Bell Rock Lighthouse lamps, c 1810.
© Science Museum / Science & Society Picture Library
Engraving showing the 24 reflectors of the light which were mounted on a rectangular frame, the longer sides housing seven reflectors each. The shorter side of the frame housed five reflectors each. Red panes of glass were placed in front of the two groups of five reflectors to provide an alternating sequence of red and white flashes. The mechanism for rotating the frame is shown at bottom left. Illustration from 'An account of the Bell Rock Light-house: including the details of the erection and peculiar structure of that edifice; to which is prefixed a historical view of the institution and progress of the Northern Light-houses' by Robert Stevenson (1772-1850), designer of the Bell Rock Lighthouse, published in Edinburgh in 1824.