of the _Atmosphere_
from this inflection of the Rays, or from the Quicksilver Experiment of the
rarifaction or extension of the Air.

Fourthly, Whether the disparity between the upper and under Air be not
sometimes so great, as to make a reflecting superficies; I have had several
Observations which seem to have proceeded from some such cause, but it
would be too long to relate and examine them. An Experiment, also somewhat
analogous to this, I have made with Salt-water and Fresh, which two
liquors, in most Positions, seem'd the same, and not to be separated by any
determinate superficies, which separating surface yet in some other
Positions did plainly appear.

And if so, Whether the reason of the equal bounding or _terminus_ of the
under parts of the clouds may not proceed from this cause; whether,
secondly, the Reason of the apparition of many Suns may not be found out,
by considering how the Rays of the Sun may so be reflected, as to describe
a pretty true Image of the body, as we find them from any regular
Superficies. Whether also this may not be found to cause the apparition of
some of those _Parelii_, of counterfeit Suns, which appear coloured, by
refracting the Rays so, as to make the body of the Sun appear in quite
another place then really it is. But of this more elsewhere.

5. Whether the _Phaenomena_ of the Clouds may not be made out by this
diversity of density in the upper and under parts of the Air, by supposing
the Air above them to be much lighter then they themselves are, and they
themselves to be yet lighter then that which is subjacent to them, many of
them seeming to be the same substance with the Cobwebs that fly in the Air
after a Fog.

Now that such a constitution of the Air and Clouds, if such there be, may
be sufficient to perform this effect, may be confirm'd by this Experiment.

Make as strong a Solution of Salt as you are able, then filling a Glass of
some depth half full with it, fill the other half with fresh Water, and
poyse a little Glass-bubble, so as that it may sink pretty quick in fresh
Water, which take and put into the aforesaid Glass, and you shall find it
to sink till it comes towards the middle, where it will remain fixt,
without moving either upwards or downwards. And by a second Experiment, of
poising such a bubble in water, whose upper part is warmer, and
consequently lighter, then the under, which is colder and heavier; the
manner of which follows in this next Quaery, w