jsnented.
The operation of introducing into the globe the
fubftances whofe conducting powers are to be de
termined, is performed in the following manner ;
the thermometer being taken out of the cylindri
cal tube, about two-thirds of the fubftance which
is to be the fubjecl of the Experiment are introdu
ced into the globe ; after which, the bulb of the
thermometer is introduced a few inches into the
cylinder ; and, after it, the remainder of the fub
ftance being placed round about the tube of the
thermometer ; and laftly, the thermometer being
introduced farther into the tube, and being brought
into its proper place, that part of the fubftance which,
being introduced laft, remains in the cylindrical
tube above the bulb of the thermometer, is pufhed
down into the globe, and placed equally round the
bulb of the thermometer by means of a brafs wire
v/hich is palled through holes made for that pur-
pofe
432 Of the Propagation of Heat
pofe in the ftopple clofmg the end of the cylindri
cal tube.
As this inftrument is calculated merely for meaf-
uring the paffage of Heat in the fubftance whofe
conducting power is examined, I mail give it the
name of paffage-thermometer 9 and I mail apply the
fame appellation to all other inftruments conftrucl-
ed upon the fame principles, and for the fame ufe,
which I may in future have occafion to mention ;
and as this inftrument has been fo particularly de-
fcribed, both here, and in my former Paper upon
the fubject of Heat, in fpeaking of any others of
the fame kind in future it will not be neceffary to
enter into fuch minute details. I mall, therefore,
only mention their J!zes 9 or the diameters of their
bulbs, the diameters of their globes, the diameters of
their cylinders, and the lengths and diviiions of
their tubes, taking it for granted that this will be
quite fufficient to give a clear idea of the inftrument.
In moft of my former Experiments, in order to
afcertain the conducling power of any body, the
body being introduced into the globe of the paf-
iage-thermometer, the inftrument was cooled to
the temperature of freezing water, after which, be
ing taken out of the ice-water, it was plunged fud-
denly into boiling water, and the times of heating
from ten to ten degrees were obferved and noted ;
and I faid that thefe times were as the conducling
power of the body inverfcly ; but in the Experi
ments of which I am now about to give an ac
count, I have in general reverfed the operation ;
that
in 'various Subftances. 433
that is to fay, inftead of obferving the times of
heating, I have firft heated the body in boiling wa
ter, and then plunging it into a mixture of pound
ed ice and ice-cold water, I have noted the times
taken up in cooling.
I have preferred this lafl method to the former,
not only on account of the greater eafe and con
venience with which a thermometer, plunged in
to a mixture of water, may be obferved, than when
placed in a veflel of boiling water, and furrounded
by hot fleam, but alfo on account of the greater
accuracy of the Experiment, the heat of boiling
water varying with the variations of the prefTure
of the atmofphere : confequently the Experiments
made upon different days will have different re-
fults, and pf courfe, ftriclly fpeaking, cannot be
compared together 5 but the temperature of
pounded ice and water is ever the fame, and of
courfe the refults of the Experiments are uniform.
In heating the thermometer, I did not in gen
eral bring it to the temperature of the boiling wa
ter, as this temperature, as I have juft obferved, is
variable ; but when the mercury had attained the
75 of its fcale, I immediately took it out of the
boiling water, and plungedit into the ice and water ;
or, which I take to be ftill more accurate, fuffering
the mercury to rife a degree or two above 75, and
then taking it out of the boiling water, I held it
over the vefTel containing the pounded ice and
water, ready to plunge it into that mixture the
moment the mercury, defcending, paffes the 75.
Having a watch at my ear which beat half fec-
onds, (which I counted) I noted the time of the
pafTagc
434 Of the Propagation of Heat
paflage of the mercury over the divifions of the
thermometer, marking 70 and every tenth degree
from it, defcending to 10 of the fcale. I contin
ued the cooling to o, or the temperature of the ice
and water, in very few inftances, as this took up
much time, and was attended with no particular
advantage, the determination of the times taken up
in cooling 60 degrees of Reaumur's fcale, that is to
fay, from 70 to 10, being quite fufficient to af-
certain the conducting power of any body whatever.
During the time of cooling in ice and water, the
thermometer was conftantly moved about in this
mixture from one place to another ; and there was
always fo much pounded ice mixed with the water,
that the ice appeared above the furface of the water ;
the veffel, which was a large earthen jar, being firft
quite filled with pounded ice, and the water being
afterwards poured upon it, and frefh quantities of
pounded ice being added as the occafion required.
Having defcribed the apparatus made ufe of in
thefe Experiments, and the manner of performing
the different operations, I fhall now proceed to give
an account of the Experiments themfelves.
My firft attempt was to difcover the relative con-
dueling powers of fuch fubftances as are commonly
made ufe of for clothing ; accordingly, having pro
cured a quantity of raw filk, as fpun by the worm,
Jheep's wool, cotton wool, linen in the form of the
fineft lint, being the fcrapings of very fine Irifli
linen, the fineft part of the fur of the beaver fepa-
rated from the fkin, and from the long hair, tlje
fineft part of the fur of a white Ruffian bare, and
Eider
in various Subftdtices. 435
ider down ; I introduced fuccefii vely 1 6 grains in
Weight of each of thefe fu'bftances into the globe of
the pafTage-thermometer, and placing it carefully
and equally round the bulb of the thermometer, I
heated the thermometer in boiling water, as be
fore defcribed, and taking it out of the boiling
water, plunged it into pounded ice and water,
and obferved the times of cooling.
But as the interflices of thefe bodies thus placed
In the globe were filled with air, 1 firft made the
Experiment with air alone, a!nd took the refult of
that Experiment, as a ftandard by which to com
pare all the others ; the remits of three Experi
ments with air were as follows :
The bulb of the thermometer furrounded by air.
Exp. No. i.
Exp. No. a
, Exp. No. 3.
Heat loft.
Heat
Time
1 Time
acquired.
Time
elapfed.
. elapfed.
elapfed.
70
;
10
60
38"
38"
20
39"
50
46
46
30
43
40"
59
59
40
53
30
80
79
50
67
20
122
122
60
96
10
231
230
70
J?5
Total' times.
576
574
'
473
VOL. II.
Kkk
43 6 Of *&* Propagation of Heat
The following Table fhows the refults of the
Experiments, with the various fubftances therein
mentioned :
8""" 1
"3
^
.
*
cfcl
3 g
^
O
.5 C
5 S
e
Wi
| u
go"
wjf
a M
So
' M)
1
"t^
34 M
Cj HI
o M
1 H
g M
K
^ ""*
CO
U
K
M
Exp. i.|Exp. 4.
Exp. 5. Exp. 6.
Exp. 7.
Exp. 8.
Exp. 9.
Ex. 10.
70
___
- _
-
_^_
__
' 60
3*
94"
79"
83"
fty
99"
97"
98"
CO?
46
no
95
95
93
116
117
III
4O
59
133
118
117
"5
153
144
146
30
80
185
162
151
150
185
193
192
20
122
273
238
a2i
a r3
265
270
I0
Ijl
489
426
378
376
478
494
485
Total times.
576
1284 mS } 1046
1031] 1296
I3T5
1305
Now the 'warmth of a body, or its power to
confine Heat, being as its power of refilling the
paffage of Heat through it, (which I mall call its
non-conducling power) and the time taken up by
any body in cooling, which is furrounded by any
medium through which the Heat is obliged to
pafs, being, cateris faribits^ as the refiftance which
the medium oppofes to the paffage of the Heat, it
appears that the warmth of the bodies mentioned
in the foregoing Table are as the times of cooling ;
the conduftingpo^vers being inverfely as thofe times,
as I have formerly mown.
From the refults of the foregoing Experiments
it appears, that of the feven different fubftances
made ufe of, hares' fur and Eider down were the
warmeft ;
in various Siibftances. 437
warmeft ; after thefe came beavers' fur ; raw filk ;
fheep's wool ; cotton wool ; and laftly, lint, or the
fcrapings of fine linen ; but I acknowledge that
the differences in the warmth of thefe fubftances
were much lefs than I expected to have found
them.
Sufpecting that this might arife from the vol
umes or folid contents of the fubftances being dif
ferent, (though their weights were the fame) arif-
ing from the difference of their fpecific gravities ;
and as it was not eafy to determine the fpecific
gravities of thefe fubftances with accuracy, in or
der to fee how far any known difference in the
volume or quantity of the fame fubftance, confined
always in the fame fpace, would add to or dimin^
ifh the time of cooling, or the apparent warmth
of the covering, I made the three following Ex.
periments.,
In the firft, the bulb of the thermometer was
{unrounded by 16 grains of Eider down ; in the
fecond by 32 grains ; and in the third by 64 grains;
and in all thefe Experiments the fubftance was
made to occupy exactly the fame fpace, viz. the
whole internal capacity of the glafs globe, in the
centre of which the bulb of the thermometer was
placed ; confequently the thicknefs of the covering
of the thermometer remained the fame, while its
denfity was varied in proportion to the numbers
i, 2, and 4.
The refults of thefe Experiments were as follow :
43?
Of the Propagation of Heat
The bulb of the thermometer being furrounded
by Eider down.
Heat loft.
1 6 grains.
32 grains.
64 grain*.
(Exp. No. II.)
(Exp. No. iz.)|(Exp. No. 13.)
70
60
50
40
30
20
10
91"
H7
H5
192
267
486
Ill' 7
128
'57
207
34
565
112"
130
I6 5
224
326
658
Total times.
i34
1472
1615
Without flopping at prefent to draw any
ticular conclufions from the refults of thefe Ex
periments, I ihall proceed to give an account of
fome others, which will afford us a little further
inllght into the nature of fome of the circumitances
upon which the warmth of covering depends.
Finding by the laft Experiments, that the density
of the covering added fo conliderably to the
warmth pf it, its thicknefs remaining the fame,
I was now defirous of difcovering how far the inter
nal ftru<5hire of it contributed to render it more or
lefs pervious to Heat, its thicknefs and quantity
of matter remaining the fame. By internal ftruc-
ture, I mean the difpofition of the parts of the
fubftance which forms the covering; thus they
may be extremely divided, or very fine, as raw
filk
in various Subjlances. 439
filk as fpun by the worms, and they may be
equally diftributed through the whole ipace they
occupy ; or they may be coarfer, or in larger
mafies, with larger interftices a as the ravelings of
cloth, or cuttings of threads.
If Heat paffed through the fubftances made ufe
of for covering, and if the warmth of the covering
depended folely upon the difficulty which the Heat
meets with in its paiTage through the fubftances, or
folid parts, of which they are compofed ; in that
cafe, the warmth of covering would be always,
eateris paribus, as the quantity of materials of
which it is compofed ; but that this is not the
caTe, the following, as well as the foregoing Expe
riments clearly evince.
Having, in the Experiment No. 4, afcertained
the warmth of 1 6 grains of raw iiik, I now re
peated the Experiment with the fame quantity,
or weight, of the ravelings of white taffety, and
afterwards with a like quantity of common fewing
lilk, cut into lengths of about two inches.
The following Table {hows the refults of thefe
three Experiments :
440
Of the Propagation of Heat
S
ts
o
SD
M
1
4-J y^
3
u oT
rt
ji
t^^ M
g bo
S ^2
VS
en \o
bO v ^
L
.s *^*
.So"
&
i
rt
IF
w
Exp. 4.
Exp. 14.
Exp. 15.
70
MM
60
94"
9 0"
67"
50
no -
1 06
79
40
133
128
99
30
185
172
135
20
273
246
. 10
489
427
342
Total times.
1284
1169
917
Here, notwithstanding that the quantities of the
filk were the fame in the three Experiments, and
though in each of them it was made to occupy the
fame fpace, yet the warmth of the coverings which
were formed were very different, owing to the dif
ferent difpofition of the material.
The raw filk was very fine, and was very equally
diftributed through the fpace it occupied, and it
formed a warm covering.
The ravelings of taffety were alfo fine, but not
fo fine as the raw filk, and of courfe the interftices
betwen its threads were greater, and it was lefs
warm ; but the cuttings of fewing filk were very
coarfe, and confequently it was very unequally dif
tributed in the fpace in which it was confined ; and
it made a very bad covering for confining Heat.
It
in various Subftanccs.
445
It is clear from the refults of the five laft Experi
ments, that the air which occupies the interitices
of bodies, made ufe of for covering, acts a very
important part in the operation of confining Heat \
yet I fliall poftpone the examination of that circum-
flance till I ihall have given an account of feveral
other Experiments, which, I think, will throw flill
more light upon that fubject.
But, before I go any further, I will give an ac
count of three Experiments which I made, or ra*
ther the fame Experiment which I repeated three
times the fame day, in order to fee how far they
may be depended on, as being regular in their re
fults.
The glafs globe of the palTagc-thermometer
being filled with 16 grains of cotton-wool, the in-
ilrument was heated and cooled three times fucccf-
fively, when the times of cooling were obferved as
follows :
Heat loft.
lxp. 1 6.
Exp. 17.
Exp. 18. I
70
__
60
82"
84"
83"
5
9 6
95
95
40
118
117
116
30
152
*53
1 S 1
20
221
221
220
10
3&o
377
377
Total times.
1049
1047
1042
The difference of the times of cooling in thefe
three Experiments were extremely fmall j but reg*
ular
442 Of the Propagation of Heat
illar as thefe Experiments appear to have been irl
their refults, they were not more fo than the other"
Experiments made in the fame way, rriariy of which
were repeated two or three times, though, for the
fake of brevity, I have put them down as iinglc
Experiments.
But to proceed in the account of my inveftiga-
tions relative to the caufes of the warmth of warm
clothing. Having found that the finenefs and equal
diftribution of a body or fubftance made ufe of to
form a covering to confine Heat, contributes fo
much to the warmth of the covering, I was de-
iirous, in the next place, to fee the effect of con*
denfmg the covering, its quantity of matter re*
maining the fame,but its thicknefs being diminifhed
in proportion to the increafe of its denfity.
The Experiment I made for this purpofe was as
follows : I took 1 6 grains of common fewing
filk, neither very fine nor very coarfe, and winding
it about the bulb of the thermometer in fuch a
manner that it entirely covered it, and was as
nearly as poffible of the fame thicknefs in every
part, I replaced the thermometer in its cylinder and
globe, and heating it in boiling water, cooled it in
ice and water, as in the foregoing Experiments*
The refults of the Experiment were as may be feen
in the following Table ; and in order that it may
be compared with thofe made with the fame quan
tity of filk differently difpofed of, I have placed
thofe Experiments by the fide of it :
in various Subftances.
443
C
M
{ 8
4.J
o T
jiii
<i5
SO
b
jg
C- < o pfa cj
C vO
i^5 M
cs ^ ^
^ s .
M
>
bfl^ *
g 3 ** -Q ii
C
'> ' -c u ^
K
1
ij
5
K **
C/2
"S *.*S
Exp. No. 4.
Exp. No. 14. Exp. No. 15.
Exp. No. 19.
70
60
94"
9 0"
6 7 "
46"
50
no
106
79
62
40
133
128
99
85
30
185
172
121
20
273
246
195
191
10
489
427
34 2
399
Total times
1214
1169
917
904
It is not a little remarkable, that, though the
covering formed of fewing filk wound round the
bulb of the thermometer in the ipth Experiment,
appeared to have fo little power of confining the
Heat when the inflrument was very hot, or when
it was firft plunged into the ice and water, yet af
terwards, when the Heat of the thermometer ap
proached much nearer to that of the furrounding
medium, its power of confining the Heat which re
mained in the bulb of the thermometer appeared to
be even greater than that of the filk in the Experi
ment N 15, tRe time of cooling from 20 to 10
being in the one 399", and in the other 342". The
fame appearance was obferved in the following
Experiments, in which the bulb of the thermome
ter was furrounded by threads of wool, of cotton,
and of linen, orjlax, wound round it, in the like
VOL. II. L 1 1 manner
444 Of *h e Propagation of Heat
manner as the fewing filk was wound round it in
the laft Experiment.
The following Table {hows the refults of thefc
Experiments, with the threads of various kinds ;
and that they may the more eafily be compared
with thofe made with the fame quantity of the fame
iubftances in a different form, I have placed the ac
counts of thefe Experiments by the fide of each
other. I have alfo added the account of an Expe
riment, in which 16 grains of fine linen cloth were
wrapped round the bulb of the thermometer, going
round it nine times, and being bound together
at the top and bottom of it, fo as completely to
cover it.
t*
R "3 .
*
G "3
Aj
- ^ v:
|8
2 "^ b
3 rQ %
'B ^ ^
S J3 v
rt g
MW
bjO ^ "v
b^ flj
So w w
*3 c
WQ qj *^
WjQ C
d
w
M^ I
>o-S |
M^ |
uT^2 4>
0^ 1
>o g-S
rt
fca H
til
:.n
ill
So*'
trl 1
M (H D
^ "O JS
bo g
2 ^ -G
-T -
X
^ S* 5
"5 "O ^
? c ^
^ -d "^
^ .s s
5 0.^0
Jc
* 9 -^
s M
"2 s J2
w ^ "
* G ^
^
v s
^3 O
g 1- ^
^
- 2 "
u^
5 i "2 "
v. W* O
\s ^ O
-w ^ ^
^* ? o
"^ u **3
S ^
_R ? J2
^
Q> ^
3
s
s
Exp. 5-
Ex. 20
Exp. 6.
Ex. 21.
Exp. 7.
Ex. 22.
Exp. 23.
7 o
__
__
_
___
79"
46"
83"
45"
80'
46"
42,"
50
95
63
95
60
9^
62
56
40
118
.to
83
Uj
83
74
30
. 162
126
15^
150
117
108
2.0
238
2OO
221
179
1 80
168
10
426
410
37S
370
376
385
338
Total times
1118
934
1046
852
10^
873
"83
That thread wound light round the bulb of the
thermometer fhould form a covering lefs warm
than the fame quantity of wool, or other raw ma
terials
in various Subjlances. 445
terials of which the thread is made, furrounding
the bulb of the thermometer in a more loofe man
ner, and confequently occupying a greater fpace,
is no more than what I expecled, from the idea I
had formed of the caufes of the warmth of cover
ing ; but I confefs I was much furprifed to find
that there is fo great a difference in the relative
warmth of thefe two coverings, when they are em
ployed to confine great degrees of Heat, and when
the Heat they confine is much lefs in proportion to
the temperature of the furrounding medium. This
difference was very remarkable ; in the Experi
ments with (heep's wool, and with woollen thread,
the warmth of the covering formed of 1 6 grains of
the former, was to that formed of 16 grains of the
latter, when the bulb of the thermometer was
heated to 70 and cooled to 60, as 79 to 46 (the
furrounding medium being at o) ; but afterwards,
when the thermometer had only fallen from 20 to
i o of Heat, the warmth of the wool was to that
of the woollen thread only as 426 to 410 ; and in
the Experiments with lint, and with linen thread,
when the Heat was much abated, the covering of
the thread appeared to be even warmer than that
of the lint, though in the beginning of the Experi
ments, when the Heat was much greater, the lint
was warmer than the thread, in the proportion of
80 to 46.
From hence it fliould feern that a covering may,
under certain circumftances, be very good for con
fining finall degrees of warmth, which would be
but
446 Of the Propagation of Heat
but very indifferent when made ufe of for confining
a more intenfe Heat, and vice verfa. This, I be
lieve, is a new fact ; and, I think the knowledge of
it may lead to further difcoveries relative to the
caufes of the warmth of coverings, or the manner
in which Heat makes its paflage through them.
But I forbear to enlarge upon this fubjecl, till I
{hall have given an account of feveral other Expe
riments, which I think throw more light upon it,
and which will confequently render the inveftiga-
tion eafier and more fatisfaclory.
With a view to determine how far the power
which certain bodies appear to poflefs of confining
Heat, when made ufe of as covering, depends
upon the natures of thofe bodies, confidered as
chymical Tubftances, or upon the chymical prin
ciples of which they are compofed, I made the
following Experiments.
As charcoal is fuppofed to be compofed almofl
entirely of phlogifton, I thought that, if that prin
ciple was the caufe either of the conducting power,
or the non-conducting power of the bodies which
contain it, I fhould difcover it by making the Ex
periment with charcoal, as I had done with various
other bodies. Accordingly, having filled the globe
of the pafTage-thermometer with 176 grains of that
fubftance in very fine powder, (it having been
pounded in a mortar, and fifted through a fine
fieve,) the bulb of the thermometer being fur-
rounded by this powder, the inftrument was heated
in boiling water, and being afterwards plunged
into
In various Sub/lances. 447
into a mixture of pounded ice and water, the
times of cooling were obferved as mentioned in the
following Table. I afterwards repeated the Expe
riment with lampblack, and with very pure and
very dry wood afhes ; the refults of which Experi
ments were as under-mentioned :
The bulb of the thermometer furrounded by
176 grains of
176 grains of
195 grains of
307 grains of
Heat loft.
fine powder
of charcoal.
fine powder
of charcoal.
lampblack.
pure dry
wood afhes.
Exp. No. 24. Exp. No. 25.
Exp. No. 26.
Exp. No. 27.
70
..
_
60
79"
91"
124"
96"
50
95
9 1
118
9 2
40
IOO
109
134
107
30
X 39
'33
164
I 3 6
20
196
192
237
I8 5
10
,33i
321
394
Total times
940
937
1171
927
The Experiment No. 25 was fimply a repetition
of that numbered 24, and was made immediately
after it ; but, in moving the thermometer about in
the former Experiment, the powder of charcoal
which filled the globe was fhaken a little together,
and to this circumftance I attribute the difference
in the refults of the two Experiments.
In the Experiments with lampblack and with
wood aflies, the times taken up in cooling from
70 to 60 were greater than thofe employed in
cooling from 66 to 50 ; this moft probably arofe
from
448 Of the Propagation of Heat
from the conliderable quantity of Heat contained
by thefe fubftances, which was firft to be difpofed
of, before they could receive and communicate to
the furrounding medium that which was contained
by the bulb of the thermometer.
The next Experiment I made was with femen
iycopodii) commonly called witch-meal, a fubitance
\vhich poiTeffes very extraordinary properties. It is
almoft impoilible to wet it 5 a quantity of it {brewed