406 
That thread wound light round 
the bulb of the thermometer should 
form a covering less warm than the 
game quantity of wool, or other 
saw materials of which the thread 
is made, surrounding the bulb of 
the thermometer in a more loose 
‘woanner, and consequently occu- 
pying a greater space, is no more 
‘than what I expected, from the 
idea I had formed of the causes of 
the warmth of covering; but I 
confess I was much surprised to 
find that there is so great a differ- 
ence in the relative warmth of these 
two coverings, when they are em- 
ployed to confine great degrees of 
“heat, and when the heat they con- 
‘fine is much Jess in proportion to 
‘the temperature of the surround- 
ing medium. This difference was 
very remarkable. In the experi- 
ments with sheep's wool, and with 
woollen thread, the warmth of the 
covering formed ‘of sixteen grains 
of the former, was to that formed 
of sixteen grains of the latter, when 
the bulb of the thermometer was 
heated to 70° and cooled to 60°, 
as 79 to 46 (the surrounding me- 
dium being at 0°) ; but afterwards, 
when the thermometer had only 
fallen from 20° to 10° of heat, the 
warmth of the wool was to that of 
the woollen thread only as 426 to 
410; andin the experiments with 
Jint, and with Jinen thread, when 
the heat was much abated, the co- 
vering of the thread appeared to 
be even warmer than that of the 
tint, though in the beginning of the 
experiinents, when the heat was 
much greater, the lint was warmer 
than the thread, in the proportion of 
80 to.46. 
From hence it-should seem that 
@ covering may, under certain 
eircumstances, be very good for 
ANNUAL REGISTER, 1792. 
confining small degrees of warmth, 
which would be but very indiffe- 
rent when made use of for confin- 
ing a more intense heat, and vice 
versa. This, I believe, is a new 
fact ; and, I think the knowledge 
of it may lead to further discove- 
ries relative to the causes of the 
warmth of coverings, or the man- 
ner in which heat makes its pas- 
sage through them. But I forbear 
to enlarge upon this subject, till I 
shall kave given an account of se- 
veral other experiments, which I 
think throw more light upon it, 
and which will consequently render 
the investigation easier and more 
satisfactory. 
With a view to determine how 
far the power which certain bodies 
appear to possess of confining heat, 
when made use of as coveiing, de- 
pends upon the natures of those 
bodies, considered as chymical sub- 
stances, or upon the chymical prin- 
ciples of which they are composed, 
I have made the following expe- 
riments. 
As charcoal is supposed to be 
composed almost entirely of phlo- 
giston, I thought that, if that prin- 
ciple was the cause either of the 
conducting power, or the non- 
conducting power of the bodies 
which contain it, I should discover 
it by making the experiment with 
charcoal, as I had done with various 
other bodies. Accordingly, having 
filled the globe of the passage-fher- 
mometer with one hundred and 
seventy-six grains of that substance 
in very fine powder (it having 
been pounded in «a mortar, and 
sifted through a fine.sieve) the bulb 
of the thermometer being surround- 
ed.by this powder, the instrament 
was heated in boiling water; and 
being afterwards plunged into a 
mixture 
