Experiments and Considerations Touching Colours (1664) by Robert Boyle

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[_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, Sphaerical, 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 _Phaenomena_ 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.

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