209 
from Dr. Dalton (in the Memoirs of this Society) and from 
Dr. Thomson’s System of Chemistry, published some sixty 
years ago, wherein the absorption and radiation of heat by 
aqueous vapour in the formation and dissolution of clouds, 
dew, fogs, &c., are clearly explained upon the established 
doctrine of the mutation of heat reciprocally from and into 
latent and sensible states; hence the doubt as to any new 
discovery on these points. 
To give the course of reasoning submitted by the author 
against the mechanical theory of heat, and to sustain that of 
a material calorific element, would require a more copious 
abstract of his paper than the limits of the printed Proceed- 
ings would allow ; so that while calling in question both the 
novelty and the soundness of the discoveries on which he has 
commented, he refers to his paper in extenso for the explana- 
tion of his own views on the nature of a material calorific 
element, and of the elastic forces exerted by the mutations of 
such elements. 
MICROSCOPICAL SECTION. 
October 19, 1863. 
Professor Williamson in the Chair. 
A letter from Captain J. Mitchell, dated Madras, the loth 
May, 1863, was read, of which the following is an extract: 
The view that the universal form of cotton hairs is a 
flattened fibre consisting of scarcely anything but membrane, 
is by no means novel ; for much the same description of the 
cotton fibre has been given by Quekett, Henfrv, and many 
others. Indeed that opinion is general. Almost every one 
you ask will tell you that the cotton fibre is flat and twisted, 
or perhaps a flat spiral. That this is not the general form of 
