WATEK PRESSURE 



127 



10 pounds; that is, the force exerted by the second piston 

 will be greater than the force applied to the smaller piston 

 by as many times as the area of the larger piston is greater 

 than the area of the smaller one. This rule holds for cylin- 

 ders and pistons of any size. Hydraulic presses are commonly 

 used in processes in which great force must be exerted, as 

 in baling cotton. 



FIG. 67. The hydraulic press 



The diameter of B is 8 times that of A, and its area is therefore 64 times as great. 



A pressure of 1 gram exerted by A upon the water surface heneath it would be 



transmitted undiminished to each of the 64 equal areas at B, and might lift a 



weight of 64 grams at B 



144. The principle of the hydraulic press. In order to under- 

 stand the principle of the hydraulic press or of other appliances 

 in which the transmission of pressure by water is important, 

 we must attempt to discover the laws of transmission of pres- 

 sure in liquids. Here again we may draw an illustration from 

 an aquarium such as we have used to illustrate other subjects 

 in this chapter. Let us suppose that the aquarium is filled 

 with water and covered on top, and that a pipe leads up 

 through the cover (fig. 68). If, now, we pour into the pipe 

 enough water to fill it to a depth of 1 inch, the total depth 



