( 51^4 ) ^ 
throft it downto I , counterballanciog the preflurc (at C) 
of the purer but Rot of the grofler Air (which I take to be 
the fum of the Caufe afBgn d by Hngens i) I am yet ta 
feck, why it may not as well penetrate D at firft to begin 
the Defccnt, as afterwards to purfueit^ and, why notes 
well begin the Defcent when the Quickfilvcr is well clean- 
fed of Air 5 as when it is not (b } and why alfo, if the pun 
Air do freely enter at it doe$ not prcfently. fall ; or,if not 
freely, why, when it does fallg it falls fuddenly and not lei- 
furely from D to I , efpecially |ince fo fmall a weight as D H 
of pure Air (for the grofler cannot enter5)is very inconfide- 
rable^ if not at all, or not freely , prejfiTed by incumbent 
on P ^ and the Adhefion not coDfidcrably lefs , by being 
feparated only at the Top ^ while it yet continues to touch 
the fides. V 
I am apt therefore, as heretofore, to adfcribe the Canfe of 
this Thsmmenon to the Spring that is in Air , and the want 
thereof in Quickfilver. For, that in Air there is a Spring or 
Elafticity^ is now undoubted 5 but in Watcrjcleans'd of Air, 
though many Experiments have been attempted to that 
purpofe, it has not yet been found that there is any : And I 
am apt to thiDk the like of Quickfilver^ though I do not 
koovv^that this has been yet fo rigoroufly examined* Now 
fuppofiog,thatMatt€r,being atRcft, will (o continue till it be 
put in motion by fome Force ^ this force may be either that 
of Per^^Jj^i?;? from fome Body already in motion (which is 
the Cafe, when the Quickfilver falls by fhaking or ftriking 
the Tubci) or of Fulf m fiom a contiguous Body beginning 
to inove, as by the Expanfion of fome adjacent Spring 
(which is the Cafe, when the Springy parts of the Air,eithef 
left in unpurged, or re-admitted in the Qnickfilver, by ex- 
panding themfelves put the^ Quickfilver in motions ) 
fome ComtHs or Erndcvour of its own 5 fuch as is that of a 
Spring (from whatever caufe it be, which I do not herein- 
quire,) but has place only in Springy bodies ; and therefore 
if Watei and Quickfilver be not fuch^ they will not on this 
account put themfelves in motion. 
