e the Horizon, whil'st the Moon has been in an Eclipse.
I shall not here instance in the great refractions, that the tops of high
mountains, seen at a distance, have been found to have; all which seem to
argue the Horizontal refraction, much greater then it is hitherto generally
believ'd.

I have further taken notice, that not onely the Sun, Moon and Starrs, and
high tops of mountains have suffer'd these kinds of refraction, but Trees,
and several bright Objects on the ground: I have often taken notice of the
twinkling of the reflections of the Sun from a Glass-window at a good
distance, and of a Candle in the night, but that is not so conspicuous, and
in observing the setting Sun, I have often taken notice of the tremulation
of the Trees and Bushes, as well as of the edges of the Sun. Divers of
these _Phaenomena_ have been taken notice of by several, who have given
several reasons of them, but I have not yet met with any altogether
satisfactory, though some of their conjectures have been partly true, but
partly also false. Setting my self therfore upon the inquiry of these
_Phaenomena_, I first endeavour'd to be very diligent in taking notice of
the several particulars and circumstances observable in them; and next, in
making divers particular Experiments, that might cleer some doubts, and
serve to determine, confirm, and illustrate the true and adaequate cause of
each; and upon the whole, I find much reason to think, that the true cause
of all these _Phaenomena_ is from the _inflection_, or _multiplicate
refraction_ of those Rays of light within the body of the _Atmosphere_, and
that it does not proceed from a _refraction_ caus'd by any terminating
_superficies_ of the Air above, nor from any such exactly defin'd
_superficies_ within the body of the _Atmosphere_.

This Conclusion is grounded upon these two Propositions:

First, that a _medium_, whose parts are unequally _dense_, and mov'd by
various motions and transpositions as to one another, will produce all
these visible effects upon the Rays of light, without any other
_coefficient_ cause.

Secondly, that there is in the Air or _Atmosphere_ such a variety in the
constituent parts of it, both as to their _density_ and _rarity_, and as to
their divers mutations and positions one to another.

By _Density_ and _Rarity_, I understand a property of a transparent body,
that does either more or less refract a Ray of light (coming obliquely upon
its superficies out of