> water-powered telegraphs This phrasing oversells it a bit too much: The water wasn't a power source and there was no long distance movement of it. They sign

> water-powered telegraphs This phrasing oversells it a bit too much: The water wasn't a power source and there was no long distance movement of it. They signaled between users with the light of a burning handheld torch, and the duration of the light corresponded to predefined messages. Water was used at each end for independent stopwatches, to measure the duration of the light. It's easy to imagine an equivalent system using sand hourglasses. https://en.m.wikipedia.org/wiki/Hydraulic_telegraph#Greek_hydraulic_semaphore_system https://en.m.wikipedia.org/wiki/Hydraulic_telegraph#Greek_hy...