ICE AND GLACIERS 



249 



FIG. 116 



aperture. With this view I place a base on the previously 

 described mould, which has a conical perforation, the ex- 

 ternal aperture of which is 

 only two thirds the diameter 

 of the cylindrical aperture of 

 the form. FIG. 116 gives a 

 section of the whole. If now 

 I insert into this one of 

 the compressed cylinders of 

 ice, and force down the plug 

 a, the ice is forced through 

 the narrow aperture in the 

 base. It at first emerges as 

 a solid cylinder of the same 

 diameter as the aperture; but 

 as the ice follows more rap- 

 idly in the centre than at 

 the edges, the free terminal surface of the cylinder becomes 

 curved, the end thickens, so that it could not be brought 

 back through the aperture, and it ultimately splits off. FIG. 

 117 exhibits a series of shapes which have resulted in 

 this manner. 3 



Here also the cracks in the emerging cylinder of ice 

 exhibit a surprising similarity with the longitudinal rifts 

 which divide a glacier current where it presses through a 

 narrow rocky pass into a wider valley. 



In the cases which we have described we see the change 

 in shape of the ice taking place before our eyes, whereby 

 the block of ice retains its coherence without breaking into 

 individual pieces. The brittle mass of ice seems rather to 

 yield like a piece of wax. 



A closer inspection of a clear cylinder of ice compressed 

 from clear pieces of ice, while the pressure is being applied, 

 shows us what takes place in the interior; for we then see 

 an innumerable quantity of extremely fine radiating cracks 

 shoot through it like a turbid cloud, which mostly disappear, 



In this experiment the lower temperature of the compressed ice some- 

 times extended so far through the iron form, that the water in the slit 

 between the base plate and the cylinder froze and formed a thin sheet of 

 ice, although the pieces of ice as well as the iron mould had previously laid 

 in ice- water, and could not be colder than o. 



