FIG. 45 BOYLE'S PNEUMATIC ENGINE OR AIR PUMP. 



The air was exhausted from the glass globe A by means of a sucking-pump 

 supported on a wooden frame 12. The insets show : i. A brass ring DE cemented 

 to the lip BC of the large glass A : it carries a glass stopper FG, pierced in the 

 middle to receive the brass key K. 2. The stopcock N, cemented above to the 

 glass DA, and below to the top PQ of the sucking-pump. 3. The brass cylinder 3, 3 

 of the sucking-pump, 14 inches long and 3 inches bore ; the sucker 44 was fitted 

 with a ring of tanned leather, and was driven by a handle 7 acting through a rack-and- 

 pinion gear 5, 5. The cylinder was charged with a little oil or water to make the 

 sucker air-tight. During the downward stroke of the sucking-pump, the valve R 

 was closed and the tap N opened to admit air from the globe ; during the upward 

 stroke N was closed and R opened. 



321 y 



