COLOR 



135 



Whenever light passes through a prism or lens, it is dis- 

 persed or separated into all the colors which it contains, and 

 a band of colors produced in this way is called a spectrum. 

 If we examine such a spectrum we find the following colors 

 in order, each color imperceptibly fading into the next : violet, 

 indigo, blue, green, yellow, orange, red. 



128. Sunlight or White Light. White light or sunlight can 

 be dispersed or separated into the seven primary colors or 

 rainbow hues, as shown in the preceding Section. What 

 seems even more wonderful is that the seven spectral colors 

 can be recombined so as to make white light. 



If a prism B (Fig. 87) exactly similar to A in every way is 

 placed behind A in a. reversed position, it will undo the 

 dispersion of A, bending 

 upward the seven different 

 beams in such a way that 

 they emerge together and 

 produce a white spot on the 

 screen. Thus we see, from ^ 

 two simple experiments, that 

 all the colors of the rainbow 

 may be obtained from white 



light, and that these colors may be in turn recombined to 

 produce white light. 



White light is not a simple light, but is composed of all the 

 colors which appear in the rainbow. 



129. Color. If a piece of red glass is held in the path of 

 the colored beam of light formed as in Section 127, all the 

 colors on the wall will disappear except the red, and instead 

 of a beautiful spectrum of seven colors there will be seen the 

 red color alone. The red glass does not allow the passage 

 through it of any light except red light ; all other colors are 

 absorbed by the red glass and do not reach the eye. Only 





