Now fourthly, if the thicker Plate chance to be cleft into two thinner Plates, as CDFE is divided into two Plates by the surface GH then from the composition arising from the three reflections in the surfaces CD, GH, and EF, there will be generated several compounded or mixt colours, which will be very differing, according as the proportion between the thicknesses of those two divided Plates CDHG, and GHFE are varied.

And fifthly, if these surfaces CD and FE are further remov’d asunder, the weaker pulse will yet lagg behind much further, and not onely be coincident with the second, cd, but lagg behind that also, and that so much the more, by how much the thicker the Plate be; so that by degrees it will be coincident with the third cd backward also, and by degrees, as the Plate grows thicker with a fourth, and so onward to a fifth, sixth, seventh, or eighth; so that if there be a thin transparent body, that from the greatest thinness requisite to produce colours, does, in the manner of a Wedge, by degrees grow to the greatest thickness that a Plate can be of, to exhibit a colour by the reflection of Light from such a body, there shall be generated several consecutions of colours, whose order from the thin end towards the thick, shall be Yellow, Red, Purple, Blue, Green; Yellow, Red, Purple, Blue, Green; Yellow, Red, Purple, Blue, Green; Yellow, &c. and these so often repeated, as the weaker pulse does lose paces with its Primary, or first pulse, and is coincident with a second, third, fourth, fifth, sixth, &c. pulse behind the first.  And this, as it is coincident, or follows from the first Hypothesis I took of colours, so upon experiment have I found it in multitudes of instances that seem to prove it.  One thing which seems of the greatest concern in this Hypothesis, is to determine the greatest or least thickness requisite for these effects, which, though I have not been wanting in attempting, yet so exceeding thin are these coloured Plates, and so imperfect our Microscope, that I have not been hitherto successfull, though if my endeavours shall answer my expectations, I shall hope to gratifie the curious Reader with some things more remov’d beyond our reach hitherto.

Thus have I, with as much brevity as I was able, endeavoured to explicate (Hypothetically at least) the causes of the Phaenomena I formerly recited, on the consideration of which I have been the more particular.

First, because I think these I have newly given are capable of explicating all the Phaenomena of colours, not onely of those appearing in the Prisme, Water-drop, or Rainbow, and in laminated or plated bodies, but of all that are in the world, whether they be fluid or solid bodies, whether in thick or thin, whether transparent, or seemingly opacous, as I shall in the next Observation further endeavour to shew.  And secondly, because this being one of the two ornaments of all bodies discoverable by the sight, whether looked on with, or without a Microscope, it seem’d to deserve (somewhere in this Tract, which contains a description of the Figure and Colour of some minute bodies) to be somewhat the more intimately enquir’d into.