292 ON CAPILLARY ACTION. 



one fluid, and its inferior in the other ; the weight of the 

 lower fluid, raised in the prism by capillary action above its 

 level in the vessel, will be equal to the weight of a similar 

 volume of the upper fluid, plus the weight of the inferior 

 fluid, that would rise in the prism above the level, if there 

 were no other fluid in the vessel, minus the weight of the 

 superior fluid, that would rise in the same prism above the 

 level, if the vessel contained this fluid only." 



Demonstration- To demonstrate this, it is to be observed, that the action 

 of the prism on the portion of the inferior fluid it contains 

 is the same as if this fluid only were in the vessel : in both 

 these cases then this fluid is drawn perpendicularly upward 

 in the same manner, both by the attraction of the prism, 

 and that of the fluid that surrounds the lower part of the 

 prism ; and these attractions united are equivalent to the 

 weight of the volume of this fluid, that would ascend in 

 the prism above the level, if it were alone in the vessel. 

 In like manner the superior fluid, contained in the upper 

 part of the prism, is drawn perpendicularly downward by 

 the attraction of the prism and the fluid that surrounds 

 this part, as it would be drawn downward by the same at- 

 tractions, if the vessel contained only the superior fluid ; 

 and these attractions united are equivalent to the weight of 

 the superior fluid, that would then rise in the prism above 

 its level in the vessel. Lastly the column of fluids within 

 the prism, which is above the level of the inferior fluid in 

 the vessel, is drawn perpendicularly downward by its own 

 weight, and perpendicularly upward by the M'eight of a 

 similar column of the superior fluid. On combining all 

 these forces, which must counterbalance each other, we 

 shall have the theorem just announced. By the same prin- 

 ciples we may determine what will take place, when a hollow 

 prism is entirely immersed in a vessel filled with any number 

 of fluids. 



Wlnerc the base In what has been .said the base of the prism was supposed 



<>f the prism is t be horizontal = but if it were inclined to the horizon, 



not Horizontal. ' 



the vertical action of the prism on the fluid would still be 



the same. For a plane of a sensible thickness, having its 



lower part, the surface of which is terminated by a right 



line inclined to the horizon, immersed in a fluid, attracts 



this 



