H9 
and the Mode of its Communication. 
clothing, or its power of preventing our bodies from being 
cooled by the influence (frigorific radiations) of surrounding 
colder bodies, depends very much on the polish of its surface. 
If, with the assistance of a microscope, we examine those 
substances which supply us with the warmest coverings, such 
for instance as furs, feathers, silk, &c. we shall find their sur- 
faces not only smooth, but also very highly polished ; we shall 
also find that, other circumstances being equal, those substances 
are the warmest which are the finest, or which are composed 
of the greatest number of fine polished detached threads or 
fibres. 
The fine white shining fur of a Russian hare, is much warmer 
than coarse hair; and fine silk, as spun by the silk-worm, is 
warmer than the same silk twisted together into coarse threads ; 
as I found by actual experiments, an account of which has 
already been laid before this Society, and published in the Phi- 
losophical Transactions. 
I formerly considered the warmth of natural and artificial 
clothing, as depending principally on the obstacle it opposes to 
the motions of the cold air by which the hot body is surrounded ; 
but, by a patient and careful examination of the subject, I have 
been convinced, that the efficacy of radiation is much greater than 
I had supposed it to be. 
From the result of the experiment No. 31, we might be led 
to conclude, that a very small part only of the heat which a hot 
body appears to lose when it is * cooled in air, is in fact commu- 
nicated to that fluid ; a much greater portion of it being com- 
municated to other surrounding bodies at a distance; and, in 
one of my former experiments, a hot body was cooled, though it 
was placed in a Torricellian vacuum. 
