£ 5 21 C Al^IL t A|IY ACT^^p N. 



Capillary ac- , ^iqtjon would b^ jtbe s^me as wliep the densest only is con- 



Uon of fluids. 



tainjcd in it, if the tension of the oommon surface were 

 simply as the difierence of the densities ; but it would be 

 always less, if the tension .werCj as the square of the differ- 

 ence. .■;,,,?...,-..,- ■. , ■ 



It is very easy tp determine this point by a simple experi- 

 ment. Take a clean capillary tube, about one tenth of an 

 inch in diameter, and iniaicrse it in water, so that about 

 Jiftlf .s^n iiich of itft^ej^tieij^^ty ciay renoain empty :• introdup? 

 slowly, with a bristle, a small quantity of oil in successive 

 drops, so as to form a thin coatinj^ on the water. It will 

 then be observed that the heij^ht of the fluid is very coiispir* 

 cuously diminished, andreduced to about thr-ee fourths, or 

 two thirds. Your readers* are not required to place implicit 

 faith in the anonymous statement of an experiment : they 

 may easily repeat it for thei;n selves ; and it is only adduced 

 in support of a cliain of reasoning founded on mathematical 

 analogy. 



In this respect therefore it cannot be allowed, that Mr. 

 Laplace's second methoc] of considering the effects of capili- 

 lary action is, so perfectly satisfactory as it ap)pears upon a 

 cursory examination :.for both demonstration and experiment 

 are in direct contradiction to his assertion, that '* If tlie in- 

 dehnite vessel, in which the parallelopipedon is immersed,^ 

 include-any number of fluids placed horizontally one above 

 another ; tiie excess of the weights of these fluids contained 

 in the tube, over the weight of the fluids which it would 

 bave contained without capilljary action, is the same as the 

 weight of th<? fluid that would rise above the level, if the 

 vessel contained only t^iat fluid in which the inferior extre- 

 mity of the parallelopipedon is immersed." Journal, Vol. 



XVII, p. 291. 



Upon these grounds we may infer, that if a great num- 

 ber of liquids, becoming insensibly less and less dense, and 

 the density of the last being inconsiderable, were contained 

 in the same tube, their capillary action would be wholly 

 destroyed: and it is not. impossible that the capillary forces 

 of various substances, of equal density, may be somewhat 

 modified by the more or less abrupt change of density at 

 their surface ; since there is reason to think, as we have al- 

 ready 



