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I. And moft vifible Thing, is the Shape and Make of their Body, not thick and clumfy, but incomparably adapted to their Flight: Sharp before, to pierce and make Way through the Air, and then by gentle Degrees rifing to its full Bulk. To which we may add, 1

II. The neat Pofition of the Feathers throughout the Body; not ruffled, or difcompos'd, or plac'd fome this, fome 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 fame 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 foft Down next the Body, and more strongly made, and curi oufly clos'd next the Air and Weather, to fence off the Injuries thereof. To which Purpose, as alfo for the more eafy and nimble gliding of the Body through the Air, the Provifion Nature hath made, and the Inftinct of these Animals to preen and dress their Feathers, is admirable; both in ref pect of their Art and Curiofity in doing it, and the Oyl-bag (b), Glands, and whole Apparatus for that Service.

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(a) See before Book IV. Chap. 12. Note (1).

(b) Mr. Willughby faith, there are two Glands for the Secretion of the unctuous Matter in the Oyl-bag. And so they appear to be in Geefe. But upon Examination, I find, that in most other Birds, (fuch at leaft 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 preffed, or drawn by the Bird's Bill, or Head, emits the liquid Oyl, as it is in fome Birds, or thicker unctuous Grease, as it is in others. The whole Oyl-bag is in its structure fomewhat conformable to the Breafts of fuch Animals as afford Milk.

III. And

III. And now having faid thus much relating to the Body's Motion, let us furvey the grand Inftrument thereof, the Wings. Which as they are principal Parts, fo are made with great Skill, and plac'd' in the most commodious Point of the Body (c), to give it an exact Equipoife in that fubtile Medium, the Air.

And here it is obfervable, with what incomparable Curiofity every Feather is made; the Shaft exceeding ftrong, but hollow below, for Strength and Lightness fake; and above, not much lefs ftrong, and fill'd with a Parenchyma or Pith, both ftrong 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 minifter to the progreffive Motion of the Bird, as alfo to the Union and Clofeness of the Wing (d).

And

(c) In all Birds that fly much, or that have the most occafion for their Wings, it is manifeft that their Wings are plac'd in the very beft Part, to balance their Body in the Air, and to give as fwift a Progreffion, as their Wings and Body are capable of: For otherwife we fhould perceive them to reel, and fly unfteadily; as we fee them to do, if we alter their Equipoife, 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 fuch Birds as have as much occafion for Swimming as Flying, and whofe Wings are therefore fet a little out of the Center of the Bodies Gravity. See Book IV. Chap. 8. Note (q). And for fuch as have more occafion for Diving than Flying, and whofe Legs are for that Reafon fet more backward, and their Wings more forward. Chap. 4. Note (k) of this Book.

(d) The wife Author of Nature hath afforded an Example of the great Nicety in the Formation of Birds, by the Nicety obferv'd in a Part no more confiderable than the Vanes of the Flag-feathers of the Wing. Among others, thefe two Things are obfervable: 1. The Edges of the exterior or narrow Vanes bend downwards, but of the interi or wider Vanes upwards; by which Means they catch, hold, and lie clofe to one another, when the Wing is spread; fo that not one Feather may miss its full Force and Impulse

upon

And no lefs exquifite is the téxtrine Art of the Plumage (e) alfo; which is fo curiously wrought,

upon the Air. 2. A yet leffer Nicety is obferv'd, "and that is, in the very floping the Tips of the Flag-feathers: The interiour Vanes being neatly flop'd away to a Point, towards the outward Part of the Wing; and the exteriour Vanes flop'd towards the Body, at leaft in many Birds; and in the Middle of the Wing, the Vanes being equal, are but little flop'd. So that the Wing, whether extended or shut, is as neatly flop'd and form'd, as if conftantly trimm'd with a Pair of Sciffors.

(e) Since no exact Account that I know of, hath been given of the Mechanism of the Vanes, or Webs of the Feathers, my Obfervations may not be unacceptable. The Vane confifts not of one continu'd Membrane; because if one broken, it would hardly be reparable: But of many Lamine, which are thin, ftiff, and fomewhat of the Nature of a thin Quill. Towards the Shaft of the Feather, (efpecially in the Flagfeathers of the Wing,) thofe Lamina are broad, ee. of a femicircular Form; which ferve for Strength, and for the clofer fhutting of the Lamina to one another, when Impulfes are made upon the Air. Towards the outer Part of the Vane, thele Lamina grow flender and taper: On their under Side they are thin and fmooth, 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 flender and bearded above the other half. I have, as well as I could, reprefented the uppermoft Edge of one of these Lamina in Fig. 18. with fome of the Hairs on each Side, magnify'd with a Microscope. Thefe bearded Briftles, or Hairs, on one Side the Lamina, have ftrait Beards, as in Fig. 19. thofe on the other Side, have hook'd Beards on one Side the flender Part of the Briftle, and ftrait ones on the other, as in Fig. 20. Both thefe Sorts of Briftles magnify'd, (only scattering, and not clofe,) are reprefented as they grow upon the upper Edge of the Lamina f. t. in Fig. 18. And in the Vane, the hook'd Beards of one Lamina, always lie next the ftrait Beards of the next Lamina; and by that Means lock and hold each other; and by a pretty Mechanism, brace the Lamina clofe to one another. And if at any Time the Vane happens to be ruffled and difcompos'd, it can by this pretty eafy Mechanifm, be reduc'd and repair'd. Vid. Book IV. Chap. 12. Note (m).

and

and fo artificially interwoven, that it cannot be viewed without Admiration, efpecially when the Eye is affifted with Glaffes.

And as curioufly made, fo no lefs curiously are the Feathers placed in the Wing, exactly according to their feveral Lengths and Strength: The Principals fet for Stay and Strength, and thefe again well lined, faced, and guarded with the Covert and Secondary Feathers, to keep the Air from paffing through, whereby the ftronger Impulfes are made thereupon.

And lastly, To fay no more of this Part, that deferves more to be faid of it, what an admirable Apparatus is there of Bones, very strong, but withal light and incomparably wrought? of Joynts, which open, fhut, and every way move, according to the Occafions 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 deferves efpecial Remark, by Reason they are much ftronger (f) in Birds than in Man, or any other Animal, not made for Flying.

IV. Next the Wings, the Tail is in Flight confiderable; greatly affifting in all Afcents and De

(f) Pectorales Mufculi Hominis flectentes humeros, parvi parum carnofi funt; non aquant 50am aut 70am partem omnium Mufculorum Hominis. E contra in Avibus, Pectorales Mufculi vaftiffimi funt, & aquant, imò excedunt, & magis pendent, quàm reliqui omnes Mufculi ejufdem Avis fimul fumpti. Borell. de Mot. Animal. Vol. I. Prop. 184.

Mr. Willughby having made the like Obfervation, hath this Reflection on it, whence, if it be poffible for Man to fly, it is thought by them who have curiously weighed and confidered the matter, that he that would attempt fuch a Thing with Hopes of Succefs, muft fo contrive and adapt his Wings, that he may make use of his Legs, and not his Arms in managing them : (becaufe the Mufcles of the Legs are ftronger, as he obferves.) Willugh; Ornith. L. 1. c. I. §, 19. Z

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fcents

Book VII. feents in the Air, as alfo ferving to fteady (g) Flight, by keeping the Body upright in that subtile and yielding Medium, by its readily turning and answering every Vacillation of the Body

And now to the Parts ferving to Flight, let usadd the nice and compleat Manner of its Performance all done according to the ftrictest Rules of Mechanifm (b). What Rower on the Waters, what Ar tift on the Land, what acuteft Mathematician could give a more agreeable and exact Motion to the Wings, than thefe untaught flying Artifts do theirs! Serving not only to bear their Bodies up in the Air, but also to waft them along therein, with a speedy progreffive Motion, as also to steer and turn them this Way and that Way, up and down, fafter or flower, as their Occafions require, or their Pleasure leads them.

V. Next to the Parts for Flight, let us view the Feet and Legs miniftering to their other Motion: Both made light, for cafier Transportation through the Airs and the former fpread, fome with Membranes for Swimming (i), fome without, for fteady Going

(8) Mr. Willughby, Ray, and many others, imagine the principal ufe of the Tail to be to fteer, and turn the Body in the Air, as a Rudder. But Borelli hath put it beyond all doubt, that this is the leaft ufe of it, and that it is chiefly to aflift the Bird in its Afcents and Defcents in the Air, and to obviate the Vacillations of the Body and Wings. For as for turning to this or that Side, it is performed by the Wings and Inclination of the Body, and, but very little by the help of the Tail.

(h) See Bonelli ubi fupr. Prop, 182, &c.

() It is confiderable in all Water-Fowl, how exactly their Legs and Feet correfpond to that way of Life. For either their Legs are long, to enable them to wade in the Waters: In which cafe, their Legs are bare of Feathers a good way above the Knees, the more conveniently for this Purpose. Their Toes alfo are all abroad, and in fuch as bear, the

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