' I 3S3 ] ■ 



tained in the pipe, and is now uniformly difRifed tliroiigh the 

 eyl"" : and as both the orifices of the pipe open into the cyl>' 

 during the defcent of the pifton, fo when this is at the bottom, 

 the whole of this air is over the pifton, except fuch a part of 

 it as is exprcffed by the ratio of the content of the cavities 

 under the pifton to that of the cyK. 



It has been fliewn, that when the pump was open at the 

 top, and the circulating-pipe confequently ufelefs, fo that the 

 air above and beneath the pifton was of the natural denftty ; 

 yet in this ftate, the rarefadion was as the capacity of the 

 cyl'^ to that of the cavities under the pifton ; but as the air 

 is rarer or denfer in the cyl'', it muft be fo alfo in the cavi- 

 ties : and it will by the addition of the circulating-pipe and 

 valve, be rarer in both thefe, in the proportion of the capacity 

 of the cyl"" to that of the circulating-pipe (for the air in the 

 latter being difFufed in the cyl"" will be rarer or denfer there, 

 as the cyU is larger or fmaller ;) fo that the rarefadion now 

 will be in a ratio compounded of the ratio of the content of 

 the cyl"", to that of the cavities under the pifton, and of the 

 . ratio of the content of the cyli" to that of the circulating-pipe : 

 for the refidual air under the pifton is inverfely in this com- 

 pound ratio, and the rarefadion is inverfely as fuch refiduum. 



However fince either the valve, or cover of the pump, or 

 the collar of the pifton, will always admit fome air, as the 

 Vol. VI. Y y pifton . 



