MACHINES 



191 



thousands of pounds pressure with what appears to be a very 

 small effort. The machine consists essentially of two connect- 

 ing cylinders of unequal diameters filled with water. When 

 pressure is applied to the water in the small cylinder, it is 

 transmitted to the large cylinder where it is multiplied as 

 many times as the cross-sectional area of the large cylinder is 

 greater than that of the smaller one. At the same time the 

 general law of machines holds good, for the piston in the small 

 cylinder moves as many times as far as the effort is multiplied. 



FIG. 64. Cross-section of a hydraulic press. (Tower, Smith and Turton.) 



Suppose a large cylinder to have an area of 1000 times that 

 of the small one. Then one pound pressure in the small 

 cylinder would give 1000 pounds pressure in the other, but the 

 piston in moving the 1000 pounds one inch would have to 

 travel a thousand inches. By making the pressure a hundred 

 pounds in the small cylinder, it would have to travel 10 inches 

 for each inch the thousand pounds was moved. Hydraulic 

 presses are often used to compress coarse materials such as 

 paper, shavings, cotton, and the like. Some elevators are 

 also run by hydraulic pressure. 



