Theory of Surface Forces. 

 calculating the value of the capillary tension : 



519 



and we may write : 



H -c?f (S)"'" (12 > 



where the indices refer to the points where the phases may 

 be considered practically as homogeneous (liquid- and vapour- 

 phase). 



For the same reason the curve PQS in fig. 5 is considered 

 as being touched respectively in the points S and P by the 

 straight lines GO' and BB' *. 



The consideration of fig. 5 gives for the curve, which 

 dV 



dh 



presents in function of h, the curve in fig. 6. 



Fisr. 6. 



The points V and W in fig. (6) correspond respectively with 

 the points G and P in fig. (4). 



* The superficies PSTP =\ Vdh in fig. 5 lias a simple signification. 

 Indeed, in integrating the two members of the equation (5), remarking 

 that ^T- is null for the homogeneous phases, we get 



\^ 2 ^dh=? 2 Vdh+<2at 2 pdh = 0. 

 Ji d/r Ji Ji 



J 2 

 pdh denotes the mass of the capillary layer per unit of 



superficies ; hence 



Superficies PSTP' = — 2am. 



This equation is independent of the potential function used. Indeed, 

 the equation (3) in the theory of surface-forces of Rayleigh (Phil. Mag. 

 Febr. 1892) gives immediately : 



J 2 Ydh = 2K J 2 pdh = 2Km. 



