COLOR (Lat., connected with Lat, crlarr, Gk. KaX6rretv, kalyptein, Ger. helacn, to hide, Ir. cctini. I conceal, Ski. garana, refuge). The color of an objeet in nature depends upon sev eral the character of the light which illuminates it, the phenomena which take place in the body its61f, the individual peculiarities of the eye which views the body. It has Lien shown by Sir Isaac Newton that ordinary white light may be regarded as a mixture of many colors: that is, it may be analyzed into parts, each part producing a different color-sensation. In scientific language. the sensation white, as perceived by looking at any ordinary 'white' ob ject-, is due to the incidence upon the eye of trains of ether-•aves of different wave-numbers, varying continuously between certain limits; while, if a train of waves of a definite wave number enters the eye, the sensation of color (if any) will be of a definite line. Thus we speak of yellow light, of led light, etc., meaning those ether-waves which produce these sense. Dons of yellow or red in a normal eye. When the ether-a ayes fall upon an object, some of the energy goes into reflected waves at the surface, the rest goes into the entering waves; there will in general be absorption in the interior; but if the body ie transparent there will be trans mitted waves, and also, in general, waves re flected and scattered by little particles in the interior of the body. The color of a green leaf is due to the fact that when viewed in ordinary daylight, out of all the waves which enter the leaf, only those combine to produce the sensation green are transmitted, the others being absorbed by the coloring matter of the leaf; thus, those waves which are scattered by the minute interior parts traverse a layer of this coloring matter, and only green light emerges from all sides. The light which in this case is
reflected at the surface is simply diffuse white light. An object whose color is due, as here, to what is called 'body absorption,' appears of the saute color when viewed by reflected light or by transmitted; that is, if We look through it at the source of light, or look at it from the same side as is the source. The colors of almost all natural objects are due to this body absorp tion.
The colors of metals, however, and some ani line dyes, are due to what is (allied 'surface ab sorption.' When white light is incident upon a piece of gold, yellow light is reflected by the surface, thus giving the yellow color. if, how ever, the gold is hammered out exceedingly thin, it will be found to transmit greenish-blue light; so that in the ease of surface color, the colors by reflection and transmission are different.
The energ'y of the waves which are absorbed in bodies generally goes to producing heat effects; but in some cases it is spent in producing other ether-waves, thus giving rise to other colors. These bodies are called 'fluorescent.' (See In these cases. then, the color as seen by transmission and by looking at the bodies sidewise will be different.
The color of the blue sky, of fine smoke, and of water in many lakes is due to the scattering of light by extremely small partieles—generally minuta solid particles: fur the short waves— that is, blue light—are reflected by minute par ticles, while the other waves simply pass around them. ln all these cases it is evident that if the incident light is altered, so will be the color perceived. A green leaf in a yellow light would appear black. For an excellent treatise on color, consult Pmod, Modern Chromatics (New York, 1879). See LIGHT.