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On the Colours of Natural Bodies. By Sir DAVID BREWSTER, 

 K. H. LL. D. F. R. S. LOND. V. P. R. S. EDIN. 



(Read 22d December 1833.) 



THERE are few of the applications of optical science so univer- 

 sally interesting as that which has for its object the explanation 

 of the colours of natural bodies. Sir ISAAC NEWTON was the first 

 person who ventured to refer to one general principle all the va- 

 riety of colours which are found in nature ; and he has maintain- 

 ed his opinions on this subject with a confidence in their accu- 

 racy which seems to have confounded his adversaries : For while 

 his analysis of light, the most perfect of ah 1 his labours, exposed 

 him to the most harassing controversies, his theory of natural 

 colours, the least perfect of his speculations, was allowed to pass 

 without examination or censure. 



During the century which has elapsed since the death of NEW- 

 TON this theory has been generally received and admired : In our 

 own day it has been ingeniously defended, and beautifully illus- 

 trated, by M. BIOT ; and, with few exceptions, it has been adopt- 

 ed by most of the distinguished philosophers of the present age. 



The author of this theory has presented it under the two 

 following propositions, one of which states the general cause of 

 the phenomena, and the other the particular constitution of na- 

 tural bodies on which their colours depend. 



1. " Every body reflects the rays of its own colour more co- 

 piously than the rest, and from their excess or predominance in 

 the reflected light, has its colour. 



