196 COLOK. 



arated into differently-colored parts. In coming out of 

 the prism on the other side at o, it is 

 refracted more, and the component col- 

 ored portions are still more widely sep- 

 arated. They go on diverging as they 

 recede, until, when they at length fall 

 upon the wall at d, or upon a screen 

 placed there to receive them, the rays 

 .KHKAOTIONOKBOLAKBAY. which entered at a as a small beam of 

 white light form an elongated band of the most brilliant 

 and beautiful colors. 



This band is called a spectrum. In this case it is the 

 spectrum of solar light, or the solar spectrum, that is pro- 

 duced. The spectrum of any other light may be produced 

 by similar means. 



In case, however, the light to be employed radiates from 

 a point that is near, so that the rays are divergent instead 

 of being parallel like the sun's rays, there is an advantage 

 in passing them first through a convex lens to bring them 

 to parallelism before they enter the prism. 



The number of colors which were developed in the solar 

 spectrum by Newton's experiments were seven, and were 

 called for a long time the seven primitive colors. It was 

 found that, by mingling these hues again by any suitable 

 means, the white light from which they originated was re- 

 produced. Thus the beam of white light, it was found, 

 could be separated by refraction into rays of seven differ- 

 ent colors, and these, by being combined again, would re- 

 produce the original beam of white light. 



There are many ways by which this reproduction can 

 be effected. One is by gathering the rays together again 

 from the spectrum by means of a lens, or of another prism, 

 in a reversed position. Another is by mixing paints of the 

 seven hues together upon a painter's pallet. A third mode 



