323 



Article XIV. 



Memoir on the Polarization of Heat ; by Macedoine 

 Melloni. 



From the ylnnales de Chimie et de Physique, vol. Ixi., April, 1836. 



xVBOUT twenty -five years since, M. Berard, of Montpellier, an- 

 nounced that heat was capable of undergoing double refraction and 

 polarization*. His experiments, which were repeated in presence of 

 Berthollet and Dulong, were universally admitted by philosophers until 

 towards the close of 1 829, when doubts as to the certainty of the con- 

 clusions which had been deduced from them were raised by Mr. Powell, 

 in his account of some unsuccessful experiments of the same kind, 

 made with an apparatus similar to that employed by Berard for the 

 purpose of polarizing heat by reflectionf. In 1834, 1 found that calo- 

 rific rays, in their passage through plates of tourmaline which com- 

 pletely polarized light, gave no apparent sign of polarization J. Nobili, 

 whose recent death science has so much cause to deplore, arrived some 

 time subsequently at the same result. He attempted also to polarize 

 heat by reflexion, but obtained no satisfactory indication §. At last 

 Mr. Forbes observed, about the close of 1834', signs of polarization 

 in the heat transmitted through tourmalines and small piles of mica 

 placed at a proper inclination to the incident rays. In these experi- 

 ments, the greatest proportion of polarized heat was given by a system 

 of piles composed of plates of mica, and amounted to -iVir when 

 Mr. Forbes operated on the calorific rays of a spiral of platina kept in 

 a state of incandescence by the flame of alcohol ; but this proportion 

 vas reduced to -rVV or -yw when the same piles were brought to act on 

 the caloric issuing from a vessel heated by mercury or by water in a 

 state of ebullition ||. 



The different temperatures of the calorific rays are to radiant heat 

 what the different colours of the luminous rays are to light. Now, it 

 is known that the latter are all equally polarized by the action of the 

 same polarizing system. The experiments of Mr. Forbes would seem 



• Memoires de Physique et de Chimie de la Societe d'Arcueil, torn. iii. page 5. 

 •f- Edinburgh Journal of Science, S. S vol. vi. and x. 

 X Annates de Chimie et de Physique, torn. Iv. p«ge 375. 

 § Bibliotheque Universelte de Geneve, torn. Ivii. p. 1. 



II Transactions of tlie Royal Society of Edinburgh, vol. xiii. part. i. p. 1.52; 

 Vol.. I Fart II. z 



