MISCELLANEOUS 
ftill more’ hidden caufe which ren- 
ders one fubftance better than an- 
other for confining heat. I have 
fhown by a direct and vnexception- 
’ able experiment, that-heat can pafs 
through the Torricellian vacuum *, 
though with rather more difficulty 
than in air (the conducting power 
of air being to that of a Torricel- 
lian vacuum as 1000 to 604, or as 
6 to 10, very nearly); but if heat 
can pafs where there is no air, it 
muft in that cafe pafs by a medium 
more fubtil than air: ——-a medium 
which moft probably pervades all 
folid bodies with the greateft facili- 
ty, and which muft certainly per- 
vade either the glafs or the mercury 
employed in making a Torricellian 
vacuum. 
Now, if there exifts a medium 
more fubtiie than air, by which heat 
may be conduéted, is it not poffi- 
ble that there may exift a certain 
affinity between that medium and 
fenfible bodies? a certain attrac- 
tion or cohefion by means of which 
bodies in general, or fome kinds of 
bodies in particular, may, jome how 
or other) impede’ this medium in its 
operations in conduéting or tranf- 
porting heat from oné place to ano- 
ther ?—-It appeared from the refult 
of feveral of my experiments, of 
which I have given an account 
in detail in my paper before men- 
tioned, publithed in the year 1786, 
in the ‘76th volume, of the Phi- 
lofophical ‘Tranfaétions, that the 
condudiing powertof a Torricellian 
vacuum is to that of air as G04 to 
1000 : — but I found by a fubfe- 
quent experiment (fee my fecond 
rhe or heat, publithed in the Phi- 
ofophical Tranfactions for the year 
BSS A YS? > aly 
1792) that fifty-five parts in bulk 
of air, with one part ot fine raw filk, 
formed a covering for confining 
heat, the conducting power of which 
was to that of air as 576 to 1284; 
or as 448 to 1000. Now, from the 
refult of this la{t-mentioned expe- 
riment, it fiould feem that the in> 
troduction into the fpace through 
which the heat paffed, of fo fmalla 
quantity of raw filk as one-fifty- 
fixth part of the volume, or capa- 
city of that {pace (which now con- 
tained fifty-five parts of airand one 
part of filk) more impervious to 
heat than even a Torricellian va- 
cuum. The filk muft therefore not 
only have completely dettroyed the 
conducting power of the air, but 
muft alfo at the fame time have ve- 
ry fenfibly impaired that of the 
etherial fluid which probably occu- 
pies the interftices of air, and which 
ferves to conduét heat through a 
Torricellian vacuum: for a Torri- 
cellian vacuum was a better con- 
duétor of heat than this medium, in 
the proportion of 604 to 448. But 
I forbear to enlarge upon this fub- 
ject, being fenfible of the danger of 
reafoning upon the properties of a 
fluid whofe exiftence is even doubt- 
ful; and feeling that our knowledge 
of the nature of heat, and of the 
manner in which it is communicat- 
ed from one body to another, is 
much too imperfect and obfcure to 
enable us to purfue thefe fpecula- 
tions with any profpect of fuccefs 
or advantage. 
Whatever may be the manner in 
which heat is communicated from 
one body to another, I think it has 
been. fufficiently proved that it 
pafles with great difficulty through 
* See my Experiments’ on Heat, publithed in the Philofophical Traafaions, 
vol. 76. i> Oli 7 
confined 
