dichroscope

[Gr. dichroia =double color, and skopeō to see.] Optics: An instrument to exhibit the two complementary colors of polarized light. The quality called the dichroism of crystals consists in transmitting different colors when viewed in different directions. There several varieties of this apparatus invented by Arago and Brewster. As constructed by Brewster, it consists of a tube about two inches long, blackened on the interior, and attached to a ball and socket. The ball contains two prisms of calcareous spar, separated by a film of sul phate of lime, so placed that each pair of the four images is tinged with the complementary colors. A lens is arranged upon or near the prisms either at front or back. On viewing the sky or any luminous object, four brilliantly colored images of the aper ture will be seen, the color of the two middle ones being complementary to that of the outer ones. By moving the ball in the socket the colors will constantly change, and the images will sometimes overlap and sometimes separate, exhibiting a great variety of hues pleasing the eye by their combinations, and by the soft harmony of their contrasts. Many beautiful variations may be obtained by using several films of sulphate of lime having their axes variously inclined to one another.