498 Mr. PRINCE'S Account of 
valve, part of the air will be ‘re tai 
ined in it; and this air, ever 
when the pifton is raifed to the higheft, will, by its expanfion,. 
in fome meafure, obftru& the opening of the valve... .When.the 
in the. receiver, or underneath the valve, - ds, rarefied . taan 
v, degree with. the air contained. in the. barrel; (the: pifon 
being, drawn up to. the higheft) the. valve. can. rife no, longer, 
becaufe the refiftance ; above is equal to the power below... The 
rom this, air, retained in.the barrel, again{t, the valve. 
at the bottom, will be uniformly the fame, when the. pifton.is 
at the fame diftance from i it; becaufe the wei ight of. the ats 
— re is, continually preffing on the pifton-valve, and will. 
vent ent the air, below paíüng: through it, while this air is. rarer 
Shen aie atmofphere :_and when the piftonis: put down to the 
aon of the barrel, it will not efeape through the pifton, but 
only be co mprefied into.the vacancy between -the .bottom sof 
Hen the. valye-plate. at the bottom of the barrel, and. 
be of. equal den ity with, the atmofphere. . Befides the refit 
ance, arifing from, th 
gi 
is. retained. air, we muft.confider the. weight 
,the valve, its cohefion to. the plate, occafioned by: the. oil; 
and its being ftretched Et over. the:hole, as.increafing the ob» 
dris lon. efpec tally -w hen the {pring of the air under the yalye 
ism much. weakened by ‘tarefaion. Andif we take into the ac- 
count the prices arifing J from thefe. caufes, the denfity of the 
air in the bar d, when compreffed into the. abovementioned vas 
cancy, | yill i as much. greater than the denfity of the. atmof- 
phere a above sewn æ pifton, as ‘the addition of. this r © ;. for 
this Qa boleng EU the.  pifton-valve, as. pe as tothe 
other. _And en ‘this, retained air is expanded 
ang a "dE da ES pifton, the air in. pede in - 
Md rarefied to the fame. degres, becaufe of this refiftance: of 
amino debel... e d 
the valy j o 21010 oi? ROIN 
eu ity y p ub à $ B * 
