If Your Lordſhip ſhould now ask me
what are the true cauſes of this varying al
titude of the Mercurial Cylinder; I ſhould
not undertake to anſwer ſo difficult a que
ſtion, and ſhould venter to ſay no more,
then that among divers poſſible cauſes to
which it may be aſcribed, it would not be,
perhaps, abſurd to reckon theſe that fol
low.
what are the true cauſes of this varying al
titude of the Mercurial Cylinder; I ſhould
not undertake to anſwer ſo difficult a que
ſtion, and ſhould venter to ſay no more,
then that among divers poſſible cauſes to
which it may be aſcribed, it would not be,
perhaps, abſurd to reckon theſe that fol
low.
Firſt then we may conſider, that the Air
in the upper part of the Tube is much
more rarified, and therefore more weak
then the external Air, as may appear by
this among other things, That upon the in
clining of the Tube the Quick-ſilver will
readily aſcend almoſt to the very top of
it, and ſo take up eight or nine tenth parts,
and perhaps more of that ſpace which it
deſerted before: which would not happen
if that whole ſpace had been full of unra
rified Air, ſince that (as tryal may eaſily
ſatisfie you) would not have ſuffer'd it
ſelf to be thruſt into ſo narrow a room by
ſo weak a preſſure. So that although in
our Tube when the included Air was
heated, the Quick-ſilver was ſomewhat
depreſſ'd: Yet there is this difference be
twixt ſuch a Tube and common Weather
Glaſſes, that in theſe the included and the
in the upper part of the Tube is much
more rarified, and therefore more weak
then the external Air, as may appear by
this among other things, That upon the in
clining of the Tube the Quick-ſilver will
readily aſcend almoſt to the very top of
it, and ſo take up eight or nine tenth parts,
and perhaps more of that ſpace which it
deſerted before: which would not happen
if that whole ſpace had been full of unra
rified Air, ſince that (as tryal may eaſily
ſatisfie you) would not have ſuffer'd it
ſelf to be thruſt into ſo narrow a room by
ſo weak a preſſure. So that although in
our Tube when the included Air was
heated, the Quick-ſilver was ſomewhat
depreſſ'd: Yet there is this difference be
twixt ſuch a Tube and common Weather
Glaſſes, that in theſe the included and the