124 DR BREWSTER on a New Analysis of Solar Light. 



Even in physical science it is an arduous task to unsettle long 

 established and deeply-rooted opinions, and that task becomes 

 Herculean when these opinions are entrenched in national feeling 

 and associated with immortal names. There are cases indeed, 

 where the simple exhibition of new truths is sufficient to dispel 

 errors the most deeply cherished, and the most venerable from 

 their antiquity ; but it is otherwise with doctrines which depend 

 on a chain of reasoning where every step in the inductive pro- 

 cess is not rigorously demonstrative ; and of this we require no 

 other proof than is to be found in the history of NEWTON'S 

 optical discoveries, and particularly in the opposition which they 

 experienced from such distinguished men as Dr HOOKE and Mr 

 HUYGENS. 



In the investigations which I am about to explain, the instru- 

 ment employed is the absorbent action which different bodies ex- 

 ercise on different rays of white light. This principle, which 

 science had hitherto scarcely recognised, was brought into no- 

 tice by the recent discoveries respecting polarization and double 

 refraction, and was, I believe, first employed as an instrument of 

 analysis, in a paper printed in the Transactions of this Society *. 

 In the experiments there described, I examined Dr WOLLAS- 

 TON'S spectrum of four colours, viz. red, green, blue, and violet, 

 by means of a purplish-blue glass. This glass absorbed the blue 

 rays, which, when mixed with the yellow, made green, and the 

 yellow rays, which, when mixed with the red, made orange; and 

 by insulating the yellow and red, it thus effected a perfect ana- 

 lysis of the compound green and the compound orange. From 

 this experiment I drew the conclusion that yellow light has an in- 



* Description of a Monochromatic Lamp for Microscopical purposes, with re- 

 marks on the absorption of the prismatic rays by Coloured Media. Read April 

 15th 1822. Vol. IX. p. 433. 



