THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FIFTH SERIES.] 



OCTOBER 1890. 



XXXIV. On the Theory of Surface Forces. 

 By Lord Rayleigh, Sec. B.S.* 



SINCE the time of Young the tendency of a liquid surface 

 to contract has always been attributed to the mutual 

 attraction of the parts of the liquid, acting through a very 

 small range, — to the same forces in fact as those by which the 

 cohesion of liquids and solids is to be explained. It is some- 

 times asserted that Laplace was the first to look at the matter 

 from this point of view, and that Young contented himself 

 with calculations of the consequences of superficial tension. 

 Such an opinion is entirely mistaken, although the authority 

 of Laplace himself may be quoted in its favour f. In the 

 introduction to his first paper f, which preceded the work of 

 Laplace, Young writes : — " It will perhaps be more agreeable 

 to the experimental philosopher, although less consistent with 

 the strict course of logical argument, to proceed in the first 

 place to the comparison of this theory [of superficial tension] 

 with the phenomena, and to inquire afterwards for its founda- 

 tion in the ultimate properties of matter." This he attempts 

 to do in Section VI., which is headed Physical Foundation of 



* Communicated by the Author. 



t Mec. Cel. Supplement au X e livre, 1805: — "Mais il n'a pas tente, 

 comme Segner, de deriver ces hypotheses, de la loi de l'attraction des 

 molecules, decroissante avec une extreme rapidite ; ce qui etait indispen- 

 sable pour les realiser." 



% " On the Cohesion of Fluids," Phil. Trans. 1805. 



Phil. Mag. S. 5. Vol. 30. No. 185. Oct, 1890. X 



