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 to
the Glass, they shall be in great measure transmitted where the Water is
adjacent to it; which argues, that their Reflexion or Transmission
depends on the constitution of the Air and Water behind the Glass, and
not on the striking of the Rays upon the parts of the Glass. Thirdly,
If the Colours made by a Prism placed at the entrance of a Beam of Light
into a darken'd Room be successively cast on a second Prism placed at a
greater distance from the former, in such manner that they are all alike
incident upon it, the second Prism may be so inclined to the incident
Rays, that those which are of a blue Colour shall be all reflected by
it, and yet those of a red Colour pretty copiously transmitted. Now if
the Reflexion be caused by the parts of Air or Glass, I would ask, why
at the same Obliquity of Incidence the blue should wholly impinge on
those parts, so as to be all reflected, and yet the red find Pores
enough to be in a great measure transmitted. Fourthly, Where two Glasses
touch one another, there is no sensible Reflexion, as was declared in
the first Observation; and yet I see no reason why the Rays should not
impinge on the parts of Glass, as much when contiguous to other Glass as
when contiguous to Air. Fifthly, When the top of a Water-Bubble (in the
17th Observation,) by the continual subsiding and exhaling of the Water
grew very thin, there was such a little and almost insensible quantity
of Light reflected from it, that it appeared intensely black; whereas
round about that black Spot, where the Water was thicker, the Reflexion
was so strong as to make the Water seem very white. Nor is it only at
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