412 
and transporting heat, yet, in a qui- 
escent state, or as a fluid whose 
parts are at rest with respect to each 
other, is not capable of conducting 
it, or giving it a passage; in short, 
that heat is incapable of passing 
through a mass of air, penetrating 
from one particle of it to another ; 
and that it is to this circumstance 
that its non-conducting power is 
principally owing. yt 
It is also to this circumstance, in 
a great measure, that it is owing 
that its non-conducting power, or 
its apparent warmth when employed 
as a covering for confining beat, is 
so remarkably increased upon being 
mixed with a small quantity of any 
very fine, light, solid substance, 
such as the raw silk, fur, eider- 
down, &c. in the foregoing experi- 
ments: for, as I have already ob- 
served, though these substances, in 
the very small quantities in which 
they were made use of, could 
hardly have prevented, in any con- 
siderable degree, the air from con- 
ducting, or giving a passage to the 
heat, had it been capable of passing 
through it, yet they might very 
much impede it in the operation of 
transporting it. ~ 
But there is another circumstance 
which it is necessary to take into 
the account, and that is, the attrac- 
tion which subsists between air and 
the bodies above mentioned, and 
other like substances, constituting 
natural and artificial clothing. For, 
though the incapacity of air to give 
a passage to heat in the manner so- 
lid bodies and non-elastic fluids peér- 
mit it to pass through them, may 
enable us to account for its warmth 
under certain circumstances, yet 
the bare admission of this principle 
does not-seem to be sufficient to ac- 
count for the very extraordinary 
ANNUAL REGISTER, 1792. 
degrees of warmth which we find 
in furs and feathers, and in va- 
rious other kinds of natural and ar- 
tificial clothing; nor even that 
which we find in snow; for if we 
suppose the particles of air to be at 
liberty to carry of the heat which 
these bodies are meant to confine 
without any other obstraction or 
hinderance than that arising from 
their vis inertie, or the force neces- 
sary to put them in motion, it seems 
probable that the succession of fresh 
particles of cold air, and the conse- 
quent loss of heat, would be much 
more rapid than we find it to be in 
fact. ’ 
That an attraction, and a very 
strong one, actually subsists between 
the particles of air and the fine hair 
or furs of beasts, the feathers of 
birds, wool, &c. appears by the ob- 
stinacy with which these substances 
retain the air which adheres to 
them, even when immersed in wa- 
ter, and put under the receiver of 
an air-pump; and that this attrac- 
tion is essential to the warmth of 
these bodies, I think is very easy to 
be demonstrated. 
In furs, for instance, the attrac- 
tion “between the particles of air 
and the fine hairs in which it is con- 
cealed, being greater than the en- 
creased elasticity, or repulsion of 
those particles with regard to each 
other, arising from the heat com- 
municated to them by the animal 
body, the air in the fur, though 
heated, is not easily displaced; and 
this coat of confined air is the real 
barrier which defends the animal 
body from the external cold. This 
air cannot in the least carry off the 
heat of the animal, because it is it- 
self confined, by its attraction to the 
hair or fur; and it transmits it with 
great difficulty, if it transmits it * 
all, 
