506 Mr. PRINCE s Account: of 
** as it could before have been. in the receiver.. It follows, 
** therefore, that. the air may now be rarefied in the receiver, . 
** in duplicate.proportion of what it could be upon the com- 
s mon. principle ; every thing elfe: being fuppofed perfect." 
The fame may be faid with regard to the valve on the top-plate 
in this machine.. It. will open. more eafily, when prefed by 
the rarefied. air above it,. than: when prefed by the weight of. 
the whole atmofphere.. Hence, as by the conftruction of the. 
valve-pump the air may be: rarefied assmuch: above the valves, - 
as it could before have been’ án. din — and. receiver, ith 
which there isa free fore follows; that: 
the. air may now be rarefied:in the receiver in duplicate-propor-- 
tion of what it could be by: Mr. Smeaton s pump';: every thing - 
elfe beng 4 ovas cee sand the-nature of the Maie 
ting. Mero : 
oe any: advantage which may arife p d 
Sugai gis the valves at. didis of the. beta and.in the- 
pifton, is not confidered.:- But if they made any. mefitance- in: 
Mr. Smeaton's p may we not conclude, that: the rarefac 
tion might be:carried: further by a machine wherein no. fuch: 
valves are’ pla WS OF Pi Nri Dait fays, that when he 
contrived to open his:valves by the winch, independent of the: 
fpring of air, he did not find it-anfwer the purpofe. better than: 
when theair was:the agent: There is: no reafoning againft ex-- 
periment : butit certainly appears probable from theory, . thaty 
there muft be confiderable refiftance. from the valves: when the 
‘ait is greatly rarefied. 
0 Hesafterwards lays, “ the degree; to which T have been able: 
@ to rarely the'air, by experiment, has generally been about one" 
© thoüfind times, "when the pam is cae clean aede but: 
^ im * the: 
