252 GRAVITY AND LEVITY OF GASES. 



It has been in subservience to the false 

 proposition, so pertinaciously maintained as 

 true, that all bodies are mutually heavy, or 

 gravitate towards each other, that philoso- 

 phers have been led to confound the attri- 

 butes of those bodies, which possess a re- 

 pulsive power, with those that neither attract 

 nor repel ; but which merely act by the rela- 

 tive degrees of density, and of rarity, which 

 they severally possess. As density, how- 

 ever subtile it may be, is inseparable from 

 the existence of materiality ; all bodies un- 

 der different circumstances, may, unques- 

 tionably, be said to possess, with relation 

 to each other, levity or gravity. In estimat- 

 ing, however, the attributes of different bo- 

 dies with each other, that estimate ought ever 

 to be derived from the attributes which are 

 primary and essential, and not from those 

 which are secondary and accidental. There 

 are a variety of bodies which possess the 

 relative and accidental property of gravity, and 

 of levity, and which do not act by virtue of the 

 one, or of the other. A muscle, for example, 

 may be said to have weight in air, and levity 

 in water ; and yet it is not from its gravity 

 or levity, that its power is derived. A 

 spring may be said to have weight, and yet 

 it will not be pretended, that it is to its 



