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Kaleidoscopes. 19th-century diagrams of one of two types of poly-angular kaleidoscopes made by the London optician Robert Brettell Bate. Kaleidoscopes contain loose, coloured objects such as beads or pebbles, creating patterns when viewed through the eyepiece due to light reflecting off the mirrors. The three figures show the metallic reflectors in the devices. The complete instrument mounted on its stand is at lower left. A longitudinal section is at top, while a transverse section is at lower right. These diagrams are from 'A Treatise on the Kaleidoscope' (1819) by Scottish physicist David Brewster (1781-1868). Brewster patented his kaleidoscope invention in 1816. (KEYSTONE/SCIENCE PHOTO LIBRARY/KING'S COLLEGE LONDON/SCIENCE PHOTO LIBRARY)