DISCUSSION. 141 



on either side of noon, and the atmosphere being 

 remarkably clear, the removal of the snow from 

 such situations can consequently afford no mea- 

 surement of the line in question. It is only 

 upon level surfaces, or upon such as, in con- 

 sequence of the obliquity of the angles, they 

 present, its rays operate with but little effect, 

 that we can form any accurate estimation of 

 its height. The reverse is naturally the case 

 in low latitudes. In consequence of the radiation 

 of the great plain of Tartary we find the snow 

 line upon the north side of the Himaleh moun- 

 tains higher by three thousand feet than it is 

 on the south. And the great plain of Titicaca 

 causes the snow line to be two thousand feet 

 higher in the latitude of 16° than it is under 

 the equator. 



Mr. Scoresby, in his " Arctic Regions," has 

 supposed the upper limit of the snow line at 

 Spitzbergen to be at the height of seven thou- 

 sand seven hundred and ninety-one feet, which, if 

 it be not a misprint, is, I presume, to be under- 

 stood as the elevation beyond which solar radia- 

 tion ceases to produce a thawing temperature in 

 the stratum immediately in contact with the hills 

 exposed to it. If otherwise, and we are to assume 

 this as the line of perpetual snow, in the general 

 acceptation of the term, we shall have this line 



