122 



ICE AND GLACIERS. 



FIG. 22. 



has lain for a while in ice- water, so as to reduce it to the tempera- 

 ture of 0, it is packed full of snow, and then the cylindrical 

 plug, C C, which fits the inner aperture, but moves in it with 

 gentle friction, is forced in with the aid of an hydraulic press. 

 The press used was such that the pressure to which the snow 

 was exposed could be increased to fifty atmospheres. Of course 

 the looser snow contracts to a very small volume under such a 

 powerful pressure. The pressure is removed, the cylindrical 

 plug taken out, the hollow 

 again filled up with snow, 

 and the process repeated un- 

 til the entire form is filled 

 with the mass of ice, which 

 no longer gives way to pres- 

 sure. The compressed snow 

 which I now take out, you 

 will see, has been transformed 

 into a hard, angular, and 

 translucent cylinder of ice; 

 and how hard it is appears 

 from the crash which ensues 

 when I throw it to the 

 ground. Just as the loose 

 snow in the glaciers is pressed 

 together to solid ice, so also 

 in many places ready-formed 

 irregular pieces of ice are 

 joined and form clear and 

 compact ice. This is most re- 

 markable at the base of the 



glacier cascades. These are glacier falls where the upper part of 

 the glacier ends at a steep rocky wall, and blocks of ice shoot 

 down as avalanches over the edge of this wall. The heap of 

 shattered blocks of ice which accumulate become joined at the 

 foot of the rock- wall to a compact, dense mass, which then con- 

 tinues its way downwards as glacier. More frequent than such 

 cascades, where the glacier-stream is quite dissevered, are places. 



