Froth) does then exhibit a very manifeſt White Colour,[a]3] (to which theſe laſt nam'd Conditions of the Bubbles do as well as their Convex figure contribute) and that for Reaſons to be mention'd anon. Beſides, it is not neceſſary that the Superficial particles that exhibit one Colour, ſhould be all of them Round, or all Conical, or all of any one Shape, but Corpuſcles of differing Figures may be mingled on the Surface of the Opacous Body, as when the Corpuſcles that make a Blew colour, and thoſe that make a Yellow, come to be Accurately and Skilfully mix'd, they make up a Green, which though it ſeem one ſimple Colour, yet in this caſe appears to be made by Corpuſcles of very differing Kinds, duely commix'd. Moreover the Figure and Bigneſs of the little Depreſſions, Cavities, Furrows or Pores intercepted betwixt theſe protuberant Corpuſcles, are as well to be conſider'd as the Sizes and Shapes of the Corpuſcles themſelves: For we may conceive the Phyſical ſuperficies of a Body, where (as we ſaid) its Colour does as it were reſide, to be cut Tranſverſly by a Mathematical plain, which you know is conceiv'd to be without any Depth or Thickneſs at all, and then as
ſome parts of the Phyſical Superficies will be Protuberant; or ſwell above this laſt plain, ſo others may be depreſs'd beneath it; as (to explane my ſelf by a groſs Compariſon) in divers places of the Surface of the Earth, there are not only Neighbouring Hills, Trees, &c. that are rais'd above the Horizontal Level of the Valley, but Rivers, Wells, Pits and other Cavities that are depreſs'd beneath it, and that ſuch Protuberant and Concave parts of a Surface may remit the Light ſo differingly, as much to vary a Colour, ſome examples and other things, that we ſhall hereafter have occaſion to take notice off in this Tract, will ſufficiently declare, till when, it may ſuffice to put you in mind, that of two Flat-ſides of the ſame piece of, for example, red Marble, the one being diligently Poliſhed, and the other left to its former Roughneſs, the differing degrees or ſorts of Aſperity, for the ſide that is ſmooth to the Touch wants not its Roughneſs, will ſo diverſifie the Light reflected from the ſeveral Plains to the Eye, that a Painter would employ two differing Colours to repreſent them.
7. And I hope, Pyrophilus, you will not think it ſtrange or impertinent, that I employ in divers paſſages of theſe Papers,
examples drawn from Bodies and Shadows far more Groſs, than thoſe minute Protuberances and ſhady Pores on which in moſt caſes the Colour of a Body as 'tis an Inherent Quality or Diſpoſition of its Surface, ſeems to depend. For ſometimes I employ ſuch Examples, rather to declare my Meaning, than prove my Conjecture; things, whom their Smallneſs makes Inſenſible, being better repreſented to the Imagination by ſuch familiar Objects, as being like them enough in other reſpects, are of a Viſible bulk. And next, though the Beams of Light are ſuch ſubtil Bodies, that in reſpect of them, even Surfaces that are ſenſibly Smooth, are not exactly ſo, but have their own degree of Roughneſs, conſiſting of little Protuberances and Depreſſions; and though conſequently ſuch Inequalities may ſuffice to give Bodies differing Colours, as we ſee in Marble that appears White or Black, or Red or Blew, even when the moſt carefully Poliſh'd, yet 'tis plain by the late Inſtance of Red Marble, and many others, that even bigger Protuberances and greater Shades may likewiſe ſo Diverſifie the Roughneſs of a Bodies Superficies, as manifeſtly to concurr to the varying of its Colour, whereby ſuch Examples appear to be proper enough
to be employ'd in ſuch a Subject as we have now in hand. And having hinted thus much on this Occaſion, I now proceed.
8. The Situation alſo of the Superficial particles is conſiderable, which I diſtinguiſh into the Poſture of the ſingle Corpuſcles, in reſpect of the Light, and of the Eye, and the Order of them in reference alſo to one another; for a Body may otherwiſe reflect the Light, when its Superficial particles are more erected upon the Plain that may be conceiv'd to paſs along their Baſis, and when the Points or Extremes of ſuch Particles are Obverted to the Eye, than when thoſe Particles are ſo Inclin'd, that their Sides are in great part Diſcernable, as the Colour of Pluſh or Velvet will appear Vary'd to you, if you carefully ſtroak part of it one way, and part of it another, the poſture of the particular Thrids, in reference to the Light, or the Eye, becoming thereby different. And you may obſerve in a Field of ripe Corn blown upon by the Wind, that there will appear as it were Waves of a Colour (at leaſt Gradually) differing from that of the reſt of the Field, the Wind by Depreſſing ſome of the Ears, and not at the ſame time others, making the one Reflect more from
the Lateral and Strawy parts, than do the reſt. And ſo, when Doggs are ſo angry, as to Erect the Hairs upon their Necks, and upon ſome other parts of their Bodies, thoſe Parts ſeem to acquire a Colour vary'd from that which the ſame Hairs made, when in their uſual Poſture they did farr more ſtoop. And that the Order wherein the Superficial Corpuſcles are Rang'd is not to be neglected, we may gueſs by turning of Water into Froth, the beating of Glaſs, and the ſcraping of Horns, in which caſes the Corpuſcles that were before ſo marſhall'd as to be Perſpicuous, do by the troubling of that Order become Diſpos'd to terminate and reflect more Light, and thereby to appear Whitiſh. And there are other ways in which the Order of the Protuberant parts, in reference to the Eye, may much contribute to the appearing of a particular Colour, for I have often obſerv'd, that when Peaſe are Planted, or Set in Parallel Lines, and are Shot up about half a Foot above the Surface of the Ground, by looking on the Field or Plot of Ground from that part towards which the Parallel Lines tended, the greater part of the Ground by farr would appear of its own dirty Colour, but if I look'd upon it Tranſverſly, the Plot
would appear very Green, the upper parts of the Peaſe hindering the intercepted parts of the Ground, which as I ſaid retain'd their wonted Colour, from being diſcover'd by the Eye. And I know not, Pyrophilus, whether I might not add, that even the Motion of the Small Parts of a Viſible Object may in ſome caſes contribute, though it be not ſo eaſie to ſay how, to the Producing or the Varying of a Colour; for I have ſeveral times made a Liquor, which when it has well ſettled in a cloſe Vial, is Tranſparent and Colourleſs, but as ſoon as the Glaſs is unſtopp'd, begins to fly away very plentifully in a White and Opacous fume; and there are other Bodies, whoſe Fumes, when they fill a Receiver, would make one ſuſpect it contains Milk, and yet when theſe Fumes ſettle into a Liquor, that Liquor is not White, but Tranſparent; And ſuch White Fumes I have ſeen afforded by unſtopping a Liquor I know, which yet is it ſelf Diaphanous and Red; Nor are theſe the only Inſtances of this Kind, that our Tryals can ſupply us with. And if the Superficial Corpuſcles be of the Groſſer ſort, and be ſo Framed, that their differing Sides or Faces may exhibit differing Colours, then the Motion or Reſt of thoſe Corpuſcles may be
conſiderable, as to the Colour of the Superficies they compoſe, upon this account, that ſometimes more, ſometimes fewer of the Sides diſpos'd to exhibit ſuch a Colour may by this means become or continue more Obverted to the Eye than the reſt, and compoſe a Phyſical Surface, that will be more or leſs ſenſibly interrupted; As, to explane my meaning, by propoſing a groſs Example, I remember, that in ſome ſorts of Leavy Plants thick ſet by one another, the two ſides of whoſe Leaves were of ſomewhat differing Colours, there would be a notable Diſparity as to Colour, if you look'd upon them both when the Leaves being at Reſt had their upper and commonly expos'd ſides Obverted to the Eye, and when a breath of Wind paſſing thorow them, made great Numbers of the uſually Hidden ſides of the Leaves become conſpicuous. And though the Little Bodies, we were lately ſpeaking of, may Singly and Apart ſeem almoſt Colourleſs, yet when Many of them are plac'd by one another, ſo near, that the Eye does not eaſily diſcern an Interruption, within a ſenſible ſpace, they may exhibit a Colour; as we ſee, that though a Slendereſt Thrid of Dy'd Silk do's, whilſt look'd on Single, ſeem almoſt quite Devoyd of Redneſs, (for inſtance)
yet when numbers of theſe Thrids are brought together into one Skein, their Colour becomes notorious.