CAPILLARY ATTRACTION. (A PP. C.) 65 



than those they would occupy if there were hydro- 

 static communication of pressure between the 

 portions of liquid in the several vessels. There 

 must be evaporation from those surfaces which are 

 too high, and condensation into the liquid at those 

 surfaces which are too low a process which goes 

 on until hydrostatic equilibrium, as if with free 

 communication of pressure from vessel to vessel, 

 is attained. Thus, for example, if there are two 

 large open vessels of water, one considerably above 

 the other in level, and if the temperature of the 

 surrounding matter is kept rigorously constant, the 

 liquid in the higher vessel will gradually evaporate 

 until it is all gone and condensed into the lower 

 vessel. Or if, as illustrated by the annexed diagram 

 (Fig. 32), a capillary tube, with a small quantity of 

 liquid occupying it from its bottom up to a certain 

 level, be placed in the neighbourhood of a quantity 

 of the same liquid with a wide free surface, vapour 

 will gradually become condensed into the liquid in 

 the capillary tube until the level of the liquid in it 

 is the same as it would be were the lower end of 

 the tube in hydrostatic communication with the 

 large mass of liquid. Whether air be present 

 above the free surface of the liquid in the several 

 vessels or not, the condition of ultimate equilibrium 

 is the same ; but the processes of evaporation 

 and condensation through which equilibrium is 

 approached will be very much retarded by the 

 presence of air. The experiments of Graham, 



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