XIIL 



ON THE ABSORPTION OF LIGHT BY 

 COLOURED MEDIA, 



VIEWED IN CONNEXION WITH THE UNDULATORY THEORY.^ 



^l/m~'B^^'^'H.'E absorption of lidit by coloured media is 

 a branch of physical optics which has only 

 since a comparatively recent epoch been 

 studied with that degree of attention which 

 its importance merits. The speculations of Newton on 

 the colours of natural bodies, however ingenious and 

 elegant, can hardly, in the present state of our know- 

 ledge, be regarded as more than a premature general- 

 ization ; and they have had the natural effect of such 

 generalizations, when specious in themselves and sup- 

 ported by a weight of authority admitting for the time 

 of no appeal, in repressing curiosity, by rendering further 

 inquiry apparently superfluous, and turning attention 



* The substance of this paper was read before the Section of 

 Physics of the British Association, at Cambridge, 1833. Some in- 

 accuracies of wording are corrected, but nothing introduced h&?^x:- 

 ing on the views more recently entertained as to the conversion oi 

 motion into heat-vibration. 



