And now to the Parts serving to Flight, let us add the nice and compleat Manner of its Performance; all done according to the strictest Rules of Mechanism[h]. What Rower on the Waters, what Artist on the Land, what acutest Mathematician could give a more agreeable and exact Motion to the Wings, than these untaught flying Artists do theirs! Serving not only to bear their Bodies up in the Air, but also to waft them along therein, with a speedy progressive Motion, as also to steer and turn them this Way and that Way, up and down, faster or slower, as their Occasions require, or their Pleasure leads them.
V. Next to the Parts for Flight, let us view the Feet and Legs ministering to their other Motion: Both made light, for easier Transportation through the Air; and the former spread, some with Membranes for Swimming[], some without, for steady Going, for Perching, for Catching and Holding of Prey[k], or for Hanging by the Heels to gather their Food[l], or to fix themselves in their Places of Retreat and Safety. And the latter, namely the Legs, all curved for their easy Perching, Roosting, and Rest, as also to help them upon their Wings in taking their Flight, and to be therein commodiously tucked up to the Body, so as not to obstruct their Flight. In some long, for Wading and Searching the Waters; in some of a moderate Length, answerable to their vulgar Occasions; and in others as remarkably short, to answer their especial Occasions and Manner of Life[m]. To all which let us add the placing these last mentioned Parts in the Body. In all somewhat out of the Center of the Body’s Gravity[n], but in such as swim, more than in others, for the better rowing their Bodies through the Waters, or to help them in that Diving[o] too.
FOOTNOTES:
[a] See before [Book IV. Chap. 12. Note (l).]
[] Mr. Willughby saith, there are two Glands for the Secretion of the unctuous Matter in the Oyl-bag. And so they appear to be in Geese. But upon Examination, I find, that in most other Birds, (such at least as I have enquir’d into,) there is only one Gland: In which are divers little Cells, ending in two or three larger Cells, lying under the Nipple of the Oyl-bag. This Nipple is perforated, and being pressed, or drawn by the Bird’s Bill, or Head, emits the liquid Oyl, as it is in some Birds, or thicker unctuous Grease, as it is in others. The whole Oyl-bag is in its structure somewhat conformable to the Breasts of such Animals as afford Milk.
[c] In all Birds that fly much, or that have the most occasion for their Wings, it is manifest that their Wings are plac’d in the very best Part, to balance their Body in the Air, and to give as swift a Progression, as their Wings and Body are capable of: For otherwise we should perceive them to reel, and fly unsteadily; as we see them to do, if we alter their Æquipoise, by cutting the End of one of the Wings, or hanging a Weight at any of the extreme Parts of the Body. But as for such Birds as have as much occasion for Swimming as Flying, and whole Wings are therefore set a little out of the Center of the Bodies Gravity. See [Book IV. Chap. 8. Note (q).] And for such as have more occasion for Diving than Flying, and whose Legs are for that Reason set more backward, and their Wings more forward. [Chap. 4. Note (k)] of this Book.
[d] The wise Author of Nature hath afforded an Example of the great Nicety in the Formation of Birds, by the Nicely observ’d in a Part no more considerable than the Vanes of the Flag-feathers of the Wing. Among others, these two Things are observable: 1. The Edges of the exterior or narrow Vanes bend downwards, but of the interior or wider Vanes upwards; by which Means they catch, hold, and lie close to one another, when the Wing is spread; so that not one Feather may miss its full Force and Impulse upon the Air. 2. A yet lesser Nicety is observ’d, and that is, in the very sloping the Tips of the Flag-feathers: The interiour Vanes being neatly slop’d away to a Point, towards the outward Part of the Wing; and the exteriour Vanes slop’d towards the Body, at least in many Birds; and in the Middle of the Wing, the Vanes being equal, are but little slop’d. So that the Wing, whether extended or shut, is as neatly slop’d and form’d, as if constantly trimm’d with a Pair of Scissors.
[e] Since no exact Account that I know of, hath been given of the Mechanism of the Vanes, or Webs of the Feathers, my Observations may not be unacceptable. The Vane consists not of one continu’d Membrane; because if one broken, it would hardly be reparable: But of many Laminæ, which are thin, stiff, and somewhat of the Nature of a thin Quill. Towards the Shaft of the Feather, (especially in the Flag-feathers of the Wing,) those Laminæ are broad, &c. of a semicircular Form; which serve for Strength, and for the closer shutting of the Laminæ to one another, when Impulses are made upon the Air. Towards the outer Part of the Vane, those Laminæ grow slender and taper: On their under Side they are thin and smooth, but their upper outer Edge is parted into two hairy Edges, each Side having a different Sort of Hairs, laminated or broad at Bottom, and slender and bearded above the other half. I have, as well as I could, represented the uppermost Edge of one of these Laminæ in [Fig. 18.] with some of the Hairs on each Side, magnify’d with a Microscope. These bearded Bristles, or Hairs, on one Side the Laminæ, have strait Beards, as in [Fig. 19.] those on the other Side, have hook’d Beards on one Side the slender Part of the Bristle, and strait ones on the other, as in [Fig. 20.] Both these Sorts of Bristles magnify’d, (only scattering, and not close,) are represented as they grow upon the upper Edge of the Lamina s. t. in [Fig. 18.] And in the Vane, the hook’d Beards of one Lamina, always lie next the strait Beards of the next Lamina; and by that Means lock and hold each other; and by a pretty Mechanism, brace the Laminæ close to one another. And if at any Time the Vane happens to be ruffled and discompos’d, it can by this pretty easy Mechanism, be reduc’d and repair’d. Vid. [Book IV. Chap. 12. Note (m).]
[f] Pectorales Musculi Hominis flectentes humeros, parvi & parum carnosi sunt; non æquant 50am aut 70am partem omnium Musculorum Hominis. E contra in Avibus, Pectorales Musculi vastissimi sunt, & aquant, imò excedunt, & magìs pendent, quàm reliqui omnes Musculi ejusdem Avis simul sumpti. Borell. de Mot. Animal. Vol. I. Prop. 184.
Mr. Willughby having made the like Observation, hath this Reflection on it, whence, if it be possible for Man to fly, it is thought by them who have curiously weighed and considered the matter, that he would attempt such a Thing with Hopes of Success, must so contrive and adapt his Wings, that he may make use of his Legs, and not his Arms in managing them: (because the Muscles of the Legs are stronger, as he observes.) Willugh. Ornith. L. 1. c. 1. §. 19.