at pass through them from the Peacock, whil'st
that Bird is yet alive, the colours again appear in their former luster,
the _interstitia_ of these Plates being fill'd with the strongly reflecting
Air.

The beauteous and vivid colours of the Feathers of this Bird, being found
to proceed from the curious and exceeding smalness and fineness of the
reflecting parts, we have here the reason given us of all those gauderies
in the apparel of other Birds also, and how they come to exceed the colours
of all other kinds of Animals, besides Insects; for since (as we here, and
elsewhere also shew) the vividness of a colour, depends upon the fineness
and transparency of the reflecting and refracting parts; and since our
_Microscope_ discovers to us, that the component parts of feathers are
such, and that the hairs of Animals are otherwise; and since we find also
by the Experiment of that Noble and most Excellent Person I formerly named;
that the difference between Silk and Flax, as to its colour, is nothing
else (for Flax reduc'd to a very great fineness of parts, both white and
colour'd, appears as white and as vivid as any Silk, but loses that
brightness and its Silken aspect as soon as it is twisted into thread, by
reason that the component parts, though very small and fine, are yet
pliable flakes, and not cylinders, and thence, by twisting, become united
into one opacous body, whereas the threads of Silk and Feathers retain
their lustre, by preserving their cylindrical form intire without mixing;
so that each reflected and refracted beam that composes the gloss of Silk,
preserves its own property of modulating the light intire); And since we
find the same confirm'd by many other Experiments elsewhere mentioned, I
think we may safely conclude this for an Axiome, that wheresoever we meet
with transparent bodies, spun out into very fine parts, either cleer, or
any ways ting'd, the colours resulting from such a _composition_ must
necessarily be very glorious, vivid, and cleer, like those of Silk and
Feathers. This may perhaps hint some usefull way of making other bodies,
besides Silk, be susceptible of bright tinctures, but of this onely by the
by.

The changeable colour'd Feathers also of Ducks, and several other Birds, I
have found by examination with my _Microscope_, to proceed from much the
same causes and textures.

* * * * *

Observ. XXXVII. _Of the Feet of _Flies_, and several other _Insect