Ch. XVI.] 



THEORY OF EEGELATION. 



373 



i 



outer shell of ice is first formed, and then another within, 



h 



1 the fuze-hole must 

 proceed from the squeezing of successive shells of ice concen- 

 trically formed, through the narrow orifice ; and yet the pro- 

 truded cylinder consistedof entire, and not of fragmentary ice.* 

 When the hypothesis of viscosity had been so admirably 

 worked out and illustrated by Forbes as to appear to be 

 firmly established, Mr. Tyndal objected that it would account 

 for a part only of the facts. Ice, he admitted, deports itself 

 as a viscous body in cases where it is subjected to pressure 

 alone, but when tension comes into play the analogy with a 



i 



viscous body ceases. c The glacier widens, bends, and narrows, 

 and its centre moves more quickly than its sides. A 



viscous 



most 



mass would undoubtedly do the same. But the 

 experiments on the capacity of ice to yield to strain, — to 

 stretch out like treacle, honey, or tar, — have failed to detect 

 this stretching power. Is there, he asks, then, any other 

 physical quality to which the power of accommodation pos- 

 sessed by glacier-ice may be referred P'f 



Faraday had called attention, in 1850, to the fact that if 

 two pieces of ice having throughout a temperature of 32° F., 



and 



meltin 



& 



are m 



to touch each 



other, they will freeze together at the points of contact. 

 This effect will take place even if the two pieces are plunged 



minute 



In 



into hot water and held together for half a 



virtue of this property, which has been called ' regelation/ a 



may 



mould 



that the parts are brought into still closer proximity. 



It is 



then converted into a coherent cake of ice. 



All the touching 



surfaces of the icy 



fragments 



are cemented 



together by 



regelation, by virtue of which property the substance may be 

 made to take any shape we please. 'It is easy therefore/ says 

 Tyndal, ' to understand how a substance so endowed can be 

 squeezed through the gorges of the Alps — can bend so as to 

 accommodate itself to the flexures of the Alpine valleys, and 



* This experiment is cited by Mr. 

 Forbes, Phil. Trans. 1846, p. 206. 



f Tyndal, Heat as a Mode of Motion, 

 1863, pp. 185, 189. 



