Optical Telegraph

You wish to delve into the realm of archaic communication, do you? Very well. Don't expect me to hold your hand.

Tower-Based Signaling Network

A semaphore telegraph is, at its core, a visual communication system. Imagine a string of towers, each positioned within sight of the next, like sentinels relaying secrets across the landscape. They convey textual information using light and shadow, a dance of visual signals. There are, fundamentally, two types: the semaphore telegraph itself, which employs articulated arms to point in various directions, and the shutter telegraph, which uses panels to obscure or reveal light.

The most prominent and widely adopted system was the Chappe telegraph, a French invention from 1792, credited to Claude Chappe and his brothers. This system, popular in the late 18th and early 19th centuries, was revolutionary. Chappe coined the term "télégraphe" for his mechanism, which eventually gave rise to the English word "telegraph". These relay towers, spaced between 5 to 20 miles apart, were interconnected by lines of sight. Operators, armed with telescopes, would meticulously observe the neighboring tower. As the semaphore arms moved, spelling out messages according to a code, the information was painstakingly passed along the chain.

This method of communication was a significant leap forward compared to the plodding pace of post riders. Once established, the long-term operational costs were also considerably lower. However, this optical marvel was eventually eclipsed by the electrical telegraph, a technology that was not only cheaper and faster but also offered a degree of privacy the optical system could never match. The limitations of line-of-sight meant that geographical features and adverse weather conditions dictated the range of these optical networks, rendering them impractical for crossing vast bodies of water without the fortunate presence of an island for a relay station. A modern descendant of this system can be seen in flag semaphore, which uses hand-held flags to convey messages.

Etymology and Terminology

The word "semaphore" itself was introduced in 1801 by Claude Chappe, the very architect of the system. He derived it from the Greek words sêma (ση̑μα), meaning "sign," and phorós (φορός), meaning "carrying," or phorá (φορά), meaning "a carrying," stemming from phérein (φέρω), "to bear." Chappe also devised the term "tachygraph," signifying "fast writer." However, the French Army, with a more practical bent, preferred "telegraph," meaning "far writer," a term attributed to the French statesman André François Miot de Mélito.

The term "semaphoric" first appeared in English print in 1808, detailing the unfortunate destruction of these nascent telegraphs. By 1816, "semaphore" was being used in reference to a simpler system developed by Sir Home Popham, installed at the Admiralty. These semaphore telegraphs were also colloquially known as "Chappe telegraphs" or "Napoleonic semaphore," a testament to their widespread use during that era.

Early Designs

The concept of optical telegraphy is far from new, dating back to antiquity with systems like hydraulic telegraphs, the use of torches, and smoke signals. However, the modern semaphore systems emerged through various, often parallel, developmental paths.

One of the earliest conceptualizations came from the British polymath Robert Hooke. In 1684, he presented a detailed outline of visual telegraphy to the Royal Society, complete with practical considerations. Though motivated by military concerns following the Battle of Vienna, Hooke's system remained theoretical.

Sir Richard Lovell Edgeworth, an Anglo-Irish inventor, conducted early experiments in optical signaling in 1767. He wagered he could transmit race results within an hour, employing a network of elevated stations where signals were relayed via telescope. His initial design featured a pointer capable of eight positions, allowing for a significant number of coded elements when combined. He revisited this concept in 1795, spurred by news of Chappe's success.

Concurrently, in 1794, William Playfair, a Scottish economist, managed to acquire the design and alphabet of the French system while traveling in Europe. Through his connections, he presented a model to the Duke of York, then commanding British forces in Flanders, effectively introducing the technology to England.

Prevalence

France

The distinction of the first truly successful optical telegraph network belongs to the French engineer Claude Chappe and his brothers. By 1792, they had established a network spanning France with 556 stations, covering a formidable 4,800 kilometers (3,000 miles). This "système Chappe" remained the backbone of French military and national communications until the 1850s.

Development in France

The turbulent years of the French Revolution (1790–1795) created an urgent need for a rapid and dependable military communications system to counter external threats. France found itself surrounded by hostile powers, with internal revolts brewing. The crucial advantage France possessed was the fractured communication among its adversaries.

In the summer of 1790, the Chappe brothers began their endeavor to create a communication system that would enable the central government to receive intelligence and transmit orders with unprecedented speed. Claude Chappe explored various methods, including acoustics and smoke, even contemplating electricity. However, the lack of suitable insulation for high-voltage electrostatic sources of the era proved a significant obstacle.

Ultimately, Chappe settled on an optical system. The first public demonstration occurred on March 2, 1791, between Brûlon and Parcé, a distance of 16 kilometers. This initial system utilized modified pendulum clocks with dials marked with ten numerals. The hands moved rapidly, synchronized by a signal, and further signals indicated when to read the dial. The numbers were then cross-referenced in a codebook. For their initial experiments, the Chappes used a pan for synchronization, but for the public demonstration, they employed black and white panels observed through telescopes. The message, chosen by local officials at Brûlon, 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 realized the synchronization system itself could convey messages, eliminating the need for clocks.

The Chappes refined their designs over the next two years. During this period, their apparatus in Paris was twice destroyed by mobs who suspected them of communicating with royalist sympathizers. Their efforts gained traction when Ignace Chappe was elected to the National Legislative Assembly. In the summer of 1792, Claude was appointed Ingénieur-Télégraphiste and tasked with establishing a line between Paris and Lille, covering 230 kilometers. This line was instrumental in relaying dispatches during the war with Austria. In 1794, it transmitted news of the French capture of Condé-sur-l'Escaut from the Austrians less than an hour after the event. The initial symbol of a message sent to Lille traversed 15 stations in a mere nine minutes. While transmission speed fluctuated with weather conditions, a full message of 36 symbols typically reached Lille in about 32 minutes. By 1798, another line, comprising 50 stations and spanning 488 kilometers, connected Paris to Strasbourg. From 1803 onwards, the French also deployed the 3-arm Depillon semaphore at coastal locations to warn of British naval activity.

The English military engineer William Congreve observed during the Battle of Vervik in 1793 that French commanders were using the sails of a local windmill as an improvised signal station, with two of the four sails removed to mimic the arms of the new telegraph.

Chappe System: Technical Operation

The Chappe brothers discovered through experimentation that the angle of a rod was more readily discernible than the presence or absence of a panel. Their semaphore consisted of two black, movable wooden arms mounted on a crossbar. The combined positions of these three components indicated specific letters. Ingeniously, counterweights, known as "forks," facilitated control via just two handles, ensuring mechanical simplicity and robustness. Each arm, measuring two meters, could adopt seven distinct positions, while the 4.6-meter crossbar offered four angles. This configuration yielded 196 unique symbols. Attempts at night operation using lamps proved unsuccessful.

To enhance transmission speed and provide a measure of security, a code book was developed for use with semaphore lines. The Chappe corporation utilized a code that combined 92 basic symbols in pairs, resulting in 8,464 possible coded words and phrases.

The revised Chappe system of 1795 introduced not only new codes but also an operational protocol designed to maximize the line's throughput. Symbols were transmitted in cycles of "2 steps and 3 movements."

Step 1, Movement 1 (Setup): The operator adjusted the indicator arms to align with the crossbar, forming a neutral symbol, and then positioned the crossbar for the next symbol.
Step 1, Movement 2 (Transmission): The operator set the indicator arms to display the current symbol and awaited confirmation from the downstream station that it had been received.
Step 2, Movement 3 (Completion): The operator returned the crossbar to a vertical or horizontal position, signaling the end of a transmission cycle.

This methodical approach allowed each symbol to propagate down the line as rapidly as operators could accurately copy it, with built-in acknowledgement and flow control mechanisms. A symbol transmitted from Paris could reach Lille in just 2 minutes via 22 stations, and Lyon in 9 minutes via 50 stations. A typical transmission rate was 2–3 symbols per minute, though higher rates were prone to errors. This equates to a mere 0.4–0.6 wpm, but by restricting messages to those within the codebook, the effective speed could be dramatically increased. A significant advantage was that, if the code remained secret, the content of messages could be concealed from observers and even the operators themselves, a principle that has persisted in encrypted communications throughout technological evolution.

History in France

Following the initial Paris-Lille line, the Paris-Strasbourg route with 50 stations was completed in 1798. Napoleon Bonaparte recognized the strategic value of the telegraph, utilizing it for rapid intelligence gathering on enemy movements. In 1801, he commissioned Abraham Chappe to construct an oversized station intended to transmit across the English Channel, in anticipation of an invasion of Britain. A pair of such stations were tested on a line of comparable distance. The line to Calais was extended to Boulogne, where a new type of station was briefly deployed, but the invasion never materialized. In 1812, Napoleon adopted Abraham Chappe's design for a mobile telegraph for use during his campaigns; this system was still in use as late as 1853 during the Crimean War.

The advent of the telegraph also ignited enthusiasm for its potential to support direct democracy. The French intellectual Alexandre-Théophile Vandermonde, citing Rousseau's concerns about the feasibility of direct democracy in large constituencies, posited:

Something has been said about the telegraph which appears perfectly right to me and gives the right measure of its importance. Such invention might be enough to render democracy possible in its largest scale. Many respectable men, among them Jean-Jacques Rousseau, have thought that democracy was impossible within large constituencies.… The invention of the telegraph is a novelty that Rousseau did not expect to happen. It enables long-distance communication at the same pace and clarity than that of conversation in a living room. This solution may address by itself the objections to large [direct] democratic republics. It may even be done in the absence of representative constitutions.

The operational costs for the telegraph in 1799-1800 amounted to 434,000 francs, equivalent to approximately $1.2 million in 2015 silver value. In December 1800, Napoleon reduced the telegraph system's budget by 150,000 francs ($ 400,000 in 2015), leading to the temporary closure of the Paris-Lyons line. Chappe sought commercial applications to offset the deficit, including proposals from industry, finance, and newspapers. Only one proposal was approved: transmitting results from the state-run lottery. This was a response to years of fraud where individuals with advance knowledge of lottery results sold tickets in provincial towns after the Paris announcement but before the news reached those locations.

A Chappe semaphore tower near Saverne, France.

In 1819, Norwich Duff, a young British Naval officer, visited Clermont-en-Argonne and engaged the signalman in conversation. Duff's notes reveal:

The signalman's pay was twenty-five sous per day, with a requirement to be on duty from dawn till dusk.
For every minute a signal remained unanswered, a penalty of five sous was incurred.
This particular station was part of the line communicating with Strasbourg, and a message reached Strasbourg from Paris in six minutes, while arriving at Duff's location in four.

The network was strictly for government use, but in 1834, an early instance of wire fraud occurred when two bankers, François and Joseph Blanc, bribed operators at a station near Tours on the Paris-Bordeaux line. They used this to relay Paris stock exchange information to an accomplice in Bordeaux. The 480-kilometer journey took three days, providing ample time for market manipulation. An accomplice in Paris would know the market's direction days before the information reached Bordeaux via newspapers, allowing the Bordeaux schemer to profit accordingly. The message couldn't be inserted directly into the telegraph system without detection. Instead, pre-arranged errors were deliberately introduced into existing messages, visible to an observer in Bordeaux. Tours was chosen as a divisional station where messages were checked for errors by an inspector privy to the secret code, unbeknownst to the regular operators. The scheme wouldn't function if errors were inserted before Tours. The operators were informed of market trends through the color of packages sent by mail coach – white for upward, grey for downward – or, according to another account, by the wife of the Tours operator receiving packages of socks (down) or gloves (up), thus avoiding written evidence. The scheme operated for two years before its discovery in 1836.

The French optical system persisted for many years after other nations had adopted the electrical telegraph. This inertia was partly due to the extensive existing optical network, making its replacement a considerable undertaking. Furthermore, proponents argued for the optical system's superiority, particularly its reduced vulnerability to sabotage compared to unguarded electrical wires. Samuel Morse failed in his attempts to sell the electrical telegraph to the French government. Ultimately, the electrical telegraph's advantages in privacy and all-weather, nighttime operation prevailed. In 1846, a decision was made to replace the optical system with the Foy–Breguet electrical telegraph following a successful trial on the Rouen line. This system featured a display that mimicked the Chappe telegraph indicators, familiarizing operators with its operation. Jules Guyot issued a stark warning about the perceived error of this transition. It took nearly a decade for the optical telegraph to be fully decommissioned. One of the final messages transmitted over the French semaphore was the report of the fall of Sebastopol in 1855.

Sweden

Sweden was the second nation, after France, to implement an optical telegraph network, which ultimately became the second most extensive globally. The central hub of this network was located at Katarina Church in Stockholm. The Swedish system was noted for its speed, attributed partly to the sophisticated Swedish control panel and the ease of transcribing its octal code, unlike the French system which relied on visual representations. Primarily used for reporting ship arrivals, it also proved valuable during wartime for monitoring enemy movements. The last stationary semaphore link in regular service was in Sweden, connecting an island to a mainland telegraph line, and it ceased operation in 1880.

Development in Sweden

Inspired by reports of the Chappe telegraph, the Swedish inventor Abraham Niclas Edelcrantz began experimenting with optical telegraphy in Sweden. In 1794, he constructed a three-station experimental line connecting the royal castle in Stockholm to Drottningholm Palace via Traneberg, a distance of 12 kilometers. The initial demonstration on November 1st involved Edelcrantz sending a poem dedicated to King Gustav IV Adolf on his fourteenth birthday. On November 7th, the king appointed Edelcrantz to his Council of Advisors, with the intention of establishing a telegraph network across Sweden, Denmark, and Finland.

Edelcrantz System: Technical Operation

After initial trials with Chappe-style indicator arms, Edelcrantz opted for a design featuring ten iron shutters. Nine shutters represented a three-digit octal number, while the tenth, when closed, indicated that the code number should be preceded by "A." This provided 1,024 codepoints, which were then decoded into letters, words, or phrases using a codebook. The telegraph incorporated an advanced control panel connected by strings to the shutters. Pressing a foot pedal simultaneously set all shutters.

The shutters were painted matte black to minimize sunlight reflection, while the frame and supporting arms were painted white or red for maximum contrast. Around 1809, Edelcrantz introduced an improved design that eliminated the surrounding frame, simplifying the structure to just arms with indicator panels at their ends. The "A" shutter was reduced in size and offset to indicate the most significant digit, addressing the ambiguity of left-to-right or right-to-left reading. This was previously indicated by a stationary indicator on the frame.

The transmission range of a station depended on the size of the shutters and the power of the observing telescope. Edelcrantz calculated that, with a 32x telescope, shutter sizes ranged from 23 centimeters for a distance of 5.3 km to 140 centimeters for 32 km, accounting for atmospheric disturbances and telescope imperfections. These figures applied to the original square shutters. The 1809 design featured long, oblong shutters, which Edelcrantz believed were more visible. Distances exceeding these specifications would necessitate impractically tall towers to overcome the Earth's curvature and larger shutters. Edelcrantz generally maintained station distances under 21 km, except where unavoidable due to large bodies of water.

The Swedish telegraph could operate at night using lamps. On smaller stations, lamps were placed behind the shutters, becoming visible when opened. Larger stations required a separate tin box matrix with glass windows below the daytime shutters. Lamps within this box were controlled by strings, similar to the daytime shutters. Windows on both sides allowed visibility for both upstream and downstream stations. Nighttime codepoints were the complements of the daytime codepoints, ensuring the pattern of open shutters at night matched the pattern of closed shutters during the day.

First Network: 1795–1809

The initial operational line, connecting Stockholm to Vaxholm, became active in January 1795. By 1797, lines also extended from Stockholm to Fredriksborg, and to 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's blockade against France prompted Sweden to join the Second League of Armed Neutrality in 1800. Fearing a British attack on Nordic countries within the league, the king ordered a telegraph link between Sweden and Denmark, establishing the world's first international telegraph connection. Edelcrantz created this link between Helsingborg in Sweden and Helsingør in Denmark, across the Öresund strait. A supporting line along the coast from Kullaberg to Malmö was planned, incorporating the Helsingborg link and providing signaling 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 aid Denmark, it was abandoned, with only one station on the supporting line ever constructed.

In 1808, the Royal Telegraph Institution was established, with Edelcrantz as its director. Initially under the jurisdiction of the military, it became part of the Swedish Engineer Troops. A new code was introduced, replacing the 1796 codebook with 5,120 possible codepoints and incorporating numerous new messages. These codes included punishments for delinquent operators, such as an order to stand on a telegraph arm (code 001-721) and a request for an adjacent station to confirm the operator's compliance (code 001-723). By 1809, the network comprised 50 stations spanning 200 km, employing 172 individuals. In contrast, the French system in 1823 had 650 km of lines and employed over three thousand people.

The Finnish War erupted in 1808 when Russia occupied Finland, then a Swedish territory. Åland was attacked by Russia, and its telegraph stations were destroyed. Although the Russians were repelled in a revolt, they attacked again in 1809. The station at Signilsskär found itself behind enemy lines but continued to signal Russian troop positions to the retreating Swedes. Following Sweden's cession of Finland in the Treaty of Fredrikshamn, the east coast telegraph stations were deemed superfluous and stored. In 1810, plans for a south coast line were revived but scrapped in 1811 due to financial constraints. Also in 1811, a new line from Stockholm via Arholma to Söderarm lighthouse was proposed but never materialized. For a period, the Swedish telegraph network dwindled, with only four telegraphists employed by 1810.

Rebuilding the Network

The position of Telegraph Inspector was established as early as 1811, but the Swedish telegraph remained largely dormant until 17 years later when new proposals emerged. In 1834, the Telegraph Institution was transferred to the Topographical Corps. The Corps' head, Carl Fredrik Akrell, conducted comparisons between the Swedish shutter telegraph and more recent systems from other countries. Of particular interest was the semaphore system developed by Charles Pasley in England, which had undergone trials in Karlskrona. Tests were conducted between Karlskrona and Drottningskär, and in 1835, nighttime tests were performed between Stockholm and Fredriksborg. Akrell concluded that the shutter telegraph was faster and easier to operate, and it was readopted for fixed stations. However, Pasley's semaphore was more cost-effective and simpler to construct, leading to its adoption 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 final expansion occurred in 1854 when the Furusund line was extended to Arholma and Söderarm. The transition to electrical telegraphy was slower and more challenging than in other countries, largely due to the numerous stretches of open ocean that needed to be crossed in the Swedish archipelagos. Akrell also echoed concerns raised in France regarding the potential for sabotage and vandalism of electrical lines. Akrell first proposed an experimental electrical telegraph line in 1852. For many years, the network comprised a mix of optical and electrical lines. The last optical stations were not decommissioned until 1881, making them the last operational optical telegraphs in Europe. In some locations, the heliograph replaced the optical telegraph rather than the electrical system.

United Kingdom

Diagram of the UK Murray six-shutter system, with shutter 6 in the horizontal position, and shutters 1–5 vertical.

In Ireland, Richard Lovell Edgeworth revisited his earlier work in 1794, proposing a telegraph to guard against a potential French invasion. However, this proposal was not implemented. Lord George Murray, inspired by reports of the Chappe semaphore, submitted a visual telegraph system to the British Admiralty in 1795. His design featured rectangular framework towers with six five-foot-high octagonal shutters mounted on horizontal axes, which flipped between horizontal and vertical positions to signal. Reverend Mr. Gamble also proposed two distinct five-element systems in 1795: one using five shutters and another using five ten-foot poles. The British Admiralty approved Murray's system in September 1795, and the first operational line comprised 15 sites connecting London to Deal. Messages traversed from London to Deal in approximately sixty seconds, and by 1808, sixty-five sites were in use.

St. Albans High Street in 1807, showing the shutter telegraph atop the city's Clock Tower. This was part of the London to Great Yarmouth line.

Chains of Murray's shutter telegraph stations were established along several routes: London to Deal and Sheerness; London to Great Yarmouth; and London to Portsmouth and Plymouth. The line to Plymouth was not completed until July 4, 1806, and thus could not relay the news of the Battle of Trafalgar. The shutter stations were temporary wooden structures, and with the conclusion of the Napoleonic Wars, their necessity diminished, leading to their decommissioning by the Admiralty in March 1816.

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

A replacement telegraph system was sought, and from the numerous proposals submitted, the Admiralty selected the simpler semaphore system invented by Sir Home Popham. A Popham semaphore consisted of a single, fixed vertical 30-foot pole with two movable 8-foot arms attached at their ends to horizontal pivots – one arm at the top and the other in the middle. The signals from the Popham semaphore were found to be significantly more visible than those of the Murray shutter telegraph. Popham's two-arm semaphore was modeled after the French 3-arm Depillon semaphore. An experimental semaphore line between the Admiralty and Chatham was installed in July 1816, and its success confirmed the Admiralty's choice.

Subsequently, the Admiralty decided to establish a permanent link to Portsmouth and constructed a chain of semaphore stations. Construction commenced in December 1820, with Popham's equipment being replaced by another two-arm system invented by Charles Pasley. Each of Pasley's arms could assume one of eight positions, providing more codepoints than Popham's design. In favorable conditions, messages were transmitted from London to Portsmouth in under eight minutes. The line remained operational from 1822 to 1847, when the advent of railways and the electric telegraph offered superior communication capabilities. The semaphore line did not utilize the exact same locations as the shutter chain but followed a similar route, with 15 stations: Admiralty (London), Chelsea Royal Hospital, Putney Heath, Coombe Warren, Coopers Hill, Chatley Heath, Pewley Hill, Bannicle Hill, Haste Hill, 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 the Landmark Trust and is available as self-catering holiday accommodation. Public access is granted on specific days following the completion of the restoration.

The Board of the Port of Liverpool secured a local act of Parliament, the Liverpool Improvement Act 1825, to construct a chain of Popham optical semaphore stations connecting Liverpool to Holyhead in 1825. The system, designed and partly owned by Barnard L. Watson, a reserve marine officer, became operational in 1827. This line is possibly the sole example of an optical telegraph built entirely for commercial purposes. It enabled observers at Holyhead to report incoming ships to the Port of Liverpool, facilitating trade of the cargo before the vessel docked. The line remained operational until 1860, when a railway line and its associated electrical telegraph rendered it obsolete.

Many of the hills on which these towers were built are still known today as 'Telegraph hills'.

British Empire

Ireland

In Ireland, R.L. Edgeworth developed an optical telegraph featuring a triangular pointer, reaching up to 16 feet in height. After years of promoting his system, he secured Admiralty approval and oversaw its construction between 1803 and 1804. The completed system stretched from Dublin to Galway, serving as a rapid warning system against potential French invasions of Ireland's west coast. Despite its operational success, the receding threat of French invasion led to the system's disestablishment in 1804.

Canada

In Canada, Prince Edward, Duke of Kent established the first semaphore line in North America. Operational by 1800, it stretched between the city of Halifax and the town of Annapolis in Nova Scotia, and extended across the Bay of Fundy to Saint John and Fredericton in New Brunswick. In addition to relaying information about approaching ships, the Duke utilized the system for transmitting military commands, particularly concerning troop discipline. The Duke envisioned the line reaching as far as the British garrison at Quebec City, but the numerous hills and coastal fog necessitated relatively close spacing of the towers to ensure visibility. The labor required to construct and maintain so many stations strained the already overextended British military, and it remains uncertain whether the New Brunswick line ever became fully operational. With the exception of the towers around Halifax harbor, the system was abandoned shortly after the Duke's departure in August 1800.

Malta

Ta' Kenuna Tower, a semaphore tower in Nadur, Gozo, Malta, built by the British in 1848.

British military authorities began considering the installation of a semaphore line in Malta in the early 1840s. Initially, it was proposed to establish stations on the bell towers and domes of the island's churches, but religious authorities rejected the plan. Consequently, in 1848, new semaphore towers were erected at Għargħur and Għaxaq on the main island, with another constructed at Ta' Kenuna on Gozo. Additional stations were established at the Governor's Palace, Selmun Palace, and the Giordan Lighthouse. Each station was staffed by the Royal Engineers.

India

In India, semaphore towers were introduced in 1810. A series of towers were built connecting Fort William in Kolkata to Chunar Fort near Varanasi. The towers in the plains were 75–80 feet tall, while those in the hills measured 40–50 feet, and they were spaced approximately 13 km apart.

Van Diemen's Land

In southern Van Diemen's Land (now Tasmania), a signaling system to announce ship arrivals was proposed by Governor-In-Chief Lachlan Macquarie during his first visit in 1811. Initially a simple flag system in 1818 between Mt. Nelson and Hobart, it evolved by 1829 into a system with two revolving arms. This system was rather rudimentary, and the arms were difficult to operate. In 1833, Charles O'Hara Booth assumed command of the Port Arthur penal settlement. As an "enthusiast in the art of signalling," he recognized the value of improved communication with the headquarters in Hobart. During his tenure, the semaphore system was extended to include 19 stations on various mountains and islands between Port Arthur and Hobart. Until 1837, three single rotating arm semaphores were employed. Subsequently, the network was upgraded to utilize signal posts with six arms—a pair at the top, middle, and bottom. This allowed the semaphore to transmit 999 signal codes. Captain George King of the Port Office and Booth collaborated on the codebook for the system. King developed shipping-related codes, while Booth added codes for government, military, and penal station matters. In 1877, Port Arthur was closed, and the semaphore was used solely for shipping signals. It was finally replaced by a simple flagstaff after the introduction of the telephone in 1880.

A restored two-arm semaphore post at Low Head in Tasmania.

In the north of the state, there was a need to report on ship arrivals entering the Tamar Estuary, approximately 56 km from the main port at Launceston at that time. The Tamar Valley Semaphore System was based on a design by Peter Archer Mulgrave. This design featured two arms, one with a cross piece at the end. The arms were rotated by ropes, and later chains. The positions of the barred arm indicated numbers 1 to 6 clockwise from the bottom left, while the unbarred arm indicated 7, 8, 9, STOP, and REPEAT. The vane positions signified code numbers. A message was transmitted by sending numbers sequentially to form a code, which was then decoded using a codebook, similar to other systems. On October 1, 1835, the Launceston Advertiser announced: "...that the signal stations are now complete from Launceston to George Town, and communication may he made, as well as received, from the Windmill Hill to George Town, in a very few minutes, on a clear day". The system comprised six stations: Launceston Port Office, Windmill Hill, Mt. Direction, Mt. George, George Town Port Office, and Low Head lighthouse. The Tamar Valley semaphore telegraph operated for twenty-two and a half years, closing on March 31, 1858, after the introduction of the electric telegraph.

In the 1990s, the Tamar Valley Signal Station Committee Inc. was formed to restore the system. The restoration work spanned several years, and the semaphore telegraph was declared complete once more on Sunday, September 30, 2001.

Iberia

Restored semaphore in Adanero, Spain.

Spain

In Spain, the engineer Agustín de Betancourt developed his own system, which was adopted by the state. He received a Royal Appointment in 1798, and the first segment of the line, connecting Madrid and Aranjuez, was operational by August 1800. Spain was covered by an extensive semaphore telegraph network during the 1840s and 1850s. The three main semaphore lines radiated from Madrid. The first ran north to Irun on the Atlantic coast, near the French border. The second extended east to the Mediterranean, then north along the coast through Barcelona to the French border. The third ran south to Cádiz on the Atlantic coast. These lines served numerous other Spanish cities, including: Aranjuez, Badajoz, Burgos, Castellón de la Plana, Ciudad Real, Córdoba, Cuenca, Girona, Pamplona, San Sebastián, Seville, Tarancon, Tarragona, Toledo, Valladolid, Valencia, Vitoria-Gasteiz, and Zaragoza.

The rugged topography of the Iberian Peninsula, which facilitated the design of semaphore lines conveying information from hilltop to hilltop, made the implementation of wire telegraph lines difficult when that technology emerged in the mid-19th century. The Madrid-Cádiz line was the first to be dismantled in 1855, but other segments of the optical system continued to function until the conclusion of the Carlist Wars in 1876.

Portugal

In Portugal, British forces engaged in the fight against Napoleon in Portugal discovered that the Portuguese Army already possessed a highly effective terrestrial semaphore system, operational since 1808. This provided the Duke of Wellington with a significant intelligence advantage. The innovative Portuguese telegraphs, designed by mathematician Francisco António Ciera, were of three types: three shutters, three balls, and one pointer/movable arm. Ciera also authored the codebook "Táboas Telegráphicas," applicable to all three telegraph types. From early 1810, the network was managed by the "Corpo Telegráfico," the first Portuguese military Signal Corps.

Other Regions

Optical telegraph in the harbor of Bremerhaven, Germany.

Once its success in France was evident, the optical telegraph was emulated in many other countries, particularly after Napoleon utilized it to coordinate his empire and army. In most of these nations, the postal authorities managed the semaphore lines. Many national services adopted signaling systems distinct from the Chappe system. For instance, the UK and Sweden adopted shutter panel systems, contrary to the Chappe brothers' assertion that angled rods were more visible. In some cases, new systems were adopted due to perceived improvements. However, many countries pursued their own, often inferior, designs driven by national pride or a reluctance to copy rivals and enemies.

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

Main article: Prussian semaphore system

Former optical telegraph tower on the Winter Palace in Saint Petersburg, Russia.

In the Kingdom of Prussia, Frederick William III ordered the construction of an experimental line in 1819. However, due to opposition from the defense minister Karl von Hake, nothing materialized until 1830, when a short, three-station line between Berlin and Potsdam was built. The design was based on the Swedish telegraph, but with twelve shutters. Postrat Carl Pistor instead proposed a semaphore system based on Watson's design from England. An operational line using this design, running from Berlin-Magdeburg-Dortmund-Köln-Bonn-Koblenz, was completed in 1833. The line employed approximately 200 people, comparable to Sweden's operation, but no further network development occurred, and no additional official lines were built. The line was decommissioned in 1849, superseded by an electrical line.

Despite the absence of further government-sponsored lines, private enterprise did emerge. Johann Ludwig Schmidt opened a commercial line from Hamburg to Cuxhaven in 1837. In 1847, Schmidt established a second line connecting Bremen to Bremerhaven. These lines were utilized for reporting the arrival of commercial ships. The two lines were later interconnected with three additional stations, forming what was possibly the sole private telegraph network during the optical telegraph era. The telegraph inspector for this network was Friedrich Clemens Gerke, who would later transition to the Hamburg-Cuxhaven electrical telegraph line and develop what became the International Morse Code. The Hamburg line ceased operation in 1850, and the Bremen line in 1852.

In Russia, Tsar Nicholas I inaugurated a 1,200-kilometer line between Moscow and Warsaw in 1833. This line required 220 stations staffed by 1,320 operators. The stations were noted to be in a state of disuse and decay by 1859, suggesting the line was likely abandoned much earlier.

In the United States, the first optical telegraph was constructed by Jonathan Grout in 1804 but ceased operation in 1807. This 104-kilometer line connected Martha's Vineyard with Boston and transmitted shipping news. An optical telegraph system linking Philadelphia and the mouth of the Delaware Bay was operational by 1809, serving a similar purpose. A second line to New York City was operational by 1834, at which point its Philadelphia terminus was moved to the tower of the Merchants Exchange. One of the prominent hills in San Francisco, California, is also named "Telegraph Hill," after the semaphore telegraph established there in 1849 to signal the arrival of ships into San Francisco Bay.

The telegraph was introduced to the United States Navy by David Porter upon his return from Europe. He proposed that the US Navy construct a telegraphic system "similar to those ... in Europe." The United States Secretary of the Navy, Robert Smith, also expressed interest in the concept. Smith replied on June 4, granting approval for Porter's idea and informing him that the Navy would provide 20 telescopes. In Europe, the typical distance between telegraph stations was 10 to 16 kilometers. Due to the winding course of the Mississippi River and the dense forests along its banks, the stations in the US were spaced 5 to 6 kilometers apart. On February 3, 1809, Porter reported that twelve stations had been constructed, extending 72 kilometers below New Orleans, halfway to the river delta's start. These shorter distances resulted in higher operating costs compared to equivalent networks in Europe. Secretary of the Navy halted further construction due to excessive costs. Had the network been extended to the river's mouth, a message from the Balize could have been sent or received in five minutes. Secretary Smith had intended for the materials to be installed in gunboats for experimental trials. In a subsequent communication in October 1808, he informed Porter that the project could not proceed without congressional authorization and funding.

In January 1812, the President approached the Secretary of the Navy to explore telegraphic communication between New York, Washington, and other locations, inquiring about the feasibility and estimated costs. A report stated, "A telegraphic communication between Sandy Hook & the Narrows, thence to the City, is immediately desirable," along with cost estimates. A prudent assessment noted that dense forests made long-distance implementation impractical. However, the proposed 39-kilometer network between Sandy Hook and New York could be established for $500, excluding staffing costs. This was approved, and Isaac Chauncey, commandant of the New York Naval Shipyard, was tasked with its construction. He encountered resistance from some affected property owners. Telegraph network operations commenced around July 1. Despite apparent interest in telegraphy from several key decision-makers, the New York-Sandy Hook line remained the only active system operated by the Navy during the War of 1812.

As First Data Networks

The optical telegraphs established at the turn of the 18th and 19th centuries represent the earliest forms of data networks. Chappe and Edelcrantz, independently, developed numerous features that are now standard in modern networks but were then considered revolutionary and essential for the smooth operation of these early systems. These included control characters, routing, error control, flow control, message priority, and symbol rate control. Edelcrantz meticulously documented the meaning and usage of all his control codes from the outset in 1794. Precise details of the early Chappe system are less clear; the earliest surviving operating instructions date to 1809, and the French system is not as comprehensively explained as the Swedish.

Some of the features incorporated into these systems are considered advanced even by modern standards and have been reinvented in recent times. For instance, the Edelcrantz code included an error control codepoint (707) used to request the retransmission of a specific recent symbol. This was followed by two symbols identifying the row and column in the current logbook page from which the symbol needed to be repeated. This represents a selective repeat mechanism, which is more efficient than the simple go back n strategy employed by many modern networks. This was a later addition; both Edelcrantz (codepoint 272) and Chappe (codepoint 2H6) initially relied on a simple "erase last character" function for error control, a concept directly inherited from Hooke's 1684 proposal.

Routing in the French system was largely fixed; only Paris and the terminal station at the end of a line were permitted to initiate messages. The early Swedish system offered greater flexibility, allowing message connections to be established between any arbitrary stations. Similar to modern networks, the initialization request included the identification of both the requesting and target stations. The target station acknowledged the request by transmitting the complement of the received code—a unique protocol with no direct modern equivalent. This capability was removed from the codebook in the 1808 revision. Subsequently, only Stockholm typically initiated messages, with other stations awaiting polling.

The Prussian system mandated that the Coblenz station (at the end of the line) transmit a "no news" message (or an actual message if one was pending) back to Berlin every hour, on the hour. Intermediate stations could only relay messages by replacing the "no news" message with their own traffic. Upon arrival in Berlin, the "no news" message was returned to Coblenz following the same procedure. This can be viewed as an early implementation of a token passing system. This arrangement necessitated precise clock synchronization across all stations. A synchronization signal was broadcast from Berlin for this purpose every three days.

Another feature considered advanced for its time in modern electronic systems is the dynamic adjustment of transmission rates. Edelcrantz included codepoints for faster (770) and slower (077) transmission speeds. Chappe's system also incorporated this functionality.

In Popular Culture

A cartoon strip from "Monsieur Pencil" (1831) by Rodolphe Töpffer.

By the mid-19th century, the optical telegraph had become sufficiently well-known to be referenced in popular works without requiring special explanation. The Chappe telegraph featured in contemporary fiction and comic strips. In "Mister Pencil" (1831), a comic strip by Rodolphe Töpffer, a dog that had fallen onto a Chappe telegraph arm—and its owner's attempt to rescue it—inadvertently triggered an international crisis by transmitting alarming messages. In Lucien Leuwen (1834), Stendhal depicts a power struggle between Lucien Leuwen and the prefect M. de Séranville, involving the telegraph's director, M. Lamorte. In Chapter 60 ("The Telegraph") of Alexandre Dumas's The Count of Monte Cristo (1844), the protagonist describes with fascination the semaphore line's moving arms: "I had at times seen rise at the end of a road, on a hillock and in the bright light of the sun, these black folding arms looking like the legs of an immense beetle." He later bribes a semaphore operator to relay a false message to manipulate the French financial market. Dumas also provides a detailed account of a Chappe telegraph line's operation. In Hector Malot's novel Romain Kalbris (1869), one of the characters, a girl named Dielette, describes her home in Paris as "...next to a church near which there was a clock tower. On top of the tower there were two large black arms, moving all day this way and that. [I was told later] that this was Saint-Eustache church and that these large black arms were a telegraph."

In the 21st century, the concept of the optical telegraph is primarily kept alive in popular culture through works of fiction such as the novel Pavane and Terry Pratchett's "Clacks" in his Discworld novels, most notably the 2004 novel Going Postal.

Notes

^ The notation here follows that given in Holzmann & Pehrson (p. 211). The two digits represent, respectively the angle of the left and right indicators. Vertical pointing up is "1" and each successive 45° from this position increments this number. "H" means the regulator is in the horizontal position and "V" the vertical.