7 
ARTICLE XIV. 
Memoir on the Polarization of Heat; by MacEpo1nE 
MELLonI. 
From the Annales de Chimie et de Physique, vol. lxi., April, 1836. 
Axsout 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 1829, 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 reflection+. In 1834, I found that calo- 
rific rays, in their passage through plates of tourmaline which com- 
pletely polarized light, gave no apparent sign of polarizationt. 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 +4, 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 
was reduced to +*,%, or +$5 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 
* Mémoires de Physique et de Chimie de la Société d’ Arcueil, tom. iii. page 5. 
+ Edinburgh Journal of Science, S.S. vol. vi. and x. 
{ Annales de Chimie et de Physique, tom. lv. page 375. 
- § Bibliothéque Universelle de Geneve, tom. lvii. p. 1. 
|| Transactions of the Royal Society of Edinburgh, vol. xiii. part. 1. p. 152: 
Vor. I.—Parrt II. Z 
