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Micrographia by Robert Hooke

R >> Robert Hooke >> Micrographia




Whether also those steams, which seem to issue out of the Earth, and mix
with the Air (and so to precipitate some _aqueous_ Exhalations, wherewith
'tis impregnated) may not be by some way detected before they produce the
effect, seems hard to determine; yet something of this kind I am able to
discover, by an Instrument I contriv'd to shew all the minute variations in
the pressure of the Air; by which I constantly find, that before, and
during the time of rainy weather, the pressure of the Air is less, and in
_dry weather_, but especially when an _Eastern Wind_ (which having past
over vast tracts of Land is heavy with Earthy Particles) blows, it is much
more, though these changes are varied according to very odd Laws.

The Instrument is this. I prepare a pretty capaceous Bolt-head AB, with
a small stem about two foot and a half long DC; upon the end of this D
I put on a small bended Glass, or brazen _syphon_ DEF (open at D, E and
F, but to be closed with cement at F and E, as occasion serves) whose
stem F should be about six or eight inches long, but the bore of it not
above half an inch diameter, and very even; these I fix very strongly
together by the help of very hard Cement, and then fit the whole Glass
ABCDEF into a long Board, or Frame, in such manner, that almost half
the head AB may lye buried in a concave Hemisphere cut into the Board
RS; then I place it so on the Board RS, as is exprest in the first
figure of the first Scheme; and fix it very firm and steady in that
posture, so as that the weight of the _Mercury_ that is afterwards to
be put into it, may not in the least shake or stir it; then drawing a
line XY on the Frame RT, so that it may divide the ball into two equal
parts, or that it may pass, as 'twere, through the center of the ball.
I begin from that, and divide all the rest of the Board towards UT into
inches, and the inches between the 25 and the end E (which need not be
above two or three and thirty inches distant from the line XY) I
subdivide into Decimals; then stopping the end F with soft Cement, or
soft Wax, I invert the Frame, placing the head downwards, and the
Orifice E upwards; and by it, with a small Funnel, I fill the whole
Glass with Quicksilver; then by stopping the small Orifice E with my
finger, I oftentimes erect and invert the whole Glass and Frame, and
thereby free the Quicksilver and Glass from all the bubbles or parcels
of lurking Air; then inverting it as before, I fill it top full with
clear and well strain'd Quicksilver, and having made ready a small ball
of pretty hard Cement, by heat made very soft, I press it into the hole
E, and thereby stop it very fast; and to secure this Cement from flying
out afterward, I bind over it a piece of Leather, that is spread over
in the inside with Cement, and wound about it while the Cement is hot:
Having thus softned it, I gently erect again the Glass after this
manner: I first let the Frame down edge-wayes, till the edge RV touch
the Floor, or ly horizontal; and then in that edging posture raise the
end RS; this I do, that if there chance to be any Air hidden in the
small Pipe E, it may ascend into the Pipe F, and not into the Pipe DC:
Having thus erected it, and hung it by the hole Q, or fixt it
perpendicularly by any other means, I open the end F, and by a small
_Syphon_ I draw out the _Mercury_ so long, till I find the surface of
it AB in the head to touch exactly the line XY; at which time I
immediately take away the _Syphon_, and if by chance it be run somewhat
below the line XY, by pouring in gently a little _Mercury_ at F, I
raise it again to its desired height, by this contrivance I make all
the sensible rising and falling of the _Mercury_ to be visible in the
surface of the _Mercury_ in the Pipe F, and scarce any in the head AB.
But because there really is some small change of the upper surface
also, I find by several Observations how much it rises in the Ball, and
falls in the Pipe F, to make the distance between the two surfaces an
inch greater then it was before; and the measure that it falls in the
Pipe is the length of the inch by which I am to mark the parts of the
Tube F, or the Board on which it lyes, into inches and Decimals: Having
thus justned and divided it, I have a large Wheel MNOP, whose outmost
limb is divided into two hundred equal parts; this by certain small
Pillars is fixt on the Frame RT, in the manner exprest in the Figure.
In the middle of this, on the back side, in a convenient frame, is
placed a small Cylinder, whose circumference is equal to twice the
length of one of those divisions, which I find answer to an inch of
ascent, or descent, of _Mercury_: This Cylinder I, is movable on a very
small Needle, on the end of which is fixt a very light Index KL, all
which are so pois'd on the Axis, or Needle, that no part is heavier
then another: Then about this Cylinder is wound a small Clew of Silk,
with two small steel Bullets at each end of it GH; one of these, which
is somewhat the heavier, ought to be so big, as freely to move to and
fro in the Pipe F; by means of which contrivance, every the least
variation of the height of the _Mercury_ will be made exceeding visible
by the motion to and fro of the small Index KL.

But this is but one way of discovering the _effluvia_ of the Earth mixt
with the Air; there may be, perhaps many others, witness the _Hygroscope_,
an Instrument whereby the watery steams volatile in the Air are discerned,
which the Nose it self is not able to find. This I have describ'd in the
following Tract in the Description of the Beard of a wild Oat. Others
there, are, may be discovered both by the Nose, and by other wayes also.
Thus the _smoak_ of burning _Wood_ is _smelt_, _seen_, and sufficiently
_felt_ by the eyes: The _fumes_ of burning _Brimstone_ are _smelt_ and
discovered also by the destroying the Colours of Bodies, as by the
_whitening of a red Rose_: And who knows, but that the Industry of man,
following this method, may find out wayes of improving this sense to as
great a degree of perfection at it is in any Animal, and perhaps yet
higher.

'Tis not improbable also, but that our _taste_ may be very much improv'd
either by _preparing_ our taste for the Body, as, after eating _bitter_
things, _Wine_, or other _Vinous liquors_, are more sensibly tasted; or
else by _preparing_ Bodies for our tast; as the dissolving of Metals with
acid Liquors, make them tastable, which were before altogether insipid;
thus _Lead_ becomes _sweeter_ then Sugar, and _Silver_ more _bitter_ then
Gall, _Copper_ and _Iron_ of most _loathsome_ tasts. And indeed the
business of this sense being to discover the presence of dissolved Bodies
in Liquors put on the Tongue, or in general to discover that a fluid body
has some solid body dissolv'd in it, and what they are; whatever
contrivance makes this discovery improves this sense. In this kind the
mixtures of Chymical Liquors afford many Instances; as the sweet Vinegar
that is impregnated with Lead may be discovered to be so by the affusion of
a little of an _Alcalizate solution_: The bitter liquor of _Aqua fortis_
and _Silver_ may be discover'd to be charg'd with that Metal, by laying in
it some plates of Copper: 'Tis not improbable also, but there may be
multitudes of other wayes of discovering the parts dissolv'd, or dissoluble
in liquors; and what is this discovery but a kind of _secundary tasting_.

'Tis not improbable also, but that the sense of _feeling_ may be highly
improv'd, for that being a sense that judges of the more _gross_ and
_robust motions_ of the _Particles_ of _Bodies_, seems capable of being
improv'd and assisted very many wayes. Thus for the distinguishing of
_Heat_ and _Cold_, the _Weather-glass_ and _Thermometer_, which I have
describ'd in this following Treatise, do exceedingly perfect it; by each of
which the least variations of heat or cold, which the most Acute sense is
not able to distinguish, are manifested. This is oftentimes further
promoted also by the help of _Burning-glasses_, and the like, which collect
and unite the radiating heat. Thus the _roughness_ and _smoothness_ of a
Body is made much more sensible by the help of a _Microscope_, then by the
most _tender_ and _delicate Hand_. Perhaps, a Physitian might, by several
other _tangible_ proprieties, discover the constitution of a Body as well
as by the _Pulse_. I do but instance in these, to shew what possibility
there may be of many others, and what probability and hopes there were of
finding them, if this method were followed; for the Offices of the five
Senses being to detect either the _subtil_ and _curious Motions_ propagated
through all _pellucid_ or perfectly _homogeneous_ Bodies; Or the more
_gross_ and _vibrative Pulse_ communicated through the _Air_ and all other
convenient _mediums_, whether fluid or solid: Or the _effluvia_ of Bodies
_dissolv'd_ in the _Air_; Or the _particles_ of bodies _dissolv'd_ or
_dissoluble_ in _Liquors_, or the more _quick_ and _violent shaking motion_
of _heat_ in all or any of these: whatsoever does any wayes promote any of
these kinds of _criteria_, does afford a way of improving some one sense.
And what a multitude of these would a diligent Man meet with in his
inquiries? And this for the helping and promoting the _sensitive faculty_
only.

Next, as for the _Memory_, or _retentive faculty_, we may be sufficiently
instructed from the _written Histories_ of _civil actions_, what great
assistance may be afforded the Memory, in the committing to writing things
observable in _natural operations_. If a Physitian be therefore accounted
the more able in his Faculty, because he has had long experience and
practice, the remembrance of which, though perhaps very imperfect, does
regulate all his after actions: What ought to be thought of that man, that
has not only a perfect _register_ of his own experience, but it grown _old_
with the experience of many hundreds of years, and many thousands of men.

And though of late, men, beginning to be sensible of this convenience,
have here and there registred and printed some few _Centuries_, yet for the
most part they are set down very lamely and imperfectly, and, I fear, many
times not so truly, they seeming, several of them, to be design'd more for
_Ostentation_ then _publique use_: For, not to instance, that they do, for
the most part, omit those Experiences they have made, wherein their
Patients have miscarried, it is very easie to be perceiv'd, that they do
all along _hyperbolically extol_ their own Prescriptions, and vilifie those
of others. Notwithstanding all which, these kinds of Histories are
generally esteem'd useful, even to the ablest Physitian.

What may not be expected from the _rational_ or _deductive Faculty_ that
is furnisht with such _Materials_, and those so readily _adapted_, and
rang'd for use, that in a moment, at 'twere, thousands of Instances,
serving for the _illustration_, _determination_, or _invention_, of almost
any inquiry, may be _represented_ even to the sight? How neer the nature of
_Axioms_ must all those _Propositions_ be which are examin'd before so many
_Witnesses_? And how difficult will it be for any, though never so subtil
an error in Philosophy, to _scape_ from being discover'd, after it has
indur'd the _touch_, and so many other _tryals_?

What kind of mechanical way, and physical invention also is there requir'd
that might not this may be found out? The _Invention_ of a way to find the
_Longitude_ of places is easily perform'd, and that to as great
_perfection_ as is desir'd, or to at great an _accurateness_ as the
_Latitude_ of places can be found at Sea; and perhaps yet also to a greater
certainty then that has been hitherto found, as I shall very speedily
freely manifest to the world. The way of _flying_ in the Air seems
principally unpracticable, by reason of the _want of strength_ in _humane
muscles_; if therefore that could be suppli'd, it were, I think, easie to
make twenty contrivances to perform the office of _Wings_: What Attempts
also I have made for the supplying that Defect, and my successes therein,
which, I think, are wholly new, and not inconsiderable, I shall in another
place relate.

'Tis not unlikely also, but that _Chymists_, if they followed this method,
might find out their so much sought for _Alkahest_. What an _universal
Menstruum_, which dissolves all sorts of _Sulphureous Bodies_, I have
discover'd (which hat not been before taken notice of as such) I have shewn
in the sixteenth Observation.

What a prodigious variety of Inventions in _Anatomy_ has this latter Age
afforded, even in our own Bodies in the very _Heart_, by which we live, and
the Brain, which is the seat of our knowledge of other things? witness all
the excellent Works of _Pecquet_, _Bartholinus_, _Billius_, and many
others; and at home, of Doctor _Harvy_, Doctor _Ent_, Doctor _Willis_,
Doctor _Glisson_. In _Celestial Observations_ we have far exceeded all the
Antients, even the _Chaldeans_ and _Egyptians_ themselves, whose _vast
Plains_, _high Towers_, and _clear Air_, did not give them so great
advantages over us, as have over them by our _Glasses_. By the help of
which, they have been very much outdone by the famous _Galileo_,
_Hevelius_, _Zulichem_; and our own Countrymen, Mr. _Rook_, Doctor _Wren_,
and the great Ornament of our Church and Nation, the _Lord Bishop of
Exeter_. And to say no more in _Aerial Discoveries_, there has been a
wonderful progress made by the _Noble Engine_ of _the most Illustrious Mr.
Boyle_, whom it becomes me to mention with all honour, not only as my
particular Patron, but as the _Patron_ of _Philosophy_ it self; which he
every day _increases_ by his _Labours_, and _adorns_ by his _Example_.

The good success of all these _great Men_, and many others, and the now
seemingly great _obviousness_ of most of their and divers other Inventions,
which from the beginning of the world have been, as 'twere, trod on, and
yet not minded till these last _inquisitive_ Ages (an Argument that there
may be yet behind multitudes of the like) puts me in mind to recommend such
Studies, and the prosecution of them by such methods, to the _Gentlemen_ of
our Nation, whose _leisure_ makes them fit to _undertake_, and the _plenty_
of their fortunes _to accomplish_, extraordinary things in this way. And I
do not only propose this kind of _Experimental Philosophy_ as matter of
high _rapture_ and _delight_ of the mind, but even as a _material_ and
_sensible Pleasure_. So vast it the _variety of Objects_ which will come
under their Inflections, so many _different wayes_ there are _of handling_
them, so great is the _satisfaction_ of _finding_ out _new things_, that I
dare compare the _contentment_ which they will injoy, not only to that of
_contemplation_, but even to that which most men prefer of _the very Senses
themselves_.

And if they will please to take any incouragement from so mean and so
imperfect endeavours as mine, upon my own experience, I can assure them,
without arrogance, That there has not been any inquiry or Problem in
_Mechanicks_, that I have hitherto propounded to my self, but by a certain
method (which I may on some other opportunity explain) I have been able
presently to examine the possibility of it; and if so, as easily to
excogitate divers wayes of performing it: And indeed it is possible to do
as much by _this method_ in _Mechanicks_, as by _Algebra_ can be perform'd
in _Geometry_. Nor can I at all doubt, but that the same method is as
applicable to _Physical Enquiries_, and as likely to find and reap thence
at plentiful a crop of Inventions; and indeed there seems to be no subject
so barren, but may with this good husbandry be highly improv'd.

Toward the prosecution of this method in _Physical Inquiries_, I have here
and there _gleaned_ up an _handful_ of Observations, in the collection of
most of which I made use of _Microscopes_, and some other _Glasses_ and
_Instruments_ that improve the sense; which way I have herein taken, not
that there are not multitudes of useful and pleasant Observables, yet
uncollected, obvious enough without the helps of Art, but only to promote
the use of Mechanical helps for the Senses, both in the surveying the
already visible World, and for the discovery of many others hitherto
unknown, and to make us, with the great Conqueror, to be affected that we
have not yet overcome one World when there are so many others to be
discovered, every considerable improvement of _Telescopes_ or _Microscopes_
producing new Worlds and _Terra-Incognita's_ to our view.

The Glasses I used were of our English make, but though very good of the
kind, yet far short of what might be expected, could we once find a way of
making Glasses Elliptical, or of some more true shape; for though both
_Microscopes_, and _Telescopes_, as they now are, will magnifie an Object
about a thousand thousand times bigger then it appears to the naked eye;
yet the Apertures of the Object-glasses are so very small, that very few
Rays are admitted, and even of those few there are so many false, that the
Object appears _dark_ and _indistinct_: And indeed these inconveniences are
such, as seem inseparable from Spherical Glasses, even when most exactly
made; but the way we have hitherto made use of for that purpose is so
imperfect, that there may be perhaps ten wrought before one be made
tolerably good, and most of those ten perhaps every one differing in
goodness one from another, which is an Argument, that the way hitherto used
is, at least, very uncertain. So that these Glasses have a double defect;
the one, that very few of them are exactly true wrought; the other, that
even of those that are best among them, none will admit a sufficient number
of Rayes to magnifie the Object beyond a determinate bigness. Against which
Inconveniences the only Remedies I have hitherto met with are these.

First, for _Microscopes_ (where the Object we view is near and within
our power) the best way of making it appear bright in the Glass, is to
cast a great quantity of light on it by means of _convex glasses_, for
thereby, though the aperture be very small, yet there will throng in
through it such multitudes, that an Object will by this means indure to
be magnifi'd as much again as it would be without it. The way for doing
which is this. I make choice of some Room that has only one window open
to the South, and at about three or four foot distance from this
Window, on a Table, I place my _Microscope_, and then so place either a
round Globe of Water, or a very deep clear_ plano convex_ Glass (whose
convex side is turn'd towards the Window) that there is a great
quantity of Rayes collected and thrown upon the Object: Or if the Sun
shine, I place a small piece of oyly Paper very near the Object,
between that and the light; then with a good large Burning-Glass I so
collect and throw the Rayes on the Paper, that there may be a very
great quantity of light pass through it to the Object; yet I so
proportion that light, that it may not singe or burn the Paper. Instead
of which Paper there may be made use of a small piece of Looking-glass
plate, one of whose sides is made rough by being rubb'd on a flat Tool
with very find sand, this will, if the heat be leisurely cast on it,
indure a much greater degree of heat, and consequently very much
augment a convenient light. By all which means the light of the Sun, or
of a Window, may be so cast on an Object, as to make it twice as light
as it would otherwise be without it, and that without any inconvenience
of glaring, which the immediate light of the Sun is very apt to create
in most Objects; for by this means the light is so equally diffused,
that all parts are alike inlightned; but when the immediate light of
the Sun falls on it, the reflexions from some few parts are so vivid,
that they drown the appearance of all the other, and are themselves
also, by reason of the inequality of light, indistinct, and appear only
radiant spots.

But because the light of the Sun, and also that of a Window, is in a
continual variation, and so many Objects cannot be view'd long enough
by them to be throughly examin'd; besides that, oftentimes the Weather
is so dark and cloudy, that for many dayes together nothing can be
view'd: And because also there are many Objects to be met with in the
night, which cannot so conveniently be kept perhaps till the day,
therefore to procure and cast a sufficient quantity of light on an
Object in the night, I thought of, and often used this, Expedient.

I procur'd me a small Pedestal, such as is describ'd in the fifth
Figure of the first _Scheme_ on the small Pillar AB, of which were two
movable Armes CD, which by means of the Screws EF, I could fix in any
part of the Pillar; on the undermost of these I plac'd a pretty large
Globe of Glass G, fill'd with exceeding clear Brine, stopt, inverted,
and fixt in the manner visible in the Figure; out of the side of which
Arm proceeded another Arm H, with many joynts; to the end of which was
fastned a deep plain _Convex glass_ I, which by means of this Arm could
be moved too and fro, and fixt in any posture. On the upper Arm was
placed a small Lamp K, which could be to mov'd upon the end of the Arm,
as to be set in a fit posture to give light through the Ball: By means
of this Instrument duly plac'd, as is exprest in the Figure, with the
small flame of a Lamp may be cast as great and convenient a light on
the Object as it will well indure; and being always constant, and to be
had at any time, I found most proper for drawing the representations of
those small Objects I had occasion to observe.

None of all which ways (though much beyond any other hitherto made use
of by any I know) do afford a sufficient help, but after a certain
degree of magnifying, they leave us again in the lurch. Hence it were
very desirable, that some way were thought of for making the
Object-glass of such a Figure as would conveniently bear a large
Aperture.

As for _Telescopes_, the only improvement they seem capable of, is the
increasing of their length; for the Object being remote, there is no
thought of giving it a greater light then it has; and therefore to augment
the. Aperture, the Glass must be ground of a very large sphere; for, by
that means, the longer the Glass be, the bigger aperture will it bear, if
the Glasses be of an equal goodness in their kind. Therefore a six will
indure a much larger Aperture then a three foot Glass, and a sixty foot
Glass will proportionably bear a greater Aperture then a thirty, and will
as much excel it also as a six foot does a three foot, as I have
experimentally observ'd in one of that length made by Mr. _Richard Reives_
here at _London_, which will bear an Aperture above three inches over, and
yet make the Object proportionably big and distinct; whereas there are very
few thirty foot Glasses that will indure an Aperture of more then two
inches over. So that for _Telescopes_, supposing we had a very ready way of
making their Object Glasses of exactly spherical Surfaces, we might, by
increasing the length of the Glass, magnifie the Object to any assignable
bigness. And for performing both these, I cannot imagine any way more
easie, and more exact, then by this following Engine, by means of which,
any Glasses, of what length soever, may be speedily made. It seems the most
easie, because with one and the same Tool may be with care ground an Object
Glass, of any length or breadth requisite, and that with very little or no
trouble in fitting the Engine, and without much skill in the Grinder. It
seems to be the most exact, for to the very last stroke the Glass does
regulate and rectifie the Tool to its exact Figure; and the longer or more
the Tool and Glass are wrought together, the more exact will both of them
be of the desir'd Figure. Further, the motions of the Glass and Tool do so
cross each other, that there is not one point of eithers Surface, but has
thousands of cross motions thwarting it, so that there can be no kind of
Rings or Gutters made either in the Tool or Glass.

The contrivance of the Engine is, only to make the ends of two large
_Mandrils_ so to move, that the Centers of them may be at any
convenient distance asunder, and that the _Axis_ of the _Mandrils_
lying both in the same plain produc'd, may meet each other in any
assignable Angle; both which requisites may be very well perform'd by
the Engine describ'd in the third Figure of the first _Scheme_: where
AB signifies the Beam of a Lath fixt perpendicularly or Horizontally,
CD the two Poppet heads, fixt at about two foot distance, EF an Iron
_Mandril_, whose tapering neck F runs in an adapted tapering brass
Collar; the other end E runs on the point of a Screw G; in a convenient
place of this is fastned H a pully Wheel, and into the end of it, that
comes through the Poppet head C, is screwed a Ring of a hollow
_Cylinder_ K, or some other conveniently shap'd Tool, of what wideness
shall be thought most proper for the cize of Glasses, about which it is
to be imploy'd: As, for Object glasses, between twelve foot and an
hundred foot long, the Ring may be about six inches over, or indeed
somewhat more for those longer Glasses. It would be convenient also and
not very chargeable, to have four or five several Tools; as one for all
Glasses between an inch and a foot, one for all Glasses between a foot
and ten foot long, another for all between ten and an hundred, a fourth
for all between a hundred and a thousand foot long; and if Curiosity
shall ever proceed so far, one for all lengths between a thousand and
ten thousand foot long; for indeed the principle is such, that
supposing the _Mandrils_ well made, and of a good length, and supposing
great care be used in working and polishing them, I see no reason, but
that a Glass of a thousand, nay of ten thousand foot long, may be as
well made as one of ten; for the reason is the same, supposing the
_Mandrils_ and Tools be made sufficiently strong, so that they cannot
bend; and supposing the Glass, out of which they are wrought, be
capable of so great a regularity in its parts as to refraction: this
hollow _Cylinder_ K is to contain the Sand, and by being drove round
very quick to and fro by means of a small Wheel, which may be mov'd
with ones foot, serves to grind the Glass: The other _Mandril_ is
shap'd like this, but it has an even neck instead of a taper one, and
runs in a Collar, that by the help of a Screw and a joynt made like M
in the Figure, it can be still adjustned to the wearing or wasting
neck: into the end of this _Mandril_ is screwed a Chock N on which with
Cement or Glew is fastned the piece of Glass Q that is to be form'd;
the middle of which Glass is to be plac'd just on the edge of the Ring
and the Lath OP is to be set and fixt (by means of certain pieces and
screws the manner whereof will be sufficiently evidenc'd by the Figure)
in such an Angle as is requisite to the forming of such a Sphere as the
Glass is design'd to be of; the geometrical ground of which being
sufficiently plain, though not heeded before, I shall, for brevities
sake, pass over. This last _Mandril_ to be made (by means of the
former, or some other Wheel) to run round very swift also, by which two
cross motions the Glass cannot chuse (if care be us'd) but be wrought
into a most exactly spherical Surface.

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