fufpended at tfie oppofite and of the Beam,could not have bov’d
them up, two Pounds being only half Balance to four, it uaift
therefore neceflirfly follow, that the Mercury in the Tube bangs
pendulous from the Crown of the trials, and becomes of no
weight hflow, whence ’fi§ plain, gfegi Quickfilver does not af«-
cend in the Tube by a preflure frqra the Quickfilver contain’d
in the G^ftern, fg^ jhad it dqpf.dG^ it would then have follové’d,
that a? the external Air prefs’d. upon the furface of the quickfil-
Yer in the Ciftern, and bythat forced upward the Mercury in
the Tube, that as the Mercury afcended in the Tube, the Bal-
lance fhoukl have fallen,lower, but a quite contrary Obfervatron
occurs for as the Mercury afcends in the Tube, at the fame
time the Ballance rifes alfo.
Fig. II. In a Glafs-Tube. four Foot long, containing half a
Pound of Quickfilver, without a Ciftern, and the. Mouth of the
Tube wide open, the Column of Quickfilver, contain’d is the
Tube, is about thirty inches, the Quickljver in this Tib© [rifes
and fallsr 9 inches, and feven tenths prependicular, for fair and
foul Weather, and prefages the change of Weather very nicely ;
there are feveral other Tubes of a fmaller fize, which perforin
the fame. This Tube hanging at the bottom of a Balknce, at
whofe oppofite end was fufpended a Weight which, was an Equilibrium
to the other, bad the external Air forced up the Mercury
in the Tube, it maft thence have follow’d; that as the Mercu-
cury afcended, the Tube would have rifm at the fame; time, but
the contrary of this is very evident, for though the Mercury
contain’d in the Tube, arife to the inches before mention’d, yet
notwithftanding that the Tube never moves at all, which Ob-
fervation plainly Demon ftrates, that the Mercury hangs pendulous
in the Tube, and only rifes and falls according to the different
Springs or Elafticities of the Air, contain’d in the top
of the Tube.
Fig. III. A Tube in the form of a Siphon, turned up 8 or
9 inches at the bottom, when filled with Mercury its afeent or
defeent is but one inch and a half.
Fig. IV. Another Tube of the fame form at the bottom,but
at the top in the form of a Bicornu, or forked, which Branches
are
long,theMercury in thisafeends three:inches,
which,doubles the Scale to the former,, [which Jhews the afeent
of t{ie Mercury' f^^rppx3tJhe^hriouV.Elafticities of;the Air at the
toP of the Tube arid not fiom the preffure,of the Ambient:
Air contain d in the. Ciftern-add to- thele one Head- more' - the
Mercury will then afeend, one inch and-a half:higher, add* two
Heads.it will rife three, and fo on piroportionabjy^which -Pfa-
nometi^ in my apprehenfion,amount to an abfolate Demonftration
of the truth.of this Hyppthefis.
Figvy. , A plain Barbmetie, in this the Mercury only rife
three inches.
Fig- VI. A Bicornu,^r-.forked Tub.e. In this the afeent;of
theMercury is the fame as in the other,which could-not have been,
kad the Gravitation of the Ambient Aircaus’Ttbe afcfhftrof; the
Quickfilver, fince according, to that Hypothecs; .the Quickfilver
in this fhould only have rife half an inch,fince the Ciftern of each
only .contain’d one Pound of Mercury, -
Fig. VII. A plain Tube . open at; the hottor®, with a Column
of Mercury about thirty inches, in this the motion; of the
Quickfilver is very difeernible at the to.p , before it is, moved at
the bottom , which plainly fhews she afeent or defeent of the
Mercury, is from the Dilatation or CofitraQien of. the Spring of
the Air contain’d in the top,of the Tube.
Fig. VIII. By movingAhis Tube a little Upwards, if the
Air incline to a fair Temperature ,, the. Mercury immediately
afcends in that final! Tube, .hut if to, foul, as quickly fubfides,
but if upon that motion it neither moves upwards nor downward^
it fhews the Air at that time to be of a fetled temper. Let the
Column of the,Mercury be what it will, as for example twenty
eight inches, when it rifes; to the top of the Scale, if will then
com,pleat thirty one, which Obfervation fully Demonftrates,that
the Mercury contracts and dilates three inches.
Fig. IX. ' Shews the Mercury moving thirty inches' upon the
Declivity,this fort of Barometre fhews the variation of the Weather
much more exabt than any other. There is a Thermomete
on the oppofite fide of .it, and in the middle may conveniently
be fixed a Looking-GIafs. To thefe Experiments may be added
the