252 DISCUSSIONS IN CLIMATOLOGY. 



Let us now consider the bearing which the foregoing 

 principles have on glacier motion. Heat can pass 

 through a mass of ice, either by radiation or by the 

 process of conduction, without visibly destroying the 

 solidity of the ice. This has been proved experi- 

 mentally by Professor Tyndall.* Although the general 

 solidity of the ice of a glacier is not sensibly affected 

 by the passage of the heat, nevertheless a process of 

 melting may be incessantly going on in the interior of 

 the ice; and as the effects of melting would doubtless 

 be counterbalanced by the opposite process of regela- 

 tion, the general solidity of the ice would thus be 

 maintained. That the passage of heat through ice will 

 melt particles in the interior is no mere hypothesis, but 

 a fact which has been established both by observation 

 and by experiment. Owing to the principle of regula- 

 tion a particle melted in the interior would, in all pro- 

 bability, in nine cases out of ten, re-solidify. Let us 

 now consider what would probably be the behaviour 

 of the melted particle under such conditions, and the 

 bearing which its solidification would have on glacier 

 motion. 



Ice is evidently not absolutely solid throughout. It 

 is composed of crystalline particles, which, though in 

 contact with one another, are, however, not packed 

 together so as to occupy the least possible space, and, 

 even though they were, the particles would not fit so 

 closely together as to exclude interstices. The crystal- 

 line particles are, however, united to one another at 

 special points determined by their polarity, and on 

 this account they require more space; and this in all 

 probability is the reason why ice, volume for volume, 

 is less dense than water. It is obvious that when a 

 crystalline particle melts it will not merely tend to 



* See "Heat as a Mode of Motion," Appendix to Chap. IX. 



