546 HISTORY OF THERM OTICS. 



But, without here tracing further the influence 

 which a knowledge of the polarization of heat 

 must exercise upon the formation of our theories, 

 we must briefly notice this important discovery, as 

 a law of phenomena. 



The analogies and connexions between light and 

 heat are so strong, that when the polarization of 

 light had been discovered, men were naturally led 

 to endeavour to ascertain whether heat possessed 

 any corresponding property. But partly from the 

 difficulty of obtaining any considerable effect of heat 

 separated from light, and partly from the want of 

 a thermometrical apparatus sufficiently delicate, 

 these attempts led, for some time, to no decisive 

 result. M. Berard took up the subject in 1813. 

 He used Malus's apparatus, and conceived that he 

 found heat to be polarized by reflection at the sur- 

 face of glass, in the same manner as light, and with 

 the same circumstances 25 . But when Professor 

 Powell, of Oxford, a few years later (1830), repeated 

 these experiments with a similar apparatus, he 

 found' 6 that though the heat which is conveyed 

 along with light is, of course, polarizable, " simple 

 radiant heat," as he terms it, did not offer the 

 smallest difference in the two rectangular azimuths 

 of the second glass, and thus showed no trace of 

 polarization. 



Thus, with the old thermometers, the point re- 



25 Ann. Chim. March, 1813. 



a6 Edin. Journ. of Science, 1830, vol. ii. p. 303. 



