PRESSURE IN WATER 



147 



issuing from the bottom of a standpipe would be just as 

 great as from a reservoir of great area, provided the depth 

 of water in each is the same. It follows, therefore, that the 

 bottom of a standpipe supporting a fifty-foot column of 

 water would have to be just as strong as the bottom of a 

 dam holding back the waters of a lake fifty feet deep. Of 

 course in a heavier liquid than water, pressure would in- 

 crease more rapidly with the depth ; and in a lighter liquid, 

 less rapidly. 



Another important property of water and of all other 

 liquids is that they transmit pressure equally in all direc- 

 tions. If a bottle be com- 

 pletely filled with water and 

 pressure be suddenly applied 

 to the stopper, the trans- 

 mitted pressure may break 

 the sides of the bottle. If 

 the area of the face of the 

 cork that pressed upon the 

 surface of the water in the 



bottle were one square inch FIGURE 76. HYDRAULIC PRESS 



and the pressure applied to 



the cork were twenty-five pounds, then the twenty-five 

 pounds of pressure on the square inch of water surface 

 would be conveyed to every square inch of the inner 

 surface of the bottle. 



This property liquids have of transmitting pressure 

 equally in all directions has many practical applications. 

 One of the most common is the hydraulic press (Figure 76) . 

 In this machine a relatively small amount of pressure on 

 the small piston achieves tremendous results at the large 

 piston. Suppose, for example, the area of the face of the 



