420 ACCOUNT OF THE ARCTIC REGIONS. 



centration and reflection of the sun's rays in the 

 sheltered valleys, a small imperfect cumulus is 

 sometimes exhibited. The most common definable 

 cloud seen at sea, is a particular modification, some- 

 what resembling the cirro-stratus, consisting of large 

 patches of cloud arranged in horizontal strata, and 

 enlightened by the sun on one edge of each stra- 

 tum. 



Rain is a meteor too well known to need any 

 description ; but the causes which operate so as to 

 produce it, under the great variety of circumstances 

 in which it occurs, are not altogether understood. 

 The known agents made use of, in the economy of 

 Nature, for the production of rain, are changes of 

 temperature and electricity. The latter principle is 

 supposed to act most powerfully in the production 

 of thunder showers ; in which case it is not unlike- 

 ly but a portion of the air of the atmosphere is, by 

 the passing of the lightning from one cloud to an- 

 other, converted into water. The former seems to be 

 the chief agent in the colder regions of the globe, 

 where electricity is either more equal in its distribu- 

 tion, or not so active in its operations, as in the 

 warmer climates. Were the capability of the at- 

 mosphere for absorbing moisture, the same at all 

 temperatures, or were its capability increased in a 

 similar ratio with the increase of heat, no change, 

 however great, produced by the admixture of two 

 streams of air of different temperatures, could ocoa- 



