﻿M. A. Heim on Glaciers. 487 



ferent results of infiltration experiments probably stand in direct 

 relation to the parts of the glacier where they were carried out. 



That even the most solid, transparent, blue ice from the inte- 

 rior of the glacier, in the warmer air, and especially through the 

 operation of the solar rays, becomes white through a network of 

 fine fissures becoming visible, which everywhere divide the ice 

 into irregularly formed grains of a certain constant magnitude 

 in any one locality, is an observation which no one has yet dis- 

 puted and which any one can repeat. But why does not this 

 happen to common ice ? How could heat call forth such a gra- 

 nular structure, if it were not already sketched out, even in the 

 u sound," compact ice ? How it is present in the " sound " ice 

 - — whether in the form of actual capillary fissurelets filled with 

 water, or whether, from some unknown cause, the ice more rea- 

 dily liquefies on surfaces irregularly permeating the mass, or how 

 otherwise it may be imagined — whether capable of infiltration 

 or not is to us indifferent, — it is sufficient that a similar granular 

 structure to that which we observe on the surface goes through 

 the whole mass, or at least is traced out therein. 



Attempts have been made to explain how this granular struc- 

 ture arises. The unproved view of MM. Hugi and Grad, above 

 quoted, that the glacier-grains are the further developed gra- 

 nules of the neve, is not what they think, a something taught by 

 direct observation, but an hypothesis. (I shall return to this ques- 

 tion.) We will for a few moments adopt it, and found upon it a 

 little calculation, which will the soonest put it in the right light. 



In glaciers of about 8000 metres length (for example, the 

 Hufi Glacier, Rhone Glacier, &c.) the glacier-grain grows from 

 the size of a wheat-grain to at least the size of a walnut (in larger 

 glaciers, according to Hugi, it may become " even 5 or 6 cubic 

 metres in volume"), thus from about 3 millims. in diameter to 

 30; the corresponding volumes are from 3 3 to 30 3 , or (which 

 gives the same proportion) from 1 to 1000. And this enlarge- 

 ment of form takes place throughout the mass of the glacier, 

 and not merely in the layers nearest to the surface. In the time 

 necessary for a point at the upper end of the glacier to arrive at 

 the lower, the glacier, but for the superficial melting away [abla- 

 tion), would become 1000 times its original volume ; the ablation, 

 then, must not only, in just this time, carry away in water the 

 mass of ice present, but also compensate for the thousandfold 

 increase. Although we shall apply our calculation to the Aletsch 

 Glacier, the length of which amounts to more than twice 8000 

 metres, we will yet, in favour of the hypothesis, content our- 

 selves with a simple increase of volume to 1000 times instead of 

 2000. The numbers we shall use will be only approximate, 

 always rounded off in favour of the hypothesis. 



2K2 



