saw this on an episode of Coast (BBC) last night
Holyhead to Liverpool Optical Telegraph
The Holyhead Sea Cadets demonstrate how the optical telegraph works Long before telephones and cables, shipping companies sent complex messages from Holyhead to Liverpool with the aid of an Optical Telegraph. Whilst most messages took three or four minutes to arrive, it is claimed that they once managed to send a message the entire 100 miles in as little as 27 seconds.
It was called an 'Optical' telegraph because the signal on the telegraph pole could be seen from one station to the next. The different positions of the arms on the telegraph represented different numbers which could be translated into a message using the telegraph code book - which could have been anything from 'sunk during the night' to 'have you many sick on board?'.