The Short History of the Telegraph
by Ken Sutton

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

  The most widely used system was the Chappe telegraph which was as shutter telegraph, and was invented in France in 1792 by Claude Chappe. It was popular in the late eighteenth to early nineteenth centuries. Chappe used the term "telegraphe" to describe the mechanism he had invented – that is the origin of the English word "telegraph". Lines of relay towers were built within line of sight of each other, at separations of 5–20 miles. Operators at each tower would watch the neighbouring tower through a telescope, and when the "shutters" 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.

  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. However, the system (which was motivated by military concerns, following the Battle of Vienna in 1683) was never put into practice.
  The image on the left is an illustration showing Robert Hooke's proposed system. At top are various symbols that might be used; ABCE indicates the frame, and D the screen behind which each of the symbols are hidden when not in use.

Sir Richard Lovell Edgeworth's proposed system

  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.

  However the 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 4,800 kilometres (3,000 mi). Le système Chappe was used for military and national communications until the 1850s.

  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.

  In 1795, the Rev. Mr Gamble proposed to the British Admiralty two distinct five-element systems: one using five shutters, and one using five ten-foot poles. However, in the same year, Lord George Murray, stimulated by reports of the Chappe semaphore, also proposed a system of visual telegraphy to the British Admiralty. He employed rectangular framework towers with six five-foot-high octagonal shutters on horizontal axes that flipped between horizontal and vertical positions to signal.

  The British Admiralty accepted Murray's system in September 1795, and the first system was the 15 site chain from London to Deal. 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 to Deal and Sheerness, London to Great Yarmouth, and London to 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.

Shutter Telegraph in St. Albans courtesy of Alf Boggis.

  The image on the right is of St. Albans High Street in 1807, showing the shutter telegraph on top of the city's Clock Tower. It was on the London to Great Yarmouth line.

   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. 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, has had a complete restoration by the Landmark Trust with the telegraph arms in working order and the original rooms turned into self-catering holiday accommodation. The Royal Navy supported the official opening of the now restored Chatley Heath Semaphore Tower in support of the official open day on Friday 10 September 2021 with The RN Communications Branch Museum providing a demonstration of semaphore using a Telegraph Semaphore trainer.

  This Telegraph Trainer was introduced in 1874 on HMS VICTORY, worked manually, by use of the operator holding the arms in the appropriate position. 6 feet in height and constructed of rather cumbersome sprockets and chains made to a special Admiralty pattern. In 1941 the firm of Thomas Haywood realized that ordinary bicycle chains would be cheaper and equally effective. Sets such as this were delivered to the Signal School at Chatham to be used as a training aid. In 1942, HMS CABBALA installed small mechanical semaphores for training V/S Wrens, just a year before mechanical semaphores were finally withdrawn from ships to save top-weight. This is one of the few remaining mechanical semaphores, as used at both the Signal School at Chatham and HMS CABBALA, and is identical to the bigger mechanical semaphores introduced to the fleet in 1874. See Chatley Heath

  It is obvious that the stations could not be constantly working, and there was no provision for night signalling. An equally successful telegraph ran between Holyhead "Mountain" and Liverpool and did valuable work in reporting the movements of merchant ships from 1827 to 1861, long after the electric telegraph had been installed in other parts of the country. The first manager was Lieutenant B.L. Watson R.N., and the first apparatus consisted of three pairs of semaphore arms on a single mast. In 1851 Watson bettered himself by organising other telegraph lines in other parts of the country on a commercial basis; then the Holyhead line devolved upon another naval officer, Lieutenant William Lord, who much improved it, the stations now being more numerous and equipped with two lattice masts side by side each carrying two pairs of semaphore arms, The line ran right across Anglesey an spanned Beumaris Bay, the estuary of the Dee, and the River Mersey, and last station but one being on Bidston Hill near Birkenhead. Four of the stations are still standing in good preservation, four others are more or less ruinous, and of three more there is not trace today.

  At a period when so many different inventors were striving to produce a telegraph that could be easily operated, it is strange that the semaphore introduced by Colonel Pasley of the Royal Engineers was received so reservedly, for its simplicity made it far more valuable that any of the other complicated methods. After several experiments his machine finally ended up in 1822 in the well-known form adopted nearly all over the world.

  It was only in 1943 that mechanical semaphores on Pasley's plan were abolished in sea-going ships of the Royal Navy owing to the need to reduce top weight. Although recognised in 1827, this machine was really intended as a telegraph and confined to shore stations and harbour flagships, and spelling out a message was of secondary interest partly because some of the letters were not complete, for instance, the setting "13" indicated either I or J, "25" indicated Q or X, and "35" indicated U, V or W. This explains why the letters, J, V, W and X are today not in their right order. It was not till 1874 that Pasley's machine was adopted at sea as a method of conversational signalling, and it was not till about 1880 that anybody thought of adapting the arms of the human body to imitate the arms of Pasley's machine, for, incredible though it may seem, where a small replica of the machine was used, the operator stood behind it and actually grasped its arms with his hands and moved them into position However, the manual version soon spread and was often in use as the mechanical, and had the advantage that it could be employed wherever a man could stand up.

  Meanwhile, after some other experiments with machines on the masts, the true semaphore was introduced in 1895 by Captain (afterwards made Admiral of The Fleet) Arthur Wilson. It was fitted at the main masthead in all men-of-war from battleships to scouts, and consisted of two sheet-metal arms 12 feet long and 15 inches wide. It was capable of being trained round from beam to beam and was worked by handles at deck level. It was supposed to be exercised daily but was rarely used in real earnest, although it had a horizon range, Wireless Telegraphy was beginning to make some headway in 1902, and at first flagships and cruisers were fitted with it. The vertical aerial was suspended from a sort of fishing-rod gaff at the main mast head and for some years shared the position with the truck semaphore, the visual apparatus being retained for the present "In case". Mast semaphores were abolished in 1907.

  The Horse Sand Fort, one of the larger Royal Commission sea forts in the Solent off Portsmouth, Hampshire, England had its own Semaphore Telegraph. In 2005 the Semaphore Telegraph was recovered from the Fort, refurbished and erected just outside Mercury Building, HMS Collingwood (the current home of the Royal Navy Communications Branch) to provide a link between the Fort and the Royal Navy in Portsmouth.

  The optical telegraphs put in place at the turn of the 18th/19th centuries were the first examples of data networks. Chappe and Edelcrantz independently invented many features that are now commonplace in modern networks, but were then revolutionary and essential to the smooth running of the systems. These features included control characters, routing, error control, flow control, message priority and symbol rate control. Edelcrantz documented the meaning and usage of all his control codes from the start in 1794.

  Some of the features of these systems are considered advanced in modern practice and have been recently reinvented. An example of this is the error control codepoint 707 in the Edelcrantz code. This was used to request the repeat of a specified recent symbol. The 707 was followed by two symbols identifying the row and column in the current page of the logbook that it was required to repeat. This is an example of a selective repeat and is more efficient than the simple go back n strategy used on many modern networks. This was a later addition; both Edelcrantz (codepoint 272), and Chappe (codepoint 2H6) initially used only a simple "erase last character" for error control, taken directly from Hooke's 1684 proposal.

Portsdown Shutter Telegraph
Portsdown Semaphore Telegraph

References:
Wikipedia -Optical Telegraph
Bob Hunt - Portsdown Tunnels