I. And most visible Thing, is the Shape and Make of their Body, not thick and clumsy, but incomparably adapted to their Flight: Sharp before, to pierce and make Way through the Air, and then by gentle Degrees rising to its full Bulk. To which we may add,
II. The neat Position of the Feathers throughout the Body; not ruffled, or discompos’d, or plac’d some this, some a contrary Way, according to the Method of Chance; but all artificially plac’d[a], for facilitating the Motion of the Body, and its Security at the same Time, by way of Cloathing: And for that End, most of the Feathers tend backward, and are laid over one another in exact and regular Method, armed with warm and soft Down next the Body, and more strongly made, and curiously clos’d next the Air and Weather, to fence off the Injuries thereof. To which Purpose, as also for the more easy and nimble gliding of the Body through the Air, the Provision Nature hath made, and the Instinct of these Animals to preen and dress their Feathers, is admirable; both in respect of their Art and Curiosity in doing it, and the Oyl-bag[], Glands, and whole Apparatus for that Service.
III. And now having said thus much relating to the Body’s Motion, let us survey the grand Instrument thereof, the Wings. Which as they are principal Parts, so are made with great Skill, and plac’d in the most commodious Point of the Body[c], to give it an exact Equipoise in that subtile Medium, the Air.
And here it is observable, with what incomparable Curiosity every Feather is made; the Shaft exceeding strong, but hollow below, for Strength and Lightness sake; and above, not much less strong, and fill’d with a Parenchyma or Pith, both strong and light too. The Vanes as nicely gaug’d on each Side as made; broad on one Side, and narrower on the other; both which incomparably minister to the progressive Motion of the Bird, as also to the Union and Closeness of the Wing[d].
And no less exquisite is the textrine Art of the Plumage[e] also; which is so curiously wrought, and so artificially interwoven, that it cannot be viewed without Admiration, especially when the Eye is assisted with Glasses.
And as curiously made, so no less curiously are the Feathers placed in the Wing, exactly according to their several Lengths and Strength: The Principals set for Stay and Strength, and these again well lined, faced, and guarded with the Covert and Secondary Feathers, to keep the Air from passing through, whereby the stronger Impulses are made thereupon.
And lastly, To say no more of this Part, that deserves more to be said of it, what an admirable Apparatus is there of Bones, very strong, but withal light and incomparably wrought? of Joynts, which open, shut, and every way move, according to the Occasions either of extending it in Flight, or withdrawing the Wing again to the Body? And of various Muscles; among which the peculiar Strength of the Pectoral Muscles deserves especial Remark, by Reason they are much stronger[f] in Birds than in Man, or any other Animal, not made for Flying.
IV. Next the Wings, the Tail is in Flight considerable; greatly assisting in all Ascents and Descents in the Air, as also serving to steady[g] Flight, by keeping the Body upright in that subtile and yielding Medium, by its readily turning and answering every Vacillation of the Body.