succeeded in covering France with a network of 556 stations stretching a total distance of 4,800 kilometres. It was used for military and national communications until the 1850s.

Many national services adopted signaling systems different from the Chappe system. For example, 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.


A Chappe semaphore tower near Saverne, France

There was a desperate need for swift and reliable communications in France during the period of 1790–1795. It was the height of the French revolution, and France was surrounded by the enemy forces of Britain, the Netherlands, Prussia, Austria, and Spain. The cities of Marseilles and Lyon were in revolt, and the British Fleet held Toulon. In this situation the only advantage France held was the lack of cooperation between the allied forces due to their inadequate lines of communications.

The Chappe brothers in the summer of 1790 set about devising a system of communication that would allow the central government to receive intelligence and to transmit orders in the shortest possible time. On March 2, 1791 at 11 A.M., Chappe and his brother sent the message “si vous réussissez, vous serez bientôt couverts de gloire” (If you succeed, you will soon bask in glory) between Brulon and Parce, a distance of ten miles (16 km). The first means used a combination of black and white panels, clocks, telescopes, and codebooks to send their message.

The Chappes carried out experiments during the next two years, and on two occasions their apparatus at Place de l'Étoile, Paris was destroyed by mobs who thought they were communicating with royalist forces. However in the summer of 1792 Claude was appointed Ingénieur-Télégraphiste and charged with establishing a line of stations between Paris and Lille, a distance of 230 kilometres (about 143 miles). It was used to carry dispatches for the war between France and Austria. In 1794, it brought news of a French capture of Condé-sur-l'Escaut from the Austrians less than an hour after it occurred. The first symbol of a message to Lille would pass through 15 stations in only nine minutes. The speed of the line varied with the weather, but the line to Lille typically transferred 36 symbols, a complete message, in about 32 minutes.

Paris to Strasbourg with 50 stations was the next line and others followed soon after. By 1824, the Chappe brothers were promoting the semaphore lines for commercial use, especially to transmit the costs of commodities. Napoleon Bonaparte saw the military advantage in being able to transmit information between locations, and carried a portable semaphore with his headquarters. This allowed him to coordinate forces and logistics over longer distances than any other army of his time. However because stations had to be within sight of each other, and because the efficient operation of the network required well trained and disciplined operators, the costs of administration and wages were a continuous source of financial difficulties. Only when the system was funded by the proceeds of its own lottery did costs come under control.

In 1821 Norwich Duff, a young British Naval officer, visiting Clermont-en-Argonne, walked up to the telegraph station there and engaged the signalman in conversation. Here is his note of the man's information:

The pay is twenty five sous per day and he [the signalman] is obliged to be there from day light till dark, at present from half past three till half past eight; there are only two of them and for every minute a signal is left without being answered they pay five sous: this is a part of the branch which communicates with Strasburg and a message arrives there from Paris in six minutes it is here in four.


The Chappe brothers determined by experiment that it was easier to see the angle of a rod than to see the presence or absence of a panel. Their semaphore was composed of black movable wooden arms, the position of which indicated alphabetic letters. With counterweights (named forks) on the arms, the Chappe system was controlled by only two handles and was mechanically simple and reasonably rugged. Each of the two 2-metre-long arms showed seven positions, and the 4.6-metre-long cross bar connecting the two arms had four different angles, for a total of 196 symbols (7x7x4). Night operation with lamps on the arms was unsuccessful.

To speed up transmission and to provide some semblance of security a code book was developed for use with semaphore lines. The Chappes' corporation used a code that took 92 of the basic symbols two at a time to yield 8,464 coded words and phrases.

From 1803 on, the French also used the 3-arm Depillon semaphore at coastal locations to provide warning of British incursions.[1]


Replica of Swedish optical telegraph tower.

At the same time as Chappe, the Swedish inventor Abraham Niclas Edelcrantz experimented with the optical telegraph in Sweden. In 1794 he inaugurated his telegraph with a poem dedicated to the Swedish King on his birthday. The message went from the Palace in Stockholm to the King at Drottningholm.

Edelcrantz eventually developed his own system which was quite different from its French counterpart and nearly twice as fast. The system was based on ten collapsible iron shutters. The various positions of the shutters formed combinations of numbers which were translated into letters, words or phrases via codebooks. The telegraph network consisted of telegraph stations positioned at about 10 kilometres from one another.

Soon telegraph circuits linking castles and fortresses in the neighbourhood of Stockholm were set up and the system was extended to Grisslehamn and Åland. Subsequently telegraph circuits were introduced between Gothenburg and Marstrand, at Helsingborg and between Karlskrona and its fortresses. Sweden was the second country in the world, after France, to introduce an optical telegraph network. The Swedish optical telegraph network was restricted to the archipelagoes of Stockholm, Gothenburg and Karlskrona. Like its French counterpart, it was mainly used for military purposes.


Lord George Murray, stimulated by reports of the Chappe semaphore, proposed a system of visual telegraphy to the British Admiralty in 1795.[3] He employed rectangular framework towers with six large octagonal shutters on horizontal axes that flipped between horizontal and vertical positions to signal [6] . The Rev. Mr Gamble also proposed two distinct five element systems in 1795: one using five shutters, and one using five ten foot poles.[3] The British Admiralty accepted Murray's system in September 1795, and the first system was the 15 site chain from London to Deal.[7] Messages passed from London to Deal in about sixty seconds, and sixty-five sites were in use by 1808.[7] Each shutter was five feet high.[1] In 1816, Murray's shutter telegraphs were replaced by simpler semaphores invented by Sir Home Popham.[2] A Popham semaphore was a single fixed vertical 30 foot pole, with two movable 8 foot arms attached to the pole by horizontal pivots at their ends, one arm at the top of the pole, and the other arm at the middle of the pole.[1][2] The signals of the Popham semaphore were found to be much more visible than those of the Murray semaphore.[1] Popham's 2-arm semaphore was modeled after the 3-arm Depillon French semaphore.[1]

Chains of Murray's shutter telegraph stations were built along these routes:

Diagram of U.K. Murray six-shutter system, with shutter 6 in the horizontal position, and shutters 1-5 vertical
Liverpool - Holyhead

Liverpool, Bidston, Hilbre Island, Voel Nant, Foryd, Llysfaen, Puffin Island, Point Lynas, Carreglwyd, Cefn Du, Holyhead [8]

London - Deal and Sheerness

Admiralty (London), West Square Southwark, New Cross, Shooter's Hill, Swanscombe, Gad's Hill, Callum Hill, Beacon Hill (Faversham, branch point), Shottenden, Barham Downs, Betteshanger, Deal.

(branch) Beacon Hill (Faversham), Tonge, Barrow Hill, Sheerness.

London - Great Yarmouth
St Albans High Street in 1807, showing the shutter telegraph on top of the city's Clock Tower.

Admiralty (London), Hampstead Heath (Telegraph Hill), Woodcock Hill, St Albans, Dunstable Downs, Lilley Hoo, Baldock, Royston, Gog Magog Hills, Newmarket (Side Hill), Icklingham, Barnham, East Harling, Carleton Rode, Wreningham, Norwich, Strumpshaw, Great Yarmouth.

London - Portsmouth and Plymouth

Admiralty (London), Chelsea Royal Hospital, Putney Heath, Cabbage Hill, Netley Heath, Hascombe, Blackdown, Beacon Hill (branch point), Portsdown Hill, Portsmouth (Southsea Common).

(branch) Beacon Hill, Chalton, Wickham, Town Hill, Toot Hill, Bramshaw, Pistle Down, Chalbury, Blandford racecourse, Belchalwell, Nettlecombe Tout, High Stoy, Toller Down, Lamberts Castle, Dalwood Common, St Cyrus, Rockbeare, Gt Haldon, South Knighton, Marley, Lee, Saltram, Plymouth.

The shutter stations were temporary wooden huts, and at the conclusion of the Napoleonic wars they were no longer necessary. In 1816 they were replaced by a simpler semaphore system.[3] However the Admiralty decided to establish a permanent link to Portsmouth and built a chain of semaphore stations. These were operational from 1822 until 1847, when the railway and electric telegraph provided a better means of communication. The semaphore did not use the same locations as the shutter chain, but followed almost the same route with 15 stations -

Admiralty (London), Chelsea Royal Hospital, Putney Heath, Coombe Warren, Coopers Hill, Chatley Heath, Pewley Hill, Bannicle Hill, Haste Hill (Haslemere), Holder Hill, (Midhurst), Beacon Hill, Compton Down, Camp Down, Lumps Fort (Southsea) and Portsmouth Dockyard. The semaphore tower at Chatley Heath, which replaced the Netley Heath station of the shutter telegraph, has been restored by Surrey County Council and is open to the public.

A semaphore-based successor for the London to Plymouth shutter telegraph chain, branching much closer to London, at Chatley Heath in Surrey, was started but abandoned before completion.

Many of the prominences on which the towers were built are known as 'Telegraph Hill' to this day. As in France the network required lavish amounts of money and manpower to operate and could only be justified as a defence need.

Other countries

Optical telegraph of Claude Chappe on the Litermont near Nalbach, Germany.
Optical telegraph in the harbour of Bremerhaven, Germany.

Once it had proved its success, the optical telegraph was imitated in many other countries, especially after it was used by Napoleon to coordinate his empire and army. In most of these countries, the postal authorities operated the semaphore lines.

In Canada, Prince Edward, Duke of Kent established the first semaphore line in North America. In operation by 1800, it ran between the city of Halifax and the town of Annapolis in Nova Scotia, and across the Bay of Fundy to Saint John and Fredericton in New Brunswick. In addition to providing information on approaching ships, the Duke used the system to relay military commands, especially as they related to troop discipline. The Duke had envisioned the line reaching as far as the British garrison at Quebec City. However, the many hills and coastal fog meant the towers needed to be placed relatively close together to ensure visibility. The required labour to build and continually man so many stations taxed the already stretched-thin British military and there is doubt the New Brunswick line was ever in operation. With the exception of the towers around Halifax harbour, the system was abandoned shortly after the Duke's departure in August 1800.[9][10]

In 1801, the Danish post office installed a semaphore line across the Great Belt strait, Storebæltstelegrafen, between islands Funen and Zealand with stations at Nyborg on Funen, on the small island Sprogø in the middle of the strait, and at Korsør on Zealand. It was in use until 1865.[11]

The Kingdom of Prussia began with a line 750 kilometres long between Berlin and Coblenz in 1833, and in Russia, Tsar Nicolas I inaugurated the line between Moscow and Warsaw (1200 km) in 1833; this needed 220 stations manned by 1320 operators.

In the United States the first optical telegraph was built by Jonathan Grout. It was a 104-kilometre line connecting Martha's Vineyard with Boston, and its purpose was to transmit news about shipping. One of the principal hills in San Francisco, California is also named "Telegraph Hill", after the semaphore telegraph which was established there in 1849 to signal the arrival of ships into San Francisco Bay.

The semaphores were successful enough that Samuel Morse failed to sell the electrical telegraph to the French government. However, France finally committed to replace semaphores with electric telegraphs in 1846. Note that electric telegraphs are both more private and almost completely unaffected by weather. Many contemporaries predicted the failure of electric telegraphs because "they are so easy to cut."[12] The last stationary semaphore link in regular service was in Sweden, connecting an island with a mainland telegraph line. It went out of service in 1880.

In Ireland, Richard Lovell Edgeworth (1744–1817) proposed a telegraph there when a French invasion was anticipated in 1794, and again in 1796; however, the proposal was not implemented. Soon, the British forces fighting Napoleon in Portugal found that the Portuguese army had a very capable semaphore system giving the Duke of Wellington a decisive advantage in intelligence.

Semaphore in fiction

  • Pavane, an alternate history novel by Keith Roberts, features a society where long distance communication is by a network of semaphores operated by the powerful Guild of Signallers.
  • Terry Pratchett's Discworld novels describe a system of 8-shutter semaphore towers, known as Clacks.
  • In Chapter 60 ("The Telegraph") of Alexandre Dumas' The Count of Monte Cristo, the title character describes with fascination the semaphore line's moving arms. "I had often seen one placed at the end of a road on a hillock, and in the light of the sun its black arms, bending in every direction, always reminded me of the claws of an immense beetle..." He later bribes a semaphore operator to relay a false message in order to manipulate the French financial market.
  • In chapter 10 of C. S. Forester's Hornblower and the Hotspur, the destruction of a French semaphore tower and a shore battery is a key plot point. A similar event is also the focus of the seventh episode of the A&E Horatio Hornblower series,
  • In David Weber's Safehold series, a world-wide Semaphore system is used by the Church to help them maintain their dominion over the world.
  • In Alastair Reynolds' Terminal World, the distant-future terrain is criss-crossed with semaphore lines relaying information between the one remaining city, Spearpoint, outlying communities and the airborne community Swarm.
  • In the young adult fiction book Death Cloud by Andy Lane, Mycroft Holmes tells 14-year-old Sherlock Holmes about semaphore stations, commenting about his school beforehand, saying "All the Latin a boy can cram into his skull, but nothing of practical use."

See also


Crowley, David and Heyer, Paul (ed) (2003) 'Chapter 17: The optical telegraph' Communication in History: Technology, Culture and Society (Fourth Edition) Allyn and Bacon, Boston pp. 123–125

  1. ^ a b c d e f Chapter 2: Semaphore Signalling ISBN 9780863413278 Communications: an international history of the formative years R. W. Burns, 2004
  2. ^ a b c Telegraph Vol 10, Encyclopaedia Britannica, 6th Edition, 1824 pp. 645-651
  3. ^ a b c d Telegraph, Volume 17 of The Edinburgh encyclopaedia, pp. 664-667, 1832 David Brewster, ed.
  4. ^ The Origin of the Railway Semaphore
  5. ^ History of the Telephone part2
  6. ^ Lieutenant Watson's Telegraph Mechanics' magazine, Volume 8 No. 222, Knight and Lacey, 1828, pages 294-299
  7. ^ a b F.B. Wrixon (2005), ISBN 9781579124854 Codes, Ciphers, Secrets and Cryptic Communication pp. 444-445 cover Murray's shutter telegraph in the U.K., with codes.
  8. ^ Faster Than The Wind, The Liverpool to Holyhead Telegraph, Frank Large, an avid publication ISBN 0952102099
  9. ^ Raddall, Thomas H. (1971), Warden of the North, Toronto, Canada: McClelland and Stewart Limited, .
  10. ^ Rens, Jean-Guy (2001), The invisible empire: A history of the telecommunications industry in Canada, Montreal, Canada: McGill-Queen's University Press, .
  11. ^ The Age of Invention 1849–1920, Post & Tele Museum Danmark, website visited on May 8, 2010.
  12. ^ Holzmann, Gerard. "Data Communications: The First 2500 Years". Retrieved 28 June 2011. 

Further reading

  • The Old Telegraphs, Geoffrey Wilson, Phillimore & Co Ltd 1976 ISBN 0900592796
  • Faster Than The Wind, The Liverpool to Holyhead Telegraph, Frank Large, an avid publication ISBN 0952102099
  • The early history of data networks, Gerard Holzmann and Bjorn Pehrson, Wiley Publ., 2003, ISBN 0-8186-6782-6
  • Semaphore Signaling, Chapter 2 of: Communications: an international history of the formative years, R.W. Burns, Institution of Electrical Engineers, 2004 ISBN 9780863413278

External links

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