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 deadened 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_.