JVo. XL 

 DESCRIPTION OF AN AIR-PUMP. 



Invented hj Elizur Wright, Esq. Feb. 1803. 



jp IS the pump plate, //^the pump barrel, which hes 

 in a horizontal position, underneath the pump plate, 

 and nearly in contact with it. A^ and B^ two ducts lead- 

 ing from the pump plate into the barrel. WM^ a solid 

 piston, without a valve, moving air tight in the leathern 

 collar 0. T^ a stirrup, designed to keep the piston rod 

 steady. NH^ is a short piston, made like the former, 

 and acted upon by the spring Z), which is firmly fixed 

 to the piston rod, and by the springs E^ F, through 

 which the rod passes, and is made to slide backward 

 and forward. G, a slide, which serves the triple purpose 

 of straining the springs Z), E, F, by the screw X, that 

 they may act in the first instance with a considerable 

 force on the short piston JVH; secondly, of keeping the 

 piston rod steady ; and thirdly, of preventing the piston 

 from moving too far in the barrel, by means of its being 

 met by the bolthead ZT, at the end of the rod. C, the 

 arch which turns on a pin in the bar US, lying under- 

 neath the barrel, and works the pump by means of a 

 chain. 



The manner in which the pump is worked is this. 

 Suppose the short piston to be in the situation JV, so as 

 to cut off a communication between the barrel and ex- 

 ternal air, and the piston JVM, in contact with it. It 

 now moves back towards T, till it has passed the duct 



R 



