l 3^7 ] 



The clouds that frequently inveft its fummit originate from 

 vapours condenfed by the abforption of eledriclty by the moun- 

 tain. It is alfo highly remarkable that the common difference of 

 the progreflion fhould fuit terms beyond the lafl, by the means of 

 which it was found. It would therefore feem that the common 

 difference thus found takes place at much fuperior heights. 



The fmaller differences between the degrees of heat calculated, 

 and thofe obferved, may well be attributed to local circumflances ; 

 Mow, in fome fituations of fmall extent, refle^ed heat often occurs ; 

 above if the fummit be graffy the heat is diminifhed in fome de- 

 gree by evaporation; if flony but narrow,* the genuine heat is 

 little affedled ; but if broad, as the flony fummit of Pinchinca, a 

 confiderable degree of heat may arife from refledion, on funny 

 days. Darker days feem more favourable to deteding the true 

 heat appropriated to the height. 



Notwithstanding the imperfedions incident to obfervations 

 on mountains, yet thefe are upon the whole much lefs exception- 

 able than thofe that hitherto have been taken in balloons, of which 

 the height is feldom determined with fufHcient precifion ; befides 

 flmultaneous obfervations of the temperatures above and below 

 larely occur, and on funny days the heat refleded by balloons 

 caufes confiderable errors. 



Zz 2 Lastly, 



