Experiments and considerations touching colours first occasionally written, among some other essays to a friend, and now suffer'd to come abroad as the beginning of an experimental history of colours / by the Honourable Robert Boyle ...

CHAP. III.

1 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 de∣ny, 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 No∣tion, for there is in the bodyes we call Co∣lour'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 di∣stinct Impression, upon whose Account we say, that the Seen body is either White or Black, or Red or Yellow, or of any one de∣terminate 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 Pro∣duction and the appearance of Colours de∣pends 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 Rea∣son,

that I ascribe Colour (in the sense formerly explan'd) chiefly to the Super∣ficial 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 In∣ternal fragments will be as Red as the Exter∣nal surface did appear, yet that is but a Par∣ticular 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 In∣stances are sufficient to overthrow the Ge∣nerality 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 Co∣lours

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 Super∣ficial; 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 concern∣ing 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 per∣ceiv'd, as we expected, the smooth and

grossie Surface of the melted matter, to be adorn'd with a ve•• glorious Colour, which being as Transitory as Delightfull, did almost immediately give place to ano∣ther 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 won∣derfully vivid Colours successively appear'd and vanish'd, (yet the same now and then appearing the second time) till the Me∣tall ceasing to be hot enough to afford any longer this pleasing Spectacle, the Co∣lours that chanc'd to adorn the Surface, when the Lead thus began to cool, re∣main'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 com∣paratively 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 mel∣ted 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 ac∣quaint You with. One that did not know me, Pyrophilus, would perchance think I endeavour'd to impose upon You by rela∣ting this Experiment, which I have several times try'd, but the Reason why the Phae∣nomena 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 Phaenomena 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 re∣main'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 follow∣ing 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 exa∣mine.

[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 Opa∣cous bodies from the various Figures of their Superficial parts; the attempt is In∣genious, and the Doctrine seems partly True, but I confess I think there are divers other things that must be taken in as con∣current to produce those differing forms of Asperity, whereon the Colours of Opa∣cous bodies seem to depend. To declare this a little, we must assume, that the Sur∣faces 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 Sur∣face, 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 ap∣pear'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 dis∣cern'd and easily 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 super∣ficies, 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 Expe∣ments, 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 Corpus∣cles, 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 pro∣tuberant 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 vari∣ously affected, after one manner from Surfaces (I now speak of Physical Sur∣faces) consisting of Sphaerical, and in ano∣ther from those that are made up of Co∣nical or Cylindrical Corpuscles; some

being fitted to reflect more of the incident Beams of Light, others less, and some to∣wards one part, others towards another. But besides this difference of Shape, there may be divers other things that may emi∣nently concurr to vary the forms of As∣perity that Colours so much depend on. For, willingly allowing the Figure of the Particles in the first place, I consider se∣condly, that the superficial Corpuscles, if I may so call them, may be bigger in one Body, and less in another, and consequent∣ly fitted to allay the Light falling on them with greater shades. Next, the protube∣rant 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 Qua∣lities may serve to produce Colour may be somewhat guess'd at, by that which hap∣pens 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, (to which these last nam'd Conditions of the Bubbles do as well as their Convex * 1.1 figure contribute) and that for Reasons to be mention'd anon. Besides, it is not necessary that the Superficial particles that exhibit one Co∣lour, 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 Yel∣low, 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. More∣over the Figure and Bigness of the little Depressions, Cavities, Furrows or Pores intercepted betwixt these protuberant Cor∣puscles, are as well to be consider'd as the Sizes and Shapes of the Corpuscles them∣selves: 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 Com∣parison) in divers places of the Surface of the Earth, there are not only Neighbour∣ing 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 dili∣gently 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.

7. And I hope, Pyrophilus, you will not think it strange or impertinent, that I em∣ploy in divers passages of these Papers,

examples drawn from Bodies and Sha∣dows 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 In∣sensible; 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, con∣sisting of little Protuberances and De∣pressions; and though consequently such Inequalities may suffice to give Bodies dif∣fering 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 con∣curr 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 pro∣ceed.

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 Discern∣able, 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 refe∣rence 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 Sur∣face 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 re∣tain'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 contri∣bute, though it be not so easie to say how, to the Producing or the Varying of a Co∣lour; for I have several times made a Li∣quor, which when it has well settled in a close Vial, is Transparent and Colourless, but as soon as the Glass is unstopp'd, be∣gins 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 con∣tains 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 Dia∣phanous 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 Su∣perficies 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 com∣monly expos'd sides Obverted to the Eye, and when a breath of Wind passing tho∣row them, made great Numbers of the usually Hidden sides of the Leaves become conspicuous. And though the Little Bo∣dies, we were lately speaking of, may Singly and Apart seem almost Colourless, yet when Many of them are plac'd by one ano∣ther, 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 al∣most quite Devoyd of Redness, (for In∣stance)

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 concern∣ing the Leaves of Trees, invites me also to give you some account of what happens in Changeable Taffities, where we see dif∣fering 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 Mi∣croscope I could easily (as I began to say) discern, that in a piece of Changeable Taffity, (that appear'd, for Instance, some∣times 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 innume∣rable 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 per∣ceive, 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 com∣paratively but Dim and Faint. And if, on the contrary, I look'd through the Mi∣croscope 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 ob∣serving 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 ob∣serv'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 advan∣tagiously 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 Co∣lours chance to be Interwoven, the result∣ing 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 Change∣ableness 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 In∣quiry into Manufactures, as a Mechanick imployment, and consequently below Them; and because also with such a Mi∣croscope as I have been mentioning, the discovery is as well Pleasant as Satisfactory, and may affor'd 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 Co∣lour, that is so Conspicuous and so Delight∣full in Mother of Pearl, in Opalls, and some

other resembling Bodies: For though I remember I did formerly attempt some∣thing 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 Re∣flected with more or less of Shade, and with that Shade more or less Interrupted, or else happens to be also otherwise Mo∣dify'd or Troubl'd, is but Conjectural. But I am not sure, that if it were not for the Dulness of our Senses, either these or some other Notions of Kin to them, might be better Countenanc'd; for I am apt to sus∣pect, 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 Phy∣sical Surfaces of Bodies, both a great many latent Ruggidnesses, and the particular

Sizes, Shapes, and Situations of the ex∣tremely little Bodies that cause them, and perhaps might perceive among other Va∣rieties that we now can but imagine, how those little Protuberances and Cavities do Interrupt and Dilate the Light, by ming∣ling 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, ac∣cording to the Nature and Degree of the particular Colour we attribute to the Vi∣sible 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 dis∣cern particular Granules, some of them of a Blew, and some of them of a Yellow colour, which Corpuscles we had before∣hand caus'd to be exquisitly mix'd to com∣pound 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 * 1.2 Dr. J. Finch, Extraordinary Ana∣tomist to that Great Patron of the Virtuosi, the now Great Duke of Toscany, and enqui∣ring of this Ingenious Person, what might be the chief Ra∣rity 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 distin∣guish 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 Membrances 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 di∣stinguish

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 Coun∣terfeited the want of it, to which I added divers other Questions, to satisfie my Self, whether there were any Likelihood of Col∣lusion 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 men∣tion 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:

That the Man's name was John Ver∣maasen, 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 Rib∣bon,

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 distin∣guish'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 Nar∣rative 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 Aspe∣rous 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 Rib∣bon, 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 dis∣criminated Colours, rather by the Smell than by the Touch; for some of the Ingre∣dients imployed by Dyers to Colour things, have Sents, that are not so Languid, nor so near of Kin, but that I thought it not im∣possible that a very Critical Nose might distinguish them, and this I the rather sus∣pected, because he requir'd, that the Rib∣bons,

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 (epecially 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 Pig∣ment 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, not∣withstanding this History, that the Blind man

distinguish'd Colours not only by the De∣grees 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, be∣cause 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 ex∣press'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 diffe∣rences 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 ra∣ther 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 e∣qually Rough, yet in such slender Corpus∣cles as those of Colour, there may easily enough be Conceiv'd, not only a greater Closeness of Parts, or else Paucity of Pro∣tuberant Corpuseles, 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

Particles of Black Bodies, as if there were Wyres I know not how many times Slen∣derer than a Hair: whether you suppose them to be Figur'd like Needles, or Cy∣lindrically, 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 distin∣guish 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 Rough∣ness, 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 Co∣lour. But more (perchance) of this else∣where.

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 Diaphanëity 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 some∣what 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 refe∣rence 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 De∣tain'd there, and prove unable to Emerge; whilst in a White Body, the Slender Par∣ticles 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 Bot∣toms 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, ac∣cording to the Judgment of his Touch, Black was the Roughest, as it is the Darkest of Colours, therefore White, which (ac∣cording 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 con∣clude, that the Rougher of any two always Reflects the least Light.

16. But this notwithstanding, (Pyro∣philus) 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 De∣grees, 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 of Asperity that may Diversifie the Surfaces of Colour'd Bodies, may perchance some∣what 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 Cor∣puscles, Liquors so Qualify'd may well enough very Nimbly alter 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 Sen∣sory.

18. Now there seen to me divers ways,

by which we may conceive that Liquors may Nimbly alter the Colour of one ano∣ther, 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 easily insi∣nuate 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 al∣ways the Bigness of the former Pores. And in what capacity soever these Corpuscles of a Liquor come to be Lodg'd or Har∣bour'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 Re∣fracted, 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 Rea∣sons as those newly mention'd, immedi∣ately 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 Co∣lour 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 after∣wards 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 ad∣ventitious 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 Imbi∣bing 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 Metal∣line mixture so Compounded, that the Im∣pression 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 Corpus∣cles that conceal'd those of the Gold, which you know that Menstruum will leave Un∣touch'd.

21. Thirdly, A Liquor may alter the

Colour of a Body by making a Commi∣nution of its Parts, and that principally two ways, the first by Disjoyning and Dissi∣pating 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 Experi∣ments, where you'l find the Colour of many Corpuscles brought to cohere by having been Precipitated together, De∣stroy'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 Oc∣casion 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 Met∣tall 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 Precipi∣tations, especially by such as are wont to be made with fair Water, as when Resi∣nous 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 Disloca∣tion of the Parts of a Body may do to∣wards the Changing its Colour, is not only evident in the Mutations of Colour obser∣vable in Quick-silver, and some other Concretes long kept by Chymists in a Con∣venient Heat, though in close Vessels, but in the Obvious Degenerations of Co∣lour, 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 Pow∣der, 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 Transpo∣sition of the Parts which is consequent to the Shaking, will shew you on the Surfaces of the Bubbles exceeding Orient and Live∣ly Colours, which when the Bubbles re∣lapse into the rest of the Oyl, do imme∣diately 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 Ge∣neral, 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 toge∣ther, 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 Dis∣solves 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 Vi∣triol 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 Bo∣dies, 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 Co∣lour of the Copper.

25. There remains yet a way, Pyro∣philus, to be mention'd, by which a Liquor may alter the Colour of another Body, and this seems the most Important of all, be∣cause though it be nam'd but as One, yet it may indeed comprehend Many, and that is, by Associating the Saline Corpus∣cles, 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 Protu∣berant Particles of the Surface of a Co∣lour'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 Philo∣sophers, 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 In∣creas'd in Bulk, they will oftentimes be Vary'd as to the Closeness or Laxity of

their Order, fewer of them being con∣tain'd within the same Sensible (though Minute) space than before; or else by ap∣proaching 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 in∣to, 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, chang∣ing 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 Degene∣rates. 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 Co∣lour, 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 Par∣ticles of Stable Bodies, divers ways Aspe∣rate the differingly Dispos'd Surfaces, and so 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 Coa∣lition of Saline Corpuscles with the Par∣ticles 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 Experi∣ments 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 Advertise∣ment, 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 Inter∣vention of a Liquor. But the other par∣ticular 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 Super∣ficial parts of a Body, as to change its Colour by either of the ways I have pro∣pos'd Single or Unassisted, yet for the most part 'tis by two or three, or perhaps by more of the fore-mention'd ways Asso∣ciated 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, whe∣ther Principles (or Manners of, Diver∣sification)

should be fitted to Change or Generate no small store of Differing Co∣lours.

27. Hitherto, Pyrophilus, we have in dis∣coursing 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, Pyrophilns, before I proceed any further, I must not conceal from you, that I have often thought it worth a Serious Enquiry, whether or no Parti∣cles of Matter, each of them singly In∣sensible, 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 sub∣tile 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 Co∣lour, 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 per∣haps 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 Cer∣tainty, 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 com∣monly called Motes, and, unless in the Sun-beams, are not taken notice of by the un∣assisted 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 Lumihous, whether Cylinder or Inverted Cone, if I may so call it, that was made up by the Un∣clouded Beams of the Sun, did in certain positions appear adorn'd with very vivid Co∣lours, like those of the Rain-bow, or rathen like those of very Minute, but Sparkling frag∣ments 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 ob∣serve, 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 ima∣gine, being purposly interpos'd betwixt my Eye plac'd in a Room, and the clear Day-light, 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 than 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 Bo∣dy be made Thin, for White Marble though of a pretty Thickness, being within a Due distance plac'd betwixt the Eye and a Con∣venient 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 Mus∣covie glass, (which some call Selenites, others Lapis Specularis) for though plates of this Mineral, though but of a moderate Thick∣ness, 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 Mi∣croscope as that of mine, which I was lately mentioning, will not appear Diaphanous. For having consider'd Mercury Precipitated perse, the little Granules that made up the powder, look'd like little fragments of Coral beheld by the naked Eye at a Di∣stance (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 Micros∣cope, 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 per∣ceiv'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 a∣ny 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 Cor∣puscles of Bigger Bodies, may have an In∣terest 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 Super∣ficial 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 Big∣ness, 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, Distin∣guish 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.

Notes

• * 1.1

  See the Discourse of the Nature of Whiteness and Blackness.
• * 1.2

  Since for his eminent Qua∣lities and Loy∣alty Grac'd, by his Majesty, with the Ho∣nour of Knight∣hood.