294 I H an d Around the Morteratsch Glacier : 



is a very important item in the economy of the glacier. It 

 is in fact the mother-liquor of the grain and provides the 

 medium in which the activity of the crystallisation and 

 dissolution of its ice develops itself. 



Every act of crystallisation in this medium furnishes 

 crystals of ice and a mother-liquor. The impurity which was 

 uniformly distributed in the original liquid is concentrated 

 in the mother- liquor and eliminated from the crystal. The 

 melting temperature of the pure ice when in contact with the 

 mother-liquor is lower than it would be if in contact with 

 absolutely pure water. It is this great natural law which 

 secures the preferential melting at the intergranular surfaces. 

 If the mass of the ice of two contiguous grains has exactly 

 the temperature o C., and the liquid between the adjacent 

 surfaces contains so much dissolved impurity as to reduce its 

 freezing temperature to, say crooi , then there is established 

 a temperature gradient from the ice to the liquid which 

 permits the ice actually in contact with the liquid to melt at 

 the lower temperature, and at the expense of the heat in the 

 mass of the grains. This example, if considered attentively, 

 will show not only that, with the limited amount of heat 

 available in the interior of a glacier, some melting must take 

 place between the grains, but also that the total amount of 

 ice so melted can never, at any one time, amount to very 

 much. It is however enough to facilitate the flow of the ice 

 in the dark ; and, when the ice comes to the light, by its 

 power of arresting certain of the solar rays, this liquid, even 

 when very sparingly present, plays an important part, inas- 

 much as it serves to initiate or induce the differential action 

 of the sun's rays, and exposes to their action in the interior 

 of a mass of ice a working surface far greater than that 

 furnished by its outer surface. 



Effect of Solar Radiation on Glacier-Ice. 



The principal effect of the action of the suns rays on the 

 glacier is the production of the white surface layer. This has 

 a thickness of from one to two metres, and, at a certain 



