An Explication of the Fourth Plate.

Figure 1. Is the Apparatus for Microscopes: Containing AC 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; GH a small Slice of Ivory, and its Muscovy Glass Circles, with the fine Objects upon them, inserted in their true Place; EF a Convex Glass, screwed into the former Cylinder, and at a due Distance casting Light on the Objects; with IL, the Handle of the Microscope.

Fig.2. Is only one of the Slices of Ivory AB, like GH 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 EF, placed very near the Object, be cast into a larger Image HI: 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 BC, 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 XY; its Pictures inverted upon the Plate EF; and its large or gygantick Images at BA 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 AB erect. Where CD is the double Convex Glass, ready to form an inverted Picture ba: Which by the Reflection of the plain Speculum EF, plac'd obliquely in an Angle of 4°, is formed in an erect Position at ab, for the View of the Spectator.