A code and signalling apparatus for visual communication. It consists of one or two mechanically-operated arms attached to an upright post, or two hand-held flags at arm's length, which are moved in a vertical plane to a sequence of positions. Each position represents a different letter of the alphabet, numeral, or punctuation feature. The system was widely used in visual telegraphy, especially at sea, before the advent of electricity. Old-style railway signals are a simple form of semaphore, with a single arm having two positions to indicate stop or go.
The semaphore or optical telegraph is an apparatus for conveying information by means of visual signals, with towers with pivoting blades or paddles, shutters, in a matrix, or hand-held flags etc.
Semaphore lines preceded the electrical telegraph.
History
Although passing mention of this idea had been made at many points in history, it was apparently the English scientist Robert Hooke who first gave a vivid and comprehensive outline of visual telegraphy to the Royal Society in a submission dated 1684;
Over a hundred years later a French engineer, Claude Chappe and his brothers took up the challenge again and succeeded to cover France with a network of 556 stations stretching a total distance of 4,800 kilometres.
Many national services adopted signaling systems different from the Chappe system.
France
There was a desperate need for swift and reliable communications in France during the period of 1790-1795.
The Chappe brothers in the summer of 1790 set about to devise a system of communication that would allow the central government to receive intelligence and to transmit orders in the shortest possible time.
Paris to Strasbourg with 50 stations was the next line and others followed soon after.
In 1821 Norwich Duff, a young British Naval officer, visiting Clermont en Argonne, walked up to the telegraph station there and engaged the signalman in conversation. Here is his note of the man's information:
'The pay is twenty five sous per day and he (the signalman) is obliged to be there from day light till dark, at present from half past three till half past eight; there are only two of them and for every minute a signal is left without being answered they pay five sous: this is a part of the branch which communicates with Strasburg and a message arrives there from Paris in six minutes it is here in four.'
Relative Costs
The semaphore system was cleverly designed, and provided a strategic advantage for France in a difficult time. Here's a brief breakdown using $US:
Semaphore line, 120 miles (Paris to Lille)
15 towers ($1,500,000) At least 15 full-time operators ($450,000/year). Cost to send one word one mile, at 10% interest: $0.0114Electric Telegraph line, 120 miles
At least six full-time operators ($180,000/year) Poles, right-of-way, wires, installation: $15,000/mile, ($1,800,000) Operates 24 hours a day.To speed transmission and to provide some semblance of security a code book was developed for use with semaphore lines.
Sweden
At the same time as Chappe, the Swede Abraham Niclas Edelcrantz experimented with the optical telegraph in Sweden.
Edelcrantz eventually developed his own system which was quite different from its French counterpart and nearly twice as fast.
Soon telegraph circuits linking castles and fortresses in the neighbourhood of Stockholm were set up and the system was extended to Grisslehamn and Åland.
England
Lord George Murray, stimulated by reports of the Chappe semaphore, proposed a system of visual telegraphy to the British Admiralty. Starting in 1795, chains of shutter telegraph stations were built along these routes:
London - Deal and Sheerness
Admiralty (London), West Square Southwark, New Cross, Shooter's Hill, Swanscombe, Gad's Hill, Callum Hill, Tonge (branch point), Beacon Hill, Shottenden, Barham Downs, Betteshanger, Deal.
(branch) Tonge, Barrow Hill, Sheerness.
London - Great Yarmouth
Admiralty (London), Hampstead Heath (Telegraph Hill), Woodcock Hill, St Albans, Dunstable Downs, Lilley Hoo, Baldock, Royston, Gogmagog Hills, Newmarket (Side Hill), Icklingham, Barnham, East Harling, Carleton Rode, Wreningham, Norwich, Strumpshaw, Great Yarmouth.
London - Portsmouth and Plymouth
Admiralty (London), Chelsea Royal Hospital, Putney Heath, Cabbage Hill, Netley Heath, Hascombe, Blackdown, Beacon Hill (branch point), Portsdown Hill, Portsmouth (Southsea Common).
(branch) Beacon Hill, Chalton, Wickham, Town Hill, Toot Hill, Bramshaw, Pistle Down, Chalbury, Blandford racecourse, Belchalwell, Nettlecombe Tout, High Stoy, Toller Down, Lamberts Castle, Dalwood Common, St Cyrus, Rockbeare, Gt Halden, South Knighton, Marley, Lee, Saltram, Plymouth.
The English shutter telegraph system was superseded by the semaphore system, and the lines of stations followed almost the same routes.
Many of the prominences on which the towers were built are known as 'Telegraph Hill' to this day.
Other countries
Once it had proved its success the optical telegraph was imitated in many other countries, especially after it was used by Napoleon to coordinate his empire and army.
Richard Lovell Edgeworth (1744-1817) proposed a telegraph for Ireland when a French invasion was anticipated in 1794, and again in 1796, but it was not taken up.
Germany began with a line 750 kilometres long between Berlin and Coblenz in 1833, and in Russia, Tsar Nicolas I inaugurated the line between Moscow and Warsaw in 1833;
In the United States the first optical telegraph was built by Jonathan Grout. One of the principal hills in San Francisco, California is also named "Telegraph Hill", after the semaphore telegraph which was established there in the 1850s to signal the arrival of ships into San Francisco Bay.
The semaphores were successful enough that Samuel Morse failed to sell the electrical telegraph to the French government. (Discuss)
Semaphores were adopted and widely used (with hand-held flags replacing the mechanical arms) in the maritime world in the early 1800s.
Wig-wag flags
In the 1850s, U.S. Army Major Albert J. (Its first use in battle was by Confederate Lieutenant Edward Porter Alexander at the First Battle of Bull Run in 1861.)
In this code, alphabet letters were equated with three positions of the flag, disk, or light. A flash demo can be found here
Modern semaphore
The newer flag semaphore system uses two short poles with square flags, which a flagperson holds in different positions to signal letters of the alphabet and numbers.
Characters
The following semaphore characters are presented as one would face the flagperson:
|
Rest position |
Numerals |
Error |
Cancel |
||
|
A / 1 |
B / 2 |
C / 3 / Ack |
D / 4 |
E / 5 |
F / 6 |
|
G / 7 |
H / 8 |
I / 9 |
J / Letters |
K / 0 |
|
|
L |
M |
N |
O |
P |
|
|
Q |
R |
S |
T |
U |
|
|
V |
W |
X |
Y |
Z |
Railway semaphores
It has been suggested that this article or section be merged into Railway signal. (Discuss)When the railway systems of Britain introduced signalling systems, the semaphore design was only one of many design including the cross-bar and disk.
The first railway semaphore was erected by Charles Hutton Gregory on the London and Croydon Railway (later the Brighton) at New Cross, southeast London, in the winter of 1842-1843 on the newly enlarged layout also accommodating the South Eastern Railway.
The first railway semaphores were mounted on the roof the controlling signal box, but gradually a system of wires and pulleys was developed to control the signals at a distance.
References in fiction
A dramatic episode in Hornblower and the Hotspur (one of C.
One of Dudley Pope's Lord Ramage books, Ramage's Signal, has Ramage's crew seize a Napoleonic semaphore station to send a signal directing a French convoy into a trap.
The Clacks system in Terry Pratchett's Discworld universe is very similar to the Chappe semaphore, and is probably based upon it.
In Alexandre Dumas' The Count of Monte Cristo the hero uses France's optical telegraph system to trick one of his adversaries into going bankrupt.
An episode of Monty Python's Flying Circus depicted a supposed dramatic production of Wuthering Heights in flag semaphore.
An episode of Due South featured the use of semaphore communication between two RCMP officers during a hostage crisis.
In Jack Vance's SF novel The Blue World, islands in the ocean communicate with "wink machines", which display binary arrays of panels, possibly derived from the system Chappe decided was less effective.
Keith Roberts's Pavane describes an extensive network of semaphores in Britain, operated by a powerful 'Guild of Signalers' who have a monopoly on communication;
Ernest Hemingway's The Sun Also Rises references a statue in Paris where "the inventor of the semaphore is engaged in doing same" near the Boulevard Raspail.
In the book Winter Holiday by Arthur Ransome, Nancy sends secret messages to the other children by means of a picture in which the people's arm positions represent semaphore letters.
In a recent strip, the webcomic Sam and Fuzzy portrays one of the two titular characters, Fuzzy, using flag-based semaphore to convey a message he has been expressly (and legally) forbidden to repeat.
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