ARCHIMEDES' PRINCIPLE 65 



Water-Pressure. The pressure of a liquid is exerted 

 equally in every direction against the sides and bottom of 

 whatever contains it. Suppose there is a tank of water at 

 the top of a house, with a pipe leading down from it and 

 branching off to different rooms. Now if you turn on the 

 water at a tap directly below the tank, will it run out 

 with any greater force than from a tap many feet away to 

 one side? You know that it will not. This illustrates 

 the principle stated above. 



It is possible to take advantage of this principle in per- 

 forming various kinds of work. Since liquids thus trans- 

 mit pressure equally in every di- 

 rection against the walls of their 

 containers, it is possible to use 

 water as a means for multiply- 

 ing the area of pressure. Thus in 

 the hydraulic press (see Fig. 28) 

 a pressure applied at ab will be 



equally exerted by the surface at AB, as well as by all the 

 other contained surfaces. If there is a pressure of one 

 pound at ab, there will be a pressure at AB of as many 

 pounds as the area of ab is contained in the area of AB. 

 This is what is meant by multiplying the pressure. If AB 

 is ten times as large as ab, then one pound laid on ab will 

 balance ten pounds laid on AB. 



Thus we have a multiplication of pressure, but this 

 must not be confused with multiplication of work. If 

 the piston ab is pushed down one inch, will the piston AB 

 rise one inch ? Certainly not. For one thing, there would 

 not be enough water to fill such an addition to the space. 

 The piston AB will rise only in proportion to the difference 

 between its area and the area of ab. If it be ten times as 



