An Explication of the Fifth PLATE.
Figure 1. Are _Otto Guerick_'s Hemispheres, with their several Screws and
Apparatus at large, set separately by themselves. They are designed to
prove that the Force of the outward Air, when the inward is extracted from
between them, is equal to the Weight of a Column of Quicksilver of about
29 Inches and a half: Of Water of about 34 Feet: And of Air to the Top of
the Atmosphere, all pressing upon the same Base with the largest Circles
of those Hemispheres.
_Fig. 2._ Is the Syringe, with its Hole; to be screw'd on to the Top of
the Receiver of the next Figure; in order to thrust Air into it, for the
Improvement of the former Experiment; or to shew that tho' common Air be
left in the Hemispheres, yet if that on their outward Surface be made
twice or thrice as dense, they will still sustain an equal, or a double
Weight respectively, before they are separated.
_Fig. 3._ Is that Instrument included in such a Receiver D B, and that
Receiver kept close to its Basis by a cross Piece and Screws, as in the
Condenser before: Together with a newly contriv'd Stiliard, to which the
upper Hemisphere is hung; with its fixed Base, and its Gage, to measure
the Degrees of Condensation of the Air, where by the Proportion of S P to
P K, the Weight 50 w. is equivalent to greater Weights, and shews how many
Pounds are required to separate the Hemispheres in all Cases. If the
Diameter be 3 Inches and a half, they will sustain about 150 Pounds; and
so in all other Proportions.
_Fig. 4._ Is the Plate which covers the upper Part of the Receiver. And
through the Hole C the Piece D E slides, which takes hold on the upper
Hemisphere.
_Fig. 5._ Shews the Gage of the same Instrument; this is like that for the
Glass Condenser before describ'd, and contains a bended Tube, whose open
End is in a small Basin of Mercury; and the other is Hermetically seal'd:
For this Mercury crowded by the condensed Air in the Receiver, will croud
the Air in the small Tube closer in Proportion to its Density, and so will
afford us the Knowledge of the Quantity thereof.
_Fig. 6._ Is a like Experiment of the Cohesion of polished Plates of
Brass, or of Marble; when the Air is excluded by a little Oil, and an
exact Application. This Cohesion may be weighed by the Stiliard, as well
as that of the Hemispheres; and is equal to the same, upon the same Base;
provided a Ring do prevent their side or sliding Motion; and provided the
Air can equally be excluded from between the Plates, as between the
Hemispheres. Which last yet is almost impossible to be done.
_Fig. 7._ Is a Number of great Weights, kept steady one over another by an
Iron Rod passing through them, and pressing upon a Bladder half blown,
plac'd below them: This Bladder, by the Elasticity of its included Air,
gradually elevates all those Weights; as soon as by the Extraction of the
other Air out of the Receiver, wherein they are all included, its
Counterpoise is gradually taken away.
_Fig. 8._ Is a Number of Jet d'Eaus, or Fountains, made by condens'd Air,
in a large Copper Vessel C D, pressing on the Surface of Water at the
Bottom of the Vessel; into which Water a hollow Brass Pipe is immers'd.
For if there be then a Stopcock at G, to open or shut the hollow Pipe at
Pleasure; and several smaller Pipes at I K, communicating therewith,
turning upon Balls or Joints, and plac'd in Order, we shall have a very
pleasant Set of these _Jet d'Eaus_, or Fountains; all whose Water will be
caught by the Bason A B, which Water may be again let into the Vessel C D,
by unscrewing the Pillar in the Center of the Bason.
[[Plate VI. ― I. Senex sculp.^t]]