Brewster's patent kaleidoscope, c 1817.
© Science Museum / Science & Society Picture Library
A kaleidoscope is an optical toy that shows the viewer many reflected copies of a single image. Invented in 1816 by Sir David Brewster (1781-1868), the Scottish scientist, the device is named after the Greek words 'kalos' (beautiful), 'eidos' (form) and 'scopos' (watcher). It consists of a tube holding angled mirrors with a peep-hole at one end. At the opposite end of the cylinder a clear glas cap retains, one of 12, hollow transparent discs containing coloured glas pieces. In operation the kaleidoscope tube is turned as the user looks inside the tube. This causes the coloured fragment to tumble and offers the viewer an ever-changing series of symmetrical patterns that are repeated several times due to multiply reflections off the mirrors.