An old engraving of an optical telegraph (semaphore). It is from a Victorian book of the 1880s. It involved a line of stations (towers about 5–20 miles apart), passing visual signals or semaphores (centre pic). Station operators watched their nearest towers through a telescope. When the ‘arms’ spelt out letters/symbols, they would pass these to the next tower. The most used type was by Frenchman Claude Chappe (1792). Long arms with 7 positions, plus a connecting crossbar with 4 different angles (left), created 196 symbols. The Prussian system (right) had 6 wings and was capable of 4096 symbols
An old engraving of optical telegraph or semaphore equipment. It is from a Victorian mechanical engineering book of the 1880s. An optical telegraph is a line of stations, typically towers, for the purpose of conveying information by means of visual signals or semaphores. 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. Relay towers with a semaphore rig at the top (centre illustration) were built within sight of each other, about 5–20 miles (8–32 km) apart. Operators at each tower would watch the neighbouring 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. The Chappe system (left) was controlled by two handles – each of the 2-metre-long arms could display 7 positions, with the crossbar connecting the two arms four different angles, for a total of 196 symbols. The Prussian system (right) had 6 wings and was capable of 4096 symbols. An English system used rotating panels (a shutter telegraph) rather than arms. Semaphore lines were a precursor of the electrical telegraph, which replaced them half a century later. It was cheaper, faster, and more private.
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Photo credit: © M&N / Alamy / Afripics
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