462 



EEPOET — 1881. 



The height of the line of perpetnal snow depends upon two factors 

 only : (1) the temperati^re of the summer months (July) ; (2) the supply 

 of aqueous vapour to form the snow. 



This fact is well illustrated by the following table, which is copied 

 from a ^laper by Mr. Joseph J. Murphy, read in 1875, before the Belfast 

 Natural Histoiy and Philosophical Society, and is constructed on the 

 principle (tolerably near the truth) that the temperature of the hottest 

 month in the year decreases in ascending at the rate of 1° F. for every 

 300 feet. 



Pyrenees ..... 

 Caucasus ..... 

 Mount Blanc .... 

 Bernese Alps .... 

 Scandinavian Fjelde 61°43' N. . 

 Mageroe, Norway, extreme north 

 Himalaya, about 31° N., noi-th side 

 Himalaya, about 31° N., south side 

 Andes, near Quito 



Do. 18° N 



Do. near Valparaiso 



Do. 37°40' S. ... 



Straits of Masrellan . 



On this table, Mr. Murphy remarks, as is stated in the foot note.' 

 Professor Forbes ^ has expressed the opinion, founded on his study of 

 the Norway glaciers, that a diminution of 4° F. in the temperature of the 

 summer months would place one-fourth of the surface of Norway within 

 the snow-line and pour glaciers into the head of every fiord In Western 

 Norway. From a personal study of the Norwegian ice-fields, I am inclined 

 to confirm this statement. 



At the latitude of 60° N., the July temperatures of Greenland and 

 Norway, are — • 



Norway . 

 Greenland 



60° F. 



47° 



Diff. = 13° F. 



' It is evident by this table that the snow-line rises above the line of 32° for the 

 hottest montli of the year where the snow-fall is small, and. sinks below it where the 

 snow-fall is great. In the Caucasus, the Alps, and the PjTenees, the snow-line is 

 about three-fourths of the height of the line of 32° for the hottest month of the .year ; 

 in the Fjelde of Norway, about two-thirds; in the Peruvian and Chilian Andes above, 

 but in Patagonia and Tierra del Fuego below ; above, on the north side of the 

 Himalaya, but below on the south side. These contrasts are all to be explained by 

 the difference in the amount of snowfall, which is greater on the south than on the 

 north side of the Himalaya, greater in Patagonia and Tierra del Fuego than in Chil6 

 and Peru, and probably greater, at least in winter, in Norway than in Central, 

 Southern, or Eastern Europe. 



The dependence of the height of the snow-line on summer temperature and on 

 amount of snowfall, to the exclusion of winter temperature, may be best shown, 

 perhaps, by two extreme cases. The mean temperature of the Altai mountains is 

 below freezing ; yet, in consequence of the comparatively warm summer, and the 

 small snowfall, the height of the snow-line is about 6,000 feet. In the Straits of 

 Magellan, on the contrary, though the mean temperature is several degrees above 

 freezing, the height of the snow-line (see table) is little more than half as much. 



- Norway and its Glaciers, p. 243. 



