REPORT ON RADIANT HEAT. 25 
Polarization of Heat from different sources: Melloni. 
M. Melloni’s first memoir ‘ On the Polarization of Heat,”’ was 
read to the Academy of Sciences in Jan. 1836; it appears in 
the Ann. de Chim. |xi. April, 1836 ; and is translated in Tay- 
lor’s Scientific Memoirs, Part II. p. 325. 
The author commences with a fair review of the previous in- 
vestigations on the subject, admitting Prof. Forbes’s discovery, 
but remarking the very small amount of the effect in the case 
of obscure heat. 
He adopts the supposition, that “‘ the different temperatures 
of the calorific rays are to radiant heat what the different 
colours of the luminous rays are to light.’’ The latter, he 
observes, are all equally polarizable, and thus he is led to regard 
the difference of polarizability in the rays of heat as rather 
apparent than real. His object then, in this memoir, is to 
examine the question of the reality of the polarization of heat, 
and of the equality of the effect in different sorts of heat. 
After some considerations on the general nature of the appa- 
ratus to be employed, and overcoming the difficulty arising 
from the small total intensity of the rays, by concentrating them 
by means of a rock-salt lens, he proceeds to detail his several 
series of experiments, the results of which he gives in the 
form of tables :— 
Table I. gives the different indices of polarization obtained 
with nine sorts of tourmalines of different colour, the source of 
heat being a locatelli lamp. 
He then tried the experiment, taking that pair of tourmalines 
which gave the greatest effect in the last set, with plates of 
various substances interposed between the lamp and the appa- 
ratus. Of these, opake black glass rendered the effect nearly 
insensible ; other solids and liquids of various degrees of trans- 
parency produced effects of different magnitude. 
In Table II. these results are registered, and the properties of 
the media, in this respect, were found to follow the same pro- 
portion as their diathermancy. 
The author considers the difference of the tourmalines in this 
respect as referrible to the same cause. 
Table III. gives similar results with another pair of tourma- 
lines, in which case the proportions are found to differ. 
In Table IV. are given the indices of polarization with four 
different pairs of tourmalines, each employed with different 
sources of heat; viz. the locatelli lamp, argand lamp, incan- 
descent platina, and copper at 400°. The effect in the latter 
Case was very small. 
