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 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.
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 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 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 disjoyn’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.
* * * * *
Observ. XXXVI. _Of _Peacocks_, _Ducks_, and other _Feathers_ of changeable
colours._
The parts of the Feathers of this glorious Bird appear, through the
_Microscope_, no less gaudy then do the whole Feathers; for, as to the
naked eye ’tis evident that the stem or quill of each Feather in the tail
sends out multitudes of _Lateral_ branches, such as AB in the third Figure
of the 22. _Scheme_ represents a small part of about ¹⁄₃₂ part of an Inch
long, and each of the _lateral_ branches emit multitudes of little sprigs,
threads or hairs on either side of them, such as CD, CD, CD, so each of
those threads in the _Microscope_ appears a large long body, consisting of
a multitude of bright reflecting parts, whose Figure ’tis no easie matter
to determine, as he that examines it shall find; for every new position of
it to the light makes it perfectly seem of another form and shape, and
nothing what it appear’d a little before; nay, it appear’d very differing
ofttimes from so seemingly inconsiderable a circumstance, that the
interposing of ones hand between the light and it, makes a very great
change, and the opening or shutting a Casement and the like, very much
diversifies the appearance. And though, by examining the form of it very
many ways, which would be tedious here to enumerate, I suppose I have
discover’d the true Figure of it, yet oftentimes, upon looking on it in
another posture, I have almost thought my former observations deficient,
though indeed, upon further examination, I have found even those also to
confirm them.
These threads therefore I find to be a _congeries_ of small _Laminæ_ or
plates, as eeeee, &c. each of them shap’d much like this of abcd, in the
fourth _Figure_, the part ac being a ridge, prominency, or stem, and b and
d the corners of two small thin Plates that grow unto the small stalk in
the middle, so that they make a kind of little feather; each of these
Plates lie one close to another, almost like a company of sloping ridge or
gutter Tyles; they grow on each side of the stalk opposite to one another,
by two and two, from top to bottom, in the manner express’d in the fifth
Figure, the tops of the lower covering the roots of the next above them;
the under side of each of these laminated bodies, is of a very dark and
opacous substance, and suffers very few Rays to be trajected, but reflects
them all toward that side from whence they come, much like the foil of a
Looking-glass; but their upper sides seem to me to consist of a multitude
of thin plated bodies, which are exceeding thin, and lie very close
together, and thereby, like mother of Pearl shells, do not onely reflect a
very brisk light, but tinge that light in a most curious manner; and by
means of various positions, in respect of the light, they reflect back now
one colour, and then another, and those most vividly.
Now, that these colours are onely _fantastical_ ones, that is, such as
arise immediately from the refractions of the light, I found by this, that
water wetting these colour’d parts, destroy’d their colours, which seem’d
to proceed from the alteration of the reflection and refraction. Now,
though I was not able to see those hairs at all transparent by a common
light, yet by looking on them against the Sun, I found them to be ting’d
with a darkish red colour, nothing a-kin to the curious and lovely greens
and blues they exhibited.
What the reason of colour seems to be in such thin plated bodies, I have
elsewhere shewn. But how water cast upon those threads destroys their
colours, I suppose to be perform’d thus; The water falling upon these
plated bodies from its having a greater congruity to Feathers then the Air,
insinuates it self between those Plates, and so extrudes the strong
reflecting Air, whence both these parts grow more transparent, as the
_Microscope_ informs, and colourless also, at best retaining a very faint
and dull colour. But this wet being wasted away by the continual
evaporations and steams that pass through them from the Peacock, whil’st
that Bird is yet alive, the colours again appear in their former luster,
the _interstitia_ of these Plates being fill’d with the strongly reflecting
Air.
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.
* * * * *