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water Is, and confequently parts with it more flowly in that pro- 

 portion. Therefore it lofes only a'' of heat in paffing through 

 12^ of latitude, and 6° degrees in paffing through 24*^ of lati- 

 tude, and 8*' in paffing through 48°. Therefore the fupra-terrene 

 intra-tropical air at the height of loooo feet is cooled down in 

 latitude 72*^, that is 48*^ beyond the northern tropic, only 8^, 

 and confequently its temperature, even in that diftant latitude, 

 is 64". But the fupra-marine intra-tropical air, whofe temperature 

 at the height of loooo feet is 57*^, is cooled down to 49^ at la- 

 titude 72*^. It is true, that the degree of moifture, in the air 

 through which the intratropical air paffes, mufi: occafion a confi- 

 derable difference as to the heat it retains, for Count Rumford 

 has alfo fhewn, that moift air is 3,9 times a better condudor of 

 heat than common air, and confequently nearly as good a con- 

 dudor as water. Ibid. But the air, in his experiments, was fa- 

 turated with moifture, a circumftance that cannot be fuppofed in 

 the cafes at prefent referred to. From thefe principles the expli- 

 cation of the above-mentioned phsenoraena is clearly deduced 



For i°. the fuperior flrata of the atmofphere are obvioufly 

 warmer than the lower, being occupied by the fuperior current, 

 whofe heat is gradually communicated to the lower ftrata, until 

 at length it becomes uniform, as in the cafes obferved by De Luc. 



2do. 



