( Si^S ) 
Gravity ot Heavioefs is , 1 know ( if we koew what it 
were,) reputed to be fuch a Conatus or Pronity to move 
downwards, and fo to put itfelf in motion : Aod the won- 
der at prefcnt is, why it does not fo here. But if thisjwhich 
we call Gravity:^ i}Rm\d chance to be not a Pcfitive quality 
or originally of it felf, but only the Effeft offome 
Pulfion or Pcrcuflion from without, ( which poiiibly may 
be the Cafe ^ and principally from the Spring of the Air a- 
bout us 3) then, while this Pulfion and Percuffion is want- 
ing (however obviated^) the Bodies, accounted Heavy, will 
not of themfel ves begin to fall : which feems to be the prc- 
ientCafe. 
And this is the more confiderable, becaufe we cannot (at 
left not yet) find, what is the Utmoft height at which the 
QuickGlvcr thus accumulated will remain fufpendcd- there 
having been (for ought I know) no height yet attempted, 
at which,if cleanfed, it will not ftand^and that of 75 iachcsj 
confidcring the weightinefs of Quickfilvcr, is a very great 
one,beiug more than equivalent to 80 foot of water* 
My Lord Brounck^r doth a little alter the cafe/rom what 
I take to be the Hypothefis of Monfieur Hugens. For he 
fuppofeth this purer part of the Air to be of like nature 
with the ^ro^r part, ( which I think Hugen s Aoih not;) 
aod , though fiacr than the reft , lb as to penetrate Glafi, 
which the grofTer will not(there being in all forts of grains^ 
fome greater than others,, and which will not pafs fo fine a 
Sieve;) yet of a Springy nature, as the grojjer parts are: 
Which therefore afts , not by its Weight only , but by its 
^P^i^g 5 and therefore when once cntredj though in a fmall 
proportion, ads as cffeftuallyj at its firft entrance, as if the 
whole incumbent Air had admiffion 5 its Spring being of a 
like tenfure with that of the outward Air 5 (as I have here- 
tofore (hewed Cap. I4* Demvtu prop.w ^12 ^ly^ But M. Hu. 
gem's more Subtile matter than Air though he rauft allow it 
Weight (for elfe its entrance would be nothiog to the pur- 
pofe,) yet whether he allow it a Spring , I cannot tell 5 nor 
doth he inform us. And when he fays^ this more Subtile 
Uuuuu 2 matter 
