OF HYDROSTATICS. 



119 



equal to the weight of all the water which is supported LECT 

 in the tube G : and the same thing would hold at g , if a 

 hole were made there. And so if the whole cover or 

 top Bfwere full of holes, and had tubes as high as the 

 middle one Ag put into them, the water in each tube 

 would rise to the same height as it is kept in the tube 

 A, by pouring more into it, to make up the deficiency 

 that it sustains by supplying the others, until they are 

 all full : and then the water in the tube A would support 

 equal heights of water in all the rest of the tubes. Or, 

 if all the tubes except A, or any other one, were taken 

 away, and a large tube equal in diameter to the whole 

 top Bfwere placed upon it, and cemented to it, and 

 then if water were poured into the tube that was left 

 in either of the holes, it would ascend through all the 

 rest of the holes, until it filled the large tube to the 

 same height that it stands in the small one, after a suf- 

 ficient quantity had been poured into it : which shews, 

 that the top I?/ was pressed upward by the water under 

 it, and before any hole was made in it, with a force 

 equal to that wherewith it is now pressed downward by 

 the weight of all the water above it in the great tube. 

 And therefore, the reaction of the fixed top Bfmust be 

 as great in pressing the water downward upon the bot- 

 tom CC, as the whole pressure of the water in the 

 great tube would have been, if the top had been taken 

 away, and the water in that tube left to press directly 

 upon the water in the cavity B D df. 



Perhaps the best machine in the world 

 for demonstrating the upward pressure ot 

 fluids, is the hydrostatic bellows A ; which 

 consists of two thick oval boards, each 

 about 16 inches broad, and 18 inches 

 long, covered with leather, to open and 

 shut like a common bellows, but without 

 valves ; only a pipe B, about three feet 

 high, is fixed into the bellows at e. Let 



hydrostatic 

 bellows. 



