340 Hydrostatics. 



a state of equilibrium. But it is pressed downward at the two 

 extremities with unequal forces. The force exerted at the free 

 surface is the action of a body terminated by a plane surface ; 

 the other in the interior of the tube is the action of the same 

 body terminated by a concave surface, or one in which there 

 is a contrary attraction upward, the little annulus cut off by a 

 horizontal plane passing through the lowest point of the meniscus, 

 and which is supported by the attraction of the glass, exerting 

 an upward force. It is necessary, therefore, in order that an 

 equilibrium may take place that the fluid should rise in the tube 

 till the weight of the column thus elevated above the natural 

 level should compensate for this difference in the downward 

 pressures exerted at the two extremities of the filament. This 

 difference is in the inverse ratio of the diameter of the tube ; the 

 height of the small column must accordingly be in the same ratio ; 

 and this is conformable to the results of our observation. 



457. The heights to which water and alcohol ascend in ca- 

 pillary tubes were observed by M. Gay Lussac with the great- 

 est care. The following are a few of his results. 



Water. 



Diameter of the tube. Height to the lowest point Temperature. 



of the concavity. 



(1.) l,29441t 23,1634 47,5 Fah. 



(2.) 1,90381 15,5861 47,5. 



Alcohol, (specific gravity being 0,81961.) 



Diameter of the tube. Height to the lowest point Temperature. 



of the concavity. 



(1.) 1,29444 9,18235 47,5 



(2.) 1,90381 6,08397 47,5. 



M.Gay Lussac measured also the ascent of water between two 

 plates of glass ground perfectly plane, and placed exactly par- 



t The measures of M. Gay Lussac are given in millimetres or 

 0,039371 of an inch. The results, in which we are principally con- 

 cerned, are reduced to English inches. 



