510 On the two great powers, [Ocr. 
the motion and vibration of caloric, or this medium, bodies become of 
equal temperature. By the atmosphere of caloric round the atoms of 
bodies, may be effected the reflection and refraction of light, in like 
manner as this medium is supposed to operate. Caloric, like this me- 
dium, is exceedingly more rare and subtle than air, and exceedingly 
more elastic and active ; for it loses much of its rarity, subtlety, and 
elasticity when attracted by the gross atoms of gases, which it encom- 
passes, endows with mutual repulsion, and in fact transforms into 
elastic air. Caloric, like this medium, readily pervades all bodies. 
Ts not caloric therefore no other than this medium ? and hence, 
material ? 
[Lastly, although we have above seen that a vibration or other mo- 
tion of the gross particles of bodies cannot in any way account for the 
dilating power of caloric, it does not at all follow that the phenomena 
of sensible heat may not depend on a peculiar condition of the particles 
of the matter of heat itself, such as vibrations in them of differ- 
ent degrees of intensity. Hence the absolute quantity of the matter 
of heat may not always be indicated by the phenomena of sensible heat, 
And in sudden or violent actions, as those of friction, detonation, and 
combustion, these phenomena may thus be considerably increased with- 
out any increase in the absolute quantity of the matter ofheat. In 
this manner the two leading hypotheses may be united, and the chief 
difficulties attendant on each being removed, a doctrine, deserving of 
reception, may be established as a well-digested theory of caloric, in 
its characters of an expanding and heating medium. ] 
Having now, I trust, shewn, that the opponent force to the attraction 
of atoms cannot be a repulsive power inherent in them, but, that it arises 
from the agency of heat; and that heat cannot be considered as arising 
from a vibrating motion in the atoms of bodies themselves, but that 
it is a very subtle fluid, whose particles are possessed of two powers, 
always inherent in them ; namely, that of repelling each other, and 
that of attracting all other matter :—having shewn this, the next in- 
quiry which would present itself, is, into. the laws governing these 
two powers of heat, were such a direct inquiry possible. 
From the extreme minuteness of the particles of heat, and from 
their attracting powerfully the atoms of all other matter, it will follow, 
that every atom of the latter is surrounded by numerous particles of 
the former ; all of which particles of heat, must tend with great force 
towards the centre of the atom they surround, and would be in ab- 
solute contact with each other, did not their other power (namely, the 
repulsion which operates between the particles of heat themselves,) 
