﻿490 M. A. Heim on Glaciers. 



could not but show itself in the form of the glacier ; but only a 

 shrinking through melting is to be recognized therein, never a 

 swelling. 



We very often find isolated air-bubbles enclosed in the large, 

 splendidly transparent glacier-grains, and sometimes, indeed, 

 quite in their centres, sometimes excentric. In the fine neve 

 the air is found only between the granules ; and if these were 

 gradually to grow larger by water freezing on them, the air 

 would remain between the grains. I cannot conceive how it 

 could be enclosed in them. On the contrary, in thawing snow 

 it is immediately evident that it becomes large-grained through 

 single minute crystals, afterwards single granules, uniting to 

 form one, and consequently that a larger grain of the neve is 

 not a small one increased in size, but corresponds to several 

 small ones. 



That the grain of the upper part of the glacier is smaller than 

 that of the lower it is easy to see ; but, often as T have sought 

 for it, I have never been able to trace the transition from the 

 neve-grain to the glacier- grain. Where the neve ends and the 

 clear ice, though rich in bubbles, appears at the surface, this 

 shows no distinct granular structure ; the glacier- grain begins to 

 make its appearance (at first rather small) further down the val- 

 ley. Also the increase of size of the grains as the end is ap- 

 proached seems to me to take place not at all so regularly as has 

 been asserted. For a long time I thought my own observation 

 was at fault, until the above calculation reassured me. 



How could the fine divisions between the individual neve- 

 granules be preserved for two or even three or more centuries, 

 often under strong pressure, without being destroyed by regela- 

 tion ? — while by this process the mightiest crevasses may disap- 

 pear and scarcely leave a trace, and two pieces of ice, gently 

 pressed together for a few days, so regelate that the piece, on 

 being fractured, will not break again at the same place. 



The network of fissures, or the structure of the glacier-ice 

 which in warm air gives rise to that network, is necessarily always 

 passing away and almost simultaneously being formed afresh; for, 

 as is proved by our calculation, the glacier-grains (bounded by the 

 capillary fissures) of the higher and lower parts of the glacier do 

 not correspond to each other. 



It was already conjectured by Forbes that these fissures might 

 be divisions produced, or at least preserved, by pressure and 

 motion. 



When we take a piece of ice from the surface of the glacier and 

 divide it into its grains, we are struck by the fact that they do 

 not all separate with equal facility. While the fissures circum- 

 scribing the grains are partially visible through the air which 



