the Hintereis Glacier. 163 



In our previous paper * we adopted the statement of 

 Finsterwalder that that led us to regard the summer velocity 

 as 15 per cent, in excess of the winter velocity. This seemed 

 likely to be correct, in view of the measurements of Forbes 

 and Tyndall. Bliimcke and Finsterwalder f , however, have 

 since given the results of a large number of measurements 

 made at many points along the tongue of the Hintereis 

 Glacier. The results of these measurements constrain them 

 to say that some outstanding irregularities and exceptions in 

 the tables urged them at the commencement, and in the 

 progress of the investigations to adopt views which they have 

 retracted in favour of others more recently brought forward, 

 and which rest on a consideration of the whole of the 

 measurements. 



Their full results clearly show that it is only along the 

 end third of the glacier tongue that the summer velocity is 

 greater than the winter velocity. In the upper two-thirds 

 of the glacier tongue the winter velocity is the greater. 

 The authors say : — " The reason for this surprising phe- 

 nomena we find in the following considerations. The 

 driving force of glacier movement is manifestly gravity, 

 and the pressure of the neve layers produced through it. 

 One resistance to glacier movement proceeds from the 

 interior friction of the ice-mass and from friction on the 

 glacier-bed. The velocity-condition of the glacier originates 

 from the cooperation of driving force and resistance; the 

 winter acceleration of movement in the upper parts is in 

 the first place attributable to the increased neve pressure 

 in the winter ; while the summer acceleration of move- 

 ment in the lower parts must be traced to lessened friction- 

 resistance, in consequence of penetration of the ice and 

 glacier-bed by melting water." 



Bliimcke and Finsterwalder found approximately that the 

 summer speed was greater than the mean velocity in the lower 

 parts of the glacier by about the following percentages : — 

 At 350 metres from the end, 27'8 per cent. ; at 600 metres, 

 15 per cent. ; and at 774 metres, 10*3 per cent. On the 

 contrary, at 1750 metres the mean velocity was 11*2 per 

 cent, and at 2700 metres 18*3 per cent, greater than the 

 summer velocity, and continued to be greater well into the 

 neve region. At section V., therefore, instead of the winter 

 velocity being less than the summer velocity, it is greater. 



* Phil. Mag. vol. xxvi. pp. 85-111 (1013). 



t Sitzungsberichte der math.-phys. Klasse der K.D. Akademie der 

 Wissenschaften zu Miinchen, Band xxxv. (1905). Miinclien, 1906. 

 Pp. 109-131. 



M 2 



