CHROMATICS. 



FIG. 316. 



(.) This recombination may be effected by means of a convex 

 lens (Fig.^316) or a concave mirror. Another simple method of 

 recombination is afforded by " Newton's disc " 

 (Fig. 317), which contains the prismatic colors 

 in proper proportion. When this disc is rapidly 

 revolved by means of the whirling table (see 

 Fig. 7), or by fastening it to a large top, the 

 colors are blended and the disc appears grayish 

 white. Still another way of producing this 

 recomposition is to pass the light as it emerges 

 from the first prism through a second prism, 

 placed in a position inverted with reference to the first. 



FIG. 317. 



64O. Color of Bodies. The color of a body is its 

 property of reflecting or transmitting to the eye light of 

 that particular color, the other rays being absorbed. This 

 power may be described as selective absorption. 



(a.) Properly speaking, color is not a property of matter, but of 

 light. A ribbon is called red, but the redness belongs to the light, 

 not to the ribbon. There would be more propriety in saying that 

 the ribbon has all the other colors of the rainbow, because it absorbs 

 the others and reflects the red. If the red ribbon be placed in the 

 green or blue of the spectrum it will appear black because it 

 receives no red rays to reflect. Colored substances decompose the 

 incident light, absorbing some rays and assuming the hue of those 

 they reflect or transmit to the eye. A body that absorbs very few 

 of the rays is white ; one that absorbs nearly all is black. There- 

 fore, black is not a color but its absence. 



