Experiments and Considerations Touching Colours (1664) by Robert Boyle

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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
Hemisphaerical (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 _Phaenomena_ 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 Vitae._

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.

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