Air- Pump in England. 335 



ture provided with a brass stopper K, to close it. The receiver 

 terminated below in a narrow neck, cemented into a brass 

 stopcock L, which was ground to fit an opening in the upper 

 end of the cylinder, near to the stoppered valve G. 



The figure represents the arrangement of parts, when the 

 pump had completed one exhaustion. The valve of the cylin- 

 der G is shut, the stopcock L of the receiver open. L was then 

 shut, G opened, and the piston driven home. The valve was 

 then closed, the stopcock again opened, and the piston drawn 

 down ; and so on ad infinitum. By reversing the order in which 

 the valve and stopcock were closed and opened, the pump could 

 be made to condense instead of rarefying the air of the re- 

 ceiver. The valve for that purpose was opened, whilst the 

 stopcock was shut, and the piston drawn down, so as to allow 

 the cylinder to be filled with atmospheric air. The valve was 

 then shut, the stopcock opened, and the piston as it ascended 

 condensed the air into the receiver. 



The pump must have been wrought very slowly. There 

 was a stopcock to turn, and a plug to pull out or to push in, 

 at each stroke of the piston. There were many apertures 

 which could not be kept air-tight ; and the cylinder was small 

 for the size of the globe it exhausted. The capacity of the 

 cylinder was about 126 cubic inches, whilst that of the re- 

 ceiver was 60 wine pints (old measure), or about 1732 cubic 

 inches. It is not surprising, therefore, that Boyle should 

 have had to confess that his air-pump produced a vacuum 

 slowly, that the vacuum was imperfect, and could not be 

 preserved. 



The most important points to be noticed about this earliest 

 English air-pump are, that it was provided with one hansel ; 

 and that, unlike any later air-pump, tlie cylinder and receiver 

 were directly connected. It appears to have been partly in 

 allusion to the latter peculiarity that Boyle named his in- 

 strument, a point of some interest in the present discussion. 

 Once he refers to Guericke's instrument as " the wind-pump, 

 as somebody," he says, "not improperly calls it." Some- 

 times, but rarely, he uses the terms " pneumatic pump,'' and 

 " air-pump ;" but the title he preferred for his own instrument 

 was that of *' Pneumatical Engine." Others called it the 



