148 Dr. Hare on the Cause of Heat. 
be useless, and the particles would in effect, possess the pre- 
dominant property alone, whether attraction or repulsion. 
If the properties were equal i in power, they would annihilate 
each other, and the matter would be, as if void of either 
property, There must, therefore, be a matter, in which the 
self-repellent power resides, as well as matter in which at- 
traction resides. 
There must also be as many kinds of matter, as there are 
kinds of repulsion, of which the affinities, means of produc- 
tion, or laws of communication are different. Hence I do 
firmly believe in the existence of material fluids, severally 
producing the phenomena of heat, light 8 paecatl 
Substances, endowed with attraction, ma emselves 
known to us, by that species of this power, shor we call 
gravitation, by which they are drawn towards the earth, 
and are therefore heavy and ponderable ;_ by their resistance 
to our bodies, producing the sensation of feeling or touch ; 
and by the Bia fatt ies — in other matter, affect- 
-ear with eye by a modified reflection 
of light. Where we we perceive none of these usual concom 
tants of matter, we are prone to infer fe ubeeaee sence 
ignorant people have no idea of air, except in the state of 
wind ; and when even in a quiescent state designate it by 
this word. But that the principles, the existence of which 
has been demonstrated, should not be thus perceived, is far 
from being a reason for doubting their existence. A very 
slight attention to their qualities will make it evident, that 
they could not produce any of the effects, by which the ex- 
istence of matter in its ordinary form is recognized. The 
self-repellent property renders it impossible that they should 
resist penetration ; their deficiency of weight, renders their 
movements nugatory. When in combination, they are not 
perceived, but the bodies with which they combine ; and it 
is only by the changes they produce in such bodies, or theif 
effects upon our nerves, that they can be detected. 
