416 On Light, 



of illuminating power may depend on this circumstance. The 

 rays separated by one prism, are not capable of being further di- 

 vided by being passed through another ; and in their relations to 

 double refraction and reflection, they appear to agree with direct 

 light. An object illuminated by any of the rays in the spectrum, 

 is seen double through island crystal, in the same manner as if it 

 had been visible by white light. 



Under Caloric, we have stated the power of heating which 

 the different coloured rays of the spectrum apparently possess. 

 Sir H. Englefield, and M. Berard, confirmed the results of Sir 

 W. Herschel, with regard to the progressive increase of calorific 

 influence from the violet to the red extremity of the spectrum ; 

 and they also found with him, that a calorific influence extended 

 beyond the limit of the red light, into the unilluminated space. 

 M. Berard, however, observed, that the maximum of effect was 

 in the light, and not beyond it. This ingenious philosopher made 

 a pencil of the sunbeam pass across a prism of island spar. The 

 division of the rays formed two spectra, which presented the same 

 properties with the single spectrum. Both possessed the calorific 

 virtue in the same manner and degree. M. Berard polarized a 

 beam of liaht by reflection from a mirror ; and he found that iu 

 all the positions in which light ceased to be reflected, heat also 

 ceased to appear. The thermometer in the focus of the apparatus 

 was no longer affected. Thus, we see that the obscure heat- 

 making principle accompanies the luminous particles, and obeys 

 the same laws of action. 



If the white luna cornea, the muriate of silver moistened, be 

 exposed to the different rays in the prismatic spectrum, it will be 

 found, that no effect is produced upon it, in the least refrangible 

 ravs, which occasion heat without light ; that only a slight disco- 

 loration will be occasioned by the red rays ; that the blackening 

 power will be greater in the violet than in any other ray ; and that 

 bevond the violet, in a space perfectly obscure to our eyes, the 

 darkening effect will be manifest on the muriate. 



This fine observation, due to M. Ritter and Dr. Wollaston, 

 proves, that there are rays more refrangible than the rays pro- 

 ducing light and heat. As it appears, from the observations of 

 M. Berthollet, thitt muriatic acid gas is formed when horn-silver 

 is blackened by light, the above rays may be called hydrogenating. 

 Sir H. Davy found, that a mixture of chlorine and hydrogen acted 

 more rapidly upon each other, combining without explosion, when 

 exposed to the red rays, than when placed in the violet rays ; but 

 that solution of chlorine in water became solution of muriatic 

 acid most rapidly, when placed in the most refrangible rays in 

 the spectrum. He also observed, that the puce-coloured oxide 

 of lead, when moistened^ gradually gained a tint of red iu the 



least 



