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 ſuâpte Naturâ nigra constare ex particulis, quarum Superficieculæ ſcabræ ſint, nec facilè 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 Ætherial 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 Sphærical 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.
7. Fourthly, In a Darkned Room, I purpoſely obſerv'd, that if the Sun-beams, which came in at the Hole were receiv'd upon White or any other Colour, and directed to a Convenient place of the Room,
they would Manifeſtly, though not all Equally, Encreaſe the Light of that Part; whereas if we Subſtituted, either a piece of Black Cloth or Black Velvet, it would ſo Dead the Incident Beams, that the place (newly mention'd) whereto I Obverted the Black Body, would be Leſs Enlightned than it was before, when it received its Light but from the Weak and Oblique Reflections of the Floor and Walls of a pretty Large Room, through which the Beams that came in at the Hole were Confuſedly and Brokenly Diſpers'd.
8. Fifthly, And to ſhew that the Beams that fall on Black Bodies, as they do not Rebound Outwards to the Eye, ſo they are Reflected towards the Body it ſelf, as the Nature of thoſe Erected Particles to which we have imputed Blackneſs, requires, we will add an Experiment that will alſo confirm our Doctrine touching Whiteneſs; Namely, that we took a Broad and Large Tile, and having Whitened over one half of the Superficies of it, and Black'd the other, we expos'd it to the Summer Sun; And having let it lye there a convenient time (for the Difference is more Apparent, if it have not lain there too long) we found, as we expected, that whilſt the Whited part of the Tile remained Cool enough, the
Black'd part of the ſame Tile was grown not only Senſible, but very Hot, (ſometimes to a ſtrong Degree.) And to ſatisfie ſome of our Friends the more, we have ſometimes left upon the Surface of the Tile, beſides the White and Black parts thereof, a part that Retain'd the native Red of the Tile it ſelf, and Expoſing them to the Sun, we obſerv'd this Laſt mention'd to have Contracted a Heat in compariſon of the White, but a Heat Inferiour to that of the Black, of which the Reaſon ſeems to be, that the Superficial Particles of Black Bodies, being, as we ſaid, more Erected, than thoſe of White or Red ones, the Corpuſcles of Light falling on their ſides, being for the moſt part Reflected Inwards from one Particle to another, and thereby engag'd as it were and kept from Rebounding Upwards, they communicate their brisk Motion, wherewith they were impell'd againſt the Black Body, (upon whoſe account had they fallen upon a White Body, they would have been Reflected Outwards) to the Small parts of the Black Body, and thereby Produce in thoſe Small parts ſuch an Agitation, as (when we feel it) we are wont to call Heat. I have been lately inform'd, that an Obſervation near of Kin to Ours, has been made by ſome Learned Men in France and
Italy, by long Expoſing to a very Hot Sun, two pieces of Marble, the one White, the other Black; But though the Obſervation be worthy of them, and may confirm the ſame Truth with Our Experiment, yet beſides that our Tryal needs not the Summer, nor any Great Heat to ſucceed, It ſeems to have this Advantage above the other, that whereas Bodies more Solid, and of a Cloſer Texture, though they uſe to be more Slowly Heated, are wont to receive a Greater Degree of Heat from the Sun or Fire, than (Cæteris paribus) Bodies of a Slightest Texture; I have found by the Information of Stone-cutters, and by other ways of Enquiry, that Black Marble is much Solider and Harder than White, ſo that poſſibly the Difference betwixt the Degrees of Heat they receive from the Sunbeams will by many be aſcrib'd to the Difference of their Texture, rather than to that of their Colour, though I think our Experiment will make it Probable enough that the greater part of that Difference may well be aſcrib'd to that Diſpoſition of Parts, which makes the one Reflect the Sunbeams Inward; and the other Outwards. And with this Doctrine accords very well, that Rooms hung with Black, are not only Darker than elſe they would be, but are
wont to be Warmer too; Inſomuch that I have known a great Lady, whoſe Conſtitution was ſomewhat Tender, complain that ſhe was wont to catch Cold, when ſhe went out into the Air, after having made any long Viſits to Perſons, whoſe Rooms were hung with Black. And this is not the only Lady I have heard complain of the Warmth of ſuch Rooms, which though perhaps it may be partly imputed to the Effluvia of thoſe Materials wherewith the hangings were Dy'd, yet probably the Warmth of ſuch Rooms depends chiefly upon the ſame Cauſe that the Darkneſs does; As (not to repeat what I formerly Noted touching my Gloves,) to ſatisfie ſome Curious Perſons of that Sex, I have convinc'd them, by Tryall, that of two Pieces of Silken Stuff given me by themſelves, and expos'd in their Preſence, to the ſame Window, Shin'd on by that Sun, the White was conſiderably Heated, when the Black was not ſo much as Senſibly ſo.
9. Sixthly, I remember, that Acquainting one Day a Virtuoſo of Unſuſpected Credit, that had Viſited Hot Countries, with part of what I have here Deliver'd concerning Blackneſs, he Related to me by way of Confirmation of it, a very notable
Experiment, which he had both others make, and Made himſelf in a Warm Climate, namely, that having carefully Black'd over Eggs, and Expos'd them to the Hot Sun, they were thereby in no very Long time well Roaſted, to which Effect I conceive the Heat of the Climate muſt have Concurr'd with the Diſpoſition of the Black Surface to Reflect the Sunbeams Inward, for I remember, that having made that among other Tryals in England, though in Summer-time, the Eggs I Expos'd, acquir'd indeed a conſiderable Degree of Heat, but yet not ſo Intenſe a One, as prov'd Sufficient to Roaſt them.
10. Seventhly, and Laſtly, Our Conjectures at the Nature of Blackneſs may be ſomewhat Confirm'd by the (formerly mention'd) Obſervation of the Blind Dutch-man, that Diſcerns Colours with his Fingers; for he Says, that he Feels a greater Roughneſs upon the Surfaces of Black Bodies, than upon thoſe of Red, or Yellow, or Green. And I remember, that the Diligent Bartholinus ſays,[a]9] that a Blind Earl of Mansfield could Diſtinguiſh White from Black only by the Touch, which would Sufficiently Argue a great Diſparity in the Aſperities, or other
Superficial Textures of Bodies of thoſe two Colours, if the Learn'd Relator had Affirm'd the Matter upon his own Knowledge.
II. Theſe, Pyrophilus, are the chief things that Occurr to me at preſent, about the Nature of Whiteneſs and Blackneſs, which it they have Rendred it ſo much as Probable, that in Moſt; or at leaſt Many Caſes, the Cauſes of theſe Qualities may be ſuch as I have Adventur'd to Deliver, it is as much as I Pretend to; for till I have Opportunity to Examine the Matter by ſome further Tryals, I am not ſure, but that in ſome White and Black Bodies, there may Concurr to the Colour ſome peculiar Texture or Diſpoſition of the Body, whereby the Motion of the Small Corpuſcles that make up the Incident Beams of Light, may be Differingly Modify'd, before they reach the Eye, eſpecially in this, that White Bodies do not only Copiouſly Reflect thoſe Incident Corpuſcles Outwards, but Reflect them Briskly, and do not otherwiſe Alter them in the manner of their Motion. Nor ſhall I now ſtay to Enquire, whether ſome of thoſe other ways, (as a Diſpoſition to Alter the Velocity, the Rotation, or the Order and Manner of Appulſe ſo the Eye of the Reflected Corpuſcles
that Compos'd the Incident Beams of Light) which we mention'd when we conſider'd the Production of Colours in General, may not in ſome Caſes be Applicable to thoſe of White and Black Bodies: For I am yet ſo much a Seeker in this Matter, and ſo little Wedded to the Opinions I have propos'd, that what I am to add ſhall be but the Beginning of a Collection of Experiments and Obſervation towards the Hiſtory of Whiteneſs and Blackneſs, without at preſent interpoſing my Explications of them, that ſo, I may aſſiſt your Enquires without much Fore-ſtalling or Biaſſing your Judgment.
