94 



merit of caloric, or by the conflict of several 

 winds., or by electric phenomena, the upper 

 strata of the atmosphere are mingled with the 

 lower strata. These movements, joined to the 

 horizontal winds that traverse great continents 

 before they reach the basis of the seas, perpetu- 

 ally tend to remove the hygrometer from the 

 extreme point of saturation. Perhaps also the 

 polar currents, which, from the effects of the ro- 

 tation of the Globe, seem to produce the appear- 

 ance of trade winds, have too much velocity to 

 suffer the air they bring, to load itself under each 

 parallel with the whole quantity of vapor cor- 

 respondent to it's temperature. 



Naturalists, who have long marked the pro- 

 gress of the hygrometer in the open air, have 

 seldom seen these instruments at a hundred de- 

 grees, except in a thick fog. In the heaviest rain, 

 even in the midst of the clouds, the hair hygro- 

 meter often keeps at ninety and ninety-five de- 

 grees *. In this case the air placed between 



* Mr, de Saassure observed it once at 84*7° during a very 

 heavy shower. Essai, § 326, p. 321. On the other hand, 

 Mr. Deluc found, that his hygrometers, which, plunged into 

 water, marked 100, kept at 83*3° when they were placed 

 under a glass jar filled with atmospheric air, and of which 

 the sides were constantly moistened. On seeing in my jour- 

 nal, that Deluc's hygrometer kept oftenest between sixty and 

 sixty-three degrees, it should be remembered, that in this 

 instrument the point of saturation in the air is not a hundred, 

 but about eightv-four or eighty-five degrees. Id€es sur la 



