Part 6

See the Discourse of the Nature of Whiteness and Blackness.

7. And I hope, Pyrophilus, you will not think it strange or impertinent, that I employ in divers passages of these Papers, examples drawn from Bodies and Shadows far more Gross, than those minute Protuberances and shady Pores on which in most cases the Colour of a Body as 'tis an Inherent Quality or Disposition of its Surface, seems to depend. For sometimes I employ such Examples, rather to declare my Meaning, than prove my Conjecture; things, whom their Smallness makes Insensible, being better represented to the Imagination by such familiar Objects, as being like them enough in other respects, are of a Visible bulk. And next, though the Beams of Light are such subtil Bodies, that in respect of them, even Surfaces that are sensibly Smooth, are not exactly so, but have their own degree of Roughness, consisting of little Protuberances and Depressions; and though consequently such Inequalities may suffice to give Bodies differing Colours, as we see in Marble that appears White or Black, or Red or Blew, even when the most carefully Polish'd, yet 'tis plain by the late Instance of Red Marble, and many others, that even bigger Protuberances and greater Shades may likewise so Diversifie the Roughness of a Bodies Superficies, as manifestly to concurr to the varying of its Colour, whereby such Examples appear to be proper enough to be employ'd in such a Subject as we have now in hand. And having hinted thus much on this Occasion, I now proceed.

8. The Situation also of the Superficial particles is considerable, which I distinguish into the Posture of the single Corpuscles, in respect of the Light, and of the Eye, and the Order of them in reference also to one another; for a Body may otherwise reflect the Light, when its Superficial particles are more erected upon the Plain that may be conceiv'd to pass along their Basis, and when the Points or Extremes of such Particles are Obverted to the Eye, than when those Particles are so Inclin'd, that their Sides are in great part Discernable, as the Colour of Plush or Velvet will appear Vary'd to you, if you carefully stroak part of it one way, and part of it another, the posture of the particular Thrids, in reference to the Light, or the Eye, becoming thereby different. And you may observe in a Field of ripe Corn blown upon by the Wind, that there will appear as it were Waves of a Colour (at least Gradually) differing from that of the rest of the Field, the Wind by Depressing some of the Ears, and not at the same time others, making the one Reflect more from the Lateral and Strawy parts, than do the rest. And so, when Doggs are so angry, as to Erect the Hairs upon their Necks, and upon some other parts of their Bodies, those Parts seem to acquire a Colour vary'd from that which the same Hairs made, when in their usual Posture they did farr more stoop. And that the Order wherein the Superficial Corpuscles are Rang'd is not to be neglected, we may guess by turning of Water into Froth, the beating of Glass, and the scraping of Horns, in which cases the Corpuscles that were before so marshall'd as to be Perspicuous, do by the troubling of that Order become Dispos'd to terminate and reflect more Light, and thereby to appear Whitish. And there are other ways in which the Order of the Protuberant parts, in reference to the Eye, may much contribute to the appearing of a particular Colour, for I have often observ'd, that when Pease are Planted, or Set in Parallel Lines, and are Shot up about half a Foot above the Surface of the Ground, by looking on the Field or Plot of Ground from that part towards which the Parallel Lines tended, the greater part of the Ground by farr would appear of its own dirty Colour, but if I look'd upon it Transversly, the Plot would appear very Green, the upper parts of the Pease hindering the intercepted parts of the Ground, which as I said retain'd their wonted Colour, from being discover'd by the Eye. And I know not, Pyrophilus, whether I might not add, that even the Motion of the Small Parts of a Visible Object may in some cases contribute, though it be not so easie to say how, to the Producing or the Varying of a Colour; for I have several times made a Liquor, which when it has well settled in a close Vial, is Transparent and Colourless, but as soon as the Glass is unstopp'd, begins to fly away very plentifully in a White and Opacous fume; and there are other Bodies, whose Fumes, when they fill a Receiver, would make one suspect it contains Milk, and yet when these Fumes settle into a Liquor, that Liquor is not White, but Transparent; And such White Fumes I have seen afforded by unstopping a Liquor I know, which yet is it self Diaphanous and Red; Nor are these the only Instances of this Kind, that our Tryals can supply us with. And if the Superficial Corpuscles be of the Grosser sort, and be so Framed, that their differing Sides or Faces may exhibit differing Colours, then the Motion or Rest of those Corpuscles may be considerable, as to the Colour of the Superficies they compose, upon this account, that sometimes more, sometimes fewer of the Sides dispos'd to exhibit such a Colour may by this means become or continue more Obverted to the Eye than the rest, and compose a Physical Surface, that will be more or less sensibly interrupted; As, to explane my meaning, by proposing a gross Example, I remember, that in some sorts of Leavy Plants thick set by one another, the two sides of whose Leaves were of somewhat differing Colours, there would be a notable Disparity as to Colour, if you look'd upon them both when the Leaves being at Rest had their upper and commonly expos'd sides Obverted to the Eye, and when a breath of Wind passing thorow them, made great Numbers of the usually Hidden sides of the Leaves become conspicuous. And though the Little Bodies, we were lately speaking of, may Singly and Apart seem almost Colourless, yet when Many of them are plac'd by one another, so near, that the Eye does not easily discern an Interruption, within a sensible space, they may exhibit a Colour; as we see, that though a Slenderest Thrid of Dy'd Silk do's, whilst look'd on Single, seem almost quite Devoyd of Redness, (for instance) yet when numbers of these Thrids are brought together into one Skein, their Colour becomes notorious.

9. But the same Occasion that invited me to say what I have mention'd concerning the Leaves of Trees, invites me also to give you some account of what happens in Changeable Taffities, where we see differing Colours, as it were, Emerge and Vanish upon the Ruffling of the same piece of Silk: As I have divers times with Pleasure observ'd, by the help of such a Microscope, as, though it do not very much Magnifie the Object, has in recompence this great Conveniency, that you may easily, as fast as you please, remove it from one part to another of a Large Object, of which the Glass taking a great part at once, you may thereby presently Survey the Whole. Now by the help of such a Microscope I could easily (as I began to say) discern, that in a piece of Changeable Taffity, (that appear'd, for Instance, sometimes Red, and sometimes Green) the Stuff was compos'd of Red thrids and Green, passing under and over each other, and crossing one another in almost innumerable points; and if I look'd through the Glass upon any considerable portion of the Stuff, that (for example sake) to the naked Eye appear'd to be Red, I could plainly see, that in that Position, the Red thrids were Conspicuous, and reflected a vivid Light; and though I could also perceive, that there were Green ones, yet by reason of their disadvantagious Position in the Physical Surface of the Taffity, they were in part hid by the more Protuberant Thrids of the other Colour; and for the same cause, the Reflection from as much of the Green as was discover'd, was comparatively but Dim and Faint. And if, on the contrary, I look'd through the Microscope upon any part that appear'd Green, I could plainly see that the Red thrids were less fully expos'd to the Eye, and obscur'd by the Green ones, which therefore made up the Predominant Colour. And by observing the Texture of the Silken Stuff, I could easisy so expose the Thrids either of the one Colour or of the other to my Eye, as at pleasure to exhibit an apparition of Red or Green, or make those Colours succeed one another: So that, when I observ'd their Succession by the help of the Glass, I could mark how the Predominant Colour did as it were start out, when the Thrids that exhibited it came to be advanagiously plac'd; And by making little Folds in the Stuff after a certain manner, the Sides that met and terminated in those Folds, would appear to the naked Eye, one of them Red, and the other Green. When Thrids of more than two differing Colours chance to be Interwoven, the resulting changeableness of the Taffity may be also somewhat different. But I choose to give an Instance in the Stuff I have been speaking off, because the mixture being more Simple, the way whereby the Changeableness is produc'd, may be the more easily apprehended: and though Reason alone might readily enough lead a considering Man to guess at the Explication, in case he knew how Changeable Taffities are made: yet I thought it not impertinent to mention it, because both Scholars and Gentlemen are wont to look upon the Inquiry into Manufactures, as a Mechanick imployment, and consequently below Them; and because also with such a Microscope as I have been mentioning, the discovery is as well Pleasant as Satisfactory, and may afford Hints of the Solution of other Phænomena of Colours. And it were not amiss, that some diligent Inquiry were made, whether the Microscope would give us an account of the Variableness of Colour, that is so Conspicuous and so Delightfull in Mother of Pearl, in Opalls, and some other resembling Bodies: For though I remember I did formerly attempt something of that Kind (fruitlesly enough) upon Mother of Pearl, yet not having then the advantage of my best Microscope, nor some Conveniences that might have been wish'd, I leave it to you, who have better Eyes, to try what you can do further; since 'twill be Some discovery to find, that, in this case, the best Eyes and Microscopes themselves can make None.

10. I confess, Pyrophilus, that a great part of what I have deliver'd, (or propos'd rather) concerning the differing forms of Asperity in Bodies, by which Differences the incident Light either comes to be Reflected with more or less of Shade, and with that Shade more or less Interrupted, or else happens to be also otherwise Modify'd or Troubl'd, is but Conjectural. But I am not sure, that if it were not for the Dullness of our Senses, either these or some other Notions of Kin to them, might be better Countenanc'd; for I am apt to suspect, that if we were Sharp sighted enough, or had such perfect Microscopes, as I fear are more to be wish'd than hop'd for, our promoted Sense might discern in the Physical Surfaces of Bodies, both a great many latent Ruggidnesses, and the particular Sizes, Shapes, and Situations of the extremely little Bodies that cause them, and perhaps might perceive among other Varieties that we now can but imagine, how those little Protuberances and Cavities do Interrupt and Dilate the Light, by mingling with it a multitude of little and singly undiscernable Shades, though some of them more, and some of them less Minute, some less, and some more Numerous; according to the Nature and Degree of the particular Colour we attribute to the Visible Object; as we see, that in the Moon we can with Excellent Telescopes discern many Hills and Vallies, and as it were Pits and other Parts, whereof some are more, and some less Vividly illustrated, and others have a fainter, others a deeper Shade, though the naked Eye can discern no such matter in that Planet. And with an Excellent Microscope, where the Naked Eye did see but a Green powder, the Assisted Eye as we noted above, could discern particular Granules, some of them of a Blew, and some of them of a Yellow colour, which Corpuscles we had beforehand caus'd to be exquisitly mix'd to compound the Green.

11. And, Pyrophilus, that you may not think me altogether extravagant in what I have said of the Possibility, (for I speak of no more) of discerning the differing forms of Asperity in the Surfaces of Bodies of several Colours, I'l here set down a Memorable particular that chanc'd to come to my Knowledge, since I writ a good part of this Essay; and it is this. Meeting casually the other Day with the deservedly Famous Dr. J. Finch, Extraordinary Anatomist to that Great Patron of the Virtuosi, the now Great Duke of Toscany, and enquiring of this Ingenious Person, what might be the chief Rarity he had seen in his late return out of Italy into England, he told me, it was a Man at Maestricht in the Low-Countrys, who at certain times can discern and distinguish Colours by the Touch with his Fingers. You'l easily Conclude, that this is farr more strange, than what I propos'd but as not Impossible; since the Sense of the Retina seeming to be much more Tender and quick than that of those Grosser Filaments, Nerves or Membranes of our Fingers, wherewith we use to handle Gross and Hard Bodies, it seems scarce credible, that any Accustomance, or Diet, or peculiarity of Constitution, should enable a Man to distinguish with such Gross and Unsuitable Organs, such Nice and Subtile Differences as those of the forms of Asperity, that belong to differing Colours, to receive whose Languid and Delicate Impressions by the Intervention of Light, Nature seems to have appointed and contexed into the Retina the tender and delicate Pith of the Optick Nerve. Wherefore I confess, I propos'd divers Scruples, and particularly whether the Doctor had taken care to bind a Napkin or Hankerchief over his Eyes so carefully, as to be sure he could make no use of his Sight, though he had but Counterfeited the want of it, to which I added divers other Questions, to satisfie my Self, whether there were any Likelihood of Collusion or other Tricks. But I found that the Judicious Doctor having gone farr out of his way, purposely to satisfie Himself and his Learned Prince about this Wonder, had been very Watchfull and Circumspect to keep Himself from being Impos'd upon. And that he might not through any mistake in point of Memory mis-inform Me, he did me the Favour at my Request, to look out the Notes he had Written for his Own and his Princes Information, the summ of which Memorials, as far as we shall mention them here, was this, That the Doctor having been inform'd at Utrecht, that there Lived one at some Miles distance from Maestricht, who could distinguish Colours by the Touch, when he came to the last nam'd Town, he sent a Messenger for him, and having Examin'd him, was told upon Enquiry these Particulars:

Since for his eminent Qualities and Loyalty Grac'd, by his Majesty, with the Honour of Knighthood.

That the Man's name was John Vermaasen, at that time about 33 Years of Age; that when he was but two years Old, he had the Small Pox, which rendred him absolutely Blind: That at this present he is an Organist, and serves that Office in a publick Quire.

That the Doctor discoursing with him over Night, the Blind man affirm'd, that he could distinguish Colours by the Touch, but that he could not do it, unless he were Fasting; Any quantity of Drink taking from him that Exquisitness of Touch, which is requisite to so Nice a Sensation.

That hereupon the Doctor provided against the next Morning seven pieces of Ribbon, of these seven Colours, Black, White, Red, Blew, Green, Yellow, and Gray, but as for mingled Colours, this Vermaasen would not undertake to discern them, though if offer'd, he would tell that they were Mix'd.

That to discern the Colour of the Ribbon, he places it betwixt the Thumb and the Fore-finger, but his most exquisite perception was in his Thumb, and much better in the right Thumb than in the left.

That after the Blind man had four or five times told the Doctor the several Colours, (though Blinded with a Napkin for fear he might have some Sight) the Doctor found he was twice mistaken, for he call'd the White Black, and the Red Blew, but still, he, before his Errour, would lay them by in Pairs, saying, that though he could easily distinguish them from all others, yet those two Pairs were not easily distinguish'd amongst themselves, whereupon the Doctor desir'd to be told by him what kind of Discrimination he had of Colours by his Touch, to which he gave a reply, for whose sake chiefly I insert all this Narrative in this place, namely, That all the difference was more or less Asperity, for says he, (I give you the Doctor's own words) Black feels as if you were feeling Needles points, or some harsh Sand, and Red feels very Smooth.

That the Doctor having desir'd him to tell in Order the difference of Colours to his Touch, he did as follows;

Black and White are the most asperous or unequal of all Colours, and so like, that 'tis very hard to distinguish them, but Black is the most Rough of the two, Green is next in Asperity, Gray next to Green in Asperity, Yellow is the fifth in degree of Asperity, Red and Blew are so like, that they are as hard to distinguish as Black and White, but Red is somewhat more Asperous than Blew, so that Red has the sixth place, and Blew the seventh in Asperity.

12. To these Informations the Obliging Doctor was pleas'd to add the welcome present of three of those very pieces of Ribbon, whose Colours in his presence the Blind man had distinguished, pronouncing the one Gray, the other Red, and the third Green, which I keep by me as Rarities, and the rather, because he fear'd the rest were miscarry'd.

13. Before I saw the Notes that afforded me the precedent Narrative, I confess I suspected this man might have thus discriminated Colours, rather by the Smell than by the Touch; for some of the Ingredients imployed by Dyers to Colour things, have Sents, that are not so Languid, nor so near of Kin, but that I thought it not impossible that a very Critical Nose might distinguish them, and this I the rather suspected, because he requir'd, that the Ribbons, whose Colours he was to Name, should be offer'd him Fasting in the morning; for I have observ'd in Setting Doggs, that the feeding of them (especially with some sorts of Aliments) does very much impair the exquisite sent of their Noses. And though some of the foregoing particulars would have prevented that Conjecture, yet I confess to you (Pyrophilus) that I would gladly have had the Opportunity of Examining this Man my self, and of Questioning him about divers particulars which I do not find to have been yet thought upon. And though it be not incredible to me, that since the Liquors that Dyers imploy to tinge, are qualifi'd to do so by multitudes of little Corpuscles of the Pigment or Dying stuff, which are dissolved and extracted by the Liquor, and swim to and fro in it, those Corpuscles of Colour (as the Atomists call them) insinuating themselves into, and filling all the Pores of the Body to be Dyed, may Asperate its Superficies more or less according to the Bigness and Texture of the Corpuscles of the Pigment; yet I can scarce believe, that our Blind man could distinguish all the Colours he did, meerly by the Ribbons having more or less of Asperity, so that I cannot but think, notwithstanding this History, that the Blind man distinguish'd Colours not only by the Degrees of Asperity in the Bodies offer'd to him, but by Forms of it, though this (latter) would perhaps have been very difficult for him to make an Intelligible mention of, because those Minute disparities having not been taken notice of by men for want of touch as Exquisite as our Blind Mans, are things he could not have Intelligibly express'd, which will easily seem Probable, if you consider, that under the name of Sharp, and Sweet, and Sour, there are abundance of, as it were, immediate peculiar Relishes or Tasts in differing sorts of Wine, which though Critical and Experienc'd Palats can easily discern themselves cannot make them be understood by others, such Minute differences not having hitherto any Distinct names assign'd them. And it seems that there was somthing in the Forms of Asperity that was requisite to the Distinction of Colours, besides the Degree of it, since he found it so difficult to distingush Black and White from one another, though not from other Colours. For I might urge, that he seems not consonant to himself about the Red, which as you have seen in one place, he represents as somewhat more Asperous than the Blew; and in another, very Smooth: But because he speaks of this Smoothness in that place, where he mentions the Roughness of Black, we may favourably presume that he might mean but a comparative Smoothness; and therefore I shall not Insist on this, but rather Countenance my Conjecture by this, that he found it so Difficult, not only, to Discriminate Red and Blew, (though the first of our promiscuous Experiments will inform you, that the Red reflects by great Odds more Light than the other) but also to distinguish Black and White from one another, though not from other Colours. And indeed, though in the Ribbonds that were offer'd him, they might be almost equally Rough, yet in such slender Corpuscles as those of Colour, there may easily enough be Conceiv'd, not only a greater Closeness of Parts, or else Paucity of Protuberant Corpuscles, and the little extant Particles may be otherwise Figur'd, and Rang'd in the White than in the Black, but the Cavities may be much Deeper in the one than the other.

14. And perhaps, (Pyrophilus) it may prove some Illustration of what I mean, and help you to conceive how this may be, if I Represent, that where the Particles are so exceeding Slender, we may allow the Parts expos'd to the Sight and Touch to be a little Convex in comparison of the Erected Particle of Black Bodies, as if there were Wyres I know not how many times Slenderer than a Hair: whether you suppose them to be Figur'd like Needles, or Cylindrically, like the Hairs of a Brush, with Hemisphærical (or at least Convex) Tops, they will be so very Slender, and consequently the Points both of the one sort and the other so very Sharp, that even an exquisite Touch will be able to distinguish no greater Difference between them, than that which our Blind man allow'd, when comparing Black and White Bodies, he said, that the latter was the less Rough of the two. Nor is every Kind of Roughness, though Sensible enough, Inconsistent with Whiteness, there being Cases, wherein the Physical Superficies of a Body is made by the same Operation both Rough and white, as when the Level Surface of clear Water being by agitation Asperated with a multitude of Unequal Bubbles, do's thereby acquire a Whiteness; and as a Smooth piece of Glass, by being Scratch'd with a Diamond, do's in the Asperated part of its Surface disclose the same Colour. But more (perchance) of this elsewhere.

15. And therefore, we shall here pass by the Question, whether any thing might be consider'd about the Opacity of the Corpuscles of Black Pigments, and the Comparative Diaphaneity of those of many White Bodies, apply'd to our present Case; and proceed, to represent, That the newly mention'd Exiguity and Shape of the extant Particles being suppos'd, it will then be considerable what we lately but Hinted, (and therefore must now somewhat Explane) That the Depth of the little Cavities, intercepted between the extant Particles, without being so much greater in Black Bodies than in White ones, as to be perceptibly so to the Gross Organs of Touch, may be very much greater in reference to their Disposition of Reflecting the imaginary subtile Beams of Light. For in Black Bodies, those Little intercepted Cavities, and other Depressions, may be so Figur'd, so Narrow and so Deep, that the incident Beams of Light, which the more extant Parts of the Physical Superficies are dispos'd to Reflect inwards, may be Detain'd there, and prove unable to Emerge; whilst in a White Body, the Slender Particles may not only by their Figure be fitted to Reflect the Light copiously outwards, but the intercepted Cavities being not Deep, nor perhaps very Narrow, the Bottoms of them may be so Constituted, as to be fit to Reflect outwards much of the Light that falls even upon Them; as you may possibly better apprehend, when we shall come to treat of Whiteness and Blackness. In the mean time it may suffice, that you take Notice with me, that the Blind mans Relations import no necessity of Concluding, that, though, because, according to the Judgment of his Touch, Black was the Roughest, as it is the Darkest of Colours, therefore White, which (according to us) is the Lightest, should be also the Smoothest: since I observe, that he makes Yellow to be two Degrees more Asperous than Blew, and as much less Asperous than Green; whereas indeed, Yellow do's not only appear to the Eye a Lighter Colour than Blew, but (by our first Experiment hereafter to be mention'd) it will appear, that Yellow reflected much more Light than Blew, and manifestly more than Green, (which we need not much wonder at, since in this Colour and the two others (Blew and Yellow) 'tis not only the Reflected Light that is to be considered, since to produce both these, Refraction seems to Intervene, which by its Varieties may much alter the Case:) which both seems to strengthen the Conjecture I was formerly proposing, that there was something else in the Kinds of Asperity, as well as in the Degrees of it, which enabled our Blind man to Discriminate Colours, and do's at least show, that we cannot in all Cases from the bare Difference in the Degrees of Asperity betwixt Colours, safely conclude, that the Rougher of any two always Reflects the least Light.

16. But this notwithstanding, (Pyrophilus) and what ever Curiosity I may have had to move some Questions to our Sagacious Blind man, yet thus much I think you will admit us to have gain'd by his Testimony, that since many Colours may be felt with the Circumstances above related, the Surfaces of such Coloured Bodies must certainly have differing Degrees, and in all probability have differing Forms or Kinds of Asperity belonging to them, which is all the Use that my present attempt obliges me to make of the History above deliver'd, that being sufficient to prove, that Colour do's much depend upon the Disposition of the Superficial parts of Bodies, and to shew in general, wherein 'tis probable that such a Disposition do's (principally at least) consist.

17. But to return to what I was saying before I began to make mention of our Blind Organist, what we have deliver'd touching the causes of the several Forms or Asperity that may Diversifie the Surfaces of Colour'd Bodies, may perchance somewhat assist us to make some Conjectures in the general, at several of the ways whereby 'tis possible for the Experiments hereafter to be mention'd, to produce the suddain changes of Colours that are wont to be Consequent upon them; for most of these Phænomena being produc'd by the Intervention of Liquors, and these for the most part abounding with very Minute, Active, and Variously Figur'd Saline Corpuscles, Liquors so Qualify'd may well enough very Nimbly after the Texture of the Body they are imploy'd to Work upon, and so may change the form of Asperity, and thereby make them Remit to the Eye the Light that falls on them, after another manner than they did before, and by that means Vary the Colour, so farr forth as it depends upon the Texture or Disposition of the Seen Parts of the Object, which I say, Pyrophilus, that you may not think I would absolutely exclude all other ways of Modifying the Beams of Light between their Parting from the Lucid Body, and their Reception into the common Sensory.

18. Now there seem to me divers ways, by which we may conceive that Liquors may Nimbly alter the Colour of one another, and of other Bodies, upon which they Act, but my present haste will allow me to mention but some of them, without Insisting so much as upon those I shall name.

19. And first, the Minute Corpuscles that compose a Liquor may early insinuate themselves into those Pores of Bodies, whereto their Size and Figure makes them Congruous, and these Pores they may either exactly Fill, or but Inadequately, and in this latter Case they will for the most part alter the Number and Figure, and always the Bigness of the former Pores. And in what capacity soever these Corpuscles of a Liquor come to be Lodg'd or Harbour'd in the Pores that admit them, the Surface of the Body will for the most part have its Asperity alter'd, and the Incident Light that meets with a Grosser Liquor in the little Cavities that before contain'd nothing but Air, or some yet Subtiler Fluid, will have its Beams either Refracted, or Imbib'd, or else Reflected more or less Interruptedly, than they would be, if the Body had been Unmoistned, as we see, that even fair Water falling on white Paper, or Linnen, and divers other Bodies apt to soak it in, will for some such Reasons as those newly mention'd, immediately alter the Colour of them, and for the most part make it Sadder than that of the Unwetted Parts of the same Bodies. And so you may see, that when in the Summer the High-ways are Dry and Dusty, if there falls store of Rain, they will quickly appear of a much Darker Colour than they did before, and if a Drop of Oyl be let fall upon a Sheet of White Paper, that part of it, which by the Imbibition of the Liquor acquires a greater Continuity, and some Transparency, will appear much Darker than the rest, many of the Incident Beams of Light being now Transmitted, that otherwise would be Reflected towards the Beholders Eyes.

20. Secondly, A Liquor may alter the Colour of a Body by freeing it from those things that hindred it from appearing in its Genuine Colour; and though this may be said to be rather a Restauration of a Body to its own Colour, or a Retection of its native Colour, than a Change, yet still there Intervenes in it a change of the Colour which the Body appear'd to be of before this Operation. And such a change a Liquor may work, either by Dissolving, or Corroding, or by some such way of carrying off that Matter, which either Veil'd or Disguis'd the Colour that afterwards appears. Thus we restore Old pieces of Dirty Gold to a clean and nitid Yellow, by putting them into the Fire, and into Aqua-fortis, which take off the adventitious Filth that made that pure Metall look of a Dirty Colour. And there is also an easie way to restore Silver Coyns to their due Lustre, by fetching off that which Discolour'd them. And I know a Chymical Liquor, which I employ'd to restore pieces of Cloath spotted with Grease to their proper Colour, by Imbibing the Spotted part with this Liquor, which Incorporating with the Grease, and yet being of a very Volatile Nature, does easily carry it away with it Self. And I have sometimes try'd, that by Rubbing upon a good Touch-stone a certain Metalline mixture so Compounded, that the Impression it left upon the Stone appear'd of a very differing Colour from that of Gold, yet a little of Aqua-fortis would in a Trice make the Golden Colour disclose it self, by Dissolving the other Metalline Corpuscles that conceal'd those of the Gold, which you know that Menstruum will leave Untouch'd.

21. Thirdly, A Liquor may alter the Colour of a Body by making a Comminution of its Parts, and that principally two ways, the first by Disjoyning and Dissipating those Clusters of Particles, if I may so call them, which stuck more Loosely together, being fastned only by some more easily Dissoluble Ciment, which seems to be the Case of some of the following Experiments, where you'l find the Colour of many Corpuscles brought to cohere by having been Precipitated together, Destroy'd by the Affusion of very peircing and incisive Liquors. The other of the two ways I was speaking of, is, by Dividing the Grosser and more Solid Particles into Minute ones, which will be always Lesser, and for the most part otherwise Shap'd than the Entire Corpuscle so Divided, as it will happen in a piece of Wood reduc'd into Splinters or Chips, or as when a piece of Chrystal heated red Hot and quench'd in Cold water is crack'd into a multitude of little Fragments, which though they fall not asunder, alter the Disposition of the Body of the Chrystal, as to its manner of Reflecting the Light, as we shall have Occasion to shew hereafter.

22. There is a fourth way contrary to the third, whereby a Liquor may change the Colour of another Body, especially of another Fluid, and that is, by procuring the Coalition of several Particles that before lay too Scatter'd and Dispers'd to exhibit the Colour that afterwards appears. Thus sometimes when I have had a Solution of Gold so Dilated, that I doubted whether the Liquor had really Imbib'd any true Gold or no, by pouring in a little Mercury, I have been quickly able to satisfie my Self, that the Liquor contain'd Gold, that Mettall after a little while Cloathing the Surface of the Quick-silver, with a Thin Film of its own Livery. And chiefly, though not only by this way of bringing the Minute parts of Bodies together in such Numbers as to make them become Notorious to the Eye, many of these Colours seem to be Generated which are produc'd by Precipitations, especially by such as are wont to be made with fair Water, as when Resinous Gumms dissolv'd in Spirit of Wine, are let fall again, if the Spirit be Copiously diluted with that weakning Liquor. And so out of the Rectify'd and Transparent Butter of Antimony, by the bare Mixture of fair Water, there will be plentifully Precipitated that Milk-white Substance, which by having its Looser Salts well wash'd off, is turn'd into that Medicine, which Vulgar Chymists are pleas'd to call Mercurius Vitæ.

23. A fifth way, by which a Liquor may change the Colour of a Body, is, by Dislocating the Parts, and putting them out of their former Order into another, and perhaps also altering the Posture of the single Corpuscles as well as their Order or Situation in respect of one another. What certain Kinds of Commotion or Dislocation of the Parts of a Body may do towards the Changing its Colour, is not only evident in the Mutations of Colour observable in Quick-silver, and some other Concretes long kept by Chymists in a Convenient Heat, though in close Vessels, but in the Obvious Degenerations of Colour, which every Body may take notice of in Bruis'd Cherries, and other Fruit, by comparing after a while the Colour of the Injur'd with that of the Sound part of the same Fruit. And that also such Liquors, as we have been speaking of, may greatly Discompose the Textures of many Bodies, and thereby alter the Disposition of their Superficial parts, the great Commotion made in Metalls, and several other Bodies by Aqua-fortis, Oyl of Vitriol, and other Saline Menstruums, may easily perswade us, and what such Vary'd Situations of Parts may do towards the Diversifying of the manner of their Reflecting the Light, may be Guess'd in some Measure by the Beating of Transparent Glass into a White Powder, but farr better by the Experiments lately Pointed at, and hereafter Deliver'd, as the Producing and Destroying Colours by the means of subtil Saline Liquors, by whose Affusion the Parts of other Liquors are manifestly both Agitated, and likewise Dispos'd after another manner than they were before such Affusion. And in some Chymical Oyls, as particularly that of Lemmon Pills, by barely Shaking the Glass, that holds it, into Bubbles, that Transposition of the Parts which is consequent to the Shaking, will shew you on the Surfaces of the Bubbles exceeding Orient and Lively Colours, which when the Bubbles relapse into the rest of the Oyl, do immediately Vanish.

24. I know not, Pyrophilus, whether I should mention as a Distinct way, because it is of a somewhat more General Nature, that Power, whereby a Liquor may alter the Colour of another Body, by putting the Parts of it into Motion; For though possibly the Motion so produc'd, does, as such, seldome suddenly change the Colour of the Body whose Parts are Agitated, yet this seems to be one of the most General, however not Immediate causes of the Quick change of Colours in Bodies. For the Parts being put into Motion by the adventitious Liquor, divers of them that were before United, may become thereby Disjoyn'd, and when that Motion ceases or decays others of them may stick together, and that in a new Order, by which means the Motion may sometimes produce Permanent changes of Colours, as in the Experiment you will meet with hereafter, of presently turning a Snowy White Body into a Yellow, by the bare Affusion of fair Water, which probably so Dissolves the Saline Corpuscles that remain'd in the Calx, and sets them at Liberty to Act upon one another, and the Metall, far more Powerfully than the Water without the Assistance of such Saline Corpuscles could do. And though you rubb Blew Vitriol, how Venereal and Unsophisticated soever it be, upon the Whetted Blade of a Knife, it will not impart to the Iron its Latent Colour, but if you moisten the Vitriol with your Spittle, or common Water, the Particles of the Liquor disjoyning those of the Vitriol, and thereby giving them the Various Agitation requisite to Fluid Bodies, the Metalline Corpuscles of the thus Dissolv'd Vitriol will Lodge themselves in Throngs in the Small and Congruous Pores of the Iron they are Rubb'd on, and so give the Surface of it the Genuine Colour of the Copper.

25. There remains yet a way, Pyrophilus to be mention'd, by which a Liquor may alter the Colour of another Body, and this seems the most Important of all, because though it be nam'd but as One, yet it may indeed comprehend Many, and that is, by Associating the Saline Corpuscles, or any other Sort of the more Rigid ones of the Liquor, with the Particles of the Body that it is employ'd to Work upon. For these Adventitious Corpuscles Associating themselves with the Protuberant Particles of the Surface of a Colour'd Body, must necessarily alter their Bigness, and will most commonly alter their Shape. And how much the Colours of Bodies depend upon the Bulk and Figure of their Superficial Particles, you may Guess by this, that eminent antient Philosophers and divers Moderns, have thought that all Colours might in a general way be made out by these two; whose being Diversify'd, will in our Case be attended with these two Circumstances, the One, that the Protuberant Particles being Increas'd in Bulk, they will oftentimes be Vary'd as to the Closness or Laxity of their Order, fewer of them being contain'd within the same Sensible (though Minute) space than before; or else by approaching to one another, they must Straighten the Pores, and it may be too, they will by their manner of Associating themselves with the Protuberant Particles, intercept new Pores. And this invites me to consider farther, that the Adventitious Corpuscles, I have been speaking of, may likewise produce a great Change as well in the Little Cavities or Pores as in the Protuberances of a Colour'd Body; for besides what we have just now taken notice of, they may by Lodging themselves in those little Cavities, fill them up, and it may well happen, that they may not only fill the Pores they Insinuate themselves into, but likewise have their Upper Parts extant above them; and partly by these new Protuberances, partly by Increasing the Bulk of the former, these Extraneous Corpuscles may much alter the Number and Bigness of the Surfaces Pores, changing the Old and Intercepting new ones. And then 'tis Odds, but the Order of the Little Extancies, and consequently that of the Little Depressions in point of Situation will be alter'd likewise: as if you dissolve Quick-silver in some kind of Aqua-fortis, the Saline Particles of the Menstruum Associating themselves with the Mercurial Corpuscles, will make a Green Solution, which afterwards easily enough Degenerates. And Red Lead or Minium being Dissolv'd in Spirit of Vinegar, yields not a Red, but a Clear Solution, the Redness of the Lead being by the Liquor Destroy'd. But a better Instance may be taken from Copper, for I have try'd, that if upon a Copper-plate you let some Drops of weak Aqua-fortis rest for a while, the Corpuscles of the Menstruum, joyning with those of the Metall, will produce a very sensible Asperity upon the Surface of the Plate, and will Concoagulate that way into very minute Grains of a Pale Blew Vitriol; whereas if upon another part of the same Plate you suffer a little strong Spirit of Urine to rest a competent time, you shall find the Asperated Surface adorn'd with a Deeper and Richer Blew. And the same Aqua-fortis, that will quickly change the Redness of Red Lead into a Darker Colour, will, being put upon Crude Lead, produce a Whitish Substance, as with Copper it did a Blewish. And as with Iron it will produce a Reddish, and on White Quills a Yellowish, so much may the Coalition of the Parts of the same Liquor, with the differingly Figur'd Particles of Stable Bodies, divers ways Asperate the differingly Dispos'd Surfaces, and to Diversifie the Colour of those Bodies. And you'l easily believe, that in many changes of Colour, that happen upon the Dissolutions of Metalls, and Precipitations made with Oyl of Tartar, and the like Fix'd Salts, there may Intervene a Coalition of Saline Corpuscles with the Particles of the Body Dissolv'd or Precipitated, if you examine how much the Vitriol of a Metall may be Heavier than the Metalline part of it alone, upon the Score of the Saline parts Concoagulated therewith, and, that in Several Precipitations the weight of the Calx does for the same Reason much exceed that of the Metall, when it was first put in to be Dissolv'd.