OF THE HYDROSTATIC PRESS. 1 19 



or some other incompressible and non-elastic fluid, into a strong 

 metallic cylinder, truly bored and furnished with a moveable piston, 

 made perfectly water-tight by means of leather collars or packing, 

 neatly fitted into the cylinder. 



123. The proportion which subsists between the diameter of this 

 piston, and that of the plunger in the forcing pump, constitutes the 

 principal element by which the power of the instrument is calculated ; 

 for, by reason of the equal distribution of pressure in the fluid, it is 

 evident, that whatever force is applied, that force must operate alike 

 on the piston in the cylinder, and on the plunger in the forcing 

 pump, and consequently, 



In proportion as the area of the transverse section of the 

 one, exceeds the area of a similar section of the other, so must 

 the pressure sustained by the one, exceed that sustained by the 

 other. 



Therefore, if the piston F in the preceding diagram, be assimilated 

 to the plunger in the barrel of a forcing pump, and the piston E to 

 that in the cylinder of the hydrostatic press ; then, the equation 

 marked (88), notwithstanding the very simple and concise form in 

 which it appears, involves every particular respecting the power and 

 effects of the engine, of which a detailed description with illustrative 

 drawings will be given a little further on. 



This being premised, we shall now proceed to exhibit the use and 

 application of the formula, by the resolution of the following practical 

 examples. 



124. EXAMPLE 1. If the diameter of the cylinder is 5 inches, and 

 that of the forcing pump one inch ; what is the pressure on the piston 

 in the cylinder, supposing the force applied on the plunger or smaller 

 piston, to be equivalent to 750 Ibs. ? 



Here we have given D =r 5 inches ; d 1 inch, and p 750 Ibs. ; 

 therefore, by substitution, equation (88) becomes 



5 ? X750 = PX1 2 ; that is, Pz= 18750 Ibs. 



Or the equation for the value of P, may be expressed in general 

 terms, as follows. 



P _/> D! 



P -^r- (89). 



And from the equation in its present form, we deduce the following 

 practical rule. 



