10. I confeſs, Pyrophilus, that a great part of what I have deliver'd, (or propos'd rather) concerning the differing forms of Aſperity in Bodies, by which Differences the incident Light either comes to be Reflected with more or leſs of Shade, and with that Shade more or leſs Interrupted, or elſe happens to be alſo otherwiſe Modify'd or Troubl'd, is but Conjectural. But I am not ſure, that if it were not for the Dullneſs of our Senſes, either theſe or ſome other Notions of Kin to them, might be better Countenanc'd; for I am apt to ſuſpect, that if we were Sharp ſighted enough, or had ſuch perfect Microſcopes, as I fear are more to be wiſh'd than hop'd for, our promoted Senſe might diſcern in the Phyſical Surfaces of Bodies, both a great many latent Ruggidneſſes, and the particular Sizes, Shapes, and Situations of the extremely little Bodies that cauſe them, and perhaps might perceive among other Varieties that we now can but imagine, how thoſe little Protuberances and Cavities do Interrupt and Dilate the Light, by mingling with it a multitude of little and ſingly undiſcernable Shades, though ſome of them more, and ſome of them leſs Minute, ſome leſs, and ſome more Numerous; according to the Nature and Degree of the particular Colour we attribute to the Viſible Object; as we ſee, that in the Moon we can with Excellent Teleſcopes diſcern many Hills and Vallies, and as it were Pits and other Parts, whereof ſome are more, and ſome leſs Vividly illuſtrated, and others have a fainter, others a deeper Shade, though the naked Eye can diſcern no ſuch matter in that Planet. And with an Excellent Microſcope, where the Naked Eye did ſee but a Green powder, the Aſſisted Eye as we noted above, could diſcern particular Granules, ſome of them of a Blew, and ſome of them of a Yellow colour, which Corpuſcles we had beforehand caus'd to be exquiſitly mix'd to compound the Green.
11. And, Pyrophilus, that you may not think me altogether extravagant in what I have ſaid of the Poſſibility, (for I ſpeak of no more) of diſcerning the differing forms of Aſperity in the Surfaces of Bodies of ſeveral Colours, I'l here ſet down a Memorable particular that chanc'd to come to my Knowledge, ſince I writ a good part of this Eſſay; and it is this. Meeting caſually the other Day with the deſervedly Famous4 Dr. J. Finch, Extraordinary Anatomiſt to that Great Patron of the Virtuoſi, the now Great Duke of Toſcany, and enquiring of this Ingenious Perſon, what might be the chief Rarity he had ſeen in his late return out of Italy into England, he told me, it was a Man at Maeſtricht in the Low-Countrys, who at certain times can diſcern and diſtinguiſh Colours by the Touch with his Fingers. You'l eaſily Conclude, that this is farr more ſtrange, than what I propos'd but as not Impoſſible; ſince the Senſe of the Retina ſeeming to be much more Tender and quick than that of thoſe Groſſer Filaments, Nerves or Membranes of our Fingers, wherewith we uſe to handle Groſs and Hard Bodies, it ſeems ſcarce credible, that any Accuſtomance, or Diet, or peculiarity of Conſtitution, ſhould enable a Man to diſtinguiſh with ſuch Groſs and Unſuitable Organs, ſuch Nice and Subtile Differences as thoſe of the forms of Aſperity, that belong to differing Colours, to receive whoſe Languid and Delicate Impreſſions by the Intervention of Light, Nature ſeems to have appointed and contexed into the Retina the tender and delicate Pith of the Optick Nerve. Wherefore I confeſs, I propos'd divers Scruples, and particularly whether the Doctor had taken care to bind a Napkin or Hankerchief over his Eyes ſo carefully, as to be ſure he could make no uſe of his Sight, though he had but Counterfeited the want of it, to which I added divers other Queſtions, to ſatisfie my Self, whether there were any Likelihood of Colluſion or other Tricks. But I found that the Judicious Doctor having gone farr out of his way, purpoſely to ſatisfie Himſelf and his Learned Prince about this Wonder, had been very Watchfull and Circumſpect to keep Himſelf from being Impos'd upon. And that he might not through any miſtake in point of Memory mis-inform Me, he did me the Favour at my Requeſt, to look out the Notes he had Written for his Own and his Princes Information, the ſumm of which Memorials, as far as we ſhall mention them here, was this, That the Doctor having been inform'd at Utrecht, that there Lived one at ſome Miles diſtance from Maestricht, who could diſtinguiſh Colours by the Touch, when he came to the laſt nam'd Town, he ſent a Meſſenger for him, and having Examin'd him, was told upon Enquiry theſe Particulars:
That the Man's name was John Vermaaſen, at that time about 33 Years of Age; that when he was but two years Old, he had the Small Pox, which rendred him abſolutely Blind: That at this preſent he is an Organiſt, and ſerves that Office in a publick Quire.
That the Doctor diſcourſing with him over Night, the Blind man affirm'd, that he could diſtinguiſh Colours by the Touch, but that he could not do it, unleſs he were Faſting; Any quantity of Drink taking from him that Exquiſitneſs of Touch, which is requiſite to ſo Nice a Senſation.
That hereupon the Doctor provided againſt the next Morning ſeven pieces of Ribbon, of theſe ſeven Colours, Black, White, Red, Blew, Green, Yellow, and Gray, but as for mingled Colours, this Vermaaſen would not undertake to diſcern them, though if offer'd, he would tell that they were Mix'd.
That to diſcern the Colour of the Ribbon, he places it betwixt the Thumb and the Fore-finger, but his moſt exquiſite perception was in his Thumb, and much better in the right Thumb than in the left.
That after the Blind man had four or five times told the Doctor the ſeveral Colours, (though Blinded with a Napkin for fear he might have ſome Sight) the Doctor found he was twice miſtaken, for he call'd the White Black, and the Red Blew, but ſtill, he, before his Errour, would lay them by in Pairs, ſaying, that though he could eaſily diſtinguiſh them from all others, yet thoſe two Pairs were not eaſily diſtinguiſh'd amongſt themſelves, whereupon the Doctor deſir'd to be told by him what kind of Diſcrimination he had of Colours by his Touch, to which he gave a reply, for whoſe ſake chiefly I inſert all this Narrative in this place, namely, That all the difference was more or leſs Aſperity, for ſays he, (I give you the Doctor's own words) Black feels as if you were feeling Needles points, or ſome harſh Sand, and Red feels very Smooth.
That the Doctor having deſir'd him to tell in Order the difference of Colours to his Touch, he did as follows;
Black and White are the moſt aſperous or unequal of all Colours, and ſo like, that 'tis very hard to diſtinguiſh them, but Black is the moſt Rough of the two, Green is next in Aſperity, Gray next to Green in Aſperity, Yellow is the fifth in degree of Aſperity, Red and Blew are ſo like, that they are as hard to diſtinguiſh as Black and White, but Red is ſomewhat more Aſperous than Blew, ſo that Red has the ſixth place, and Blew the ſeventh in Aſperity.
12. To theſe Informations the Obliging Doctor was pleas'd to add the welcome preſent of three of thoſe very pieces of Ribbon, whoſe Colours in his preſence the Blind man had diſtinguiſhed, pronouncing the one Gray, the other Red, and the third Green, which I keep by me as Rarities, and the rather, becauſe he fear'd the reſt were miſcarry'd.
13. Before I ſaw the Notes that afforded me the precedent Narrative, I confeſs I ſuſpected this man might have thus diſcriminated Colours, rather by the Smell than by the Touch; for ſome of the Ingredients imployed by Dyers to Colour things, have Sents, that are not ſo Languid, nor ſo near of Kin, but that I thought it not impoſſible that a very Critical Noſe might diſtinguiſh them, and this I the rather ſuſpected, becauſe he requir'd, that the Ribbons, whoſe Colours he was to Name, ſhould be offer'd him Faſting in the morning; for I have obſerv'd in Setting Doggs, that the feeding of them (especially with ſome ſorts of Aliments) does very much impair the exquiſite ſent of their Noſes. And though ſome of the foregoing particulars would have prevented that Conjecture, yet I confeſs to you (Pyrophilus) that I would gladly have had the Opportunity of Examining this Man my ſelf, and of Queſtioning him about divers particulars which I do not find to have been yet thought upon. And though it be not incredible to me, that ſince the Liquors that Dyers imploy to tinge, are qualifi'd to do ſo by multitudes of little Corpuſcles of the Pigment or Dying ſtuff, which are diſſolved and extracted by the Liquor, and ſwim to and fro in it, thoſe Corpuſcles of Colour (as the Atomiſts call them) inſinuating themſelves into, and filling all the Pores of the Body to be Dyed, may Aſperate its Superficies more or leſs according to the Bigneſs and Texture of the Corpuſcles of the Pigment; yet I can ſcarce believe, that our Blind man could diſtinguiſh all the Colours he did, meerly by the Ribbons having more or leſs of Aſperity, ſo that I cannot but think, notwithſtanding this Hiſtory, that the Blind man diſtinguiſh'd Colours not only by the Degrees of Aſperity in the Bodies offer'd to him, but by Forms of it, though this (latter) would perhaps have been very difficult for him to make an Intelligible mention of, becauſe thoſe Minute diſparities having not been taken notice of by men for want of touch as Exquiſite as our Blind Mans, are things he could not have Intelligibly expreſs'd, which will eaſily ſeem Probable, if you conſider, that under the name of Sharp, and Sweet, and Sour, there are abundance of, as it were, immediate peculiar Reliſhes or Taſts in differing ſorts of Wine, which though Critical and Experienc'd Palats can eaſily diſcern themſelves cannot make them be underſtood by others, ſuch Minute differences not having hitherto any Diſtinct names aſſign'd them. And it ſeems that there was ſomthing in the Forms of Aſperity that was requiſite to the Diſtinction of Colours, beſides the Degree of it, ſince he found it ſo difficult to diſtinguſh Black and White from one another, though not from other Colours. For I might urge, that he ſeems not conſonant to himſelf about the Red, which as you have ſeen in one place, he repreſents as ſomewhat more Aſperous than the Blew; and in another, very Smooth: But becauſe he ſpeaks of this Smoothneſs in that place, where he mentions the Roughneſs of Black, we may favourably preſume that he might mean but a comparative Smoothneſs; and therefore I ſhall not Inſiſt on this, but rather Countenance my Conjecture by this, that he found it ſo Difficult, not only, to Diſcriminate Red and Blew, (though the firſt of our promiſcuous Experiments will inform you, that the Red reflects by great Odds more Light than the other) but alſo to diſtinguiſh Black and White from one another, though not from other Colours. And indeed, though in the Ribbonds that were offer'd him, they might be almoſt equally Rough, yet in ſuch ſlender Corpuſcles as thoſe of Colour, there may eaſily enough be Conceiv'd, not only a greater Cloſeneſs of Parts, or elſe Paucity of Protuberant Corpuſcles, and the little extant Particles may be otherwiſe Figur'd, and Rang'd in the White than in the Black, but the Cavities may be much Deeper in the one than the other.
14. And perhaps, (Pyrophilus) it may prove ſome Illuſtration of what I mean, and help you to conceive how this may be, if I Repreſent, that where the Particles are ſo exceeding Slender, we may allow the Parts expos'd to the Sight and Touch to be a little Convex in compariſon of the Erected Particle of Black Bodies, as if there were Wyres I know not how many times Slenderer than a Hair: whether you ſuppoſe them to be Figur'd like Needles, or Cylindrically, like the Hairs of a Bruſh, with Hemiſphærical (or at leaſt Convex) Tops, they will be ſo very Slender, and conſequently the Points both of the one ſort and the other ſo very Sharp, that even an exquiſite Touch will be able to diſtinguiſh no greater Difference between them, than that which our Blind man allow'd, when comparing Black and White Bodies, he ſaid, that the latter was the leſs Rough of the two. Nor is every Kind of Roughneſs, though Senſible enough, Inconſiſtent with Whiteneſs, there being Caſes, wherein the Phyſical Superficies of a Body is made by the ſame Operation both Rough and white, as when the Level Surface of clear Water being by agitation Aſperated with a multitude of Unequal Bubbles, do's thereby acquire a Whiteneſs; and as a Smooth piece of Glaſs, by being Scratch'd with a Diamond, do's in the Aſperated part of its Surface diſcloſe the ſame Colour. But more (perchance) of this elſewhere.
15. And therefore, we ſhall here paſs by the Queſtion, whether any thing might be conſider'd about the Opacity of the Corpuſcles of Black Pigments, and the Comparative Diaphaneity of thoſe of many White Bodies, apply'd to our preſent Caſe; and proceed, to repreſent, That the newly mention'd Exiguity and Shape of the extant Particles being ſuppos'd, it will then be conſiderable what we lately but Hinted, (and therefore muſt now ſomewhat Explane) That the Depth of the little Cavities, intercepted between the extant Particles, without being ſo much greater in Black Bodies than in White ones, as to be perceptibly ſo to the Groſs Organs of Touch, may be very much greater in reference to their Diſpoſition of Reflecting the imaginary ſubtile Beams of Light. For in Black Bodies, thoſe Little intercepted Cavities, and other Depreſſions, may be ſo Figur'd, ſo Narrow and ſo Deep, that the incident Beams of Light, which the more extant Parts of the Phyſical Superficies are diſpos'd to Reflect inwards, may be Detain'd there, and prove unable to Emerge; whilſt in a White Body, the Slender Particles may not only by their Figure be fitted to Reflect the Light copiouſly outwards, but the intercepted Cavities being not Deep, nor perhaps very Narrow, the Bottoms of them may be ſo Conſtituted, as to be fit to Reflect outwards much of the Light that falls even upon Them; as you may poſſibly better apprehend, when we ſhall come to treat of Whiteneſs and Blackneſs. In the mean time it may ſuffice, that you take Notice with me, that the Blind mans Relations import no neceſſity of Concluding, that, though, becauſe, according to the Judgment of his Touch, Black was the Rougheſt, as it is the Darkeſt of Colours, therefore White, which (according to us) is the Lighteſt, ſhould be alſo the Smootheſt: ſince I obſerve, that he makes Yellow to be two Degrees more Aſperous than Blew, and as much leſs Aſperous than Green; whereas indeed, Yellow do's not only appear to the Eye a Lighter Colour than Blew, but (by our firſt Experiment hereafter to be mention'd) it will appear, that Yellow reflected much more Light than Blew, and manifeſtly more than Green, (which we need not much wonder at, ſince in this Colour and the two others (Blew and Yellow) 'tis not only the Reflected Light that is to be conſidered, ſince to produce both theſe, Refraction ſeems to Intervene, which by its Varieties may much alter the Caſe:) which both ſeems to ſtrengthen the Conjecture I was formerly propoſing, that there was ſomething elſe in the Kinds of Aſperity, as well as in the Degrees of it, which enabled our Blind man to Diſcriminate Colours, and do's at leaſt ſhow, that we cannot in all Caſes from the bare Difference in the Degrees of Aſperity betwixt Colours, ſafely conclude, that the Rougher of any two always Reflects the leaſt Light.
16. But this notwithſtanding, (Pyrophilus) and what ever Curioſity I may have had to move ſome Queſtions to our Sagacious Blind man, yet thus much I think you will admit us to have gain'd by his Teſtimony, that ſince many Colours may be felt with the Circumſtances above related, the Surfaces of ſuch Coloured Bodies muſt certainly have differing Degrees, and in all probability have differing Forms or Kinds of Aſperity belonging to them, which is all the Uſe that my preſent attempt obliges me to make of the Hiſtory above deliver'd, that being ſufficient to prove, that Colour do's much depend upon the Diſpoſition of the Superficial parts of Bodies, and to ſhew in general, wherein 'tis probable that ſuch a Diſpoſition do's (principally at leaſt) conſiſt.
17. But to return to what I was ſaying before I began to make mention of our Blind Organiſt, what we have deliver'd touching the cauſes of the ſeveral Forms or Aſperity that may Diverſifie the Surfaces of Colour'd Bodies, may perchance ſomewhat aſſiſt us to make ſome Conjectures in the general, at ſeveral of the ways whereby 'tis poſſible for the Experiments hereafter to be mention'd, to produce the ſuddain changes of Colours that are wont to be Conſequent upon them; for moſt of theſe Phænomena being produc'd by the Intervention of Liquors, and theſe for the moſt part abounding with very Minute, Active, and Variouſly Figur'd Saline Corpuſcles, Liquors ſo Qualify'd may well enough very Nimbly after the Texture of the Body they are imploy'd to Work upon, and ſo may change the form of Aſperity, and thereby make them Remit to the Eye the Light that falls on them, after another manner than they did before, and by that means Vary the Colour, ſo farr forth as it depends upon the Texture or Diſpoſition of the Seen Parts of the Object, which I ſay, Pyrophilus, that you may not think I would abſolutely exclude all other ways of Modifying the Beams of Light between their Parting from the Lucid Body, and their Reception into the common Senſory.
18. Now there ſeem to me divers ways, by which we may conceive that Liquors may Nimbly alter the Colour of one another, and of other Bodies, upon which they Act, but my preſent haſte will allow me to mention but ſome of them, without Inſiſting ſo much as upon thoſe I ſhall name.
19. And firſt, the Minute Corpuſcles that compoſe a Liquor may early inſinuate themſelves into thoſe Pores of Bodies, whereto their Size and Figure makes them Congruous, and theſe Pores they may either exactly Fill, or but Inadequately, and in this latter Caſe they will for the moſt part alter the Number and Figure, and always the Bigneſs of the former Pores. And in what capacity ſoever theſe Corpuſcles of a Liquor come to be Lodg'd or Harbour'd in the Pores that admit them, the Surface of the Body will for the moſt part have its Aſperity alter'd, and the Incident Light that meets with a Groſſer Liquor in the little Cavities that before contain'd nothing but Air, or ſome yet Subtiler Fluid, will have its Beams either Refracted, or Imbib'd, or elſe Reflected more or leſs Interruptedly, than they would be, if the Body had been Unmoiſtned, as we ſee, that even fair Water falling on white Paper, or Linnen, and divers other Bodies apt to ſoak it in, will for ſome ſuch Reaſons as thoſe newly mention'd, immediately alter the Colour of them, and for the moſt part make it Sadder than that of the Unwetted Parts of the ſame Bodies. And ſo you may ſee, that when in the Summer the High-ways are Dry and Duſty, if there falls ſtore of Rain, they will quickly appear of a much Darker Colour than they did before, and if a Drop of Oyl be let fall upon a Sheet of White Paper, that part of it, which by the Imbibition of the Liquor acquires a greater Continuity, and ſome Tranſparency, will appear much Darker than the reſt, many of the Incident Beams of Light being now Tranſmitted, that otherwiſe would be Reflected towards the Beholders Eyes.
20. Secondly, A Liquor may alter the Colour of a Body by freeing it from thoſe things that hindred it from appearing in its Genuine Colour; and though this may be ſaid to be rather a Reſtauration of a Body to its own Colour, or a Retection of its native Colour, than a Change, yet ſtill there Intervenes in it a change of the Colour which the Body appear'd to be of before this Operation. And ſuch a change a Liquor may work, either by Diſſolving, or Corroding, or by ſome ſuch way of carrying off that Matter, which either Veil'd or Diſguis'd the Colour that afterwards appears. Thus we reſtore Old pieces of Dirty Gold to a clean and nitid Yellow, by putting them into the Fire, and into Aqua-fortis, which take off the adventitious Filth that made that pure Metall look of a Dirty Colour. And there is alſo an eaſie way to reſtore Silver Coyns to their due Luſtre, by fetching off that which Diſcolour'd them. And I know a Chymical Liquor, which I employ'd to reſtore pieces of Cloath ſpotted with Greaſe to their proper Colour, by Imbibing the Spotted part with this Liquor, which Incorporating with the Greaſe, and yet being of a very Volatile Nature, does eaſily carry it away with it Self. And I have ſometimes try'd, that by Rubbing upon a good Touch-ſtone a certain Metalline mixture ſo Compounded, that the Impreſſion it left upon the Stone appear'd of a very differing Colour from that of Gold, yet a little of Aqua-fortis would in a Trice make the Golden Colour diſcloſe it ſelf, by Diſſolving the other Metalline Corpuſcles that conceal'd thoſe of the Gold, which you know that Menstruum will leave Untouch'd.
21. Thirdly, A Liquor may alter the Colour of a Body by making a Comminution of its Parts, and that principally two ways, the firſt by Diſjoyning and Diſſipating thoſe Cluſters of Particles, if I may ſo call them, which ſtuck more Looſely together, being faſtned only by ſome more eaſily Diſſoluble Ciment, which ſeems to be the Caſe of ſome of the following Experiments, where you'l find the Colour of many Corpuſcles brought to cohere by having been Precipitated together, Deſtroy'd by the Affuſion of very peircing and inciſive Liquors. The other of the two ways I was ſpeaking of, is, by Dividing the Groſſer and more Solid Particles into Minute ones, which will be always Leſſer, and for the moſt part otherwiſe Shap'd than the Entire Corpuſcle ſo Divided, as it will happen in a piece of Wood reduc'd into Splinters or Chips, or as when a piece of Chryſtal heated red Hot and quench'd in Cold water is crack'd into a multitude of little Fragments, which though they fall not aſunder, alter the Diſpoſition of the Body of the Chryſtal, as to its manner of Reflecting the Light, as we ſhall have Occaſion to ſhew hereafter.
22. There is a fourth way contrary to the third, whereby a Liquor may change the Colour of another Body, eſpecially of another Fluid, and that is, by procuring the Coalition of ſeveral Particles that before lay too Scatter'd and Diſpers'd to exhibit the Colour that afterwards appears. Thus ſometimes when I have had a Solution of Gold ſo Dilated, that I doubted whether the Liquor had really Imbib'd any true Gold or no, by pouring in a little Mercury, I have been quickly able to ſatisfie my Self, that the Liquor contain'd Gold, that Mettall after a little while Cloathing the Surface of the Quick-ſilver, with a Thin Film of its own Livery. And chiefly, though not only by this way of bringing the Minute parts of Bodies together in ſuch Numbers as to make them become Notorious to the Eye, many of theſe Colours ſeem to be Generated which are produc'd by Precipitations, eſpecially by ſuch as are wont to be made with fair Water, as when Reſinous Gumms diſſolv'd in Spirit of Wine, are let fall again, if the Spirit be Copiouſly diluted with that weakning Liquor. And ſo out of the Rectify'd and Tranſparent Butter of Antimony, by the bare Mixture of fair Water, there will be plentifully Precipitated that Milk-white Subſtance, which by having its Looſer Salts well waſh'd off, is turn'd into that Medicine, which Vulgar Chymiſts are pleas'd to call Mercurius Vitæ.
23. A fifth way, by which a Liquor may change the Colour of a Body, is, by Diſlocating the Parts, and putting them out of their former Order into another, and perhaps alſo altering the Poſture of the ſingle Corpuſcles as well as their Order or Situation in reſpect of one another. What certain Kinds of Commotion or Diſlocation of the Parts of a Body may do towards the Changing its Colour, is not only evident in the Mutations of Colour obſervable in Quick-ſilver, and ſome other Concretes long kept by Chymiſts in a Convenient Heat, though in cloſe Veſſels, but in the Obvious Degenerations of Colour, which every Body may take notice of in Bruis'd Cherries, and other Fruit, by comparing after a while the Colour of the Injur'd with that of the Sound part of the ſame Fruit. And that alſo ſuch Liquors, as we have been ſpeaking of, may greatly Diſcompoſe the Textures of many Bodies, and thereby alter the Diſpoſition of their Superficial parts, the great Commotion made in Metalls, and ſeveral other Bodies by Aqua-fortis, Oyl of Vitriol, and other Saline Menſtruums, may eaſily perſwade us, and what ſuch Vary'd Situations of Parts may do towards the Diverſifying of the manner of their Reflecting the Light, may be Gueſs'd in ſome Meaſure by the Beating of Tranſparent Glaſs into a White Powder, but farr better by the Experiments lately Pointed at, and hereafter Deliver'd, as the Producing and Deſtroying Colours by the means of ſubtil Saline Liquors, by whoſe Affuſion the Parts of other Liquors are manifeſtly both Agitated, and likewiſe Diſpos'd after another manner than they were before ſuch Affuſion. And in ſome Chymical Oyls, as particularly that of Lemmon Pills, by barely Shaking the Glaſs, that holds it, into Bubbles, that Tranſpoſition of the Parts which is conſequent to the Shaking, will ſhew you on the Surfaces of the Bubbles exceeding Orient and Lively Colours, which when the Bubbles relapſe into the reſt of the Oyl, do immediately Vaniſh.
24. I know not, Pyrophilus, whether I ſhould mention as a Diſtinct way, becauſe it is of a ſomewhat more General Nature, that Power, whereby a Liquor may alter the Colour of another Body, by putting the Parts of it into Motion; For though poſſibly the Motion ſo produc'd, does, as ſuch, ſeldome ſuddenly change the Colour of the Body whoſe Parts are Agitated, yet this ſeems to be one of the moſt General, however not Immediate cauſes of the Quick change of Colours in Bodies. For the Parts being put into Motion by the adventitious Liquor, divers of them that were before United, may become thereby Diſjoyn'd, and when that Motion ceaſes or decays others of them may ſtick together, and that in a new Order, by which means the Motion may ſometimes produce Permanent changes of Colours, as in the Experiment you will meet with hereafter, of preſently turning a Snowy White Body into a Yellow, by the bare Affuſion of fair Water, which probably ſo Diſſolves the Saline Corpuſcles that remain'd in the Calx, and ſets them at Liberty to Act upon one another, and the Metall, far more Powerfully than the Water without the Aſſiſtance of ſuch Saline Corpuſcles could do. And though you rubb Blew Vitriol, how Venereal and Unſophiſticated ſoever it be, upon the Whetted Blade of a Knife, it will not impart to the Iron its Latent Colour, but if you moiſten the Vitriol with your Spittle, or common Water, the Particles of the Liquor diſjoyning thoſe of the Vitriol, and thereby giving them the Various Agitation requiſite to Fluid Bodies, the Metalline Corpuſcles of the thus Diſſolv'd Vitriol will Lodge themſelves in Throngs in the Small and Congruous Pores of the Iron they are Rubb'd on, and ſo give the Surface of it the Genuine Colour of the Copper.
25. There remains yet a way, Pyrophilus to be mention'd, by which a Liquor may alter the Colour of another Body, and this ſeems the moſt Important of all, becauſe though it be nam'd but as One, yet it may indeed comprehend Many, and that is, by Aſſociating the Saline Corpuſcles, or any other Sort of the more Rigid ones of the Liquor, with the Particles of the Body that it is employ'd to Work upon. For theſe Adventitious Corpuſcles Aſſociating themſelves with the Protuberant Particles of the Surface of a Colour'd Body, muſt neceſſarily alter their Bigneſs, and will moſt commonly alter their Shape. And how much the Colours of Bodies depend upon the Bulk and Figure of their Superficial Particles, you may Gueſs by this, that eminent antient Philoſophers and divers Moderns, have thought that all Colours might in a general way be made out by theſe two; whoſe being Diverſify'd, will in our Caſe be attended with theſe two Circumſtances, the One, that the Protuberant Particles being Increas'd in Bulk, they will oftentimes be Vary'd as to the Cloſneſs or Laxity of their Order, fewer of them being contain'd within the ſame Senſible (though Minute) ſpace than before; or elſe by approaching to one another, they muſt Straighten the Pores, and it may be too, they will by their manner of Aſſociating themſelves with the Protuberant Particles, intercept new Pores. And this invites me to conſider farther, that the Adventitious Corpuſcles, I have been ſpeaking of, may likewiſe produce a great Change as well in the Little Cavities or Pores as in the Protuberances of a Colour'd Body; for beſides what we have juſt now taken notice of, they may by Lodging themſelves in thoſe little Cavities, fill them up, and it may well happen, that they may not only fill the Pores they Inſinuate themſelves into, but likewiſe have their Upper Parts extant above them; and partly by theſe new Protuberances, partly by Increaſing the Bulk of the former, theſe Extraneous Corpuſcles may much alter the Number and Bigneſs of the Surfaces Pores, changing the Old and Intercepting new ones. And then 'tis Odds, but the Order of the Little Extancies, and conſequently that of the Little Depreſſions in point of Situation will be alter'd likewiſe: as if you diſſolve Quick-ſilver in ſome kind of Aqua-fortis, the Saline Particles of the Menstruum Aſſociating themſelves with the Mercurial Corpuſcles, will make a Green Solution, which afterwards eaſily enough Degenerates. And Red Lead or Minium being Diſſolv'd in Spirit of Vinegar, yields not a Red, but a Clear Solution, the Redneſs of the Lead being by the Liquor Deſtroy'd. But a better Inſtance may be taken from Copper, for I have try'd, that if upon a Copper-plate you let ſome Drops of weak Aqua-fortis reſt for a while, the Corpuſcles of the Menſtruum, joyning with thoſe of the Metall, will produce a very ſenſible Aſperity upon the Surface of the Plate, and will Concoagulate that way into very minute Grains of a Pale Blew Vitriol; whereas if upon another part of the ſame Plate you ſuffer a little ſtrong Spirit of Urine to reſt a competent time, you ſhall find the Aſperated Surface adorn'd with a Deeper and Richer Blew. And the ſame Aqua-fortis, that will quickly change the Redneſs of Red Lead into a Darker Colour, will, being put upon Crude Lead, produce a Whitiſh Subſtance, as with Copper it did a Blewiſh. And as with Iron it will produce a Reddiſh, and on White Quills a Yellowiſh, ſo much may the Coalition of the Parts of the ſame Liquor, with the differingly Figur'd Particles of Stable Bodies, divers ways Aſperate the differingly Diſpos'd Surfaces, and to Diverſifie the Colour of thoſe Bodies. And you'l eaſily believe, that in many changes of Colour, that happen upon the Diſſolutions of Metalls, and Precipitations made with Oyl of Tartar, and the like Fix'd Salts, there may Intervene a Coalition of Saline Corpuſcles with the Particles of the Body Diſſolv'd or Precipitated, if you examine how much the Vitriol of a Metall may be Heavier than the Metalline part of it alone, upon the Score of the Saline parts Concoagulated therewith, and, that in Several Precipitations the weight of the Calx does for the ſame Reaſon much exceed that of the Metall, when it was firſt put in to be Diſſolv'd.
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.
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 Sphærical 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 Cæleſtes, 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 Scaliger5, Latet natura hæc, (ſays he, Speaking of that of Colour) & ſicut aliarum rerum ſpecies in profundiſſima caligine inſcitiæ humanæ.