Mr. J. T. Riley on Capillary Phenomena. 191 



foundation of his exposition of the subject, he would have 

 removed what I take to be the only serious blemish in his 

 excellent book. 



In conclusion, I would point out that the wider scope here 

 sought to be given to the fundamental theorems of Statics 

 can be justified on other grounds. It is now generally held 

 that the ultimate particles of bodies apparently at rest are 

 really in a state of more or less violent agitation. If we 

 regard Statics as the theory of equilibrium, and if by equili- 

 brium we mean relative rest, there is a manifest awkwardness 

 in applying the principles established on this basis to bodies 

 so constituted. On the other hand, in the form advocated in 

 this paper, the fundamental theorems are directly applicable 

 to such cases, without any modification whatever. 



Adelaide, November 25, 1882. 



XXV. On Capillary Phenomena. By John T. Riley, B.Se. 

 (London), A.R.C.Sc.L, Demonstrator in the Physical 

 Laboratories of the Mason College*. 

 [Plate IV.] 



ALTHOUGH the mathematical theories of capillary action 

 which have been advanced by Laplace, Gauss, Poisson, 

 and others agree in one point, which may be tested by 

 experiment, they differ in the fundamental hypotheses. In 

 all the theories the equation of the capillary surface is of the 

 same form, involving a certain constant which can be deter- 

 mined by experiment only. They, however, differ in the 

 manner in which this constant is made to depend on the 

 molecular forces and the law of density of the fluid near the 

 surface. 



Laplace | supposes the density of the fluid to be uniform: 

 he commences by considering an infinitely slender canal of 

 the fluid perpendicular externally to the surface of a sphere, 

 and calculates the total action of the sphere on the canal. 

 The law of attraction is such a function of the distance 

 that this function becomes insensible when the distance be- 

 comes sensible. He finds that the resultant attraction may 



TT 



be represented in the form K — =~ 9 where K and H are 

 both independent of b, the radius of the sphere. He 

 observes that K is much larger than ~r, and that K repre- 



* Communicated by the Author. 



t Mecanique Celeste, Supplement au Livre x. 



