An Explication of the Fourth PLATE.
Figure 1. Is the Apparatus for Microscopes: Containing A C a Cylinder of
Brass or Ivory; to which, near the Eye at K, the Microscope it self, or
very small Sphere of Glass set Ivory, is apply'd; G H a small Slice of
Ivory, and its _Muscovy_ Glass Circles, with the fine Objects upon them,
inserted in their true Place; E F a Convex Glass, screwed into the former
Cylinder, and at a due Distance casting Light on the Objects; with I L,
the Handle of the Microscope.
_Fig. 2._ Is only one of the Slices of Ivory A B, like G H
before-mentioned, set by it self; with the double Circles of _Muscovy_
Glass, and kept down by circular Wire; between which, on one of those
Glasses, the small Objects are commonly plac'd.
_Fig. 3._ Is a Scheme to demonstrate how the double Microscope comes to
magnify so much. Where G is the small Object; which, if there be Light
sufficient, may by the small Microscope Glass E F, placed very near the
Object, be cast into a larger Image H I: Which by the Means of the two Eye
Glasses, are reduc'd into a Compass fit to enter into the Eye. And here by
the way it is to be noted that die small Glasses, whereby single
Microscope do magnify so much, and whereby the Magnitude is in Part
increas'd in this double Microscope, is only a very small spherical Glass,
or Segment of it, which does so suddenly reduce distant Rays to
Parallelism, or nearly to it, that a small Object, which by its great
Nearness could not be otherwise seen, is hereby made visible.
_Fig. 4._ Is the double Microscope, with all its Apparatus and
Contrivances, as to the Position of the Object, the Light to be thrown
upon it, and the Elevation and Depression of the Instrument it self, as
the Case requires, _&c._ all which the Figure does plainly shew to the
Eye.
_Fig 5._ Is a circular Plate of Ivory, with a small Sphere of Glass in its
Center, and a Screw round the Center, to be put upon the first Figure at
B C, as a single Microscope.
_Fig. 6._ Is a small Fish, represented in a Cylindrical hollow Glass, so
as it is to be placed when the Circulation of Blood in its Tail is to be
seen by the single Microscope.
_Fig. 7._ Is the Magick Lanthorn, with its Pedestal T: its Lamp W; its
double Convex Glass X Y; its Pictures inverted upon the Plate E F; and its
large or gygantick Images at B A projected upon the white Wall, to the
Surprize of the Spectators.
_Fig. 8._ Is the Demonstration of the _Camera obscura_, or dark Chamber;
which will shew the Object as A B erect. Where C D is the double Convex
Glass, ready to form an inverted Picture _b a_: Which by the Reflection of
the plain Speculum E F, plac'd obliquely in an Angle of 4°, is formed in
an erect Position at _a b_, for the View of the Spectator.
[[Plate V. ― Sutton Nicholls sculp:]]