‘In the Pentland Firth, for instance where several lights would eventually be visible at one time, it was necessary to distinguish each with an individual pattern of flashes. At the time, all lights were fixed, sending out a steady beam in one direction throughout the night..... (Robert Louis Stevenson)  began slowly to devise methods of rotating the reflectors on a central axis so they appeared instead to flash. His first few experiments were troublesome, since it seemed almost impossible to devise a smoothly balanced mechanism for the cumbersome rank of lamps. In  practice, it often required one of the keepers to spend the night pushing the light round in circles. Nevertheless, by 1908, the new lighthouse at Start Point included a clockwork mechanism...  

From The Lighthouse Stevensons by Bella Bathurst