Semaphore telegraph

A replica of one of Chappe's semaphore towers in Nalbach, Germany
Illustration of signaling 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.

A semaphore telegraph is a system of conveying information by means of visual signals, using towers with pivoting shutters, also known as blades or paddles. Information is encoded by the position of the mechanical elements; it is read when the shutter is in a fixed position. 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.[1][2][3] Lines of relay towers with a semaphore rig at the top were built within line-of-sight of each other, at separations of 5 to 20 miles. Operators at each tower would watch the neighboring tower through a spyglass, and when the semaphore arms 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. Semaphore lines were a precursor of the electrical telegraph, which would replace them half a century later, and would also be cheaper, faster, and more private. The line-of-sight distance between relay stations was limited by geography and weather, and prevented the optical telegraph from crossing wide expanses of water, unless a convenient island could be used for a relay station. Modern derivatives of the semaphore system include flag semaphore (a flag relay system) and the heliograph (optical telegraphy using mirror-directed sunlight reflections).

Etymology and terminology

The word semaphore was coined in 1801 by the French inventor of the semaphore line itself, Claude Chappe.[4] He composed it from the Greek elements σῆμα (sêma, "sign"); and from φορός (phorós, "carrying"),[5] or φορά (phorá, "a carrying") from φέρειν (phérein, "to bear").[6] Chappe also coined the word tachygraph, meaning "fast writer"[7]. However, the French Army preferred to call Chappe's semaphore system the telegraph, meaning "far writer", which was coined by French statesman André François Miot de Mélito.[8] The word semaphoric was first printed in English in 1808: "The newly constructed Semaphoric telegraphs", referring to the destruction of telegraphs in France.[9] The word semaphore was first printed in English in 1816: "The improved Semaphore has been erected on the top of the Admiralty", referring to the installation of a simpler telegraph invented by Sir Home Popham.[citation needed] Semaphore telegraphs are also called "optical telegraphs", "shutter telegraph chains", "Chappe telegraphs" or "Napoleonic semaphore".

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