126 Dr BREWSTER on a New Analysis of Solar Light. 



To these remarks Mr HERSCHEL has added an illustrative 

 figure of the spectrum, in which it is made to consist of four co- 

 lours, red, yellow, blue, and violet ; the red extending to the mid- 

 dle of the yellow, the yellow beginning at the extremity of the 

 orange and terminating at the indigo, the blue beginning at the 

 middle of the yellow, and terminating at the end of the 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 cha- 

 racter 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 surfaces, 

 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. 



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

 each of them consisting of red, yellow, and blue light in different 

 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 spec- 

 trum, and may, at some points, be exhibited in an insulated 

 state. 



