THE HYDRAULIC PRESS. Ill 



M. In the large cylinder there is also a piston P, having at 

 its upper end a large iron plate, which moves freely up and 

 down in a strong frame-work Q. Between the iron plate 

 and the top of this framework the body to be pressed is 

 placed. Now, when the small piston is raised, the cylinder 

 A is filled with water drawn from the reservoir H, below, 

 and when it is pushed down this water is forced into the 

 large cylinder through the pipe K. There is a valve in this 

 tube which prevents the water from returning, so that each 

 stroke of the small piston pushes an additional quantity of 

 water into the large cylinder. By this means the large 

 piston is pushed up against the body to be pressed. To cal- 

 culate the pressure exerted by the large piston we must 

 remember that the force acting upon the piston in A, will 

 be exerted upon every equal amount of surface in B. To 

 illustrate this : suppose the area of the large piston to be 10 

 times the area of the small one ; then one pound at A will 

 produce a pressure of ten pounds at P. The handle M in- 

 creases the advantage still more, according to the principle 

 of the lever to be explained in a future chapter. By in- 

 creasing the size of the large cylinder, and diminishing the 

 size of the small one, the pressure exerted by a given power 

 will be increased proportionately. The weight of a man's 

 hand might thus be made to lift a ship with all its cargo. 

 The only limit to the increase of power would be the strength 

 of the material of which the machine is made. 



