OF SMALL FLOATING EODfES. 1 65 



from beinir wetted. Each plane is then pressed toward the Force of this 



alt ruction 



other plane by a force equal to the weight of.a parallelo pipe- 

 don of the fluid, the height of which is half the sum of the 

 elevations above the level, or depressions below it, of the ex- 

 treme points of contact of the interior and exterior surfaces 

 of the fluid with the plane ; and the base of which is that 

 part of the plane included between the two horizontal lines 

 drawn through those points. This theorem includes the true 

 cause of the apparent attraction of bodies swimming on a 

 fluid, when it is elevated or depressed around them. But 

 experience shows, that bodies repel each other, when the But they are 

 fluid rises toward one of them, and is depressed toward the eiev^the "* 

 other. Having applied my analysis to these repulsions, it fluid, the other 

 has led me to the following results, which T conceive may be de P resslt - 

 deemed interesting by the natural philosopher and geome- 

 trician, and complete the theory of capillary attraccion. 



If we still suppose the bodies to be vertical and parallel Theory. 

 planes, the section of the surface of the fluid included be- Circumstances 



tween them by another vertical plane perpendicular to these imtler wluch 



•iit - • n t the repulsion 



will have a point ot inflexion, when the two planes are a takes place. ; 



few centimetres [a centimetre is near four lines English] 

 from each other. If they be brought nearer together, the 

 point of inflexion will approach nearer to that plane, toward 

 which the fluid is depressed; if the depression of the fluid in 

 contact with the exterior side of that plane be less than the ele- 

 vation of the fluid in contact Avith the exterior side of the other 

 plane. If the contrary be the case, the point of inflexion will 

 approach the other plane. This point is always in the level of 

 the fluid in the vessel, in which the planes are immersed. The 

 elevation and depression of the fluid in contact with these 

 planes are less at the interior surface than at the exterior. 

 In this state the planes repel each other. On continuing to 

 bring them nearer, the repulsion still subsists, as long as 

 there is a point of inflexion. This point at length coincides ^1^5^ and 

 with one of the planes, The repulsion still continues be- becomes 'at- 

 yond this period; but on continuing to bring the plants [JJ^J 1 ^ 

 nearer together, the repulsion becomes null, and is qdii- equally elevat- 

 ' verted into attraction.- At this instant the fluid is equally e ^neach.side 

 i j t • i n t , r OI one plane, 



elevated on each side of the plane that is capable of being and as much 



wetted ; and it is as much elevated above the level at the depressed on 



one side of 

 interior the other. 



