Of BAROMETRICAL MEASUREMENTS. 97 



Hence, making log.(i m) g, 



py_ . x 



_ 



P 1>y+p log- C = 



z) 



IF D denote the denfity of the air at the furface of the earth, 

 D will be the value of y> when x o, and fo 



p (log. D+ log. C") = - - - -. Therefore 



plog.C -- pkg.D; and f o by fubftituting for 

 \?(i z) 



. C, p(log.ylog. D) + - i^ - - = 



or changing the figns, 

 . Dlog.y) 



THIS equation exhibits, in general, the relation between the 

 denfity of any ftratum of air, and the height of that flratum 

 above the furface of the earth, on the fuppofitions that the heat 

 of the atmofphere decreafes uniformly as wfiTafcend, and that 

 the contraction produced in air by cold, obferves the law defcri- 

 bed in 5. It might be confidered as an equation to a 

 curve, of which the abfciffae reprefented the height of the diffe- 

 rent flrata of the atmofphere, and the ordinates, the denudes of 

 thofe flrata : This curve would evidently be different from the 

 logarithmic, but would be found to have certain relations to it 

 not uninterefling, and not difficult to trace, if we had leifure 

 for fuch a digreffion. 



N 14. LET 



