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Experiments and Considerations Touching Colours (1664)
by Robert Boyle
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[4] Since for his eminent Qualities and Loyalty Grac'd, by his Majesty, with the Honour of Knighthood.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

26. But, Pyrophilus, to consider these Matters more particularly would be to forget that I declar'd against Adventuring, at least for this time, at particular Theories of Colours, and that accordingly you may justly expect from me rather Experiments than Speculations, and therefore I shall Dismiss this Subject of the Forms of Superficial Asperity in Colour'd Bodies, as soon as I shall but have nam'd to you by way of Supplement to what we have hitherto Discours'd in this Section, a Couple of Particulars, (which you'l easily grant me) The one, That there are divers other ways for the speedy Production even of True and Permanent Colours in Bodies, besides those Practicable by the help of Liquors; for proof of which Advertisement, though several Examples might be alleged, yet I shall need but Re-mind you of what I mention'd to you above, touching the change of Colours suddenly made on Temper'd Steel, and on Lead, by the Operation of Heat, without the Intervention of a Liquor. But the other particular I am to observe to you is of more Importance to our present Subject and it is, That though Nature and Art may in some cases so change the Asperity of the Superficial parts of a Body, as to change its Colour by either of the ways I have propos'd Single or Unassisted, yet for the most part 'tis by two or three, or perhaps by more of the fore-mention'd ways Associated together, that the Effect is produc'd, and if you consider how Variously those several ways and some others Ally'd unto them, which I have left unmention'd, may be Compounded and Apply'd, you will not much wonder that such fruitfull, whether Principles (or Manners of Diversification) should be fitted to Change or Generate no small store of Differing Colours.

27. Hitherto, Pyrophilus, we have in discoursing of the Asperity of Bodies consider'd the little Protuberances of other Superficial particles which make up that Roughness, as if we took it for granted, that they must be perfectly Opacous and Impenetrable by the Beams of Light, and so, must contribute to the Variety of Colours as they terminate more or less Light, and reflect it to the Eye mix'd with more or less of thus or thus mingl'd Shades. But to deal Ingenuously with you, Pyrophilus, before I proceed any further, I must not conceal from you, that I have often thought it worth a Serious Enquiry, whether or no Particles of Matter, each of them sing'y Insensible, and therefore small enough to be capable of being such Minute Particles as the Atomists both of old and of late have (not absurdly) called Corpuscula Coloris, may not yet consist each of them of divers yet Minuter Particles, betwixt which we may conceive little Commissures where they Adhere to one another, and, however, may not be Porous enough to be, at least in some degree, Pervious to the unimaginably subtile Corpuscles that make up the Beams of Light, and consequently to be in such a degree Diaphanous. For, Pyrophilus, that the proposed Enquiry may be of moment to him that searches after the Nature of Colour, you'l easily grant, if you consider, that whereas Perfectly Opacous bodies can but reflect the incident Beams of Light, those that are Diaphanous are qualified to refract them too, and that Refraction has such a stroak in the Production of Colours, as you cannot but have taken notice of, and perhaps admir'd in the Colours generated by the Trajection of Light through Drops of Water that exhibit a Rain-bow, through Prismatical glasses, and through divers other Transparent bodies. But 'tis like, Pyrophilus, you'l more easily allow that about this matter 'tis rather Important to have a Certainty, than that 'tis Rational to entertain a Doubt; wherefore I must mention to you some of the Reasons that make me think it may need a further Enquiry, for I find that in a Darkned Room, where the Light is permitted to enter but at One hole, the little wandering Particles of Dust, that are commonly called Motes, and, unless in the Sunbeams, are not taken notice of by the unassisted Sight, I have, I say, often observ'd, that these roving Corpuscles being look'd on by an Eye plac'd on one side of the Beams that enter'd the Little hole, and by the Darkness having its Pupill much Enlarg'd, I could discern that these Motes as soon as they came within the compass of the Luminous, whether Cylinder or Inverted Cone, if I may so call it, that was made up by the Unclouded Beams of the Sun, did in certain positions appear adorn'd with very vivid Colours, like those of the Rain-bow, or rather like those of very Minute, but Sparkling fragments of Diamonds; and as soon as the Continuance of their Motion had brought them to an Inconvenient position in reference to the Light and the Eye, they were only visible without Darting any lively Colours as before, which seems to argue that these little Motes, or minute Fragments, of several sorts of bodies reputed Opacous, and only crumbled as to their Exteriour and Looser parts into Dust, did not barely Reflect the Beams that fell upon them, but remit them to the Eye Refracted too. We may also observe, that several Bodies, (as well some of a Vegetable, as others of an Animal nature) which are wont to pass for Opacous, appear in great part Transparent, when they are reduc'd into Thin parts, and held against a powerful Light. This I have not only taken notice of in pieces of Ivory reduc'd but into Thick leaves, as also in divers considerable Thick shells of Fishes, and in shaving of Wood, but I have also found that a piece of Deal, far thicker than one would easily imagine, being purposly interposed betwixt my Eye plac'd in a Room, and the clear Daylight, was not only somewhat Transparent, but (perhaps by reason of its Gummous nature) appear'd quite through of a lovely Red. And in the Darkned Room above mention'd, Bodies held against the hole at which the Light enter'd, appear'd far less Opacous then they would elsewhere have done, insomuch that I could easily and plainly see through the whole Thickness of my Hand, the Motions of a Body plac'd (at a very near distance indeed, but yet) beyond it. And even in Minerals, the Opacity is not always so great as many think, if the Body be made Thin, for White Marble though of a pretty Thickness, being within a Due distance plac'd betwixt the Eye and a Convenient Light, will Suffer the Motions of ones Finger to be well discern'd through it, and so will pieces, Thick enough, of many common Flints. But above all, that Instance is remarkable, that is afforded us by Muscovie glass, (which some call Selenites, others Lapis Specularis) for though plates of this Mineral, though but of a moderate Thickness, do often appear Opacous, yet if one of these be Dextrously split into the thinnest Leaves 'tis made up of, it will yield such a number of them, as scarce any thing but Experience could have perswaded me, and these Leaves will afford the most Transparent sort of consistent Bodies, that, for ought I have observ'd, are yet known; and a single Leaf or Plate will be so far from being Opacous, that 'twill scarce be so much as Visible. And multitudes of Bodies there are, whose Fragments seem Opacous to the naked Eye, which yet, when I have included them in good Microscopes, appear'd Transparent; but, Pyrophilus, on the other side I am not yet sure that there are no Bodies, whose Minute Particles even in such a Microscope as that of mine, which I was lately mentioning, will not appear Diaphanous. For having consider'd Mercury Precipitated per se, the little Granules that made up the powder, look'd like little fragments of Coral beheld by the naked Eye at a Distance (for very Near at hand Coral will sometimes, especially if it be Good, shew some Transparency.) Filings likewise of Steel and Copper, though in an excellent Microscope, and a fair Day, they show'd like pretty Big Fragments of those Metalls, and had considerable Brightness on some of their Surfaces, yet I was not satisfi'd, that I perceiv'd any Reflection from the Inner parts of any of the Filings. Nay, having look'd in my best Microscope upon the Red Calx of Lead, (commonly call'd Minium) neither I, nor any I shew'd it to, could discern it to be other than Opacous, though the Day were Clear, and the Object strongly Enlightned. And the deeply Red Colour of Vitriol appear'd in the same Microscope (notwithstanding the great Comminution effected by the Fire) but like Grossy beaten Brick. So that, Pyrophilus, I shall willingly resign you the care of making some further Enquiries into the Subject we have now been considering; for I confess, as I told you before, that I think that the Matter may need a further Scrutiny, nor would I be forward to Determine how far or in what cases the Transparency or Semi-diaphaniety of the Superficial Corpuscles of Bigger Bodies, may have an Interest in the Production of their Colours, especially because that even in divers White bodies, as Beaten Glass, Snow and Froth, where it seems manifest that the Superficial parts are singly Diaphanous, (being either Water, or Air, or Glass) we see not that such Variety of Colours are produc'd as usually are by the Refraction of Light, even in those Bodies, when by their Bigness, Shape, &c. they are conveniently qualify'd to exhibit such Various and Lively Colours as those of the Rain-bow, and of Prismatical Glasses.

28. By what has been hitherto discours'd, Pyrophilus, we may be assisted to judge of that famous Controversie which was of Old disputed betwixt the Epicureans and other Atomists on the one side, and most other Philosophers on the other side. The former Denying Bodies to be Colour'd in the Dark, and the Latter making Colour to be an Inherent quality, as well as Figure, Hardness; Weight, or the like. For though this Controversie be Reviv'd, and hotly Agitated among the Moderns, yet I doubt whether it be not in great part a Nominal dispute, and therefore let us, according to the Doctrine formerly deliver'd, Distinguish the Acceptions of the word Colour, and say, that if it be taken in the Stricter Sense, the Epicureans seem to be in the Right, for if Colour be indeed, though not according to them, but Light Modify'd, how can we conceive that it can Subsist in the Dark, that is, where it must be suppos'd there is no Light; but on the other side, if Colour be consider'd as a certain Constant Disposition of the Superficial parts of the Object to Trouble the Light they Reflect after such and such a Determinate manner, this Constant, and, if I may so speak, Modifying disposition persevering in the Object, whether it be Shin'd upon or no, there seems no just reason to deny, but that in this Sense, Bodies retain their Colour as well in the Night as Day; or, to Speak a little otherwise, it may be said, that Bodies are Potentially Colour'd in the Dark, and Actually in the Light. But of this Matter discoursing more fully elsewhere, as 'tis a difficulty that concerns Qualities in general, I shall forbear to insist on it here.

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CHAP. IV

1. Of greater Moment in the Investigation of the Nature of Colours is the Controversie, Whether those of the Rain-bow, and those that are often seen in Clouds, before the Rising, or after the Setting of the Sun; and in a word, Whether those other Colours, that are wont to be call'd Emphatical, ought or ought not to be accounted True Colours. I need not tell you that the Negative is the Common Opinion, especially in the Schools, as may appear by that Vulgar distinction of Colours, whereby these under Consideration are term'd Apparent, by way of Opposition to those that in the other Member of the Distinction are call'd True or Genuine. This question I say seems to me of Importance, upon this Account, that it being commonly Granted, (or however, easie enough to be Prov'd) that Emphatical Colours are Light it self Modify'd by Refractions chiefly, with a concurrence sometimes of Reflections, and perhaps some other Accidents depending on these two; if these Emphatical Colours be resolv'd to be Genuine, it will seem consequent, that Colours, or at least divers of them, are but Diversify'd Light, and not such Real and Inherent qualities as they are commonly thought to be.

2. Now since we are wont to esteem the Echoes and other Sounds of Bodies, to be True Sounds, all their Odours to be True Odours, and (to be short) since we judge other Sensible Qualities to be True ones, because they are the proper Objects of some or other of our Senses, I see not why Emphatical Colours, being the proper and peculiar Objects of the Organ of Sight, and capable to Affect it as Truly and as Powerfully as other Colours, should be reputed but Imaginary ones.

And if we have (which perchance you'l allow) formerly evinc'd Colour, (when the word is taken in its more Proper sense) to be but Modify'd Light, there will be small Reason to deny these to be true Colours, which more manifestly than others disclose themselves to be produc'd by Diversifications of the Light.

3. There is indeed taken notice of a Difference betwixt these Apparent colours, and those that are wont to be esteem'd Genuine, as to the Duration, which has induc'd some Learned Men to call the former rather Evanid than Fantastical. But as the Ingenious Gassendus does somewhere Judiciously observe, if this way of Arguing were Good, the Greeness of a Leaf ought to pass for Apparent, because, soon Fading into a Yellow, it Scarce lasts at all, in comparison of the Greeness of an Emerauld. I shall add, that if the Sun-beams be in a convenient manner trajected through a Glass-prism, and thrown upon some well-shaded Object within a Room, the Rain-bow thereby Painted on the Surface of the Body that Terminates the Beams, may oftentimes last longer than Some Colours I have produc'd in certain Bodies, which would justly, and without scruple be accounted Genuine Colours, and yet suddenly Degenerate, and lose their Nature.

4. A greater Disparity betwixt Emphatical Colours, and others, may perhaps be taken from this, that Genuine Colours seem to be produc'd in Opacous Bodies by Reflection, but Apparent ones in Diaphanous Bodies, and principally by Refraction, I say Principally rather than Solely, because in some cases Reflection also may concurr, but still this seems not to conclude these Latter Colours not to be True ones. Nor must what has been newly said of the Differences of True and Apparent Colours, be interpreted in too Unlimited a Sense, and therefore it may perhaps somewhat Assist you, both to Reflect upon the two fore-going Objections, and to judge of some other Passages which you'l meet with in this Tract, if I take this Occasion to observe to you, that if Water be Agitated into Froth, it exhibits you know a White colour, which soon after it Loses upon the Resolution of the Bubbles into Air and Water, now in this case either the Whiteness of the Froth is a True Colour or not, if it be, then True Colours, supposing the Water pure and free from Mixtures of any thing Tenacious, may be as Short-liv'd as those of the Rain-bow; also the Matter, wherein the Whiteness did Reside, may in a few moments perfectly Lose all foot-steps or remains of it. And besides, even Diaphanous Bodies may be capable of exhibiting True Colours by Reflection, for that Whiteness is so produc'd, we shall anon make it probable. But if on the other side it be said, that the Whiteness of Froth is an Emphatical Colour, then it must no longer be said, that Fantastical Colours require a certain Position of the Luminary and the Eye, and must be Vary'd or Destroy'd by the Change thereof, since Froth appears White, whether the Sun be Rising or Setting, or in the Meridian, or any where between it and the Horizon, and from what (Neighbouring) place soever the Beholders Eye looks upon it. And since by making a Liquor Tenacious enough, yet without Destroying its Transparency, or Staining it with any Colour, you may give the Little Films, whereof the Bubbles consist, such a Texture, as may make the Froth last very many Hours, if not some Days, or even Weeks, it will render it somewhat Improper to assign Duration for the Distinguishing Character to Discriminate Genuine from Fantastical Colours. For such Froth may much outlast the Undoubtedly true Colours of some of Nature's Productions, as in that Gaudy Plant not undeservedly call'd the Mervail of Peru, the Flowers do often Fade, the same Day they are Blown; And I have often seen a Virginian Flower, which usually Withers within the compass of a Day; and I am credibly Inform'd, that not far from hence a curious Herborist has a Plant, whose Flowers perish in about an Hour. But if the Whiteness of Water turn'd into Froth must therefore be reputed Emphatical, because it appears not that the Nature of the Body is Alter'd, but only that the Disposition of its Parts in reference to the Incident Light is Chang'd, why may not the Whiteness be accounted Emphatical too, which I shall shew anon to be Producible, barely by such another change in Black Horn? and yet this so easily acquir'd Whiteness seems to be as truly its Colour as the Blackness was before, and at least is more Permanent than the Greenness of Leaves, the Redness of Roses, and, in short, than the Genuine Colours of the most part of Nature's Productions. It may indeed be further Objected, that according as the Sun or other Luminous Body changes place, these Emphatical Colours alter or vanish. But not to repeat what I have just now said, I shall add, that if a piece of Cloath in a Drapers Shop (in such the Light being seldome Primary) be variously Folded, it will appear of differing Colours, as the Parts happen to be more Illuminated or more Shaded, and if you stretch it Flat, it will commonly exhibit some one Uniform Colour, and yet these are not wont to be reputed Emphatical, so that the Difference seems to be chiefly this, that in the Case of the Rain-bow, and the like, the Position of the Luminary Varies the Colour, and in the Cloath I have been mentioning, the Position of the Object does it. Nor am I forward to allow that in all Cases the Apparition of Emphatical Colours requires a Determinate position of the Eye, for if Men will have the Whiteness of Froth Emphatical, you know what we have already Inferr'd from thence. Besides, the Sun-beams trajected through a Triangular Glass, after the manner lately mention'd, will, upon the Body that Terminates them, Paint a Rain-bow, that may be seen whether the Eye be plac'd on the Right Hand of it or the Left, or Above or Beneath it, or Before or Behind it; and though there may appear some Little Variation in the Colours of the Rain-bow, beheld from Differing parts of the Room, yet such a Diversity may be also observ'd by an Attentive Eye in Real Colours, look'd upon under the like Circumstances, Nor will it follow, that because there remains no Footsteps of the Colour upon the Object, when the Prism is Remov'd, that therefore the Colour was not Real, since the Light was truly Modify'd by the Refraction and Reflection it Suffer'd in its Trajection through the Prism; and the Object in our case serv'd for a Specular Body, to Reflect that Colour to the Eye. And that you may not be Startled, Pyrophilus, that I should Venture to say, that a Rough and Coiour'd Object may serve for a Speculum to Reflect the Artificial Rain-bow I have been mentioning, consider what usually happens in Darkned Rooms, where a Wall, or other Body conveniently Situated within, may so Reflect the Colours of Bodies, without the Room, that they may very clearly be Discern'd and Distinguish'd, and yet 'tis taken for granted, that the Colours seen in a Darkned Room, though they leave no Traces of themselves upon the Wall or Body that Receives them, are the True Colours of the External Objects, together with which the Colours of the Images are Mov'd or do Rest. And the Errour is not in the Eye, whose Office is only to perceive the Appearances of things, and which does Truly so, but in the Judging or Estimative faculty, which Mistakingly concludes that Colour to belong to the Wall, which does indeed belong to the Object, because the Wall is that from whence the Beams of Light that carry the Visible Species, do come in Straight Lines directly to the Eye, as for the same Reason we are wont at a certain Distance from Concave Sphaerical Glasses, to perswade our Selves that we see the Image come forth to Meet us, and Hang in the Air betwixt the Glass and Us, because the Reflected Beams that Compose the image cross in that place, where the Image seems to be, and thence, and not from the Glass, do in Direct Lines take their Course to the Eye, and upon the like Cause it is, that divers Deceptions in Sounds and other Sensible Objects do depend, as we elsewhere declare.

5. I know not, whether I need add, that I have purposely Try'd, (as you'l find some Pages hence, and will perhaps think somewhat strange) that Colours that are call'd Emphatical, because not Inherent in, the Bodies in which they Appear, may be Compounded with one another, as those that are confessedly Genuine may. But when all this is said, Pyrophilus, I must Advertise you, that it is but Problematically Spoken, and that though I think the Opinion I have endeavour'd to fortifie Probable, yet a great part of our Discourse concerning Colours may be True, whether that Opinion be so or not.

* * * * *

CHAP. V.

1. There are you know, Pyrophilus, besides those Obsolete Opinions about Colours which have been long since Rejected, very Various Theories that have each of them, even at this day, Eminent Men for its Abetters; for the Peripatetick Schools, though they dispute amongst themselves divers particulars concerning Colours, yet in this they seem Unanimously enough to Agree, that Colours are Inherent and Real Qualities, which the Light doth but Disclose, and not concurr to Produce. Besides there are Moderns, who with a slight Variation adopt the Opinion of Plato, and as he would have Colour to be nothing but a Kind of Flame consisting of Minute Corpuscles as it were Darted by the Object against the Eye, to whose Pores their Littleness and Figure made them congruous, so these would have Colour to be an Internal Light of the more Lucid parts of the Object, Darkned and consequently Alter'd by the Various Mixtures of the less Luminous parts. There are also others, who in imitation of some of the Ancient Atomists, make Colour not to be Lucid steam, but yet a Corporeal Effluvium issuing out of the Colour'd Body, but the Knowingst of these have of late Reform'd their Hypothesis, by acknowledging and adding that some External Light is necessary to Excite, and as they speak, Sollicit these Corpuscles of Colour as they call them, and Bring them to the Eye. Another and more principal Opinion of the Modern Philosophers, to which this last nam'd may by a Favourable explication be reconcil'd, is that which derives Colours from the Mixture of Light and Darkness, or rather Light and Shadows. And as for the Chymists 'tis known, that the generality of them ascribes the Origine of Colours to the Sulphureous Principle in Bodies, though I find, as I elsewhere largely shew, that some of the Chiefest of them derive Colours rather from Salt than Sulphur, and others, from the third Hypostatical Principle, Mercury. And as for the Cartesians I need not tell you, that they, supposing the Sensation of Light to bee produc'd by the Impulse made upon the Organs of Sight, by certain extremely Minute and Solid Globules, to which the Pores of the Air and other Diaphanous bodies are pervious, endeavour to derive the Varieties of Colours from the Various Proportion of the Direct Progress or Motion of these Globules to their Circumvolution or Motion about their own Centre, by which Varying Proportion they are by this Hypothesis suppos'd qualify'd to strike the Optick Nerve after several Distinct manners, so to produce the perception of Differing Colours.

2. Besides these six principal Hypotheses, Pyrophilus, there may be some others, which though Less known, may perhaps as well as thesc deserve to be taken into consideration by you; but that I should copiously debate any of them at present, I presume you will not expect, if you consider the Scope of these Papers, and the Brevity I have design'd in them, and therefore I shall at this time only take notice to you in the general of two or three things that do more peculiarly concern the Treatise you have now in your hands.

3. And first, though the Embracers of the Several Hypotheses I have been naming to you, by undertaking each Sect of them to explicate Colours indefinitely, by the particular Hypotheses they maintain, seem to hold it forth as the only Needful Theory about that Subject, yet for my part I doubt whether any one of all these Hypotheses have a right to be admitted Exclusively to all others, for I think it Probable, that Whiteness and Blackness may be explicated by Reflection alone without Refraction, as you'l find endeavour'd in the Discourse you'l meet with e're long Of the Origine of Whiteness and Blackness, and on the other side, since I have not found that by any Mixture of White and True Black, (for there is a Blewish Black which many mistake for a Genuine) there can be a Blew, a Yellow, or a Red, to name no other Colours, produced, and since we do find that these Colours may be produc'd in the Glass-prism and other Transparent bodies, by the help of Refractions, it seems that Refraction is to be taken in into the Explication of some Colours, to whose Generation they seem to concurr, either by making a further or other Commixture of Shades with the Refracted Light, or by some other way not now to be discours'd. And as it seems not improbable, that in case the Pores of the Air, and other Diaphanous bodies be every where almost fill'd with such Globuli as the Cartesians suppose, the Various kind of Motion of these Globuli, may in many cases have no small stroak in Varying our Perception of Colour, so without the Supposition of these Globuli, which 'tis not so easie to evince, I think we may probably enough conceive in general, that the Eye may be Variously affected, not only by the Entire Beams of Light that fall upon it as they are such, but by the Order, and by the Degree of Swiftness, and in a word by the Manner according to which the Particles that compose each Particular Beam arrive at the Sensory, so that whatever be the Figure of the Little Corpuscles, of which the Beams of Light consist, not only the Celerity or Slowness of their Revolution or Rotation in reference to their Progressive Motion, but their more Absolute Celerity, their Direct or Undulating Motion, and other Accidents, which may attend their Appulse to the Eye, may fit them to make Differing Impressions on it.

4. Secondly, For these and the like Considerations, Pyrophilus, I must desire that you would look upon this little Treatise, not as a Discourse written Principally to maintain any of the fore-mention'd Theories, Exclusively to all others, or substitute a New one of my Own, but as the beginning of a History of Colours, upon which, when you and your Ingenious friends shall have Enrich'd it, a Solid Theory may be safely built. But yet because this History is not meant barely for a Register of the things recorded in it, but for an Apparatus to a sound and comprehensitive Hypothesis, I thought fit, so to temper the whole Discourse, as to make it as conducible, as conveniently I can to that End, and therefore I have not scrupled to let you see that I was willing, as to save you the labour of Cultivating some Theories that I thought would never enable you to reach the Ends you aim at, so to contract your Enquiries into a Narrow compass, for both which purposes I thought it requisite to do these two things, the One, to set down some Experiments which by the help of the Reflections and Insinuations that attend them, may assist you to discover the Infirmness and Insufficiency both of the common Peripatetick Doctrine, and of the now more applauded Theory of the Chymists about Colour, because those two Doctrines having Possess'd themselves, the one of the most part of the Schools, and the other of the Esteem of the Generality ef Physicians and other Learned Men, whose Professions and Ways of Study do not exact that they should Scrupulously examine the very First and Simplest Principles of Nature, I fear'd it would be to little purpose, without doing something to discover the Insufficiency of these Hypotheses, that I should, (which was the Other thing I thought requisite for me to do) set down among my other Experiments those in the greatest Number, that may let you see, that, till I shall be Better Inform'd, I encline to take Colour to be a Modification of Light, and would invite you chiefly to Cultivate that Hypothesis, and Improve it to the making out of the Generation of Particular Colours, as I have Endeavour'd to apply it to the Explication of Whiteness and Blackness.

5. Thirdly. But, Pyrophilus, though this be at present the Hypothesis I preferr, yet I propose it but in a General Sense, teaching only that the Beams of Light, Modify'd by the Bodies whence they are sent (Reflected or Refracted) to the Eye, produce there that Kind of Sensation, Men commonly call Colour; But whether I think this Modification of the Light to be perform'd by Mixing it with Shades, or by Varying the Proportion of the Progress and Rotation of the Cartesian Globuli Caelestes, or by some other way which I am not now to mention, I pretend not here to Declare. Much less do I pretend to Determine, or scarce so much as to Hope to know all that were requisite to be Known, to give You, or even my Self, a perfect account of the Theory of Vision and Colours, for in Order to such an undertaking I would first Know what Light is, and if it be a Body (as a Body or the Motion of a Body it seems to be) what Kind of Corpuscles for Size and Shape it consists of, with what Swiftness they move Forwards, and Whirl about their own Centres. Then I would Know the Nature of Refraction, which I take to be one of the Abstrusest things (not to explicate Plausibly, but to explicate Satisfactorily) that I have met with in Physicks; I would further Know what Kind and what Degree of Commixture of Darkness or Shades is made by Refractions or Reflections, or both, in the Superficial particles of those Bodies, that being Shin'd upon, constantly exhibit the one, for Instance, a Blew, the other a Yellow, the third a Red Colour; I would further Know why this Contemperation of Light and Shade, that is made, for Example, by the Skin of a Ripe Cherry, should exhibit a Red, and not a Green, and the Leaf of the same Tree should exhibit a Green rather than a Red; and indeed, Lastly, why since the Light that is Modify'd into these Colours consists but of Corpuscles moved against the Retina or Pith of the Optick Nerve, it should there not barely give a Stroak, but produce a Colour, whereas a Needle wounding likewise the Eye, would not produce Colour but Pain. These, and perhaps other things I should think requisite to be Known, before I should judge my Self to have fully Comprehended the True and Whole Nature of Colours; and therefore, though by making the Experiments and Reflections deliver'd in this Paper, I have endeavour'd somewhat to Lessen my Ignorance in this Matter, and think it far more Desireable to discover a Little, than to discover Nothing, yet I pretend but to make it Probable by the Experiments I mention, that some Colours may be Plausibly enough Explicated in the General by the Doctrine here propos'd; For whensoever I would Descend to the Minute and Accurate Explication of Particulars, I find my Self very Sensible of the great Obscurity of things, without excepting those which we never see but when they are Enlightned, and confess with Scaliger[5], Latet natura haec, (says he, Speaking of that of Colour) & sicut aliarum rerum species in profundissima caligine inscitiae humanae.

[5] Exercitat. 325 Parag. 4

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THE EXPERIMENTAL HISTORY OF COLOURS.

* * * * *

PART. II.

Of the Nature of Whiteness and Blackness.

CHAP. I.

1. Though after what I have acknowledged, Pyrophilus, of the Abstruse Nature of Colours in particular, you will easily believe, that I pretend not to give you a Satisfactory account of Whiteness and Blackness; Yet not wholly to frustrate your Expectation of my offering something by way of Specimen towards the Explication of some Colours in particular, I shall make choice of These as the most Simple Ones, (and by reason of their mutual Opposition the Least hardly explicable) about which to present you my Thoughts, upon condition you will take them at most to be my Conjectures, not my Opinions.

2. When I apply'd my Self to consider, how the cause of Whiteness might be explan'd by Intelligible and Mechanical Principles, I remembred not to have met with any thing among the Antient Corpuscularian Philosophers, touching the Quality we call Whiteness, save that Democritus is by Aristotle said to have ascrib'd the Whiteness of Bodies to their Smoothness, and on the contrary their Blackness to their Asperity.[6] But though about the Latter of those Qualities his Opinion be allowable, as we shall see anon, yet that he heeds a Favourable Interpretation in what is Deliver'd concerning the First, (at least if his Doctrine be not Mis-represented in this point, as it has been in many others) we shall quickly have Occasion to manifest. But amongst the Moderns, the most Learned Gassendus in his Ingenious Epistle publish'd in the Year 1642. De apparente Magnitudine solis humilis & sublimis, reviving the Atomical Philosophy, has, though but Incidentally, deliver'd something towards the Explication of Whiteness upon Mechanical Principles: And because no Man that I know of, has done so before him, I shall, to be sure to do him Right, give you his Sense in his own Words:[7] Cogites velim (says he) lucem quidem in Diaphano nullius coloris videri, sed in Opaco tamen terminante Candicare, ac tanto magis, quanto densior seu collectior fuerit. Deinde aquam non esse quidem coloris ex se candidi & radium tamen ex ea reflexum versus oculum candicare. Rursus cum plana aquae Superficies non nisi ex una parte eam reflexionem faciat: si contigerit tamen illam in aliquot bullas intumescere, bullam unamquamque reflectionem facere, & candoris speciem creare certa Superficiei parte. Ad haec Spumam ex aqua pura non alia ratione videri candescere & albescerere quam quod sit congeries confertissima minutissimarum bullarum, quarum unaquaeque suum radium reflectit, unde continens candor alborve apparet. Denique Nivem nihil aliud videri quam speciem purissimae spumae ex bullulis quam minutissimis & confertissimis cohaerentis. Sed ridiculam me exhibeam, si tales meas nugas uberius proponem.

[6] Album quippe & agrum, hoc quidem asperum esse dicit, hoc vero laeve. de Sensu & Sensib. 3. 3.

[7] Epist. 2. pag. 45.

3. But though in this passage, that very Ingenous Person has Anticipated part of what I should say; Yet I presume you will for all that expect, that I should give you a fuller Account of that Notion of Whiteness, which I have the least Exceptions to, and of the Particulars whence I deduce it, which to do, I must mention to you the following Experiments and Observations.

Whiteness then consider'd as a Quality in the Object, seems chiefly to depend upon this, That the Superficies of the Body that is call'd White, is Asperated by almost innumerable Small Surfaces, which being of an almost Specular Nature, are also so Plac'd, that some Looking this way, and some that way, they yet Reflect the Rays of Light that fall on them, not towards one another, but outwards towards the Spectators Eye. In this Rude and General account of Whiteness, it seems that besides those Qualities, which are common to Bodies of other Colours, as for instance the Minuteness and Number of the Superficial parts, the two chief things attributed to Bodies as White are made to be, First, that its Little Protuberances and Superficial parts be of somewhat a Specular Nature, that they may as little Looking-glasses each of them Reflect the Beams it receives, (or the little Picture of the Sun made on it) without otherwise considerably Altering them; whereas in most other Colours, they are wont to be much Chang'd, by being also Refracted, or by being Return'd to the Eye, mixt with Shades or otherwise. And next, that its Superficial parts be so Situated, that they Retain not the Incident Rays of Light by Reflecting them Inwards, but Send them almost all Back, so that the Outermost Corpuscles of a White Body, having their Various Little Surfaces of a Specular Nature, a Man can from no place Behold the Body, but that there will be among those Innumerable Superficieculae, that Look some one way, and some another, enough of them Obverted to his Eye, to afford like a broken Looking-glass, a confused Idaea, or Representation of Light, and make such an Impression on the Organ, as that for which Men are wont to call a Body White. But this Notion will perhaps be best Explan'd by the same Experiments and Observations, on which it is Built, And therefore I shall now advance to Them.

4. And in the first place I consider, that the Sun and other Powerfully Lucid Bodies, are not only wont to Offend, which we call to Dazle our Eyes, but that if any Colour be to be Ascrib'd to them as they are Lucid, it seems it should be Whiteness: For the Sun at Noon-day, and in Clear weather, and when his Face is less Troubled, and as it were Stained by the Steams of Sublunary Bodies, and when his Beams have much less of the Atmosphere to Traject in their Passage to our Eyes, appears of a Colour more approaching to White, than when nearer the Horizon, the Interposition of certain Sorts of Fumes and Vapours make him oftentimes appear either Red, or at least more Yellow. And when the Sun Shines upon that Natural Looking-glass, a Smooth water, that part of it, which appears to this or that particular Beholder, the most Shin'd on, does to his Eye seem far Whiter than the rest. And here I shall add, that I have sometimes had the Opportunity to observe a thing, that may make to my present purpose, namely, that when the Sun was Veil'd over as it were, with a Thin White Cloud, and yet was too Bright to be Look'd upon Directly without Dazling, by casting my Eyes upon a Smooth water, as we sometimes do to observe Eclipses without prejudice to our Eyes, the Sun then not far from the Meridian, appear'd to me not Red, but so White, that 'twas not without some Wonder, that I made the Observation. Besides, though we in English are wont to say, a thing is Red hot, as an Expression of its being Superlatively Ignitum, (if I may so Speak for want of a proper English word) yet in the Forges of Smiths, and the Furnaces of other Artificers, by that which they call a White heat, they mean a further Degree of Ignition, than by that which both they and we call a Red heat.

5. Secondly, I consider, that common Experience informs us, that as much Light Over-powers the Eye, so when the Ground is covered with Snow, (a Body extremely White) those that have Weak Eyes are wont to complain of too much Light: And even those that have not, are generally Sensible of an Extraordinary measure of Light in the Air; and if they are fain to Look very long upon the Snow, find their Sight Offended by it. On which occasion we may call to mind what Xenophon relates, that his Cyrus marching his Army for divers days through Mountains covered with Snow, the Dazling splendor of its Whiteness prejudic'd the Sight of very many of his Souldiers, and Blinded some of them; and other Stories of that Nature be met with in Writers of good Note. And the like has been affirm'd to me by credible Persons of my own Acquaintance, and especially by one who though Skill'd in Physick and not Ancient confess'd to me when I purposely ask'd him, that not only during his stay in Muscovy, he found his Eyes much Impair'd, by being reduc'd frequently to Travel in the Snow, but that the Weakness of his Eyes did not Leave him when he left that Country, but has follow'd him into these Parts, and yet continues to Trouble him. And to this doth agree what I as well as others have observ'd, namely, that when I Travell'd by Night, when the Ground was all cover'd with Snow, though the Night otherwise would not have been Lightsome, yet I could very well see to Choose my way. But much more Remarkable to my present purpose is that, which I have met with in Olaus Magnus,[8] concerning the way of Travelling in Winter in the Northern Regions, where the Days of that Season are so very Short; for after other things not needfull to be here Transcribed: Iter, says he, Diurnum duo scilicet montana milliaria (quae 12 Italica sunt) consiciunt. Nocte vero sub splendissima luna, duplatum iter consumunt aut triplatum. Neque id incommode fit, cum nivium reverberatione lunaris splendoris sublimes & declives campos illustret, ac etiam montium praecipitia ac noxias feras a lorge prospiciant evitandas. Which Testimony I the less Scruple to allege, because that it agrees very well with what has been Affirm'd to me by a Physician of Mosco, whom the Notion I have been Treating of concerning Whiteness invited me to ask whether he could not See much farther when he Travell'd by Night in Russia than he could do in England, or elsewhere, when there was no Snow upon the Ground; For this Ingenious Person inform'd me, that he could See Things at a farr greater Distance, and with more Clearness, when he Travell'd by Night on the Russian Snow, though without the Assistance of Moon-shine, than we in these Parts would easily be perswaded. Though it seems not unlikely to me, that the Intenseness of the Cold may contribute something to the considerableness of the Effect, by much Clearing the Air of Darkish Steams, which in these more Temperate Climates are wont to Thicken it in Snowy weather: For having purposely inquir'd of this Doctor, and consulted that Ingenious Navigator Captain James's Voyage hereafter to be further mention'd, I find both their Relations agree in this, that in Dark Frosty Nights they could Discover more Stars, and See the rest Clearer than we in England are wont to do.

[8] Gent. Septen. Histor. lib. 4 cap. 13.

6. I know indeed that divers Learned Men think, that Snow so strongly Affects our Eye, not by a Borrow'd, but a Native Light; But I venture to give it as a Proof, that White Bodies reflect more Light than Others, because having once purposely plac'd a parcel of Snow in a Room carefully Darkned, that no Celestial Light might come to fall upon it; neither I, nor an ingenous Person, (Skill'd in Opticks) whom I desir'd for a Witness, could find, that it had any other Light than what it receiv'd. And however, 'tis usual among those that Travel in Dark Nights, that the Guides wear something of White to be Discern'd by, there being scarce any Night so Dark, but that in the Free Air there remains some Light, though Broken and Debilitated perhaps by a thousand Reflections from the Opacous Corpuscles that Swim in the Air, and lend it to one another before it comes to arrive at the Eye.

7. Thirdly, And the better to shew that White Bodies reflect store of Light, in comparson of those that are otherwise Colour'd, I did in the Darkn'd Room, formerly mention'd, hold not far from the Hole, at which the Light was admitted, a Sheet only of White Paper, from whence casting the Sun-beams upon a White Wall, whereunto it was Obverted, it manifestly appear'd both to Me, and to the Person I took for a Witness of the Experiment, that it Reflected a far greater Light, than any of the other Colours formerly mention'd, the Light so thrown upon one Wall notably Enlightning it, and by it a good part of the Room. And yet further to show you, that White Bodies Reflect the Beams From them, and not Towards themselves, Let me add, that Ordinary Burning-glasses, such as are wont to be employ'd to light Tobacco, will not in a great while Burn, or so much as Discolour a Sheet of White Paper. Insomuch that even when I was a Boy, and Lov'd to make Tryals with Burning-glasses, I could not but wonder at this Odd Phaenomenon, which set me very Early upon Guessing at the Nature of Whiteness, especially because I took notice, that the Image of the Sun upon a White Paper was not so well Defin'd (the Light seeming too Diffus'd) as upon Black, and because I try'd, that Blacking over the Paper with Ink, not only the Ink would be quickly Dry'd up, but the Paper that I could not Burn before, would be quickly set on Fire. I have also try'd, that by exposing my Hand with a Thin Black Glove over it to the Warm Sun, it was thereby very quickly and considerably more Heated, than if I took off the Glove, and held my Hand Naked, or put on it another Glove of Thin but White Leather. And having thus shewn you, Pyrophilus, that White Bodies reflect the most Light of any, let us now proceed, to consider what is further to be taken notice of in them, in order to our present Enquiry.

8. And Fourthly, whereas among the Dispositions we attributed to White Bodies, we also intimated this, That such Bodies are apt, like Speculums, though but Imperfect ones, to Reflect the Light that falls on them Untroubled or Unstain'd, we shall besides other particulars to be met with in these Papers, offer you this in favour of the Conjecture; That in the Darkned Room several times mention'd in this Treatse, we try'd that the Sun-beams being cast from a Coloured Body upon a neighbouring White Wall, the Determinate Colour of the Body was from the Wall reflected to the Eye; whereas we could in divers cases manifestly Alter the Colour arriving at the Eye, by Substituting at a convenient Distance, a (conveniently) Colour'd (and Glossy) Body instead of the White Wall. As by throwing the Beams from a Yellow Body upon a Blew, there would be Exhibited a kind of Green, as in the Experiments about Colours is more fully Declar'd.

9. I know not whether I should on this Occasion take notice, that when, as when looking upon the Calm and Smooth Surface of a River betwixt my Eye and the Sun, it appear'd to be a natural Speculum, wherein that Part which Reflected to my Eye the Entire and defin'd Image of the Sun, and the Beams less remote from those which exhibited That Image, appear'd indeed of a great and Whitish Brightness, but the rest Comparatively Dark enough: if afterwards the Superficies chanc'd to be a little, but not much troubled, by a gentle Breath of Wind, and thereby reduc'd into a Multitude of Small and Smooth Speculums, the Surface of the River would suitably to the Doctrine lately deliver'd, at a Distance appear very much of Kin to White, though it would lose that Brightness or Whiteness upon the Return of the Surface to Calmness and an Uniform Level. And I have sometimes for Tryals sake brought in by a Lenticular Glass, the Image of a River, Shin'd upon by the Sun, into an Upper Room Darkn'd, and Distant about a Quarter of a Mile from the River, by which means the Numerous Declining Surfaces of the Water appear'd so Contracted, that upon the Body that receiv'd the Images, the whole River appear'd a very White Object at two or three paces distance. But if we drew Near it, this Whiteness appear'd to proceed from an Innumerable company of Lucid Reflections, from the several Gently wav'd Superficies of the Water, which look'd Near at hand like a Multitude of very Little, but Shining Scales of Fish, of which many did every moment Disappear, and as many were by the Sun, Wind and River generated anew. But though this Observation seem'd Sufficiently to discover, how the Appearing Whiteness in that case was Produc'd, yet in some other cases Water may have the Same, though not so Vivid a Colour upon other Accounts; for oftentimes it happens that the Smooth Surface of the Water does appear Bright or Whitish, by reason of the Reflection not immediatly of the Images of the Sun, but of the Brightness of the Sky; and in such cases a Convenient Wind may where it passes along make the Surface look Black, by causing many such Furrows and Cavities, as may make the Inflected Superficies of the Water reflect the Brightness of the Sky rather Inward than Outward. And again if the Wind increase into a Storm, the Water may appear White, especially near the Shore and the Ship, namely because the Rude Agitation Breaks it into Fome or Froth. So much do Whiteness and Blackness depend upon the Disposition of the Superficial parts of a Body to Reflect the Beams of Light Inward or Outward. But that as White Bodies reflect the most Light of any, so there Superficial Particles are, in the Sense newly Deliver'd, of a Specular Nature, I shall now further endeavour to shew both by the making of Specular bodies White, and the making of a White body Specular.

10. In the Fifth place then, I will inform You, that (not to repeat what Gassendus observes concerning Water) I have for Curiosity sake Distill'd Quicksilver in a Cucurbit, fitted with a Capacious Glass-head, and observ'd that when the Operation was perform'd by the Degrees of Fire requisite for my purpose, there would stick to the Inside of the Alembick a multitude of Little round drops of Mercury. And as you know that Mercury is a Specular Body, so each of these Little drops was a small round Looking-glass, and a Multitude of them lying Thick and Near one another, they did both in my Judgment, and that of those I Invited to see it, make the Glass they were fastened to, appear manifestly a White Body. And yet as I said, this Whiteness depended upon the Minuteness and Nearness of the Little Mercurial Globuli, the Convexity of whose Surfaces fitted them to represent in a Narrow compass a Multitude of Little Lucid Images to differingly situated Beholders. And here let me observe a thing that seems much to countenance the Notion I have been recommending: namely, that whereas divers parts of the Sky, and especially the Milky-way, do to the naked Eye appear White, (as the name it self imports) yet the Galaxie look'd upon through the Telescope, does not shew White, but appears to be made up of a Vast multitude of Little Starrs; so that a Multitude of Lucid Bodies, if they be so Small that they cannot Singly or apart be discern'd by the Eye, and if they be sufficiently Thick set by one another, may by their confus'd beams appear to the Eye One White Body. And why it is not possible, that the like may be done, when a Multitude of Bright and Little Corpuscles being crowded together, are made to send together Vivid beams to the Eye, though they Shine but as the Planets by a Borrow'd Light?

11. But to return to our Experiments. We may take notice, That the White of an Egg, though in part Transparent, yet by its power of Reflecting some Incident Rays of Light, is in some measure a Natural Speculum, being long agitated with a Whisk or Spoon, loses its Transparency, and becomes very White, by being turn'd into Froth, that is into an Aggregate of Numerous small Bubbles, whose Convex Superficies fits them to Reflect the Light every way Outwards. And 'tis worth Noting, that when Water, for instance, is Agitated into Froth, if the Bubbles be Great and Few, the Whiteness will be but Faint, because the number of Specula within a Narrow compass is but Small, and they are not Thick set enough to Reflect so Many Little Images or Beams of the Lucid Body, as are requisite to produce a Vigorous sensation of Whiteness: And partly least it should be said, that the Whiteness of such Globulous Particles proceeds from the Air Included in the Froth; (which to make good, it should be prov'd that the Air it self is White) and partly to illustrate the better the Notion we have propos'd of Whiteness, I shall add, that I purposely made this Experiment, I took a quantity Fair water, & put to it in a clear Glass phial, a convenient quantity of Oyl or Spirit of Turpentine, because that Liquor will not incorporate with Water, and yet is almost as Clear and Colourless as it; these being Gently Shaken together, the Agitation breaks the Oyl (which as I said, is Indispos'd to Mix like Wine or Milk per minima with the Water) into a Multitude of Little Globes, which each of them Reflecting Outwards a Lucid Image, make the Imperfect Mixture of the two Liquors appear Whitish; but if by Vehemently Shaking the Glass for a competent time you make a further Comminution of the Oyl into far more Numerous and Smaller Globuli, and thereby confound it also better with the Water, the Mixture will appear of a Much greater Whiteness, and almost like Milk; whereas if the Glass be a while let alone, the Colour will by degrees Impair, as the Oyly globes grow Fewer and Bigger, and at length will quite Vanish, leaving both the Liquors Distinct and Diaphanous as before. And such a Tryal hath not ill succeeded, when insteed of the Colourless Oyl of Turpentine I took a Yellow Mixture made of a good Proportion of Crude Turpentine dissolv'd in that Liquor; and (if I mis-remember not) it also Succeeded better than one would expect, when I employ'd an Oyl brought by Filings of Copper infused in it, to a deep Green. And this (by the way) may be the Reason, why often times when the Oyls of some Spices and of Anniseeds &c. are Distilled in a Limbec with Water, the Water (as I have several times observ'd) comes over Whitish, and will perhaps continue so for a good while, because if the Fire be made too Strong, the subtile Chymical Oyl is thereby much Agitated and Broken, and Blended with the Water in such Numerous and Minute Globules, as cannot easily in a short time Emerge to the Top of the Water, and whilst they Remain in it, make it, for the Reason newly intimated, look Whitish; and perhaps upon the same Ground a cause may be rendred, why Hot water is observ'd to be usually more Opacous and Whitish, than the same Water Cold, the Agitation turning the more Spirituous or otherwise Conveniently Dispos'd Particles of the Water into Vapours, thereby Producing in the Body of the Liquor a Multitude of Small Bubbles, which interrupt the Free passage, that the Beams of Light would else have Every way, and from the Innermost parts of the Water Reflect many of them Outwards. These and the like Examples, Pyrophilus, have induc'd me to Suspect, that the Superficial Particles of White bodies, may for the Most part be as well Convex as Smooth; I content my self to say Suspect and for the most part, because it seems not Easie to prove, that when Diaphanous bodies, as we shall see by and by, are reduc'd into White Powders, each Corpuscle must needs be of a Convex Superficies, since perhaps it may Suffice that Specular Surfaces look severally ways. For (as we have seen) when a Diaphanous Body comes to be reduc'd to very Minute parts, it thereby requires a Multitude of Little Surfaces within a Narrow compass. And though each of these should not be of a Figure Convenient to Reflect a Round Image of the Sun, yet even from such an Inconveniently Figur'd body, there may be Reflected some (either Streight or Crooked) Physical Line of Light, which Line I call Physical, because it has some Breadth in it, and in which Line in many cases some Refraction of the Light falling upon the Body it depends on, may contribute to the Brightness, as if a Slender Wire, or Solid Cylinder of Glass be expos'd to the Light, you shall see in some part of it a vivid Line of Light, and if we were able to draw out and lay together a Multitude of these Little Wires or Thrids of Glass, so Slender, that the Eye could not discern a Distance betwixt the Luminous Lines, there is little doubt (as far as I can guess by a Tryal purposely made with very Slender, but far less Slender Thrids of Glass, whose Aggregate was Look'd upon one way White) but the whole Physical Superficies compos'd of them, would to the Eye appear White, and if so, it will not be always necessary that the Figure of those Corpuscles, that make a Body appear White, should be Globulous. And as for Snow it self, though the Learned Gassendus (as we have seen above) makes it to seem nothing else but a pure Frozen Froth, consisting of exceedingly Minute and Thickset Bubbles; yet I see no necessity of Admitting that, since not only by the Variously and Curiously Figur'd Snow, that I have divers times had the Opportunity with Pleasure to observe, but also by the Common Snow, it rather doth appear both to the Naked Eye, and in a Microscope, often, if not most commonly, to consist principally of Little Slender Icicles of several Shapes, which afford such Numerous Lines of Light, as we have been newly Speaking of.

12. Sixthly, If you take a Diaphanous Body, as for instance a Piece of Glass, and reduce it to Powder, the same Body, which when it was Entire, freely Transmitted the Beams of Light, acquiring by Contusion a multitude of Minute Surfaces, each of which is as it were a Little, but Imperfect Speculum, is qualify'd to Reflect in a Confus'd manner, so many either Beams, or Little and Singly Unobservable Images of the Lucid Body, that from a Diaphanous it Degenerates into a White Body. And I remember, I have for Trials sake taken Lumps of Rock Crystal, and Heating them Red hot in a Crucible, I found according to my Expectation, that being Quench'd in Fair water, even those that remain'd in seemingly entire Lumps exchang'd their Translucency for Whiteness, the Ignition and Extinction having as it were Crack'd each Lump into a multitude of Minute Bodies, and thereby given it a great multitude of new Surfaces. And ev'n with Diaphanous Bodies, that are Colour'd, there may be this way a Greater Degree of Whiteness produced, than one would lightly think; as I remember, I have by Contusion obtain'd Whitish Powders of Granates, Glass of Antimony, and Emeralds finely Beaten, and you may more easily make the Experiment, by taking Good Venereal Vitriol of a Deep Blew, and comparing with some of the Entire Crystalls purposely reserv'd, some of the Subtile Powder of the same Salt, which will Comparatively exhibit a very considerable degree of Whitishness.

13. Seventhly, And as by a Change of Position in the Parts, a Body that is not White, may be made White, so by a Slight change of the Texture of its Surface, a White Body may be Depriv'd of its Whiteness. For if, (as I have try'd in Gold-smiths Shops) you take a piece of Silver that has been freshly Boyl'd, as the Artificers call it, (which is done by, first Brushing, and then Decocting it with Salt and Tartar, and perhaps some other Ingredients) you shall find it to be of a Lovely White. But if you take a piece of Smooth Steel, and therewith Burnish a part of it, which may be presently done, you shall find that Part will Lose its Whiteness, and turn a Speculum, looking almost every where Dark, as other Looking-glasses do, which may not a little confirm our Doctrine. For by this we may guess, what it is chiefly that made the Body White before, by considering that all that was done to deprive it of that Whiteness, was only to Depress the Little Protuberances that were before on the Surface of the Silver into one Continu'd Superficies, and thereby effect this, that now the Image of the Lucid Body, and consequently a Kind of Whiteness shall appear to your Eye, but in some place of the greater Silver Looking-glass (whence the Beams reflected at an Angle Equal to that wherewith they fall on it, may reach your Eye) whilst the Asperity remain'd Undestroy'd, the Light falling on innumerable Little Specula Obverted some one way, and some another, did from all Sensibly Distinguishable parts of the Superficies reflect confus'd Beams or Representations of Light to the Beholders Eye, from whence soever he chance to Look upon it. And among the Experiments annex'd to this Discourse, you will find One, wherein by the Change of Texture in Bodies, Whiteness is in a Trice both Generated and Destroy'd.

* * * * *

CHAP. II.

1. What we have Discours'd of Whiteness, may somewhat Assist us to form a Notion of Blackness, those two Qualities being Contrary enough to Illustrate each other. Yet among the Antient Philosophers I find less Assistance to form a Notion of Blackness than of Whiteness, only Democritus in the passage above Recited out of Aristotle has given a General Hint of the Cause of this Colour, by referring the Blackness of Bodies to their Asperity. But this I call but a General Hint, because those Bodies that are Green, and Purple, and Blew, seem to be so as well as Black ones, upon the Account of their Superficial Asperity. But among the Moderns, the formerly mention'd Gassendus, perhaps invited by this Hint of Democritus, has Incidentally in another Epistle given us, though a very Short, yet a somewhat Clearer account of the Nature of Blackness in these words: Existimare par est corpora suapte Natura nigra constare ex particulis, quarum Superficieculae scabrae sint, nec facile lucem extrorsum reflectant. I wish this Ingenious Man had enlarg'd himself upon this Subject; For indeed it seems, that as that which makes a Body White, is chiefly such a Disposition of its Parts, that it Reflects (I mean without much Interruption) more of the Light that falls on it, than Bodies of any other Colour do, so that which makes a Body Black is principally a Peculiar kind of Texture, chiefly of its Superficial Particle, whereby it does as it were Dead the Light that falls on it, so that very little is Reflected Outwards to the Eye.

2. And this Texture may be Explicated two, and perhaps more than two several ways, whereof the first is by Supposing in the Superficies of the Black Body a Particular kind of Asperity, whereby the Superficial Particles reflect but Few of the Incident Beams Outwards, and the rest Inwards towards the Body it self. As if for Instance, we should conceive the Surface of a Black Body to be Asperated by an almost Numberless throng of Little Cylinders, Pyramids, Cones, and other such Corpuscles, which by their being Thick Set and Erected, reflect the Beams of Light from one to another Inwards, and send them too and fro so often, that at length they are Lost before they can come to Rebound out again to the Eye. And this is the first of the two mention'd ways of Explicating Blackness. The other way is by Supposing the Texture of Black Bodies to be such, that either by their Yielding to the Beams of Light, or upon some other Account, they do as it were Dead the Beams of Light, and keep them from being Reflected in any Plenty, or with any Considerable Vigour of Motion, Outwards. According to this Notion it may be said, that the Corpuscles that make up the Beams of Light, whether they be Solary Effluviums, or Minute Particles of some AEtherial Substance, Thrusting on one another from the Lucid Body, do, falling on Black Bodies, meet with such a Texture, that such Bodies receive Into themselves, and Retain almost all the Motion communicated to them by the Corpuscles that make up the Beams of Light, and consequently Reflect but Few of them, or those but Languidly, towards the Eye, it happening here almost in like manner as to a ball, which thrown against a Stone or Floor, would Rebound a great way Upwards, but Rebounds very Little or not at all, when it is thrown against Water, or Mud, or a Loose Net, because the Parts yield, and receive into themselves the Motion, on whose Account the Ball should be Reflected Outwards. But this Last way of Explicating Blackness, I shall content my Self to have Propos'd, without either Adopting it, or absolutely Rejecting it. For the Hardness of Touchstones, Black Marble and other Bodies, that being Black are Solid, seem to make it somewhat Improbable, that such Bodies should be of so Yielding a Texture, unless we should say, that some Bodies may be more Dispos'd to Yield to the Impulses of the Corpuscles of Light by reason of a Peculiar Texture, than other Bodies, that in other Tryals appear to be Softer than they. But though the Former of these two Explications of Blackness be that, by which we shall Endeavour to give an Account of it, yet as we said, we shall not Absolutely Reject this Latter, partly because they both Agree in this, that Black Bodies Reflect but Little of the Light that falls on them, and partly because it is not Impossible, that in some Cases both the Disposition of the Superficial particles, as to Figure and Position, and the Yielding of the Body, or some of its Parts, may joyntly, though not in an Equal measure concurr to the rendring of a Body Black. The Considerations that induc'd me to propose this Notion of Blackness, as I Explan'd it, are principally these:

3. First, That as I lately said, Whiteness and Blackness being generally reputed to be Contrary Qualities, Whiteness depending as I said upon the Disposition of the Parts of a Body to Reflect much Light, it seems likely, that Blackness may depend upon a Contrary Disposition of the Black Bodies Surface; But upon this I shall not Insist.

4. Next then we see, that if a Body of One and the same Colour be plac'd, part in the Sun-beams, and part in the Shade, that part which is not Shin'd on will appear more of Kin to Blackness than the other, from which more Light Rebounds to the Eye; And Dark Colours seem the Blacker, the less Light they are Look'd upon in, and we think all Things Black in the Dark, when they send no Beams to make Impressions on our Organs of Sight, so that Shadows and Darkness are near of Kin, and Shaddow we know is but a Privation of Light; and accordingly Blackness seems to proceed from the Paucity of Beams Reflected from the Black Body to the Eye, I say the Paucity of Beams, because those Bodies that we call Black, as Marble, Jeat, &c. are Short of being perfectly so, else we should not See them at all. But though the Beams that fall on the Sides of those Erected Particles that we have been mentioning, do Few of them return Outwards, yet those that fall upon the Points of those Cylinders, Cones, or Pyramids, may thence Rebound to the Eye, though they make there but a Faint Impression, because they Arrive not there, but Mingl'd with a great Proportion of Little Shades. This may be Confirm'd by my having procur'd a Large piece of Black Marble well Polish'd, and brought to the Form of a Large Sphaerical and Concave Speculum; For on the Inside this Marble being well Polish'd, was a kind of Dark Looking-glass, wherein I could plainly see a Little Image of the Sun, when that Shin'd upon it. But this Image was very far from Offending and Dazling my Eyes, as it would have done from another Speculum; Nor, though the Speculum were Large, could I in a Long time, or in a Hot Sun set a piece of Wood on Fire, though a far less Speculum of the same Form, and of a more Reflecting Matter, would have made it Flame in a Trice.

5. And on this Occasion we may as well in Reference to something formerly deliver'd concerning Whiteness, as in Reference to what has been newly said, Subjoyn what we further observ'd touching the Differing Reflections of Light from White and Black Marble, namely, that having taking a pretty Large Mortar of White Marble, New and Polish'd in the Inside, and Expos'd it to the Sun, we found that it Reflected a great deal of Glaring Light, but so Dispers'd, that we could not make the Reflected Beams concurr in any such Conspicuous Focus, as that newly taken notice of in the Black Marble, though perhaps there may enough of them be made to meet near the Bottom, to make some Kind of Focus, especially since by holding in the Night-time a Candle at a convenient Distance, we were able to procure a Concourse of some, though not many of the Reflected Beams, at about two Inches distant from the Bottom of the Mortar: But we found the Heat even of the Sunbeams so Dispersedly Reflected to be very Languid, even in Comparison of the Black Marbles Focus. And the Little Picture of the Sun, that appear'd upon the White Marble as a Speculum, was but very Faint and exceeding ill Defin'd. Secondly, That taking two pieces of Plain and Polish'd Surfaces, and casting on them Successively the Beams of the Same Candle, In such manner, as that the Neighbouring Superficies being Shaded by an Opacous and Perforated Body, the Incident Beams were permitted to pass but through a Round Hole of about Half an Inch Diameter, the Circle of Light that appear'd on the White Marble was in Comparison very Bright, but very ill Defin'd; whereas that on the Black Marble was far less Luminous, but much more precisely Defin'd.

6. Thirdly, When you Look upon a piece of Linnen that has Small Holes in it, those Holes appear very Black, and Men are often deceiv'd in taking Holes for Spots of Ink; And Painters to represent Holes, make use of Black, the Reason of which seems to be, that the Beams that fall on those Holes, fall into them So Deep, that none of them is Reflected back to the Eye. And in narrow Wells part of the Mouth seems Black, because the Incident Beams are Reflected Downwards from one side to another, till they can no more Rebound to the Eye.

We may consider too, that if Differing parts of the same piece of Black Velvet be stroak'd Opposite ways, the piece of Velvet will appear of two Distinct kinds of Blackness, the one far Darker than the other, of which Disparity the Reason Seems to be, that in the Less obscure part of the Velvet, the Little Silken Piles whereof 'tis made up, being Inclin'd, there is a Greater part of each of them Obverted to the Eye, whereas in the other part the Piles of Silk being more Erected, there are far Fewer Beams Reflected Outwards from the Lateral parts of each Pile, So that most of those that Rebound to the Eye, come from the Tops of the Piles, which make but a small part of the whole Superficies, that may be cover'd by the piece of Velvet. Which Explication I propose, not that I think the Blackness of the Velvet proceeds from the Cause assign'd, since each Single Pile of Silk is Black by reason of its Texture, in what Position soever you Look upon it; But that the Greater Blackness of one of these Tuffts seems to proceed from the Greater Paucity of Beams Reflected from it, and that from the Fewness of those Parts of a Surface that Reflect Beams, and the Multitude of those Shaded Parts that Reflect none. And I remember, that I have oftentimes observ'd, that the Position of Particular Bodies far greater than Piles of Silk in reference to the Eye, may notwithstanding their having each of them a Colour of its own, make one part of their Aggregate appear far Darker than the other; For I have near Great Towns often taken notice, that a Cart-load of Carrots pack'd up, appear'd of a much Darker Colour when Look'd upon, where the Points of the Carrots were Obverted to the Eye, than where the Sides of them were so.

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