26 REPORT—1 840. 
In recapitulating his views, the author refers to the wnequal 
absorption of the two pencils in different tourmalines, as cau- 
sing the differences observed. 
A further paper by the same author, on Tourmaline, &c., in 
the dnn. de Chim., April, 1836, displays much ingenuity, but 
nothing of peculiar novelty or fundamental importance. 
From the Comptes Rendus, 1836, i. 194, it appears, that 
on the 15th Feb. 1836, M. Arago communicated to the Aca- 
demy of Sciences a letter from Prof. Forbes, announcing his 
discovery of the circular polarization of heat of the rock-salt 
rhomb. 
At the next meeting of the same body (Feb. 22), MM. Biot 
and Melloni stated, that in following up Prof. Forbes’s experi- 
ment, they had found that quartz possessed the same “‘rotative”’ 
quality for heat as for light. 
Dr. Thomson, in the second edition of his Treatise on Heat, 
&c. (1840), while giving an outline of the discoveries of Forbes 
and Melloni, has by no means clearly distinguished the share 
borne by each of those philosophers in the investigation. In 
particular, with respect to the fact of polarization, he has not 
given Prof. Forbes the credit so unquestionably due to him for 
the priority of the discovery. He observes (p. 139), ‘ In the 
earlier experiments of Melloni, he did not find that the rays of 
heat were polarized when passed through the tourmaline. But 
he afterwards found that this conclusion was hasty, and that 
the tourmaline polarizes heat as well as light. The truth of 
this statement is shown very clearly by Prof. Forbes. They 
also polarized heat by plates of mica, and also by reflexion,”’ &c. 
These expressions certainly assign the priority to Melloni, as 
well as an equal share in the subsequent results ; both of which 
we have seen are greatly at variance with the truth. 
Further Researches: Forbes. 
Prof. Forbes’s second series of Researches on Heat was read 
to the Royal Society of Edinburgh, May 2, 1836, and printed 
both in the Edinburgh Transactions, vol. xiii., and in the London 
and Edinburgh Journal of Science, vol. xii. 1838. 
The author remarks at the outset, that in his former memoir 
he had confined himself to the establishment of the general 
facts of the polarization and dipolarization of heat, without pre- 
tending to accurate quantitative results ; he now proceeds, there- 
fore, to a more detailed investigation of the subject, with a view 
to more precise numerical determinations. 
The first section relates to the methods of observation em- 
ployed, and the examination of the values of the degrees of the 
