110 HYDROSTATICS. 



it will always stand at the same height in both, 

 consequently there is an equilibrium between them. 

 And whatever shape the vessels are of, the effect 

 will be the same. 



It may also be illustrated in this manner : 

 Let A B D G represent a cylindrical vessel, to 

 the inside of which is fitted the cover C (Fig. 4.) 

 which, by means of leather at the edge, will easily 

 slide up and down in the internal cavity without 

 permitting any water to pass between its edges and 

 the surface of the cvlinder. In the cover is in- 

 serted the small tube C F, which is open at top, 

 and communicates with the inside of the cylinder 

 beneath the cover at C. The cylinder is filled 

 with water, and the cover put on. Then, if the 

 cover be loaded with the weight, suppose of a 

 pound, it will be depressed, the water will rise in 

 the tube to E, and the weight will be sustained. 

 If another pound be added, the water will rise to 

 F, and the weight will be sustained, and so on, 

 according to the weight added, and the length of 

 the tube. Now, the weight of the water in the 

 tube is but a few grains, yet its lateral pressure 

 serves to sustain as much as the weight of a 

 column of water whose base is equal to that of the 

 cylinder, and height equal to that in the tube. 

 Thus, the column E C produces a pressure in the 

 water contained in the cylinder, equal to what 

 would have been produced by the column A a d D ; 

 and as this pressure is exerted every way equally, 

 the cover will be pressed upwards with a force 

 equal to the weight of A a d D ; consequently if 

 A a d D would weigh a pound, E C will sustain a 

 pound j and the like of other heights and weights. 

 And by diminishing the diameter of the tube, any 



