8 Professor Forbes' Account of his recent 



the effect of the frost had not penetrated farther into the ice 

 than it might be expected to have done into the earth under 

 the same circumstances. All the superficial rills were indeed 

 frozen over ; there were no cascades in the " moulins ;'' all 

 was as still as it could be in mid- winter ; yet even on the Gla- 

 cier de Lechaud, my wooden poles, sunk to a depth of less 

 than a foot in the ice, were quite wet, literally 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. Is it possible, then, that the mere passing 

 chill of a summer night, or the mere cold of the ice itself at 

 all times, can produce the congelation which has been so much 

 insisted on ? 



But (3), What was the effect of the congelation, trifling as it 

 was, upon the motion of the glacier? So sharp and sudden a 

 cold succeeding summer weather, must inevitably, it seems to 

 me, were this theory true, have produced an instantaneous ac- 

 celeration of the mean motion of the glacier. But the con- 

 trary was the fact ; the diurnal motion fell rather short of its 

 previous value, and so soon as the severe weather was past, 

 and the little congelation which had taken place thawed, and 

 the snow reduced to water, than the glacier, saturated in all 

 its pores, resumed its march nearly as in the height of sumr- 

 mer. 



(4.) It has been inferred from the dilatation theory that whilst 

 the surface of the glacier continually wastes, it at the same 

 time heaved bodily upAvards from beneath, so that its absolute 

 level is unchanged. My experiments, as well as the most 

 ordinary observation (as has been already remarked) disprove 

 this hypothesis. I find that between the 26th June and the 

 ICth September, the surface of the ice near the side of the Mer 

 de Glace had lowered absolutely twenty-five /ee/ 1.5 inches^ 

 and the centre had undoubtedly fallen more. The observa- 

 tion of the waste of the surface by the protrusion of a stick 

 sunk to a determina+e depth in a hole, is very inaccurate, and 

 gives results helow the truth. 



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

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



