Ae amont. o aor dd Ai 
a nean acted | dr ur s gor 
3 meii. hus adhere: to-the infide-of dheibottel ie well 
**.as the other internal parts, upon letting in the air, is, im the 
** fame facceeding: trials, worked together with the oil, which 
** {oon renders it. fo clammy. as-to-obftru& the action of: the 
^ pump, upon.a fluid fo fubtle as the air is, when:fo much 
** expanded.—But in this cafe it feldom. fails ito a& upon the 
s ‘i air in the receiver, tillit is expanded five hundred times : and 
“this I have found it to do, after being frequently -- "AU 
'** months withoutcleaning.” Does it notapy , that - 
this clamminefs muft have a bad effect upon the valves, as well as 
the other Henpex parts of the pump, in thofe fame fuccéeding 
trials ? and that the ftiffnels: which the pib aequis irepo 
:muft — epin ePi vds, sia insta pid: 
ciple part in g the rarefa&ion-from one thoufand to five 
dautidred: tices 2 x TE MET 
. I fuppofed the: im to bea ipreit:obitrmttion;. and Qader lene 
Aant to:avoid them : and if. no.further. advantage be- des 
;rived. from it, themachine is morefimple without them.. 
s) Upon this conftru&ion, alfo, we are able to make the pump 
swith, two barrels, like the common purnpy which ‘cannot. be 
-done conveniently where the lower valve is retained’; becaufe it 
would be difficult to make the pifton in- one barrel ‘come: èx 
_,aétly ‘tothe bottom, at the fame time that the: pifton in the 
«other, touched as exactly, at. the top: it would, at leaft, require 
a AA inthe vaD which wesild, be tronblefome : to 
In chis alic the giltons do not move the whole length of 
the barrels : there is a horizontal fection made in them, a little 
nore than half way: from the bettom, where the top-plates are 
Qa qz infected 
