(From Page 2 of the Instruction Manual)
The use of the first mentioned Instrument is thus: Take one of your flat pieces of Ivory, O. or Sliders, in which the Objects are put, and slide it in betwixt the two thin plates of Brass EE, in the body of the Microscope, so that the Object you design to look upon be just in the middle, remarking that you put the side of the Plate O where the Ring is, farthest from your eye: Then you are to screw into o o, (the hollow screw at the end of the Body of the Microscope ) the 1st, 2d, 3d, or 4th, &c. Magnifying Glasses M; which being done; while you are looking through your Magnifying Glass upon the Object, you are to screw in or out, the long Screw D, in the other end of the Body of your Microscope, till you bring your Object into true distance, which you will know by seeing the Object clearly and distinctly. But seeing that in the greater-Magnifiers you can see but a small part of the Object, viz. the Legs or Claws of a Flea: While you are looking upon any part of the Object, if you take hold of the end of the Plate or Slider, o. whereon the Object lies, and move it gently, you may see the whole Object successively, or any part of the Object you please; and if that part of the Object you design to look upon, be out of the true distance, remember your end Screw D can always bring it in, by screwing it nearer of farther off.
After this manner may be seen all Transparent Objects, Dust, Liquids, Crystals of Salts, small Insects, such as Fleas, Mites, &c. If they be Insects that will creep away, or such Objects as one intends to keep, they may be placed between the Register-Glasses d d d d. For by taking out (with the point of a Pen-knife or small Plyers) the Ring that keeps it in the Glass dd, where the Object lies, they will fall out of themselves; so you may lay the Object between the two thin Glasses or Talks, and put the Ring in as it was before: But if the Object be Dust, or Liquids, a small drop of the Liquid, or a little of the Dust laid on the outside of the Glass dd, and applied as before, will be seen very easily