172 Reflections on Heat. 



From this course of reasoning we might conclude 

 that the particles which compose a body are of necessity 

 in motion ; and if we admit the existence of an emi- 

 nently elastic fluid, an ether which fills all space 

 throughout the universe, with the exception of that 

 occupied by the scattered particles of ponderable bodies, 

 it is easy to conceive that the movements of the 

 particles which make up material objects must cause 

 undulations in this fluid ; and, on the other hand, the 

 undulations of this fluid must affect to a sensible de- 

 gree and modify the motions of the particles of these 

 bodies. 



It might perhaps seem that these motions among the 

 particles of solid bodies would be incompatible with the 

 preservation of the forms of those bodies ; but by re- 

 flecting attentively on this subject it will be found that 

 such motions as are here supposed can well exist with- 

 out diminishing at all the stability of the external form 

 of the bodies. 



It would follow necessarily, from the state of things 

 supposed by the hypothesis in question, first, that the 

 sum of the active forces in the universe must always 

 remain constant, in spite of all actions and reactions 

 taking place among the various bodies ; secondly, that 

 the particles of all ponderable bodies must of necessity 

 have the property of producing radiations. 



Now, if we admit the existence of the ether, it is pos- 

 sible to explain the radiations of bodies in still an- 

 other manner ; it is by supposing that the particles 

 are kept apart from each other, not in consequence of 

 the action of the centrifugal force of those particles, but 

 by atmospheres composed of ether or of some other 

 fluid unknown to us, which is extremely elastic, and 



