Dr Brewster on a New Analysis of Solar Light. 199 



violet, and the violet beginning at the indigo, and terminating 

 at the extremity of the spectrum. 



I have not been able to discover what the general objections 

 are which Mr Herschel refers to in the preceding passage : but 

 the formidable one which he distinctly specifies will be found 

 to have no weight. An obscure physiological fact occurring in 

 one eye out of a million, could not, on any principle, affect the 

 result of a legitimate induction ; but even if we invest it with 

 the character of a general fact, it will be found to be a direct 

 argument in support of the very views which it was supposed 

 to contradict. 



These views, or the analysis of the spectrum to which they 

 lead, may be expressed in the following propositions : 



1. White light consists of three simple colours, red, yellow, 

 and blue, by the mixture of which all other colours are formed. 



2. The solar spectrum, whether formed by prisms of trans- 

 parent bodies, or by grooves in metallic and transparent sur- 

 faces, consists of three spectra of equal length, beginning and 

 terminating at the same points, viz. a red spectrum, a yellow 

 spectrum, and a blue spectrum. 



8. All the colours in the solar spectrum are compound colours, 

 each of them consisting of red, yellow, and blue light in differ- 

 ent proportions. 



4. A certain quantity of white light, incapable of being de- 

 composed by the prism, in consequence of all its component 

 rays having the same refrangibility, exists at every point of the 

 spectrum, and may, at some points, be exhibited in an insu- 

 lated state. 



This remarkable structure of the spectrum will be better 

 understood from Plate II., where Figs. 1, 2, and 3, represent 

 the three separate spectra, which is shown in their combined 

 state in Fig. 4 N 



In all these figures the point M corresponds with the red, 

 or least refrangible extremity of the spectrum, and N with 

 the violet, or most refrangible extremity ; and the ordinates 

 ax, hx, ex, of the different curves MUN, MYN, MRN, re- 

 present the intensity of the red, yellow, and blue ray at any 

 point x of the spectrum. 



If the distance M x in all these spectra be equal, then, in 



