180 Messrs. J. P. Kuenen and W. Gh Robson on 



therefore from 10 * , 



, _ /ip(2n.+ l) rf n {kr) dCl n - fi 

 (n -f l)&acr f n (ka.) ds 



4:7r(n+l) Vyv 



n{n + l)(a — r) 

 I) \rJ * 4/^ar 



xcos{^-^(a-r)fx}^, .... (30) 





1 

 2Jfe, 



where 



™ n X= 1 n(n+l)(a-r) 





2& x -iA^ar 



Hence 



tan x = l approximately, 



therefore 



x- 77 " 



Hence when the inducing system is the circular circuit 

 before mentioned, ds = rdB, and we find 



C'= ^^ e -*i(a-*> cos Lf-jfe^a-r.) + | 1 



XVII. On ^/t<? Mutual Solubility of Liquids. — Vapour-pressure 

 and Critical Points. By J. P. Kuenex and W. Gr. Robson *. 



THE experiments recorded in this paper have reference to 

 the equilibrium between liquid and vapour, for two 

 substances which, in the liquid state, do not mix in all propor- 

 tions at all temperatures. Our attention has been especially 

 directed to the equilibrium-pressure of some of these mixtures 

 at different temperatures, and to the nature of the critical 

 phenomena which may occur in different cases. Regnault f 

 measured the vapour-pressures of two mixtures of this kind — 

 carbon disulphide and water, and ether and water. The 

 vapour-pressures for the first pair were found to be only a 

 little less than the sum of the A-apour-pressures of the com- 

 ponents ; and Regnault rightly connected this fact with the 



* Communicated by the Authors. 



t Kegnault, Relation des experiences, t. xxvi. 



