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.