MARSH AIR. 429 



marflies. Heretofore mankind feem to have viewed their 

 exiftence as noxious to them and unnecefl'ary to their happi- 

 nefs. I confefs my former opinion refpedting them coincided 

 perfedly with that of the majority, but at prefent my ideas 

 are very different : I confider them as very neceffary to 

 keep the atmofphere in a proper degree of purity, for it is 

 not only the impure atmolphere which kills animals, but 

 the too pure alio ; and an ingenious philofopher has well 

 obfcrved, that animals live too fail in atmoipheres over- 

 charged with oxygen gas. They appear to me to have 

 been inflituted by the Author of Nature in order to ope- 

 rate againft the powers which vegetables and other caufes 

 poffefs of purifying the atmofphere, fo that the oxygen 

 may exift in a proper proportion, fit to fupport animal life 

 and combuftion. I am of opinion that ere long marfhes 

 will be looked upon by mankind as gifts from Heaven to 

 prolong the life and happinels of the grcateft portion of the 

 animal kingdom. Perhaps it was originally intended that 

 they fhould remain uninhabited and that their only ufe 

 fliould be that of correding the too pure atmofpheres. Al- 

 though their immediate inhabitants fuffer difeafe from them, 

 ftill but a fmall portion of the human race choofe marfhy 

 fituations for their refidence. 



After I had read the above before the fociety, a friend 

 in converfation with me, objected to the operation of 

 inarfhes on the atmofphere being intended to prevent a fu- 

 perabundance of oxygen gas ; he obferved that this effedl 

 would be fully accompllflied by the ordinary combuftion 

 and the refpiration of animals. Upon refledtion, his ob- 

 jections gave rife to new confirmations of what 1 afferted : 

 I remarked to him, that very extenfive tra(3:s of country 

 were fufficiently warm without fires ; that in thefe places 

 nature gave uncommon powers to vegetable adion, but at 

 the fame time ordained, that, in thefe very fituations 

 marflies Iliould be moft abundant. If we view moft Ibuth- 



ern 



