110 RELATIONS OF CALORIC AND P. MATTER. 



that if the particles of ponderable matter could 

 be wholly deprived of caloric, they would be 

 passive and motionless. At the same time it is 

 highly probable, that if universal space were 

 filled with caloric alone, (without any ponderable 

 matter,) it would also be inactive, and constitute 

 a boundless ocean of powerless or quiescent aether, 

 because it would then have nothing on which to 

 act. And we shall find that, however inactive of 

 itself, ponderable matter has certain properties 

 by which it modifies and controls the actions of 

 caloric, both of which are governed by immutable 

 laws that have their origin in the mutual relations 

 and specific properties of each. 



That atoms of the same nature repel one ano- 

 ther, and attract those of a different nature, would 

 appear from the best known phenomena of che- 

 mistry and physical optics. For example, it has 

 been long known that similarity of properties 

 among the elements of ponderable matter causes 

 them to repel each other, as if by a mutual anti- 

 pathy ; but that diversity of properties is favour- 

 able to chemical combination. We have also 

 found that transparent media transmit rays of 

 light of their own colour, but attract and absorb 

 those of different colours. 



I now proceed to shew, that all the expansions 

 and contractions of gaseous bodies depend on the 

 relative proportions of caloric and ponderable mat- 

 ter of which they are composed ; and that the force 

 by which caloric tends to unite ivith the particles 



