asneiv-conjirudted: dirk Pung. ie 
niiflakonasaccencines, tóexhauft it; the other from | the valve 
son the t , is opened to the atmofphere by ‘the other pat- 
fage dhicough; Mire códk Bardi ardet ap rarefy the air above 
the valve in my pump, it is neceflary this laft paffige fhould be 
fhut-up,; when the valve-pump isufed.’ Initead,. therefore, of 
placing: tho three ducts at equal m aes round the cock, Ihave 
divided the whole into five equal parts 5 leaving the diftance of 
P oar 
one-fifth. between. the: ducts leading from the ciftern and the 
valves. to the cock, and.two-fifths between each of theíe and 
ithe-one leading from the cock to the receiver. By this adjuft- 
ament, "when the communication is open between ‘the receiver 
and valves, for condenfation, the other hole through the cock 
‘opens: the cifterns to the atmofphere =z- but when. en communi- 
-— baie > between the cifterns, and the re PT 
iati a DUM part of. the key comes againft the. dua ipte to 
ihe valves, and fhuts it.up ; and the air, which is forced out of 
athe barrel, paffes into theatmofphere through the -valve-pump ; 
for the valve of the. pd Selita mg be Ms open while the 
nct is worked. o 
Now, to apply Mr. —-— n afoning to FEE confirucios. 
atiis died taking off. the weight) of the at 
from the pifton, by fhutting up the top of the b barrel, ‘he fays, 
*)'The confequence of this conftruction is, that when the pif- 
© ton is. put down to thé bottom of the cylinder, the air in the 
E ‘lodgement under the pifton will evacuate itfelf fo much the 
*é:more, as the valve of the pifton opens more éafily; when 
sst preffed by the rarefied air above it, than when preffed by the 
whole weight of the atmofphere. Hence, as the pifton may 
** be made, to fit jas nearly to the top of the cylinder, as it can to 
** the bottom, the air may be rarefied as much aboye meee 
.Q.a4 —- 
