87 



extreme slowness ; and on the summit of moun- 

 tains, as I have frequently experienced to my 

 great regret, we are often uncertain whether we 

 have not ceased our observations before the in- 

 strument has ceased it's movement. On the 

 other hand, this hygrometer, furnished with a 

 spring, has the advantages of being strong, 

 marking with great exactness in very moist air 

 the least increment of the quantity of vapor in 

 solution, and acting in all positions ; while Saus- 

 sure's hygrometer must be suspended, and is 

 often deranged by the wind, which raises the 

 counterpoise of the index. I have thought it 

 might prove useful to travellers, to mention in 

 this place the results of an experience of several 

 years. 



During the whole of the passage, the apparent 

 humidity of the atmosphere, that indicated by 

 the hygrometer not corrected by the temper- 

 ature, augmented sensibly, notwithstanding the 

 progressive increment of the heat. In the month 

 of July, in the thirteenth and fourteenth degrees 

 of latitude, Saussure's hygrometer marked at sea 

 from eighty-eight to ninety-two degrees*, in per- 



* The hair hygrometer being much better known than that 

 of whalebone, in order to preserve a uniform rate, the hygro- 

 metrical results have been given according to Saussure's instru- 

 ment, even when the observations were made with that of 

 Deluc. It is only in the meteorological journal, that the hy- 

 grometer employed for each series of experiments is men- 



