I . CAPILLABY ACTION*. 



the other constituents of the solution, and to form a thin skin on the outer 



free of the bubble. 



In 1787 Monge* !>! 1 that "by supposing the adherence of the par- 

 tfpjj, ^ a fl u y to have a sensible effect only at the surface itself and in the 

 direction of the surface it would be easy to determine the curvature of the 

 of fluids in the neighbourhood of the solid boundaries which contain 



r that these surfaces would be lintearice of which the tension, constant 

 in all directions, would be everywhere equal to the adherence of two particles, 

 and the phenomena of capillary tubes would then present nothing which could 

 not be determined by analysis." He applied this principle of surface-tension 

 to the explanation of the apparent attractions and repulsions between bodies 

 floating on a liquid. 



In 1802 Leslie t gave the first correct explanation of the rise of a liquid 

 in a tube by considering the effect of the attraction of the solid on the very 

 thin stratum of the liquid in contact with it. He does not, like the earlier 

 speculators, suppose this attraction to act in an upward direction so as to 

 support the fluid directly. He shews that the attraction is everywhere normal 

 to the surface of the solid. The direct effect of the attraction is to increase 

 the pressure of the stratum of the fluid in contact with the solid, so as to 

 make it greater than the pressure in the interior of the fluid. The result of 

 this pressure if unopposed is to cause this stratum to spread itself over the 

 surface of the solid as a drop of water is observed to do when placed on a 

 clean horizontal glass plate, and this even when gravity opposes the action, as 

 when the drop is placed on the under surface of the plate. Hence a glass 

 tube plunged into water would become wet all over were it not that the 

 ascending liquid film carries up a quantity of other liquid which coheres to it, 

 so that when it has ascended to a certain height the weight of the column 

 balances the force by which the film spreads itself over the glass. This ex- 

 planation of the action of the solid is equivalent to that by which Gauss 

 afterwards supplied the defect of the theory of Laplace, except that, not being 

 expressed in terms of mathematical symbols, it does not indicate the mathe- 

 matical relation between the attraction of individual particles and the final 

 result Leslie's theory was afterwards treated according to Laplace's mathe- 

 matical methods by James Ivory in the article on capillary action, under the 



* Memovres de FAcad. des Sciences, 1787, p. 506. 

 t Philosophical Magazine, 1802, Vol. xiv. p. 193. 



