180 M. MELLONI ON THE POLARIZATION OP HEAT. 



tensity ? Now the sense of vision, reduced to this state of sim- 

 pHcity, would become, as to Hght, what our thermometers are as 

 to heat. Wherefore, if the two complementary pencils of obscure 

 heat were transmitted by a substance possessing a high degree 

 of diathermancy, it is very possible that they might not be 

 equally absorbed, in which case we should have an indirect 

 proof of the interference of the two calorific pencils. I have 

 tried the experiment with several sorts of plates, and have al- 

 ways obtained the same relation of transmission in the two 

 cases. These results do not decide the question negatively. 

 It is very possible, I will even say probable, reasoning from 

 analogy, that the calorific rays interfere ; but, in my opinion, 

 we have not yet a single fact whence any experimental proof 

 whatever, direct or indirect, of these interferences, may be de- 

 duced. 



As to the polarization of heat, its existence and its general 

 laws appear to me to be fully proved by the numerous facts 

 recorded in this memoir. I have endeavoured to describe 

 the fiindamental experiments as clearly as possible, in order 

 that all who are interested in the progress of physics may study 

 them with facility. I may add, they are neither difficult nor 

 uncertain ; I have repeated them very many times, and in the 

 presence of several physicists, and always with perfect success. 



At the commencement of these researches we proposed to 

 explain the contradictions jDresented in the results obtained by 

 diflferent experimenters upon calorific polarization ; but this 

 task becomes needless after the long investigation, into which 

 we found it necessary to enter in relation to Mr. Forbes's expe- 

 riments. 



All the differences observed in the polarization of heat de- 

 veloped by the forces of reflection and refraction, are attribu- 

 table to the MORE OR LESS SENSIBLE HEATING of the appa- 

 ratus of polarization ; excepting in the case of the tourmalines, 

 which render the phaenomena of polarization sensible or not, ac- 

 cording to the quality of those minerals. 



The portion of heat regularly reflected by the mirrors, and re- 

 fracted or transmitted immediately by the piles, is very small, 

 relatively to the quantity of heat absorbed by the mirrors or 

 laminae. If the thermoscopic body be placed so as to be simul- 

 taneously affected by these two species of heat, the difference 

 existing between the feeble reflected or refracted rays in the 



