BY COLOURED MEDIA. 479 



(3.) Now, as regards only the general fact of the ob- 

 struction and ultimate extinction of light in its passage 

 through gross media, if we compare the corpuscular and 

 undulatory theories, we shall find that the former appeals 

 to our ignorance, the latter to our knowledge, for its 

 explanation of the absorptive phenomena. In attempt- 

 ing to explain the extinction of light, on the corpuscular 

 doctrine, we have to account for the light so extinguished 

 as a material body, which we must not suppose anni- 

 hilated. It may, however, be transformed ; and among 

 the imponderable agents, heat, electricity, &c., it may 

 be that we are to search for the light which has become 

 thus comparatively stagnant. The heating power of the 

 solar rays gives a prima facie plausibility to the idea of 

 a transformation of light into heat by absorption. But 

 when we come to examine the matter more nearly, we 

 find it encumbered on all sides with difficulties. How is 

 it, for instance, that the most luminous rays are not the 

 most calorific, but that, on the contrary, the calorific 

 energy accompanies, in its greatest intensity, rays which 

 possess comparatively feeble illuminating powers 1 These 

 and other questions of similar nature may perhaps admit 

 of answer in a more advanced stage of our knowledge ; 

 but at present there is none obvious. It is not without 

 reason, therefore, that the question, "What becomes of 

 light 1 ?" which appears to have been agitated among the 

 photologists of the last century, has been regarded as one 

 of considerable importance as well as obscurity by the 

 corpuscular philosophers. 



(4.) On the other hand, the answer to this question 



