95 



the drops of water, or the vesicular vapor, is far 

 from being saturated ; and I doubt whether the 

 atmosphere, preserving a perfect transparency, 

 ever attains the maximum of humidity, which 

 we obtain under our glass jars. Mr. de Saus- 

 sure, after having explained the long series of 

 his manometrical and hygrometrical experi- 

 ments, made at different degrees of temperature, 

 admits, that the last degrees of his instrument 

 are perhaps only degrees of super saturation, and 

 that the quantity of vapor that a certain volume 

 of free air can contain, is probably less than 

 might be admitted from the experiments made 

 in our laboratories *. 



The naturalists, who accompanied the Che- 

 valier Krusenstern in his voyage round the world, 

 assert, that Deluc's hygrometer enabled the 

 mariners to foresee stormy weather, during the 

 passage from Washington Islands to Sanga- 

 sacky ; and in all other parts of the torrid zone, 

 where the changes of the atmosphere have scarce- 

 ly any influence on the barometer. Mr. Peron, 



Meteorologie, 1786, t. i, p. 72; t. ii, p. 473. TJrenna, 

 Anaies de Historia natural, 1803, p. 229. 



* In determining the point of extreme humidity, it is sup- 

 posed, that the air in the jar is not yet saturated, when the 

 vapors begin to be precipitated in an almost imperceptible 

 manner. (Saussure, Essai, § 107 and 123.) Mr. Gay-Lus- 

 sac has shown, that the hygroscopical property of the glass 

 becomes a source of errors difficult to avoid. 



