Editing Optical telegraph (section)

===Sweden===
[[File:Optical telegraph01 4484.jpg|thumb|A replica of an optical telegraph in Stockholm, Sweden]]
Sweden was the second country in the world, after France, to introduce an optical telegraph network.<ref name="Greene2016">David Greene, ''Light and Dark: An Exploration in Science, Nature, Art and Technology'', p. 159, CRC Press, 2016 {{isbn|1420034030}}.</ref> Its network became the second most extensive after France.<ref>Holzmann & Pehrson, p. x</ref> The central station of the network was at the [[Katarina Church]] in [[Stockholm]].<ref>Edelcrantz, p. 174</ref> The system was faster than the French system, partly due to the Swedish control panel<ref name="Holzmann & Pehrson, pp. 104–105">Holzmann & Pehrson, pp. 104–105</ref> and partly to the ease of transcribing the octal code (the French system was recorded as [[pictogram]]s).<ref name="Holzmann & Pehrson, p. 180">Holzmann & Pehrson, p. 180</ref> The system was used primarily for reporting the arrival of ships, but was also useful in wartime for observing enemy movements and attacks.<ref name="Holzmann & Pehrson, p. 117">Holzmann & Pehrson, p. 117</ref>

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<!-- "Sweden" required to avoid repeated heanding name per [[MOS:HEAD]] -->====
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 Palace|Drottningholm Castle]], a distance of {{convert|12|km}}. 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.<ref>Holzmann & Pehrson, pp. 101–103</ref>

====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.<ref>Holzmann & Pehrson, p. 103</ref> 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.<ref name="Holzmann & Pehrson, pp. 104–105"/>

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.<ref>Edelcrantz, p. 164</ref> 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).<ref name="Holzmann & Pehrson, p. 117"/> This was previously indicated with a stationary indicator fixed to the side of the frame, but without a frame this was no longer possible.<ref>Edelcrantz, pp. 144, 146</ref>

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 ({{nowrap|22 cm}}) for a distance of half a [[Swedish mile]] ({{nowrap|5.3 km}}) to 54 inches ({{nowrap|134 cm}}) for 3 Swedish miles ({{nowrap|32 km}}).<ref>Edelcrantz, pp. 166–167</ref> 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.<ref>Edelcrantz, p. 165</ref> 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 ({{nowrap|21 km}}) except where large bodies of water made it unavoidable.<ref>Edelcrantz, p. 169</ref>

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 [[diminished radix complement|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.<ref>Edelcrantz, pp. 170–171</ref>

====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 [[Gothenburg]] 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. [[Battle of Copenhagen (1801)|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.<ref>Holzmann & Pehrson, pp. 105–109</ref>

In 1808 the Royal Telegraph Institution was created and Edelcrantz was made director.<ref>Holzmann & Pehrson, p. 114</ref> The Telegraph Institution was put under the jurisdiction of the military, initially as part of the [[Swedish Engineer Troops|Royal Engineering Corps]].<ref name="Holzmann & Pehrson, p. 120">Holzmann & Pehrson, p. 120</ref> 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).<ref>Holzmann & Pehrson, p. 116</ref> By 1809, the network had 50 stations over {{nowrap|200 km}} of line employing 172 people.<ref name="Holzmann & Pehrson, p. 117"/> In comparison, the French system in 1823 had {{nowrap|650 km}} of line and employed over three thousand people.<ref name="Greene2016"/>

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.<ref>Holzmann & Pehrson, pp. 117–118</ref> For a while, the telegraph network in Sweden was almost non-existent, with only four [[telegraphist]]s employed by 1810.<ref>Holzmann & Pehrson, pp. 118, 120</ref>

====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.<ref name="Holzmann & Pehrson, p. 120"/>

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]].<ref name="Holzmann & Pehrson, p. 120"/> 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,{{sfn|Greene|2003|page=159}} the last in operation in Europe. In some places, the [[heliograph]] replaced the optical telegraph rather than the electrical telegraph.<ref>Holzmann & Pehrson, pp. 120–126</ref>}