Two treatises in the one of which the nature of bodies, in the other, the nature of mans soule is looked into in way of discovery of the immortality of reasonable soules.

THE ONE AND THIRTIETH CHAPTER. The causes of certaine appearances in luminous Colours; with a conclusion of the discourse touching the senses and the sensible qualities.

1OVt of these groundes, we are to seeke the resolution of all such symptomes as appeare vnto vs in this kind of colours. First therefore calling to mind, how we haue already declared, that the red colour is made by a greater proportion of light mingled with darkenesse, and the blew with a lesse proportion: it must follow, that when light passeth through a glasse in such sort as to make colours; the mixture of the light and darkenesse on that side where the light is strongest will incline to a red: and their mixture on the other side, where the light is weakest, will make a violet or blew: and this we see to fall out accordingly, in the light which is tincted by going through a prisme; for a red colour appeareth on that side from which the light doth dilate or decrease, and a blew is on that side towardes which it decreaseth.

Now, if a darke body be placed within this light, so as to haue the light come on both sides of it: we shall see the contrary happen about the borders of the picture or shadow of the darke body: that is to say, the red colour will be on that side of the picture which is towardes or ouer against the blew colour that is made by the glasse: and the blew of

the picture, will be on that side which is towardes the red that is made by the glasse, as you may experience if you place a slender opacous body a long the prisme in the way of the light, eyther before or behind the prisme. The reason whereof is; that the opacous body standing in the middle, enuironned by light, diuideth the light, and maketh two lights of that which was but one; each of which lights, is comprised betweene two darkenesses, to witt, betweene each border of shadow that ioyneth to each extreme of the light that cometh from the glasse, and each side of the opacous bodies shadow. Wherefore, in each of these lights; or rather in each of their commixtions with darkenesse, there must be red on the one side, and blew on the other; according to the course of light which we haue explicated.

And thus it falleth out agreable to the rule we haue giuen, that blew cometh to be on that side of the opacous bodies shadow, on which the glasse casteth red, and red on that side of it on which the glasse casteth blew: likewise when light going through a conuexe glasse maketh two cones, the edges of the cone betwixt the glasse and the point of concurse will appeare red, if the roome be darke enough: and the edges of the further cone, will appeare blew, both for the reason giuen: for in this case the point of concurse is the strong light betwixt the two cones: of which, that betwixt the glasse and the point, is the stronger, that beyond the point, the weaker: and for this very reason, if an opacous body be put in the axis of th••se two cones, both the sides of its picture will be red, if it be held in the first cone which is next to the glasse; and both will be blew if the body be situated in the further cone; for both sides being equally situated to the course of the light, within its owne cone, there is nothing to vary the colours, but only the strength and the weakenesse of the two lights of the cones, on this side, and on that side the point of concurse: which point, being in this case the strong and cleare light whereof we made generall mention in our precedent note, the cone towardes the glasse and the illuminant, is the stronger side, and the cone from the glasse, is the weaker.

In those cases, where this reason is not concerned, we shall see the victory carried in the question of colours, by the shady side of the opacous body: that is, the blew colour will still appeare, on that side of th•• opacous bodies shadow that is furthest from the illuminant. But where both causes do concurre and contrast for precedence, there the course of the light carryeth it: that is to say, the red will be on that side of the opacous bodies shadow, where it is thicker and darker, and blew on the other side where the shadow is not so strong; although the shadow be cast that way that the red appeareth: as is to be seene, when a slender body is placed betwixt the prisme and the reflectent body, vpon which the light and colours are cast through the prisme: and it is euident, that this cause of the course of the shadow, is in it selfe a weaker cause, then the other of the course of light, and must giue way vnto it whensoeuer

they encounter (as it can not be expected, but that in all circumstances▪ shadowes should to light) because the colours which the glasse casteth in this case, are much more faint and dusky then in the other.

For effects of this later cause, we see that when an opacous body lyeth crosse the prisme, whiles it standeth endwayes, the red or blew colour, will appeare on the vpper or lower side of its picture, according as the illuminant is higher or lower thē the transuerse opacous body: the blew euer keeping to that side of the picture, that is furthest from the body, and the illuminant that make it: and the red the contrary; likewise if an opacous body be placed out of the axis, in eyther of the cones we haue explicated before, the blew will appeare on that side of the picture which is furthest aduanced in the way that the shadow is cast: and the red, on the contrary: and so, if the opacous body be placed in the first cone (beside the axis) the red will appeare on that side of the picture in the basis of the second cone, which is next to the circumference; and the blew, on that side which is next the axis: but if it be placed on one side of the axis in the second cone, then the blew will appeare on that side the picture which is next the circumference; and the red, on that side which is next the center of the basis of the cone.

2There remayneth yet one difficulty of moment to be determined: which is why, when through a glasse, two colours (namely blew and red) are cast from a candle vpon a paper or wall, if you put your eye in the place of one of the colours that shineth vpon the wall, and so that colour cometh to shine vpon your eye, in such sort that an other man who looketh vpon it, will see that colour plainely vpon your eye, neuerthelesse, you shall see the other colour in the glasse? As for example, if on your eye there shineth a red, you shall see a blew in the glasse; and if a blew shineth vpon your eye, you shall see a red.

The reason hereof is, that the colours which appeare in the glasse, are of the nature of those luminous colours which we first explicated, that arise from looking vpon white and blacke bordering together: for a candle standing in the ayre, is as it were a white situated betweene two blackes: the circumstant dusky ayre, hauing the nature of a blacke: so then, that side of the candle which is seene through the thicker part of the glasse, appeareth red; and that which is seene through the thinner, appeareth blew: in the same manner as when we looke through the glasse; whereas, the colours shine cōtrarywise vpon a paper or reflecting obiect, as we haue already declared, together with the reasons of both these appearances; each fitted to its proper case, of looking through the glasse vpon the luminous obiect serrownded with darkenesse, in the one; and of obseruing the effect wrought by the same luminous obiect in some medium or vpon some reflectent superficies, in the other.

And to confirme this, if a white paper be sett standing hollow before the glasse (like halfe a hollow pillar, whose flatt standeth edgewayes towardes the glasse, so as both the edges may be seene through it) the

further edge will seeme blew and the neerer will be red; and the like will happen, if the paper be held in the free ayre parallele to the lower superficies of the glasse, without any blacke carpet to limit both endes of it (which serueth to make the colours the smarter) so that in both cases, the ayre serueth manifestly for a blacke; in the first, betweene the two white edges; and in the second, limiting the two white endes: and by consequence, the ayre about the candle must likewise serue for two blackes, including the light candle betweene them.

Seuerall other delightfull experiments of luminous colours I might produce, to confirme the groundes I haue layed, for the nature and making of them. But I conceiue that these I haue mentioned, are aboundantly enough for the end I propose vnto my selfe: therefore I will take my leaue of this supple and nice subiect; referring my Reader (if he be curious to entertaine himselfe with a full variety of such shining wonders) to our ingenious countryman and my worthy frend, Mr. Hall: who at my last being at Liege, shewed me there most of the experiences I haue mentioned; together with seuerall other very fine and remarkable curiosities concerning light; which he promised me he would shortly publish in a worke, that he had already cast and almost finished vpon that subiect: and in it, I doubt not but he will giue entire satisfaction to all the doubts and Problemes that may occurre in this subiect: whereas my litle exercise formerly, in making experiments of this kind, and my lesse conueniency of attempting any now, maketh me content my selfe with thus spinning of a course thridde frō wooll carded me by others, that may runne through the whole doctrine of colours, whose causes haue hitherto beene so much admired: and that it will do so, I am strōgly persuaded, both because if I looke vpō the causes which I haue assigned a priori, me thinkes they appeare very agreeable to nature and to reason; and if I apply them to the seuerall Phoenomēs which M^r. Hall shewed me, and to as many others, as I haue otherwise mett with, I find they agree exactly with them, and render a full account of them.

And thus, you haue the whole nature of luminous colours, resolued into the mixtion of light and darkenesse: by the due ordering of which, who hath skill therein, may produce any middle colour he pleaseth: as I my selfe haue seene the experience of infinite changes in such sort made; so that it seemeth vnto me, nothing can be more manifest, then that luminous colours are generated in the way that is here deliuered. Of which how that gentle and obedient Philosophy of Qualities (readily obedient to what hard taske soeuer you assigne it) will render a rationall account; and what discreet vertue, it will giue the same thinges to produce different colours, and to make different appearances, meerely by such nice changes of situation, I do not well vnderstand: but peraduenture the Patrones of it, may say that euery such circumstance is a Conditio sine qua non: and therewith (no doubt) their Auditors will be much the wiser in comprehending the particular nature of light,

and of the colours that haue their origine from it.

3The Rainebow, for whose sake most men handle this matter of luminous colours, is generated in the first of the two wayes we haue deliuered for the production of such colours: and hath its origine from refraction, when the eye being at a conuenient distance from the refracting body, looketh vpon it to discerne what appeareth in it. The speculation of which may be found in that excellent discourse of Monsieur des Cartes, which is the sixt of his Meteors; where he hath with great acuratenesse deliuered a most ingenious doctrine of this mystery: had not his bad chance of missing in a former principle (as I conceiue) somewhat obscured it. For he there giueth the cause so neate, and so iustly calculated to the appearances, as no man can doubt but that he hath found out the true reason of this wonder of nature, which hath perplexed so many great witts: as may almost be seene with our very eyes; when looking vpon the fresh deaw in a sunneshiny morning, we may in due positions perceiue the raynebow colours, not three yardes distant from vs: in which we may distinguish euen single droppes with their effects. But he hauing determined the nature of light to consist in motion, and proceeding consequently, he concludeth colours to be but certaine kindes of motion: by which I feare it is impossible that any good account should be giuen of the experiences we see.

But what we haue already said in that point, I conceiue is sufficient to giue the reader satisfaction therein: and to secure him, that the generation of the colours in the rainebow, as well as all other coulours, is likewise reduced to the mingling of light and darkenesse: which is our principall intent to proue: adding therevnto by way of aduertissement, for others whose leisure may permitt them to make vse thereof, that who shall ballance the proportions of luminous colours, may peraduenture make himselfe a steppe to iudge of the natures of those bodies, which really and constantly do weare like dyes; for, the figures of the least partes of such bodies, ioyntly with the connexion or mingling of them with pores, must of necessity be that which maketh them reflect light vnto our eyes, in such proportions, as the luminous colours of their tincture and semblance do.

For two thinges are to be considered in bodies, in order to reflecting of light: eyther the extancies and cauities of them; or their hardenesse and softenesse. As for the first; the proportions of light mingled with darkenesse will be varied, according as the extancies or the cauities do exceed, and as each of them is great or small: since cauities haue the nature of darknesse, in respect of extancies, as our moderne Astronomers do shew, when they giue account of the face (as some call it) in the orbe of the moone. Likewise in regard of soft or of resistent partes, light will be reflected by them, more or lesse strongly, that is, more or lesse mingled with darkenesse; for whereas it reboundeth smartly backe, if it striketh vpon a hard and a resistent body, and accordingly

〈◊〉〈◊〉 ••hew it selfe in a bright colour: it must of necessity not reflect at all, 〈…〉〈…〉 very f••ebly, if it penetrateth into a body of much humidity, or if ••••••oseth it selfe in the pores of it▪ and that litle which cometh so weakely from it, must consequently appeare of a dusky dye: and these two, being all the causes of the great variety of colours we see in bodies, according to the quality of the body, in which the reall colour appeareth, it may easily be determined from which of them it proceedeth: and then, by the colour, you may iudge of the composition and mixture of the rare and dense partes, which by reflecting light begetteth it.

In fine,4 out of all we haue hitherto said in this Chapter, we may conclude the primary intent of our so long discourse; which is, that as well the senses of liuing creatures, as the sensible qualities in bodies, are made by the mixtion of rarity and density, as well as the naturall qualities we spoke of in their place: for it can not be denyed but that heate and cold, and the other couples or payres, which beate vpon our touch, are the very same as we see in other bodies: the qualities which moue our tast and smell, are manifestly a kinne and ioyned with them: ligh•• we haue concluded to be fire: and of motion (which affecteth our eare) it is not disputable: so that it is euident, how all sensible qualities, are as truly bodies, as those other qualities which we call naturall.

To this we may adde, that the proprieties of these sensible qualities, are such as proceed euidently from rarity and density; for (to omitt those which our touch taketh notice of, as too plaine to be questioned) Physitians iudge and determine the naturall qualities of meates, and of medecines, and of simples, by their tastes and smels: by those qualities they find out powers in them to doe materiall operatiōs; and such as our instrumēts for cutting, filing, brushing, and the like, doe vnto ruder and grosser bodies. All which vertues, being in these instruments by the different tempers of rarity and density, is a conuincing argument, that it must be the same causes, which must produce effects of the same kind in their smels and tastes: and as for light, it is knowne how corporeally it worketh vpon our eyes.

Againe, if we looke particularly into the composition of the organes of our senses; we shall meet with nothing but such qualities as we find in the composition of all other naturall bodies. If we search into our eye, we shall discouer in it nothing but diaphaneity, softenesse, diuers colours, and consistencies; which all Anatomistes, to explicate, doe parallele in other bodies: the like is of our tongue, our nosethrilles, and our eares. As for our touch; that is so materiall a sense, and so diffused ouer the whole body, we can haue no difficulty about it. Seeing then that all the qualities we can discouer in the organes of our senses, are made by the various minglings of rarity with density, how can we doubt, but that the actiue powers ouer these patients, must be of the same nature and kind.

Againe, seing that the examples aboue brought, doe conuince, that the obiects of one sense, may be knowne by an other; who can doubt of a

community among them, if not of degree, at ••••e least of the whole kind? As we see that the touch, is the groundworke of all the rest; and consequently, that being euidently corpore••••••, and consisting in a temper of rarity and density, why should we m••••e difficulty in allowing the like of the rest?

Besides, lett vs compose of rarity and density, such tempers as we find in our sēses; and lett vs againe compose of rarity and density, such actors, as we haue determined the qualities, which we call sensible, to be; and will it not manifestly follow, that these two applyed to one an other, must produce such effects, as we affirme our senses haue? that is, to passe the outward obiects, by different degrees, vnto an inward receiuer.

5Againe, lett vs cast our eyes vpon the naturall resolution of bodies, and how they moue vs, and we shall th••reby discouer, both what the senses are, and why they are iust so many, and that they can not be more. For an outward body may moue vs, eyther in its owne bulke or quantity; or as it worketh vpon an other. The first is done by the touch: the second by the eare, when a body mouing the ayre, maketh vs take notice of his motion. Now in resolution, there are three actiue partes proceeding from a body, which haue power to moue vs. The fiery part; which you see worketh vpon our eyes, by the vertue of light. The ayry part, which we know moueth our nosethrilles, by being sucked in with the ayre. And lastly the salt; which dissolueth in water, and so moueth our watry sense; which is our taste.

And these being all the actiue partes, that shew themselues in the resolution of a body; how can we imagine there should be any more senses to be wrought vpon? for what the stable body sheweth of it selfe, will be reduced to the touch: what as it moueth, to hearing: what the resolutions of it, according to the nature of the resolued atomes that fly abroade; will concerne the other three senses, as we haue declared. And more wayes of working, or of actiue partes, we can not conceiue to spring out of the nature of a body.

Finally, if we cast our eyes vpon the intention of nature: to what purpose are our senses, but to bring vs into knowledge of the natures of the substances we conuerse with all? surely, to effect this, there can not be inuented a better, or more reasonable expedient, then to bring vnto our iudgement seate the likenesses or extractes of those substances, in so delicate a modell, that they may not be offensiue or cumbersome; like so many patternes presented vnto vs, to know by them, what the whole piece is: for all similitude, is a communication betweene two thinges in that quality, wherein there likenesse consisteth: and therefore we can not doubt, but that nature hath giuen vs, by the meanes we haue explicated, an essay of all the thinges in the world, that fall vnder our commerce, whereby to iudge whether they be profitable or nociue vnto vs; and yet in so delicate and subtile a quantity, as may in no wayes be offensiue to vs, whiles we take our measures to attract what is good, and auoyde what is noxious.

Notes

• 1

  The reason of each seuerall colour in particular caused by light passing through a prisme.
• 2

  A difficult pro∣bleme resolued touching the prisme.
• 3

  Of the raine∣bow, and how by the colour of any body wee may know the compositiō of the body it selfe.
• 4

  That all the sēsible qualities are reall bodies resulting out of seuerall mixtures of rarity and den∣sity.
• 5

  Why the senses are only fiue in number: with a conclusion of all the former doctrine con∣cerning them.