First therefore, if we consider the manner of the progress of the pulse, it will seem rational to conclude, that that part or end of the pulse which precedes the other, must necessarily be somwhat more obtunded, or impeded 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 AAAHB will have its side HH more deadned by the resistance of the dark or quiet medium PPP, Whence there will be a kind of deadness superinduc’d on the side HHH, which will continually increase from B, and strike deeper and deeper into the Ray by the line BR; Whence all the parts of the triangle, RBHO will be of a dead Blue colour, and so much the deeper, by how much the nearer they lie to the line BHH, 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 AAN, the end A of the pulse AH 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 QQ the adjacent dark or quiet medium, which faint motion will spread further and further into QQ as the Ray is propagated further and further from A, namely, as far as the line MA, whence all the triangle MAN will be ting’d with a Red, and that Red will be the deeper the nearer it approaches the line MA, and the paler or yellower the nearer it is the line NA.  And if the Ray be continued, so that the lines AN and BR (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 AKSB and ANOB, which arc the terminating:  For in this case the Ray AKSB will have its Red triangle intire, as lying next to the dark or quiet medium, but the other side of it BS will have no Blue, because the medium adjacent to it SBO, is mov’d or enlightned, and consequently that light does destroy the colour.  So likewise will the Ray ANOB 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, AHO will preserve its Blue entire, and these Rays must be so far produc’d as till AN and BR 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 Phaenomena of the prisme, and of the Globules or drops of Water which conduce to the production of the Rainbow.