Colours. 203 



that the red rays continued red, the orange 

 the same, he. The cause of the phenomenon, 

 therefore, was no longer a secret. It was plain 

 that every beam of light consisted of particles 

 different in colour, or which rather have the effect 

 of producing different colours, and that all of 

 them blended together formed white. It was 

 further evident, that the particles of one colour 

 were more refrangible than those of another ; 

 and therefore those which formed the upper part 

 of the image or spectrum suffered a much greater 

 refraction than those at the bottom; in other 

 words, were more under the influence of the at- 

 tractive powers of the glass. Hence it was further 

 evident why the figure or spectrum was of an 

 oblong form instead of round ; for the particles 

 of light, being differently refrangible, were spread 

 out longitudinally by the action of the prism. 



Various experiments will convince you that 

 white light is no more than a compound of 

 these parti-coloured rays or particles. Thus, if, 

 instead of the sheet of paper MN, you sub- 

 stitute the large convex glass D, see fig. 78, in 

 its place, the scattered rays will be converged and 

 united at W, where, if the paper is placed to 

 receive them, you will see a circular spot of a 

 lively white. At W also the rays will cross 

 each other ; and if the paper is removed a little 

 further, you will see the prismatic colours again 

 displayed as at RV, only in an inverted order, 

 owing to the crossing of the rays. 



