_EXPERIMENT V._
[Illustration: _The Explication of the Scheme._]
_PPP_. An Aequilaterotriangular Crystalline Prism, one of whose edges _P_.
is placed directly towards the Sun.
_A B_ & [alpha] [beta] Two rays from the Sun falling on the Prism at _B_
[beta]. and thence partly reflected towards _C_ & [gamma]. and partly
refracted towards _D_ & [delta].
_B C_ & [beta] [gamma]. Those reflected Rays.
_B D_ & [beta] [delta]. Those refracted Rays which are partly refracted
towards _E_ & [epsilon]. and there paint an Iris 1 2 3 4 5. denoting the
five consecutions of colours Red, Yellow, Green, Blew, and Purple; and are
partly reflected towards _F_ & [zeta].
_D F_ & [delta] [zeta]. Those Reflected Rays which are partly refracted
towards _G_ & [eta]. colourless, and partly reflected, towards _H_ &
[theta].
_F H_ & [zeta] [theta]. Those reflected Rays which are refracted towards
_I_ & [iota]. and there paint an other fainter Iris, the colours of which
are contrary to the former 5 4 3 2 1. signifying Purple, Blew, Green,
Yellow, Red, so that the Prism in this posture exhibits four Rainbows.
I know not whether you will think it Inconsiderable to annex to this
Experiment, That we observ'd in a Room not Darken'd, that the Prismatical
Iris (if I may so call it) might be Reflected without losing any of its
several _Colours_ (for we now consider not their _Order_) not onely from a
plain Looking-glass and from the calm Surface of Fair Water, but also from
a Concave Looking-glass; and that Refraction did as little Destroy those
Colours as Reflection.
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