436 ACCOUNT OF THE ARCTIC REGIONS. 



it exchanges situations with the stratum of air im- 

 mediately ahove it, and rises in the atmosphere un- 

 til it gets cooled down, by admixture with other 

 air to the common temperature. But its capacity 

 for moisture diminishing more rapidly than its tem- 

 perature, prevents it, on Dr Hutton'^ principle, from 

 sustaining the water absorbed from the surface of the 

 sea, in consequence of which, the surplus moisture is 

 gradually deposited, and being immediately frozen, 

 is exhibited in the air in the form of frost-rime. 



An aqueous vapour, consisting of very minute 

 frozen particles, sometimes occupies the lowest re- 

 gion of the atmosphere, in both temperate and fri- 

 gid climates, during frosty weather ; and is deposit- 

 ed upon the ground, upon surfaces of ice, or almost 

 any other substance with which it comes in contact. 

 This vapour, M'hich seems to be of the nature of 

 koa?^-f/'Ost, generally appears in the evening, after a 

 bright sunshiny day. When the sun declines 

 towards the horizon, and its rays, struggling through 

 the obliquity of a dense atmosphere, begin to lose 

 their power, the excess of moisture evaporated du- 

 ring the meridian heat, is again precipitated. The 

 first precipitation is discovered in a slight mistiness 

 appearing to rise from the surface of the ice : as the 

 cold increases, this mistiness attains a greater eleva- 

 tion, until an obscurity, like that of frost-rime, or of 

 a considerable fog, is produced. Such of the particles 



