reflecting surface of the Air very vividly reflected, so that more Rays
were reflected to the eye by this surface, though the Ray in entring and
getting out of the Crystal had suffer'd a double refraction, than there
were from the outward surface of the Glass where the Ray had suffer'd no
reflection at all.

And that this was the surface of the Air that gave so vivid a
_re-percussion_ I try'd by this means I sunk half of a _stiria_ in Water,
so that only Water was contiguous to the under surface, and then the
internal reflection was so exceedingly faint, that it was scarce
discernable. Again, I try'd to alter this vivid reflection by keeping off
the Air, with a body not fluid, and that was by rubbing and holding my
finger very hard against the under surface, so as in many places the pulp
of my finger did touch the Glass, without any _interjacent_ air between,
then observing the reflection, I found, that wheresoever my finger or skin
toucht the surface, from that part there was no reflection, but in the
little furrows or creases of my skin, where there remain'd little small
lines of air, from them was return'd a very vivid reflection as before. I
try'd further, by making the surface of very pure Quicksilver to be
contiguous to the under surface of this _pellucid_ body, and then the
reflection from that was so exceedingly more vivid than from the air, as
the reflection from air was than the reflection from the Water; from all
which trials I plainly saw, that the strong reflecting air was the cause of
this _Phænomenon_.

And this agrees very well with the _Hypothesis_ of light and _Pellucid_
bodies which I have mention'd in the description of _Muscovy-glass_; for we
there suppose Glass to be a _medium_, which does less resist the pulse of
light, and consequently, that most of the Rays incident on it enter into
it, and are refracted towards the _perpendicular_; whereas the air I