But, _Pyrophilus_, I would not by all that I have hitherto discours'd, be
thought to have forgotten the Distinction (of Colour) that I mentioned to
you about the beginning of the third Section of the former Chapter; and
therefore, after all I have said of Colour, as it is modifi'd Light, and
immediately affects the Sensory, I shall now re-mind you, that I did not
deny, but that Colour might in some sense be consider'd as a Quality
residing in the body that is said to be Colour'd, and indeed the greatest
part of the following Experiments referr to Colour principally under that
Notion, for there is in the bodyes we call Colour'd, and chiefly in their
Superficial parts, a certain disposition, whereby they do so trouble the
Light that comes from them to our Eye, as that it there makes that distinct
Impression, upon whose Account we say, that the Seen body is either White
or Black, or Red or Yellow, or of any one determinate Colour. But because
we shall (God permiting) by the Experiments that are to follow some Pages
hence, more fully and particularly shew, that the Changes, and consequently
in divers places the Production and the appearance of Colours depends upon
the continuing or alter'd Texture of the Object, we shall in this place
intimate (and that too but as by the way) two or three things about this
Matter.
2. And first it is not without some Reason, that I ascribe Colour (in the
sense formerly explan'd) _chiefly_ to the Superficial parts of Bodies, for
not to question how much Opacous Corpuscles may abound even in those Bodies
we call Diaphanous, it seems plain that of Opacous bodies we do indeed see
little else than the Superficies, for if we found the beams of Light that
rebound from the Object to the Eye, to peirce deep into the Colour'd body,
we should not judge it Opacous, but either Translucid, or at least
Semi-diaphanous, and though the Schools seem to teach us that Colour is a
Penetrative Quality, that reaches to the Innermost parts of the Object, as
if a piece of Sealing-wax be broken into never so many pieces, the Internal
fragments will be as Red as the External surface did appear, yet that is
but a Particular Example that will not overthrow the Reason lately offer'd,
especially since I can alleage other Examples of a contrary Import, and two
or three Negative Instances are sufficient to overthrow the Generality of a
Positive Rule, especially if that be built but upon One or a Few Examples.
Not (then) to mention Cherries, Plums, and I know not how many other
Bodies, wherein the skin is of one Colour, and what it hides of another, I
shall name a couple of Instances drawn from the Colours of Durable bodies
that are thought far more Homogeneous, and have not parts that are either
Organical, or of a Nature approaching thereunto.
3 To give you the first Instance, I shall need but to remind you of what I
told you a little after the beginning of this Essay, touching the Blew and
Red and Yellow, that may be produc'd upon a piece of temper'd Steel, for
these Colours though they be very Vivid, yet if you break the Steel they
adorn, they will appear to be but Superficial; not only the innermost parts
of the Metall, but those that are within a hairs breadth of the
Superficies, having not any of these Colours, but retaining that of the
Steel it self. Besides that, we may as well confirm this Observation, as
some other particulars we elsewhere deliver concerning Colours, by the
following Experiment which we purposely made.
4 We took a good quantity of clean Lead, and melted it with a strong Fire,
and then immediately pouring it out into a clean Vessel of a convenient
shape and matter, (we us'd one of Iron, that the great and sudden Heat
might not injure it) and then carefully and nimbly taking off the Scum that
floated on the top, we perceiv'd, as we expected, the smooth and glossie
Surface of the melted matter, to be adorn'd with a very glorious Colour,
which being as Transitory as Delightfull, did almost immediately give place
to another vivid Colour, and that was as quickly succeeded by a third, and
this as it were chas'd away by a fourth, and so these wonderfully vivid
Colours successively appear'd and vanish'd, (yet the same now and then
appearing the second time) till the Metall ceasing to be hot enough to
afford any longer this pleasing Spectacle, the Colours that chanc'd to
adorn the Surface, when the Lead thus began to cool, remain'd upon it; but
were so Superficial, that how little soever we scrap'd off the Surface of
the Lead, we did in such places scrape off all the Colour, and discover
only that which is natural to the Metall it self, which receiving its
adventitious Colours, only when the heat was very Intense, and in that part
which was expos'd to the comparatively very cold Air, (which by other
Experiments seems to abound with subtil Saline parts, perhaps not uncapable
of working upon Lead so dispos'd:) These things I say, together with my
observing that whatever parts of the so strongly melted Lead were expos'd a
while to the Air, turn'd into a kind of Scum or Litharge, how bright and
clean soever they appear'd before, suggested to me some Thoughts or
Ravings, which I have not now time to acquaint You with. One that did not
know me, _Pyrophilus_, would perchance think I endeavour'd to impose upon
You by relating this Experiment, which I have several times try'd, but the
Reason why the _Phænomena_ mention'd have not been taken notice of, may be,
that unless Lead be brought to a much higher degree of Fusion or Fluidity
than is usual, or than is indeed requisite to make it melt, the _Phænomena_
I mention'd will scarce at all disclose themselves; And we have also
observ'd that this successive appearing and vanishing of vivid Colours, was
wont to be impair'd or determin'd whilst the Metal expos'd to the Air
remain'd yet hotter than one would readily suspect. And one thing I must
further Note, of which I leave You to search after the Reason, namely, that
the same Colours did not always and regularly succeed one another, as is
usually in Steel, but in the diversify'd Order mention'd in this following
Note, which I was scarce able to write down, the succession of the Colours
was so very quick, whether that proceeded from the differing degrees of
Heat in the Lead expos'd to the cool Air, or from some other Reason, I
leave you to examine.
[_Blew, Yellow, Purple, Blew; Green, Purple, Blew, Yellow, Red; Purple,
Blew, Yellow and Blew, Yellow, Blew, Purple, Green mixt, Yellow, Red,
Blew, Green, Yellow, Red, Purple, Green_.]
5. The _Atomists_ of Old, and some Learned men of late, have attempted to
explicate the variety of Colours in Opacous bodies from the various Figures
of their Superficial parts; the attempt is Ingenious, and the Doctrine
seems partly True, but I confess I think there are divers other things that
must be taken in as concurrent to produce those differing forms of
Asperity, whereon the Colours of Opacous bodies seem to depend. To declare
this a little, we must assume, that the Surfaces of all such Bodies how
Smooth or polite soever they may appear to our Dull Sight and Touch, are
exactly smooth only in a popular, or at most in a Physical sense, but not
in a strict and rigid sense.
6. This, excellent _Microscopes_ shew us in many Bodies, that seem Smooth
to our naked Eyes; and this not only as to the little Hillocks or
Protuberancies that swell above that which may be conceiv'd to be the Plain
or Level of the consider'd Surface, for it is obvious enough to those that
are any thing conversant with such Glasses, but as to numerous Depressions
beneath that Level, of which sort of Cavities by the help of a
_Microscope_, which the greatest Artificer that makes them, judges to be
the greatest Magnifying Glass in _Europe_, except one that equals it, we
have on the Surface of a thin piece of Cork that appear'd smooth to the
Eye, observ'd about sixty in a Row, within the length of less then an 31
and 32 part of an Inch, (for the Glass takes in no longer a space at one
view) and these Cavities (which made that little piece of Cork look almost
like an empty Honey-comb) were not only very distinct, and figur'd like one
another, but of a considerable bigness, and a scarce credible depth;
insomuch that their distinct shadows as well as sides were plainly
discern'd and easiy to be reckon'd, and might have been well distinguish'd,
though they had been ten times lesser than they were; which I thought it
not amiss to mention to you _Pyrophilus_ upon the by, that you may thence
make some Estimate, what a strange Inequality, and what a multitude of
little Shades, there may really be, in a scarce sensible part of the
Physical superficies, though the naked Eye sees no such matter. And as
Excellent _Microscopes_ shew us this Ruggedness in many Bodies that pass
for Smooth, so there are divers Experiments, though we must not now stay to
urge them, which seem to perswade us of the same thing as to the rest of
such Bodies as we are now treating off; So, that there is no sensible part
of an Opacous body, that may not be conceiv'd to be made up of a multitude
of singly insensible Corpuscles, but in the giving these surfaces that
disposition, which makes them alter the Light that reflects thence to the
Eye after the manner requisite to make the Object appear Green, Blew, &c.
the Figures of these Particles have _a great_, but not _the only_ stroak.
'Tis true indeed that the protuberant Particles may be of very great
variety of Figures, Sphærical, Elliptical, Conical, Cylindrical,
Polyedrical, and some very irregular, and that according to the Nature of
these, and the situation of the Lucid body, the Light must be variously
affected, after one manner from Surfaces (I now speak of Physical Surfaces)
consisting of Sphaerical, and in another from those that are made up of
Conical or Cylindrical Corpuscles; some being fitted to reflect more of the
incident Beams of Light, others less, and some towards one part, others
towards another. But besides this difference of Shape, there may be divers
other things that may eminently concurr to vary the forms of Asperity that
Colours so much depend on. For, willingly allowing the Figure of the
Particles in the first place, I consider secondly, that the superficial
Corpuscles, if I may so call them, may be bigger in one Body, and less in
another, and consequently fitted to allay the Light falling on them with
greater shades. Next, the protuberant Particles may be set more or less
close together, that is, there may be a greater or a smaller number of them
within the compass of one, than within the compass of another small part of
the Surface of the same Extent, and how much these Qualities may serve to
produce Colour may be somewhat guess'd at, by that which happens in the
Agitation of Water; for if the Bubbles that are thereby made be Great, and
but Few, the Water will scarce acquire a sensible Colour, but if it be
reduc'd to a Froth, consisting of Bubbles, which being very Minute and
Contiguous to each other, are a multitude of them crowded into a narrow
Room, the Water (turned to Froth) does then exhibit a very manifest White
Colour,[3] (to which these last nam'd Conditions of the Bubbles do as well
as their Convex figure contribute) and that for Reasons to be mention'd
anon. Besides, it is not necessary that the Superficial particles that
exhibit one Colour, should be all of them Round, or all Conical, or all of
any one Shape, but Corpuscles of differing Figures may be mingled on the
Surface of the Opacous Body, as when the Corpuscles that make a Blew
colour, and those that make a Yellow, come to be Accurately and Skilfully
mix'd, they make up a Green, which though it seem one simple Colour, yet in
this case appears to be made by Corpuscles of very differing Kinds, duely
commix'd. Moreover the Figure and Bigness of the little Depressions,
Cavities, Furrows or Pores intercepted betwixt these protuberant
Corpuscles, are as well to be consider'd as the Sizes and Shapes of the
Corpuscles themselves: For we may conceive the Physical superficies of a
Body, where (as we said) its Colour does as it were reside, to be cut
Transversly by a Mathematical plain, which you know is conceiv'd to be
without any Depth or Thickness at all, and then as some parts of the
Physical Superficies will be Protuberant; or swell above this last plain,
so others may be depress'd beneath it; as (to explane my self by a gross
Comparison) in divers places of the Surface of the Earth, there are not
only Neighbouring Hills, Trees, &c. that are rais'd above the Horizontal
Level of the Valley, but Rivers, Wells, Pits and other Cavities that are
depress'd beneath it, and that such Protuberant and Concave parts of a
Surface may remit the Light so differingly, as much to vary a Colour, some
examples and other things, that we shall hereafter have occasion to take
notice off in this Tract, will sufficiently declare, till when, it may
suffice to put you in mind, that of two Flat-sides of the same piece of,
for example, red Marble, the one being diligently Polished, and the other
left to its former Roughness, the differing degrees or sorts of Asperity,
for the side that is smooth to the Touch wants not its Roughness, will so
diversifie the Light reflected from the several Plains to the Eye, that a
Painter would employ two differing Colours to represent them.
[3] _See the Discourse of the Nature of Whiteness and Blackness._
7. And I hope, _Pyrophilus_, you will not think it strange or impertinent,
that I employ in divers passages of these Papers, examples drawn from
Bodies and Shadows far more Gross, than those minute Protuberances and
shady Pores on which in most cases the Colour of a Body as 'tis an Inherent
Quality or Disposition of its Surface, seems to depend. For sometimes I
employ such Examples, rather to declare my Meaning, than prove my
Conjecture; things, whom their Smallness makes Insensible, being better
represented to the Imagination by such familiar Objects, as being like them
enough in other respects, are of a Visible bulk. And next, though the Beams
of Light are such subtil Bodies, that in respect of them, even Surfaces
that are sensibly Smooth, are not exactly so, but have their own degree of
Roughness, consisting of little Protuberances and Depressions; and though
consequently such Inequalities may suffice to give Bodies differing
Colours, as we see in Marble that appears White or Black, or Red or Blew,
even when the most carefully Polish'd, yet 'tis plain by the late Instance
of Red Marble, and many others, that even bigger Protuberances and greater
Shades may likewise so Diversifie the Roughness of a Bodies Superficies, as
manifestly to concurr to the varying of its Colour, whereby such Examples
appear to be proper enough to be employ'd in such a Subject as we have now
in hand. And having hinted thus much on this Occasion, I now proceed.
8. The Situation also of the Superficial particles is considerable, which I
distinguish into the Posture of the single Corpuscles, in respect of the
Light, and of the Eye, and the Order of them in reference also to one
another; for a Body may otherwise reflect the Light, when its Superficial
particles are more erected upon the Plain that may be conceiv'd to pass
along their Basis, and when the Points or Extremes of such Particles are
Obverted to the Eye, than when those Particles are so Inclin'd, that their
Sides are in great part Discernable, as the Colour of Plush or Velvet will
appear Vary'd to you, if you carefully stroak part of it one way, and part
of it another, the posture of the particular Thrids, in reference to the
Light, or the Eye, becoming thereby different. And you may observe in a
Field of ripe Corn blown upon by the Wind, that there will appear as it
were Waves of a Colour (at least Gradually) differing from that of the rest
of the Field, the Wind by Depressing some of the Ears, and not at the same
time others, making the one Reflect more from the Lateral and Strawy parts,
than do the rest. And so, when Doggs are so angry, as to Erect the Hairs
upon their Necks, and upon some other parts of their Bodies, those Parts
seem to acquire a Colour vary'd from that which the same Hairs made, when
in their usual Posture they did farr more stoop. And that the Order wherein
the Superficial Corpuscles are Rang'd is not to be neglected, we may guess
by turning of Water into Froth, the beating of Glass, and the scraping of
Horns, in which cases the Corpuscles that were before so marshall'd as to
be Perspicuous, do by the troubling of that Order become Dispos'd to
terminate and reflect more Light, and thereby to appear Whitish. And there
are other ways in which the Order of the Protuberant parts, in reference to
the Eye, may much contribute to the appearing of a particular Colour, for I
have often observ'd, that when Pease are Planted, or Set in Parallel Lines,
and are Shot up about half a Foot above the Surface of the Ground, by
looking on the Field or Plot of Ground from that part towards which the
Parallel Lines tended, the greater part of the Ground by farr would appear
of its own dirty Colour, but if I look'd upon it Transversly, the Plot
would appear very Green, the upper parts of the Pease hindering the
intercepted parts of the Ground, which as I said retain'd their wonted
Colour, from being discover'd by the Eye. And I know not, _Pyrophilus_,
whether I might not add, that even the Motion of the Small Parts of a
Visible Object may in some cases contribute, though it be not so easie to
say how, to the Producing or the Varying of a Colour; for I have several
times made a Liquor, which when it has well settled in a close Vial, is
Transparent and Colourless, but as soon as the Glass is unstopp'd, begins
to fly away very plentifully in a White and Opacous fume; and there are
other Bodies, whose Fumes, when they fill a Receiver, would make one
suspect it contains Milk, and yet when these Fumes settle into a Liquor,
that Liquor is not White, but Transparent; And such White Fumes I have seen
afforded by unstopping a Liquor I know, which yet is it self Diaphanous and
Red; Nor are these the only Instances of this Kind, that our Tryals can
supply us with. And if the Superficial Corpuscles be of the Grosser sort,
and be so Framed, that their differing Sides or Faces may exhibit differing
Colours, then the Motion or Rest of those Corpuscles may be considerable,
as to the Colour of the Superficies they compose, upon this account, that
sometimes more, sometimes fewer of the Sides dispos'd to exhibit such a
Colour may by this means become or continue more Obverted to the Eye than
the rest, and compose a Physical Surface, that will be more or less
sensibly interrupted; As, to explane my meaning, by proposing a gross
Example, I remember, that in some sorts of Leavy Plants thick set by one
another, the two sides of whose Leaves were of somewhat differing Colours,
there would be a notable Disparity as to Colour, if you look'd upon them
both when the Leaves being at Rest had their upper and commonly expos'd
sides Obverted to the Eye, and when a breath of Wind passing thorow them,
made great Numbers of the usually Hidden sides of the Leaves become
conspicuous. And though the Little Bodies, we were lately speaking of, may
Singly and Apart seem almost Colourless, yet when Many of them are plac'd
by one another, so near, that the Eye does not easily discern an
Interruption, within a sensible space, they may exhibit a Colour; as we
see, that though a Slenderest Thrid of Dy'd Silk do's, whilst look'd on
Single, seem almost quite Devoyd of Redness, (for instance) yet when
numbers of these Thrids are brought together into one Skein, their Colour
becomes notorious.
9. But the same Occasion that invited me to say what I have mention'd
concerning the Leaves of Trees, invites me also to give you some account of
what happens in Changeable Taffities, where we see differing Colours, as it
were, Emerge and Vanish upon the Ruffling of the same piece of Silk: As I
have divers times with Pleasure observ'd, by the help of such a
_Microscope_, as, though it do not very much Magnifie the Object, has in
recompence this great Conveniency, that you may easily, as fast as you
please, remove it from one part to another of a Large Object, of which the
Glass taking a great part at once, you may thereby presently Survey the
Whole. Now by the help of such a _Microscope_ I could easily (as I began to
say) discern, that in a piece of Changeable Taffity, (that appear'd, for
Instance, sometimes Red, and sometimes Green) the Stuff was compos'd of Red
thrids and Green, passing under and over each other, and crossing one
another in almost innumerable points; and if I look'd through the Glass
upon any considerable portion of the Stuff, that (for example sake) to the
naked Eye appear'd to be Red, I could plainly see, that in that Position,
the Red thrids were Conspicuous, and reflected a vivid Light; and though I
could also perceive, that there were Green ones, yet by reason of their
disadvantagious Position in the _Physical Surface_ of the Taffity, they
were in part hid by the more Protuberant Thrids of the other Colour; and
for the same cause, the Reflection from as much of the Green as was
discover'd, was comparatively but Dim and Faint. And if, on the contrary, I
look'd through the _Microscope_ upon any part that appear'd Green, I could
plainly see that the Red thrids were less fully expos'd to the Eye, and
obscur'd by the Green ones, which therefore made up the Predominant Colour.
And by observing the Texture of the Silken Stuff, I could easisy so expose
the Thrids either of the one Colour or of the other to my Eye, as at
pleasure to exhibit an apparition of Red or Green, or make those Colours
succeed one another: So that, when I observ'd their Succession by the help
of the Glass, I could mark how the Predominant Colour did as it were start
out, when the Thrids that exhibited it came to be advanagiously plac'd; And
by making little Folds in the Stuff after a certain manner, the Sides that
met and terminated in those Folds, would appear to the naked Eye, one of
them Red, and the other Green. When Thrids of more than two differing
Colours chance to be Interwoven, the resulting changeableness of the
Taffity may be also somewhat different. But I choose to give an Instance in
the Stuff I have been speaking off, because the mixture being more Simple,
the way whereby the Changeableness is produc'd, may be the more easily
apprehended: and though Reason alone might readily enough lead a
considering Man to guess at the Explication, in case he knew how Changeable
Taffities are made: yet I thought it not impertinent to mention it, because
both Scholars and Gentlemen are wont to look upon the Inquiry into
Manufactures, as a _Mechanick_ imployment, and consequently below Them; and
because also with such a _Microscope_ as I have been mentioning, the
discovery is as well Pleasant as Satisfactory, and may afford Hints of the
Solution of other _Phænomena_ of Colours. And it were not amiss, that some
diligent Inquiry were made, whether the _Microscope_ would give us an
account of the Variableness of Colour, that is so Conspicuous and so
Delightfull in Mother of Pearl, in Opalls, and some other resembling
Bodies: For though I remember I did formerly attempt something of that Kind
(fruitlesly enough) upon Mother of Pearl, yet not having then the advantage
of my best _Microscope_, nor some Conveniences that might have been wish'd,
I leave it to you, who have better Eyes, to try what you can do further;
since 'twill be _Some_ discovery to find, that, in this case, the best Eyes
and _Microscopes_ themselves can make _None_.
10. I confess, _Pyrophilus_, that a great part of what I have deliver'd,
(or propos'd rather) concerning the differing forms of Asperity in Bodies,
by which Differences the incident Light either comes to be Reflected with
more or less of Shade, and with that Shade more or less Interrupted, or
else happens to be also otherwise Modify'd or Troubl'd, is but Conjectural.
But I am not sure, that if it were not for the Dullness of our Senses,
either these or some other Notions of Kin to them, might be better
Countenanc'd; for I am apt to suspect, that if we were Sharp sighted
enough, or had such perfect _Microscopes_, as I fear are more to be wish'd
than hop'd for, our promoted Sense might discern in the Physical Surfaces
of Bodies, both a great many latent Ruggidnesses, and the particular Sizes,
Shapes, and Situations of the extremely little Bodies that cause them, and
perhaps might perceive among other Varieties that we now can but imagine,
how those little Protuberances and Cavities do Interrupt and Dilate the
Light, by mingling with it a multitude of little and singly undiscernable
Shades, though some of them more, and some of them less Minute, some less,
and some more Numerous; according to the Nature and Degree of the
particular Colour we attribute to the Visible Object; as we see, that in
the Moon we can with Excellent _Telescopes_ discern many Hills and Vallies,
and as it were Pits and other Parts, whereof some are more, and some less
Vividly illustrated, and others have a fainter, others a deeper Shade,
though the naked Eye can discern no such matter in that Planet. And with an
Excellent _Microscope_, where the _Naked_ Eye did see but a Green powder,
the _Assisted_ Eye as we noted above, could discern particular Granules,
some of them of a Blew, and some of them of a Yellow colour, which
Corpuscles we had beforehand caus'd to be exquisitly mix'd to compound the
Green.
11. And, _Pyrophilus_, that you may not think me altogether extravagant in
what I have said of the Possibility, (for I speak of no more) of discerning
the differing forms of Asperity in the Surfaces of Bodies of several
Colours, I'l here set down a Memorable particular that chanc'd to come to
my Knowledge, since I writ a good part of this _Essay_; and it is this.
Meeting casually the other Day with the deservedly Famous[4] Dr. _J.
Finch_, Extraordinary _Anatomist_ to that Great Patron of the _Virtuosi_,
the now Great Duke of _Toscany_, and enquiring of this Ingenious Person,
what might be the chief Rarity he had seen in his late return out of
_Italy_ into _England_, he told me, it was a Man at _Maestricht_ in the
Low-Countrys, who at certain times can discern and _distinguish Colours by
the Touch_ with his Fingers. You'l easily Conclude, that this is farr more
strange, than what I propos'd but as _not Impossible_; since the Sense of
the _Retina_ seeming to be much more Tender and quick than that of those
Grosser Filaments, Nerves or Membranes of our Fingers, wherewith we use to
handle Gross and Hard Bodies, it seems scarce credible, that any
Accustomance, or Diet, or peculiarity of Constitution, should enable a Man
to distinguish with such Gross and Unsuitable Organs, such Nice and Subtile
Differences as those of the forms of Asperity, that belong to differing
Colours, to receive whose Languid and Delicate Impressions by the
Intervention of Light, Nature seems to have appointed and contexed into the
_Retina_ the tender and delicate Pith of the Optick Nerve. Wherefore I
confess, I propos'd divers Scruples, and particularly whether the Doctor
had taken care to bind a Napkin or Hankerchief over his Eyes so carefully,
as to be sure he could make no use of his Sight, though he had but
Counterfeited the want of it, to which I added divers other Questions, to
satisfie my Self, whether there were any Likelihood of Collusion or other
Tricks. But I found that the Judicious Doctor having gone farr out of his
way, purposely to satisfie Himself and his Learned Prince about this
Wonder, had been very Watchfull and Circumspect to keep _Himself_ from
being Impos'd upon. And that he might not through any mistake in point of
Memory mis-inform _Me_, he did me the Favour at my Request, to look out the
Notes he had Written for his Own and his Princes Information, the summ of
which Memorials, as far as we shall mention them here, was this, That the
Doctor having been inform'd at _Utrecht_, that there Lived one at some
Miles distance from _Maestricht_, who could distinguish Colours by the
Touch, when he came to the last nam'd Town, he sent a Messenger for him,
and having Examin'd him, was told upon Enquiry these Particulars:
[4] Since for his eminent Qualities and Loyalty Grac'd, by his Majesty,
with the Honour of Knighthood.
That the Man's name was _John Vermaasen_, at that time about 33 Years of
Age; that when he was but two years Old, he had the Small Pox, which
rendred him absolutely Blind: That at this present he is an _Organist_, and
serves that Office in a publick Quire.
That the Doctor discoursing with him over Night, the Blind man affirm'd,
that he could distinguish Colours by the Touch, but that he could not do
it, unless he were Fasting; Any quantity of Drink taking from him that
Exquisitness of Touch, which is requisite to so Nice a Sensation.
That hereupon the Doctor provided against the next Morning seven pieces of
Ribbon, of these seven Colours, Black, White, Red, Blew, Green, Yellow, and
Gray, but as for _mingled_ Colours, this _Vermaasen_ would not undertake to
discern them, though if offer'd, he would tell that they were _Mix'd_.
That to discern the Colour of the Ribbon, he places it betwixt the Thumb
and the Fore-finger, but his most exquisite perception was in his Thumb,
and much better in the right Thumb than in the left.
That after the Blind man had four or five times told the Doctor the several
Colours, (though Blinded with a Napkin for fear he might have some Sight)
the Doctor found he was twice mistaken, for he call'd the White Black, and
the Red Blew, but still, he, before his Errour, would lay them by in Pairs,
saying, that though he could easily distinguish them from all others, yet
those two Pairs were not easily distinguish'd amongst themselves, whereupon
the Doctor desir'd to be told by him what kind of Discrimination he had of
Colours by his Touch, to which he gave a reply, for whose sake chiefly I
insert all this Narrative in this place, namely, That all the difference
was more or less Asperity, for says he, (I give you the Doctor's own words)
Black feels as if you were feeling Needles points, or some harsh Sand, and
Red feels very Smooth.
That the Doctor having desir'd him to tell in Order the difference of
Colours to his Touch, he did as follows;
Black and White are the most asperous or unequal of all Colours, and so
like, that 'tis very hard to distinguish them, but Black is the most Rough
of the two, Green is next in Asperity, Gray next to Green in Asperity,
Yellow is the fifth in degree of Asperity, Red and Blew are so like, that
they are as hard to distinguish as Black and White, but Red is somewhat
more Asperous than Blew, so that Red has the sixth place, and Blew the
seventh in Asperity.
12. To these Informations the Obliging Doctor was pleas'd to add the
welcome present of three of those very pieces of Ribbon, whose Colours in
his presence the Blind man had distinguished, pronouncing the one Gray, the
other Red, and the third Green, which I keep by me as Rarities, and the
rather, because he fear'd the rest were miscarry'd.
13. Before I saw the Notes that afforded me the precedent Narrative, I
confess I suspected this man might have thus discriminated Colours, rather
by the Smell than by the Touch; for some of the Ingredients imployed by
Dyers to Colour things, have Sents, that are not so Languid, nor so near of
Kin, but that I thought it not impossible that a very Critical Nose might
distinguish them, and this I the rather suspected, because he requir'd,
that the Ribbons, whose Colours he was to Name, should be offer'd him
Fasting in the morning; for I have observ'd in Setting Doggs, that the
feeding of them (especially with some sorts of Aliments) does very much
impair the exquisite sent of their Noses. And though some of the foregoing
particulars would have prevented that Conjecture, yet I confess to you
(_Pyrophilus_) that I would gladly have had the Opportunity of Examining
this Man my self, and of Questioning him about divers particulars which I
do not find to have been yet thought upon. And though it be not incredible
to me, that since the Liquors that Dyers imploy to tinge, are qualifi'd to
do so by multitudes of little Corpuscles of the Pigment or Dying stuff,
which are dissolved and extracted by the Liquor, and swim to and fro in it,
those Corpuscles of Colour (as the _Atomists_ call them) insinuating
themselves into, and filling all the Pores of the Body to be Dyed, may
Asperate its Superficies more or less according to the Bigness and Texture
of the Corpuscles of the Pigment; yet I can scarce believe, that our Blind
man could distinguish all the Colours he did, meerly by the Ribbons having
more or less of Asperity, so that I cannot but think, notwithstanding this
History, that the Blind man distinguish'd Colours not only by the _Degrees_
of Asperity in the Bodies offer'd to him, but by _Forms_ of it, though this
(latter) would perhaps have been very difficult for him to make an
Intelligible mention of, because those Minute disparities having not been
taken notice of by men for want of touch as Exquisite as our Blind Mans,
are things he could not have Intelligibly express'd, which will easily seem
Probable, if you consider, that under the name of Sharp, and Sweet, and
Sour, there are abundance of, as it were, immediate peculiar Relishes or
Tasts in differing sorts of Wine, which though Critical and Experienc'd
Palats can easily discern themselves cannot make them be understood by
others, such Minute differences not having hitherto any Distinct names
assign'd them. And it seems that there was somthing in the Forms of
Asperity that was requisite to the Distinction of Colours, besides the
Degree of it, since he found it so difficult to distingush Black and White
from one another, though not from other Colours. For I might urge, that he
seems not consonant to himself about the _Red_, which as you have seen in
one place, he represents as somewhat more Asperous than the _Blew_; and in
another, very Smooth: But because he speaks of this Smoothness in that
place, where he mentions the Roughness of _Black_, we may favourably
presume that he might mean but a _comparative Smoothness_; and therefore I
shall not Insist on this, but rather Countenance my Conjecture by this,
that he found it so Difficult, not only, to Discriminate Red and Blew,
(though the first of our promiscuous Experiments will inform you, that the
Red reflects by great Odds more Light than the other) but also to
distinguish Black and White from one another, though not from other
Colours. And indeed, though in the Ribbonds that were offer'd him, they
might be almost equally Rough, yet in such slender Corpuscles as those of
Colour, there may easily enough be Conceiv'd, not only a greater Closeness
of Parts, or else Paucity of Protuberant Corpuscles, and the little extant
Particles may be otherwise Figur'd, and Rang'd in the White than in the
Black, but the Cavities may be much Deeper in the one than the other.
14. And perhaps, (_Pyrophilus_) it may prove some _Illustration of what I
mean_, and help you to conceive how _this may_ be, if I Represent, that
where the Particles are so exceeding Slender, we may allow the Parts
expos'd to the Sight and Touch to be a little Convex in comparison of the
Erected Particle of Black Bodies, as if there were Wyres I know not how
many times Slenderer than a Hair: whether you suppose them to be Figur'd
like Needles, or Cylindrically, like the Hairs of a Brush, with
Hemisphærical (or at least Convex) Tops, they will be so very Slender, and
consequently the Points both of the one sort and the other so very Sharp,
that even an exquisite Touch will be able to distinguish no greater
Difference between them, than that which our Blind man allow'd, when
comparing Black and White Bodies, he said, that the latter was the less
Rough of the two. Nor is every Kind of Roughness, though Sensible enough,
Inconsistent with Whiteness, there being Cases, wherein the Physical
Superficies of a Body is made by the same Operation both _Rough_ and
_white_, as when the Level Surface of clear Water being by agitation
Asperated with a multitude of Unequal Bubbles, do's thereby acquire a
Whiteness; and as a Smooth piece of Glass, by being Scratch'd with a
Diamond, do's in the Asperated part of its Surface disclose the same
Colour. But more (perchance) of this elsewhere.
15. And therefore, we shall here pass by the Question, whether any thing
might be consider'd about the Opacity of the Corpuscles of Black Pigments,
and the _Comparative_ Diaphaneity of those of many White Bodies, apply'd to
our present Case; and proceed, to represent, That the newly mention'd
Exiguity and Shape of the extant Particles being suppos'd, it will then be
considerable what we lately but Hinted, (and therefore must now somewhat
Explane) That the Depth of the little Cavities, intercepted between the
extant Particles, without being so much greater in Black Bodies than in
White ones, as to be perceptibly so to the Gross Organs of Touch, may be
very much greater in reference to their Disposition of Reflecting the
imaginary subtile Beams of Light. For in Black Bodies, those Little
intercepted Cavities, and other Depressions, may be so Figur'd, so Narrow
and so Deep, that the incident Beams of Light, which the more extant Parts
of the Physical Superficies are dispos'd to Reflect inwards, may be
Detain'd there, and prove unable to Emerge; whilst in a White Body, the
Slender Particles may not only by their Figure be fitted to Reflect the
Light copiously outwards, but the intercepted Cavities being not Deep, nor
perhaps very Narrow, the Bottoms of them may be so Constituted, as to be
fit to Reflect outwards much of the Light that falls even upon Them; as you
may possibly better apprehend, when we shall come to treat of Whiteness and
Blackness. In the mean time it may suffice, that you take Notice with me,
that the Blind mans Relations import no necessity of Concluding, that,
though, because, according to the Judgment of his Touch, Black was the
Roughest, as it is the Darkest of Colours, therefore White, which
(according to us) is the Lightest, should be also the Smoothest: since I
observe, that he makes Yellow to be two Degrees more Asperous than Blew,
and as much less Asperous than Green; whereas indeed, Yellow do's not only
appear to the Eye a Lighter Colour than Blew, but (by our first Experiment
hereafter to be mention'd) it will appear, that Yellow reflected much more
Light than Blew, and manifestly more than Green, (which we need not much
wonder at, since in this Colour and the two others (Blew and Yellow) 'tis
not _only_ the _Reflected Light_ that is to be considered, since to produce
both these, _Refraction_ seems to Intervene, which by its Varieties may
much alter the Case:) which both seems to strengthen the Conjecture I was
formerly proposing, that there was something else in the _Kinds_ of
Asperity, as well as in the _Degrees_ of it, which enabled our Blind man to
Discriminate Colours, and do's at least show, that we cannot in all Cases
from the bare Difference in the Degrees of Asperity betwixt Colours, safely
conclude, that the Rougher of any two always Reflects the least Light.
16. But this notwithstanding, (_Pyrophilus_) and what ever Curiosity I may
have had to move some Questions to our Sagacious Blind man, yet thus much I
think you will admit us to have gain'd by his Testimony, that since many
Colours may be felt with the Circumstances above related, the Surfaces of
such Coloured Bodies must certainly have differing _Degrees_, and in all
probability have differing _Forms_ or Kinds of Asperity belonging to them,
which is all the Use that my present attempt obliges me to make of the
History above deliver'd, that being sufficient to prove, _that_ Colour do's
much depend upon the Disposition of the Superficial parts of Bodies, and to
shew in general, _wherein_ 'tis probable that such a Disposition do's
(principally at least) consist.
17. But to return to what I was saying before I began to make mention of
our Blind _Organist_, what we have deliver'd touching the causes of the
several Forms or Asperity that may Diversifie the Surfaces of Colour'd
Bodies, may perchance somewhat assist us to make some Conjectures in the
general, at several of the ways whereby 'tis possible for the Experiments
hereafter to be mention'd, to produce the suddain changes of Colours that
are wont to be Consequent upon them; for most of these _Phænomena_ being
produc'd by the Intervention of Liquors, and these for the most part
abounding with very Minute, Active, and Variously Figur'd Saline
Corpuscles, Liquors so Qualify'd may well enough very Nimbly after the
Texture of the Body they are imploy'd to Work upon, and so may change the
form of Asperity, and thereby make them Remit to the Eye the Light that
falls on them, after another manner than they did before, and by that means
Vary the Colour, so farr forth as it depends upon the Texture or
Disposition of the Seen Parts of the Object, which I say, _Pyrophilus_,
that you may not think I would absolutely exclude all other ways of
Modifying the Beams of Light between their Parting from the Lucid Body, and
their Reception into the common Sensory.
18. Now there seem to me divers ways, by which we may conceive that Liquors
may Nimbly alter the Colour of one another, and of other Bodies, upon which
they Act, but my present haste will allow me to mention but some of them,
without Insisting so much as upon those I shall name.
19. And first, the Minute Corpuscles that compose a Liquor may early
insinuate themselves into those Pores of Bodies, whereto their Size and
Figure makes them Congruous, and these Pores they may either exactly Fill,
or but Inadequately, and in this latter Case they will for the most part
alter the Number and Figure, and always the Bigness of the former Pores.
And in what capacity soever these Corpuscles of a Liquor come to be Lodg'd
or Harbour'd in the Pores that admit them, the Surface of the Body will for
the most part have its Asperity alter'd, and the Incident Light that meets
with a Grosser Liquor in the little Cavities that before contain'd nothing
but Air, or some yet Subtiler Fluid, will have its Beams either Refracted,
or Imbib'd, or else Reflected more or less Interruptedly, than they would
be, if the Body had been Unmoistned, as we see, that even fair Water
falling on white Paper, or Linnen, and divers other Bodies apt to soak it
in, will for some such Reasons as those newly mention'd, immediately alter
the Colour of them, and for the most part make it Sadder than that of the
Unwetted Parts of the same Bodies. And so you may see, that when in the
Summer the High-ways are Dry and Dusty, if there falls store of Rain, they
will quickly appear of a much Darker Colour than they did before, and if a
Drop of Oyl be let fall upon a Sheet of White Paper, that part of it, which
by the Imbibition of the Liquor acquires a greater Continuity, and some
Transparency, will appear much Darker than the rest, many of the Incident
Beams of Light being now Transmitted, that otherwise would be Reflected
towards the Beholders Eyes.
20. Secondly, A Liquor may alter the Colour of a Body by freeing it from
those things that hindred it from appearing in its Genuine Colour; and
though this may be said to be rather a Restauration of a Body to its own
Colour, or a Retection of its native Colour, than a Change, yet still there
Intervenes in it a change of the Colour which the Body appear'd to be of
before this Operation. And such a change a Liquor may work, either by
Dissolving, or Corroding, or by some such way of carrying off that Matter,
which either Veil'd or Disguis'd the Colour that afterwards appears. Thus
we restore Old pieces of Dirty Gold to a clean and nitid Yellow, by putting
them into the Fire, and into _Aqua-fortis_, which take off the adventitious
Filth that made that pure Metall look of a Dirty Colour. And there is also
an easie way to restore Silver Coyns to their due Lustre, by fetching off
that which Discolour'd them. And I know a _Chymical_ Liquor, which I
employ'd to restore pieces of Cloath spotted with Grease to their proper
Colour, by Imbibing the Spotted part with this Liquor, which Incorporating
with the Grease, and yet being of a very Volatile Nature, does easily carry
it away with it Self. And I have sometimes try'd, that by Rubbing upon a
good Touch-stone a certain _Metalline_ mixture so Compounded, that the
Impression it left upon the Stone appear'd of a very differing Colour from
that of Gold, yet a little of _Aqua-fortis_ would in a Trice make the
Golden Colour disclose it self, by Dissolving the other _Metalline_
Corpuscles that conceal'd those of the Gold, which you know that
_Menstruum_ will leave Untouch'd.
21. Thirdly, A Liquor may alter the Colour of a Body by making a
Comminution of its Parts, and that principally two ways, the first by
Disjoyning and Dissipating those Clusters of Particles, if I may so call
them, which stuck more Loosely together, being fastned only by some more
easily Dissoluble Ciment, which seems to be the Case of some of the
following Experiments, where you'l find the Colour of many Corpuscles
brought to cohere by having been Precipitated together, Destroy'd by the
Affusion of very peircing and incisive Liquors. The other of the two ways I
was speaking of, is, by Dividing the Grosser and more Solid Particles into
Minute ones, which will be always Lesser, and for the most part otherwise
Shap'd than the Entire Corpuscle so Divided, as it will happen in a piece
of Wood reduc'd into Splinters or Chips, or as when a piece of Chrystal
heated red Hot and quench'd in Cold water is crack'd into a multitude of
little Fragments, which though they fall not asunder, alter the Disposition
of the Body of the Chrystal, as to its manner of Reflecting the Light, as
we shall have Occasion to shew hereafter.
22. There is a fourth way contrary to the third, whereby a Liquor may
change the Colour of another Body, especially of another Fluid, and that
is, by procuring the Coalition of several Particles that before lay too
Scatter'd and Dispers'd to exhibit the Colour that afterwards appears. Thus
sometimes when I have had a Solution of Gold so Dilated, that I doubted
whether the Liquor had really Imbib'd any true Gold or no, by pouring in a
little _Mercury_, I have been quickly able to satisfie my Self, that the
Liquor contain'd Gold, that Mettall after a little while Cloathing the
Surface of the _Quick-silver_, with a Thin Film of its own Livery. And
chiefly, though not only by this way of bringing the Minute parts of Bodies
together in such Numbers as to make them become Notorious to the Eye, many
of these Colours seem to be Generated which are produc'd by Precipitations,
especially by such as are wont to be made with fair Water, as when Resinous
Gumms dissolv'd in Spirit of Wine, are let fall again, if the Spirit be
Copiously diluted with that weakning Liquor. And so out of the Rectify'd
and Transparent Butter of _Antimony_, by the bare Mixture of fair Water,
there will be plentifully Precipitated that Milk-white Substance, which by
having its Looser Salts well wash'd off, is turn'd into that Medicine,
which Vulgar _Chymists_ are pleas'd to call _Mercurius Vitæ._
23. A fifth way, by which a Liquor may change the Colour of a Body, is, by
Dislocating the Parts, and putting them out of their former Order into
another, and perhaps also altering the Posture of the single Corpuscles as
well as their Order or Situation in respect of one another. What certain
Kinds of Commotion or Dislocation of the Parts of a Body may do towards the
Changing its Colour, is not only evident in the Mutations of Colour
observable in _Quick-silver_, and some other Concretes long kept by
_Chymists_ in a Convenient Heat, though in close Vessels, but in the
Obvious Degenerations of Colour, which every Body may take notice of in
Bruis'd Cherries, and other Fruit, by comparing after a while the Colour of
the Injur'd with that of the Sound part of the same Fruit. And that also
such Liquors, as we have been speaking of, may greatly Discompose the
Textures of many Bodies, and thereby alter the Disposition of their
Superficial parts, the great Commotion made in Metalls, and several other
Bodies by _Aqua-fortis_, Oyl of _Vitriol_, and other Saline _Menstruums_,
may easily perswade us, and what such Vary'd Situations of Parts may do
towards the Diversifying of the manner of their Reflecting the Light, may
be Guess'd in some Measure by the Beating of Transparent Glass into a White
Powder, but farr better by the Experiments lately Pointed at, and hereafter
Deliver'd, as the Producing and Destroying Colours by the means of subtil
Saline Liquors, by whose Affusion the Parts of other Liquors are manifestly
both Agitated, and likewise Dispos'd after another manner than they were
before such Affusion. And in some _Chymical_ Oyls, as particularly that of
Lemmon Pills, by barely Shaking the Glass, that holds it, into Bubbles,
that Transposition of the Parts which is consequent to the Shaking, will
shew you on the Surfaces of the Bubbles exceeding Orient and Lively
Colours, which when the Bubbles relapse into the rest of the Oyl, do
immediately Vanish.
24. I know not, _Pyrophilus_, whether I should mention as a Distinct way,
because it is of a somewhat more General Nature, that Power, whereby a
Liquor may alter the Colour of another Body, by putting the Parts of it
into Motion; For though possibly the Motion so produc'd, does, as such,
seldome suddenly change the Colour of the Body whose Parts are Agitated,
yet this seems to be one of the most General, however not Immediate causes
of the Quick change of Colours in Bodies. For the Parts being put into
Motion by the adventitious Liquor, divers of them that were before United,
may become thereby Disjoyn'd, and when that Motion ceases or decays others
of them may stick together, and that in a new Order, by which means the
Motion may sometimes produce Permanent changes of Colours, as in the
Experiment you will meet with hereafter, of presently turning a Snowy White
Body into a Yellow, by the bare Affusion of fair Water, which probably so
Dissolves the Saline Corpuscles that remain'd in the _Calx_, and sets them
at Liberty to Act upon one another, and the Metall, far more Powerfully
than the Water without the Assistance of such Saline Corpuscles could do.
And though you rubb Blew _Vitriol_, how Venereal and Unsophisticated soever
it be, upon the Whetted Blade of a Knife, it will not impart to the Iron
its Latent Colour, but if you moisten the _Vitriol_ with your Spittle, or
common Water, the Particles of the Liquor disjoyning those of the
_Vitriol_, and thereby giving them the Various Agitation requisite to Fluid
Bodies, the Metalline Corpuscles of the thus Dissolv'd _Vitriol_ will Lodge
themselves in Throngs in the Small and Congruous Pores of the Iron they are
Rubb'd on, and so give the Surface of it the Genuine Colour of the Copper.
25. There remains yet a way, _Pyrophilus_ to be mention'd, by which a
Liquor may alter the Colour of another Body, and this seems the most
Important of all, because though it be nam'd but as One, yet it may indeed
comprehend Many, and that is, by Associating the Saline Corpuscles, or any
other Sort of the more Rigid ones of the Liquor, with the Particles of the
Body that it is employ'd to Work upon. For these Adventitious Corpuscles
Associating themselves with the Protuberant Particles of the Surface of a
Colour'd Body, must necessarily alter their Bigness, and will most commonly
alter their Shape. And how much the Colours of Bodies depend upon the Bulk
and Figure of their Superficial Particles, you may Guess by this, that
eminent antient _Philosophers_ and divers _Moderns_, have thought that all
Colours might in a general way be made out by these two; whose being
Diversify'd, will in our Case be attended with these two Circumstances, the
One, that the Protuberant Particles being Increas'd in Bulk, they will
oftentimes be Vary'd as to the Closness or Laxity of their Order, fewer of
them being contain'd within the same Sensible (though Minute) space than
before; or else by approaching to one another, they must Straighten the
Pores, and it may be too, they will by their manner of Associating
themselves with the Protuberant Particles, intercept new Pores. And this
invites me to consider farther, that the Adventitious Corpuscles, I have
been speaking of, may likewise produce a great Change as well in the Little
Cavities or Pores as in the Protuberances of a Colour'd Body; for besides
what we have just now taken notice of, they may by Lodging themselves in
those little Cavities, fill them up, and it may well happen, that they may
not only fill the Pores they Insinuate themselves into, but likewise have
their Upper Parts extant above them; and partly by these new Protuberances,
partly by Increasing the Bulk of the former, these Extraneous Corpuscles
may much alter the Number and Bigness of the Surfaces Pores, changing the
Old and Intercepting new ones. And then 'tis Odds, but the Order of the
Little Extancies, and consequently that of the Little Depressions in point
of Situation will be alter'd likewise: as if you dissolve _Quick-silver_ in
some kind of _Aqua-fortis_, the Saline Particles of the _Menstruum_
Associating themselves with the Mercurial Corpuscles, will make a Green
Solution, which afterwards easily enough Degenerates. And Red Lead or
_Minium_ being Dissolv'd in Spirit of Vinegar, yields not a Red, but a
Clear Solution, the Redness of the Lead being by the Liquor Destroy'd. But
a better Instance may be taken from Copper, for I have try'd, that if upon
a Copper-plate you let some Drops of weak _Aqua-fortis_ rest for a while,
the Corpuscles of the _Menstruum_, joyning with those of the Metall, will
produce a very sensible Asperity upon the Surface of the Plate, and will
Concoagulate that way into very minute Grains of a Pale Blew _Vitriol_;
whereas if upon another part of the same Plate you suffer a little strong
Spirit of Urine to rest a competent time, you shall find the Asperated
Surface adorn'd with a Deeper and Richer Blew. And the same _Aqua-fortis_,
that will quickly change the Redness of Red Lead into a Darker Colour,
will, being put upon Crude Lead, produce a Whitish Substance, as with
Copper it did a Blewish. And as with Iron it will produce a Reddish, and on
White Quills a Yellowish, so much may the Coalition of the Parts of the
same Liquor, with the differingly Figur'd Particles of Stable Bodies,
divers ways Asperate the differingly Dispos'd Surfaces, and to Diversifie
the Colour of those Bodies. And you'l easily believe, that in many changes
of Colour, that happen upon the Dissolutions of Metalls, and Precipitations
made with Oyl of _Tartar_, and the like Fix'd Salts, there may Intervene a
Coalition of Saline Corpuscles with the Particles of the Body Dissolv'd or
Precipitated, if you examine how much the _Vitriol_ of a Metall may be
Heavier than the Metalline part of it alone, upon the Score of the Saline
parts Concoagulated therewith, and, that in Several Precipitations the
weight of the _Calx_ does for the same Reason much exceed that of the
Metall, when it was first put in to be Dissolv'd.
26. But, _Pyrophilus_, to consider these Matters more particularly would be
to forget that I declar'd against Adventuring, at least for this time, at
particular Theories of Colours, and that accordingly you may justly expect
from me rather Experiments than Speculations, and therefore I shall Dismiss
this Subject of the Forms of Superficial Asperity in Colour'd Bodies, as
soon as I shall but have nam'd to you by way of Supplement to what we have
hitherto Discours'd in this Section, a Couple of Particulars, (which you'l
easily grant me) The one, That there are divers other ways for the speedy
Production even of True and Permanent Colours in Bodies, besides those
Practicable by the help of Liquors; for proof of which Advertisement,
though several Examples might be alleged, yet I shall need but Re-mind you
of what I mention'd to you above, touching the change of Colours suddenly
made on Temper'd Steel, and on Lead, by the Operation of Heat, without the
Intervention of a Liquor. But the other particular I am to observe to you
is of more Importance to our present Subject and it is, That though Nature
and Art may in some cases so change the Asperity of the Superficial parts
of a Body, as to change its Colour by either of the ways I have propos'd
Single or Unassisted, yet for the most part 'tis by two or three, or
perhaps by more of the fore-mention'd ways Associated together, that the
Effect is produc'd, and if you consider how Variously those several ways
and some others Ally'd unto them, which I have left unmention'd, may be
Compounded and Apply'd, you will not much wonder that such fruitfull,
whether Principles (or Manners of Diversification) should be fitted to
Change or Generate no small store of Differing Colours.
27. Hitherto, _Pyrophilus_, we have in discoursing of the Asperity of
Bodies consider'd the little Protuberances of other Superficial particles
which make up that Roughness, as if we took it for granted, that they must
be perfectly Opacous and Impenetrable by the Beams of Light, and so, must
contribute to the Variety of Colours as they terminate more or less Light,
and reflect it to the Eye mix'd with more or less of thus or thus mingl'd
Shades. But to deal Ingenuously with you, _Pyrophilus_, before I proceed
any further, I must not conceal from you, that I have often thought it
worth a Serious Enquiry, whether or no Particles of Matter, each of them
sing'y Insensible, and therefore small enough to be capable of being such
Minute Particles as the _Atomists_ both of old and of late have (not
absurdly) called _Corpuscula Coloris_, may not yet consist each of them of
divers yet Minuter Particles, betwixt which we may conceive little
Commissures where they Adhere to one another, and, however, may not be
Porous enough to be, at least in some degree, Pervious to the unimaginably
subtile Corpuscles that make up the Beams of Light, and consequently to be
in such a degree Diaphanous. For, _Pyrophilus_, that the proposed Enquiry
may be of moment to him that searches after the Nature of Colour, you'l
easily grant, if you consider, that whereas Perfectly Opacous bodies can
but reflect the incident Beams of Light, those that are Diaphanous are
qualified to refract them too, and that Refraction has such a stroak in the
Production of Colours, as you cannot but have taken notice of, and perhaps
admir'd in the Colours generated by the Trajection of Light through Drops
of Water that exhibit a Rain-bow, through Prismatical glasses, and through
divers other Transparent bodies. But 'tis like, _Pyrophilus_, you'l more
easily allow that about this matter 'tis rather Important to have a
Certainty, than that 'tis Rational to entertain a Doubt; wherefore I must
mention to you some of the Reasons that make me think it may need a further
Enquiry, for I find that in a Darkned Room, where the Light is permitted to
enter but at One hole, the little wandering Particles of Dust, that are
commonly called Motes, and, unless in the Sunbeams, are not taken notice of
by the unassisted Sight, I have, I say, often observ'd, that these roving
Corpuscles being look'd on by an Eye plac'd on one side of the Beams that
enter'd the Little hole, and by the Darkness having its Pupill much
Enlarg'd, I could discern that these Motes as soon as they came within the
compass of the Luminous, whether Cylinder or Inverted Cone, if I may so
call it, that was made up by the Unclouded Beams of the Sun, did in certain
positions appear adorn'd with very vivid Colours, like those of the
Rain-bow, or rather like those of very Minute, but Sparkling fragments of
Diamonds; and as soon as the Continuance of their Motion had brought them
to an Inconvenient position in reference to the Light and the Eye, they
were only visible without Darting any lively Colours as before, which seems
to argue that these little Motes, or minute Fragments, of several sorts of
bodies reputed Opacous, and only crumbled as to their Exteriour and Looser
parts into Dust, did not barely Reflect the Beams that fell upon them, but
remit them to the Eye Refracted too. We may also observe, that several
Bodies, (as well some of a Vegetable, as others of an Animal nature) which
are wont to pass for Opacous, appear in great part Transparent, when they
are reduc'd into Thin parts, and held against a powerful Light. This I have
not only taken notice of in pieces of Ivory reduc'd but into Thick leaves,
as also in divers considerable Thick shells of Fishes, and in shaving of
Wood, but I have also found that a piece of Deal, far thicker than one
would easily imagine, being purposly interposed betwixt my Eye plac'd in a
Room, and the clear Daylight, was not only somewhat Transparent, but
(perhaps by reason of its Gummous nature) appear'd quite through of a
lovely Red. And in the Darkned Room above mention'd, Bodies held against
the hole at which the Light enter'd, appear'd far less Opacous then they
would elsewhere have done, insomuch that I could easily and plainly see
through the whole Thickness of my Hand, the Motions of a Body plac'd (at a
very near distance indeed, but yet) beyond it. And even in Minerals, the
Opacity is not always so great as many think, if the Body be made Thin, for
White Marble though of a pretty Thickness, being within a Due distance
plac'd betwixt the Eye and a Convenient Light, will Suffer the Motions of
ones Finger to be well discern'd through it, and so will pieces, Thick
enough, of many common Flints. But above all, that Instance is remarkable,
that is afforded us by _Muscovie_ glass, (which some call _Selenites_,
others _Lapis Specularis_) for though plates of this Mineral, though but of
a moderate Thickness, do often appear Opacous, yet if one of these be
Dextrously split into the thinnest Leaves 'tis made up of, it will yield
such a number of them, as scarce any thing but Experience could have
perswaded me, and these Leaves will afford the most Transparent sort of
consistent Bodies, that, for ought I have observ'd, are yet known; and a
single Leaf or Plate will be so far from being Opacous, that 'twill scarce
be so much as Visible. And multitudes of Bodies there are, whose Fragments
seem Opacous to the naked Eye, which yet, when I have included them in good
_Microscopes_, appear'd Transparent; but, _Pyrophilus_, on the other side I
am not yet sure that there are no Bodies, whose Minute Particles even in
such a _Microscope_ as that of mine, which I was lately mentioning, will
not appear Diaphanous. For having consider'd _Mercury_ Precipitated _per
se_, the little Granules that made up the powder, look'd like little
fragments of Coral beheld by the naked Eye at a Distance (for very Near at
hand Coral will sometimes, especially if it be Good, shew some
Transparency.) Filings likewise of Steel and Copper, though in an excellent
_Microscope_, and a fair Day, they show'd like pretty Big Fragments of
those Metalls, and had considerable Brightness on some of their Surfaces,
yet I was not satisfi'd, that I perceiv'd any Reflection from the Inner
parts of any of the Filings. Nay, having look'd in my best _Microscope_
upon the Red _Calx_ of Lead, (commonly call'd _Minium_) neither I, nor any
I shew'd it to, could discern it to be other than Opacous, though the Day
were Clear, and the Object strongly Enlightned. And the deeply Red Colour
of _Vitriol_ appear'd in the same _Microscope_ (notwithstanding the great
Comminution effected by the Fire) but like Grossy beaten Brick. So that,
_Pyrophilus_, I shall willingly resign you the care of making some further
Enquiries into the Subject we have now been considering; for I confess, as
I told you before, that I think that the Matter may need a further
Scrutiny, nor would I be forward to Determine how far or in what cases the
Transparency or Semi-diaphaniety of the Superficial Corpuscles of Bigger
Bodies, may have an Interest in the Production of their Colours, especially
because that even in divers White bodies, as Beaten Glass, Snow and Froth,
where it seems manifest that the Superficial parts are singly Diaphanous,
(being either Water, or Air, or Glass) we see not that such Variety of
Colours are produc'd as usually are by the Refraction of Light, even in
those Bodies, when by their Bigness, Shape, &c. they are conveniently
qualify'd to exhibit such Various and Lively Colours as those of the
Rain-bow, and of Prismatical Glasses.
28. By what has been hitherto discours'd, _Pyrophilus_, we may be assisted
to judge of that famous Controversie which was of Old disputed betwixt the
_Epicureans_ and other _Atomists_ on the one side, and most other
_Philosophers_ on the other side. The former Denying Bodies to be Colour'd
in the Dark, and the Latter making Colour to be an Inherent quality, as
well as Figure, Hardness; Weight, or the like. For though this Controversie
be Reviv'd, and hotly Agitated among the _Moderns_, yet I doubt whether it
be not in great part a Nominal dispute, and therefore let us, according to
the Doctrine formerly deliver'd, Distinguish the Acceptions of the word
Colour, and say, that if it be taken in the Stricter Sense, the
_Epicureans_ seem to be in the Right, for if Colour be indeed, though not
according to them, but Light Modify'd, how can we conceive that it can
Subsist in the Dark, that is, where it must be suppos'd there is no Light;
but on the other side, if Colour be consider'd as a certain Constant
Disposition of the Superficial parts of the Object to Trouble the Light
they Reflect after such and such a Determinate manner, this Constant, and,
if I may so speak, Modifying disposition persevering in the Object, whether
it be Shin'd upon or no, there seems no just reason to deny, but that in
this Sense, Bodies retain their Colour as well in the Night as Day; or, to
Speak a little otherwise, it may be said, that Bodies are Potentially
Colour'd in the Dark, and Actually in the Light. But of this Matter
discoursing more fully elsewhere, as 'tis a difficulty that concerns
Qualities in general, I shall forbear to insist on it here.
* * * * *