CHROMATICS is that part of the science of optics (q.v.) which explains the properties of the colors of light and of natural bodies. Before 166G, when sir Isaac Newton began to investigate this subject. the notions which prevailed respecting the nature of colors were purely fanciful. Till Descartes' time, indeed, it seems not to have been conceived that color had anything to do with light. As examples of the notions prevalent at very early times, we may cite those propounded by Pythagoras and Zeno. According to the former, color was the superfieies of bodies; according to the latter, it was " the first con figuration of matter"—whatever that may be. It is now settled that white light is not homogeneous, but consists of rays of different colors, endued with different degrees of refrangibility, and that the different colors of bodies arise from their reflecting this or that kind of rays most copiously. According to this, a body that appears red reflects red rays in greater abundance than the others; and one that appears black reflects none of the•rays—in other words, absorbs all the light that falls upon it. The analysis of a beam of the sun's light by a prism was the experiment by which Newton demonstrated his great optical discovery of the unequal refrangibility of the variously colored rays, and laid the foundations for the above theory of color. The reader will find an account
of this experiment, and of the most interesting phenomena presented by the spectrum, tinder the article SPECTRUM. Newton concluded from his experiments that white light is composed of seven colors, which he called the primary colors—viz., red, orange, yel low, green, blue, indigo, and violet, and that all other shades of color arise from the admixture of these in different proportions. Sir David Brewster, on the other hand. conceives that he has established that the primary colors are only three in number—red, yellow, and blue. This result he obtained by examining the rays of the spectrum through different absorbing media—a mode of experiment now admitted to be fallacious in principle. Professor Maxwell, by oircct examination of the rays, concludes that the three primary colors are red, green, and blue. Recently, a theory has been propounded, that all the colors are the results of the admixture of white light and of shade, or dark ness; but as yet ny attempt has been made to support this theory by direct experiment on the sun's rays. It is re-ted on rf obtained by combining by motion certain pro portions of white and black pigments on a revolving card. See the articles LIGHT, DIS PF;HSION, and NEWTON'S RINGS.