Engraving showing George Murray's (1761-1803) six-shutter system, comprising of a frame with six octagonal boards or shutters which can be individually opened and closed by rope or cable, to transmit mesages from the Admiralty in London to a given destination which would also be equipped with the telegraph. The shutters were able to generate 64 permutations of numbers and letters in code. A mesage could be sent and a reply received within 20 minutes. Published by S W Fores of London.
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