: 



CAPILLARY ACTION. 



capillary action also vanishes. The early writers on capillary action supposed 

 that the diminution of capillary action was due simply to the change of density 

 oomcpooding to the rise of temperature, and, therefore, assuming the surface- 

 tension to vary as the square of the density, they deduced its variations from 

 the observed dilatation of the liquid by heat. This assumption, however, does 

 not appear to be verified by the experiments of Brunner and Wolff on the 

 rue of water in tubes at different temperatures. 



3. The tension of the surface separating two liquids which do not mix 

 cannot be deduced by any known method from the tensions of the surfaces 

 of the liquids when separately in contact with air. 



When the surface is curved, the effect of the surface-tension is to make 

 the pressure on the concave side exceed the pressure on the convex side by 



T(-K+-n), where T is the intensity of the surface-tension and JR lt 72, are 

 the radii of curvature of any two sections normal to the surface and to each 



If three fluids which do not mix are in contact with each other, the three 

 surfaces of separation meet in a line, straight or curved. 

 Let (fig. 3) be a point in this line, and let the 

 plane of the paper be supposed to be normal to the 

 line at the point 0. The three angles between the 

 tangent planes to the three surfaces of separation at 

 the point are completely determined by the tensions 

 of the three surfaces. For if in the triangle abc the 

 side ab is taken so as to represent on a given scale 

 the tension of the surface of contact of the fluids a 

 and 6, and if the other sides be and ca are taken so 

 as to represent on the same scale the tensions of the surfaces between b and 

 ,md between c and a respectively, then the condition of equilibrium at O 

 for the corresponding tensions R, P, and Q is that the angle ROP shall be 

 the supplement of abc, POQ of bca, and, therefore, QOR of cab. Thus the 

 angles at which the surfaces of separation meet are the same at all parts of 

 the line of concourse of the three fluids. When three films of the same liquid 

 meet, their tensions are equal, and, therefore, they make angles of 120 with 

 each other. The froth of soap-suds or beat-up eggs consists of a multitude 

 of small films which meet each other at angles of 120. 



Fig. 3. 



