Observations on Glaciers. 9 



portant part of their functions ; onl)", I conceive that it occurs 

 but once a year to any effective extent, instead of clail}^ or con- 

 tinually, as he supposes. Every thing which I have seen on 

 the glacier, during cold weather and when covered with snow, 

 confirms the idea I have always entertained, that the progress 

 of congelation in the mass of the glacier is very similar to that 

 of a mass of moist earth, and that, therefore, the daily varia- 

 tions of temperature can make no sensible impression, with 

 respect to the mass of the infiltrated ice. The prolonged cold 

 of winter must, however, produce a very sensible effect ; and 

 considering that the temperature of the mass is never above 

 32°, it may be expected that the congelation of the water in 

 capillary fissures in ice will, in the course of months of tran- 

 quillity, reach a great depth. I apprehend that there is only 

 an annual congelation, and that its effect is not to move the 

 glacier onwards by sliuiuy down its bed — for that the friction 

 of so enormous a body seems evidently to render impossible — 

 but (what Mr Hopkins has very well shewn is the only alter- 

 native, and which he has used as an argument against Char- 

 pentier's theory) to dilate the ice in the direction of least re- 

 sistance, that is, vertically, and consequently to increase its 

 thickness. The tendency of such a force would, therefore, 

 be to restore during the winter the thickness of ice lost during 

 the summer ; and in those winters which are less severe, a less 

 depth of ice being frozen, a less expansion would occur, and a 

 permanent diminution of the glacier would result. Nothing 

 can be more certain than the fact, so well stated by Charpen- 

 tier in his 10th section, that the glacier does not owe its in- 

 crease to the snow of avalanches, nor indeed to any snow which 

 falls on the greater part of its surface. 



In conclusion, the admission of semifluid motion produced 

 by the weight of the ice itself, appears to explain the chief 

 facts of glacier-movement, viz. (1.) That it is more rapid at 

 the centre than at the sides ; (2.) For the most part, most 

 rapid near the lower extremity of glaciers, but varying rather 

 with the transverse section than the length ; (3.) That it is 

 more rapid in summer than in winter, in hot than in cold 

 weather, and especially more rapid after rain, and less rapid 

 in sudden frosts ; (4.) It is farther in conformity with what 



