I 300 ] 



yet however, fince it far exceeds any variable degree of moifture, 

 ever difcovered in air, it is fully fufficient for all meteorological 

 purpofes. 



The maximum of deficcation is marked o on the fcale of this 

 inftrument*, and the maximum of moifture, or point of fatura- 

 tion, 98''. To prevent confounding thefe vixih. thermometrical 

 degrees, which often accompany them, I denote them by Roman 

 numerals. XXV. marks the gr^ateft drynefs, which according to 

 Sauffure can never be found in the open airf. XL. the greateft 

 drynefs ever obferved by him ; confequently even L denotes a 

 confiderable degree of deficcation. But LXX denotes a degree 

 of moifture often perceptible on glafs. 



Here it muft be carefully remarked, that hygrometrical degrees 

 denote very nearly the ratios which the quantity of moifture 

 poftxAed by a Jiratum of air, bears to the quantity that would 

 faturate that air in its aElual temperature ; and as this faturating 

 quantity varies more or lefs in every degree of temperature, it 



follows, 



• 1 have ofteu produced a deficcation far below o by means of fulphuric acid 

 highly concentrated. 



f I dont know that the drynefs of the fcirocco or harmattan was ever explored by 



this inftvuroeni. 



