[ 38' ] 



The equator and tropics lie chiefly over fea, but partly over 

 land, and the temperatures of each of thefe are very different. 



Mean heat of the equatorial air . 84^ 



of the fupra-marine S. intra-tropical air 85* 



' ■ of ditto incumbent over land - 98° 



fupra-marine N. intra-tropical air 80* 



of ditto incumbent over land - 908 



At the level of the fea and furface of land, mean of all 87'' 



Mean heat of the extra-tropical fupra-marine air in 



this feafon*, from latitude 23** to latitude 33*^ 66*' 



Ditto of that incumbent over land - 70® 



Mean of both at the level of the fea and furface of 

 the land - - - 68<? 



To reprefent the adion of thefe on each other, we fhall fuppofe 

 each to form a diftind; column, and both columns to be conti- 

 guous to each other, and each to fupport mercury in the barometer 

 to the height of 30 inches, at the furface of the earth. 



* See Eftiraate of the temperatures of different latitudes. 



Vol. Vlil. 3 B And 



