HERMANN VON HELMHOLTZ 



each other at zero (centigrade) freeze into one block. 

 James Thomson, the brother of Lord Kelvin, had 

 explained this by showing that pressure causes a 

 lowering of the freezing point. James Thomson de- 

 duced this fact from the mechanical theory of heat. 

 Lord Kelvin soon after gave the complete theory 

 connecting melting point and pressure, and verified 

 by experiment his brother's calculation that each in- 

 crease of a pressure of one atmosphere causes a 

 lowering of the freezing point to T y^ of a degree 

 cent. A mixture of snow and ice becomes colder 

 as pressure increases, just as theory requires. In 

 Faraday's experiment mentioned above, some free 

 heat becomes latent during pressure, a part of the ice 

 along the side of the block melts and then freezes 

 again, cementing the blocks into one piece. These 

 facts, and also the remarkable phenomenon of the 

 well-known movements of a hard, and, in popular 

 belief, a brittle body, like ice in great glaciers, 

 were originally accounted for by regarding ice as a 

 viscous fluid, a suggestion due to Rendu, a Savoyard 

 priest, and very fully developed by the celebrated 

 natural philosopher, James Forbes. Helmholtz, by 

 a large number of experiments, in which ice was 

 submitted to varying degrees of pressure, succeeded 

 in imitating the formation of glacial ice. Lord 

 Kelvin also showed that cobbler's wax behaved like 

 a viscous fluid. In the course of months or years, 

 it will gradually flow down an inclined plane as a 



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