Semaphore Line

An optical telegraph is a line of stations, typically towers, for the purpose of conveying textual information by means of visual signals. There are two main types of such systems; the semaphore telegraph which uses pivoted indicator arms and conveys information according to the direction the indicators point, and the shutter telegraph which uses panels that can be rotated to block or pass the light from the sky behind to convey information.

The most widely used system was invented in 1792 in France by Claude Chappe, and was popular in the late eighteenth to early nineteenth centuries. This system is often referred to as ''semaphore'' without qualification. Lines of relay towers with a semaphore rig at the top were built within line of sight of each other, at separations of . Operators at each tower would watch the neighboring 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 system was much faster than post riders for conveying a message over long distances, and also had cheaper long-term operating costs, once constructed. Half a century later, semaphore lines were replaced by the electrical telegraph, which was cheaper, faster, and more private. The line-of-sight distance between relay stations was limited by geography and weather, and prevented the optical telegraph from crossing wide expanses of water, unless a convenient island could be used for a relay station. A modern derivative of the semaphore system is flag semaphore, signalling with hand-held flags.

Etymology and terminology

The word ''semaphore'' was coined in 1801 by the French inventor of the semaphore line itself, Claude Chappe. He composed it from the Greek elements σῆμα (sêma, "sign"); and from φορός (phorós, "carrying"), or φορά (phorá, "a carrying") from φέρειν (phérein, "to bear"). Chappe also coined the word ''tachygraph'', meaning "fast writer". However, the French Army preferred to call Chappe's semaphore system the ''telegraph'', meaning "far writer", which was coined by French statesman André François Miot de Mélito.

The word ''semaphoric'' was first printed in English in 1808: "The newly constructed Semaphoric telegraphs (...) have been blown up", in a news report in The Naval Chronicle. The first use of the word ''semaphore'' in reference to English use was in 1816: "The improved Semaphore has been erected on the top of the Admiralty", referring to the installation of a simpler telegraph invented by Sir Home Popham. Semaphore telegraphs are also called, "Chappe telegraphs" or "Napoleonic semaphore".

Early designs

Optical telegraphy dates from ancient times, in the form of hydraulic telegraphs, torches (as used by ancient cultures since the discovery of fire) and smoke signals. Modern design of semaphores was first foreseen by the British polymath Robert Hooke, who gave a vivid and comprehensive outline of visual telegraphy to the Royal Society in a 1684 submission in which he outlined many practical details. The system (which was motivated by military concerns, following the Battle of Vienna in 1683) was never put into practice.

One of the first experiments of optical signalling was carried out by the Anglo-Irish landowner and inventor, Sir Richard Lovell Edgeworth in 1767. He placed a bet with his friend, the horse racing gambler Lord March, that he could transmit knowledge of the outcome of the race in just one hour. Using a network of signalling sections erected on high ground, the signal would be observed from one station to the next by means of a telescope. The signal itself consisted of a large pointer that could be placed into eight possible positions in 45 degree increments. A series of two such signals gave a total 64 code elements and a third signal took it up to 512. He returned to his idea in 1795, after hearing of Chappe's system.

Prevalence

France

Credit for the first successful optical telegraph goes to the French engineer Claude Chappe and his brothers in 1792, who succeeded in covering France with a network of 556 stations stretching a total distance of . ''Le système Chappe'' was used for military and national communications until the 1850s.

Development in France

During 1790–1795, at the height of the French Revolution, France needed a swift and reliable military communications system to thwart the war efforts of its enemies. France was surrounded by the forces of Britain, the Netherlands, Prussia, Austria, and Spain, the cities of Marseille and Lyon were in revolt, and the British Fleet held Toulon. The only advantage France held was the lack of cooperation between the allied forces due to their inadequate lines of communication. In mid-1790, the Chappe brothers 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. Chappe considered many possible methods including audio and smoke. He even considered using electricity, but could not find insulation for the conductors that would withstand the high-voltage electrostatic sources available at the time.

Chappe settled on an optical system and the first public demonstration occurred on 2 March 1791 between Brûlon and Parcé, a distance of . The system consisted of a modified pendulum clock at each end with dials marked with ten numerals. The hands of the clocks almost certainly moved much faster than a normal clock. The hands of both clocks were set in motion at the same time with a synchronisation signal. Further signals indicated the time at which the dial should be read. The numbers sent were then looked up in a codebook. In their preliminary experiments over a shorter distance, the Chappes had banged a pan for synchronisation. In the demonstration, they used black and white panels observed with a telescope. The message to be sent was chosen by town officials at Brûlon and sent by René Chappe to Claude Chappe at Parcé who had no pre-knowledge of the message. The message read "si vous réussissez, vous serez bientôt couverts de gloire" (If you succeed, you will soon bask in glory). It was only later that Chappe realised that he could dispense with the clocks and the synchronisation system itself could be used to pass messages.

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. Their cause was assisted by Ignace Chappe being elected to the Legislative Assembly. 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. Another line of 50 stations was completed in 1798, covering 488 km between Paris and Strasbourg. From 1803 on, the French also used the 3-arm Depillon semaphore at coastal locations to provide warning of British incursions.

Chappe system technical operation

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 two black movable wooden arms, connected by a cross bar; the positions of all three of these components together indicated an alphabetic letter. With counterweights (named ''forks'') on the arms, the Chappe system was controlled by only two handles and was mechanically simple and reasonably robust. Each of the two 2-metre-long arms could display seven positions, and the 4.6-metre-long cross bar connecting the two arms could display four different angles, for a total of 196 symbols (7×7×4). 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.

The revised Chappe system of 1795 provided not only a set of codes but also an operational protocol intended to maximize line throughput. Symbols were transmitted in cycles of "2 steps and 3 movements."

* Step 1, movement 1 (setup): The operator turned the indicator arms to align with the cross bar, forming a non-symbol, and then turned the cross bar into position for the next symbol.
* Step 1, movement 2 (transmission): The operator positioned the indicator arms for current symbol and waited for the downline station to copy it.
* Step 2, movement 3 (completion): The operator turned the cross bar to a vertical or horizontal position, indicating the end of a cycle.

In this manner, each symbol could propagate down the line as quickly as operators could successfully copy it, with acknowledgement and flow control built into the protocol. A symbol sent from Paris took 2 minutes to reach Lille through 22 stations and 9 minutes to reach Lyon through 50 stations. A rate of 2–3 symbols per minute was typical, with the higher figure being prone to errors. This corresponds to only 0.4–0.6 wpm, but with messages limited to those contained in the code book, this could be dramatically increased.

History in France

After Chappe's initial line (between Paris and Lille), the Paris to Strasbourg with 50 stations followed soon after (1798). Napoleon Bonaparte made full use of the telegraph by obtaining speedy information on enemy movements. In 1801 he had Abraham Chappe build an extra-large station to transmit across the English Channel in preparation for an invasion of Britain. A pair of such stations were built on a test line over a comparable distance. The line to Calais was extended to Boulogne in anticipation and a new design station was briefly in operation at Boulogne, but the invasion never happened. In 1812, Napoleon took up another design of Abraham Chappe for a mobile telegraph that could be taken with him on campaign. This was still in use in 1853 during the Crimean War.

The invention of the telegraph was followed by an enthusiasm concerning its potential to support direct democracy. For instance, based on Rousseau's argument that direct democracy was improbable in large constituencies, the French Intellectual Alexandre-Théophile Vandermonde commented:

The operational costs of the telegraph in the year 1799/1800 were 434,000 francs ($1.2 million in 2015 in silver costsRodney Edvinsson
Historical Currency Converter, accessed 8 January 2021.
/ref>). In December 1800, Napoleon cut the budget of the telegraph system by 150,000 francs ($400,000 in 2015) leading to the Paris-Lyons line being temporarily closed. Chappe sought commercial uses of the system to make up the deficit, including use by industry, the financial sector, and newspapers. Only one proposal was immediately approved—the transmission of results from the state-run lottery. No non-government uses were approved. The lottery had been abused for years by fraudsters who knew the results, selling tickets in provincial towns after the announcement in Paris, but before the news had reached those towns.

In 1819 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 network was reserved for government use, but an early case of wire fraud occurred in 1834 when two bankers, François and Joseph Blanc, bribed the operators at a station near Tours on the line between Paris and Bordeaux to pass Paris stock exchange information to an accomplice in Bordeaux. It took three days for the information to travel the 300 mile distance, giving the schemers plenty of time to play the market. An accomplice at Paris would know whether the market was going up or down days before the information arrived in Bordeaux via the newspapers, after which Bordeaux was sure to follow. The message could not be inserted in the telegraph directly because it would have been detected. Instead, pre-arranged deliberate errors were introduced into existing messages which were visible to an observer at Bordeaux. Tours was chosen because it was a division station where messages were purged of errors by an inspector who was privy to the secret code used and unknown to the ordinary operators. The scheme would not work if the errors were inserted prior to Tours. The operators were told whether the market was going up or down by the colour of packages (either white or grey paper wrapping) sent by mail coach, or, according to another anecdote, if the wife of the Tours operator received a package of socks (down) or gloves (up) thus avoiding any evidence of misdeed being put in writing. The scheme operated for two years until it was discovered in 1836.

The French optical system remained in use for many years after other countries had switched to the electrical telegraph. Partly, this was due to inertia; France had the most extensive optical system and hence the most difficult to replace. But there were also arguments put forward for the superiority of the optical system. One of these was that the optical system is not so vulnerable to saboteurs as an electrical system with many miles of unguarded wire. Samuel Morse failed to sell the electrical telegraph to the French government. Eventually the advantages of the electrical telegraph of improved privacy, and all-weather and nighttime operation won out. A decision was made in 1846 to replace the optical telegraph with the Foy–Breguet electrical telegraph after a successful trial on the Rouen line. This system had a display which mimicked the look of the Chappe telegraph indicators to make it familiar to telegraph operators. Jules Guyot issued a dire warning of the consequences of what he considered to be a serious mistake. It took almost a decade before the optical telegraph was completely decommissioned. One of the last messages sent over the French semaphore was the report of the fall of Sebastopol in 1855.

Sweden

Sweden was the second country in the world, after France, to introduce an optical telegraph network.David Greene, ''Light and Dark: An Exploration in Science, Nature, Art and Technology'', p. 159, CRC Press, 2016 . Its network became the second most extensive after France. The central station of the network was at the Katarina Church in Stockholm. The system was faster than the French system, partly due to the Swedish control panelHolzmann & Pehrson, pp. 104–105 and partly to the ease of transcribing the octal code (the French system was recorded as pictograms).Holzmann & Pehrson, p. 180 The system was used primarily for reporting the arrival of ships, but was also useful in wartime for observing enemy movements and attacks.Holzmann & Pehrson, p. 117

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.

Development in Sweden

Inspired by news of the Chappe telegraph, the Swedish inventor Abraham Niclas Edelcrantz experimented with the optical telegraph in Sweden. He constructed a three-station experimental line in 1794 running from the royal castle in Stockholm, via Traneberg, to the grounds of Drottningholm Castle, a distance of . The first demonstration was on 1 November, when Edelcrantz sent a poem dedicated to the king, Gustav IV Adolf, on his fourteenth birthday. On 7 November the king brought Edelcrantz into his Council of Advisers with a view to building a telegraph throughout Sweden, Denmark, and Finland.

Edelcrantz system technical operation

After some initial experiments with Chappe-style indicator arms, Edelcrantz settled on a design with ten iron shutters. Nine of these represented a 3-digit octal number and the tenth, when closed, meant the code number should be preceded by "A". This gave 1,024 codepoints which were decoded to letters, words or phrases via a codebook. The telegraph had a sophisticated control panel which allowed the next symbol to be prepared while waiting for the previous symbol to be repeated on the next station down the line. The control panel was connected by strings to the shutters. When ready to transmit, all the shutters were set at the same time with the press of a footpedal.

The shutters were painted matte black to avoid reflection from sunlight and the frame and arms supporting the shutters were painted white or red for best contrast. Around 1809 Edelcrantz introduced an updated design. The frame around the shutters was dispensed with leaving a simpler, more visible, structure of just the arms with the indicator panels on the end of them. The "A" shutter was reduced to the same size as the other shutters and offset to one side to indicate which side was the most significant digit (whether the codepoint is read left-to-right or right-to-left is different for the two adjacent stations depending on which side they are on). This was previously indicated with a stationary indicator fixed to the side of the frame, but without a frame this was no longer possible.

The distance that a station could transmit depended on the size of the shutters and the power of the telescope being used to observe them. The smallest object visible to the human eye is one that subtends an angle of 40 seconds of arc, but Edelcrantz used a figure of 4 minutes of arc to account for atmospheric disturbances and imperfections of the telescope. On that basis, and with a 32× telescope, Edelcrantz specified shutter sizes ranging from 9 inches () for a distance of half a Swedish mile () to 54 inches () for 3 Swedish miles (). These figures were for the original design with square shutters. The open design of 1809 had long oblong shutters which Edelcrantz thought was more visible. Distances much further than these would require impractically high towers to overcome the curvature of the Earth as well as large shutters. Edelcrantz kept the distance between stations under 2 Swedish miles () except where large bodies of water made it unavoidable.

The Swedish telegraph was capable of being used at night with lamps. On smaller stations lamps were placed behind the shutters so that they became visible when the shutter was opened. For larger stations, this was impractical. Instead, a separate tin box matrix with glass windows was installed below the daytime shutters. The lamps inside the tin box could be uncovered by pulling strings in the same way the daytime shutters were operated. Windows on both sides of the box allowed the lamps to be seen by both the upstream and downstream adjacent stations. The codepoints used at night were the complements of the codepoints used during the day. This made the pattern of lamps in open shutters at night the same as the pattern of closed shutters in daytime.

First network: 1795–1809

The first operational line, Stockholm to Vaxholm, went into service in January 1795. By 1797 there were also lines from Stockholm to Fredriksborg, and Grisslehamn via Signilsskär to Eckerö in Åland. A short line near Göteborg to Marstrand on the west coast was installed in 1799. During the War of the Second Coalition, Britain tried to enforce a blockade against France. Concerned at the effect on their own trade, Sweden joined the Second League of Armed Neutrality in 1800. Britain was expected to respond with an attack on one of the Nordic countries in the league. To help guard against such an attack, the king ordered a telegraph link joining the systems of Sweden and Denmark. This was the first international telegraph connection in the world. Edelcrantz made this link between Helsingborg in Sweden and Helsingør in Denmark, across the Öresund, the narrow strait separating the two countries. A new line along the coast from Kullaberg to Malmö, incorporating the Helsingborg link, was planned in support and to provide signalling points to the Swedish fleet. Nelson's attack on the Danish fleet at Copenhagen in 1801 was reported over this link, but after Sweden failed to come to Denmark's aid it was not used again and only one station on the supporting line was ever built.

In 1808 the Royal Telegraph Institution was created and Edelcrantz was made director. The Telegraph Institution was put under the jurisdiction of the military, initially as part of the Royal Engineering Corps.Holzmann & Pehrson, p. 120 A new code was introduced to replace the 1796 codebook with 5,120 possible codepoints with many new messages. The new codes included punishments for delinquent operators. These included an order to the operator to stand on one of the telegraph arms (code 001-721), and a message asking an adjacent station to confirm that they could see him do it (code 001-723). By 1809, the network had 50 stations over of line employing 172 people. In comparison, the French system in 1823 had of line and employed over three thousand people.

In 1808, the Finnish War broke out when Russia seized Finland, then part of Sweden. Åland was attacked by Russia and the telegraph stations destroyed. The Russians were expelled in a revolt, but attacked again in 1809. The station at Signilsskär found itself behind enemy lines, but continued to signal the position of Russian troops to the retreating Swedes. After Sweden ceded Finland in the Treaty of Fredrikshamn, the east coast telegraph stations were considered superfluous and put into storage. In 1810, the plans for a south coast line were revived but were scrapped in 1811 due to financial considerations. Also in 1811, a new line from Stockholm via Arholma to Söderarm lighthouse was proposed, but also never materialised. For a while, the telegraph network in Sweden was almost non-existent, with only four telegraphists employed by 1810.

Rebuilding the network

The post of Telegraph Inspector was created as early as 1811, but the telegraph in Sweden remained dormant until 1827 when new proposals were put forward. In 1834, the Telegraph Institution was moved to the Topographical Corps. The Corps head, Carl Fredrik Akrell, conducted comparisons of the Swedish shutter telegraph with more recent systems from other countries. Of particular interest was the semaphore system of Charles Pasley in England which had been on trial in Karlskrona. Tests were performed between Karlskrona and Drottningskär, and, in 1835, nighttime tests between Stockholm and Fredriksborg. Akrell concluded that the shutter telegraph was faster and easier to use, and was again adopted for fixed stations. However, Pasley's semaphore was cheaper and easier to construct, so was adopted for mobile stations. By 1836 the Swedish telegraph network had been fully restored.

The network continued to expand. In 1837, the line to Vaxholm was extended to Furusund. In 1838 the Stockholm- Dalarö- Sandhamn line was extended to Landsort. The last addition came in 1854 when the Furusund line was extended to Arholma and Söderarm. The conversion to electrical telegraphy was slower and more difficult than in other countries. The many stretches of open ocean needing to be crossed on the Swedish archipelagos was a major obstacle. Akrell also raised similar concerns to those in France concerning potential sabotage and vandalism of electrical lines. Akrell first proposed an experimental electrical telegraph line in 1852. For many years the network consisted of a mix of optical and electrical lines. The last optical stations were not taken out of service until 1881, the last in operation in Europe. In some places, the heliograph replaced the optical telegraph rather than the electrical telegraph.}

United Kingdom

In Ireland, Richard Lovell Edgeworth returned to his earlier work in 1794, and proposed a telegraph there to warn against an anticipated French invasion; however, the proposal was not implemented. Lord George Murray, stimulated by reports of the Chappe semaphore, proposed a system of visual telegraphy to the British Admiralty in 1795. He employed rectangular framework towers with six five-foot-high octagonal shutters on horizontal axes that flipped between horizontal and vertical positions to signal.Lieutenant Watson's Telegraph
Mechanics' magazine, Volume 8 No. 222, Knight and Lacey, 1828, pages 294-299 The Rev. Mr Gamble also proposed two distinct five-element systems in 1795: one using five shutters, and one using five ten-foot poles. The British Admiralty accepted Murray's system in September 1795, and the first system was the 15 site chain from London to Deal.F.B. Wrixon (2005), Codes, Ciphers, Secrets and Cryptic Communication pp. 444-445 cover Murray's shutter telegraph in the U.K., with codes. Messages passed from London to Deal in about sixty seconds, and sixty-five sites were in use by 1808.

Chains of Murray's shutter telegraph stations were built along the following routes: London–Deal and Sheerness, London–Great Yarmouth, and London–Portsmouth and Plymouth. The line to Plymouth was not completed until 4 July 1806, and so could not be used to relay the news of Trafalgar. The shutter stations were temporary wooden huts, and at the conclusion of the Napoleonic wars they were no longer necessary, and were closed down by the Admiralty in March 1816.Military Signals from the South Coast, John Goodwin, 2000

Following the Battle of Trafalgar, the news was transmitted to London by frigate to Falmouth, from where the captain took the dispatches to London by coach along what became known as the Trafalgar Way; the journey took 38 hours. This delay prompted the Admiralty to investigate further.

A replacement semaphore system was sought, and of the many ideas and devices put forward the Admiralty chose the simpler semaphore system invented by Sir Home Popham. 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. The signals of the Popham semaphore were found to be much more visible than those of the Murray shutter telegraph. Popham's 2-arm semaphore was modelled after the 3-arm Depillon French semaphore. An experimental semaphore line between the Admiralty and Chatham was installed in July 1816, and its success helped to confirm the choice.

Subsequently, the Admiralty decided to establish a permanent link to Portsmouth and built a chain of semaphore stations. Work started in December 1820 with Popham's equipment replaced with another two-arm system invented by Charles Pasley. Each of the arms of Pasley's system could take on one of eight positions and it thus had more codepoints than Popham's. In good conditions messages were sent from London to Portsmouth in less than eight minutes. The line was operational from 1822 until 1847, when the railway and electric telegraph provided a better means of communication. The semaphore line 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, is currently being restored by the Landmark Trust as self-catering holiday accommodation. There will be public access on certain days when the restoration is complete.

The Board of the Port of Liverpool obtained a Private Act of Parliament to construct a chain of Popham optical semaphore stations from Liverpool to Holyhead in 1825. The system was designed and part-owned by Barnard L. Watson, a reserve marine officer, and came into service in 1827. The line is possibly the only example of an optical telegraph built entirely for commercial purposes. It was used so that observers at Holyhead could report incoming ships to the Port of Liverpool and trading could begin in the cargo being carried before the ship docked. The line was kept in operation until 1860 when a railway line and associated electrical telegraph made it redundant. Many of the prominences on which the towers were built ('telegraph hills') are known as Telegraph Hill to this day.

British empire

=Ireland

=
In Ireland R.L. Edgeworth was to develop an optical telegraph based on a triangle pointer, measuring up to 16 feet in height. Following several years promoting his system, he was to get admiralty approval and engaged in its construction during 1803–1804. The completed system ran from Dublin to Galway and was to act as a rapid warning system in case of French invasion of the west coast of Ireland. Despite its success in operation, the receding threat of French invasion was to see the system disestablished in 1804.

=Canada

=
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, but the many hills and coastal fog meant the towers needed to be placed relatively close together to ensure visibility. The labour needed to build and continually man so many stations taxed the already stretched-thin British military and there is doubt the New Brunswick line was