280 



THE HYDRAULIC RAM. 



the receiver and the cylinder. When the piston descends, 

 the valves A and B close, and the air in the cylinder below 

 the piston is compressed until it opens the valve M, and 

 passes above the piston. As the piston is raised a second 

 time the valve A is opened by the compressed air in AM, 

 which flows out through it as before; and thus at each 

 stroke of the piston a portion of the air in the receiver is 

 forced out through A. 



Let A and B denote the volumes of the receiver and 

 cylinder respectively, and p and p n the densities of atmos- 

 pheric air and of air in the receiver after n strokes. Then, 

 us in Art. 150, we have 



p n (A + BY^pA*, 



from which it appears as in the previous article that, 

 although the density of the air will become less and less 

 at every stroke, yet it can never be reduced to nothing, 

 however great n may be, 



SCH. An advantage of this instrument is that, the upper 

 end of the cylinder being closed, when the piston descends 

 the valve A is closed by the external pressure, and therefore 

 the valve M is then opened easily by the air beneath. Also 

 the labor of working the piston is diminished by the 

 removal, during the greater part of the stroke, of the 

 atmospheric pressure on M, which is exerted only during 

 the latter part of the ascent of the piston, when the valve 

 A is open. 



152.J The Hydraulic 

 Ram.* The hydraulic ram 

 is a machine by which a fall 

 of water from a small height 

 produces a momentum which 

 is made to force a portion of 

 the water to a much greater 



height. Fig. 81 



* Invented by Montgolfler. 



