3io In and Around the Morteratsch Glacier : 



for' melting ice in the interior of the glacier is very small ; 

 consequently very little of it melts. What does melt, however, 

 is sufficient to maintain everywhere a liquid nucleus between 

 the grains. This compact but granular mass is the primary 

 ice of the glacier, its colour is blue, and it persists unaltered in 

 obscurity. 



Among the rays emitted by the sun, there are some which 

 are absorbed by water with production of heat, although they 

 are transmitted abundantly and without alteration by ice. 

 When the primary ice is exposed to the sun, these rays 

 penetrate its mass and are absorbed by the intergranular 

 liquid, the temperature of which would be raised, but, as it is 

 contained in a space bounded by two parallel and almost 

 contiguous surfaces of ice, the rise of temperature is checked 

 and an equivalent amount of ice is melted instead. 



When a volume of ice is melted, its place is taken to the 

 extent of ninety per cent, by liquid water, and to the extent 

 of ten per cent, by gaseous water of very low pressure. The 

 latter strikes the eye as a discontinuity in the ice : such 

 discontinuities, when present in adequate proportion in a 

 transparent substance, produce the impression of whiteness. 



We have seen that such discontinuities are found in the 

 artificial grotto. When the ice-wall in which they have been 

 developed is at the entrance of the grotto, or not more than 

 about two metres distant from it, the disintegration produced 

 by the radiation from the sky is so considerable that the 

 ice- wall does not remain water-tight, and not only does the 

 ten per cent, gaseous discontinuity fill itself with air, and for 

 the moment become really an air-bell, but the air continues 

 to enter, and permits the ninety per cent, of water to run out, 

 when the hundred per cent, replacement of the volume of ice 

 by air is achieved. In this way the apparent discontinuity 

 caused by the direct effect of radiation in the intergranular 

 spaces has been increased ninefold by its indirect effect in 

 bringing about drainage by destroying the staunchness of the 

 ice-wall and causing it to leak. By our studies in the artificial 

 grotto it has thus been established, not only that the drainage 



