A \ B \ C \ D \ E \ F \ G \ H \ I \ J \ K \ L \ M \ N \ O \ P \ R \ S \ T \ U \ V \ W \Z

Micrographia by Robert Hooke

R >> Robert Hooke >> Micrographia




To proceed therefore, I say, that the dropping of this expanded Body into
cold Water, does make the parts of the Glass suffer a double contraction:
The first is, of those parts which are neer the Surface of the Drop. For
Cold, as I said before, contracting Bodies, that is, _by the abatement of
the agitating faculty the parts falling neerer together_; the parts next
adjoyning to the Water must needs lose much of their motion, and impart it
to the Ambient-water (which the Ebullition and commotion of it manifests)
and thereby become a solid and hard crust, whilst the innermost parts
remain yet fluid and expanded; whence, as they grow cold also by degrees,
their parts must necessarily be left at liberty to be condensed, but
because of the hardness of the outward crust, the contraction cannot be
admitted that way; but there being many very small, and before
inconspicuous, bubbles in the substance of the Glass, upon the subsiding of
the parts of the Glass, the agil substance contained in them has liberty of
expanding it self a little, and thereby those bubbles grow much bigger,
which is the second Contraction. And both these are confirmed from the
appearance of the Drop it self: for as for the outward parts, we see,
first, that it is irregular and shrunk, as it were, which is caused by the
yielding a little of the hardened Skin to a Contraction, after the very
outmost Surface is settled; and as for the internal parts, one may with
ones naked Eye perceive abundance of very conspicuous bubbles, and with the
_Microscope_ many more.

The Consideration of which Particulars will easily make the Third Position
probable, that is, that the parts of the drop will be of a very hard,
though of a rarified Texture; for if the outward parts of the Drop, by
reason of its hard crust, will indure very little Contraction, and the agil
Particles, included in those bubbles, by the losing of their agitation, by
the decrease of the Heat, lose also most part of their Spring and Expansive
power; it follows (the withdrawing of the heat being very sudden) that the
parts must be left in a very loose Texture, and by reason of the
implication of the parts one about another, which from their sluggishnes
and glutinousness I suppose to be much after the manner of the sticks in a
Thorn-bush, or a Lock of Wool; it will follow, I say, that the parts will
hold each other very strongly together, and indeavour to draw each other
neerer together, and consequently their Texture must be very hard and
stiff, but very much rarified.

And this will make probable my next Position, That _the parts of the Glass
are under a kind of tension or flexure, out of which they indeavour to
extricate and free themselves_, and thereby all the parts draw towards the
Center or middle, and would, if the outward parts would give way, as they
do when the outward parts cool leisurely (as in baking of Glasses) contract
the bulk of the drop into a much less compass. For since, as I proved
before, the Internal parts of the drop, when fluid, were of a very rarified
Texture, and, as it were, tos'd open like a Lock of Wool, and if they were
suffered leisurely to cool, would be again prest, as it were, close
together: And since that the heat, which kept them bended and open, is
removed, and yet the parts not suffered to get as neer together as they
naturally would; It follows, that the Particles remain under a kind of
_tension_ and _flexure_, and consequently have an indeavour to free
themselves from that _bending_ and _distension_, which they do, as soon as
either the tip be broken, or as soon as by a leisurely heating and cooling,
the parts are nealed into another posture.

And this will make my next Position probable, that _the parts of the Glass
drops are contignated together in the form of an Arch_, cannot any where
yield or be drawn inwards, till by the removing of some one part of it (as
it happens in the removing one of the stones of an Arch) the whole Fabrick
is shatter'd, and falls to pieces, and each of the Springs is left at
liberty, suddenly to extricate it self: for since I have made it probable,
that the internal parts of the Glass have a contractive power inwards, and
the external parts are incapable of such a Contraction, and the figure of
it being spherical; it follows, that the superficial parts must bear
against each other, and keep one another from being condens'd into a less
room, in the same manner as the stones of an Arch conduce to the upholding
each other in that Figure. And this is made more probable by another
Experiment which was communicated to me by an excellent Person, whose
extraordinary Abilities in all kind of Knowledg, especially in that of
Natural things, and his generous Disposition in communicating, incouraged
me to have recourse to him on many occasions. The Experiment was this:
Small Glass-balls (about the bigness of that represented in the _Figure
&._) would, upon rubbing or scratching the inward Surface, fly all
insunder, with a pretty brisk noise; whereas neither before nor after the
inner Surface had been thus scratcht, did there appear any flaw or crack.
And putting the pieces of one of those broken ones together again, the
flaws appeared much after the manner of the black lines on the Figure, _&._
These Balls were small, but exceeding thick bubbles of Glass, which being
crack'd off from the _Puntilion_ whilst very hot, and so suffered to cool
without nealing them in the Oven over the Furnace, do thereby (being made
of white Glass, which cools much quicker then green Glass, and is thereby
made much brittler) acquire a very _porous_ and very brittle _texture_: so
that if with the point of a Needle or Bodkin, the inside of any of them be
rubbed prety hard, and then laid on a Table, it will, within a very little
while, break into many pieces with a brisk noise, and throw the parts above
a span asunder on the Table: Now though the pieces are not so small as
those of a _fulminating_ drop, yet they as plainly shew, that the outward
parts of the Glass have a great _Conatus_ to fly asunder, were they not
held together by the _tenacity_ of the parts of the inward Surface: for we
see as soon as those parts are crazed by hard rubbing, and thereby their
tenacity spoiled, the springiness of the more outward parts quickly makes a
divulsion, and the broken pieces will, if the concave Surface of them be
further scratcht with a Diamond, fly again into smaller pieces.

From which preceding considerations it will follow Sixthly, That the sudden
flying asunder of the parts as soon as this Arch is any where disordered or
broken, proceeds from the springing of the parts; which, indeavouring to
_extricate_ themselves as soon as they get the liberty, they perform it
with such a quickness, that they throw one another away with very great
violence: for the Particles that compose the Crust have a _Conatus_ to lye
further from one another, and therefore as soon as the external parts are
loosened they dart themselves outward with great violence, just as so many
Springs would do, if they were detained and fastened to the body, as soon
as they should be suddenly loosened; and the internal parts drawing inward,
they contract so violently; that they rebound back again and fly into
multitude of small shivers or sands. Now though they appear not, either to
the naked Eye, or the _Microscope_, yet I am very apt to think there may be
abundance of small flaws or cracks, which, by reason the strong reflecting
Air is not got between the _contiguous_ parts, appear not. And that this
may be so, I argue from this, that I have very often been able to make a
crack or flaw, in some convenient pieces of Glass, to appear and disappear
at pleasure, according as by pressing together, or pulling asunder the
contiguous parts, I excluded or admitted the strong reflecting Air between
the parts: And it is very probable, that there may be some Body, that is
either very rarified Air, or something _analogous_ to it, which fills the
bubbles of these drops; which I argue, first, from the roundness of them,
and next, from the vivid reflection of Light which they exhibite: Now
though I doubt not, but that the Air in them is very much rarified, yet
that there is some in them, to such as well consider this Experiment of the
disappearing of a crack upon the _extruding_ of the Air, I suppose it will
seem more then probable.

The Seventh and last therefore that I shall prove, is, _That the gradual
heating and cooling of these so extended bodies does reduce the parts of
the Glass to a looser and softer temper_. And this I found by heating them,
and keeping them for a prety while very red hot in a fire; for thereby I
found them to grow a little lighter, and the small Stems to be very easily
broken and snapt any where, without at all making the drop fly; whereas
before they were so exceeding hard, that they could not be broken without
much difficulty; and upon their breaking the whole drop would fly in pieces
with very great violence. The Reason of which last seems to be, that the
leisurely heating and cooling of the parts does not only wast some part of
the Glass it self, but ranges all the parts into a better order, and gives
each Particle an opportunity of _relaxing_ its self, and consequently
neither will the parts hold so strongly together as before, nor be so
difficult to be broken: The parts now more easily yielding, nor will the
other parts fly in pieces, because the parts have no bended Springs. The
_relaxation_ also in the temper of hardned Steel, and hammered Metals, by
nealing them in the fire, seems to proceed from much the same cause. For
both by quenching suddenly such Metals as have _vitrifed_ parts
interspers'd, as Steel has, and by hammering of other kinds that do not so
much abound with them, as Silver Brass, &c. the parts are put into and
detained in a bended posture, which by the agitation of Heat are shaken,
and loosened, and suffered to unbend themselves.

* * * * *


Observ. VIII. _Of the fiery Sparks struck from a Flint or Steel._

It is a very common Experiment, by striking with a Flint against a Steel,
to make certain fiery and shining Sparks to fly out from between those two
compressing Bodies. About eight years since, upon casually reading the
Explication of this odd _Phaenomenon_, by the most Ingenious _Des Cartes_,
I had a great desire to be satisfied, what that Substance was that gave
such a shining and bright Light: And to that end I spread a sheet of white
Paper, and on it, observing the place where several of these Sparks seemed
to vanish, I found certain very small, black, but glittering Spots of a
movable Substance, each of which examining with my _Microscope_, I found to
be a small round _Globule_; some of which, as they looked prety small, so
did they from their Surface yield a very bright and strong reflection on
that side which was next the Light; and each look'd almost like a prety
bright Iron-Ball, whose Surface was prety regular, such as is represented
by the Figure A. In this I could perceive the Image of the Window prety
well, or of a Stick, which I moved up and down between the Light and it.
Others I found, which were, as to the bulk of the Ball, prety regularly
round, but the Surface of them, as it was not very smooth, but rough, and
more irregular, so was the reflection from it more faint and confused. Such
were the Surfaces of B. C. D. and E. Some of these I found cleft or
cracked, as C, others quite broken in two and hollow, as D. which seemed to
be half the hollow shell of a Granado, broken irregularly in pieces.
Several others I found of other shapes; but that which is represented by E,
I observed to be a very big Spark of fire, which went out upon one side of
the Flint that I struck fire withall, to which it stuck by the root F, at
the end of which small Stem was fastened-on a _Hemisphere_, or half a
hollow Ball, with the mouth of it open from the stemwards, so that it
looked much like a Funnel, or an old fashioned Bowl without a foot. This
night, making many tryals and observations of this Experiment, I met, among
a multitude of the Globular ones which I had observed, a couple of
Instances, which are very remarkable to the confirmation of my
_Hypothesis_.

And the First was of a pretty big Ball fastened on to the end of a small
sliver of Iron, which _Compositum_ seemed to be nothing else but a long
thin chip of Iron, one of whose ends was melted into a small round Globul;
the other end remaining unmelted and irregular, and perfectly Iron.

The Second Instance was not less remarkable then the First; for I found,
when a Spark went out, nothing but a very small thin long sliver of Iron or
Steel, unmelted at either end. So that it seems, that some of these Sparks
are the slivers or chips of the Iron _vitrified_, Others are only the
slivers melted into Balls without vitrification, And the third kind are
only small slivers of the Iron, made red-hot with the violence of the
stroke given on the Steel by the Flint.

He that shall diligently examine the _Phaenomena_ of this Experiment, will,
I doubt not, find cause to believe, that the reason I have heretofore given
of it, is the true and genuine cause of it, namely, That _the Spark,
appearing so bright in the falling, is nothing else but a small piece of
the Steel or Flint, but most commonly of the Steel, which by the violence
of the stroke is at the same time sever'd and heat red-hot, and that
sometimes to such a degree, as to make it melt together into a small
Globule of Steel; and sometimes also is that heat so very intense, as
further to melt it and vitrifie it; but many times the heat is so gentle,
as to be able to make the sliver only red hot, which notwithstanding
falling upon the tinder_ (that is only a very curious small Coal made of
the small threads of Linnen burnt to coals and char'd) _it easily sets it
on fire_. Nor will any part of this _Hypothesis_ seem strange to him that
considers, First, that either hammering, or filing or otherwise violently
rubbing of Steel, will presently make it so hot as to be able to burn ones
fingers. Next, that the whole force of the stroke is exerted upon that
small part where the Flint and Steel first touch: For the Bodies being each
of them so very hard, the puls cannot be far communicated, that is, the
parts of each can yield but very little, and therefore the violence of the
concussion will be _exerted_ on that piece of Steel which is cut off by the
Flint. Thirdly, that the filings or small parts of Steel are very apt, as
it were, to take fire, and are presently red hot, that is, there seems to
be a very _combustible sulphureous_ Body in Iron or Steel, which the Air
very readily preys upon, as soon as the body is a little violently heated.

And this is obvious in the filings of Steel or Iron cast through the flame
of a Candle; for even by that sudden _transitus_ of the small chips of
Iron, they are heat red hot, and that _combustible sulphureous_ Body is
presently prey'd upon and devoured by the _aereal_ incompassing
_Menstruum_, whose office in this Particular I have shewn in the
Explication of Charcole.

And in prosecution of this Experiment, having taken the filings of Iron and
Steel, and with the point of a Knife cast them through the flame of a
Candle, I observed where some conspicuous shining Particles fell, and
looking on them with my _Microscope_, I found them to be nothing else but
such round Globules, as I formerly found the Sparks struck from the Steel
by a stroke to be, only a little bigger; and shaking together all the
filings that had fallen upon the sheet of Paper underneath and observing
them with the _Microscope_, I found a great number of small Globules, such
as the former, though there were also many of the parts that had remained
untoucht and rough filings or chips of Iron. So that, it seems, Iron does
contain a very _combustible sulphureous_ Body, which is, in all likelihood,
one of the causes of this _Phaenomenon_, and which may be perhaps very much
concerned in the business of its hardening and tempering: of which somewhat
it said in the Description of _Muscovy-glass_.

So that, these things considered, we need not trouble our selves to find
out what kind of Pores they are, both in the Flint and Steel, that contain
the _Atoms of fire_, nor how those _Atoms_ come to be hindred from running
all out, when a dore or passage in their Pores is made by the concussion:
nor need we trouble our selves to examine by what _Prometheus_ the Element
of Fire comes to be fetcht down from above the Regions of the Air, in what
Cells or Boxes it is kept, and what _Epimetheus_ lets it go: Nor to
consider what it is that causes so great a conflux of the atomical
Particles of Fire, which are said to fly to a flaming Body, like Vultures
or Eagles to a putrifying Carcass, and there to make a very great pudder.
Since we have nothing more difficult in this _Hypothesis_ to conceive,
first, as to the kindling of Tinder, then how a large Iron-bullet, let fall
red or glowing hot upon a heap of Small-coal, should set fire to those that
are next to it first: Nor secondly, is this last more difficult to be
explicated, then that a Body, as Silver for Instance, put into a weak
_Menstruum_, as unrectified _Aqua fortis_ should, when it is put in a great
heat, be there dissolved by it, and not before; which _Hypothesis_ is more
largely explicated in the Description of Charcoal. To conclude, we see by
this Instance, how much Experiments may conduce to the regulating of
_Philosophical notions_. For if the most Acute _Des Cartes_ had applied
himself experimentally to have examined what substance it was that caused
that shining of the falling Sparks struck from a Flint and a Steel, he
would certainly have a little altered his _Hypothesis_, and we should have
found, that his Ingenious Principles would have admitted a very plausible
Explication of this _Phaenomenon_; whereas by not examining so far as he
might, he has set down an Explication which Experiment do's contradict.

But before I leave this Description, I must not forget to take notice of
the Globular form into which each of these is most curiously formed. And
this _Phaenomenon_, as I have elsewhere more largely shewn, proceeds from a
propriety which belongs to all kinds of fluid Bodies more or less, and is
caused by the Incongruity of the Ambient and included Fluid, which so acts
and modulates each other, that they acquire, as neer as is possible, a
_spherical_ or _globular_ form, which propriety and several of the
_Phaenomena_ that proceed from it, I have more fully explicated in the
sixth Observation.

One Experiment, which does very much illustrate my present Explication, and
is in it self exceeding pretty, I must not pass by: And that is a way of
making small _Globules_ or _Balls_ of Lead, or Tin, as small almost as
these of Iron or Steel, and that exceeding easily and quickly, by turning
the filings or chips of those Metals also into perfectly round _Globules_.
The way, in short, as I received it from the _Learned Physitian Doctor_
I.G. is this;

Reduce the Metal you would thus shape, into exceeding fine filings, the
finer the filings are, the finer will the Balls be: _Stratifie_ these
filings with the fine and well dryed powder of quick Lime in a _Crucible_
proportioned to the quantity you intend to make: When you have thus filled
your _Crucible_, by continual _stratifications_ of the filings and powder,
so that, as neer as may be, no one of the filings may touch another, place
the _Crucible_ in a _gradual fire_, and by degrees let it be brought to a
heat big enough to make all the filings, that are mixt with the quick Lime,
to melt, and no more; for if the fire be too hot, many of these filings
will joyn and run together; whereas if the heat be proportioned, upon
washing the Lime-dust in fair Water, all those small filings of the Metal
will subside to the bottom in a most curious powder, consisting all of
exactly round _Globules_, which, if it be very fine, is very excellent to
make Hour-glasses of.

Now though quick Lime be the powder that this direction makes choice of,
yet I doubt not, but that there may be much more convenient ones found out,
one of which I have made tryal of, and found very effectual; and were it
not for discovering, by the mentioning of it, another Secret, which I am
not free to impart, I should have here inserted it.

* * * * *


Observ. IX. _Of the Colours observable in Muscovy Glass, and other thin
Bodies_.

Moscovy-glass, or _Lapis specularis_, is a Body that seems to have as many
Curiosities in its Fabrick as any common Mineral I have met with: for
first, It is transparent to a great thickness: Next, it is compounded of an
infinite number of thin flakes joyned or generated one upon another so
close & smooth, as with many hundreds of them to make one smooth and thin
Plate of a transparent flexible substance, which with care and diligence
may be flit into pieces so exceedingly thin as to be hardly perceivable by
the eye, and yet even those, which I have thought the thinnest, I have with
a good _Microscope_ found to be made up of many other Plates, yet thinner;
and it is probable, that, were our _Microscopes_ much better, we might much
further discover its divisibility. Nor are these flakes only regular as to
the smoothness of their Surfaces, but thirdly, In many Plates they may be
perceived to be terminated naturally with edges of the figure of a
_Rhomboeid_. This Figure is much more conspicuous in our English talk, much
whereof is found in the Lead Mines, and is commonly called _Spar_, and
_Kauck_, which is of the same kind of substance with the _Selenitis_, but
is seldom found in so large flakes as that is, nor is it altogether so
tuff, but is much more clear and transparent, and much more curiously
shaped, and yet may be cleft and flak'd like the other _Selenitis_. But
fourthly, this stone has a property, which in respect of the _Microscope_,
is more notable, and that is, that it exhibits several appearances of
Colours, both to the naked Eye, but much more conspicuously to the
_Microscope_; for the exhibiting of which, I took a piece of
_Muscovy-glass_, and splitting or cleaving it into thin Plates, I found
that up and down in several parts of them I could plainly perceive several
white specks or flaws, and others diversly coloured with all the Colours of
the _Rainbow_; and with the _Microscope_ I could perceive, that these
Colours were ranged in rings that incompassed the white speck or flaw, and
were round or irregular, according to the shape of the spot which they
terminated; and the position of Colours, in respect of one another, was the
very same as in the _Rainbow_. The consecution of those Colours from the
middle of the spot outward being Blew, Purple, Scarlet, Yellow, Green;
Blew, Purple, Scarlet, and so onwards, sometimes half a score times
repeated, that is, there appeared six, seven, eight, nine or ten several
coloured rings or lines, each incircling the other, in the same manner as I
have often seen a very _vivid Rainbow_ to have four or five several Rings
of Colours, that is, accounting all the Gradations between Red and Blew for
one: But the order of the Colours in these Rings was quite contrary to the
primary or innermost _Rainbow_, and the same with those of the secondary or
outermost Rainbow; these coloured Lines or _Irises_, as I may so call them,
were some of them much brighter then others, and some of them also very
much broader, they being some of them ten, twenty, nay, I believe, neer a
hundred times broader then others; and those usually were broadest which
were neerest the center or middle of the flaw. And oftentimes I found, that
these Colours reacht to the very middle of the flaw, and then there
appeared in the middle a very large spot, for the most part, all of one
colour, which was very vivid, and all the other Colours incompassing it,
gradually ascending, and growing narrower towards the edges, keeping the
same order, as in the _secundary Rainbow_, that is, if the middle were
Blew, the next incompassing it would be a Purple, the third a Red, the
fourth a Yellow, &c. as above; if the middle were a Red, the next without
it would be a Yellow, the third a Green, the fourth a Blew, and so onward.
And this order it alwayes kept whatsoever were the middle Colour.

There was further observable in several other parts of this Body, many
Lines or Threads, each of them of some one peculiar Colour, and those so
exceedingly bright and vivid, that it afforded a very pleasant object
through the _Microscope_. Some of these _threads_ I have observed also to
be pieced or made up of several short lengths of differently coloured
_ends_ (as I may so call them) as a line appearing about two inches long
through the _Microscope_, has been compounded of about half an inch of a
Peach colour, 1/8 of a lovely Grass-green, 3/4 of an inch more of a bright
Scarlet, and the rest of the line of a Watchet blew. Others of them were
much otherwise coloured; the variety being almost infinite. Another thing
which is very observable, is, that if you find any place where the colours
are very broad and conspicuous to the naked eye, you may, by pressing that
place with your finger, make the colours change places, and go from one
part to another.

Copyright (c) 2007. bestextbooks.com. All rights reserved.

Anonymous - "Sir Gawayne and the Green Knight"

Erasmus Darwin - "Zoonomia, Vol. I"

Caroline E. Jacobs - "The S. W. F. Club"

Therese Albertine Louise von Jacob Robinson - "Historical View of the Languages and Literature of the Slavic"

The green room: Carol Ann Duffy, poet
Articles published by guardian.co.uk Books

Audio slideshow: Robert Shaw discusses his production of Sylvia Plath's only play
What is your biggest guilty green secret?

Stephen King fan publishes Shining's Jack Torrance's novel
Three Women was first heard as a radio drama and then published as a poem. Robert Shaw explains his desire to stage the piece as it was intended