110 ICE AXD GLACIERS. 



in winter it is less — 1° for about 720 feet of ascent. 

 In the Alps the differences of temperature at great heights 

 are accordingly far more considerable, so that upon the 

 higher parts of their peaks and slopes the snow which has 

 fallen in winter no longer melts in summer. This line, 

 above which snow covers the ground throughout the entire 

 year, is well known as the snow-line; on the northern 

 side of the Alps it is about 8,000 feet high, on the 

 southern side about 8,800 feet. Above the snow-line it 

 may on sunny days be very warm ; the unrestrained radi- 

 ation of the sun, increased by the light reflected from the 

 snow, often becomes utterly unbearable ; so that the 

 tourist of sedentary habits, apart from the dazzling of his 

 eyes, which he must protect by dark spectacles or by a 

 veil, usually gets severely sunburnt in the face and hands, 

 the result of which is an inflammatory swelling of thei 

 skin and great blisters on the surface. More pleasant 

 testimonies to the power of the sunshine are the vivid 

 colours and the powerful odour of the small Alpine flowers 

 which bloom in the sheltered rocky clefts amoug the snow- 

 fields. Notwithstanding the powerful radiation of the sun 

 the temperature of the air above the snow-fields only rises 

 to 5°, or at most 8° ; this, however, is sufficient to melt a 

 tolerable amount of the superficial layers of snow. But 

 the warm hours and days are too short to overpower the 

 great masses of snow which have fallen during colder 

 times. Hence the height of the snow-line does not de- 

 pend merely on the temperature of the mountain slope, 

 but also essentially on the amount of the yearly snow-fall. 

 It is lower, for instance, on the moist and warm south 

 slope of the Himalayas, than on the far colder but also far 

 drier north slope of the same mountain. Corresponding 

 to the moist climate of western Europe, the snow-fall 

 upon the Alps is very great, and hence the number and 

 extent of their glaciers are comparatively considerable, so 



