620 On the Materiality of Caloric. 
bodies, that have a strong chemical affinity, 
are. kept perfectly distinct, even when placed 
in contact, by the affinity of aggregation. 
The only inference, then, that can fairly be 
deduced from the effects of pressure, in pre- 
~venting the formation of gasses, is, that it is a 
power, sometimes superior, in energy, to that 
of chemical affinity. 
Since, therefore, caloric is characterized 7 
all the properties, except gravity, that enter 
into the definition of matter, we may venture 
to consider it as a distinct and peculiar body. 
Nor is its deficiency of gravity sufficient to 
exclude it from the class of material substances. 
Such nicety of arrangement might, with equal 
propriety, lead us to deny the materiality of 
light, the gravity of which has never yet been 
proved: for, besides the experiments. of Mr. 
Michell, which: failed in ascertaining this pro- 
perty of light, we have several chemical facts 
tending to the same conclusion. Thus Mr. 
Cavendish, after firing a mixture of hydroge- 
nous and oxygenous gases, in a close vessel, 
a process during which much light is always 
emitted, found not the smallest diminution of 
weight. 
To have completed this defence of the mate- 
rial nature of heat, it would have been proper to — 
have pointed out the circumstances, in which the 
— ye ee ae 
