• Air -Tump in England. 337 



out them, I could not do my work." I have called the second 

 engine, accordingly, Boyle and Hooke's Air-pump. 



The second pneumatical engine, represented in fig. 3, copied 



Fig. 3. 



from Boyle's tract, mentioned above, did not resemble the 

 first in appearance, but, like it, had a single brass bai rel A. 

 This stood with its mouth upwards, in a large wooden box or 

 trough, B, filled with water, which rose above the mouth of 

 the cylinder, so that the latter was entirely under water. The 

 object of this arrangement was to keep the leather of the 

 sucker or piston always wet, and, therefore, *• turgid and 

 plump," so as to move air-tight in tlie barrel. The latter had 

 no valve in it. The piston C, which was moved by a rack 

 D, and pinion E, had an aperture F, passing vertically through 

 it, which was closed and opened alternately by thrusting 

 in and pulling out a long stick G. managed by the hand 

 of the operator. But the great peculiarity in the engine was 



