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HYDROSTATICS. 



423 



;1 



A Is a box that holds about 



a pound of water, abode 



a glass tube fixed in the top 



of the box, having a small 



wire within it; one end of 



the wire being hooked to the 



end P of the beam of a 



balance, and the other end 



of the wire fixed to a move- 

 able bottom, on which the 



water lies, within the box; 



the bottom and wire being of 



equal weight with an empty 



scale (out of sight in the 



figure) hanging at the other 



end of the balance. If this 



scale be pulled down, the 



bottom will be drawn up 



within the box, and that mo- 

 tion will cause the water to rise in the glass-tube. 

 Put one pound weight into the scale, which will move 

 the bottom a little, and cause the water to appear just 

 in the lower end of the tube at a ; which shews that the 

 water presses with the force of one pound on the bot- 

 tom : put another pound into the scale, and the water 

 will rise from a to b in the tube, just twice as high 

 above the bottom as it was when at a ; and then, as its 

 pressure on the bottom supports two pound weight in 

 the scale, it is plain that the pressure on the bottom is 

 then equal to two pounds. Put a third pound weight 

 in the scale, and the water will be raised from b to c, 

 in the tube, three times as high above the bottom as 

 when it began to appear in the tube at a ; which shews, 

 that the same quantity of water that pressed, but with 

 the force of one pound on the bottom, when raised no 

 higher than a, presses with the force of three pounds 



