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Micrographia by Robert Hooke

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Now, that the Fly is able to walk on Glass, proceeds partly from some
ruggedness of the surface: and chiefly from a kind of tarnish, or dirty
smoaky substance, which adheres to the surface of that very hard body; and
though the pointed parts cannot penetrate the substance of Glass, yet may
they find pores enough in the tarnish, or at least make them.

This Structure I somewhat the more diligently survey'd, because I could not
well comprehend, how, if there were such a glutinous matter in those
supposed Sponges, as most (that have observ'd that Object in a
_Microscope_) have hitherto believ'd, how, I say, the Fly could so readily
unglew and loosen its feet: and, because I have not found any other
creature to have a contrivance any ways like it, and chiefly, that we might
not be cast upon unintelligible explications of the _Phaenomena_ of Nature,
at least others then the true ones, where our senses were able to furnish
us with an intelligible, rationall and true one.

Somewhat a like contrivance to this of Flies shall we find in most other
Animals, such as all kinds of Flies and case-wing'd creatures; nay, in a
Flea, an Animal abundantly smaller then this Fly. Other creatures, as
Mites, the Land-Crab, &c. have onely one small very sharp Tallon at the end
of each of their legs, which all drawing towards the center or middle of
their body, inable these exceeding light bodies to suspend and fasten
themselves to almost any surface.

Which how they are able to do, will not seem strange, if we consider,
first, how little body there is in one of these creatures compar'd to their
superficies, or outside, their thickness, perhaps, oftentimes, not
amounting to the hundredth part of an Inch: Next, the strength and agility
of these creatures compar'd to their bulk, being, proportionable to their
bulk, perhaps, an hundred times stronger then an Horse or Man. And thirdly,
if we consider that Nature does always appropriate the instruments, so as
they are the most fit and convenient to perform their offices, and the most
simple and plain that possibly can be; this we may see further verify'd
also in the foot of a Louse which is very much differing from those I have
been describing, but more convenient and necessary for the place of its
habitation, each of his leggs being footed with a couple of small claws
which he can open or shut at pleasure, shap'd almost like the claws of a
Lobster or Crab, but with appropriated contrivances for his peculiar life,
which being to move its body to and fro upon the hairs of the creature it
inhabits, Nature has furnish'd one of its claws with joints, almost like
the joints of a man's fingers, so as thereby it is able to encompass or
grasp a hair as firmly as a man can a stick or rope.

Nor, is there a less admirable and wonderfull _Mechanism_ in the foot of a
Spider, whereby he is able to spin, weave, and climb, or run on his curious
transparent clew, of which I shall say more in the description of that
Animal.

And to conclude, we shall in all things find, that Nature does not onely
work Mechanically, but by such excellent and most compendious, as well as
stupendious contrivances, that it were impossible for all the reason in the
world to find out any contrivance to do the same thing that should have
more convenient properties. And can any be so sottish, as to think all
those things the productions of chance? Certainly, either their
Ratiocination must be extremely depraved, or they did never attentively
consider and contemplate the Works of the Al-mighty.

* * * * *


Observ. XXXVIII. _Of the Structure and motion of the Wings of _Flies_._

The Wings of all kinds of Insects, are, for the most part, very beautifull
Objects, and afford no less pleasing an Object to the mind to speculate
upon, then to the eye to behold. This of the blue Fly, among the rest,
wants not its peculiar ornaments and contrivances; it grows out of the
_Thorax_, or middle part of the body of a Fly, and is seated a little
beyond the center of gravity in the body towards the head, but that
_Excentricly_ is curiously balanc'd; first, by the expanded _Area_ of the
wings which lies all more backwards then the root, by the motion of them,
whereby the center of their vibration is much more backwards towards the
tail of the Fly then the root of the wing is. What the vibrative motion of
the wings is, and after what manner they are moved, I have endeavoured by
many trials to find out: And first for the manner of their motion, I
endeavoured to observe several of those kind of small Spinning Flies, which
will naturally suspend themselves, as it were, pois'd and steady in one
place of the air, without rising or falling, or moving forwards or
backwards; for by looking down on those, I could by a kind of faint shadow,
perceive the utmost extremes of the vibrative motion of their wings, which
shadow, whil'st they so endeavoured to suspend themselves, was not very
long, but when they endeavour'd to flie forwards, it was somewhat longer;
next, I tried it, by fixing the leggs of a Fly upon the top of the stalk of
a feather, with Glew, Wax, &c. and then making it endeavour to flie away;
for being thereby able to view it in any posture, I collected that the
motion of the wing was after this manner. The extreme limits of the
vibrations were usually somewhat about the length of the body distant from
one another, oftentimes shorter, and sometimes also longer; that the
formost limit was usually a little above the back, and the hinder somwhat
beneath the belly; between which two limits, if one may ghess by the sound,
the wing seem'd to be mov'd forwards and backwards with an equal velocity:
And if one may (from the shadow or faint representation the wings afforded,
and from the consideration of the nature of the thing) ghess at the posture
or manner of the wings moving between them, it seem'd to be this: The wing
being suppos'd placed in the upmost limit, seems to be put so that the
plain of it lies almost _horizontal_, but onely the forepart does dip a
little, or is somewhat more deprest; in this position is the wing vibrated
or mov'd to the lower limit, being almost arrived at the lower limit, the
hinder part of the wing moving somewhat faster then the former, the _Area_,
of the wing begins to dip behind, and in that posture seems it to be mov'd
to the upper limit back again, and thence back again in the first posture,
the former part of the _Area_ dipping again, as it is moved downwards by
means of the quicker motion of the main stem which terminates or edges the
forepart of the wing. And these vibrations or motions to and fro between
the two limits seem so swift, that 'tis very probable (from the sound it
affords, if it be compar'd with the vibration of a musical string, tun'd
unison to it) it makes many hundreds, if not some thousands of vibrations
in a second minute of time. And, if we may be allow'd to ghess by the
sound, the wing of a Bee is yet more swift, for the tone is much more
acute, and that, in all likelihood, proceeds from the exceeding swift
beating of the air by the small wing. And it seems the more likely too,
because the wing of a Bee is less in proportion to its body, then the other
wing to the body of a Fly; so that for ought I know, it may be one of the
quickest vibrating _spontaneous_ motions of any in the world; and though
perhaps there may be many Flies in other places that afford a yet more
shrill note with their wings, yet 'tis most probable that the quickest
vibrating _spontaneous_ motion is to be found in the wing of some creature.
Now, if we consider the exceeding quickness of these Animal spirits that
must cause these motions, we cannot chuse but admire the exceeding
vividness of the governing faculty or _Anima_ of the Insect, which is able
to dispose and regulate so the the motive faculties, as to cause every
peculiar organ, not onely to move or act so quick, but to do it also so
regularly.

Whil'st I was examining and considering the curious _Mechanism_ of the
wings, I observ'd that under the wings of most kind of Flies, Bees, &c.
there were plac'd certain _pendulums_ or extended drops (as I may so call
them from their resembling motion and figure) for they much resembled a
long hanging drop of some transparent viscous liquor; and I observed them
constantly to move just before the wings of the Fly began to move, so that
at the first sight I could not but ghess, that there was some excellent
use, as to the regulation of the motion of the wing, and did phancy, that
it might be something like the handle of a Cock, which by vibrating to and
fro, might, as 'twere, open and shut the Cock, and thereby give a passage
to the determinate influences into the Muscles; afterwards, upon some other
trials, I suppos'd that they might be for some use in respiration, which
for many reasons I suppose those Animals to use, and, me thought, it was
not very improbable, but that they might have convenient passages under the
wings for the emitting, at least, of the air, if not admitting, as in the
gills of Fishes is most evident; or, perhaps, this _Pendulum_ might be
somewhat like the staff to a Pump, whereby these creatures might exercise
their _Analogous_ lungs, and not only draw in, but force out, the air they
live by: but these were but conjectures, and upon further examination
seem'd less probable.

The fabrick of the wing, as it appears through a moderately magnifying
_Microscope_, seems to be a body consisting of two parts, as is visible in
the 4. _Figure_ of the 23. _Scheme_; and by the 2. _Figure_ of the 26.
_Scheme_; the one is a quilly or finny substance, consisting of several
long, slender and variously bended quills or wires, something resembling
the veins of leaves; these are, as 'twere, the finns or quills which
stiffen the whole _Area_, and keep the other part distended, which is a
very thin transparent skin or membrane variously folded, and platted, but
not very regularly, and is besides exceeding thickly bestuck with
innumerable small bristles, which are onely perceptible by the bigger
magnifying _Microscope_, and not with that neither, but with a very
convenient augmentation of sky-light projected on the Object with a burning
Glass, as I have elsewhere shew'd, or by looking through it against the
light.

In steed of these small hairs, in several other Flies, there are infinite
of small Feathers, which cover both the under and upper sides of this thin
film as in almost all the sorts of Butterflies and Moths: and those small
parts are not onely shap'd very much like the feathers of Birds, but like
those variegated with all the variety of curious bright and vivid colours
imaginable; and those feathers are likewise so admirably and delicately
rang'd, as to compose very fine flourishings and ornamental paintings, like
_Turkie_ and _Persian_ Carpets, but of far more surpassing beauty, as is
evident enough to the naked eye, in the painted wings of Butterflies, but
much more through an ordinary _Microscope_.

Intermingled likewise with these hairs, may be perceived multitudes of
little pits, or black spots, in the exended membrane, which seem to be the
root of the hairs that grow on the other side; these two bodies seem
dispers'd over the whole surface of the wing.

The hairs are best perceiv'd, by looking through it against the light, or,
by laying the wing upon a very white piece of Paper, in a convenient light,
for thereby every little hair most manifestly appears; a _Specimen_ of
which you may observe drawn in the fourth _Figure_ of the 23. _Scheme_, AB,
CD, EF whereof represent some parts of the bones or quills of the wing,
each of which you may perceive to be cover'd over with a multitude of
scales, or bristles, the former AB, is the biggest stem of all the wing,
and may be properly enough call'd the cut-air, it being that which
terminates and stiffens the formost edge of the wing; the fore-edge of this
is arm'd with a multitude of little brisles, or Tenter-hooks, in some
standing regular and in order, in others not; all the points of which are
directed from the body towards the tip of the wing, nor is this edge onely
thus fring'd, but even all the whole edge of the wing is covered with a
small fringe, consisting of short and more slender brisles.

This Subject, had I time, would afford excellent matter for the
contemplation of the nature of wings and of flying, but, because I may,
perhaps, get a more convenient time to prosecute that speculation, and
recollect several Observations that I have made of that particular. I shall
at present proceed to

* * * * *


Observ. XXXIX. _Of the Eyes and Head of a _Grey drone-Fly_,
and of several other creatures._

I took a large grey _Drone-Fly_, that had a large head, but a small and
slender body in proportion to it, and cutting off its head, I fix'd it with
the forepart or face upwards upon my Object Plate (this I made choice of
rather then the head of a great blue Fly, because my enquiry being now
about the eyes, I found this Fly to have, first the biggest clusters of
eyes in proportion to his head, of any small kind of Fly that I have yet
seen, it being somewhat inclining towards the make of the large
_Dragon-Flies_. Next, because there is a greater variety in the knobs or
balls of each cluster, then is of any small Fly.) Then examining it
according to my usual manner, by varying the degrees of light, and altering
its position to each kinde of light, I drew that representation of it which
is delineated in the 24. _Scheme_, and found these things to be as plain
and evident, as notable and pleasant.

_First_, that the greatest part of the face, nay, of the head, was nothing
else but two large and _protuberant_ bunches, or _prominent_ parts, ABCDEA,
the surface of each of which was all cover'd over, or shap'd into a
multitude of small _Hemispheres_, plac'd in a _triagonal_ order, that being
the closest and most compacted, and in that order, rang'd over the whole
surface of the eye in very lovely rows, between each of which, as is
necessary, were left long and regular trenches, the bottoms of every of
which, were perfectly intire and not at all perforated or drill'd through,
which I most certainly was assured of, by the regularly reflected Image of
certain Objects which I mov'd to and fro between the head and the light.
And by examining the _Cornea_ or outward skin, after I had stript it off
from the several substances that lay within it, and by looking both upon
the inside and against the light.

_Next_, that of those multitudes of _Hemispheres_, there were observable
two degrees of bigness, the half of them that were lowermost, and look'd
toward the ground or their own leggs, namely, CDE, CDE being a pretty deal
smaller then the other, namely, ABCE, ABCE, that look'd upward, and
side-ways, or foreright, and backward, which variety I have not found in
any other small Fly.

_Thirdly_, that every one of these _Hemispheres_, as they seem'd to be
pretty neer the true shape of a _Hemisphere_, so was the surface exceeding
smooth and regular, reflecting as exact, regular, and perfect an Image of
any Object from the surface of them, as a small Ball of Quick-silver of
that bigness would do, but nothing neer so vivid, the reflection from these
being very languid, much like the reflection from the outside of Water,
Glass, Crystal, &c. In so much that in each of these _Hemispheres_, I have
been able to discover a Land-scape of those things which lay before my
window, one thing of which was a large Tree, whose trunk and top I could
plainly discover, as I could also the parts of my window, and my hand and
fingers, if I held it between the Window and the Object; a small draught of
nineteen of which, as they appear'd in the bigger Magnifying-glass to
reflect the Image of the two windows of my Chamber, are delineated in the
third _Figure_ of the 23. _Scheme_.

_Fourthly_, that these rows were so dispos'd, that there was no quarter
visible from his head that there was not some of these _Hemispheres_
directed against, so that a Fly may be truly said to have _an eye every
way_, and to be really _circumspect_. And it was further observable, that
that way where the trunk of his body did hinder his prospect backward,
these _protuberances_ were elevated, as it were, above the plain of his
shoulders and back, so that he was able to see backwards also over his
back.

_Fifthly_, in living Flies, I have observ'd, that when any small mote or
dust, which flies up and down the air, chances to light upon any part of
these knobs, as it is sure to stick firmly to it and not fall, though
through the _Microscope_ it appears like a large stone or stick (which one
would admire, especially since it is no ways probable that there is any wet
or glutinous matter upon these _Hemispheres_, but I hope I shall render the
reason in another place) so the Fly presently makes use of his two
fore-feet in stead of eye-lids, with which, as with two Brooms or Brushes,
they being all bestuck with Brisles, he often sweeps or brushes off what
ever hinders the prospect of any of his _Hemispheres_, and then, to free
his leggs from that dirt, he rubs them one against another, the pointed
Brisles or Tenters of which looking both one way, the rubbing of them to
and fro one against another, does cleanse them in the same manner as I have
observ'd those that Card Wool, to cleanse their Cards, by placing their
Cards, so as the teeth of both look the same way, and then rubbing them one
against another. In the very same manner do they brush and cleanse their
bodies and wings, as I shall by and by shew; other creatures have other
contrivances for the cleansing and cleering their eyes.

_Sixthly_ that the number of the _Pearls_ or _Hemispheres_ in the clusters
of this Fly, was neer 14000. which I judged by numbering certain rows of
them several ways, and casting up the whole content, accounting each
cluster to contain about seven thousand Pearls, three thousand of which
were of a size, and consequently the rows not so thick, and the foure
thousand I accounted to be the number of the smaller Pearls next the feet
and _proboscis_. Other Animals I observ'd to have yet a greater number, as
the _Dragon-Fly_ or _Adderbolt_: And others to have a much less company, as
an _Ant_, &c. and several other small Flies and Insects.

_Seventhly_, that the order of these eies or _Hemispheres_ was altogether
curious and admirable, they being plac'd in all kind of Flies, and _aerial_
animals, in a most curious and regular ordination of triangular rows, in
which order they are rang'd the neerest together that possibly they can,
and consequently leave the least pits or trenches between them. But in
_Shrimps_, _Crawfishes_, _Lobsters_, and such kinds of _Crustaceous_ water
Animals, I have yet observ'd them rang'd in a quadrangular order, the rows
cutting each other at right angles, which as it admits of a less number of
Pearls in equal surfaces; so have those creatures a recompence made them,
by having their eyes a little movable in their heads, which the other
altogether want. So infinitely wise and provident do we find all the
Dispensations in Nature, that certainly _Epicurus_, and his followers, must
very little have consider'd them, who ascrib'd those things to the
production of chance, that wil, to a more attentive considerer, appear the
products of the highest Wisdom and Providence.

Upon the Anatomy or Dissection of the Head, I observ'd these particulars:

First, that this outward skin, like the _Cornea_ of the eyes of the greater
Animals, was both flexible and transparent, and seem'd, through the
_Microscope_ perfectly to resemble the very substance of the _Cornea_ of a
man's eye; for having cut out the cluster, and remov'd the dark and
_mucous_ stuff that is subjacent to it, I could see it transparent like a
thin piece of skin, having as many cavities in the inside of it, and rang'd
in the same order as it had _protuberances_ on the outside, and this
propriety, I found the same in all the Animals that had it, whether Flies
or Shell-Fish.

Secondly, I found that all Animals that I have observ'd with those kind of
eyes; have within this _Cornea_, a certain cleer liquor or juice, though in
a very little quantity, and,

I observ'd thirdly, that within that cleer liquor, they had a kind of dark
_mucous_ lining, which was all spread round within the cavity of the
clutter, and seem'd very neer adjoining to it, the colour of which, in some
Flies, was grey; in others, black, in others red; in others, of a mix'd
colour; in others, spotted; and that the whole clusters, when look'd on
whilst the Animal was living, or but newly kill'd, appear'd of the same
colour that this coat (as I may so call it) appear'd of, when that outward
skin, or _Cornea_, was remov'd.

Fourthly, that the rest of the capacity of the clusters was in some, as in
Dragon Flies, &c. hollow, or empty; in others fill'd with some kind of
substance; in blue Flies, with a reddish musculous substance, with _fibres_
tending from the center or bottom outwards; and divers other, with various
and differing kinds of substances.

That this curious contrivance is the organ of sight to all those various
_Crustaceous_ Animals, which are furnish'd with it, I think we need not
doubt, if we consider but the several congruities it has with the eyes of
greater creatures.

As first, that it is furnish'd with a _Cornea_, with a _transparent
humour_, and with a _uvea_ or _retina_, that the Figure of each of the
small _Hemispheres_ are very _Spherical_, exactly polish'd, and most vivid,
lively and plump, when the Animal is living, as in greater Animals, and in
like manner dull, flaccid, and irregular, or shrunk, when the Animal is
dead.

Next, that those creatures that are furnish'd with it, have no other organs
that have any resemblance to the known eyes of other creatures.

Thirdly, that those which they call the eyes of Crabs, Lobsters, Shrimps,
and the like, and are really so, are _Hemispher'd_, almost in the same
manner as these of Flies are. And that they really are so, I have very
often try'd, by cutting off these little movable knobs, and putting the
creature again into the water, that it would swim to and fro, and move up
and down as well as before, but would often hit it self against the rocks
or stones; and though I put my hand just before its head, it would not at
all start or fly back till I touch'd it, whereas whil'st those were
remaining, it would start back, and avoid my hand or a stick at a good
distance before it touch'd it. And if in _crustaceous_ Sea-animals, then it
seems very probable also, that these knobs are the eyes in _crustaceous_
Insects, which are also of the same kind, onely in a higher and more active
Element; this the conformity or congruity of many other parts common to
either of them, will strongly argue, their _crustaceous_ armour, their
number of leggs, which are six, beside the two great claws, which answer to
the wings in Insects; and in all kind of Spiders, as also in many other
Insects that want wings, we shall find the compleat number of them, and not
onely the number, but the very shape, figure, joints, and claws of Lobsters
and Crabs, as is evident in Scorpions and Spiders, as is visible in the
second _Figure_ of the 31. _Scheme_, and in the little Mite-worm, which I
call a Land-crab, describ'd in the second Figure of the 33. _Scheme_, but
in their manner of generation being oviparous, &c. And it were very worthy
observation, whether there be not some kinds of transformation and
metamorphosis in the several states of _crustaceous_ water-animals, as
there is in several sorts of Insects; for if such could be met with, the
progress of the variations would be much more conspicuous in those larger
Animals, then they can be in any kind of Insects our colder Climate
affords.

These being their eyes, it affords us a very pretty Speculation to
contemplate their manner of vision, which, as it is very differing from
that of _biocular_ Animals, so is it not less admirable.

That each of these Pearls or _Hemispheres_ is a perfect eye, I think we
need not doubt, if we consider onely the outside or figure of any one of
them, for they being each of them cover'd with a transparent protuberant
_Cornea_, and containing a liquor within them, resembling the watry or
glassie humours of the eye, must necessarily refract all the parallel Rays
that fall on them out of the air, into a point not farr distant within
them, where (in all probability) the _Retina_ of the eye is placed, and
that opacous, dark, and mucous inward coat that (I formerly shew'd) I found
to subtend the concave part of the cluster is very likely to be that
_tunicle_ or coat, it appearing through the _Microscope_ to be plac'd a
little more than a Diameter of those Pearls below or within the _tunica
cornea_. And if so, then is there in all probability, a little Picture or
Image of the objects without, painted or made at the bottom of the _Retina_
against every one of those Pearls, so that there are as many impressions on
the _Retina_ or opacous skin, as there are Pearls or _Hemispheres_ on the
cluster. But because it is impossible for any protuberant surface
whatsoever, whether _sphaerial_ or other, so to refract the Rays that come
from farr remote _lateral_ points of any Object as to collect them again,
and unite them each in a distinct point, and that onely those Rays which
come from some point that lies in the _Axis_ of the Figure produc'd, are so
accurately refracted to one and the same point again, and that the
_lateral_ Rays, the further they are remov'd, the more imperfect is their
refracted confluence; It follows therefore, that onely the Picture of those
parts of the external objects that lie in, or neer, the _Axis_ of each
_Hemisphere_, are discernably painted or made on the _Retina_ of each
_Hemisphere_, and that therefore each of them can distinctly sensate or see
onely those parts which are very neer perpendicularly oppos'd to it, or lie
in or neer its optick _Axis_. Now, though there may be by each of these
eye-pearls, a representation to the Animal of a whole _Hemisphere_ in the
same manner as in a man's eye there is a picture or sensation in the
_Retina_ of all the objects lying almost in an _Hemisphere_; yet, as in a
man's eye also, there are but some very few points which liyng in, or neer,
the optick _Axis_ are distinctly discern'd: So there may be multitudes of
Pictures made of an Object in the several Pearls, and yet but one, or some
very few that are distinct; The representation of any object that is made
in any other Pearl, but that which is directly, or very neer directly,
oppos'd, being altogether confus'd and unable to produce a distinct vision.

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