228 Mr POWER'S THEORY OF 



Now in the same experiment p diminishes and r increases as the 

 experiment proceeds, and therefore the variation of p + r is small com- 

 pared with that of p — r; the quantities absorbed will therefore be 

 pretty nearly in the ratio of the difference of densities, as Dutrochet 

 found them to be. Whether the proportion 



Q:Q' :: -E^ : -IzL 

 y/p + r Vp + r' 



may be a more accurate representation of nature than the law of 

 Dutrochet, is left to the test of experiment. 



25. It may perhaps be objected to the theory of No. (12), that 

 the ordinary theory of capillary attraction supposes the dimensions of 

 the tube to be incomparably greater than the sphere of sensible attrac- 

 tion, whereas the fact, that these pores are so small as to elude 

 microscopic observation, might lead us to apprehend that their dimensions 

 were of a size comparable with that sphere. The example which has 

 been calculated in No. (7), does not seem to leave any cause for such 

 an apprehension. But supposing this were the case, the only difference 

 it would make in the theory is this : that, whereas, on the former 

 supposition, the quantities \cH, \c K, &c., denoted the results of 

 integrations extending from nothing to infinity, and not otherwise 

 depending on the form of the tubes than by involving the contour c 

 as a multiplier; on the second supposition, the limits of the integra- 

 tion will depend on the form of the tubes and the texture of the 

 membrane : but these limits being the same in the cases compared, it is 

 easy to see that the theory will be still true on the latter hypothesis, 

 provided we look upon ^c{H), ^c{K), &c., as denoting certain 

 unknown limited integrals depending not only upon the nature of the 

 materials, but also upon the form and size of the capiUary pores. The 

 residual force will, therefore, on this hypothesis also, be of the form 

 a{p-r) + h{p'-r'). 



26. By the application of similar reasoning to the theory of No. (15), 

 it is not difficult to conclude that the moving forces upon the normal 



