Sir DAVID BREWSTER on the Colours of Natural Bodies. 545 



and gases, the points at which the spectrum is attacked are ge- 

 nerally coincident with the deficient lines of FRAUNHOFER ; and 

 particularly with those which are common to the light of the 

 sun, and that of some of the fixed stars. Hence it appears, that 

 these rays or lines are weak parts of the spectrum, or the parts 

 of white light which have the greatest affinity for those elements 

 of matter, which, while they enter into the composition of sublu- 

 nary bodies, exist also in the atmospheres of the central lumina- 

 ries of other systems. 



From the preceding experiments, it is impossible to resist 

 the conclusion, that the second and leading proposition of NEW- 

 TON'S theory of colours is incompatible with the actual pheno- 

 mena ; and we may demonstrate the incorrectness of the first 

 proposition by simply stating the fact, that there are red, yellow, 

 green, and blue media, which are absolutely incapable of reflect- 

 ing or transmitting certain definite rays of the same colour with 

 themselves. 



The true cause of the colours of natural bodies may be thus 

 stated : When light enters any body, and is either reflected or 

 transmitted to the eye, a certain portion of it, of various refrangi- 

 bilities, is lost within the body ; and the colour of the body, 

 which evidently arises from the loss of part of the intromitted 

 light, is that which is composed of all the rays which are not 

 lost ; or, what is the same thing, the colour of the body is that 

 which, when combined with that of all the rays which are lost, 

 compose the original light. Whether the lost rays are reflected 

 or detained by a specific affinity for the material atoms of the 

 body, has not been rigorously demonstrated. In some cases of 

 opalescence, they are either partly or wholly reflected ; but it 

 seems almost certain, that in all transparent bodies, and in that 

 great variety of substances in which no reflected tints can be 

 seen, the rays are detained by absorption. 



