ker: which two _Phaenomena_, (for I shall take
notice of no more at present, though I could instance in multitudes of
others) must necessarily be caus'd by an _inflection_ of the Rays within
the terminating superficies of the compounded _medium_, since the surfaces
of the transparent body through which the Rays pass to the eye, are not at
all altered or chang'd.

This _inflection_ (if I may so call it) I imagine to be nothing else, but a
_multiplicate refraction_, caused by the unequal _density_ of the
constituent parts of the _medium_, whereby the motion, action or progress
of the Ray of light is hindred from proceeding in a streight line, and
_inflected_ or _deflected_ by a _curve_. Now, that it is a _curve_ line is
manifest by this Experiment: I took a Box, such as ADGE, in the first
_Figure_ of the 37. _Scheme_, whose sides ABCD, and EFGH, were made of two
smooth flat plates of Glass, then filling it half full with a very strong
solution of Salt, I filled the other half with very fair fresh water, then
exposing the opacous side, DHGC, to the Sun, I observ'd both the
_refraction_ and _inflection_ of the Sun beams, ID & KH, and marking as
exactly as I could, the points, P, N, O, M, by which the Ray, KH, passed
through the compounded _medium_, I found them to be in a _curve_ line; for
the parts of the _medium_ being continually more dense the neerer they were
to the bottom, the Ray _pf_ was continually more and more deflected
downwards from the streight line.

This Inflection may be mechanically explained, either by Monsieur _Des
Cartes_ principles by conceiving the Globuls of the third Element to find
less and less resistance against that side of them which is downwards, or
by a way, which I have further explicated in the Inquisition about Colours,
to be from an obliquation of the pulse of light, whence the under part is
continually promoted, and consequently refracted towards the perpendicular,
which cuts the Orbs at right angles. What the particular Figure of the
_Curve line_, describ'd by this way of light, is, I shall not now stand to
examine, especially since there may be so many sorts of it as there may be
varieties of the Positions of the _intermediat_ degrees of _density_ and
_rarity_ between the bottom and the top of the inflecting Medium.

I could produce many more Examples and Experiments, to illustrate and prove
this first Proposition, _viz._ that there is such a constitution of some
bodies as will cause