Dr. Hare on the Cause of Heat. 147 
totally different from any it can itself possess, and at the 
same time capable of such wonderful effects, as are produ- 
ced by the agency of steam. Is it to be imagined that in 
particles whose weight does not exceed a few ounces, suffi- 
cient momentum can be accumulated to move as many tons ? 
There appears to me another very serious obstacle to this 
explanation of the nature of heat. How are we to account 
for its relation in vacuo, which the distinguished advocate 
_of the hypothesis has himself shown to ensue ? There can 
be no motion without matter. ‘To surmount this difficulty, 
he calls up a suggestion of Newton’s, that the calorific vi- 
brations of matter may send off radiant particles, which lose 
their own momentum in communicating vibrations to bo- 
dies remote from those, whence they emanate. Thus ac- 
cording to Sir Humphrey, there is radiant matter producing 
heat, and radiant matter producing light. Now, the only 
serious objection made by him to the doctrine which con- 
siders heat as material, will apply equally against the exist- 
enee of material calorific emanations. ‘That the cannon, 
heated by friction in the noted experiment of Rumford, 
would have radiated as well as if heated in any other way, 
there can, I think, be no doubt; and as well in vacuo, as the 
heat excited by Sir Humphrey in a similar situation. That 
its emission in this way would have been as inexhaustible as 
by the conducting process cannot be questioned. Why 
then is it notas easy to have an inexhaustible supply of heat 
as a material substance, as to have an inexhaustible supply 
of radiant matter, communicating the vibrations in which he 
represents heat to consist ? : 
We see the same matter, at different times, rendered self- 
attractive, or self-repellent ; now cohering in the solid form 
with great tenacity, and now flying apart with explosive vio- 
lence in the state of vapour. Hence the existence, in na- 
ture, of two opposite kinds of reaction, between particles, 
is self evident. ‘There can be no property without mat- 
ter, in which it may be inherent. Nothing can have no 
property. The question then is, whether these opposite 
properties can belong to the same particles. Is it not evi- 
dent, that the same particles cannot, at the same time, be 
self-repellent, and self-attractive ? Suppose them to be so, 
one of the two properties must predominate, and in that case 
we should not perceive the existence of the other. It would 
