fjv 



THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[SIXTH SERIES.] 



/ 



MARCH 1909. 



XXXI. On the Theory of Surface Forres. — IV. On very thin 

 Liquid Films and very small Liquid Drops. By G. Barker*. 



■§ 1. At a fixed temperature the structure of a plane capillary 

 layer in contact with its vapour is fully determined. 



ON the supposition that the capillary layer is not under 

 the influence of an external force, such as that of 



gravitation, magnetism, electricity, or the adhesion of the 

 walls of the vessel, we can demonstrate in the following way, 

 thataJ a fixed temperature the plane capillary layer of a given 

 fluid in contact with its vapour is always the same thing. 

 That is to say, the plane capillary layer which limits a large 

 bulk of liquid has exactly the same structure as the capillary 

 layer which limits for instance a black spot in a very thin 

 liquid film of the same body. 



For a point of the plane capillary layer the hydrostatic 

 pressure in a direction perpendicular to the surface is, as I 

 have demonstrated t, equal to the vapour-pressure (pi). If 

 we thus consider with 5Toung { the hydrostatic pressure as 

 the difference of the thermic pressure 6 (repulsive force of 

 Young) and the cohesion (force of cohesion of Young) and, 

 if we denote the cohesion in the mentioned direction by S l5 

 we have 



/>i=0-S, (1) 



* Communicated by the Author. 



t '' On the Theory oi Surface Forces, 11./* Phil. Mag. October 1907, 

 ]> 515. 



X Thomas Young, " On the Cohesion of Fluids," Phil. Trans. 1805. 



F/dl. Mag. S. 6. Vol. 17. No. 99. March 1909. 2 A 



