[ 309 3 



The faturabilily of air he eftimates by the number of grains, 

 over and above thofe i t already poffeffes, which i t requires to arrive at 

 faturation, in its adual temperature. Thefe grains he therefore 

 calls degrees of faturability (or drynefs). He thus found : i*^. that 

 in air, whofe denfity is about one-third fmaller than ufual (as 

 where the barometer ftands at twenty inches) the influence or eva- 

 porating effed of a difference of one degree of Reaumur (2°, 25 

 Fahr.) is fomewhat more than three times greater than the in- 

 fluence of a difference of one degree of drynefs or faturability. 



2do. That in air of the ufual denfity, or only a few inches 

 above or below it, the influence of a difference of one degree of 

 faturability is about three times greater than the influence of a 

 difference of one degree of Reaumur (2,25 Fahrent.) Therefore 

 in an atmofphere of the ufual denfity, on plains, the influence 

 of a difference of nearly 7*^ of Fahren*. is nearly equal to the in- 

 fluence of a difference of one degree of faturability. 



Hence our northerly and eafterly winds, though fome degrees 

 colder than the foutherly and wefterly, yet promote evaporation 

 much more ; the air they convey being farthcf from faturation. 

 Thus Achard found the evaporation from his atmedometef t« be 

 13, on the~4th of May 1788, under an ENE. wind, therm<&iTieter 

 51*^, hygrometer XLVIII. but on the 7th of the farfie month 

 the evaporation was but 8, the wind being- -^WSW. theugh the 

 Vol. VIII. Q^q mean 



