On the Materiality of Caloric. 609 
that we have no accurate conceptions of quantity, 
as appertaining to heat, all arguments against 
its materiality, derived from supposed determi- 
nations of its quantity, must be inconclusive. 
The only clear conceptions, which the mind 
has of quantity, are derived either from a com- 
parison of the magnitude, or of the gravity, of 
bodies. In the instance of caloric, both these 
modes of mensuration fail us. We cannot 
estimate the bulk of a substance, which eludes 
-our grasp and our vision; nor have we yet suc- 
ceeded in comparing its gravity, with that of 
the grosser kinds of matter, which it surpasses 
in tenuity, beyond all comparison. Our no- 
tions of the quantity of caloric are derived, not 
from such simple judgments, but from compli- 
cated processes of reasoning, in the steps of 
which, errors, fatal to the whole, may, pase a 
sometime appear. 
Whatever be the nature of caloric—whether 
it be a body suc generis, or a quality of other 
bodies,—its effects are peculiar and appropriate ; - 
and, like all other effects, bear a proportion to 
the energy of their cause. Expansion, for ex- 
ample, it is proved by experiment, keeps pace 
with the actual increments of heat; and on this 
principle is founded the thermometer, the great 
agent in the acquirement of all our ideas res- - 
pecting heat, both absolute and relative, The 
