

CA PILLAR Y A TTRA CTION. \ 9 



The dynamics of the subject, so far as a single 

 liquid is concerned, is absolutely comprised in 

 the mathematics without symbols which I have 

 put before you. Twenty pages covered with 

 sextuple integrals could tell us no more. 



Hitherto we have only considered mutual at- 

 traction between the parts of two portions of 

 one and the same liquid water for instance 

 Consider, now, two different kinds of liquid : 

 for instance, water and carbon disulphide (which, 

 for brevity, I shall call sulphide). Deal with 

 them exactly as we dealt with the two pieces 

 of water. I need not go through the whole 

 process again ; the result is obvious. Thirty 

 times the excess of the sum of the surface- 

 tensions of the two liquids separately, above the 

 tension of the interface between them, is equal 

 to the work done in letting the two bodies 

 come together directly over the supposed area 

 of thirty square centimetres. Hence the inter^ 

 facial tension per unit area of the interface, is 

 equal to the excess of the sum of the surface- 

 tensions of the two liquids separately, above the 



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