M. MELLONI ON THE POLARIZATION OF HEAT. 165 



the passage of rays of so distinct a nature^ that the emergent 

 heat of the first can scarcely pass by the second, and vice versa ; 

 of them I form laminae of such thicknesses that tlie quantities of 

 heat transmitted through each of them and the whole of the two 

 piles may be equal ; I then place one of these laminae against the 

 opening of the screen, and observe the calorific actions produced 

 by the rays which reach the thermoscopic body in the two principal 

 directions of the planes of refraction of the mica piles. I repeat 

 the same observations with another lamina, and obtain exactly 

 the same deviations upon the galvanometer. 



If we take in the table of reduction the forces corresponding 

 to the two galvanometrical deflections observed in either case, and 

 calculate the index of polarization from these data, we shall have 

 a value equal to that indicated by Table V., \dz. for example, 

 iMj T^j ^^ ^Tw; according as the calorific rays traverse the piles 

 under the obUquities of 41°, 35°, or 29° ; and that whatever be 

 the natiire of the lamina placed against the opening. 



The substances best adapted for these experiments of com- 

 parison are opake black glass, or green glass which is imper- 

 meable to red rays, on the one hand ; and water, citric acid, 

 or alum, on the other. It may be remembered that the heat 

 transmitted by this latter class of bodies undergoes, under the 

 influence of tourmahnes, a polarization which reaches y%^Q, while 

 the emergent heat of the antagonistic substances, green or black 

 glasses, submitted to the same polarizing system, give scarcely 

 any sensible trace of this phaenomenon, the apparent index of 

 polarization being, in certain cases, scarcely elevated to one or two 

 hundredths. And then these indices, determined by the system 

 of the two piles, no longer present any appreciable difference. 

 Thus the calorific fluxes transmitted by bodies of different natures, 

 and which fluxes are of a constitution so different, are all equally 

 polarizable by refraction ; which proves that the polai'ization pro- 

 duced by the refractive forces of the media is independent of the 

 quality of the calorific rays. 



Though this consequence is rigorously estabUshed by the ex- 

 periments that have been just related, it appeared to be not altoge- 

 ther useless to verifj' it also upon calorific rays emanating from dif- 

 ferent sources. To this end I replaced the Locatelli lamp by a 

 spiral of platina maintained in a state of incandescence, by means 

 of the flame of alcohol. The indices of polarization were again 

 equal to those indicated by our eight tables. The same thing 



