138 Of the insalubrity of FLAT 



been remarked by Phyficians and Hiftorians in every 

 age. 



But although they have agreed with refpedt to the 

 fadt, they have differed materially with rerpc(ft to the 

 caufe of this circumftance. 



A delire of afcertaining the true caufe of this infalu- 

 brity induced me to engage in the enquiry which I am 

 now about to fubmit to this refpedable fociety, and I 

 hope the time and attention which I have be flowed upon 

 a fubjefl; fo interefting to mankind, will not be deemed 

 labour mifemployed. 



The atmofphere in falutary lituations, has been demon- 

 ftrated by Mr. Lavorfier and his colleagues, to be a com- 

 pound body confifting of two diftind; gafes or aeriform 

 fluids, the one called azote or nitrogen gas, and the other 

 oxygen-gas or pure relpirable air ; and that in one hun- 

 dred parts of the atmofphere, the proportions of thefe 

 gafes are 72 of the azote and 2J) of oxygene, or as three 

 to one. 



From Mr. Vanbreda's experiments, on the atmofphere 

 of marfhes in the autumnal feafon, which he fubjeded 

 to the common tefl of nitrous air in the eudiometer, it 

 appears that thefe proportions were very different ; there 

 being but 14 or 15 parts of oxygene, 1084 or 85 of 

 azote, but that the bulk was fupplied, and the fame 

 weight preferved by a certain quantity of carbonic gas 

 or fixed air, and a fmall portion of hydrogene and am- 

 moniacal gales or aeriform fluids. 



All thefe gafes are the effetts of vegetable and animal 

 putrefadlion, and muft be derived from the foil, or the 

 vegetable and animal fubftances connected with the foil. 



The foil of marfhes is compofed entirely of vegetable 

 and animal fubftances, which have undergone the pro- 

 cefs of putrefaction, and confifts principally of vegetable 

 earth, carbon or charcoal and nitre, mixed with more or 



lefs 



