168 Messrs. R. M. Deeley and P. H. Parr on 



The fair agreement in all essential particulars between 

 the actual and theoretical curves strongly supports the theory 

 that " slip " is proportional to the shear force on the bottom 

 and is independent of the load. It also favours the inference 

 that slip is responsible for a large proportion of the total 

 surface-velocity. 



Many other glaciers give a different form of surface- 

 velocity curve from that of the Hintereis. This no doubt 

 results from different forms of the valley cross-sections. 



Temperature of Ice. — Glacier ice, resulting as it does from 

 the consolidation of snow in the neve regions, may, for 

 several seasons, contain interstitial water. The presence of 

 such water would have a considerable effect upon the fluidity 

 of the mass. The question is one, therefore, of considerable 

 interest from the point of view of the theory of glacier 

 motion. 



During the greater part of the day in summer in the 

 region of the neve, in the case of glaciers in low latitudes, 

 the heat of the sun melts and softens the snow very con- 

 siderably. It is to this moistened snow-surface that the 

 brilliant reflexion is due which adds so considerably to the 

 beauty of a snow scene in high alpine regions. The water 

 thus produced sinks into the snow, and, except in high 

 latitudes and at great altitudes, it may not all be frozen 

 again by the cold of night. On this account glacier ice may 

 contain water-cavities. It does not follow that such water 

 would exist in a capillary condition. Rather should we 

 expect to find it as globular masses in otherwise solid ice. 



During the winter the temperature of the neve regions is 

 much below the freezing-point, and the snow which falls 

 is at a very low temperature. Although snow is a bad con- 

 ductor — and on this account it has been argued by Hess that 

 the snow T -covering would prevent the cold of winter from 

 penetrating the ice — it might also be argued, as Hess did 

 at a later date, that as the snow falls at a low temperature, 

 heat could not penetrate it, and it would remain cold. 

 Unfortunately we know very little concerning the tempe- 

 rature of the ice in the neve regions. A tunnel driven 

 into the ice-cap on Mont Blanc showed that the temperature 

 at a depth of 13 metres was — 16°*5 G. Indeed, a good 

 deal of the ice coming down from the higher regions must 

 be considerably below the freezing-point, and tend to prevent 

 the accumulation of water in the ice due to the heat of the 

 summer. 



Another cause w T hich tends to produce water in glacier ice 

 is the pressure resulting from the accumulation of snow. 



