IN THE INTERIOR OF TRANSPARENT BODIES. 437 



§ 45. It is evident that a j3 7 represent a wave, or system of waves, 

 regularly transmitted through the ether composing the common refracted 

 light : but e t) £ represent a disturbance of quite a different character, 

 propagated with a very slow velocity, and therefore such as makes each 

 cluster (at least, those at or near the bounding surfaces of the transparent 

 body,) an origin of waves spreading into vacuum as if from a point, 

 so that the bounding surfaces will appear to produce light, in the same 

 manner as luminous surfaces. 



That the natural colours of bodies, and the absorption of light by 

 coloured media, are the effects of these waves, I hope to shew in a future 

 paper in the following manner, viz. I shall prove that the intensity of 

 the waves represented by e >? £ depends on the length of the waves 

 represented by a J3 7 ; and then, that the intensity of the latter waves 

 depends in general upon the intensity of the former, and thus I shall 

 establish a relation between the intensity of light transmitted through a 

 medium and the length of the wave, such a relation as, I believe, is 

 capable of accounting for the apparently irregular manner in which 

 absorption takes place. 



Vol. VII. Pabt III. 3D 



