Optical telegraph
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An optical telegraph is a line of stations, typically towers, for the purpose of conveying textual information by means of visual signals. There are two main types of such systems: the semaphore teleg
A replica of one of Chappe's semaphore towers in Nalbach, Germany
Illustration of signalling by semaphore in 18th-century France. The operators would move the semaphore arms to successive positions to spell out text messages in semaphore code, and the people in the next tower would read them.
An optical telegraph during World War I
19th-century demonstration of the semaphore
Telegraphy
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Telegraphy is the long-distance transmission of messages where the sender uses symbolic codes, known to the recipient, rather than a physical exchange of an object bearing the message. Thus flag semap
Optical telegraph
…to early nineteenth centuries. Chappe used the term télégraphe to describe the mechanism he had invented – that is the origin of the English word "telegraph". Lines of relay towers with a semaphore rig at the top were built within line of sight of each other, at separations of 5–20 miles (8–32 km). Operators…
A section of the Great Wall of China built during the Ming dynasty (1368–1644)
A site in Hammersmith London (UK) where Sir Francis Ronalds constructed the first electric telegraph in 1816