134 



ELEMENTS OF GENERAL SCIENCE 



distant below the free surface of the water, the pressure on 

 each square inch will be the same ; that is, each square inch 

 of surface will have the pressure upon it increased by the 

 weight of 1 cubic inch of water. Likewise, the pressure upon 

 each square inch of the sides or top is increased by the same 

 amount. We have put 1 cubic inch of water into the pipe, 

 and its weight presses upon the square inch of the original 

 surface at the lower end of the 

 pipe, with the result that every 

 square inch of the whole interior 

 of the tank receives that much 

 additional pressure. 



When pressure is exerted upon 

 the water in one cylinder of the 

 hydraulic press, this pressure is 

 transmitted undiminished to every 

 equal area of the interior of the 

 apparatus, and therefore to every 

 equal area of the bottom of the 

 large piston. If the end of the 

 small piston has an area of 1 inch, 

 a pressure of a pound exerted here 

 will produce a pressure of a pound 

 on each square inch of the end of 

 the larger piston. The total force 

 exerted by the larger piston will be the sum of the pressures 

 on all these areas, and is therefore as many times greater 

 than the force applied to the smaller one as the area of the 

 larger piston is greater than the area of the smaller one. 



In the case of a house supply of water from an elevated 

 tank, the pressure on each square inch of the ulterior of the 

 pipes or faucets depends upon the depth of the water in the 

 pipes and tank and is exerted equally on every square inch 

 of the interior of the pipe and faucet at any particular level. 

 The violence with which the water will spurt from an open 



FIG. 68. Pressure in a closed 

 vessel of water 



If the pipe is partly filled with 

 water, the additional pressure 

 due to its weight is transmitted 

 to all the walls of the water- 

 filled vessel 



