Optical telegraphy. 19th-century artwork of French soldiers using optical telegraphy. One such early device was the Mangin projector, invented by a co
Optical telegraphy. 19th-century artwork of French soldiers using optical telegraphy. One such early device was the Mangin projector, invented by a colonel Mangin in the early 1880s. Optical telegraphy systems used a telescopic device for observing a distant signal. The range of visibility varied from 20-100 kilometres, depending on the weather. In the day, reflected sunlight was used to send the signal. The sequences of flashes was read out by the observer and recorded and decoded by the other soldiers. Artwork from the 6th volume (second period of 1890) of the French popular science weekly 'La Science Illustree'.
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Photo credit: © Science Photo Library / Alamy / Afripics
License: Licensed
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