The works of the Honourable Robert Boyle, Esq., epitomiz'd by Richard Boulton ... ; illustrated with copper plates.

Containing Part the First.

THO there are some, especially Chymists, who think that a considerable Diversity of Colours,* 1.1 must always imploy a Di∣versity of Nature; yet we see, that Taffaties are endued with changable Colours, as well as the Feathers of several Birds, which have as great an Affinity in Nature as in Place; and not only several Feathers vary in Colour from one another, but sometimes several parts of the same Feather: And there is no less variety of Colour in several Leaves of Flowers, tho no difference can be discovered in their Pro∣perties: A considerable Instance in which, we have in Marvail of Peru, which tho it pro∣duces several Scores of Flowers in its Season, yet I have scarce found two coloured alike.

* 1.2But tho I believe that a variety of Colours does not always imply a Diversity of Proper∣ties, yet I question not, but that an altera∣tion, in point of Colour, signifies a Variation in the Disposition of Parts of Bodies; which is evident in the Extraction of Tinctures, and several other Chymical Operations, wherein the Change of Colours is the only Observation by which the Artist regulates his Process. So we see, that several Degrees of Maturation produces various Colours in Fruit; and Steel, if it be heated glowing hot in the fire, and held over a Basion of Water, till it changes its white to a red Colour, so far as is then quench'd will be hard'ned, and when polish'd at the end, will look whitish; but if the end of the Steel be held in a Candle, so that the polish'd part may not be sully'd, that which is almost contiguous to the Candle, would change from a bright Yellow to a deep one, or a sanguine Blew, and from that to a fainter, and then to a deeper Blew; and in each of these diffetent Appearances, its Texture is so much different, that if whilst it is yellow it be cooled, it is fit for Gravers Drills, but when blew, it is softer and fit for Springs of Watches; and if it be kept long in the flame after this blew appears, it will be too soft for Drills till hardned again. And it is not a little pleasant to see how these Colours will succeed one another and run along the Steel very fast. But because the flame of a Candle usually sullies the Steel, we generally make use of a red-hot Iron to heat it with.

But not to prosecute these Experiments out of their due Place, before I descend more Par∣ticularly

to present you with my Considera∣tions concerning Colours,* 1.3 I think it requisite to premise, That Colour being a Word of a twofold Signification, in the following Dis∣course, I shall sometimes use it to signifie on∣ly the Sensation of those reflected and modified Rays of Light, which cause that Effect on the Sensory; and generally, in the vulgar Accep∣tation, intimating by it, the Disposition in the Object which causes the Rays of Light to be reflected, so as to produce on the Sensory this or that Colour.

* 1.4And, perhaps, it may not be inconvenient to add, that it is the Opinion of several Modern Atomists, that the Sensation of Colours depends not so much on the inherent Qualities of the Object in the Sense, but that such a Motion is given to the Spirits in the Retina, that that communicated to the Brain, and causing a Lo∣cal Motion in some part of it, we always think we see such a colour, when the slender strings of the Retina are put into a like Motion, whe∣ther the Light concurs to the Production of that Motion or not; whence dreaming Men often think they see several things in their sleep; and distracted Persons fancy they see several things before them, which depends only upon an Internal Local Motion of their Spirits: And so upon a violent blow upon the Eye, we some∣times fancy we see Lightning and flashes of Fire; and even upon a blow on the Head, or when internal Humours cause such a Concussion in the extremities of the Optick Nerves, as is wont to produce a Sensation of Light. And I remember, that having my self a violent

Cough, I fancy'd I saw flashes of Light, which presently disappear'd again: and a very discreet Lady observ'd, that the day before she was seiz'd with some violent Hysterick and Hypo∣chondriacal Fits, which for the time gave her a bastard Palsey, every thing before her seem'd to be dyed with bright and vivid, but unusual colours: And I am told by an ingenious Gen∣tleman, that several that were seiz'd with the Plague, sometime before, fancy'd every thing coloured over very beautifully; and this Symp∣tom was successfully remov'd, as well as the other Symptoms of that Distemper by a Vomit The Vomit which was successfully given in this was made of about 8 or 10 Drachms of Cro∣cus Metallorum, and half a Drachm of white Vitriol.

But further, as the Apparition of a Colour may be caus'd by the Motion of the Humors within, so the Sensory being Indisposed, that Indisposition may vary the appearance of Ex∣ternal Objects: For I have taken notice, that after looking upon the Sun or Moon with a Telescope, my Eye hath been so alter'd, that the flame of a Candle seem'd to vary much in its colour from what it used to be, and if I often open'd and shut my Eye whilst that ad∣ventitious Colour seem'd to last, I could discern it gradually diminish, till the Candle appear'd to me as before; and one thing worthy of no∣tice was, that if I looked upon the Object with one Eye, when the dazled Eye was shut, the Adventitious Colour disappear'd, but was visible again, upon opening the dazled Eye.

To this Observation I shall add, that a Lady, who had by a Fall, got a Hurt near her Eye, for six Weeks together fancy'd every thing co∣ver'd over with very dazling and glorious Co∣lours, especially white Bodies, some of which were such as she could not describe. And a Learned Gentleman told me, that looking upon the Sun with a good Telescope, without a co∣lour'd Glass to guard his Sight, the Brightness of the Object left such an Indisposition in his Eye, that nine or ten Years after, whenever he look'd upon the Window, he fancy'd he saw a light Body before his Eye, of the Size and Brightness of the Sun, as it appear'd to him in the Telescope; to which Instances, I could add others from the Experien'd Epiphanius Ferdi∣nandus, of the Symptoms of those Bitten by a Tarantula; from whence it would appear, that an Indisposition in the Organ of Vision, is suf∣ficient to vary our Judgment of Colours, but these may be more properly deliver'd in ano∣ther place.

* 1.5But to proceed, from what hath been said it appears, I allow and teach, that the superficial Parts of a Body, reflecting the Rays of Light, and modifying them, may in one sense be said to be the Cause of that Colour it represents, since as the Beams of Light are variously modify'd, we perceive several Sensations.

And tho' some hold, that the Rays of Light which conveigh Colours, are not reflected bare∣ly from the Superficies of a Body, but penetrate deeper into it's Substance; yet we are apt to call those Bodies transparent or semidiaphonous, whose Substance the Rays of Light visibly insinu∣ate

themselves into: And that in all Bodies there is no such Penetration of Light is evident, since several Substances appear to be of one Colour on the outside, and of another within; which is evident not only in Fruit, but temper'd Steel; for tho' it be furnish'd with very vivid Colours on the Superficies, yet within a Hairs breadth of it, it retains it's Steel Colour: And a more Eminent Instance is, that Lead being melted and pour'd into an Iron Vessel, when the Scum was taken off, several Colours succeeded one an∣other, upon it's Superficies, and that which ap∣pear'd last, before the Metal cool'd, remaining upon the Superficies of it, we found, that if never so little was taken off, that adventitious Colour would be taken off too, and the Metal would appear in it's own Colour; which shews not only what I alledg'd it for; but also, that probably an adventitious Colour may be acquir'd by the Effects the saline Parts of the Air, have on Lead so dispos'd to receive it's Impressions, which it will not do, till brought to a much higher degree of Fusion than bare melting. One thing remarkable in these Colours was, that they succeed not so regularly as those in Steel, but in the following order,

Viz. Blew, Yellow, Purple, Blew; Green, Purple Blew, Yellow, Red; Purple, Blew, Yellow and Blew; Yellow, Blew, Purple, Green mixt, Yel∣low; Red, Blew, Green, Yellow, Red, Purple, Green.

Tho' it is held by antient Atomists, that the Figure of a Body is sufficient to vary it's Colour;

yet I am perswaded, that there are other things requisite; since we see by the help of good Te∣lescopes, that the Superficies of Bodies are not only full of several Protuberances, but like∣wise several Cavities, which appear not to the naked Eye; so that the very Figures of those may have a great stroke in causing various Colours, and differently forming the Superfi∣cies of a Body, so as to enable it variously to reflect the Rays of Light, and cause different Effects in our Organ of Sense.

* 1.6But besides the various Figures of these su∣perficial Particles, the Surface of a Body may be enabled variously to reflect the Rays of Light, as they are bigger or less; and the Protuberant Particles are set closer, or at a greater distance: So Water if it have but a few Bubbles on the Top of it, hath scarce any sensible Colour, but if it be beaten into a Froth, and a great number of Bubbles are close set, it presently varies it's Co∣lour, and seems white; to which not only the Number, but the Convex Superficies of the Bub∣bles conduce; nor is it requisite, that all the Pro∣tuberant Corpuscles should be of one Figure, since, those which produce a Blew, and those that yield a Yellow being mix'd together, afford a green Co∣lour. But further, the Cavities intercepted betwixt the Protuberant Parts and their Figures, are to be consider'd in the Production of Colours, as well as the Figure and Size of the Particles them∣selves: For the Superficies of a Body may be cut transversly with a Methamatical Plain, void of Depth or Thickness, above which as well as be∣low, may be several Superficies, as in the Super∣ficies of the Earth, there may be several Parts a∣bove

the Horizontal Plain as well as below; upon which Account, the Rays of Light may be so differently reflected, as to cause diffe∣rent Colours; so the two sides of a Piece of red Glass seem differently colour'd, when the one is Rough, and the other Polish'd; and tho' several sorts of Marbles are never so curiously Polish'd, yet their Superficies so far vary, as to exhibit distinct Colours.

* 1.7Besides, in variously reflecting the Rays of Light, the Situation of the superficial Parts of a Body are considerable, in reference to the Light and the Position of the Eye, and also their order in reference to each other; for the Rays of Light will be differently reflected to the Eye, from Parts which are erected upon a superficial Plain, from what it will be from those Parts inclined and obverted to the Eye; so Plush or Velvet va∣ries it's Colour as the Parts of it are different∣ly inclin'd; and a Field of Corn varies it's Co∣lour as the Wind depresses the Ears of Corn suc∣cessively, or in different places: And for a like Reason the Hair of a Dog exhibits a different Colour, when the order of them is changed; and so the Parts of Water in Froth, and the Parts of Harts-horn shaved, alter their Colours, and Glass by being beaten, loses it's Transpa∣rency with the order of it's Parts, and becomes white; And for a Reason not very different, I have observed, that Pease set in parallel Lines, when they are risen about half a quarter a∣bove the Ground, by casting one Eye the same way with the parallel Lines, the Ground would appear of it's own dirty Colour, but if I look'd upon it transversly, it would wholly appear

green, the Rays which were reflected from the Soil being intercepted.

* 1.8And that the motion of the Parts of a Li∣quor, may contribute to the change of a Colour, I am perswaded, since I have elsewhere men∣tion'd a Liquor, which, whilst it was at rest, would be clear and transparent, but when it's Parts were put into Motion, they would rise up and form a white Fume; and the like Fumes I have observ'd to rise from a Liquor diapha∣nous, and another red. And if the Superficies of a Body be made up of Parts, whose different sides afford several Colours, then the Motion or Rest of that Body may contribute to the variation or continuance of a Colour, since a new side being turn'd towards the Eye, we must consequently see a new Colour; so when the Leaves of a Tree, whose Colour on each side varies, are forced by the Wind, to appear with their other sides outward, they exhibit a new Colour, tho' a few of them makes no considerable Alteration; as a single Thred of Scarlet, seems almost void of Redness; but when several of them are pla∣ced together, their Colour becomes more con∣spicuous. So likewise in a Piece of Taffety which is made of red and blew Threds inter∣woven, I found by a Microscope, that when the Silk was so commodiously placed, that the blew Threds were not intercepted by the red ones, the Colour would be blew; but when the red Threds were more commodiously placed than the others, the Colour would vary: Where∣fore it would not be amiss to endeavour to dis∣cover a Reason, by the Use of Microscopes, why Mother of Pearl, Opals and such like Bo∣dies

are of such curious Colours, and what con∣texture of Parts is apt to produce Colours so delightful.

* 1.9But till we are furnish'd with better Micro∣scopes, or more exquisite Senses, I fear these things must be undiscover'd, since there are se∣veral degrees of Asperity, and the Parts which form them are so minute, that we are not able to know how their Shades are mix'd with, or intercepted one by another; tho' I was told by Dr. Finch, that there was a Blind Man at Ma∣stricht, not far from Ʋtretcht, who was able to distinguish simple Colours by the Touch, tho' mix'd Colours he could not discern: And

The Account this Man gave the Doctor of his Sensations of those Colours was, that Black and White were the most Asperous Colours, and so like, that it was hard to distinguish them; but Black was the rougher of the two; Green next to it, Gray next to Green, Yellow a degree below that, Red and Blew so much alike, that they were hard to be distinguish'd, but that Blew was the least rough of the two; and these Diversities of Surfaces this Man discover'd, by placing the Body whose Colours he was to try betwixt his Thumb and his Fore-finger; And it was very remarkable, that his Thumb was not only the most sensible of the two, but that he had only this Exquisiteness of Sense when fasting, the least drink disabling him, to di∣stinguish so nicely the difference of Colours.

But I am apt to suspect, that this blind Man rather discriminated these different Colours by the Smell of the ingredients, than the Touch; and that if the Organ of Touch contributed to

it, it rather did it, by discovering the several Forms than Degrees of Asperity, since he found it so difficult to distinguish Black and White from one another, tho' not from other Colours; and indeed tho' the Ribbons which were offer'd might be almost equally rough, yet in such slender Corpuscles as those which reflect the Rays of Light, we may easily conceive, not only a greater closeness of Parts, or a paucity of extant Parts, but that they may be otherwise ranged, and the Cavities left betwixt, much deeper in one than the other; for supposing the Pro∣tuberant Particles to be very slender, and cylin∣drical like the Hair of a Brush, and furnish'd with Hemispherical Tops, they may be so very sharp, that a less exquisite Touch, cannot di∣stinguish them, than that of this blind Man. Nor is every kind of Roughness inconsistent with Whiteness since the level Superficies of Water being made rough by Bubbles, present∣ly acquires a Whiteness, and so does Glass when scratch'd with a Diamond.

But to proceed, supposing the sharp pointed Particles which are ranged upon the Superfi∣cies of black and white Bodies were so like, that the Touch could not distinguish them ea∣sily; yet upon the Account of some difference in the Cavities, which intercept the Rays of Light, they may variously reflect it; as if the Cavities of a black Body be deep, and the other superficial, the one will drown and detain the Rays of Light, whilst the others undisturbedly reflect them. From whence it appears, that Co∣lours rather depend on different Forms of Aspe∣rities, than on different degrees of it; and tho'

the blind Man tells us, that Black was the roughest of Colours, yet it does not therefore follow, that those Bodies which have the least Asperities, must be the lightest, and reflect the Rays of Light most, since according to him, White is the roughest next to Black; and tho' he assigns Yellow two degrees less of Asperity than Green, and as many more than Blew, yet it is manifestly to the Eye a lighter Colour, and reflects the Rays of Light more plentifully than either.

* 1.10But to return to what I was saying of the different Asperities of Bodies, by which Co∣lours may be diversify'd: To assist us to judge of the Reason of the Changes in Colours pro∣duc'd by corrosive saline Corpuscles in a fluid Form, I shall consider how many ways such Liquors may, by working upon them, alter the Superficies of Bodies upon which they act, and consequently cause them variously to reflect the Rays of Light.

And First, Such Liquors may alter the Co∣lours of Bodies, by insinuating and lodging their small Particles in the Pores of a Body: So Oyl or Water dropp'd upon Paper, alters the Co∣lour of it; and the High Road upon Rain loses it's dry Colour, and changes it for another.

Secondly, A Liquor may alter the Colour of a Body, by freeing it from an adventitious Co∣lour; as when the dirty Colour of Gold is ta∣ken off by putting it into the fire or Aq. Fortis. And not only Silver may be restored by the like means to it's genuine Lustre, but I know a vola∣tile Liquor, which, incorporating with Grease, will take such Stains out of Cloaths. And I have try'd, that having rubb'd a Compound Metalline Body

on a Touch-stone, Aq. Fortis would take off all the other Ingredients, and leave the Gold, ap∣pearing with its genuine Colour.

Thirdly, A Liquor may alter the Colour of a Body, either by destroying or subdividing the Parts of it; as when Wood is cut into Chips, or a piece of hot Crystal quench'd in cold Water, for it being by that means crack'd, will not re∣flect the Rays of Light as before.

Fourthly, A Liquor may change the Colour of another Body, by collecting together Parts of Matter scatter'd and dispers'd; so Quick∣silver pour'd into a Solution of Gold, acquires a thin Film, of a yellow golden Colour; and by a like Method all those Colours, that seem to be produc'd by Precipitation, are generated; tho' Resinous Gums dissolv'd in Spirit of Wine being unites into a Mass again; and so rectify••d transparent Butter of Antimony, upon a Mix∣ture of Water precipitates that white Substance, which when it's Salts are wash'd off, is called Mercurius Vitae.

A Fifth way, by which a Liquor may alter the Colour of another Body, is, by altering the Texture of it's Parts, as, when Quicksilver is kept long in a convenient Heat; Metals are corroded, or Fruit is bruised; or when the Parts of a Liquor are agitated by the Affusion of an∣other Body; or when Chymical Oyls are shaken in a Bottle; for the Bubbles by that means rais'd will exhibit very lively Colours.

Another way, is, by putting the Parts of a Body into Motion, after which they may unite in a new Form; so Vitriol rubb'd upon the Blade of a Knife, imparts not any new Colour to it;

but if the Vitriol be moisten'd, it will impart a true Copper Colour to the Iron.

Another way by which a new Colour may be imparted to a Liquor, is, by an Association of it's saline Parts with those of the Body it is made use of to work upon, by which means the super∣ficial Parts of a Body, may be alter'd both in Shape and Figure; and not only a greater num∣ber or a less, may be compriz'd in the same space, but the Pores betwixt the Protuberant Parts may be much straitned, and the old ones partly fill'd up, as well as new ones intercept∣ed; as when Quicksilver is dissolv'd in Aq. Fortis, the saline Parts of the Menstruum associating themselves with the Mercurial Corpuscles, will af∣ford a Green, which afterwards degenerates easily. And so Minium by being dissolv'd in Spirit of Vinegar, yields a clear Solution; and if Aqua Fortis be dropp'd upon a Copper Plate, the Parts of the Metal being corroded, acquire an Asperity, and coagulating with the Menstruum form Grains of blew Vitriol, whereas Spirit of Urine will produce a much deeper Blew. And Aqua Fortis, which will give Red Lead a dark Colour, with crude Lead will produce a white one, with Iron, a reddish, and upon white Quills a yellowish Colour. And that in Chy∣mical Dissolutions and Precipitations the saline Parts of the Body made use of to precipitate, unite with metalline Parts they precipitate, we shall have reason to believe if we consider how much Vitriol, and the Calces of Metals are heavier than the Metals themselves.

After what we have laid down concerning the Causes of Changes of Colours, there are

two things to be taken Notice of; The one is, that there are other ways to vary Colours spee∣dily, besides those we have taken notice of by the help of Liquors; as in Tempering Steel, &c. The second Particular requisite to be noted is, that tho' a Change of Colour may be effected a∣ny one of the ways above-mention'd, yet gene∣rally at least three of them are at once con∣cerned.

* 1.11From what we have been discoursing of the Asperities of Bodies in causing a Reflection of the Rays of Light, one would think that the Sub∣stances themselves are perfectly opacous and impenetrable by the Rays of Light, and so con∣tribute to the Variety of Colours, reflected to the Eye: But I am apt to believe, that even those Bodies which we call Insensible, are com∣pounded of Parts still more minute, whose Com∣missures are not utterly impervious to the Rays of Light, and that the Bodies compounded of those are in some degree Diaphanous. For in a dark Room, where the Light is only permitted to enter at one Hole, I have observ'd, that those Motes which were otherwise insen∣sible; in the Beams of Light, would represent several vivid and florid Colours, like those of a Rainbow, or of sparkling Fragments of Dia∣monds; and as soon as that Position, which they had at that time, in reference to the Eye and the Light, was lost, they ceas'd to repre∣sent those Colours, tho' still remain'd visible; so that from hence it appear'd, that these small Fragments of Matter, commonly reputed Opa∣cous, did not barely reflect, but also refracted the Rays of Light: And it is not a Phaenomenon

altogether to be slighted, that Water, tho' a diaphanous Body, hath a manifest Power in re∣fracting the Rays of Light so, that by passing through it, they represent the lively Colours of a Rainbow.

And it is further observable, that several Bo∣dies which are generally esteem'd Opacous, ap∣pear in a great measure transparent, when they are reduc'd into thin Parts, and interpos'd be∣twixt the Eye and a Powerful Light, which is evident in thin Plates of Ivory, thick Leaves of Trees, Shells of Fishes and shavings of Wood. And in a darkned Room I found, that the Sub∣stance of my Hand was in a great measure tran∣sparent, when it was held betwixt my Eyes and the Rays of Light which came in at a small Hole.

And not only white Marble of a convenient Thickness, but Lapis Specularis, or Muscovite Glass, being divided into thin Plates, will be considerably transparent; and even Coral it self will manifest the same Transparency if held near the Light.

But on the other hand, I must own, that having look'd upon Mercury precipitate per se, Filings of Copper and Steel, the Red Calx of Lead, and the Red Colour of Vitriol, they appear'd not to have the least Transparency.

How far the Transparency or Semidiapha∣neity of Bodies may contribute to the Variety of Colours produc'd by them, I shall not take upon me to determine, since beaten Glass, Snow and Ice, whose superficial Parts are manifestly transparent, represent not the lively Colours

which they do when conveniently qualifi'd by their Bigness, Shape and Texture.

But to draw an Inference from what hath been said of the Cause of Colours; It appears, that according to the Hypothesis we have laid down, Bodies can only be said to be coloured when placed in the Light; but that, according to the Antients, if we take the Sense of the Word Colour, to mean only that Disposition of the superficial Surface of a Body, which enables it to modifie the Rays of Light; They may be said to have Colours in the Dark, since they have that Disposition, which enables them to re∣flect the Rays of Light in such a Form as to pro∣duce Colours.

* 1.12And from what hath been deliver'd, it like∣wise appears, that tho' Colours which are eva∣nid, and last but for a while, as the Colours of the Rain-bow, and all Emphatical Colours, are generally distinguish'd from True and Ge∣nuine ones, in as much as the latter are pro∣duc'd by Reflection, and these proceed from Refraction; yet, since we usually account all Ecchoes genuine Sounds, and all Smells true Smells, in as much as they are real Objects of the respective Sensories they affect, by the same Reason we may conclude these Emphatical Co∣lours genuine, since the Rays of Light equally affect our Sensory for the time: And tho' the shortness of their Continuance hath been offer'd as an Argument of their not being genuine, by the same Rule we might say, that the Colour of Grass is not genuine, because the Colour of an Emerald is more lasting; but white Co∣lour of Froth is held to be genuine, tho' it is

soon generated, and in a little time destroy'd. Besides, were the Whiteness of Froth accounted an imaginary Colour, we must no longer be∣lieve such to be distinguish'd from genuine ones, by Refraction; since Froth retains it's White∣ness, whether the Sun be setting, rising, or at the Meridian; the Position of the Sun in refe∣rence to the Eye, and the Object not at all di∣versifying it.

Moreover, were a Colour to be pronounced genuine by the time of it's Duration, the white Froth of a Tenacious Body, might be said to be more genuine, because it will continue much longer, than the Colour of those Flowers of the Mervail of Peru, which fade the very day they are Blown: And I have seen a Virginian Flower, which seldom continues longer than a day.

And that the bare Disposition of the Parts of a Body, by which it is said to reflect or re∣fract the Rays of Light is sufficient to produce different Colours, is not only evident in Cloth held in several Positions, by which means it variously reflects the Rays of Light; but it is further evident, since the Beams of the Sun tra∣jected through a Prismatical Glass, represent a lively and vivid Rain-bow, upon any Body up∣on which they terminate, which may be dis∣cern'd by the Eye, plac'd in any Position what∣soever, viz. whether above, or below, or on the side of the Glass. And tho' when the Prism is taken away, the Rain-bow disappears, yet nevertheless, the Light, for the time being truly reflected and refracted from the Prism, and reflected again from the Body, which those 〈2 pages missing〉〈2 pages missing〉

as the Cartesians suppose, the several kinds of Motions of these Globuli might contribute to vary the Perception of Colours, so I think that without such Globuli, the Rays of Light may variously affect the Eye themselves, as their Mo∣tion is vary'd in order, or degrees of Swift∣ness when they affect our Sensory, or as their Motion is undulating or more or less di∣rect.

But since I pretend not this Discourse to be a compleat History of Colours, I shall only in their proper Place deliver some Experiments, which may shew the Insufficiency of the Peripa∣teticks and the Doctrine of the Chymists, and in favour of that opinion which I am most inclin'd to be of; which is, that Colour is a Modification of the Beams of Light, which they receive from the Object, from whence being reflected to the Eye, they cause that Sensation we call Colour. But how they come to be so modify'd, I shall not take upon me to declare, till I know both what Light is it self, and what figur'd Cor∣puscles it consists of, and likewise their Size and Motion: And before I pretend to lay down my Opinion, I would further be satisfy'd what is the Nature of Refraction, and what degrees of Commixture of Shades with the Light, made in the superficial Parts of a Body is requisite to produce this or that Colour.

Notes

• * 1.1

  Diversity of Colour not always an Argu∣ment of a variety in Qualities.
• * 1.2

  Yet changes of Colour oft signify Alteration in the Pro∣perties of Bodies.
• * 1.3

  What is meant by Colour.
• * 1.4

  What the Perception of Colours depends up∣on.
• * 1.5

  The Super∣ficies of a Body consi∣der'd as the cause of Co∣lours.
• * 1.6

  The vari∣ous Figures of the Super∣ficial Parts requisite for the Produ∣ction of Co∣lours.
• * 1.7

  The Situa∣tion of them likewise re∣quisite.
• * 1.8

  The Motion of the part of a Body contribute to the Co∣lour.
• * 1.9

  How far Asperity contributes to Colours.
• * 1.10

  How many ways Li∣quors may alter Co∣lours.
• * 1.11

  Several Bo∣dies gene∣rally esteem∣ed opacous semidia∣phanous.
• * 1.12

  The short duration of Colours no Argument of their not being ge∣nuine.