162 



Messrs. K. M. Deeley and P. H. Parr on 



In our previous paper we took the slip of the Hintereis 

 Glacier to be 21*46 metres per annum. That the two 

 figures should be so nearly alike is due to the accident 



of the roughness of the slab. 



D* r 



Fig. 7. 



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The experimental results tend to show that the theoretical 

 movement, or slip, is of the right order of magnitude, and 

 that, therefore, the slip of a glacier is due very probably to 

 the melting and refreezing which takes place where each 

 little irregularity of the glacier-bed projects into the ice. 



The Conditions of Flow of the Hintereis Glacier. — In our 

 previous communication we assumed that the rate of slip 

 was proportional to the load on the glacier as well as the 

 downward force of gravity, and also that the channel was an 

 ellipse. A consideration of the conditions of shear stress in 

 a glacier moving down a channel of the form of Parr's curve, 

 and with a velocity proportional to the shear force on the 

 bed, leads to some results which agree well with the actual 

 surface-velocity of the Hintereis Glacier, and tend to support 

 the theory of slip we have described. 



We will in the first instance assume that the actual 

 surface-velocities of the glacier are the sum of the slip and 

 viscous velocities, and that the rate of slip at various points 

 is not modified by the high viscosity of the ice tending to 

 make the slip more regular across the section. 



