er_: but
_Allum water_ has a less refraction then common _Water_, though heavier
also. So that it seems, as to the _refraction_ made in a Liquor, the
_specifick 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, _caeteris paribus_, far excel any
other that had a greater number. And hence it is, that if you take a
very clear pi