Now, though the second refraction made at Nn be convenient, that is, do
make the Rays glance the more, yet is it not altogether requisite; for it
is plain from the calculation, that the pulse dn is sufficiently _oblique_
to the Rays KN and kn, as wel as the pulse fc is _oblique_ to the Rays FK &
fk. And therefore if a piece of very fine Paper be held close against Nn
and the eye look on it either through the Ball as from D, or from the other
side, as from B. there shall appear a Rainbow, or colour'd line painted on
it with the part toward X appearing _Red_, towards O, _Blue_; the same also
shall happen, if the Paper be placed about Kk, for towards T shall appear a
_Red_, and towards V a _Blue_, which does exactly agree with this my
_Hypothesis_, as upon the calculation of the progress of the pulse will
most easily appear.
Nor do these two observations of the colours appearing to the eye about p
differing from what they appear on the Paper at N contradict each other;
but rather confirm and exactly agree with one another, as will be evident
to him that examines the reasons set down by the ingenious. _Des Cartes_ in
the 12. _Sect._ of the 8. _Chapter of his Meteors_, where he gives the true
reason why the colours appear of a quite contrary order to the eye, to what
they appear'd on the Paper if the eye be plac'd in steed of the Paper: And
as in the Prisme, so also in the Water-drop, or Globe the _Phaenomena_, and
reason are much the same.
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