Micrographia by Robert Hooke

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The _Thorax_ seem'd cas'd with another kind of substance then the belly,
namely, with a thin transparent horny substance, which upon the fasting of
the Creature did not grow flaccid; through this I could plainly see the
blood, suck'd from my hand, to be variously distributed, and mov'd to and
fro; and about G there seem'd a pretty big white substance, which seem'd to
be moved within its _thorax_; besides, there appear'd very many small
milk-white vessels, which crost over the breast between the legs, out of
which, on either side, were many small branchings, these seem'd to be the
veins and arteries, for that which is analogus to blood in all Insects is
milk-white.

The belly is covered with a transparent substance likewise, but more
resembling a skin then a shell, for 'tis grain'd all over the belly just
like the skin in the palms of a man's hand, and when the belly is empty,
grows very flaccid and wrinkled; at the upper end of this is placed the
stomach HH, and perhaps also the white spot II may be the liver or
_pancreas_, which, by the _peristalick_ motion of the guts, is a little
mov'd to and fro, not with a _systole_ and _diastole_, but rather with a
thronging or justling motion. Viewing one of these Creatures, after it had
fasted two dayes, all the hinder part was lank and flaccid, and the white
spot II hardly mov'd, most of the white branchings disappear'd, and most
also of the redness or sucked blood in the guts, the _peristaltick_ motion
of which was scarce discernable; but upon the suffering it to suck, it
presently fill'd the skin of the belly, and of the six scolop'd embosments
on either side, as full as it could be stuft, the stomach and guts were as
full as they could hold; the _peristaltick_ motion of the gut grew quick,
and the justling motion of II accordingly; multitudes of milk-white vessels
seem'd quickly filled, and turgid, which were perhaps the veins and
arteries and the Creature was so greedy, that though it could not contain
more, yet it continued sucking as fast as ever, and as fast emptying it
self behind: the digestion of this Creature must needs be very quick, for
though I perceiv'd the blood thicker and blacker when suck'd, yet, when in
the guts, it was of a very lovely ruby colour, and that part of it, which
was digested into the veins, seemed white; whence it appears, that a
further digestion of blood may make it milk, at least of a resembling
colour: What is else observable in the figure of this Creature, may be seen
by the 35. _Scheme_.

* * * * *

Observ. LV. _Of _Mites_._

The least of _Reptiles_ I have hitherto met with, is a Mite, a Creature
whereof there are some so very small, that the sharpest sight, unassisted
with Glasses, is not able to discern them, though, being white of
themselves, they move on a black and smooth surface; and the Eggs, out of
which these Creatures seem to be hatch'd, are yet smaller, those being
usually not above a four or five hundredth part of a well grown Mite, and
those well grown Mites not much above one hundredth of an inch in
thickness; so that according to this reckoning there may be no less then a
million of well grown Mites contain'd in a cubick inch, and five hundred
times as many Eggs.

Notwithstanding which minuteness a good _Microscope_ discovers those small
movable specks to be very prettily shap'd Insects, each of them furnished
with eight well shap'd and proportion'd legs, which are each of them
joynted or bendable in eight several places, or joynts, each of which is
covered, for the most part, with a very transparent shell, and the lower
end of the shell of each joynt is fringed with several small hairs; the
contrivance of the joynts seems the very same with that of Crabs and
Lobsters legs, and like those also, they are each of them terminated with a
very sharp claw or point; four of these legs are so placed, that they seem
to draw forwards, the other four are placed in a quite contrary position,
thereby to keep the body backwards when there is occasion.

[15]The body, as in other larger Insects, consists of three regions or
parts; the hinder or belly A, seems covered with one intire shell, the
middle, or chest, seems divided into two shells BC. which running one
within the other, the Mite is able to shrink in and thrust out as it finds
occasion, as it can also the snout D. The whole body is pretty transparent,
so that being look'd on against the light, divers motions within its body
may be perceived; as also all the parts are much more plainly delineable,
then in other postures, to the light. The shell, especially that which
covers the back, is curiously polisht, so that 'tis easie to see, as in a
_convex_ Looking-glass, or _foliated_ Glass-ball, the picture of all the
objects round about; up and down, in several parts of its body, it has
several small long white hairs growing out of its shell, which are often
longer then the whole body, and are represented too short in the first and
second Figures; they seem all pretty straight and plyable, save only two
upon the fore-part of its body, which seem to be the horns, as may be seen
in the Figures; the first whereof is a prospect of a smaller sort of Mites
(which are usually more plump) as it was _passant_ to and fro; the second
is the prospect of one fixt on its tail (by means of a little mouth-glew
rub'd on the object plate) exhibiting the manner of the growing of the
legs, together with their several joynts.

This Creature is very much diversify'd in shape, colour, and divers other
properties, according to the nature of the substance out of which it seems
to be ingendred and nourished, being in one substance more long, in another
more round, in some more hairy, in others more smooth, in this nimble, in
that slow, here pale and whiter, there browner, blacker, more transparent,
&c. I have observed it to be resident almost on all kinds of substances
that are mouldy, or putrifying, and have seen it very nimbly meshing
through the thickets of mould, and sometimes to lye _dormant_ underneath
them; and 'tis not unlikely, but that it may feed on that vegetating
substance, _spontaneous Vegetables_ seeming a food proper enough for
_spontaneous Animals_,

But whether indeed this Creature, or any other, be such or not, I cannot
positively, from any Experiment, or Observation, I have yet made,
determine. But, as I formerly hinted, it seems probable, that some kind of
wandring Mite may sow, as 'twere, the first seeds, or lay the first eggs,
in those places, which Nature has instructed them to know convenient for
the hatching and nourishing their young; and though perhaps the prime
Parent might be of a shape very differing from what the offspring, after a
little while, by reason of the substance they feed on, or the Region (as
'twere) they inhabite; yet perhaps even one of these alter'd progeny,
wandering again from its native soil, and lighting on by chance the same
place from whence its prime Parent came, and there settling, and planting,
may produce a generation of Mites of the same shapes and properties with
the first wandring Mite: And from some such accidents as these, I am very
apt to think, the most sorts of Animals, generally accounted _spontaneous_,
have their _origination_, and all those various sorts of Mites, that are to
be met with up and down in divers putrifying substances, may perhaps be all
of the same kind, and have sprung from one and the same sort of Mites at
the first.

* * * * *

Observ. LVI. _Of a small Creature hatch'd on a Vine._

There is, almost all the Spring and Summer time, a certain small, round,
white Cobweb, as 'twere, about the bigness of a Pea, which sticks very
close and fast to the stocks of Vines nayl'd against a warm wall: being
attentively viewed, they seem cover'd, upon the upper side of them, with a
small husk, not unlike the scale, or shell of a Wood-louse, or Hog-louse, a
small Insect usually found about rotten wood, which upon touching presently
rouls it self into the form of a peppercorn: Separating several of these
from the stock, I found them, with my _Microscope_, to consist of a shell,
which now seemed more likely to be the husk of one of these Insects: And
the fur seem'd a kind of cobweb, consisting of abundance of small
filaments, or sleaves of cobwebs. In the midst of this, if they were not
hatch'd, and run away before, the time of which hatching was usually about
the latter end of _June_, or beginning of _July_, I have often found
abundance of small brown Eggs, such as A and B in the second Figure of the
36. _Scheme_, much about the bigness of Mites Eggs; and at other times,
multitudes of small Insects, shaped exactly like that in the third Figure
marked with X. Its head large, almost half the bigness of its body, which
is usual in the _foetus_ of most Creatures. It had two small black eyes
_aa_, and two small long joynted and brisled horns _bb_. The hinder part of
its body seem'd to consist of nine scales, and the last ended in a forked
tayl, much like that of a _Cutio_, or Wood louse, out of which grew two
long hairs; they ran to and fro very swiftly, and were much of the bigness
of a common Mite, but some of them less: The longest of them seem'd not the
hundredth part of an inch, and the Eggs usually not above half as much.
They seemed to have six legs, which were not visible in this I have here
delineated, by reason they were drawn under its body.

If these Minute creatures were _Wood-lice_ (as indeed from their own shape
and from the frame, the skin, or shell, that grows on them, one may with
great probability ghess) it affords us an Instance, whereof perhaps there
are not many like in Nature, and that is, of the prodigious increase of
these Creatures, after they are hatch'd and run about; for a common
Wood-louse, of about half an inch long, is no less then a hundred and
twenty five thousand times bigger then one of these, which though indeed it
seems very strange, yet I have observed the young ones of some Spiders have
almost kept the same proportion to their Dam.

This, methinks, if it be so, does in the next place hint a Quaery, which
may perhaps deserve a little further examination: And that is, Whether
there be not many of those minute Creatures, such as Mites, and the like,
which, though they are commonly thought of otherwise, are only the _pully_,
or young ones, of much bigger Insects, and not the generating, or parent
_Insect_, that has layd those Eggs; for having many times observ'd those
Eggs, which usually are found in great abundance where Mites are found, it
seems something strange, that so small an Animal should have an Egg so big
in proportion to its body. Though on the other side, I must confess, that
having kept divers of those Mites inclosed in a box for a good while, I did
not find them very much augmented beyond their usual bigness.

What the husk and cobweb of this little white substance should be, I cannot
imagine, unless it be, that the old one, when impregnated with Eggs, should
there stay, and fix it self on the Vine, and dye, and all the body by
degrees should rot, save only the husk, and the Eggs in the body: And the
heat, or fire, as it were, of the approaching Sun-beams should vivifie
those Relicts of the corrupted Parent, and out of the ashes, as 'twere, (as
it is fabled of the _Phoenix_) should raise a new _offspring_ for the
perpetuation of the _Species_. Nor will the cobweb, as it were, in which
these Eggs are inclos'd, make much against this Conjecture; for we may, by
those cobwebs that are carried up and down the Air after a Fog (which with
my _Microscope_ I have discovered to be made up of an infinite company of
small filaments or threads) learn, that such a texture of body may be
otherwise made then by the spinning of a Worm.

* * * * *

Observ. LVII. _Of the _Eels_ in Vinegar._

Of these small Eels, which are to be found in divers sorts of Vinegar, I
have little to add besides their Picture, which you may find drawn in the
third Figure of the 25. _Scheme_: That is, they were shaped much like an
Eel, save only that their nose A, (which was a little more opacous then the
rest of their body) was a little sharper, and longer, in proportion to
their body, and the wrigling motion of their body seem'd to be onely
upwards and downwards, whereas that of Eels is onely side wayes: They
seem'd to have a more opacous part about B, which might, perhaps, be their
Gills; it seeming always the same proportionate distant from their nose,
from which, to the tip of their tail, C, their body seem'd to taper.

Taking several of these out of their Pond of Vinegar, by the net of a small
piece of filtring Paper, and laying them on a black smooth Glass plate, I
found that they could wriggle and winde their body, as much almost as a
Snake, which made me doubt, whether they were a kind of Eal or Leech.

I shall add no other observations made on this minute Animal, being
prevented herein by many excellent ones already publish'd by the ingenious,
Doctor _Power_, among his _Microscopical_ Observations, save onely that a
quantity of Vinegar repleat with them being included in a small Viol, and
stop'd very close from the ambient air, all the included Worms in a very
short time died, as if they had been stifled.

And that their motion seems (contrary to what we may observe in the motion
of all other Infects) exceeding slow. But the reason of it seems plain, for
being to move to and fro after that manner which they do, by waving onely,
or wrigling their body; the tenacity, or glutinousness, and the density or
resistance of the fluid _medium_ becomes so exceeding sensible to their
extremely minute bodies, that it is to me indeed a greater wonder that they
move them so fast as they do, then that they move them no faster. For what
a vastly greater proportion have they of their superficies to their bulk,
then Eels or other larger Fishes, and next, the tenacity and density of the
liquor being much the same to be moved, both by the one and the other, the
resistance or impediment thence arising to the motions made through it,
must be almost infinitely greater to the small one then to the great. This
we find experimentally verify'd in the Air, which though a _medium_ a
thousand times more rarify'd then the water, the resistance of it to
motions made through it, is yet so sensible to very minute bodies, that a
Down-feather (the least of whose parts seem yet bigger then these Eels, and
many of them almost incomparably bigger, such as the quill and stalk) is
suspended by it, and carried to and fro as if it had no weight.

* * * * *

Observ. LVIII. _Of a new Property in the _Air_, and several other
transparent _Mediums_ nam'd _Inflection_, whereby very many considerable
_Phaenomena_ are attempted to be solv'd, and divers other uses are hinted._

Since the Invention (and perfecting in some measure) of _Telescopes_, it
has been observ'd by several, that the Sun and Moon neer the Horizon, are
disfigur'd (losing that exactly-smooth terminating circular limb, which
they are observ'd to have when situated neerer the Zenith) and are bounded
with an edge every way (especially upon the right and left sides) ragged
and indented like a Saw: which inequality of their limbs, I have further
observ'd, not to remain always the same, but to be continually chang'd by a
kind of fluctuating motion, not unlike that of the waves of the Sea, so as
that part of the limb, which was but even now nick'd or indented in, is now
protuberant, and will presently be sinking again; neither is this all but
the whole body of the Luminaries, do in the _Telescope_, seem to be
depress'd and slatted, the upper, and more especially the under side
appearing neerer to the middle then really they are, and the right and left
appearing more remote: whence the whole _Area_ seems to be terminated by a
kind of Oval. It is further observ'd, that the body, for the most part,
appears red, or of some colour approaching neer unto it, as some kind of
yellow; and this I have always mark'd, that the more the limb is slatted or
ovalled, the more red does the body appear, though not always the contrary.
It is further observable, that both fix'd Stars and Planets, the neerer
they appear to the Horizon, the more red and dull they look, and the more
they are observ'd to twinkle; in so much, that I have seen the Dog-starr to
vibrate so strong and bright a radiation of light, as almost to dazle my
eyes, and presently, almost to disappear. It is also observable, that those
bright scintillations neer the Horizon, are not by much so quick and sudden
in their consecutions of one another, as the nimbler twinklings of Stars
neerer the Zenith. This is also notable, that the Starrs neer the Horizon,
are twinkled with several colours; so as sometimes to appear red, sometimes
more yellow, and sometimes blue, and this when the Starr is a pretty way
elevated above the Horizon. I have further, very often seen some of the
small Starrs of the fifth or sixth magnitude, at certain times to disappear
for a small moment of time, and again appear more conspicuous, and with a
greater luster. I have several times, with my naked eye, seen many smaller
Starrs, such as may be call'd of the seventh or eighth magnitude to appear
for a short space, and then vanish, which, by directing a small _Telescope_
towards that part they appear'd and disappear'd in; I could presently find
to be indeed small Starrs so situate, as I had seen them with my naked eye,
and to appear twinkling like the ordinary visible Stars; nay, in examining
some very notable parts of the Heaven, with a three foot Tube, me thought I
now and then, in several parts of the constellation, could perceive little
twinklings of Starrs, making a very short kind of apparition, and presently
vanishing, but noting diligently the places where they thus seem'd to play
at boe-peep, I made use of a very good twelve foot Tube, and with that it
was not uneasie to see those, and several other degrees of smaller Starrs,
and some smaller yet, that seem'd again to appear and disappear, and these
also by giving the same Object-glass a much bigger aperture, I could
plainly and constantly see appear in their former places; so that I have
observ'd some twelve several magnitudes of Starrs less then those of the
six magnitudes commonly recounted in the Globes.

It has been observ'd and confirm'd by the accuratest Observations of the
best of our modern Astronomers, that all the Luminous bodies appear above
the Horizon, when they really are below it. So that the Sun and Moon have
both been seen above the Horizon, whil'st the Moon has been in an Eclipse.
I shall not here instance in the great refractions, that the tops of high
mountains, seen at a distance, have been found to have; all which seem to
argue the Horizontal refraction, much greater then it is hitherto generally
believ'd.

I have further taken notice, that not onely the Sun, Moon and Starrs, and
high tops of mountains have suffer'd these kinds of refraction, but Trees,
and several bright Objects on the ground: I have often taken notice of the
twinkling of the reflections of the Sun from a Glass-window at a good
distance, and of a Candle in the night, but that is not so conspicuous, and
in observing the setting Sun, I have often taken notice of the tremulation
of the Trees and Bushes, as well as of the edges of the Sun. Divers of
these _Phaenomena_ have been taken notice of by several, who have given
several reasons of them, but I have not yet met with any altogether
satisfactory, though some of their conjectures have been partly true, but
partly also false. Setting my self therfore upon the inquiry of these
_Phaenomena_, I first endeavour'd to be very diligent in taking notice of
the several particulars and circumstances observable in them; and next, in
making divers particular Experiments, that might cleer some doubts, and
serve to determine, confirm, and illustrate the true and adaequate cause of
each; and upon the whole, I find much reason to think, that the true cause
of all these _Phaenomena_ is from the _inflection_, or _multiplicate
refraction_ of those Rays of light within the body of the _Atmosphere_, and
that it does not proceed from a _refraction_ caus'd by any terminating
_superficies_ of the Air above, nor from any such exactly defin'd
_superficies_ within the body of the _Atmosphere_.

This Conclusion is grounded upon these two Propositions:

First, that a _medium_, whose parts are unequally _dense_, and mov'd by
various motions and transpositions as to one another, will produce all
these visible effects upon the Rays of light, without any other
_coefficient_ cause.

Secondly, that there is in the Air or _Atmosphere_ such a variety in the
constituent parts of it, both as to their _density_ and _rarity_, and as to
their divers mutations and positions one to another.

By _Density_ and _Rarity_, I understand a property of a transparent body,
that does either more or less refract a Ray of light (coming obliquely upon
its superficies out of a third _medium_) toward its perpendicular: As I
call Glass a more dense body then Water, and Water a more rare body then
Glass, because of the refractions (more or less deflecting towards the
perpendicular) that are made in them, of a Ray of light out of the Air that
has the same inclination upon either of their superficies.

So as to the business of Refraction, spirit of Wine is a more _dense_ body
then Water, it having been found by an accurate Instrument that measures
the angles of Refractions to Minutes that for the same refracted angle of
30 deg..00'. in both those _Mediums_, the angle of incidence in Water was
but 41 deg..35'. but the angle of the incidence in the trial with spirit of
Wine was 42 deg.45'. But as to gravity, Water is a more _dense_ body then
spirit of Wine, for the proportion of the same Water, to the same very well
rectify'd spirit of Wine was, as 21. to 19.

So as to Refraction, Water is more Dense then Ice; for I have found by a
most certain Experiment, which I exhibited before divers illustrious
Persons of the _Royal Society_, that the Refraction of Water was greater
then that of Ice, though some considerable Authors have affirm'd the
contrary, and though the Ice be a very hard, and the Water a very fluid
body.

That the former of the two preceding Propositions is true, may be
manifested by several Experiments; As first, if you take any two liquors
differing from one another in density, but yet such as will readily mix: as
Salt Water, or Brine, & Fresh; almost any kind of Salt dissolv'd in Water,
and filtrated, so that it be cleer, spirit of Wine and Water; nay, spirit
of Wine, and spirit of Wine, one more highly rectify'd then the other, and
very many other liquors; if (I say) you take any two of these liquors, and
mixing them in a Glass Viol, against one side of which you have fix'd or
glued a small round piece of Paper, and shaking them well together (so that
the parts of them may be somewhat disturb'd and move up and down) you
endeavour to see that round piece of Paper through the body of the liquors,
you shall plainly perceive the Figure to wave, and to be indented much
after the same manner as the limb of the Sun through a _Telescope_ seems to
be, save onely that the mutations here, are much quicker. And if, in steed
of this bigger Circle, you take a very small spot, and fasten and view it
as the former, you will find it to appear much like the twinkling of the
Starrs, though much quicker: which two _Phaenomena_, (for I shall take
notice of no more at present, though I could instance in multitudes of
others) must necessarily be caus'd by an _inflection_ of the Rays within
the terminating superficies of the compounded _medium_, since the surfaces
of the transparent body through which the Rays pass to the eye, are not at
all altered or chang'd.

This _inflection_ (if I may so call it) I imagine to be nothing else, but a
_multiplicate refraction_, caused by the unequal _density_ of the
constituent parts of the _medium_, whereby the motion, action or progress
of the Ray of light is hindred from proceeding in a streight line, and
_inflected_ or _deflected_ by a _curve_. Now, that it is a _curve_ line is
manifest by this Experiment: I took a Box, such as ADGE, in the first
_Figure_ of the 37. _Scheme_, whose sides ABCD, and EFGH, were made of two
smooth flat plates of Glass, then filling it half full with a very strong
solution of Salt, I filled the other half with very fair fresh water, then
exposing the opacous side, DHGC, to the Sun, I observ'd both the
_refraction_ and _inflection_ of the Sun beams, ID & KH, and marking as
exactly as I could, the points, P, N, O, M, by which the Ray, KH, passed
through the compounded _medium_, I found them to be in a _curve_ line; for
the parts of the _medium_ being continually more dense the neerer they were
to the bottom, the Ray _pf_ was continually more and more deflected
downwards from the streight line.

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