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Micrographia by Robert Hooke

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It were endless to describe the multitudes of Figures I have met with in
these kind of minute bodies, such as _Spherical_, _Oval_, _Pyramidal_,
_Conical_, _Prismatical_, of each of which kinds I have taken notice.

But amongst many others, I met with none more observable than this pretty
Shell (described in the _Figure_ X. of the fifth _Scheme_) which, though as
it was light on by chance, deserv'd to have been omitted (I being unable to
direct any one to find the like) yet for its rarity was it not
inconsiderable, especially upon the account of the information it may
afford us. For by it we have a very good instance of the curiosity of
Nature in another kind of Animals which are remov'd, by reason of their
minuteness, beyond the reach of our eyes, so that as there are several
sorts of Insects, as Mites, and others, so small as not yet to have had any
names; (some of which I shall afterwards describe) and small Fishes, as
Leeches in Vineger; and smal vegetables, as Moss, and Rose-Leave-plants;
and small Mushroms, as mould: so are there, it seems, small Shel-fish
likewise, Nature shewing her curiosity in every Tribe of _Animals_,
_Vegetables_, and _Minerals_.

I was trying several small and single Magnifying Glasses, and casually
viewing a parcel of white Sand, when I perceiv'd one of the grains exactly
shap'd and wreath'd like a Shell, but endeavouring to distinguish it with
my naked eye, it was so very small, that I was fain again to make use of
the Glass to find it; then, whilest I thus look'd on it, with a Pin I
separated all the rest of the granules of Sand, and found it afterwards to
appear to the naked eye an exceeding small white spot, no bigger than the
point of a Pin. Afterwards I view'd it every way with a better _Microscope_
and found it on both sides, and edge-ways, to resemble the Shell of a small
Water-Snail with a flat spiral Shell: it had twelve wreathings, a, b, c, d,
e, &c. all very proportionably growing one less than another toward the
middle or center of the Shell, where there was a very small round white
spot. I could not certainly discover whether the Shell were hollow or not,
but it seem'd fill'd with somewhat, and 'tis probable that it might be
_petrify'd_ as other larger Shels often are, such as are mention'd in the
seventeenth _Observation_.

* * * * *


Observ. XII. _Of _Gravel_ in Urine._

I Have often observ'd the Sand or Gravel of Urine, which seems to be a
_tartareous_ substance, generated out of a _saline_ and a _terrestrial_
substance _crystalliz'd_ together, in the form of _Tartar_, sometimes
sticking to the sides of the _Urinal_, but for the most part sinking to the
bottom, and there lying in the form of coorse common Sand; these, through
the _Microscope_, appear to be a company of small bodies, partly
transparent and partly _opacous_, some White, some Yellow, some Red, others
of more brown and duskie colours.

The Figure of them is for the most part flat, in the manner of Slats or
such like plated Stones, that is, each of them seem to be made up of
several other thinner Plates, much like _Muscovie Glass_, or _Englsh Sparr_
to the last of which, the white plated Gravel seems most likely; for they
seem not onely plated like that, but their sides shap'd also into _Rhombs_,
_Rhomboeids_, and sometimes into _Rectangles_ and _Squares_. Their bigness
and Figure may be seen in the second _Figure_ of the seventh _Plate_, which
represents about a dozen of them lying upon a plate ABCD, some of which, as
a, b, c, d seem'd more regular than the rest, and e, which was a small one,
sticking on the top of another, was a perfet _Rhomboeid_ on the top, and
had four _Rectangular_ sides.

The line E which was the the measure of the _Microscope_, is 1/32 part of
an _English_ Inch, so that the greatest bredth of any of them, exceeded not
1/128 part of an Inch.

Putting these into several liquors, I found _oyl of Vitriol_, _Spirit of
Urine_, and several other _Saline menstruums_ to dissolve them; and the
first of these in less than a minute without _Ebullition_, Water, and
several other liquors, had no sudden operation upon them. This I mention,
because those liquors that dissolve them, first make them very white, not
_vitiating_, but rather rectifying their Figure, and thereby make them
afford a very pretty object for the _Microscope_.

How great an advantage it would be to such as are troubled with the Stone,
to find some _menstruum_ might dissolve them without hurting the Bladder,
is easily imagin'd, since some _injections_ made of such bodies might
likewise dissolve the stone, which seems much of the same nature.

It may therefore, perhaps, be worthy some Physicians enquiry, whether there
may not be something mixt with the Urine in which the Gravel or Stone lies,
which may again make it dissolve it, the first of which seems by it's
regular Figures to have been sometimes _Crystalliz'd_ out of it. For
whether this _Crystallization_ be made in the manner as _Alum_, _Peter_,
&c. are _crystallized_ out of a cooling liquor, in which, by boyling they
have been dissolv'd; or whether it be made in the manner of _Tartarum
Vitriolatum_, that is, by the _Coalition_ of an _acid_ and a _Sulphureous_
substance, it seems not impossible, but that the liquor it lies in, may be
again made a _dissolvent_ of it. But leaving these inquiries to Physicians
or Chymists, to whom it does more properly belong, I shall proceed.

* * * * *


Observ. XIII. _Of the small _Diamants_, or _Sparks_ in _Flints_._

Chancing to break a Flint stone in pieces, I found within it a certain
cavity all crusted over with a very pretty candied substance, some of the
parts of which, upon changing the posture of the Stone, in respect of the
_Incident_ light, exhibited a number of small, but very vivid reflections;
and having made use of my _Microscope_, I could perceive the whole surface
of that cavity to be all beset with a multitude of little _Crystaline_ or
_Adamantine_ bodies, so curiously shap'd, that it afforded a not unpleasing
object.

Having considered those vivid _repercussions_ of light, I found them to be
made partly from the plain external surface of these regularly figured
bodies (which afforded the vivid reflexions) and partly to be made from
within the somewhat _pellucid_ body, that is, from some surface of the
body, opposite to that superficies of it which was next the eye.

And because these bodies were so small, that I could not well come to make
Experiments and Examinations of them, I provided me several small _stiriae_
of Crystals or Diamants, found in great quantities in _Cornwall_ and are
therefore commonly called _Cornish Diamants_: these being very _pellucid_,
and growing in a hollow cavity of a Rock (as I have been several times
informed by those that have observ'd them) much after the same manner as
these do in the Flint, and having besides their outward surface very
regularly shap'd, retaining very near the same Figures with some of those I
observ'd in the other, became a convenient help to me for the Examination
of the proprieties of those kinds of bodies.

And first for the Reflections, in these I found it very observable, That
the brightest reflections of light proceeded from within the _pellucid_
body; that is, that the Rays admitted through the _pellucid_ substance in
their getting out on the opposite side, were by the contiguous and strong
reflecting surface of the Air very vividly reflected, so that more Rays
were reflected to the eye by this surface, though the Ray in entring and
getting out of the Crystal had suffer'd a double refraction, than there
were from the outward surface of the Glass where the Ray had suffer'd no
reflection at all.

And that this was the surface of the Air that gave so vivid a
_re-percussion_ I try'd by this means I sunk half of a _stiria_ in Water,
so that only Water was contiguous to the under surface, and then the
internal reflection was so exceedingly faint, that it was scarce
discernable. Again, I try'd to alter this vivid reflection by keeping off
the Air, with a body not fluid, and that was by rubbing and holding my
finger very hard against the under surface, so as in many places the pulp
of my finger did touch the Glass, without any _interjacent_ air between,
then observing the reflection, I found, that wheresoever my finger or skin
toucht the surface, from that part there was no reflection, but in the
little furrows or creases of my skin, where there remain'd little small
lines of air, from them was return'd a very vivid reflection as before. I
try'd further, by making the surface of very pure Quicksilver to be
contiguous to the under surface of this _pellucid_ body, and then the
reflection from that was so exceedingly more vivid than from the air, as
the reflection from air was than the reflection from the Water; from all
which trials I plainly saw, that the strong reflecting air was the cause of
this _Phaenomenon_.

And this agrees very well with the _Hypothesis_ of light and _Pellucid_
bodies which I have mention'd in the description of _Muscovy-glass_; for we
there suppose Glass to be a _medium_, which does less resist the pulse of
light, and consequently, that most of the Rays incident on it enter into
it, and are refracted towards the _perpendicular_; whereas the air I
suppose to be a body that does more resist it, and consequently more are
_re-percuss'd_ then do enter it: the same kind of trials have I made, with
_Crystalline Glass_, with drops of fluid bodies, and several other ways,
which do all seem to agree very exactly with this _Theory_. So that from
this Principle well establish'd, we may deduce severall Corollaries not
unworthy observation.

And the first is; that it plainly appears by this, that the production of
the Rainbow is as much to be ascribed to the reflection of the concave
surface of the air, as to the refraction of the _Globular_ drops: this will
be evidently manifest by these Experiments, if you _foliate_ that part of a
Glass-ball that is to reflect an _Iris_, as in the _Cartesian_ Experiment,
above mention'd, the reflections will be abundantly more strong, and the
colours more vivid: and if that part of the surface be touch'd with Water,
scarce affords any sensible colour at all.

Next we learn, that the great reason why _pellucid_ bodies beaten small are
white, is from the multitude of reflections, not from the particles of the
body, but from the _contiguous_ surface of the air. And this is evidently
manifested, by filling the _Interstitia_ of those powder'd bodies with
Water, whereby their whiteness presently disappears. From the same reason
proceeds the whiteness of many kinds of Sands, which in the _Microscope_
appear to be made up of a multitude of little _pellucid_ bodies, whose
brightest reflections may by the _Microscope_ be plainly perceiv'd to come
from their internal surfaces; and much of the whiteness of it may be
destroy'd by the affusion of fair Water to be contiguous to those surfaces.

The whiteness also of froth, is for the most part to be ascribed to the
reflection of the light from the surface of the air within the Bubbles, and
very little to the reflection from the surface of the Water it self: for
this last reflection does not return a quarter so many Rays, as that which
is made from the surface of the air, as I have certainly found by a
multitude of Observations and Experiments.

The whiteness of _Linnen_, _Paper_, _Silk_, &c. proceeds much from the same
reason, as the _Microscope_ will easily discover; for the Paper is made up
of an abundance of _pellucid_ bodies, which afford a very plentifull
reflection from within, that is, from the concave surface of the air
contiguous to its component particles; wherefore by the affusion of Water,
Oyl, Tallow, Turpentine, &c. all those reflections are made more faint, and
the beams of light are suffer'd to traject & run through the Paper more
freely.

Hence further we may learn the reason of the whiteness of many bodies, and
by what means they maybe in part made _pellucid_: As white Marble for
instance, for this body is composed of a _pellucid_ body exceedingly
flaw'd, that is, there are abundance of thin, and very fine cracks or
chinks amongst the multitude of particles of the body, that contain in them
small parcels of air, which do so _re-percuss_ and drive back the
penetrating beams, that they cannot enter very deep within that body; which
the _Microscope_ does plainly inform us to be made up of a _Congeries_ of
_pellucid_ particles. And I further found it somewhat more evidently by
some attempts I made towards the making transparent Marble, for by heating
the Stone a little, and baking it in Oyl, Turpentine, Oyl of Turpentine,
&c., I found that I was able to see much deeper into the body of Marble
then before; and one trial, which was not with an unctuous substance,
succeeded better than the rest, of which, when I have a better opportunity,
I shall make further trial.

This also gives us a probable reason of the so much admired _Phaenomena_,
of the _Oculus Mundi_, an _Oval_ stone, which commonly looks like white
Alabaster, but being laid a certain time in Water, it grows _pellucid_, and
transparent, and being suffer'd to lie again dry, it by degrees loses that
transparency, and becomes white as before. For the Stone being of a hollow
spongie nature, has in the first and last of these appearances, all those
pores fill'd with the obtunding and reflecting air; whereas in the second,
all those pores are fill'd with a _medium_ that has much the same
refraction with the particles of the Stone, and therefore those two being
_contiguous_, make, as 'twere, one _continued medium_, of which more is
said in the 15. _Observation_.

There are a multitude of other _Phaenomena_, that are produc'd from this
same Principle, which as it has not been taken notice of by any yet that I
know, so I think, upon more diligent observation, will it not be found the
least considerable. But I have here onely time to hint _Hypotheses_, and
not to prosecute them so fully as I could wish; many of them having a vast
extent in the production of a multitude of _Phaenomena_, which have been by
others, either not attempted to be explain'd, or else attributed to some
other cause than what I have assign'd, and perhaps than the right; and
therefore I shall leave this to the prosecution of such as have more
leisure: onely before I leave it, I must not pretermit to hint, that by
this Principle, multitudes of the _Phaenomena_ of the air, as about
_Mists_, _Clouds_, _Meteors_, _Haloes_, &c. are most plainly and (perhaps)
truly explicable; multitudes also of the _Phaenomena_ in colour'd bodies,
as liquors, &c. are deducible from it.

And from this I shall proceed to a second considerable _Phaenomenon_ which
these Diamants exhibit, and that is the regularity of their _Figure_, which
is a propriety not less general than the former, It comprising within its
extent, all kinds of _Metals_, all kinds of _Minerals_, most _Precious
stones_, all kinds of _Salts_, multitudes of _Earths_, and almost all kinds
of _fluid bodies_. And this is another propiety, which, though a little
superficially taken notice of by some, has not, that I know, been so much
as attempted to be explicated by any.

This propriety of bodies, as I think it the most worthy, and next in order
to be consider'd after the contemplation of the _Globular Figure_, so have
I long had a desire as wel as a determination to have prosecuted it if I
had had an opportunity, having long since propos'd to my self the method of
my enquiry therein, it containing all the allurements that I think any
enquiry is capable of: For, first I take it to proceed from the most simple
principle that any kind of form can come from, next the _Globular_, which
was therefore the first I set upon, and what I have therein perform'd, I
leave the Judicious Reader to determine. For as that form proceeded from a
propiety of fluid bodies, which I have call'd _Congruity_, or
_Incongruity_; so I think, had I time and opportunity, I could make
probable, that all these regular Figures that are so conspicuously
_various_ and _curious_, and do so adorn and beautifie such multitudes of
bodies, as I have above hinted, arise onely from three or four several
positions or postures of _Globular_ particles, and those the most plain,
obvious, and necessary conjunctions of such figur'd particles that are
possible, so that supposing such and such plain and obvious causes
concurring the _coagulating particles_ must necessarily compose a body of
such a determinate regular Figure, and no other, and this with as much
necessity and obviousness as a fluid body encompast with a _Heterogeneous_
fluid must be protruded into a _Spherule_ or _Globe_. And this I have _ad
oculum_ demonstrated with a company of bullets, and some few other very
simple bodies; so that there was not any regular Figure, which I have
hitherto met withall, of any of those bodies that I have above named, that
I could not with the composition of bullets or globules, and one or two
other bodies, imitate, even almost by shaking them together. And thus for
instance may we find that the _Globular_ bullets will of themselves, if put
on an inclining plain, so that they may run together, naturally run into a
_triangular_ order, composing all the variety of figures that can be
imagin'd to be made out of _aequilateral triangles_; and such will you
find, upon trial, all the Surfaces of _Alum_ to be compos'd of: For three
bullets lying on a plain, as close to one another as they can compose an
_aequilatero-triangular_ form, as in A in the 7. _Scheme_. If a fourth be
joyn'd to them on either side as closely as it can, they four compose the
most regular Rhombus consisting of two _aequilateral triangles_, as B. If a
fifth be joyn'd to them on either side in as close a position as it can,
which is the propriety of the _Texture_, it makes a _Trapezium_, or
four-sided Figure, two of whole angles are 120. and two 60. degrees, as C.
If a sixth be added, as before, either it makes an _aequilateral triangle_,
as D, or a Rhomboeid, as E, or an _Hex-angular Figure_, as F, which is
compos'd of two _primary Rhombes_. If a seventh be added, it makes either
an _aequilatero-hexagonal_ Figure, as G, or some kind of six-sided
_Figure_, as H, or I. And though there be never so many placed together,
they may be rang'd into some of these lately mentioned Figures, all the
angles of which will be either _60_. degrees, or 120. as the figure K.
which is an _aequiangular hexagonal_ Figure is compounded of 12.
_Globules_, or may be of 25, or 27, or 36, or 42, &c. and by these kinds of
texture, or position of globular bodies, may you find out all the variety
of regular shapes, into which the smooth surfaces of _Alum_ are form'd, as
upon examination any one may easily find; nor does it hold only in
superficies, but in solidity also, for it's obvious that a fourth _Globule_
laid upon the third in this texture, composes a regular _Tetrahedron_,
which is a very usual Figure of the _Crystals_ of _Alum_. And (to hasten)
there is no one Figure into which _Alum_ is observ'd to be crystallized,
but may by this texture of _Globules_ be imitated, and by no other.

I could instance also in the Figure of _Sea-salt_, and _Sal-gem_, that it
is compos'd of a texture of _Globules_, placed in a _cubical_ form, as L,
and that all the Figures of those Salts may be imitated by this texture of
_Globules_ and by no other whatsoever. And that the forms of _Vitriol_ and
of _Salt-Peter_, as also of _Crystal_, _Hore-frost_, &c. are compounded of
these two textures, but modulated by certain proprieties: But I have not
here time to insist upon, as I have not neither to shew by what means
_Globules_ come to be thus context, and what those _Globules_ are, and many
other particulars requisite to a full and intelligible explication of this
propriety of bodies. Nor have I hitherto found indeed an opportunity of
prosecuting the inquiry so farr as I design'd; nor do I know when I may, it
requiring abundance of time, and a great deal of assistance to go through
with what I design'd; the model of which was this:

First, to get as exact and full a collection as I could, of all the
differing kinds of Geometrical figur'd bodies, some three or four several
bodies of each kind.

Secondly, with them to get as exact a History as possibly I could learn of
their places of Generation or finding, and to enquire after as many
circumstances that tended to the Illustrating of this Enquiry, as possibly
I could observe.

Thirdly, to make as many trials as upon experience I could find requisite,
in Dissolutions and Coagulations of several crystallizing Salts; for the
needfull instruction and information in this Enquiry.

Fourthly, to make several trials on divers other bodies, as Metals,
Minerals, and Stones, by dissolving them in several _Menstruums_, and
crystalizing them, to see what Figures would arise from those several
_Compositums_.

Fifthly, to make Compositions and Coagulations of several Salts together
into the same mass, to observe of what Figure the product of them would be;
and in all, to note as many circumstances as I should judge conducive to my
Enquiry.

Sixthly, to enquire the closeness or rarity of the texture of these bodies,
by examining their gravity, and their refraction, &c.

Seventhly, to enquire particularly what operations the fire has upon
several kinds of Salts, what changes it causes in their Figures, Textures,
or Energies.

Eighthly, to examine their manner of dissolution, or acting upon those
bodies dissoluble in them; The texture of those bodies before and after the
process. And this for the History.

Next for the Solution, To have examin'd by what, and how many means, such
and such Figures, actions and effects could be produc'd possibly.

And lastly, from all circumstances well weigh'd, I should have endeavoured
to have shewn which of them was most likely, and (if the informations by
these Enquiries would have born it) to have demonstrated which of them it
must be, and was.

But to proceed, As I believe it next to the Globular the most simple; so do
I, in the second place, judge it not less pleasant; for that which makes an
Enquiry pleasant, are, first a noble _Inventum_ that promises to crown the
successfull endeavour; and such must certainly the knowledge of the
efficient and concurrent causes of all these curious Geometrical Figures
be, which has made the Philosophers hitherto to conclude nature in these
things to play the Geometrician, according to that saying of _Plato_,
[Greek: Ho Theos geometrei]. Or next, a great variety of matter in the
Enquiry; and here we meet with nothing less than the _Mathematicks_ of
nature, having every day a new Figure to contemplate, or a variation of the
same in another body,

Which do afford us a third thing, which will yet more sweeten the Enquiry,
and that is, a multitude of information; we are not so much to grope in the
dark, as in most other Enquiries, where the _Inventum_ is great; for having
such a multitude of instances to compare, and such easie ways of
generating, or compounding and of destroying the form, as in the _Solution_
and _Crystallization_ of Salts, we cannot but learn plentifull information
to proceed by. And this will further appear from the universality of the
Principle which Nature has made use of almost in all inanimate bodies. And
therefore, as the contemplation of them all conduces to the knowledg of any
one; so from a Scientifical knowledge of any one does follow the fame of
all, and every one.

And fourthly, for the usefulness of this knowledge, when acquir'd;
certainly none can doubt, that considers that it caries us a step forward
into the Labirinth of Nature, in the right way towards the end we propose
our selves in all Philosophical Enquiries. So that knowing what is the form
of Inanimate or Mineral bodies, we shall be the better able to proceed in
our next Enquiry after the forms of Vegetative bodies; and last of all, of
Animate ones, that seeming to be the highest step of natural knowledge that
the mind of man is capable of.

* * * * *


Observ. XIV. _Of several kindes of frozen _Figures_._

I have very often in a Morning, when there has been a great _hoar-frost_,
with an indifferently magnifying _Microscope_, observ'd the small
_Stiriae_, or Crystalline beard, which then usually covers the face of
most bodies that lie open to the cold air, and found them to be generally
_Hexangular prismatical_ bodies, much like the long Crystals of
_Salt-peter_, save onely that the ends of them were differing: for whereas
those of _Nitre_ are for the most part _pyramidal_, being terminated either
in a point or edge; these of Frost were hollow, and the cavity in some
seem'd pretty deep, and this cavity was the more plainly to be seen,
because usually one or other of the six _parallelogram_ sides was wanting,
or at least much shorter then the rest.

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