150 Br. G. Bakker on the 



The equation of energy of the curved capillary layer 

 becomes, therefore, for values of R of the order of a wave- 

 length of light or greater : 



Td v = de + v(Sdi; + £d$)-?^Rd$, . . (36) 



where R must be conceived as constant. 



If R is measurable or has a value not smaller than a micron, 

 we have : 



Srf?+rdS = <fo and EC&RasH, 



and (36) becomes : 



Td v = de + pdv-KdS. 



The equation (30), however, is contrary to (36) quite 



exact. 



§ 5. The plane capillary layer considered as the 

 limit of a cylindrical. 



The formulae simplify when we consider a cylindrical 

 capillary layer instead of a spherical one. The condition for 

 the equilibrium e. g. gives instead of the equation (11, § 2) 

 the more simple one : 



Pl - Pv JVr_m, (37 ) 



in the case when the liquid is inside the capillary layer 

 (liquid drop). 



If, however, the cylindrical capillary turns its concave 

 side to the vapour (bubble of vapour), we get : 



»-*£=¥* ^ 



In order to deduce the equation (37) we consider the 

 cylindrical capillary layer simply like a tube under the 

 influence of an inward pressure pi and an outward one p v . 

 Instead of p v and p t> we put as above : p 2 and p x . If the 

 corresponding quantities are represented by the same letters 

 as in the consideration of the spherical 1 ayer, and z denote 

 the total length of the cylindrical capillary layers of equal 

 curvature, the condition for the equilibrium gives immediately: 



%B^zpi — *2U 2 zp 2 = — z \ jh 



dh, . . . (39) 



^.tftjai,. .... ( 40) 



where R represents again half the sum -~ — 2 - of the inner 

 and outer radii. " 



