and uniformly
adorned with some one vivid colour: this, if examined with the
_Microscope_, may be plainly perceived to be in all parts of it equally
thick. Two, three, or more of these lying one upon another, exhibit
oftentimes curious compounded colours, which produce such a _Compositum_,
as one would scarce imagine should be the result of such _ingredients_: As
perhaps a _faint yellow_ and a _blew_ may produce a very _deep purple_. But
when anon we come to the more strict examination of these _Phaenomena_, and
to inquire into the causes and reasons of these productions, we shall, I
hope, make it more conceivable how they are produced, and shew them to be
no other then the natural and necessary effects arising from the peculiar
union of concurrent causes.

These _Phaenomena_, being so various, and so truly admirable, it will
certainly be very well worth our inquiry, to examine the causes and reasons
of them, and to consider, whether from these causes demonstratively
evidenced, may not be deduced the true causes of the production of all kind
of Colours. And I the rather now do it, instead of an Appendix or
Digression to this History, then upon the occasion of examining the Colours
in Peacocks, or other Feathers, because this Subject, as it does afford
more variety of particular Colours, so does it afford much better wayes of
examining each circumstance. And this will be made manifest to him that
considers, first, that this laminated body is more simple and regular then
the parts of Peacocks feathers, this consisting only of an indefinite
number of plain and smooth Plates, heaped up, or _incumbent_ on each other.
Next, that the parts of this body are much more manageable, to be divided
or joyned, then the parts of a Peacocks feather, or any other substance
that I know. And thirdly, because that in this we are able from a
colourless body to produce several coloured bodies, affording all the
variety of Colours imaginable: And several others, which the subsequent
Inquiry will make manifest.

To begin therefore, it is manifest from several circumstances, that the
material cause of the _apparition_ of these several Colours, is some
_Lamina_ or Plate of a transparent or pellucid body of a thickness very
determinate and proportioned according to the greater or less refractive
power of the _pellucid_ body. And that this is so, abundance of Instances
and particular Circumstances will make manifest.

As _first_, if you take any