COMPLEMENTARYCOLORS. Colorswhich. when combined. produce white light. Examples of pairs of such colors are given in the follow ing table: Red Green-blue Orange Cyan blue Yellow Ultramarillo GreNdsh-y..11nw Cif dot Green Purple These colors may be observed readily with a simple polaris•ope, where polarized light from a Nicol's prism (q.v.) falls iip(m a prism of cale spar and glass, in which by virtue of the doubly refracting, power of the •alc-spar (see LIGHT. paragraph Double Refraction) there is furnished a double image of the aperture through -which the polarized light from the Nicol passes. If a strip of selenite be interposed between the polar izing prism and the crystal. the two images re ferred to will he different in color. one shade being complementary to the other. These strips of selenite may he of various thicknesses, and will this produce various colors. This follOWS from the well-known principle that, when plane polarized light is transmitted through a thin plate of a doubly refracting,' medium. the ordinary and extraordinary rays when examined with a doubly refracting analyzer will give image: brightly colored. which where they overlap are white. showing that the two colors are comple mentary. If two complementary colors are com bined—and it must be remembered that the colors themselves. not the pil.onents, are here meant— then NI hit(' light is produced. This can be ac complished best, perhaps, with the .Maxnell color
disk where a disk of cardboard composed of segments of complementary colors is rapidly rotated. The impre,dons of the two colors fol low each other so rapidly that the sensations are blended, and if the colors (ire used in the right proportions we have a gray tint produced, as the luminosity of the two colors either singly or jointly is not so great as that of a white surface With which it would be compared. Complemen tary colons vary with the light by which they are dewed. and are different when :ieen by gaslight from what they are in the daytime. The explana tion is to be found in Voting's theory, where the colo•-sensation is considered to be furnished by three groups of nerves corresponding to the red. green, and violet-blue waves. If all of these nerves are stimulated together, the sensation pro duced is that of white light. Consequently, a certain red acts on the red nerves while its corresponding ownplementary color. green-blue. would stimulate the other sets of nerves, and the result of all acting together would be the sensa tion of white light. For a thorough discussion of this subject. which may be appreciated by the general reader as as the stud(•t of physics. consult Rood, Moiler), Chromulies, a new edition of which was published (New York. IS99) under the title of A Test-Book of Color. See VISI'AL SENSATION.