its axis, leaving only an opening fufficient to admit
the tube of the thermometer. The thermometer
being introduced into the cylinder in fuch a man
ner that the centre of its bulb coincided with
the centre of the globe, I marked a place in the
cylinder, about three-quarters of an inch above the
Both degree or boiling point upon the tube of the
inclofed thermometer,and taking out the thermom
eter, I choaked the cylinder again in this place.
Introducing
398 Of the Propagation of Heat
Introducing now the thermometer for the laft
time, I clofed the opening at the bottom of the
globe at the lamp, taking care before J brought it
ito the fire, to turn the cylinder upfide down, and
to let the bulb of the thermometer fall into the
cylinder till it refted upon the lower choak in the
cylinder. By this means the bujb pf the thermom
eter was removed more than 3 inches from the
flame of the lamp. The opening at the bottom of
the globe being now clofed, and the bulb of tfye
thermometer being fuffered to return into the
globe, the encj of the cylinder was cut off to within
about half an inch of the upper choak. This being
done, it is plain, that the tube of the thermometer
projected beyond the end of the cylinder. Taking
hold of the end of the tube, I placed the bulb of
the thermometer as nearly as poflible in the centre
of the globe, and obferving and marking a point in
the tube immediately above the upper choak of the
.cylinder, I turned the cylinder upfide down, and
fuffering the bulb of the thermometer to enter the
cylinder, and reft upon the firft or lower choak, (by
which means the end of the tube of the thermom
eter came further out of the cylinder) the end of
the tube was cut off at the mark juft mentioned,
(care having firft been taken to meljt the internal
cavity or bore of the tube together at that place)
and a fmall folid ball of glafs, a little larger than
the internal diameter or opening of the choak,
was foldered to the end of the tube, forming a
little button or knob, which refting upon the upper
phoak of the cylinder ferved to fufpend the ther
mometer
iu various Subftances. 399
momcter in fuch a manner that the centre of its bulb
coincided with the centre of the globe in which it
was {hut up. The end of the cylinder above the
upper choak being now heated and drawn out to
a point, or rather being formed into the figure of
the fruftum of a hollow cone, the end of it was
foldered to the end of a barometrical tube, by the
help of which the cavity of the cylinder and globe
containing the thermometer was completely voided
of air with mercury ; when, the end of the cylinder
being hermetically fealed, the barometrical tube
was detached from it with a file, and the thermom
eter was left completely fhut up in a Torricellian
vacuum, the centre of the bulb of the thermome
ter being confined in the centre of the glafs globe,
without touching it in any part, by means of the
two choaks in the cylinder, and the button upon
the end of the tube. (See Fig. 2.)
Of thefe inflruments I provided myfelf with two,
as nearly as poffible of the fame dimenfions ; the
one, which I {hall call No. i. being voided of air,
in the manner above defcribed the other, No. 2.
bcng filled with air, and hermetically fealed.
With thefe two inflruments (fee Fig. 2.) I made
the following Experiments upon the nth of July
laft at Manheim, between the hours of ten and
twelve, the weather being very fine and clear, the
mercury in the barometer flanding at 27 inches 1 1
lines, Reaumur's thermometer at 15, and the
quill hygrometer of the academy of Manheim
at 47.
Experiments.,
40 o Of the Propagation of Heat
Experiments i No 3, 4, 5, and 6.
Putting both the inftruments into a mixture of
pounded ice and water, I let them remain there till
the mercury in the inclofed thermometers refted at
the point o, that is to fay, till they had acquired
exactly the temperature of the cold mixture ; and
then taking them out of it I plunged them fud-
denly into a large veifel of boiling water, and ob-
fcrved the time required for the mercury to rife in
the thermometers from ten degrees to ten degrees,
from o to 80, taking care to keep the water con^
flantly boiling during the whole of this time, and
taking care alfo to keep the inftruments immerfed
to the fame depth, that is to fay, juft fo deep that
the point o of the inclofed thermometer was even
with the furface of the water.
Thefe Experiments I repeated twice with the ut-
moft care ; and the following Table gives the refult
of therrio
in various Sub/iances*
401
Thermometer N I.
Thermometer N 2.
Its bulb half an inch in diame
Its bulb half an inch in diame
ter, fhut up in the centre of a hol-
ter, fhut up in the centre of a hol
ow glafs globe, i\ inch in diam
low glafs globe, \\ inch in diam-
eter, void of air, and hermetically eter, filed with air, and hermetic-
Pealed, 'ally fealed.
Taken out of freezing water, and
plunged into boiling water.
Taken out of freezing water, and
plunged into boiling water.
Time elapfed.
Time elapfed.
E*p.N 3 . Exp.N 4 . ac< l uired -
Exp. N 5. Exp. N 6. ac 1 uirtd -
M. S. M. S.
M. S. M. S.
51 51 10'
30 30 10
o 59 o 59 20
o 35 o 37 20
ii 12 30
o 41 o 41 30
I l8 I 22 40
49 53 4
I 24 I 23 50
ii o 59 50
20 I 51 60
i 24 i 20 60
3 30 36 70
2 45 2 25 70
ii 41 10 27 80
9 10 9 38 80
22 44 21 i z= total time
*6 55 17 3 = total time
of heating from o to 80.
of heating from o to 80.
Total time from o to 70 :
Total time from o to 70 :
M. S.
M. S.
In Exp. N 3.= ii 3
In Exp. N 5.= 7 45
In Exp. N 4z= 10 34
In Exp. N 6. = 7 25
Medium = i o 48^
Medium =7 35
It appears from thefe Experiments that the con-
dudling power of air to that of the Torricellian va
cuum, under the circumftances defcribed, is as 7^-
to io inverfely 5 or as 1000 to 702 nearly ; for the
quantities of Heat communicated being equal, the
intenfity of the communication is as the times
inverfely.
In thefe Experiments the Heat patted through the
furrounding medium into the bulb of the thermom
eter :
402
Of the Propagation of Heat
eter : in order to reverfe the Experiment, and
make the Heat pafs out of the thermometer, I put
the inftruments into boiling water, and let them
remain therein till they had acquired the tempera
ture of the water \ that is to fay, till the mercury
in the inclofed thermometers flood at 3o ; and
then, taking them out of the boiling water, I
plunged them fuddenly into a mixture of water
and pounded ice, and moving them about contin
ually in this mixturej I obferved the times en>
ployed in cooling as follows ;
Thermometer N I.
Surrounded by a Torricellian
'vacuum.
Taken out of boiling water, and
plunged into freezing water.
Thermometer N 2.
Surrounded by air*
Taken cut of boiling water, and
plunged into freezing water.
Time elapfed.
Heat loft
Time elapfed.
Heat loft
Exp. N 7. Exp. N 8.
Exp. N 9. Exp. N 10.
So
80
M. S. M. S;
12 o 54 70
58 12 60
i 17 i 1 8 50
i 46 i 37 40
25 2 16 30
3 14 3 10 20
5 42 9 10
Not obferved. Not obferved. o
M. S. M. S.
o 33 o 33 7
o 39 o 34 60
o 44 o 44 50
o 55 o 55 40
i 17 i 18 30
i 57 i 57 20
3 44 3 40 !
40 i o Not obferved. o
Total time of cooling from 80
to 10.
M. S.
In Exp. N 6 7.= 1 6 4
In Exp. N 8.3=16 16
Medium =r 1 6 10
Total time of cooling from 80
to io*
M. S.
In Exp. N 9. = 9 49'
In Exp.-N io.= 9 41
Medium rr q 4.7
in various Svbftarices. 403
By thefe Experiments it appears, that the con-
dueling power of air is to that of the Torricellian
vacuum as 9^ to i6~~ inverfely, or as 1000 to
603.
To determine whether the fame law would hold
good when the heated thermometers, inftead of be
ing plunged into freezing water, were fuffered to
cool in the open air, I made the following Experi
ments. The thermometers No. i . and No. 2. being
again heated in boiling water, as in the laft Experi
ments, I took them out of the water, and fufpend-
ed them in the middle of a large room, where the
air (which appeared to be perfectly at reft, the win
dows and doors being all fhut) was warm to the
1 6th degree of REAUMUR'S thermometer, and the
times of cooling were obferved as follows :
(Exp. J>r u.)
Thermometer N I.
Surrounded by a Torricellian
vacuum.
Heated to 80, and fufpended in the
open air 'warm to 1 6.
(Exp. N 12.)
Thermometer N 2.
Surrounded by air.
Heated to 80, and fufpended in the
open air warm to 1 6.
Time elapfed. Heat loft.
80
Time elapfed. Heat loft.
80
M. S.
Not obferved. 70
o 51 6jo
i S S<*
* 34 40
2 41 30
6 1 1 =: total time
ployed in cooling from 70 to
em-
30.
M. S.
Not obferved. 70
i 24 60
i 44. 50
2 28 40
4 16 30
10 12 = total time em
ployed in cooling from 70 to 30.
Here the difference in the conducting powers of
air and of the Torricellian vacuum appears to be
VOL. IL F f f nearly
404 Of the Propagation of Heat
nearly the fame as in the foregoing Experiments,
being as 6^ to io~- inverfely, or as 1000 to 605.
I could not obferve the time of cooling from 80
to 70, being at that time bulled in fufpending the
inftruments.
As it might poflibly be objected to the conclu-
fions drawn from thefe Experiments that, notwith-
ftanding all the care that was taken in the con-
ftructing of the two inftruments made ufe of that
they mould be perfectly alike, yet they might in
reality be fo far different either in fliape or fize, as
to occafion a very fenfible error in the refult of the
Experiments ; to remove thefe doubts I made the
following Experiments :
In the morning towards eleven o'clock, the wea
ther being remarkably fine, the mercury in the ba
rometer flan ding at 27 inches 1 1 lines, REAUMUR'S
thermometer at 15, and the hygrometer at 47, I
repeated the Experiment No. 3. (of heating the ther
mometer No. i. in boiling water, &c.) and imme
diately afterwards opened the cylinder containing
the thermometer at its upper end, where it had
been fealed, and letting the air into it, I re-fealed
it hermetically, and repeated the Experiment again
with the fame inftrument, the thermometer being
now furrounded with air, like the thermometer
No. 2.
The refult of thefe Experiments, which may be
feen in the following Table, mews evidently, that
the error ariling from the difference of the lhapes
or dimenfions of the two inftruments in queftion
was inconfiderable, if not totally imperceptible.
in various Subftanccs.
405
(Exp.Ni 3 .)
(Exp.Ni 4 .)
Thermometer N I.
The fame Thermometer (N I.)
Its bulb half an inch in diame
ter, fhut up in the centre of a
glafs globe, i| inch in diameter,
voided of air, and hermetically
fealed.
The glafs globe, containing the
bulb of the thermometer, being
no r A r jilled ivith air, and hermet
ically fealed.
Taken out of freezing water, and
Taken out of freezing water, and
plunged into boiling water.
plunged into boiling water.
Time elapfed. Heat acquired.
Time elapfed. Heat acquired.
,
. . . , o 9
M. S. o
M. S.
o 55 jo
o 32 10
o 55 20
o 32 20
i 7 30
o 43 3
i 15 40
o 50 40
i 29 50
ii 50
22 60
i 24 60
3 21 70
2 38 70
13 44 80
10 25 So
24 48 = total time of heat
1 8 5 = total time of heat
ing from o to 80.
ing from o to 80.
Total time from o to 70 s=
Total time from o to 7o 9 =
1 1' 4".
f 40".
It appears, therefore, from thefe Experiments,
that the conducting power of common atmofpheric
air is to that of the Torricellian vacuum as 7-|~ to
i i T 4 -inverfely, or as 1000 to 602 ; which differs
but very little from the refult of all the foregoing
Experiments.
Notwithftanding that it appeared, from the re-
fult of thefe laft Experiments, that any difference
there might poffibly have been in the forms or
dirnenfions of the inftruments No. i. and No. 2,
could hardly have produced any fenfible error
in the refult of the Experiments in queflion ; I
was willing, however, to fee how far any con-
fiderable
40 6 Of the Propagation of Heat
fiderable alterations of fize in the inftrument
would effecl: the Experiment : I therefore provided
myfelf with another inftrument which I {hall call
Thermometer No. 3. different from thofe already de-^
fcribed in fize, and a little different in its conr
ftruclion.
The bulb of the thermometer was of the fame
form and iize as in the inftruments No. i. and No.
2. that is to fay, it was globular, and half an inch
in diameter ; but the glafs globe, in the centre of
which it was confined, was much larger, being
3 inches J~ n ' nes m diameter ; and the bore of
the tube of the thermometer was much finer,
and cpnfequently its length, and the divifions of
its fcale, were greater. The divifions were marked
upon the tube with jthreads of filk of different
colours at every tenth degree, from o to 80,
as in the before-mentioned inftruments. The
tube or cylinder belonging to the glafs globe was
8 lines in diameter, a little longer than the tube
of the thermometer, and perfectly cylindrical from
its upper end to its junction with the globe, being
without any choak; the thermometer being con
fined in the centre of the globe by a different con
trivance^ which was as follows. To the opening
of the cylinder was fitted a ftopple of dry wood,
covered with a coating of hard varnifh, through
the centre or axis of which paffed the end of the
tube of the thermometer : this ftopple confined the
tube in the axis of the cylinder at its upper end.
To confine it at its lower end, there was fitted to it
a fmall fteel fpring, a little below the point o ;
which, being faftened to the tube of the thermom
eters
m 'various Sub/lances. .407
,eter, had three elaftic points projecting outwards,
which, prefling againft the infide of the cylinder,
confined the thermometer in its place. The total
length of this inftrument, from the bottom of the
globe to the upper end of the cylinder, was 1 8
inches, and the freezing point upon the thermome
ter fell about 3 inches above the bulb ; confequently
this point lay about i inch aboye the junction of
the cylinder with the globe, when the thermometer
wa$ confined in its place, the centre of its bulb
coinciding with the centre of the globe. Through
the ftopple which clofed the end of the cylinder
pafled two fmall glafs tubes, about a line in di
ameter, which bf ing about a line longer than the
ftopple were ciofed occalionally with fmall floppies
fitted to their bores. Thefe tubes (which were
fitted exactly in the holes bored in the great ftopple
of the cylinder to receive them, and fixed in their
places with cement) ferved to convey air, or any
Other fluid ? into the glafs ball, without its being
neceflary to remove the ftopple doling the end of
the cylinder ; which ftopple, in order to prevent
the pofition of the thermometer from being eafily
deranged, was cemented in its place.
I have been the more particular in the defcription
of thefe inftruments, as I conceive it to be ab-
folutely necefTary to have a perfect idea of them
in order to judge of the Experiments made with
them, and of their refults.
With the inftrument laft defcribed (which I have
called Thermometer No. 3.) I made the following
Experi-
40 8 Of the Propagation of Heat
Experiment. It was upon the i8th of July 17855
in the afternoon, the weather variable, alternate
clouds and fun-fliine ; wind ftrong at S. E. with
now and then a fprinkling of rain ; barometer
at 27 inches 10^- lines, thermometer at 18-, and
hygrometer variable from 44 to extreme moifture.
In order to compare the refult of the Ex
periment made with this inftrument with thofe
made with the thermometer No. 2. I have placed
together in the fame Table the different Experi
ments made with them.
(Exp. N^ 15.)
Thermometer N 3.
Its bulb half an inch in diam
eter, {hut up in the centre of
a g'lafs tube, 3 inche3 7^ lines
in diameter, and furrounded by
air.
(Exp. N 4 and N 5.)
Thermometer N 2.
Its bulb half an inch in diameter, fhut up
in the centre of a glafs globe, i-| inch in di
ameter, and furrounded by air.
Taken out of freezing ivater, and plunged inti
boiling "water.
plunged into boiling 'water.
Time elapfed. ^^
Time elapfed. Heat acquired.
M. S. o
o 33 10
38 20
54 30
o 51 40
i 7 50
i 28 60
2 28 70
90 80
acquired
Exp. N 4 . Exp. N 5. Medium.
, QQ
M. S. M. S. M. S.
o 30 o 30 o 30 10
o 35 o 37 o 36 ao
o 41 o 41 o 41 30
o 49 o 53 o 51 40
II o 59 10 50
i 24 i ao i 22 60
2 45 * 25 2 35 70
9 10 9 38 9 24 80
1 6 59 = total time of
heating from o to 8o-
1'ime from o to 70 = f 59".
*6 55 J 7 3 I ^ 59= total time
of heating from o to 80.
Time from o to 70 = 7' 35".
If the agreement of thefe Experiments with the
thermometers No. 2. and No. 3. furprifed me, I was
not lefs furprifed with their difagreernent in the-
Experiment which follows :
Experiment,
in various Subftances. 409
Experiment, No. 1 6.
Taking the thermometer No. 3. out of the boiling
water, I immediately fufpended it in the middle
of a large room, where the air, which was quiet,
was at the temperature of i8 ~R* and obferved
the times of cooling as follows :
Time elapfed. Heat loft, .
80
M. S.
1 55 7
O 12 6O
33 5
2 15 40
40 30
9 5 5= total time of cooling from 80 to 30*,
Time from 70 to 30 ~S' o"; but in the Exper
iment No. 12. with the thermometer No. 2. the
time employed in cooling from 70 to 30 was
only 6' n". In this Experiment, with the ther
mometer No. 3. the time employed in cooling from
60 to 30 was 7' 48" ; but in the above-mentioned
Experiment, with the thermometer No. 2. it was
only 5' 20". It is true, the air of the room
was fomewhat cooler when the former Experiment
was made, than when this latter was made, with
the thermometer No. 3. ; but this difference of tem
perature, which was only 2-^, (in the former cafe
the thermometer in the room {landing at 16%
and in the latter at 18 - ) certainly could not have
occafioned
410 Of the Propagation of Heat
occafioned the whole of the apparent difference ia
the refults of the Experiments.
Does air receive Heat more readily than its part.?
with it ? This is a queftion highly deferving of
further inveftigation, and I hope to be able to give
it a full examination in the courfe of my projected
inquiries ; but leaving it for the prefent, I ihall pro
ceed to give an account of the Experiments which I
have already made. Conceiving it to be a ftep of
confiderable importance towards coming at a
further knowledge of the nature of Heat, to
afcertain, by indifputable evidence, its pailage
through the Torricellian vacuum, and to deter
mine, with as much precificn as poffible, the law
of its motions in that medium ; and bekig appre-
heniive that doubts might arife with refpecl to the
Experiments before defcribed, on account of the
contact of the tubes of the inclofed thermometers in
the inftruments made ufe of with the containing
glafs globes, or rather with their cylinders : by
means of which (it might be fufpected) that a cer
tain quantity, if not all the Heat acquired, might
poffibly be communicated ; to put this matter
beyond all doubt, I made the following Experi
ment.
In the middle of a glafs body, of a pear-like
form, about 8 inches long, and 2- inches in its
greateft diameter, I fufpended a fmall mercurial
thermometer, 5-1 inches long, by a fine thread of
filk, in fuch a manner that neither the bulb of the
thermometer, nor its tube, touched the contain
ing glafs body in any part. The tube of the ther
mometer
in various Sub/dances. 411
mometcr was graduated, and marked with fine
threads of filk of different colours, bound round
it, as in the thermometers belonging to the other
inflruments already defcribed ; and the thermome
ter was fufpended in its place by means of a fmall
fleel fpring, to which the end of the thread of filk
which held the thermometer being attached, it
(the fpring) was forced into a fmall globular pro
tuberance or cavity, blown in the upper extremity
of the glafs body, about half an inch in diameter,
where the fpring remaining, the thermometer ne-
ceiTarily remained fufpended in the axis of the glafs
body. There was an opening at the bottom of
the glafs body, through which the thermometer
was introduced ; and a barometrical tube being
foldered to this opening, the infide of the glafs
body was voided of air by means of mercury ;
and this opening being afterwards fealed herme
tically, and the barometrical tube being taken away,
the thermometer was left fufpended in a Torri
cellian vacuum,
In this inftrument, as the inclofed thermometer
did not touch the containing glafs body in any part,
on the contrary, being diftant from its internal
furface an inch or more in every part, it is clear,
that whatever Heat palled into or out of the ther
mometer muft have palled through the furrounding
Torricellian vacuum : for it cannot be fuppofed,
that the fine thread of filk, by which the ther
mometer was fufpended, was capable of conduct
ing any Heat at all, or at leaft any fenfible quantity.
I therefore flattered myfelf with hopes of being
VOL. II. G g g able.
412 Of the Propagation of Heat
able, with the affiftance of this inftrument, to
determine pofitively with regard to the paffage"
of Heat in the Torricellian vacuum : and this, I
think, I have done, notwithftanding an unfortu
nate accident that put it out of my power to purfue
the Experiment fo far as I intended.
This inftrument being fitted to a fmall ftand or
foot of wood, in fuch a manner that the glafs body
remained in a perpendicular fituation, I placed it in
my room, by the fide of another inclofed ther
mometer (No. 2.) which was furrounded by air,
and obferved the effects produced on it by the
variation of Heat in the atmofphere. I foon dif-
covered, by the motion of the mercury in the in
clofed thermometer, that the Heat paffed through
the Torricellian vacuum ; but it appeared plainly
from the fluggifhnefs, or great infeniibility of
the thermometer, that the Heat paffed with much
greater difficulty in this medium than in common
air. I now plunged both the thermometers into a
bucket of cold water ; and I obferved that the
mercury in the thermometer furrounded by air
defcended much fafter than that in the thermome
ter furrounded by the Torricellian vacuum. I took
them out of the cold water, and plunged them
into a veffel of hot water (having no conveniencies
at hand to repeat the Experiment in due form with
the freezing and with the boiling water ;) and the
thermometer furrounded by the Torricellian va
cuum appeared ftill to be much more infenfible or
flugrilh than that furrounded by air.
Thefe
m various Sub/dances. 4 T 3
Thefe trials were quite fufficient to convince
me of the paiTage of Heat in the Torricellian
vacuum, and alfo of the greater difficulty of its
paffage in that medium than in common air ; but,
not fatisfied to reft my inquiries here, I took the
firft opportunity that offered, and fet myfelf to
repeat the Experiments which I had before made
with the inftruments No. i. and No, 2. I plunged
this inftrument into a mixture of pounded ice and
water, where I let it remain till the mercury in the
inclofed thermometer had defcendecl to o ; when,
taking it out of this cold mixture, I plunged it
fuddenly into a veffel of boiling water, and pre
pared myfelf to obferve the afcent of the mercury
in the inclofed thermometer, as in the foregoing
Experiments ; but unfortunately the moment the
end of the glafs body touched the boiling water, it
cracked with the Heat at the point where it had
been hermetically fealed,and the water rufhing into
the body, fpoiled the Experiment : and I have not
fince had an opportunity of providing myfelf with
another inftrument to repeat it.
It having been my intention from the beginning
to examine the conducting powers of the artificial
airs or gaffes, the thermometer No. 3. was con-
ftrucled with a view to thofe Experiments ; and
having now provided myfelf with a ftock of thofe
different kinds of airs, I began with/m/<2/>, with
which, by means of water, I filled the globe and
cylinder containing the thermometer; and flopping
up the two holes in the great ftopple clofing the
end of the cylinder, I expofed the inftrument in
freezing
414 Of tie Propagation of Heat
freezing water till the mercury in the inclofed
thermometer had defcended to o ; when, taking
it out of the freezing water, I plunged it into a