Ye Sae. a'204 121 AM. Bop 
ida. br L'article BEM as 10 2109 MI 
figa orde to T lu Ice a greater ra » TOM 
Bion of che air fh the rè 
ceiver than what the common er will eea, the "valvet: 
where ufed, thuft bé made tó open cafier, by removing, as fat 
ás poflible, thefeobftructions. In the common pump thefé 
impediments are gréat ; ‘becaufe the furface of the valve, which 
is expofed to the ‘air underneath, is generally very final $ and 
f “ancy betccn'the pifton and the bottom “öf the barrel 
Bes a greater proportion to the whole barrel that it keni e 
the work were propetly executed. ^^^ M 
AUTRE imperfe&ions Mr. Smeaton confidered and endeavoured 
to remove in the conftruction of his pump. For this purpofé 
héexpófed a much larger furface of the lower valve. to the ae 
ting in vp 
die sibus auto" The ined dabis fios ad 
air retained in the barrel be removed, in Am inei 
making the pifton fit more nicely to the bottom, and by taking 
the weight of the atmofphere from off the pifton, which allowed 
the valve in it to be more eafily opened, fo that sareen e 1 
ait could pafs through it. - +The weight of the ata 
removed from the pifton, ‘by clofing the ip a RE ale di 
plate, on which he fixed a collar of leathers ; through this 
thé cylindrical part of the pifton-rod moves air-tight. And the 
air, having paffed through the pifton, is forced out of the bar- 
fel through a hole in the top-plate, over which is a valve to 
ib RAM when the pifton defcends. "The pif- 
nie to fitas eral to the top, as © the bottom of tha 
Ainipróvelüeüt Mz, Smeaton fays, ^ T have been Bm 
sft te rie thoufand ‘times, when the pump was 
Ppp2 " dem 
