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 Insects._

The foot of a Fly (delineated in the first Figure of the 23. Scheme, which represents three joints, the two Tallons, and the two Pattens in a flat posture; and in the second Figure of the same Scheme, which represents onely one joint, the Tallons and Pattens in another posture) is of a most admirable and curious contrivance, for by this the Flies are inabled to walk against the sides of Glass, perpendicularly upwards, and to contain themselves in that posture as long as they please; nay, to walk and suspend themselves against the under surface of many bodies, as the ceiling of a room, or the like, and this with as great a seeming facility and firmness, as if they were a kind of Antipodes,