[io04] 
That there is, iii our Jir, a body more fubtle then are 
the Fumes and Vapours mingled with it, iu our lower re- 
gion, and which with it do make up that heterogeneous 
mixture which we commonly call Air\ I think to be very 
certain. But whether that lubtile body, be fas Dr. G^r- 
den leenis to fuppofe,) much heavier, then our common 
Air ; I much doubt. And do rather think it is not; not 
having hitherto oblerved any cogent experiment, either 
to prove it heavy or elaftick. But it may, for ought I 
know , be void as well of weight as fpring ; and, 
what we find of either, in our common Air^ may be at- 
tributed to the other mixtures with it. 
I know that this notion ( of the greater weight of that 
^ubtler matter,) hath, by fome, been made ufe of, to 
folve that (furprifing,J experiment of ^mch^Stlver (well 
clenfqd oiAir^ being fuftained in a Tube inverted (after 
the manner of the Torricellian experiment,^ at a much 
greater higl}t then the ufual ftandard (of 28, 29, or Jo, 
Inches, even to the height of 40, jo, do, or even 70, In- 
ches,- being fteadyly managed, and with great care. But 
leonfefsl am not fatisfied with thatreafon: and think 
that it may better be accounted for otherwife , or elfe we 
are yet to feek for the true caufe of it. 
But we have no need of this particular notion, in the 
prefentdifcourfe,and therefore need not be here folicitous 
about it .* and (hall therefore proceed without it. 
The y^/r being, as hath been faid, of a different gravi- 
ty, in different times and places, (arifing I fuppofe, 
from the different kinds and quantities of the Fumes and 
Vapours and other particles which are ingredients in it, 
and the different force of the Suns heat acting thereupon, 
increafing or allaying the fpring thereof, and otherwife,) 
we are therefore to confider of the Air as a fluid who's 
parts are in fome places heavier, and others lighter. And 
therefore much of a like nature as if they were different 
fluids, of different fpecifick gravities (as the word is now 
a- days 
