(From page 3)
As to the first and second Magnifying-Glasses, being marked 1, 2, upon the Brass, or Ivory wherein they are set they being the greatest Magnifyers, and consequently the Object must be screwed very near to the Magnifying-Glass, to prevent the spoyling of these Glasses, only remember to be careful when you put in or pull out the Plate or Slider O, whereon the Object lies, or move it from one Object to another, not to let it rub your Magnifying-Glass, which is done by unscrewing a little the end Screw D, when you put in or pull out your Plate, or move it from one Object to another.
For seeing the Circulation of the Blood at the Extremities of the Arteries and Veins, in the transparent part of Fishes, Eels, &c. There must be a Glass-Tube, such as Y, wherein the Fish is to be put. When the Tube is to be used, you are to unscrew D in the Body of the Microscope, until the Tube Y can be received easily into that little Cavity G of the Brass Plate fastned to the Leather F, under the other two thin Plates of Brass EE. When the tail of your Fish lies flat to the Glass-Tube, set it opposite to your Magnifying-Glass, and by screwing in or out, your End-Screw D as is said before, you may easily bring it to the true distance, and see the Blood Circulate with great Pleasure.
If you would see the Blood Circulate in a Frog’s Foot, chuse (sic) such a Frog as will just go into your Tube; then with a little Stick, &c. expand the hinder Foot or of the Frog, and apply it close to the side of the Tube, observing that no part of the Frog hinders the Light coming on its Foot; and when you have it at the just distance by means of the Screw D, you see the Rapid motion of the Blood in its Vessels, which are very numerous in the transparent thin Membranes that’s between the Frog’s Toes; For this Object, the 3d and 4th Magnifiers will do very well; but you may see the Circulation in the Tails of Water Nutes with the 5th or 6th Glasses, by reason the Globules of the Blood of those Nutes, are as big again as those of Frogs or small Fish.
N.B. The Circulation of the Blood cannot be so well seen by the 1st and 2nd Magnifiers because the thickness of the Galss (sic) wherein the Fifth lies, hinders the Approximation of the Object from the true Focus of the Glass.
