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Micrographia by Robert Hooke

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Therefore twelfthly, it seems reasonable to think that there is no such
thing as an Element of Fire that should attract or draw up the flame, or
towards which the flame should endeavour to ascend out of a desire or
appetite of uniting with that as its _Homogeneal_ primitive and generating
Element; but that that shining transient body which we call _Flame_, is
nothing else but a mixture of Air, and volatil sulphureous parts of
dissoluble or combustible bodies, which are acting upon each other whilst
they ascend, that is, flame seems to be a mixture of Air, and the
combustible volatil parts of any body, which parts the encompassing Air
does dissolve or work upon, which action, as it does intend the heat of the
_aerial_ parts of the dissolvent, so does it thereby further rarifie those
parts that are acting, or that are very neer them, whereby they growing
much lighter then the heavie parts of that _menstruum_ that are more
remote, are thereby protruded and driven upward; and this may be easily
observ'd also in dissolution made by any other _menstruum_, especially such
as either create heat or bubbles. Now, this action of the _menstruum_, or
_Air_, on the dissoluble parts, is made with such violence, or is such,
that it imparts such a motion or pulse to the _diaphanous_ parts of the
Air, as I have elsewhere shewn is requisite to produce light.

This _Hypothesis_ I have endeavoured to raise from an Infinite of
Observations and Experiments, the process of which would be much too long
to be here inserted, and will perhaps another time afford matter copious
enough for a much larger Discourse, the Air being a Subject which (though
all the world has hitherto liv'd and breath'd in, and been unconversant
about) has yet been so little truly examin'd or explain'd, that a diligent
enquirer will be able to find but very little information from what has
been (till of late) written of it: But being once well understood, it will,
I doubt not, inable a man to render an intelligible, nay probable, if not
the true reason of all the _Phaenomena_ of Fire, which, as it has been
found by Writers and Philosophers of all Ages a matter of no small
difficulty, as may be sufficiently understood by their strange
_Hypotheses_, and unintelligible Solutions of some few _Phaenomena_ of it;
so will it prove a matter of no small concern and use in humane affairs, as
I shall elsewhere endeavour to manifest when I come to shew the use of the
Air in respiration, and for the preservation of the life, nay, for the
conservation and restauration of the health and natural constitution of
mankind as well as all other aereal _animals_, as also the uses of this
principle or propriety of the Air in chymical, mechanical, and other
operations. In this place I have onely time to hint an _Hypothesis_, which,
if God permit me life and opportunity, I may elsewhere prosecute, improve
and publish. In the mean time, before I finish this Discourse, I must not
forget to acquaint the Reader, that having had the liberty granted me of
making some trials on a piece of _Lignum fossile_ shewn to the Royal
Society, by the eminently Ingenious and Learned Physician, Doctor _Ent_,
who receiv'd it for a Present from the famous _Ingenioso Cavalliero de
Pozzi_, it being one of the fairest and best pieces of _Lignum fossile_ he
had seen; Having (I say) taken a small piece of this Wood, and examin'd it,
I found it to burn in the open Air almost like other Wood, and insteed of a
resinous smoak or fume, it yielded a very bituminous one, smelling much of
that kind of sent: But that which I chiefly took notice of, was, that
cutting off a small piece of it, about the bigness of my Thumb, and
charring it in a _Crucible_ with Sand, after the manner I above prescrib'd,
I found it infinitely to abound with the smaller sort of pores, so
extreamly thick, and so regularly perforating the substance of it
long-ways, that breaking it off a-cross, I found it to look very like an
Honey-comb; but as for any of the second, or bigger kind of pores, I could
not find that it had any; so that it seems, whatever were the cause of its
production, it was not without those small kind of pores which we have
onely hitherto found in Vegetable bodies: and comparing them with the pores
which I have found in the Charcoals that I by this means made of several
other kinds of Wood, I find it resemble none so much as those of Fire, to
which it is not much unlike in grain also, and several other proprieties.

And therefore, what ever is by some, who have written of it, and
particularly by _Francisco Stelluto_, wrote a Treatise in _Italian_ of that
Subject, which was Printed at _Rome_, 1637, affirm'd that it is a certain
kind of Clay or Earth, which in tract of time is turn'd into Wood; I rather
suspect the quite contrary, that it was at first certain great Trees of Fir
or Pine, which by some Earthquake, or other casualty, came to be buried
under the Earth, and was there, after a long time's residence (according to
the several natures of the encompassing adjacent parts) either rotted and
turn'd into a kind of Clay, or _petrify'd_ and turn'd into a kind of Stone,
or else had its pores fill'd with certain Mineral juices, which being
stay'd in them, and in tract of time coagulated, appear'd, upon cleaving
out, like small Metaline Wires, or else from some flames or scorching forms
that are the occasion oftentimes, and usually accompany Earthquakes, might
be blasted and turn'd into Coal, or else from certain _subterraneous_ fires
which are affirm'd by that Authour to abound much about those parts
(namely, in a Province of _Italy_, call'd _Umbria_, now the _Dutchie_ of
_Spoletto_, in the Territory of _Todi_, anciently call'd _Tudor_; and
between the two Villages of _Collesecco_ and _Rosaro_ not far distant from
the high-way leading to _Rome_, where it is found in greater quantity then
elsewhere) are by reason of their being encompassed with Earth, and so kept
close from the dissolving Air, charr'd and converted into Coal. It would be
too long a work to describe the several kinds of pores which I met withall,
and by this means discovered in several other Vegetable bodies; nor is it
my present design to expatiate upon Instances of the same kind, but rather
to give a Specimen of as many kinds as I have had opportunity as yet of
observing, reserving the prosecution and enlarging on particulars till a
more fit opportunity; and in prosecution of this design, I shall here add:

* * * * *


Observ. XVII. _Of _Petrify'd wood_, and other _Petrify'd bodies_._

Of this sort of substance, I observ'd several pieces of very differing
kinds, both for their outward shape, colour, grain, _texture_, hardness,
&c. some being brown and redish; others gray, like a Hone; others black,
and Flint-like: some soft, like a Slate or Whetstone, others as hard as a
Flint, and as brittle. That which I more particular examin'd, was a piece
about the bigness of a mans hand, which seem'd to have been a part of some
large tree, that by rottenness had been broken off from it before it began
to be _petrify'd_.

And indeed, all that I have yet seen, seem to have been rotten Wood before
the petrifaction was begun; and not long since, examining and viewing a
huge great _Oak_, that seem'd with meer age to be rotten as it stood, I was
very much confirm'd in this opinion; for I found, that the grain, colour,
and shape of the Wood, was exactly like this _petrify'd_ substance; and
with a _Microscope_, I found, that all those _Microscopical_ pores, which
in sappy or firm and sound Wood are fill'd with the natural or innate
juices of those Vegetables, in this they were all empty, like those of
_Vegetables charr'd_; but with this difference, that they seem'd much
larger then I have seen any in _Char-coals_; nay, even then those of Coals
made of great blocks of Timber, which are commonly call'd _Old-coals_.

The reason of which difference may probably be, that the charring of
Vegetables, being an operation quickly perform'd, and whilest the Wood is
sappy, the more solid parts may more easily shrink together, and contract
the pores or _interstitia_ between them, then in the rotten Wood, where
that natural juice seems onely to be wash'd away by _adventitious_ or
unnatural moisture; and so though the natural juice be wasted from between
the firm parts, yet those parts are kept asunder by the _adventitious_
moystures, and so by degrees settled in those postures.

And this I likewise found in the _petrify'd_ Wood, that the pores were
somewat bigger then those of _Charcoal_, each pore being neer upon half as
bigg again, but they did not bear that disproportion which is exprest in
the tenth _Scheme_, between the small specks or pores in the first Figure
(which representeth the pores of Coal or Wood charr'd) and the black spots
of the second Figure (which represent the like _Microscopical pores_ in the
_petrify'd_ Wood) for these last were drawn by a _Microscope_ that
magnify'd the object above six times more in Diameter then the _Microscope_
by which those pores of Coal were observ'd.

Now, though they were a little bigger, yet did they keep the exact figure
and order of the pores of Coals and of rotten Wood, which last also were
much of the same cize.

The other Observations on this _petrify'd_ substance, that a while since,
by the appointment of the _Royal Society_, I made, and presented to them an
account of, were these that follow, which had the honour done them by the
most accomplish'd Mr. _Evelin_, my highly honoured friend, to be inserted
and published among those excellent Observations wherewith his _Sylva_ is
replenish'd, and would therefore have been here omitted, had not the Figure
of them, as they appear'd through the _Microscope_ been before that
engraven.

This _Petrify'd_ substance resembled Wood, in that

First, all the parts of it seem'd not at all _dislocated_, or alter'd from
their natural Position, whil'st they were Wood, but the whole piece
retain'd the exact shape of Wood, having many of the conspicuous pores of
wood still remaining pores, and shewing a manifest difference visible
enough between the grain of the Wood and that of the bark, especially when
any side of it was cut smooth and polite; for then it appear'd to have a
very lovely grain, like that of some curious close Wood.

Next (it resembled Wood) in that all the smaller and (if I may so call
those which are onely visible with a good magnifying Glass) _Microscopical_
pores of it appear (both when the substance is cut and polish'd
_transversly_ and _parallel_ to the pores of it) perfectly like the
_Microscopical_ pores of several kinds of Wood, especially like and equal
to those of several sorts of rotten Wood which I have since observ'd,
retaining both the shape, position and magnitude of such pores. It was
differing from Wood:

First; in _weight_, being to common water as 31/4 to 1. whereas there are
few of our _English_ Woods, that when very dry are found to be full as
heavie as water.

Secondly, in _hardness_, being very neer as hard as a Flint; and in some
places of it also resembling the grain of a Flint: and, like it, it would
very readily cut Glass, and would not without difficulty, especially in
some parts of it, be scratch'd by a black hard Flint: It would also as
readily strike fire against a Steel, or against a Flint, as any common
Flint.

Thirdly, in the _closeness_ of it, for though all the _Microscopical_ pores
of this _petrify'd_ substance were very conspicuous in one position, yet by
altering that position of the polish'd surface to the light, it was also
manifest, that those pores appear'd darker then the rest of the body, onely
because they were fill'd up with a more duskie substance, and not because
they were hollow.

Fourthly, in its _incombustibleness_, in that it would not burn in the
fire; nay, though I kept it a good while red-hot in the flame of a Lamp,
made very _intense_ by the blast of a small Pipe, and a large Charcoal, yet
it seem'd not at all to have diminish'd its extension; but only I found it
to have chang'd its colour, and to appear of a more dark and duskie brown
colour; nor could I perceive that those parts which seem'd to have been
Wood at first, were any thing wasted, but the parts appear'd as solid and
close as before. It was further observable also, that as it did not consume
like Wood, so neither did it crack and flie like a Flint, or such like hard
Stone, nor was it long before it appear'd red-hot.

Fifthly, in its _dissolubleness_; for putting some drops of distill'd
_Vinegar_ upon the Stone, I found it presently to yield very many Bubbles,
just like those which may be observ'd in spirit of _Vinegar_ when it
corrodes _corals_, though perhaps many of those small Bubbles might proceed
from some small parcels of Air which were driven out of the pores of this
_petrify'd_ substance by the insinuating liquid _menstruum_.

Sixthly, in its _rigidness_, and _friability_, being not at all flexible
but brittle like a Flint, insomuch that I could with one knock of a Hammer
break off a piece of it, and with a few more, reduce that into a pretty
fine powder.

Seventhly, it seem'd also very differing from Wood to the _touch_,
_feeling_ more cold then Wood usually does, and much like other close
stones and Minerals.

The Reasons of all which _Phaenomena_ seem to be,

That _petrify'd_ Wood having lain in some place where it was well soak'd
with _petrifying_ water (that is, such a water as is well _impregnated_
with stony and earthy particles) did by degrees separate, either by
straining and _filtration_, or perhaps, by _precipitation_, _cohesion_ or
_coagulation_, abundance of stony particles from the permeating water,
which stony particles, being by means of the fluid _vehicle_ convey'd, not
onely into the _Microscopical_ pores, and so perfectly stoping them up, but
also into the pores or _interstitia_, which may, perhaps, be even in the
texture or _Schematisme_ of that part of the Wood, which, through the
_Microscope_, appears most solid, do thereby so augment the weight of the
Wood, as to make it above three times heavier then water, and perhaps, six
times as heavie as it was when Wood.

Next, they thereby so lock up and fetter the parts of the Wood, that the
fire cannot easily make them flie away, but the action of the fire upon
them is onely able to _Char_ those parts, as it were, like a piece of Wood,
if it be clos'd very fast up in Clay, and kept a good while red-hot in the
fire, will by the heat of the fire be charr'd and not consum'd, which may,
perhaps, also be somewhat of the cause, why the _petrify'd_ substance
appear'd of a dark brown colour after it had been burnt.

By this _intrusion_ of the _petrifying_ particles, this substance also
becomes hard and _friable_; for the smaller pores of the Wood being
perfectly wedg'd, and stuft up with those stony particles, the small parts
of the Wood have no places or pores into which they may slide upon bending,
and consequently little or no flexion or yielding at all can be caus'd in
such a substance.

The remaining particles likewise of the Wood among the stony particles, may
keep them from cracking and flying when put into the fire, as they are very
apt to do in a Flint.

Nor is Wood the onely substance that may by this kind of _transmutation_ be
chang'd into stone; for I my self have seen and examin'd very many kinds of
substances, and among very credible Authours, we may meet with Histories of
such _Metamorphoses_ wrought almost on all kind of substances, both
_Vegetable_ and _Animal_, which Histories, it is not my business at
present, either to relate, or _epitomise_, but only to set down some
Observation I lately made on several kind of _petrify'd_ Shels, found about
_Keinsham_, which lies within four or five miles of _Bristol_, which are
commonly call'd _Serpentine-stones._

Examining several of these very curiously figur'd bodies (which are
commonly thought to be Stones form'd by some extraordinary _Plastick
virtue_ _latent_ in the Earth itself) I took notice of these particulars:

First, that these figured bodies, or stones, were of very differing
substances, as to hardness: some of Clay, some Marle, some soft Stone,
almost of the hardness of those soft stones which Masons call Fire-stone,
others as hard as Portland stone, others as hard as Marble, and some as
hard as a Flint or Crystal.

Next, they were of very differing substances as to transparency and colour;
some white, some almost black, some brown, some Metalline, or like
Marchasites; some transparent like white Marble, others like flaw'd
Crystal, some gray, some of divers colours; some radiated like those long
_petrify'd drops_, which are commonly found at the _Peak_, and in other
_subterraneous caverns_, which have a kind of pith in the middle.

Thirdly, that they were very different as to the manner of their outward
figuration; for some of them seem'd to have been the substance that had
fill'd the Shell of some kind of Shel-fish; others, to have been the
substance that had contain'd or enwrapp'd one of those Shels, on both
which, the perfect impression either of the inside or outside of such
Shells seem'd to be left, but for the most part, those impressions seem'd
to be made by an imperfect or broken Shell, the great end or mouth of the
Shell being always wanting, and often times the little end, and sometimes
half, and in some there were impressions, just as if there had been holes
broken in the figurating, imprinting or moulding Shell; some of them seem'd
to be made by such a Shell very much brused or flaw'd, insomuch that one
would verily have thought that very figur'd stone had been broken or brused
whilst a gelly, as 'twere, and so hardned, but within in the grain of the
stone, there appear'd not the least sign of any such bruse or breaking, but
onely on the very uttermost superficies.

Fourthly, they were very different, as to their outward covering, some
having the perfect Shell, both in figure, colour, and substance, sticking
on upon its surface, and adhering to it, but might very easily be separated
from it, and like other common _Cockle_ or _Scolop-shels_, which some of
them most accurately resembled, were very dissoluble in common _Vinegar_,
others of them, especially those _Serpentine_, or _Helical stones_ were
cover'd or retained the shining or Pearl-colour'd substance of the inside
of a Shel, which substance, on some parts of them, was exceeding thin, and
might very easily be rubbed off; on other parts it was pretty thick, and
retained a white coat, or flaky substance on the top, just like the
outsides of such Shells; some of them had very large pieces of the Shell
very plainly sticking on to them, which were easily to be broken or flaked
off by degrees: they likewise, some of them retain'd all along the surface
of them very pretty kind of _sutures_, such as are observ'd in the skulls
of several kinds of living creatures, which _sutures_ were most curiously
shap'd in the manner of leaves, and every one of them in the same Shell,
exactly one like another, which I was able to discover plainly enough with
my naked eye, but more perfectly and distinctly with my _Microscope_; all
these sutures, by breaking some of these stones, I found to be the
_termini_, or boundings of certain _diaphragms_, or partitions, which
seem'd to divide the cavity of the Shell into a multitude of very
proportionate and regular _cells_ or _caverns_, these _Diaphragms_, in many
of them, I found very perfect and compleat, of a very distinct substance
from that which fill'd the cavities, and exactly of the same kind with that
which covered the outside, being for the most part whitish, or
_mother-of-pearl_ colour'd.

As for the cavities between those _Diaphragms_, I found some of them fill'd
with Marle, and others with several kinds of stones, others, for the most
part hollow, onely the whole cavity was usually covered over with a kind of
_tartareous petrify'd_ substance, which stuck about the sides, and was
there shot into very curious regular Figures, just as _Tartar_, or other
dissolv'd Salts are observ'd to stick and _crystallize_ about the sides of
the containing Vessels; or like those little _Diamants_ which I before
observed to have covered the vaulted cavity of a Flint; others had these
cavities all lin'd with a kind of _metalline_ or _marchasite-like_
substance, which with a _Microscope_ I could as plainly see most curiously
and regularly figured, as I had done those in a Flint.

From all which, and several other particulars which I observ'd, I cannot
but think, that all these, and most other kinds of stony bodies which are
found thus strangely figured, do owe their formation and figuration, not to
any kind of _Plastick virtue_ inherent in the earth, but to the Shells of
certain Shel-fishes, which, either by some Deluge, Inundation, Earthquake,
or some such other means, came to be thrown to that place, and there to be
fill'd with some kind of Mudd or Clay, or _petrifying_ Water, or some other
substance, which in tract of time has been settled together and hardned in
those shelly moulds into those shaped substances we now find them; that the
great and thin end of these Shells by that Earthquake, or what ever other
extraordinary cause it was that brought them thither, was broken off; and
that many others were otherwise broken, bruised and disfigured; that these
Shells which are thus _spirallied_ and separated with _Diaphragmes_, were
some kind of _Nautili_ or _Porcelane shells_; and that others were shells
of _Cockles_, _Muscles_, _Periwincles_, _Scolops_, &c. of various sorts;
that these Shells in many, from the particular nature of the containing or
enclos'd Earth, or some other cause, have in tract of time rotted and
mouldred away, and onely left their impressions, both on the containing and
contained substances; and so left them pretty loose one within another, so
that they may be easily separated by a knock or two of a Hammer. That
others of these Shells, according to the nature of the substances adjacent
to them, have, by a long continuance in that posture, been _petrify'd_ and
turn'd into the nature of stone, just as I even now observ'd several sorts
of Wood to be. That oftentimes the Shell may be found with one kind of
substance within, and quite another without; having, perhaps, been fill'd
in one place, and afterwards translated to another, which I have very
frequently observ'd in _Cockle_, _Muscle_, _Periwincle_, and other shells,
which I have found by the Sea side. Nay, further, that some parts of the
same Shell may be fill'd in one place, and some other caverns in another,
and others in a third, or a fourth, or a fifth place, for so many differing
substances have I found in one of these _petrify'd_ Shells, and perhaps all
these differing from the encompassing earth or stone; the means how all
which varieties may be caus'd, I think, will not be difficult to conceive,
to any one that has taken notice of those Shells, which are commonly found
on the Sea shore: And he that shall throughly examine several kinds of such
curiously form'd stones, will (I am very apt to think) find reason to
suppose their generation or formation to be ascribable to some such
accidents as I have mention'd, and not to any _Plastick virtue_: For it
seems to me quite contrary to the infinite prudence of Nature, which is
observable in all its works and productions, to design every thing to a
determinate end, and for the attaining of that end, makes use of such ways
as are (as farr as the knowledge of man has yet been able to reach)
altogether consonant, and most agreeable to man's reason, and of no way or
means that does contradict, or is contrary to humane Ratiocination; whence
it has a long time been a general observation and _maxime_, that _Nature
does nothing in vain_; It seems, I say, contrary to that great Wisdom of
Nature, that these prettily shap'd bodies should have all those curious
Figures and contrivances (which many of them are adorn'd and contriv'd
with) generated or wrought by a _Plastick virtue_, for no higher end, then
onely to exhibite such a form; which he that shall throughly consider all
the circumstances of such kind of Figur'd bodies, will, I think, have great
reason to believe, though, I confess, one cannot presently be able to find
out what Nature's designs are. It were therefore very desirable, that a
good collection of such kind of figur'd stones were collected; and as many
particulars, circumstances, and informations collected with them as could
be obtained, that from such a History of Observations well rang'd, examin'd
and digested, the true original or production of all those kinds of stones
might be perfectly and surely known; such as are _Thunder-stones_, _Lapides
Stellares_, _Lapides Judaici_, and multitudes of other, whereof mention is
made in _Aldonandus_, _Wormius_, and other Writers of Minerals.

* * * * *

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