250 DISCUSSIONS IN CLIMATOLOGY. 



moist surfaces in contact. But when we reflect that 

 it requires the pressure of a mile of ice — 135 tons on 

 the square foot — to lower the melting-point one degree, 

 it must be obvious that the lowering effect resulting 

 from capillary attraction in the case under considera- 

 tion must be infinitesimal indeed. 



The following clear and concise account of Faraday's 

 theory, I quote from Professor Tyndall's " Forms of 

 Water : " — 



"Faraday concluded that in the interior of any 

 body, whether solid or liquid, where every particle is 

 grasped, so to speak, by the surrounding particles, and 

 grasps them in turn, the bond of cohesion is so strong 

 as to require a higher temperature to change the state 

 of aggregation than is necessary at the surface. At 

 the surface of a piece of ice, for example, the molecules 

 are free on one side from the control of other molecules ; 

 and they, therefore, yield to heat more readily than in 

 the interior. The bubble of air or steam in overheated 

 water also frees the molecules on one side ; hence the 

 ebullition consequent upon its introduction. Practically 

 speaking, then, the point of liquefaction of the interior 

 ice is higher than that of the superficial ice. 



" 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."* 



* "The Forms of Water," p. 173. 



