﻿494 M. A. Heim on Glaciers. 



bent, the same noise, proceeding from the sliding on each other 

 of the grains, was audible as in plates of real glacier-ice. When 

 forcibly bent more than the movement of the grains permitted, 

 fracture gave origin to new primary fissures. It is, in all pro- 

 bability, the reciprocal friction of the grains, some of which are 

 strongly pressed against each other, together with the "rude 

 rupture " (or the origination of new fissures), that produces the 

 noise often perceived (and first noticed by Agassiz) in glaciers 

 when otherwise deep stillness reigns — for example, in the night 

 or early morning, ere yet the brooks from the melted ice have 

 begun to purl and babble. 



The aspect of the granular ice obtained from the experiments 

 is, at the first glance, exactly that of genuine glacier-ice, the sole 

 difference being that there the size of the grain is more regular 

 than could be obtained in our little experiment. 



Could we suddenly take away the property of regelation from 

 the glacier-ice, the glacier would behave in its movements like 

 sand, earth, or a heap of gravel*. 



When, in the above experiments, a weaker pressure (stroke) 

 was applied, the plate of ice separated into not very numerous 

 fragments or grains. The stronger the pressure, the more ac- 

 curately must the ice conform to the cavity, and the smaller the 

 grains. Each new fissure begins and proceeds where the cohe- 

 sion is least. If there are air-bubbles in the ice, the capillary 

 fissures have a tendency to strike through them. Ice abounding 

 in air-bubbles presents a mass of less cohesion ; and the same 

 pressure will in such a case produce more numerous divisions, a 

 smaller grain, than in ice which is more compact. 



To this the conditions in the glacier precisely correspond. In 

 the upper parts the ice appears white through a multitude of 

 bubbles; and there it is small-grained, and the air-bubbles are 

 penetrated by many times their number of capillary fissures. 

 Through these water can reach the cavities of the former, and 

 freeze therein, and the air escape. Thus the number of bubbles 

 diminishes, the ice becomes continually more compact as it moves 

 forward, and hence the grain larger. In the upper parts of the 

 glacier, where the transverse section is larger, the pressure 

 which the individual parts have to sustain is also greater ; further 

 down, it is diminished with the transverse section, and hence the 

 new capillary fissures become less numerous. 



Hugi made the observation (I confess I have never repeated 



* The welding of metals (iron, platinum) is probably quite the same 

 process as the regelation of ice ; at least I know of no essential difference. 

 When two badly welded pieces of iron break asunder again, the surface of 

 fracture is also wrinkled. It is likely that accurate comparison of the two 

 processes would throw more light on their nature. 



