by the resistance of the transparent medium, than the other part or end of it which is subsequent, whose way is, as it were, prepared by the other; especially if the adjacent medium be not in the same manner enlightned or agitated. And therefore (in the fourth Figure of the sixth Iconism) the Ray A A A H B will have its side H H more deadned by the resistance of the dark or quiet medium P P P, Whence there will be a kind of deadness superinduc'd on the side H H H, which will continually increase from B, and strike deeper and deeper into the Ray by the line B R; Whence all the parts of the triangle, R B H O will be of a dead Blue colour, and so much the deeper, by how much the nearer they lie to the line B H H, which is most deaded or impeded, and so much the more dilute, by how much the nearer it approaches the line BR. Next on the other side of the Ray A A N, the end A of the pulse A H will be promoted, or made stronger, having its passage already prepar'd as 'twere by the other parts preceding, and so its impression wil be stronger; And because of its obliquity to the Ray, there will be propagated a kind of faint motion into Q Q the adjacent dark or quiet medium, which faint motion will spread further and further into Q Q as the Ray is propagated further and further from A, namely, as far as the line M A, whence all the triangle M A N will be ting'd with a Red, and that Red will be the deeper the nearer it approaches the line M A, and the paler or yellower the nearer it is the line N A. And if the Ray be continued, so that the lines A N and B R (which are the bounds of the Red and Blue diluted) do meet and cross each other, there will be beyond that intersection generated all kinds of Greens.
Now, these being the proprieties of every single refracted Ray of light, it will be easie enough to consider what must be the result of very many such Rays collateral: As if we suppose infinite such Rays interjacent between A K S B and A N O B, which are the terminating: For in this case the Ray A K S B will have its Red triangle intire, as lying next to the dark or quiet medium, but the other side of it B S will have no Blue, because the medium adjacent to it S B O, is mov'd or enlightned, and consequently that light does destroy the colour. So likewise will the Ray A N O B lose its Red, because the adjacent medium is mov'd or enlightned, but the other side of the Ray that is adjacent to the dark, namely, A H O will preserve its Blue entire, and these Rays must be so far produc'd as till A N and B R cut each other, before there will be any Green produc'd. From these Proprieties well consider'd, may be deduc'd the reasons of all the Phænomena of the prisme, and of the Globules or drops of Water which conduce to the production of the Rainbow.
Next for the impression they make on the Retina, we will further examine this Hypothesis: Suppose therefore A B C D E F, in the fifth Figure, to represent the Ball of the eye: on the Cornea of which A B C two Rays G A C H and K C A I (which are the terminating Rays of a luminous body) falling, are by the refraction thereof collected or converg'd into two points at the bottom of the eye. Now, because these terminating Rays, and all the intermediate ones which come from any part of the luminous body, are suppos'd by some sufficient refraction before they
