i7i 
and the Mode of its Communication . 
satisfactory. One of the most plausible of them, is that which 
is founded on a supposition that caloric is emitted continually, 
under the form of radiant heat, by all bodies, at all temperatures; 
but in greater abundance by hot bodies than by such as are 
colder; and that a body, at the same time that it sends off’ 
radiant caloric in all directions, to the bodies by which it is sur- 
rounded, receives it in return, in greater or less quantities, from 
all those bodies;— that, in all cases where a body, in any given 
time, receives more radiant caloric than it gives off, an accumu- 
lation of caloric in the body takes place, in consequence of which 
accumulation it becomes hotter; — but, when it gives off more 
caloric in any given time than it receives, its quantity of caloric 
is gradually diminished, and it becomes colder and, that a con- 
stant temperature results, from the quantities of caloric emitted 
and received continually being equal. But, besides the difficulty 
of explaining how, or by what mechanism, it can be possible 
for the same body to receive and retain, and reject and drive 
away, the same kind of substance, at one and the same time, 
(an operation not only incomprehensible, but apparently im- 
possible, and to which there is nothing to be found analogous, 
to render it probable,) many other reasons might be brought to 
show, that this hypothesis, of the supposed continual interchanges 
of caloric between neighbouring bodies, is very improbable; 
and, among the rest, there is one which appears to me to be 
quite conclusive. 
As the point in dispute seems to be of great importance to 
the science of heat, I shall endeavour to examine it with all 
possible attention ; and, in order to put the hypothesis in ques- 
tion to the test, we will see if it will accord with the results of 
Zs 
