SECT, xxv.] NATURE OF CALORIC. 253 



(N. 213). So, likewise, beings may exist on earth, in the air, 

 or in the waters, which hear sounds our ears are incapable 

 of hearing, and which see rays of light and heat of which we 

 are unconscious. Our perceptions and faculties are limited 

 to a very small portion of that immense chain of existence 

 which extends from the Creator to evanescence. 



The identity of action under similar circumstances is one 

 of the strongest arguments in favour of the common nature 

 of the chemical, visible, and calorific rays. They are all 

 capable of reflection from polished surfaces, of refraction 

 through diaphanous substances, of polarization by reflection 

 and by doubly refracting crystals : none of these rays add 

 sensibly to the weight of matter ; their velocity is prodigious ; 

 they may be concentrated and dispersed by convex and con- 

 cave mirrors ; they pass with equal facility through rock-salt, 

 and are capable of radiation; the chemical rays are subject 

 to the same law of interference with those of light ; and, al- 

 though the interference of the calorific rays has not yet been 

 proved directly, the indirect evidence places it beyond a 

 doubt. As the action of matter in so many cases is the same 

 on the whole assemblage of rays, visible and invisible, which 

 constitute a solar beam, it is more than probable that the 

 obscure as well as the luminous part is propagated by the 

 undulations of an imponderable ether, and consequently 

 comes under the same laws of analysis. 



When radiant heat falls upon a surface, part of it is re- 

 flected and part of it is absorbed ; consequently, the best 

 reflectors possess the least absorbing powers. The tempera- 

 ture of very transparent fluids is not raised by the passage 

 of the sun's rays, because they do not absorb any of them ; 

 and, as his heat is very intense, transparent solids arrest a 

 very small portion of it. The absorption of the sun's rays 

 is the cause both of the colour and temperature of solid 

 bodies. A black substance absorbs all the rays of light, 

 and reflects none ; and since it absorbs, at the same time, 

 all the calorific rays, it becomes sooner warm, and rises to a 



