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Greek hydraulic semaphore system

Greek hydraulic semaphore system


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50.5 MB (7.7 MB compressed)

3717 x 4748 pixels

31.5 x 40.1 cm ⏐ 12.4 x 15.8 in (300dpi)

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This illustration is based on the description by the 2nd century BC Greek military historian Polybius of the visual system of fire signals devised by Aeneas Tacticus, an early Greek writer on the art of war in the 4th century BC. It was an improvement on the simple beacon system in that by using identical water vessels containing a graduated column floating in the vessel and synchronised by visual signals from hand-held torches, it was possible to transmit a limited range of predetermined messages. The sender signalled to the receiving operator with his torch to start the synchronisation, then adjusted the height of the column by draining out some water until the required graduation reached the appropriate level, at which point he immediately lowered his torch. The receiver simultaneously stopped the flow of water from his vessel to decode and read the message.

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