Lighthouse lamp reflector mirror, early 19th century.
© Science Museum / Science & Society Picture Library
This reflector is a compound mirror made of 720 separate flat pieces held together in a metal framework. They form a parabolic mirror, one of three, formerly used to focus the light beam of the Walney Island lighthouse off the Lancashire coast. Consisting of three oil lamps with individual reflectors, the whole asembly rotated over a period of quarter of an hour providing flashes of light every 5 minutes.