Micrographia, by Robert Hooke

Observ. xxxv. Of the contexture and shape of the particles of Feathers.

Examining several sorts of Feathers, I took notice of these particulars in all sorts of wing-Feathers, especially in those which serv'd for the beating of the air in the action of flying.

That the outward surface of the Quill and Stem was of a very hard, stiff, and horny substance, which is obvious enough, and that the part above the Quill was fill'd with a very white and light pith, and, with the Microscope, I found this pith to be nothing else, but a kind of natural congeries of small bubbles, the films of which seem to be of the same substance with that of the Quill, that is, of a stiff transparent horny substance.

Which particular seems to me, very worthy a more serious consideration; For here we may observe Nature, as 'twere, put to its shifts, to make a substance, which shall be both light enough, and very stiff and strong, without varying from its own establish'd principles, which we may observe to be such, that very strong bodies are for the most part very heavie also, a strength of the parts usually requiring a density, and a density a gravity; and therefore should Nature have made a body so broad and so strong as a Feather, almost, any other way then what it has taken, the gravity of it must necessarily have many times exceeded this; for this pith seems to be like so many stops or cross pieces in a long optical tube, which do very much contribute to the strength of the whole, the pores of which were such, as that they seem'd not to have any communication with one another, as I have elsewhere hinted.

But the Mechanism of Nature is usually so excellent, that one and the same substance is adapted to serve for many ends. For the chief use of this, indeed, seems to be for the supply of nourishment to the downy or feathery part of the stem; for 'tis obvious enough in all sorts of Feathers, that 'tis plac'd just under the roots of the branches that grow out of either side of the quill or stalk, and is exactly shap'd according to the ranking of those branches, coming no lower into the quill, then just the beginning of the downy branches, and growing onely on the under side of of the quill where those branches do so. Now, in a ripe Feather (as one may call it) it seems difficult to conceive how the Succus nutritius should be convey'd to this pith; for it cannot, I think, be well imagin'd to pass through the substance of the quill, since, having examin'd it with the greatest diligence I was able, I could not find the least appearance of pores; but he that shall well examine an unripe or pinn'd Feather, will plainly enough perceive the Vessel for the conveyance of it to be the thin filmy pith (as 'tis call'd) which passes through the middle of the quill.

scheme22

As for the make and contexture of the Down it self, it is indeed very rare and admirable, and such as I can hardly believe, that the like is to be discover'd in any other body in the world; for there is hardly a large Feather in the wing of a Bird, but contains neer a million of distinct parts, and every one of them shap'd in a most regular & admirable form, adapted to a particular Design: For examining a middle ciz'd Goose-quill, I easily enough found with my naked eye, that the main stem of it contain'd about 300. longer and more Downy branchings upon one side, and as many on the other of more stiff but somewhat shorter branchings. Many of these long and downy branchings, examining with an ordinary Microscope, I found divers of them to contain neer 1200. small leaves (as I may call them, such as EF of the Schem. 22.
Fig. 1.
first Figure of the 22. Scheme) and as many stalks on the other side, such as IK of the same Figure, each of the leaves or branchings, EF, seem'd to be divided into about sixteen or eighteen small joints, as may be seen plainly enough in the Figure, out of most of which there seem to grow small long fibres, such as are express'd in the Figure, each of them very proportionably shap'd according to its position, or place on the stalk EF; those on the under side of it, namely, 1, 2, 3, 4, 5, 6, 7, 8, 9, &c. being much longer then those directly opposite to them on the upper; and divers of them, such as 2, 3, 4, 5, 6, 7, 8, 9, &c. were terminated with small crooks, much resembling those small crooks, which are visible enough to the naked eye, in the seed-buttons of Bur-docks. The stalks likewise, IK on the other side, seem'd divided into neer as many small knotted joints, but without any appearance of strings or crooks, each of them about the middle K, seem'd divided into two parts by a kind of fork, one side of which, namely, KL, was extended neer the length of KI, the other, M, was very short.

The transverse Sections of the stems of these branchings, manifested the shape or figure of it to be much like INOE, which consisted of a horny skin or covering, and a white seemingly frothy pith, much like the make of the main stem of a Feather.

The use of this strange kind of form, is indeed more admirable then all the rest, and such as deserves to be much more seriously examin'd and consider'd, then I have hitherto found time or ability to do; for certainly, it may very much instruct us in the nature of the Air, especially as to some properties of it.

The stems of the Downy branches INOE, being rang'd in the order visible enough to the naked eye, at the distance of IF, or somewhat more, the collateral stalks and leaves (if I may so call those bodies I newly described) are so rang'd, that the leaves or hairy stalks of the one side lie at top, or are incumbent on the stalks of the other, and Schem. 22.
Fig. 2.
cross each other, much after the manner express'd in the second Figure of the 22. Scheme, by which means every of those little hooked fibres of the leaved stalk get between the naked stalks, and the stalks being full of knots, and a prety way dis-join'd, so as that the fibres can easily get between them, the two parts are so closely and admirably woven together, that it is able to impede, for the greatest part, the transcursion of the Air; and though they are so exceeding small, as that the thickness of one of these stalks amounts not to a 500. part of an Inch, yet do they compose so strong a texture, as, notwithstanding the exceeding quick and violent beating of them against the Air, by the strength of the Birds wing, they firmly hold together. And it argues an admirable providence of Nature in the contrivance and fabrick of them; for their texture is such, that though by any external injury the parts of them are violently dis-joyn'd, so as that the leaves and stalks touch not one another, and consequently several of these rents would impede the Bird's flying; yet, for the most part, of themselves they readily re-join and re-contex themselves, and are easily by the Birds stroking the Feather, or drawing it through its Bill, all of them settled and woven into their former and natural posture; for there are such an infinite company of those small fibres in the under side of the leaves, and most of them have such little crooks at their ends, that they readily catch and hold the stalks they touch.

From which strange contexture, it seems rational to suppose that there is a certain kind of mesh or hole so small, that the Air will not very easily pass through it, as I hinted also in the sixth Observation about small Glass Canes, for otherwise it seems probable, that Nature would have drawn over some kind of thin film which should have covered all those almost square meshes or holes, there seeming through the Microscope to be more then half of the surface of the Feather which is open and visibly pervious; which conjecture will yet seem more probable from the texture of the brushie wings of the Tinea argentea, or white Feather wing'd moth, which I shall anone describe. But Nature, that knows best its own laws, and the several properties of bodies, knows also best how to adapt and fit them to her designed ends, and whoso would know those properties, must endeavour to trace Nature in its working, and to see what course she observes. And this I suppose will be no inconsiderable advantage which the Schematisms and Structures of Animate bodies will afford the diligent enquirer, namely, most sure and excellent instructions, both as to the practical part of Mechanicks and to the Theory and knowledge of the nature of the bodies and motions.

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