164 S VENTEENTH CEXTUR Y. PT. in. 



the same spot on the wall ; it was more bent in passing 

 through the prism, and made an orange spot at o, above the 

 point R. By this Newton knew that an orange ray is more 

 refracted in passing through a prism than a red ray is. He 

 moved his prism, A B c, again, so as to let the yellow ray 

 o 



FIG. 31. 



Diagram showing the Different Refraction of Rays of Different Colours. 

 D E, Shutter. F, Round hole. ABC, First prism. M N, Screen receiving the 

 spectrum, g, Small hole through which the rays of only one colour can pass. 

 H i K, Second prism refracting those rays. 



through. This was still more bent, and fell above o on the 

 point Y. In this way he let all the different coloured rays 

 pass through the hole, marking the points on which they 

 fell, and he found that each ray was more bent than the last 

 one, till he had marked out a second complete spectrum on 

 the wall. Only the two extreme rays, red and violet, are 

 traced out in Fig. 31, to avoid confusion. 



This experiment proved clearly, ist, that light is made up 

 of differently coloured rays ; and 2d, that these rays are 

 differently refracted in passing through a prism. The red rays 

 are least bent, and the violet ones most, while each of the 

 other rays between these have their own course through the 

 prism. I must warn you, however, not to think that there 

 are exactly seven colours: there are really an infinite number, 

 passing gradually into each other; Newton only divided them 

 roughly into seven for convenience. 



