50 THEORY OF LIGHT. 



transmission through other bodies subsequently, it would appear 

 to partake so immediately of the nature and properties of light, 

 as that I should impute to them a direct identity ; and that as 

 light pervades all bodies, and that in its separation from fixed 

 bodies in which it was temporally retained, and while approxi- 

 mating the state of visible radiancy or perfection, it may assume 

 an intermediate state of an invisible nature, affording the sensa- 

 tion and qualities of heat, without any other cause than the 

 energy of action to effect its transition, and not in the least sup- 

 porting the idea that heat is a body distinct from light ; and 

 further, that the separations that have been effected of the calo- 

 rific invisible rays from the colorific visible rays can only be 

 considered as a divisional state, produced between perfect light 

 and the residuary uncombined constituents of light, when ap- 

 proximating union to produce that splendour which CELESTIAL 

 light, in its complete effulgence, so manifestly exhibits. 



It has been observed by sir John Herschel, that the heating 

 power of the solar rays gives a primd facie plausibility to the 

 idea of a transformation of light into heat by absorption, but 

 that it is incumbered with difficulties, as the most luminous rays 

 are not the most calorific ; while, on the contrary, the calorific 

 energy is of greatest intensity in the feebly illuminating rays. 



He also observes, that although without explanation at pre- 

 sent, we may yet have it in a more advanced state of knowledge. 

 " What becomes of light?" A perplexing question to the 

 corpuscular philosophers ! while he says the answer afforded 

 by the undulatory theory is simple and distinct; that it 

 merges on the more general question, What becomes of 

 motion ? And the answer, he repeats, on dynamical principles, 

 is, <( that it continues for ever" 



Now the circumstance of the greater portion of calorific 

 intensity being afforded by * the less luminous rays, is in ac- 

 cordance with the theory that I beg to advance, that HEAT is 

 but a modification of light, from the absence or abstraction of 

 some one or more of its original principles of composition, 



