m 



in that case there would always remain in the barrel a cyliH- 

 der of air of the external density whose height would be the 

 space through which the piston moved in closing the valve. It 

 is therefore necessary that this should be closed before the pistoiv 

 moves from the bottom in the ascending part of the stroke. I have 

 attained this object in a manner that will be easily understood 

 by a reference to Fig. 3, which represents a front section of the' 

 pump, where A B is the barrel, C, the piston which is solid, D, a 

 collar of leathers, through which the piston-rod passes, E, Fig. 2,. 

 a hole drilled through the barrel, aud communicating with the re- 

 ceiver by means of the pipe L, this hole is so placed, that when the 

 piston is drawn up to the top, it just passes it by. F, the valve 

 opening outwards, and having a projecting wire or tail to which 

 the wire frame (G G) is attached. This valve is gently pressed 

 up to its seat by a weak spring, and is covered by a cap (I) with 

 holes in it for to let the air through. H, the rack which is move- 

 able on the piston-rod, having a play of about i. of an inch betweea. 

 two knobs. 



The action of the pump is as follows : when the piston is made 

 to descend, it expels all the air that is in the barrel through the- 

 valve F, and when it nearly reaches the bottom, the end of th© 

 rack comes in contact with the upper cross-piece of the wire frame 

 G G, and depresses it, by this means the valve is kept open until 

 after the stroke is completed. The winch is now turned back, and 

 before the rack can move the piston from the bottom, it (the rack) 

 must move through the space between it and tlie upper knob, 

 in doing which, the pressure is taken oiF the wire-frame, which 

 now rises by the action of spiral springs concealed in the tubes 

 M M. The pbton is still at the bottom of the barrel, and thejf- 



