218 Mr POWER'S THEORY OF 



experiments seemed to indicate. But the preceding theory being 

 perfectly independent of the mode in which the fluids communicate, 

 it is better not to have recourse to a supposition, which is in the 

 slightest degree precarious, especially as I am now prepared to show, 

 that, in whatever way the fluids may arrange themselves within the 

 tube, the rapidity of the mixing process will depend upon the mag- 



nitude of (X)- (^);W . 



15. In fact, in whatever manner the mixing process may be 

 effected,- we may at any moment imagine the fluid to be divided 

 into an indefinite number of contiguous strata, of any arbitrary or 

 convoluted form, the density being the same for the whole extent of 

 any one stratum, but varying from one to another. 



If the surface which separates two contiguous strata be a perfect 

 plane, it is evident, by the equality of action and re-action, that this 

 would be a position of momentary equilibrium, (abstracting from 

 gravity, which I am not here considering.) 



Suppose, now, that this surface becomes 

 undulated in an arbitrary way, and take any 

 point A upon it, and draw a tangent plane 

 BAD, including with the surface EAC, a kind 

 of lens BDEC, which, with La Place, we 

 may call a meniscus. Draw the normal FAG ; 

 and let Ri, and R^ be the radii of greatest and 

 least curvature at the point A. 



Now La Place has shown that the attraction of such a meniscus 



upon the column of fluid AF is ("»"+ p")--^> where H is the 



capillary affinity between the material of the meniscus, and that of 

 the fluid in the sense already defined. (See Supp. au X* Liv. 

 page 14 — 17.) 



