64 RADIATION OF CALORIC. 



The radiating power of the body heated is in the same ratio 

 with its absorbing power. Charcoal has the highest radiating 

 power of any known substance, and may, therefore, contain 

 oxygen, azote, and hydrogen. According to Mr. Leslie's inge- 

 nious researches, taking the radiating power of lamp-black at 

 100, the following radiate in the proportions thus expressed : 

 sealing-wax 95, crown glass 90, China ink 88, ice 85, minium 

 80, isinglass 80, plumbago 75, tarnished lead 45, clean lead 19, 

 polished iron 15, tin-plate, gold, silver, and copper 12. 



Of the influence of radiant matter in producing chemical 

 changes, we have an instance exemplified by MM. Gay Lussac 

 and Theynard, and Mr. Dalton. When a mixture of chlorine 

 and hydrogen is exposed to the solar beams, they detonate, though 

 the same effect is not produced by the application of a heat be- 

 low ignition. Sir H. Davy, in explanation, says, he supposes 

 the temperature of particles of substances is raised considerably 

 arid instantaneously by the rays ; but it may be likewise, and 

 with more probability, be supposed to depend upon a specific 

 and peculiar influence of radiant matter : and that such an in- 

 fluence exists, is proved by many circumstances. 



When moist horn-silver is exposed to the influence of the 

 violet ray, and those invisible rays beyond it, it is blackened, 

 and muriatic acid gas is formed, as proved by Messrs. Hitter, 

 Wollaston, and Berthollet, so that they may be termed the 

 hydrogenating rays. 



The general facts of refraction and effects of the solar beam 

 offer analogy to the agency of electricity. In the Voltaic cir- 

 cuit the maximum of heat seems to be at the positive pole, 

 where the power of combining with oxygen is given to bodies, 

 and the agency of rendering bodies inflammable is excited at 

 the opposite surface ; and similar effects are produced by nega- 

 tive electricity, and by the most refrangible rays of the solar 

 beam. See Davy's Elements of Chemical Philosophy, p. 212. 



It has been remarked that the health of vegetation, with the 

 color of plants and flowers, depend on the presence of light ; 



