128 



ELEMENTS OF GENERAL SCIENCE 



of water will be not 12 inches but 13 inches. The pressure 

 on a single square inch of the bottom will be 13 x 0.0362 

 pound. Since each square inch of the bottom is equally dis- 

 tant from 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 re- 

 ceives that much additional pres- 

 sure. (Calculate the total pressure 

 upon the interior of the tank due 

 to the added inch of water.) 



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 pres- 

 sure 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. It should there- 

 fore be 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. This is the case, as we have 

 seen from the discussion in section 143. 



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 



