8 THE CHEMISTRY OF THE SUN. [CHAP. 



his work so germane to the purpose of this book : " The light 

 of the sun consists of rays differently refrangible ; " that is to 

 say, if, instead of using two coloured beams as in the last 

 experiment, we take a beam of sunlight, we find that, the 

 white light itself is compounded of light of different degrees of 

 refrangibiltey. 



But how is it possible to show the truth of Newton's asser- 

 tion, that white light is compounded of these different colours ? 

 We can do so by simply placing in the path of the coloured 

 beam another prism placed in a contrary direction, as shown 

 in Fig. 3. It will be seen that we get white light back again ; 

 for the second prism exactly undoes the work of the first. 



FIG. 3. Recomposition of white light by means of a second prism. 



The idea of white light, then, is simply an idea built up by 

 the brain, because there is a multitude of light waves of all 

 colours perpetually pouring into the eye with a velocity much 

 greater than anything which can be translated into words. It is 

 an idea which represents the integral of all the colours of which 

 the prism shows us that white light is really composed. 



It is quite easy by experiment to determine that the law 

 which, as we have seen, Newton found at work in sunlight, 

 is really equally operative in all white light, whether we get 

 it from a lamp, or candle, or, indeed, from any white flame. We 



