On the Materiality of Caloric. 605 
i shall take the liberty. of offering a statement of 
the argument, rather different from that of Mr. 
Davy ; though I trust without misrepresentation, 
or any material omission, 
Let heat be considered.as matter ;, and let it 
be granted, that the temperature of bodies de- 
pends on the presence of uncombined caloric. 
Now, if the temperature of a body be, increased, 
the free caloric, occasioning that elevation, must 
proceed from one of two sources; either istly. 
it may be communicated by surrounding sub- 
stances; or 2dly. it may proceed from an inter- 
nal source, i.e. from a disengagement of what 
before existed in the body, Jatent. or combined. 
But the temperature of) bodies. is uniformly 
increased by friction-and percussion, and, neces- 
sarily, in one of the foregoing modes, 
I. Mr. Davy found, by experiment, that a thin 
metallic plate was heated, by friction in the 
exhausted receiver of an air pump, even when 
the apparatus was insulated, from _ bodies 
capable of supplying caloric, by being placed 
on ice. This experiment he considers as de- 
monstrating, that, the evolved caloric could 
not be communicated by surrounding bodies, 
To the inference deduced from this experi- 
ment, it may be objected, that the mode of 
insulation was. by no means perfect, Admitting . 
the vacuum, produced by the air pump, to: have 
