and the Mode of its Communication. 3 59 
motions, can be advanced; for we have abundant reason to 
conclude, that if there be in fact any indivisible solid particles 
of matter, (which however is very problematical,) these particles 
must be so extremely small, compared to the spaces they occupy, 
that there must be ample room for all kinds of motions among 
them. 
And, whatever the nature or directions of these internal mo- 
tions may be, among the constituent particles of a solid body, as 
long as these constituent particles, in their motions, do not 
break loose from the systems to which they belong, (and to 
which they are attached by gravitation,) and run wild in the 
vast void by which each system is bounded, (which, as long as 
the known laws of nature exist, is no doubt impossible,) the 
form or external appearance of the solid cannot be sensibly 
changed by them. 
But, if the motions of the constituent particles of any solid 
body be either increased or diminished, in consequence of the 
actions, or radiations, of other distant bodies, this event could 
not happen without producing some visible change in the solid 
body. 
If the motions of its constituent particles were diminished by 
these radiations, it seems reasonable to conclude, that their 
elongations would become less, and consequently, that the vo- 
lume of the body would be contracted; but, if the motions of 
these particles were increased, we might conclude, a priori, that 
the volume of the body would be expanded. 
We have not sufficient data to enable us to form distinct ideas 
of the nature of the change which takes place when a solid body 
is melted ; but, as fusion is occasioned by heat, that is to say, by 
