CLOUDS AND RIVERS, ICE AND GLACIERS. 173 



too high to permit of the slightest deposit upon the 

 adjacent glass. A similar remark applies to sulphur, 

 phosphorus, and the metals in a state of fusion. They 

 are deposited upon solid portions of their own substance 

 at temperatures not low enough to cause them to soli- 

 dify against other substances. 



438. Water furnishes an eminent example of this 

 special solidifying power. It may be cooled ten 

 degrees and more below its freezing point without 

 freezing. But this is not possible if the smallest frag- 

 ment of ice be floating in the water. It then freezes 

 accurately at 32° Fahr., depositing itself, however, not 

 upon the sides of the containing vessel, but upon the ice. 

 Faraday observed in a freezing apparatus thin crystals 

 of ice growing in ice-cold water to a length of six, 

 eight, or ten inches, at a temperature incompetent to 

 produce their deposition upon the sides of the contain- 

 ing vessel. 



439. And now we are prepared for Faraday's view of 

 re gelation. When the surfaces of two pieces of ice, 

 covered with a film of the water of liquefaction, are 

 brought together, the covering 'film is transferred from 

 the surface to the centre of the ice, where the point 

 of liquefaction, as before shown, is higher than at the 

 surface. The special solidifying power of ice upon water 

 is now brought into play on both sides of the film. Under 

 these circumstances, Faraday held that the film would 

 congeal, and freeze the two surfaces together- 



