$66 On the PROGRESS of HE At 



17. Let us then fuppofe, that the ftrata of the atmofphere 

 have a capacity for heat, which increafes as the air becomes 



rarer, fo as to be proportional to m b * , x denoting, as be- 

 fore, the diftance from the centre of the earth, r the radius 

 of the earth, m and b determinate, but unknown quan- 

 tities, fuch that m b or —, exprefles the capacity of air for 



heat, when of its ordinary denfity, at the furface of the earth. 



The formula thus aflumed, agrees with the extreme cafes ; 



tn 

 for, when x =r r, the capacity of heat 2= r» a finite 



r 

 quantity 3 when x increafes, - diminifhes, and fo alfo does 



r 



b* , if b is greater than unity, and therefore -*» increafes conti- 



b* 



nually. It does not, however, increafe beyond a certain limit, 



for when x is infinite — becomes — , or m. 



0* 



18. Hence, 



