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.
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