always weaken the impulse the oftner it is repeated. 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 _Phænomena_, and reason are much the same. Having therefore shewn that there is such a propriety in the _prisme_ and water _Globule_ whereby the pulse is made _oblique_ to the progressive, and that so much the more, by how much greater the refraction is, I shall in the next place consider, how this conduces to the production of colours, and what kind of impression it makes upon the bottom of the eye; and to this end it will be requisite to examine this _Hypothesis_ a little more particularly.