34 FOURTH LETTER ON GLACIERS. [1842. 



observation of the waste of the surface by the protrusion of a 

 stick sunk to a determinate depth in a hole, is very inaccurate, 

 and gives results Mow the truth. 



I ain perfectly ready to admit, with M. de Charpentier, that 

 the congelation of the infiltrated water of glaciers is an import- 

 ant part of their functions ; only, I conceive that it occurs but 

 once a year to any effective extent, instead of daily or 

 continually, 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 

 variations 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 sliding 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 resist- 

 ance, 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 Charpentier in 

 his 10th section, that the glacier does not owe its increase 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 



