﻿M. A. Heini on Glaciers. 495 



it myself) that, in a glacier which has to follow a sharp curve in 

 the valley, the grain is smaller on the concave side than on the 

 convex one. In the middle the pressure is the usual, normal 

 pressure, on the concave side a maximum, and on the convex a 

 minimum ; there the capillary fissures are more numerous than 

 here : therefore this also is concordant. 



If these explanations are correct, it is clear why, immediately 

 below the limit of the neve, a distinct glacier-grain never occurs 

 in the middle of the surface ; for these parts of the ice have never 

 yet been compelled by strong pressure to considerable differen- 

 tial motions. The greater the pressure, differential motion, and 

 porosity of the ice, the more will it be divided, and the volume of 

 the grain the smaller ; with the diminution of the pressure the di- 

 vision diminishes, and the volume of the grain increases. 



This theorem could have been arrived at by deduction ; it 

 agrees with the facts known to me, and thereby commends itself 

 to further examination. 



That the number of bubbles diminishes in the manner above 

 indicated I will not positively assert. We know the properties 

 of glacier-ice only near the surface. There is a vast interval 

 between this and the knowledge of what goes on within the 

 glacier. 



In the badly conducting mass of the glacier the cold of winter 

 can only penetrate to the depth of about 8 metres. In the spring, 

 where the first water penetrates from above into the refrigerated 

 layer it is frozen and occasions an increase of volume (a swell- 

 ing). But this is very limited; it only affects the uppermost 

 layers, and is confined to a few brief periods. 



M. Grad ascribes to the freezing of the infiltrated water in the 

 capillary fissures, not only the enlargement, but also the " crys- 

 tallographic orientation" of glacier-ice, discovered by Bertin, 

 and afterwards confirmed and generalized by MM. Grad and 

 Dupre. But he seems to me to form no accurate conception of 

 how this is to be produced by the water freezing round the sur- 

 face of the grains. It might be very difficult to do so. I am 

 inclined rather to look upon the " crystallographic orientation " 

 as a function of the pressure. The ice masses of the lower part 

 of the glacier, in which it has been observed, are not the same 

 which in the upper part did not exhibit the phenomenon ; they 

 are those which, during many years, have sustained the mighty 

 pressure of the overlying layers of ice, now melted away. When 

 we consider that, in a body the temperature of which is always 

 near its melting-point, molecular derangements readily take 

 place, and that there is no lack of shocks which go through the 

 mass of ice (such as occurs, for example, in the crash whenever 

 a crevasse opens or closes), the latter notion becomes still more 



