An ancient hydraulic telegraph being used by Aeneas to send a message.

A hydraulic telegraph was one of two hydraulic-telegraphic telecommunication systems, one developed in 4th century BCE Greece, and the other in 19th century AD Britain. The Greek system was deployed in combination with semaphoric fires, while the latter British system was purely hydraulic.

Although both systems employed water in their sending and receiver devices, their transmission media were completely different. The ancient Greek system transmitted its semaphoric information to the receiver visually, which limited its use to line-of-sight distances in good visibility weather conditions only. The 19th century British system used water-filled pipes to effect changes to the water level in the receiver unit (similar to a transparent water-filled flexible tube used as a level indicator), thus limiting its range to the hydraulic pressure that could be generated at the transmitter's device.^[1]

While the Greek device was extremely limited in the codes (and hence the information) it could convey, the British device was never deployed in operation other than for very short-distance demonstrations.^[1] The British device could, however, be used in any visibility within its range of operation so long as its conduits, if unheated, did not freeze in sub-zero temperatures —which contributed to its impracticality.

Greek hydraulic semaphore system[link]

The ancient Greek design was described in the 4th century BC by Aeneas Tacticus and the 3rd century BC by the historian Polybius. According to Polybius, it was used during the First Punic War to send messages between Sicily and Carthage.

The system involved identical containers on separate hills; each container would be filled with water, and a vertical rod floated within it. The rods were inscribed with various predetermined codes at various points along its height.

To send a message, the sending operator would use a torch to signal the receiving operator; once the two were synchronized, they would simultaneously open the spigots at the bottom of their containers. Water would drain out until the water level reached the desired code, at which point the sender would lower his torch, and the operators would simultaneously close their spigots. Thus the length of time the sender's torch was visible could be correlated with specific predetermined codes and messages.

A contemporary description of the ancient telegraphic method was provided by Polybius. In The Histories, Polybius wrote:^[2]

^[2]

British hydraulic semaphore system[link]

The British civil engineer Francis Whishaw, who latter become a principal in the General Telegraph Company, publicized a hydraulic telegraph in 1838 but was unable to deploy it commercially. By applying pressure (or a negative pressure vacuum) at a transmitter device connected to a water-filled pipe which travelled all the way to a similar receiver device, he was able to effect a change in the water level which would then indicate coded information to the receiver's operator.^[1]

See also[link]

• Signal lamp
• Telegraph
• Heliograph

References[link]

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External links[link]

• Connected Earth

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