f 5029 ) 
glafs, behind which they arc placed i they retain one another^ 
and they remain all fufpended , becaufe there is much lefs 
prcflure on the furface of the quickfilver that is connguoiis 
CO the glafs, than upon that below, which is all expofed to 
the adion of chat matter which makes this fccond preffure. 
The ingenious and candid Author of this folution acknow- 
ledges himfel^ that it doth not fo fully fatisfie him as not to 
leave fomc fcruple behiodibut then he adds,that that keeps him 
not from being very well aflured of that ncwpreflure, which 
he hath fuppofed befides that of the Air, by reaion as vi^ell of 
the Experiment already allcdged, as of two others, which he 
lubjoins to this effcft , 
Firfiy When two plates of mcttal or msrblc, whofe furfaces 
arc pcrfcdily plain, are put one upon apother^they do fo ftick 
together, that the uppermoft being lifted up, the undermoft 
follows without quitting it ; And the caufe hereof is juftly ad« 
fcribed to the preffure of the Air againft their two external 
furfaccs* He taking then two plates,each of them but about 
an inch fquare, being of that matter, of which anciently they 
madcLooking-glaflesj and clofing foexaftly together, that 
without putting any thing between, the uppermoft keeps not 
only up the other, but fometimcsalfo with it three pounds of 
lead fatten d t© the lowermoft,and thus they remain together 
as long as you plcafc^Having thus joyned them and charged 
them with three pounds weight, he fufpended them in the 
Recipient of his Engioj ana exhauftedit of Air fofar as that 
there remained not enough to fuftain by its preffure as much 
as an inch high of water ; and yet his plates disjoy ned not* He 
adds, that he made the fame Experiment by putting Spirit of 
Wine between the two plates 3 and found, that in the Reci- 
pient evacuated of Air they fuftain d, without being fever *d, 
the fame weight they did when it was full of Air.This,he thinks, 
fliews dearly enough, that there remains yet in the flecipient 
a preffure great enough after that of the Air is thence 
taken away 5 and that there is no more reafon to doubt of it, 
than of the preffure of the Air it felf. 
i The 5^rofai Experiment is , That whereas the effed of a 
fiphon of unequal legs, by which you make the water of a 
veffelto run over,is no longer adfcribed to a fi^ga vaci^r^ but 
Cccc 2 to 
