ICE AND GLACIERS. 



141 



Ihe base. It at first emerges as a solid cylinder of the 



same diameter as the aper- _ 



1 . ^ ,f Fig. 25. 



tore ; but as the ice follows 



more rapidly 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. 



26 exhibits a series of 



shapes which have resulted 



in this manner.^ 



Here also the cracks in the emerging cylinder of ice 



exhibit a surprising similarity with the longitudinal rifts 



Fig. 26. 



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 



' Id 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 0°. 



