30 



FLUID PRESSURE 



FIG. 15 



41. Hydraulic Press. The use of liquid bodies 

 to transmit pressure is common and important. 

 The principle may be stated as follows : If a body 

 of liquid be entirely closed up in any vessel, and 

 any part of its surface be put under pressure from 

 without, that pressure will be felt just as greatly 

 upon every equal part of the inside surface of the 

 closed vessel. For example, the inside surface of a 

 bottle is fifty square inches and the lower surface 

 of its stopper is one square inch ; if the bottle is 

 full of water, the stopper fits tightly, and a force of 

 two pounds pushes the stopper 

 down upon the water, and every 

 one of the fifty square inches of 

 inside surface in the bottle feels 

 a pressure of two pounds upon it. The pressure on the 

 whole inside surface of the bottle is (50 x 2)= 100 pounds. 



Experiment 28. Get a shallow circular pan, make a small hole 

 in its side, and 

 solder into 

 this a short 

 metal tube 

 (Fig. 15). To 

 this tube at- 

 tach a rub- 

 ber tube two 

 or more feet 

 long. Tie a 

 piece of sheet 

 rubber very 

 firmly over 



the top of the pan. Fill the whole with water, keeping the tube 

 full. Raise the tube as high as possible. See how great a weight 



FIG. 16 



