The Theory of Glacier motion. 79 



a depth of less than a foot in the ice, were quite wet, Hterally 

 standing in water, and consequently unfrozen to the walls,. 

 and in the hollows beneath the stones of the moraines, by 

 breaking the crust of ice, pools of unfrozen water might be 

 found almost on the surface" {Theory of Glaciers, 32 — 33, 

 Travels, 359 — 360). Forbes goes on to say that "if the 

 dilatation theory were correct, a sudden frost succeeding wet 

 weather must inevitably cause the glacier to advance 

 far more rapidly than in summer, or indeed at any other 

 season, for there could never possibly be more water to be 

 frozen or could cold ever act with more energy than at 

 the time in question, but the contrary was found to be 

 the case, and directly the severe weather passed and 

 the little congelation which had taken place thawed ^ 

 and the snow was reduced to water, then the glacier, 

 saturated in all its pores, resumed its march nearly as 

 in the height of summer." Thirdly, he urges that 

 the well-established motion of glaciers in winter is directly 

 inconsistent with the views of those who urge dilata- 

 tion as the result of alternate congelation and thaw, and 

 as the motive force which impels them, since, when the 

 glacier is completely frozen, this cannot occur. The 

 fact that the motion of the glacier during the day and 

 night is sensibly uniform points the same way. If the 

 theory were true, again, the motion of the glacier ought to 

 vanish near its origin and increase continually towards its 

 lower extremity. " I have found," he says, " the motion of 

 the higher part of the Mer de Glace to differ very little from 

 that several leagues further down ; while in the middle, 

 owing to the expansion of the glacier in breadth, its march 

 was slower than in either of the other parts " ( Theory of 

 Glaciers, 33—34, Travels, 363—4)- 



In addition to these arguments Heim urged that, since 

 water only expands to the extent of one-ninth of its volume 

 in freezing, the total motion which ensues from the 



