fick gravity is of no efficacy. By this I have also found that look what proportion the Sine of the Angle of one Inclination has to the Sine of the Angle of Refraction, correspondent to it, the same proportion have all the Sines of other Inclinations to the Sines of their appropriate Refractions.
My way for measuring how much a Glass magnifies an Object, plac'd at a convenient distance from my eye, is this. Having rectifi'd the Microscope, to see the desir'd Object through it very distinctly, at the same time that I look upon the Object through the Glass with one eye, I look upon other Objects at the same distance with my other bare eye; by which means I am able, by the help of a Ruler divided into inches and small parts, and laid on the Pedestal of the Microscope, to cast, as it were, the magnifi'd appearance of the Object upon the Ruler, and thereby exactly to measure the Diameter it appears of through the Glass, which being compar'd with the Diameter it appears of to the naked eye, will easily afford the quantity of its magnifying.
The Microscope, which for the most part I made use of, was shap'd much like that in the sixth Figure of the first Scheme, the Tube being for the most part not above six or seven inches long, though, by reason it had four Drawers, it could very much be lengthened, as occasion required; this was contriv'd with three Glasses; a small Object Glass at A, a thinner Eye Glass about B, and a very deep one about C: this I made use of only when I had occasion to see much of an Object at once; the middle Glass conveying a very great company of radiating Pencils, which would go another way, and throwing them upon the deep Eye Glass. But when ever I had occasion to examine the small parts of a Body more accurately, I took out the middle Glass, and only made use of one Eye Glass with the Object Glass, for always the fewer the Refractions are, the more bright and clear the Object appears. And therefore 'tis not to be doubted, but could we make a Microscope to have one only refraction, it would, cæteris paribus, far excel any other that had a greater number. And hence it is, that if you take a very clear piece of a broken Venice Glass, and in a Lamp draw it out into very small hairs or threads, then holding the ends of these threads in the flame, till they melt and run into a small round Globul, or drop, which will hang at the end of the thread; and if further you stick several of these upon the end of a stick with a little sealing Wax, so as that the threads stand upwards, and then on a Whetstone first grind off a good part of them, and afterward on a smooth Metal plate, with a little Tripoly, rub them till they come to be very smooth; if one of these be fixt with a little soft Wax against a small needle hole, prick'd through a thin Plate of Brass, Lead, Pewter, or any other Metal, and an Object, plac'd very near, be look'd at through it, it will both magnifie and make some Objects more distinct then any of the great Microscopes. But because these, though exceeding easily made, are yet very troublesome to be us'd, because of their smallness, and the nearness of the Object; therefore to prevent both these, and yet have only two Refractions, provided me a Tube of Brass, shap'd much like that in the fourth Figure of the first Scheme; into the smaller end of this I fixt with Wax a good plano con-
