( Si5s ) 
Gravity or Hcaviocfs is ^ i know ( if we knew what it 
were,) reputed to be fuch a Conatus ox Pronity to move 
downwards, and fo to put it felf in motion : And the won- 
der at prefcnt is, why it docs not fo here. But if this^which 
we call Gravity^ fiiould chance to be not a Pofitive quality 
or ConatHs originally of it felfj bun only the Effeft of fome 
Pulfion or Percuffion from without, ( which poflibly may 
be the Cafe 5 and principally from the Spring of the Air a- 
bout us$) then, while this Pulfion and Percuffion is want- 
ing (however obviated J the Bodies, accounted Heavy, will 
not of themfel ves begin to fall : which feems to be the pre- 
fcnt Cafe. 
And this is the more confiderable, becaufe we cannot (at 
left not yet) find, what is the Utmoft height at which the 
Quickfilver thus accumulated will remain fufpended^ there 
having been (for ought I know) no height yet attempted, 
at which,if cleanlcd, it will not ftandjand that of 75 sochesj 
confidcring the weightinefs of Quickfilver, is a very great 
one,being more than equivalent to 80 foot of water* 
My Lord Brounck^r doth a little alter the cafe,from what 
I take to be the Hypothcfis 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 M.f/«ge»/ doth not;) 
and 5 though finer than the reft, (b as to penetrate Glafij 
which the groffer 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 
Spring 5 and therefore when once entred, though in a fmali 
proportion^aCts asefFeftually, 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- 
tofottihtvjtA Cap.n^Demotu prop.\\^i2^i^:) But M.Hu. 
gem's more Subtile matter than Air though he muft allow it 
Weight (for elfe its entrance would be nothing to the pur- 
pofe,) yet whether he allow ic a Spring , I cannot tell 5 nor 
doth he inform us. And when he fays, this more Subtile 
U u u u u % matter 
