I cannot much suspect the last, because I
have observed of some small Plates of Muscovy Glass which were of an
even thickness, that through a Microscope they have appeared of the same
Colour at their edges and corners where the included Medium was
terminated, which they appeared of in other places. However it will add
much to our Satisfaction, if those Corpuscles can be discover'd with
Microscopes; which if we shall at length attain to, I fear it will be
the utmost improvement of this Sense. For it seems impossible to see the
more secret and noble Works of Nature within the Corpuscles by reason of
their transparency.

PROP. VIII.

_The Cause of Reflexion is not the impinging of Light on the solid or
impervious parts of Bodies, as is commonly believed._

This will appear by the following Considerations. First, That in the
passage of Light out of Glass into Air there is a Reflexion as strong as
in its passage out of Air into Glass, or rather a little stronger, and
by many degrees stronger than in its passage out of Glass into Water.
And it seems not probable that Air should have more strongly reflecting
parts than Water or Glass. But if that should possibly be supposed, yet
it will avail nothing; for the Reflexion is as strong or stronger when
the Air is drawn away from the Glass, (suppose by the Air-Pump invented
by _Otto Gueriet_, and improved and made useful by Mr. _Boyle_) as when
it is adjacent to it. Secondly, If Light in its passage out of Glass
into Air be incident more obliquely than at an Angle of 40 or 41 Degrees
it is wholly reflected, if less obliquely it is in great measure
transmitted. Now it is not to be imagined that Light at one degree of
obliquity should meet with Pores enough in the Air to transmit the
greater part of it, and at another degree of obliquity should meet with
nothing but parts to reflect it wholly, especially considering that in
its passage out of Air into Glass, how oblique soever be its Incidence,
it finds Pores enough in the Glass to transmit a great part of it. If
any Man suppose that it is not reflected by the Air, but by the outmost
superficial parts of the Glass, there is still the same difficulty:
Besides, that such a Supposition is unintelligible, and will also appear
to be false by applying Water behind some part of the Glass instead of
Air. For so in a convenient obliquity of the Rays, suppose of 45 or 46
Degrees, at which they are all reflected where the Air is adjacent t