appearance of so-called rainbow colors. This appear- 

 ance is called chromatic aberration and is a result of 

 refraction. It is caused by dispersion or the dispersive 

 quality, the separation of light into its primary colors, 

 violet, indigo, blue, green, yellow, orange and red, in the 

 Order given. 



indiifo 

 iolet 



Fig. 11. 



The dispersion of light by a prism is shown in 

 Fig. 1 1 , and it will be seen that the ray of white light 

 a b on entering the prism at b is separated into the 

 different colors in the order given, and that on 

 emergence at the second surface the violet ray at v has 

 undergone the greatest amount of refraction and the 

 red ray at r the least. The band of colors formed 

 is called the spectrum. The results of dispersion are 

 nicely illustrated in the diamond, this having a very 

 high degree of refracting power and is polished or cut 

 to make a many-sided prism in which each face or 



ii 



