SNOW AND ICE. 
I I I 
differed in the explanation of the fact, but into this 
part of the question I need not now enter. Sir 
Joseph Hooker suggested the term “Regelation,” by 
which it is now generally known, and Tyndall has 
applied it to explain the motion of glaciers. 
Place a number of fragments of ice in a basin 
of water, and they will freeze together wherever they 
touch. Again, a mass of ice placed in a mould and 
subjected to pressure breaks in pieces, but as the 
pieces reunite by regelation they assume the form of 
the mould, and by a suitable mould the ice may be 
forced to assume any given form. The Alpine val- 
leys are such moulds. When subject to tension, the 
ice breaks and crevasses are formed, but under 
pressure it freezes together again, and thus preserves 
its continuity. 
Professor Helmholtz in his scientific lectures sums 
up the question in these words — “I do not doubt 
that Tyndall has assigned the essential and principal 
cause of glacier-motion, in referring it to fracture and 
regelation.” Other authorities, however, do not re- 
gard the problem as being yet by any means solved.* 
Heim points out that, as in the case of water, a 
large glacier moves under similar conditions more 
* Heim, Gletscherkimde. 
