50 Mr. J. LeConte on the Apparent Attractions 



pressure. It seems to me that, by referring the motions of 

 such bodies directly to the action of this tensile superficial film, 

 a fundamental principle in the physical theory of capillarity is 

 secured in the mind of the student ; while the resulting dis- 

 turbances of hydrostatic equilibrium are not primary facts, but 

 secondary consequences of the more fundamental cause. 



The general explanation which I am about to offer of 

 the "apparent attractions and repulsions of small floating 

 bodies "is so simple and obvious a deduction from the funda- 

 mental laws of capillary action, as expounded by Laplace 

 and Poisson, that it is difficult to bring myself to believe that 

 it has hitherto escaped the attention of physicists. Neverthe- 

 less I have not, thus far, been able to find it in any of the 

 treatises on physics. 



In order to render my explanation more clear, it will be 

 necessary to present the commonly received popular explana- 

 tions of these phenomena, and to indicate their defects. 



Two methods of experimental illustration may be adopted, 

 viz.: — 1st, by floating in water two small bodies whose sur- 

 faces have been so prepared as to be moistened or non-mois- 

 tened by liquid; and 2nd, by plunging vertically into water 

 or into mercury two parallel plates of clean glass suspended 

 by threads. 



Ordinary Popular Explanations. 



Case 1. When both bodies are moistened. — In this case 

 (Plate I. fig. 1, A, B, and A / B / ), when the two bodies are 

 brought so near that their intervening concave meniscusesjoin 

 each other, the bodies are drawn together by the weight of the 

 column of the liquid m, elevated above the level a b, acting 

 like a loaded cork secured to each of the bodies. 



Case 2. When both bodies are not moistened. In this case 

 (fig. 2, A, B, and A / B'), when the two bodies are brought so 

 near that the intervening convex meniscuses unite, e and g are 

 more depressed than d and /; consequently the two bodies are 

 pushed toward each other by the greater exterior hydrostatic 

 pressure exercised by the portions dh and/^. 



Case 3. When one body is moistened and the other is not mois- 

 tened. — In this case (fig. 3, A, B, and A' B'), if the moistened 

 body B or B / were alone, the concave meniscus would be 

 elevated to o ; in like manner, if the non-moistened body A or 

 A / were alone, the convex meniscus would be depressed to r. 

 Now if the two bodies are brought so near that their menis- 

 cuses join each other, the intervening liquid surface will take 

 an intermediate position n k. Hence the point n will be below 

 the point o; and the point k will be above the point r. It is 



