ICE AND GLACIEHS. 135 



pies more space than the water from which it is formed. 

 When water freezes in closed vessels, it can burst not 

 only glass vessels, but even iron shells. Inasmuch, there- 

 fore, as in the compressed mixture of ice and water some 

 of the ice melts and is converted into water, the volume 

 of the mass diminishes, and the mass can yield more to 

 the pressure upon it than it could have done without 

 such an alteration of the freezing-point. Pressure fur- 

 thers in this case, as is usual in the interaction of various 

 natural forces, the occurrence of a change, that is fusion, 

 which is favourable to the development of its own 

 activity. 



In Sir W. Thomson's experiments, water and ice were 

 confined in a closed vessel, from which nothing could 

 escape. The case is somewhat different when, as with 

 glaciers, the water disseminated in the compressed ice can 

 escape through fissures. The ice is then compressed, 

 but not the water which escapes. The compressed ice 

 becomes colder in conformity with the lowering of its 

 freezing-point by pressure ; but the freezing-point of 

 water which is not compressed is not lowered. Thus 

 under these circumstances we have ice colder than 0° in 

 contact with water at 0°. The consequence is that 

 around the compressed ice water continually freezes and 

 forms new ice, while on the other hand part of the com- 

 pressed ice melts. 



This occurs, for instance, when only two pieces of ice 

 are pressed against each other. By the water which 

 freezes at their surfaces of contact they are firmly joined 

 into one coherent piece of ice. With powerful pressure, 

 and the chilling therefore great, this is quickly effected ; 

 but even with a feeble pressure it takes place, if suffi- 

 cient time be given. Faraday, who discovered this pro- 

 perty, called it the regelation of ice-, the explanation 



