LAWS OF REFRACTION, ETC. 75 



nine millions of millions per second." * In this way the 

 scale of colors in the solar spectrum is compared to the scale 

 of musical notes and intervals. Indeed, Helmholtz has con- 

 structed a theoretical scale of colors to correspond with mu- 

 sical tones and semitones. 3 



The analysis of white light into the different colors of the 

 spectrum shows that it is compound ; and, by synthesis, the 

 colored rays may again be brought together, producing white 

 light. Colors may be obtained by decomposition of light 

 by transparent bodies, the different colored rays being re- 

 fracted, or bent by a prism at different angles. It is not in 

 this way, however, that the colors of different objects are 

 produced. Certain objects have the property of reflecting 

 the rays of light. A perfectly smooth, polished surface, 

 like a mirror, may reflect all of the rays ; and the object then 

 has no color, only the reflected light being appreciated by 

 the eye. Certain other objects do not reflect all of the 

 rays of light, some of them being lost to view, or absorbed. 

 When an object absorbs all of the rays, it has no color, and 

 is called black. "When an object absorbs the rays equally, 

 and reflects a portion of these rays without decomposition, it 

 is gray or white. There are many objects, however, that de- 

 compose white light, absorbing certain rays of the spectrum 

 and reflecting others. The rays not absorbed, but returned 

 to the eye by reflection, give color to the object. Thus, if an 

 object absorb all of the rays of the spectrum except the red, 

 the red rays strike the eye, and the color of the object is red. 

 So it is with objects of different shades, the colors of which 

 are given simply by the unabsorbed rays. 



It is a curious fact that the mixture of different colors in 

 certain proportions will result in white. Two colors, which, 

 when mixed, result in white, are called complementary. The 

 following colors of the spectrum bear such a relation to 

 each other : 



1 TYNDALL, Light and Electricity, New York, 1871, p. 65. 



2 HELMHOLTZ, Optique physiologique, Paris, 1867, p. 319. 



