198 Mr. A. M. Worthington on the Horizontal Motion of 



account for a surface-tension. The investigations which 

 Laplace gave of the rise of liquids in capillary tubes and 

 between plates, and of the apparent attractions and repulsions 

 of small floating bodies, cannot be considered as giving 

 definite support to his theory, since the existence of the 

 phenomena may be deduced from any mathematical theory 

 which explains surface-tension. 



All that Laplace did was to show that, with certain 

 assumptions respecting the density of the liquid near the 

 surface and the law of molecular attractions, he could prove 

 that capillary phenomena would occur. 



With other assumptions, Poisson also showed they would 

 occur; but whether his assumptions or those of Laplace have 

 a physical reality is an altogether different matter. 



The Mason College, February 5th. 



XXVI. On the Horizontal Motion of Floating Bodies under the 

 Action of Capillary Forces. By A. M. Wokthington. 



[Plate V.] 



To the Editors of the Philosophical Magazine and Journal. 



Gentlemen, 



WITH respect to the phenomena of capillary attraction 

 and repulsion of floating bodies, which are the subject 

 of Mr. J. LeConte's paper in the Phil. Mag. of January last, 

 I would remark that in most writings on capillarity in which 

 the elevation or depression of liquids in contact with solid 

 plates is discussed, attention is confined to the vertical com- 

 ponent of the surface-tension at its contact with the solid, and 

 to its relation with the weight of liquid elevated or depressed. 

 The horizontal component is generally neglected as not af- 

 fecting the results; and the very interesting relation which 

 exists between its variation and the resulting hydrostatic 

 pressure or tension is overlooked. The consequence of this is 

 that the explanations which are afterwards given of the 

 horizontal motions of floating bodies are expressed in terms 

 which apply only to each special case as it is dealt with, and 

 do not reveal the important underlying relationship to which 

 I refer. 



This relationship is indeed made use of by Quincke in 

 treating of flat drops and bubbles; and he deduces it from the 

 differential equation to the surface by a rather long process. 

 It does not seem to have occurred to any one that the same 

 relationship underlies the attraction and repulsion of plates, 

 or that it can be very easily deduced from the well-established 



