RESIDUO-CAPILLARY ATTRACTION. 209 



to which it belongs ; 2dly, the attraction of the opposite liquid. If then 

 the latter attraction be superior to the former, the fluid which fills the 

 tube, he says, will be drawn in an uninterrupted stream into the 

 opposite vessel. 



Dutrochet justly objects to this theory, that it will only account for 

 a motion in one direction, whereas the phenomenon of exosmose requires 

 a corresponding motion in the opposite direction. 



Professor Henslow, in a number of the Foreign Quarterly, suggests 

 as a modification of Poisson's theory, that whilst the fluid within the 

 tube is carried in the direction of the stronger attraction, the natural 

 tendency of the fluids to mix, may carry the other fluid (or, perhaps, 

 a slight infusion of it) in the opposite direction, and thus produce the 

 exosmose. 



I perfectly agree with Professor Henslow that the natural process 

 of mixture is the cause of the exosmose, it being only necessary to 

 suppose that the rapidity with which this process extends itself witliin 

 the tube is somewhat greater than the velocity with which the whole 

 mass of fluid which fills the tube is drawn in the opposite direction. 



But the theory of Poisson is further objectionable on this account, 

 that it makes the continuation of the process solely dependent on the 

 action of the fluids, whereas the experiments of Dutrochet incontestably 

 demonstrate that it depends mainly on the action of the membrane. 

 No doubt, the effect both of the fluids upon themselves, and of the 

 membrane upon the fluids, ought to be taken into consideration, and 

 this will be done in the following theory. 



9. If a capillary tube be divided into two parts by a plane perpen- 

 dicular to its axis ; the attraction of one of these parts upon a fluid 

 which exactly fills the other part is \cH, c being the contour of the 

 inner surface of the tube, and H a certain definite integral or constant, 

 depending solely on the materials of which the tube and the fluid 

 consist. The contour of the tube may be of any shape whatever, curved 

 or polygonal. (See Mec. Cel. Sup. au X* Liv. pp. 14 — 21.) 



