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the air inferior to the leaves of trees ? 

 Does not this conjecture get fome 

 weight, if we confider that dephlo- 

 gifcicated air is in reality fpecifically 

 heavier than common air, and thus 

 tends rather to fall downwards ? 



If we add to thefe reflexions ano« 

 ther of no lefs importance, viz. that 

 moil forts of foul air are fpeci- 

 fically lighter than common air, we 

 iliall be inclined to believe that the 

 difference of the fpecifical gravity of 

 that beneficial air of which I treat, 

 and that which is become hurtful 

 to our conftitution by corruption, 

 breathing, and other caufes, indi- 

 cates one of thofe fpecial bleflings 

 deflgned by the hand of God: for 

 by this arrangement we get foon rid 5 

 in a great meafure, of that air which 

 Is become hurtful to us, as it rifes 

 fpon up out of our reach ; whereas 



the 



