200 Dr Brewster on a Neio Analysis of Solar Light. 



the combination of them shown in Fig. 4, the ordinates ax, 

 bx, ex, will indicate the nature and intensity of the colour at 

 any point x of the red spectrum. Thus, let 



The ordinate for red light ax = 30 

 yclloxo bx — 16 



blue ex = 2 



ax -f bx -{- c x = 4>8 rays, 



then the point x will be illuminated with 48 rays of light, viz. 

 30 of red, 16 of yellow, and 2 of blue light. 



Now, as there must be certain quantities of red and yellow 

 light, which will form white, when combined with 2 blue rays, 

 let us assume these, and suppose that white light, whose in- 

 tensity is 10, will be formed by 3 red, 5 yellow, and 2 blue 

 rays ; hence it follows that the point x is illuminated by 



Red rays, 27 



Yellow rays, 11 



White light, 10 



48 rays, 



or what is the same thing, the light at x will be orange, ren- 

 dered brighter by a mixture of white light. The tzvo blue 

 rays, therefore, which enter into the composition of the light 

 at x, will not communicate any blue tinge to the prevailing 

 colour. 



If the point x is taken nearer M, and if, at that point, the 

 blue rays are more numerous in proportion to the yclloiv than 

 2 to 5, that is, if they are as 3 to 5, then there will be 1 blue 

 ray more than what is necessary to make white light with the 

 2 yellow and the 3 red rays, and this blue ray will give a blue 

 tinge to that part of the spectrum, or will modify the peculiar 

 colour of pure red light. In like manner, the blue extremity 

 of the spectrum may have its peculiar colour modified by an 

 excess of red rays so as to convert it into violet light. In this 

 manner the tinge of red light at the blue extremity of the 

 spectrum, and of blue light at the red extremity, may be ex- 

 plained, even if the least refrangible branch BM of the blue 



