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Show The Reafonis, that fome Rays are refracted more than others; and by that means exhibit feveral Images of the Sam, extended lengthwife, inftead of one. ‘amet 3. Thofe Rays which exhibit Yellow, are turned farther from the Reétilineal Courfe, than thofe which exhibit Red; thofe which exhibit Green, than thofe which exhibit Yellow: but of all others, thofe which exhibit the Violet, the moft. cordingly, aceCe A cee VA VA f if the Prifm through which the Light is tranfmitted be turn’d about its Axis, foasthe Red, Yellow, Green, &c. Rays be projected in order through a narrow Aperture, into anotherPrifm plac’d at the Diftance of about twelve Feet; the Yellow, Green, &c. Rays; tho’ falling through the fame Aperture in the fame Manner, and on the fame Point of the fecond Prifm, will not be refraéted to the fame Place as the Red, buttoa Point at fome Diftance from it, on that Side to which the VA 6. If the Rays of the Sun fall very obliquely on the inner Surface of a Prifm, ‘thofe’ that are reflected will be Violet, thofe tranfinitted Red. For the Rays were colour’d before any Sepa- ration; and by how muchthe more they are refrangible, by fo much they are the more eafily reflected, and by that Meansare feparated, 7. If two hollow Prifms, the onefill’d with a blue Fluid, and the other with a red one, be join’d together, they will be Opaque, tho’ each apart be tranfparent. Forthe one tranfmitting none but d/ve Rays, and the other none but red ones ; the two together will tranfmit none atall. 8. All natural Bodies, efpecially white ones, view’d through a Prifm held to the Eye, ap- pear fimbriated or bordered on one Side with Red and Yellow, and on the other Side with Blue and Violet. For thofe Fimbrie are the Extremes ofin- Rotation was made. This is what Sir [aac Newton calls Experi- tire Images, which the Rays ofany kind, as mentumCrucis, being that which led him out of nearer, or at a greater Diftance fromthe real the Difficulties into which the firft Phanomenon, &c. had brought him, andplainly fhew’d a different Degree of Refrangibility, and a different Colour correfponding thereto in the Rays of Light ; and that Yellow Rays, v. g. are more refracted than Red ones, and Blue and Fiolet mott of all. 4. The Colours of coloured Rays, well fepa- rated by the Prifm, are not at all changed or deftroy’d by paffing an illuminated Medium, nor by their mutual Decuffation, their bordering on a deep Shadow, nor being reflected from any natural Body, or reflected gh any one, in a Place how obfcure they are moreorlefs refraéted, would exhibit Place of the Object. g. If two Prifms be fo plac’d, as that the Red of the one, and the Purple of the other meet together, ina Paper fit for the Purpofe, incompafs’d with Darknefs, the Image will appear pale ; and if view’d through a third Prifm, held to the Eye at a proper Diftance, it will appear double, the one Red, the other Purple. In like manner, if two Powders, the one perfectly Red, the other Blue, be mix’d, any little Body cover’d pretty deeply with this Mixture, and view’d thro’ a Prifm held tothe Eye, will exhibit a double Image, the one Red, and the other Ble ; in regard that the but immutable Properties, and fuch as belong Red and Purple, or Blue Rays are feparated by their unequal Refraétion. 10. If the Rays tranfmitted thro’ a Convex- to the Natureof the Rays. Lens, cations arifing from Refraétion or Reflection, 5. An Affemblage of all Kinds of coloured Rays, colleéted either by feveral Prifms, bya Convex Lens, or a Concave Mirrour, orin any other Manner, from what we call Whitene/s ; yet each ofthefe, after Decuflation, becoming feparated, again exhibits its proper Colour: For as the Ray was white before its Parts were feparated, fo the Parts being mix’d, it becomes white again; and colour’d Rays, when be receiv’d on a Paper, before they meet in a Focus, the Confines or Boundary of Light and Shadow, will appear ting’d with a red Colour; but if they be receiv’d beyond the Focus, with a dive one. i Hence a red, green, yellow, blue and violet the Eye, the Extremes of Bodies, plac’d as i by the Interpofition of any opaque Body nea view’d through a Prifm, will appear ting d es from White and Black mix’d together, and would be plainly white, if fome Rays were not abforb’d and loft. In like manner, if a Paper cut into a Circle reft of the Pupil will be feparated by Ref 5 be mix’d together in the Eye by the Brifknefs of the Motion, the feveral Colours will difappear, and the whole Paper appear of one conunual Colour, which will be a Mean betwixt White and Black. denfer thanthe Mediumcontained in their In- 3 7. e, the Plates correfponding ber 1, 3, 5,7, €%c. will refleét the fame Rays that th correfponding to terftices; but that in the Tails of Peacocks, and. fome Silks, and generally in all Bodies, whofe Colour varies according to the Situation ofthe the even ones 2, 4, 6, 8, &c. tran{mit. Hence an Homogeneal Colour in a Plate, is faid to be of the firOrder, if the Plate reflect all the Rays of that Colour: Ina Plate whote Thinnefs i le the firft, itis faid to be of the /econd In another, whofe Thinnefs is five faid to be of the A Colourofthe fir 3 and fu vely the Vividnefs of the es: The more the Thicknef$ of the Plate Colour, being mix’d in a certain Proportion, appear whilifh, i. e. are of fuch a Colouras andin a certain Proportion, then fwiftly turn’d round its Center, fo as the Species of Colours ame Rayalternately reflected wr increaies as the Quantity of the Order either Side of the Pupilla, be not intercepted be ftained with eachof thofe Colours feparately, in the thin Lamelle or Plates of any pellucid tions within the Body, the Body in that Cafe Becaufe in the firft Cafe, the red Rays being they meet together, don’t deftroy one another, but areonly interfpers’d. with Colowrs, tho’ thofe are not very vivid. For then the Rays tran{fmitted throwgh double, and alfo tinged with Colour. Ofthe Corours of thin Plates.) As of different Colours are feparated by the Refra tion of Prifms, and other thick Bodies, iQO are they feparated, tho’ in a different manner, Eye, it is lefs; and that the Colour of the Body is lefs vivid to the Eye, as it has a denfer Medium within its Pores, Now, ofthe feveral Opaque Bodies, thofe which confift of the thinneft Lamelle are Black, thofe confifting either of the thickeft Lamelle, or of Lamelle very different from each other in Thicknef$, and on that account fitted to reflect all Cosours, as the Froth of Water, &c. are White. Thofe again, which confift of Lamell. moft of which are of fome intermediate Thick is increas’d, the more Colours it reflects, and thofe of more different Orders: In fome Plates nefs, are Blue, Green, Yellow or Red; inaf~ much as theyreflect the Rays of that parti- the Colour will vary as the Pofition of the Eye s.] Bodies only cular Colour much more copioufly than that of any other Colour ; moft of which laft they either abforb and extinguifh, by intercepting -s, astheir Surfacesare difpos'd to refleét Rays of this or that Colour alone, or of this or that Colour more abun- them, orelfe tranfmit. Hence it is, that fome Liquors, v. g. an Infufion of L mn Nepbriticum, appear Red ly than a into Colours, without being diluted wi , Admixture of the intercepted Rays, wAlch would be refracted in a different manne Andhenceit is, that a Body view’d th a Paper pierced with two Ho Wea Matter ; v. g. the Bubbles rais’d in Water becomes opaque. thickned by Soap, &c. : The Rays whichare not refle@ed from an For all Lamei/@ under a determined Thick- opaque Body, penetrate into it, and there fufnefs, in Arithmetical Proportion, begin to fering innumerable RefleCtions and Refractireflect firft Blue Rays; then in order Green, ons, at length unite themfelves to the Particles Yellow and Red, all pure; then again Biwe, of the Bodies themfelves, Green, Yellow, and Red, all pure; then Henceit is that an Opaque Body grows hot again Blue, Green, Yellow and Red, more the fooner, as it refleéts Light lef copioufly : and more mix’d anddiluted; till at length hence we fee, that a White Body, which re« arriving at a certain Thicknefs, they refleét flects almoft all the Rays that ftrike upon it, Rays ofall Colours perSétly intermix’d, viz. heats much more flowly than a Black one, bite. which reflects fearce any. But in whatfoever Part a flender Lamella In order to determine the Conftitution of reflects any one Colour, v. g. Blue, in that the Surface of Bodies wherein their Colour de= Part it always tranfinits the oppofite Colour, pends, it muft be obferved, That the fimalleft v.g. Red or Yell Corpufcles or Particles whereof Surfaces are It is found by Experiment, that the Diffe- made up, are moft thin and tran{parent, and rence of Colourof a Plate, does not depend on feparated by a Medium of a different Denfity the Medium that encompaffes it; but the from the Particles themfelves. Degree of Vividnefs does, ceteris paribus, the In the Surface then of every coloured Body Colour will be more vivid, if the denfér are innumerable fmaller thin Plates, an{wering Medium be incompafs’d with the rarer: A to thofe of Bubbles, Plate, ceteris paribus, refle&ts more Light, Hence it may be gathered, that the Co/our as itis thinner, as far as a certain Degree of of a Body depends upon the Denfity and Thinnefs, beyond which it refleéts no Light Thicknefs of the Parts of the Body between at all. the Pores of the Surface; that the Colour is In Plates whofe ThicknefS increafeé in an more vivid and homogeneous,as the Parts are ithmetical Proportion of the natural Num- thinner ; that, cateris paribus, the faid Parts 19,uh5 4 4, 5, ec. ifthe firft or thinneft are the thickeft when the Body is Red, and mogeneal Ray, the fecond will thinneft when Violet, e third again will refle@ it; That the Parts ofBodies are ufually much fomething more refracted, are the higher; but in the fecond, after Decuffation in the Focus, the blue ones. Laftly, if the Rays about to pafs through ee the other: hence Bodies appear orYellow, if view’d byreflected Light, and that arifes from the Mixture of Blue bytran ed Light; and Gold Leaves w it r Circumftances, but Green ies confift of very thin : ich, if they be fo To this m ided, that fome of the ‘as that happen no Reflectionsor Rarefractionsin Interftices, thofe Bodies become pellu r tran{fparent: but if their Intervals be fo 5 fe filled with ch Matte mpty (and with regard to the Denfity Powders ufed -ainters, have their Colours changed by be I ry finely gro ind 3 wh ch mutt be occafionc d by the Comminution or Breaking of their {mall Parts into othersftill fmaller ; juftasa Lay 7 has its Colour alter’d, byaltering its ‘I hic knefs, themielves) as that there hapNumber ofReflections and Refrac. In fine; Thofe odd Phznomena arifing from the Mixture of Liquors of — ir 8H VOLOUTS y |
