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I ft, When the pifton was feveral times raifed to the top, 

 and depreffed again without turning the cock ; the reCf-pipe 

 being conftantly kept open ; at every fuch elevation or ftroke, 

 the mercy rofe a little in the gage; and generally in fix ftrokes 

 about ith of an inch. In thefe circumftances, fome air remain- 

 ing in the rcC^, was at each ftroke, drawn into the barrel, as 

 the pifton rofe, and returned again when it was depreffed. 



adly, When the recr-dud and circulating-du6t were clofed by 

 a half turn of the key, the pifton being previoufly put down, 

 and the fame number of ftrokes were repeated, then on open- 

 ing the communication with the gage, after deprefling the pifton, 

 the mercy did not rife nor fall in the gage; but when, after 

 the communication with the gage v/as open, the pifton was 

 once more raifed and depreffed, the mercy rofe much more than 

 it did at any other fingle ftroke, made when the recr-pipe was 

 open. In thefe circumftances there was no air in the barrel, 

 during the motion of the pifton,^ except in the laft ftroke, by 

 which alone the mercy was raifed. 



3dly, When the mercy was at the Jlated height in the gage, 

 before the pifton was raifed from the bottom, if it was ele- 

 vated a part of its ftroke, before the recr and circulating-pipes 

 were ftopt, by which means a part of the rarefied air in the 

 gage-recr was drawn into the barrel, and imprifoned there on 

 flopping the duds, then, after the pifton had been raifed and 



depreffed 



