157 
and the Mode of its Communication. 
these surrounding bodies should happen to be already vibrating, 
and with the same velocity as that with which the bell is made 
to vibrate by the blow, the undulations in the elastic fluid, occa- 
sioned by the bell, would neither increase nor diminish the 
velocity or frequency of the vibrations of the surrounding bodies ; 
neither would the undulations caused by the vibrations of these 
bodies , tend to accelerate, or to retard, the vibrations of the bell. 
But, if the vibrations of the bell were more frequent than those 
of the surrounding bodies, the undulations it would occasion in 
the elastic fluid, would tend to accelerate the vibrations of the 
surrounding bodies : on the other hand, the undulations oc- 
casioned by the slower vibrations of the surrounding bodies, 
would retard the vibrations of the bell ; and the bell, and the 
surrounding bodies, would continue to affect each other, until, by 
the vibrations of the latter being gradually increased, and those 
of the former diminished, in consequence of their actions on 
each other, they would all be reduced to the same tone. 
Supposing now, that heat be nothing more than the motions 
of the constituent particles of bodies among themselves, (an 
hypothesis of ancient date, and which always appeared to me to 
be very probable,) if for the bell we substitute a hot body, the 
cooling of it will be attended by a series of actions and reactions, 
exactly similar to those just described. 
The rapid undulations occasioned in the surrounding ethereal 
fluid, by the swift vibrations of the hot body, will act as calorific 
rays on the neighbouring colder solid bodies ; and the slower 
undulations, occasioned by the vibrations of those colder bodies, 
will act as ffigorific rays on the hot body ; and these reciprocal 
actions will continue, but with decreasing intensity, till the hot 
body, and those colder bodies which surround it, shall, in 
