An entire body of philosophy according to the principles of the famous Renate Des Cartes in three books, (I) the institution ... (II) the history of nature ... (III) a dissertation of the want of sense and knowledge in brute animals ... / written originally in Latin by the learned Anthony Le Grand ; now carefully translated from the last corrections, alterations, and large additions of the author, never yet published ... by Richard Blome.

CHAP. IX. Of Colours.

I. Whether the Colours of a Pea∣cocks Tail, and the Necks of Doves be true Co∣lours. A Peacocks Tail, and the Feathers of a Pigeon do wonderfully change their Colours; as LUCRETIUS elegantly expresseth it.

So Plumes that grow around the Pigeons Head, Sometimes look brisker with a Deeper Red; And then in different position seen, Shew a gay Skie, all intermixt with Green: And so in Peacocks Tails, all fill'd with Light, The Colour varies with the change of sight.

These Colours are caused when the Peacocks Tails, and Necks of Pigeons are turned towards the Light; and by reflexion or refraction do send back the said Rays to the Eye. They are com∣monly called appearing Colours only, and reckon'd amongst those Images that deceive us, and whose entire Essence or Nature consists in their appearance, or seeming such. But the reason why they assert this, I cannot apprehend: For if they admit Co∣lour to be nothing else, than the Light it self, modified in the surface of Bodies, why may not they own those Colours, which they call seeming, to have as truly the Nature of Colour as any other? For can the short duration of the Cause, destroy the Truth of the Effect? Or doth not a Son de∣serve that name, because he dies almost as soon as he is born? Who will affirm, that the Greenness of Grass or Herbs, which for some days only doth delight our Eyes, is less a Colour than the Greenness of an Emrald, which continues so much

longer? For by the same Argument, the flame of Lightning or Gun-powder will be no true Flame, because of its suddain vanishing and disappearance. For the lasting or continuance of Colours imports nothing to their Truth and Reality; and those which continue only for a moment, are no less Colours, than those which lastingly do affect the Eyes.

II. How Co∣lours come to be vari∣ed. The Cause therefore of the variation of Colours in the Peacocks Tail, and the Necks of Doves, is the different Reflexion and Refr••ction of the Rays, made by the thin Hairs of their Feathers, because of their various admission of the Luminous Beams. Thus those Pictures, made of Feathers, which are brought out of the East Indies, according to the variety of their situation, do exhibit a Violet Colour, or bright Blue, or a curious Emrald Green; forasmuch as the soft Feathers whereof they do consist, have their surfaces so ordered, as diversly to reflect the Light.

But this being besides my present scope, I re∣turn to prosecute my Experiments.

III. Two Look∣ing-Glasses, made of different Marble, do differently reflect the Image of the Sun. Let two Llooking-Glasses be made, the one of white, the other of black Marble; that of white being exposed to the Suns Beams, will represent to us a more clear and distinct Image of the Sun, than that of the black, from which only some weak Rays will rebound, which being not suffici∣ently united together, will only produce a confu∣sed Image or Similitude of the Object.

The Reason of this is, because the action of the Light, whereby the Parts of the Subtil Matter, push'd on by the Lucid Body, do tend towards the Black Marble, is almost quite extinguish'd or swallowed up by it, so as that very few of the Rays are reflected: Whereas the White doth altogether remit the Action of Light, and almost reflect all the Beams that fall upon them. For tho' White and Black Marble, consist almost of the very same parts, and no difference is discernible between them by sense; yet it is not to be questioned, but that in the Black some soft parts are to be found, which swallow up part of the Beams, and break the force of them. So that the Black Marble dif∣fers from the White, much alike as a Pumice-stone, whose Pores are filled with melted Pitch, differs from another Pumice-stone, whose Pores are only filled with Air: For as the Grains of Sand cast against the latter, would rebound thence, whereas those cast against the other would be deaded; in like manner, all the Light which falls upon the White Marble is reflected; whereas that which lights on the Black, is mostly swallowed up.

IV. What is the Cause of the White∣ness that is in Bodies. The same is apparent in other Bodies; for if Water, for instance, be strongly agitated and sha∣ken together, it becomes of a White Colour, and after that the Bubbles of the Froth are broken, it is Transparent; which is a great Argument, that the cause of this Whiteness is, when the Light is wholly and entirely reflected from the small Bub∣bles of the Froth, as from so many Looking-Glas∣ses. And accordingly the Black Marble is like Hangings, which upon the casting of a Ball a∣against it, doth receive motion, but doth not re∣bound; whereas the White is like a hard Wall, which sends it back, and without any motion of its own, doth reflect it.

V. W••y White Marble is less su••••••∣ptive of Heat, than Black Mar∣ble. Hence it is, that if you take 2 Polish'd pieces of Marble, the one White, the other Black; and in hot weather expose them to the Sun-beams for some time, you'l find that the Black will be very hot, whereas the White will, for all that, in a great measure, continue cold. Whereof no other reason can be given, but that the Black, because of its many Cavities, doth freely admit the Globuli of Light; whereas the White, because of its closeness, doth reverberate the received Light, retaining no∣thing of it. Accordingly as we daily observe in whited Rooms, which do reflect more Light, and do, in a manner, send it all back again from them. Hence it is, that when the Light of the Sun is ad∣mitted into a Darkned Room, through a little hole, if the Rays be received upon a white Paper, they appear very bright and shining; whereas they shew very weak and faint, when they light upon a black Body.

VI. Polish'd Marble ap∣pears of a blacker Co∣lour than that which is Rough. Polish'd Marble is of a blacker Colour, than that which is Rough.

The Reason is, because in the Rough there be many Prominences, which every way reflect the Light. For the Ray which is reflected from one part of the Body, goes one way, and that which is reverberated from another part, another way. But a Polish'd Body, forasmuch as it consists only of one continued Superficies, therefore it reflects fewer Rays to the Eye. Moreover, seeing there is no Body, in Nature, so Black, which doth not consist of many parts, which being separated from the rest, would constitute a white Body, as the difference there is between the Polish'd and Rough Marble doth abundantly testifie: We may say that Polish'd Marble is most black, because its white parts do reflect the Light they receive, to∣wards the same part; where if there be never an Eye to admit it, it is the same with respect to it, as if the Light were quite extinquish'd. But when the Eye is placed in that part to which the re∣flexion tends, it perceives this Light in the Mar∣ble, together with the Colours and Figure of the Objects, from whence the Light doth proceed; no otherwise than if it did proceed from a Look∣ing-Glass.

VII. A perfectly Polish'd Bo∣dy can only be seen on one side. Now that an absolutely Polish'd Body doth on∣ly reflect one Ray to the same point of the Eye, may be thus demonstrated. Let BF, be suppos'd to be a perfectly polish'd Plain, and let the Light be in the Point A, and the Eye at H, let the re∣flex Ra•• be DH, so as that the Angles ADB, and HDF be equal; it is evident, that no other Ray derived from A, will be reflected to H, sup∣posing that the surface BF, be absolutely smooth and even. For let there be any other Ray of in∣cidence, * 1.1suppose AC, I say, that the Angle ACB, is greater than the Angle ADB; wherefore sup∣posing an equal Angle of Reflexion ACI, the re∣flected Ray, CI, will never reach to H, nor will ever concur with DH, but rather fall wider from it, the further it is drawn. And the same must be said of all the other direct incident Rays be∣tween B and D. Wherefore there will only one Ray be reflected at H, viz. DH. I have said before, if the Body be perfectly smooth, for if it be not, the case will be otherwise, upon the chan∣ging of the nature of the Plain.

VIII. Some Bodies retain al∣ways the same con∣stant Colou••▪ as Coals, Snow, &c. Some Bodies do constantly keep the same Co∣lour, and which way soever they are turned to∣wards the Light, do always reflect it a••ter same manner; so Coals always appear Black, common Snow, White.

The cause of this constant Colour is to be ascribed to the Disposition and Situation of the Parts, which as long as it continues the same in Bodies, they admit the Light at certain Angles, and accordingly reflect it to the Sight. For Char∣coal is black, because its surface is rough and un∣even, by reason of innumerable furrows and chinks, which choak the Rays of Light, and break their force. Which may be evinced, not only by reason, but by our very Senses. For if a man do gently handle Charcoal, he will be sensible of a kind of Roughness, something like that we feel in a Pumice-stone; which, as I said before, is not capable of being polished. For whilst Wood is burning, much Smoak and Exhalation flies away from it, by the force of the Heat; and therefore the Fire being rarefied between the Cavities of the Wood, doth break its prison and dilate the pores; into which, when the Rays of Light enter, they are there swallowed up and entangled, so that they cannot rebound to the Eye.

IX. In what sense it is that Co∣lours are said to be in Bodies. But yet we must not imagine with some, that Colours do formally exist in Bodies, but effectively only, inasmuch as they produce them in the Eye, by means of a certain disposition of the Insensible parts, and the Reflexion of the Light: In the same manner as a Needle, which is destitute of all pain, yet being thrust into the Skin, doth by its motion, figure and hardness, produce Pain there.

Thus all Sulphurous matters exhibit a Red Colour: As when the Spirit of Turpentine being digested with the Calx of Lead, yields a deep Red; and the Spirit of Soot mixt with any acid Liquor, or Common water, affords a white or milky Colour. Thus the Light proceeding from 2 Lanthorns, the one of red Glass, the other of blew, being receiv'd on a Paper, will represent there a Purple Colour. All which Instances manifestly evince, that Colour is not inherent or fixed in a Body, but only a result of the Reflexion of Light.

X. Why beaten Glass seems to be white. Glass, when it is whole and extended in Panes, is transparent, that is, of no Colour, or if it have any, it is rather of a black than white Colour; but when beaten in a Mortar, it appears white.

The Reason is, because beaten Glass hath many Surfaces, which every one of them do receive the Light and reflect it again, as so many Looking-Glasses. For seeing that Glass is destitute of all Moisture, and that all its parts are of a round figure, as may be experienc'd by the help of a Microscope, one of them reflects one part of the Light, and the other, another, and so on, so that they reflect the whole Light, and that after the very same manner as they have received it. Hence it is that White Bodies are, of all others, the least opake; be∣cause they reflect the Rays of Light from every point of them, and suffer none to be swallowed up of any of their Cavities.

XI. What is the Cause of the Whiteness in Snow. Neither is there any other Cause of the white∣ness of Snow, which consisting of Bubbles, doth send the Rays to the Eye, according to the multi∣tude of the Bubbles whereof it is composed. No•• is this contrary to what hath been said before, tha•• from every Bubble, one Ray only is sent to the Eye: For since they are not sensible, neither do they hinder, but that abundance of continual Rays may be directed to the Eye. Hence it is that Snow, which is nothing else but Frozen-water, yet doth appear whiter than Ice; for seeing that the surface of Ice is not so much curled, as the surface of Snow, and that there are many Devexities or Roundings in Snow, from whence the Light may be reflected, which are not to be found in Ice; i•• cannot be, but that Snow must appear whiter than Ice. And for the same Reason it is, that water beaten together, turns to froth, by its being divided into round and small parts: For if the Bubbles, whereof the Froth consists, be so great, they will cease to yield a white Colour. Thus likewise the Whites of Eggs, when beaten, lose their Transpa∣rency, and become white; and Crystalline Glass, heated in a strong Fire, and quenched with water, is resolved into so many slits, that it appears altoge∣ther white.

XII. Fishes tending to putrefacti∣on, do yield no Colour at all in the Pneu∣matick Engin. Rotten Wood, as also stinking Fish, are of a kind of whitish Colour, when exposed to the Air; but when put into the Pneumatick Engin, upon the extraction of the Air, do lose all Colour.

The Reason is, because the particles of putre∣fying Bodies, are agitated in such a manner as is necessary, for the causing of the Sense of Light. For the Corruption of any Body is caused by the motion of its parts, whereof some fly away and are separated from the rest; and those that remain, impart their Vibration or Motion to the inter∣jacent Air, and by this means do afford a weak Light to it. But seeing that all the Air is supposed to be extracted out of the Pneumatick Engin, it needs not seem strange to us, if the Fish which shined before, doth no longer shed any Light. For the Air, by its Elastick virtue, doth assist the agitation of the Light, and where its motion is stronger, there the Light also is increased.

XIII. Why the lower part of the Blood in a Porringer appears of a darker Colour, than that at the top. Thus FRACASI is of Opinion, that the Reason why the Blood appears of a darker Colour at the bottom of a Porringer, than at the top, is not because, as the common Opinion is, that part is the more Melancholy portion of the Blood; but because the lower part of the Blood is not so much exposed to the Air, and therefore appears less Ruddy and Florid, than that which is on the top.

XIV. Why the Blood that is contain'd in the Ar∣teries and Veins, is Red. Why the Blood that is in the Arteries and Veins is Red, appears from what hath been said in my Institution of Philosophy, viz. That the motion of the Globuli of the second Element, which are the Cause of Light, is twofold, the one whereby in a strait Line they are carried to our Eye; the other, whereby they are whirled about their own Centers. So that if they be whirl'd about much slower, than they move in a right Line, then the Body whence they are reflected will appear blew to us; but if they be whirl'd about much swifter, then it will seem red. Now no Body can be dis∣posed to make them whirl about more swiftly, but such an one as consists of Branchy parts, and those so thin and near one another, as to have nothing about them, save only the Matter of the first Element, such as the Parts of Blood are. For the Globuli of the second Element meeting with the Matter of the first Element in the sur∣face of the Blood; which Matter doth without ceasing obliquely pass through the same, and that with great swiftness, out of one pore into another, so as to be moved after a different manner from the Globuli; they are forced to whirl about their own Centers, by the Matter of the first Element,

and that more swiftly than they could be forced by any other Cause, because the first Element exceeds all other Bodies in swiftness.

XV. Why bu••n∣ing Coals, or Red hot-Iron are not so red as Blood. And the same is the Reason, why Red-hot-Iron and Burning-Coals are red; even because very many of their pores are fill'd only with the first Element. But because the said pores are not so narrow as those of the Blood, and that there is much of the first Element in them, to produce Light, hence it is that their Redness differs from the Redness of the Blood.

XVI. Of a Person that distin∣guisheth Colours by the touch of his hand. Very Famous and Credible persons give us an account of a certain blind Organist, who lived near Utrecht upon the Maes, who had such an ••xactness of Feeling, that by the touch of his Hand only, he was able to distinguish several Colours.

It will not be very difficult to assign the Rea∣son of this wonderful Effect, if we consider that the interruption of parts in Bodies, doth very much conduce to the production of Colours; forasmuch as it is evident, that most Colours proce••d from the roughness of Bodies, and the figure, order, situation and motion of the parts. As is evident in red Marble, the polisht part whereof is very different in Colour, from that which is rough. So likewise we may perceive by a Microscope, that the yellow parts in a piece of Silk, are very different from the blew. Forasmuch therefore as there is so great a variety of Parts in Colour'd Bodies, which may admit a Reflexion or Refraction of Rays, we may conclude, that it seems probable enough that the foresaid blind Man might have such a quick Touch, as to be able to distinguish colour'd Objects by the roughness or unevenness of their parts.

XVII. The mix∣ture of Bodies produceth new Co∣lours. Several Bodies mingled together obtain a diffe∣rent Colour from what they had before: Thus Oil of Anniseed, mixed with Oil of Vitriol, turns red; Spirit of Turpentine poured upon Sugar of Lead, or calcin'd Lead, produceth a red Tincture; and the yellow Gall in Animal Bodies, according to the Opinion of Physicians, is the product of the mixture of adust Sulphur and Salt.

This production of different Colours is caused by the inward disposition of the parts of Bodies. For it is certain, that from the alteration of the least parts of one Body, a different Colour must arise; as appears evidently to the Eye in Herbs that are beaten in a Mortar. For the temperament and ranging of the Parts, is, as it were, the first Rudiment of Colours, which upon the appearance of Light, and its being diversly reflected and re∣fracted from those particles, doth super▪add the last and most absolute perfection to Colours. Thus the Stone Magnesia, which for colour and hard∣ness doth resemble a Load-Stone, being in a cer∣tain proportion added to Glass, renders it per∣spicuous, and quits it of its green Colour; but if more than is necessary be added to it, it makes it black. Thus an Apple cut in two, at first appears white, then turns yellow, and last of all black, according as the surface of it becomes differently disposed, by the drying of its parts.

XVIII. How two pe••••••••id Bo••••es can pr••duce a black Body. The transparent and clear Infusion of Galls being mixed with a Solution of Vitriol, makes Ink; to which if you afterwards add Spirit of Vitriol, or Aqua-fortis, the black Ink will become trans∣parent again, as Spring▪water; and if you drop some Drops of Oil of Tartar into this clear Li∣quor, it will be turned again into Ink. The blew Tincture of Violets, infused into the Oil of Vitriol, becomes of a purple Colour; to which if you add a few Drops of Spirit of Harts-horn, the purple Colour will be changed to a green.

The Reason why 2 clear Liquors mingled toge∣ther make Ink, is, because the particles of either of them are brought nearer together, so as to hinder the passage of the Rays of Light. And whereas the said Ink afterwards, upon the pouring another Liquor into it, becomes clear again, the Reason is, because the particles of the new added Body, do separate the Parts that before were contiguous, and consequently make an open passage for the Light, to pass freely, as be∣fore.

XIX. The Cause of the variety of Colours, proceeding from the mixture of Liquors. The Difference of Colours proceeding from the mixture of Liquors, is to be fetch'd from the small particles contained within the pores of each Liquor, which being changed in situation and position by the Liquor that is poured into them, do transmit the Rays of Light, variously refract or reflect them, and consequently produce different appearances of Colours. For, as was mentioned before, when the Globuli have more Right motion than Circular, they afford a Violet Colour; if they have more Circular motion than Strait, the Liquor appears yellow; but if the Globuli have much more Circular motion, than Right motion, they produce a Red colour'd Liquor: Again, if the Aethereal Globuli have more Right motion, than Circular; but yet less than the Globuli of those Rays that produce a Violet Colour, then they yield a blew. And in like manner we are to conclude concerning all other Colours, the variety and sud∣den changes whereof, in Liquid Bodies, is chiefly to be attributed to precipitation.

XX. Sharp and sowre Salts alter the Colours of Bodies. Thus we find, that sharp and acid Salts cause a thousand changes in the Colours of those Liquors with which they are mixed, according to the diffe∣rent Nature of the said Liquors. As for Instance, the Oil of Vitriol makes a black composition, with the infusion of Galls. Common Brimstone dissolved in the Oil of Tartar, becomes of a fair Citron colour. Spirit of Nitre turns the Juice of Herbs as white as Milk. Spirit of Wine turns red, when it hath been digested a while with the Salt of Tartar. The Syrup of Violets turns green, by the mixture of an Alkali; and red, by adding an Acid to it. Acids, or Sowre things destroy blew Colours, and Alkali's do restore them again. The Infusion of the Indian Wood, affords an amber Colour, when mingled with Acids. And the Solu∣tion of Common Brimstone, made by an Alkali, turns white, by adding an Acid to it. All which solely proceeds from those Dispositions which Acid and Alkali Salts produce in the pores of those Liquors to which they are added, which is such, that the Light which penetrates them, re∣ceives all the Modifications that are necessary for the several Colours we find produced by these mixtures.

XXI. Why Pow∣ders are generally white. Most Powders are white, if they be dry and beaten, or ground very small.

Because all those small Bodies into which the Powder is resolved, are Spherical, and like so many Globuli, which reflect all the Rays of Light to one point. And if it happen that the grains of any

Powder do terminate in a Point or Angle; then they do not give a white Colour, but some other. For I have often taken notice, by making use of a good Microscope, that the grains of white Sand are either Round, or approaching to a Conical figure, that is, of a smooth crooked surface; but that the grains of Sand of any Colour, were Rough and furnished with many prominent An∣gles.

XXII. Why Veal, after it is drest by the Fire, looks white. Veal, and Hens or Capons, are of a white Colour, when boiled or roasted, and lose the red Colour they had, when they were yet Raw.

The Reason is, because the Heat hath chas'd away the Moisture that was before in the Veal, as well as in the flesh of Hens, &c. for moisture shut up in the pores of Bodies, is a hindrance to White∣ness, as is evident in all dry things, which by the separation of their moisture become white; be∣cause Moisture doth not permit so much fraction as the Air doth; and yet so much is necessary to cause Reflexion. Hence it is, that a Body that is newly whited with Quick-lime, appears at first to be of a dusky Colour, and afterwards, in success of time, becomes white; because at first it hath much moisture mixed with it; which being exhal'd into the Air, and the Quick-lime dried, yields a white Colour.

XXIII. Cloth ex∣pos••d to the Sun chang∣et•• its Colour. Colours wherewith Cloth or Silks are died, do soon lose their Lustre, by being long exposed to the Sun, and degenerate into a faint Liveless Colour.

This proceeds from a twofold Cause: First, Because many of the particles of Dyed Bodies, which compose the Tincture are exhaled, by the Suns agitation. Secondly, Because many little Bodies, that wander up and down the Air, do thrust themselves into the pores of the Cloth, which by covering its Lustre, efface its former Colour. Wherefore they that deal in Cloaths, have a care that they be not long exposed to the Air, but keep them shut up.

XXIV. The Spirit of Vitriol is hurtful to the Teeth. Some make use of the Spirit of Vitriol, to whiten their Teeth.

But this may well be reckon'd amongst Vulgar Errors, since it is notorious, that the Spirit of Vitriol, in conjunction with an Alkali, doth pro∣duce a yellow: And forasmuch as something of an Alkalous Nature is continually transfused from the Gums and other parts of the Body, it must follow that the Spirit of Vitriol being commixt with such a Salt, must rather make them of a yellow Colour, than any whit conduce to the whitening of them.

XXV. Sugar, and hot Meat, blacken the Teeth. It is observed, that the frequent use of Sugar, and too hot Meat, does blacken the Teeth; because Sugar abounds with Volatile Salt, whose sharp∣pointed particles do Worm-eat the substance of the Teeth, and make great pores in them; wherein the Lucid Rays being suffocated, do produce a black Colour. And the same effect is also caused by hot Meat, the agitation of whose particles do likewise bore many Cavities in the Teeth.

XXVI. What is the cause of those various Colours which appear in a long figur'd Glass ex∣pos'd to the Su••. A Glass Vessel of a long figure, like a Gourd or Cucurbit, being fill'd with water, and expos'd to the Sun-beams, so as that they may enter obliquely through the narrow Mouth, at the upper part of the Vessel; these Sun-beams falling upon a white Paper, or piece of Linnen, will represent various Colours. For the uppermost Colour will be Red, the Lowermost Blew, and the Middlemost Whitish.

The Reason of this appearance, is to be fetch'd from the various Transmission of the Rays: For Experience tells us, that Rays passing obliquely or slantingly through a Hole, must needs be refracted, which Refraction is the cause of all this variety of Colours; forasmuch as the parts of the subtil matter, which we conceive as so many little round Bodies, which role continually through the pores of Earthly Bodies, are variously moved, according to the diversity of the Causes which determine their motion. So as that the Colour, which is represented at the upper part of the Glass, is red; because the Heavenly Globuli, which transmit the Action of the Light, are much more swiftly whirl'd round, than they tend in a Right line. But a blue Colour is represented in the lower part, because the same Globuli are more slowly in their circular motion, than in their direct and strait tendency. Because there is supposed to be a Caus•• which hinders their Circumvolution. But in the Midst a white Colour is seen, because the Heavenly Matter there hath an equal proportion of Circum∣rotation and Procession. For those Bodies are called White, in which the circular motion of the Globuli is equal to their tendency in Right lines. So that the whole difference of Colours doth only depend on the different proportion of these moti∣ons of the Celestial Matter. As hath been more at large declared in my Institution of Philo∣sophy.

XXVII. Of a Wood brought from Mexi∣co, which gives a various colour to Water. ATHANASIUS KIRCHERUS, in his Book of the Art of Light and Darkness, tells us of a sort of Wood growing about Mexico, which the Inhabitants call Coati, which communicates a great variety of Colours to water. For if a Vessel be made of the same, and filled with the clearest water, it after a little time standing turns the water into a blue Colour, which continues in the water as long as it stands in the said Vessel; but being poured out into a Crystalline Bottle, and expos'd to a full Light, it recovers its former per∣spicuity; but if it be brought into the shade, it turns green, and if it be brought into a yet darker shade, it appears red, and that very deep, as ap∣proaching somewhat to blackness.

The water put into a Vessel of this Wood, appears first to be of a blue Colour, because it cannot be question'd, but that the infused Liquor doth enter the pores of the Wood, and fetcheth out many of the small particles thereof; which being mixed with the moisture, are the cause why the Rays of Light are in that manner refracted and reflected, as is necessary for the production of a blue Colour. Again, when this water is pour'd into a Glass Bottle, it appears clear and transparent, because of the full brightness of the Sun, to which it is exposed. For tho' the par∣ticles, which the water had fetched out of the wood, did reflect or refract some of the beams; yet now the prevailing power of the Light doth efface that disposition of Parts, and makes its way without any let or hindrance through the water. Thus we find by daily Experience, that the Sun shining through a Glass Prism, doth not exhibit the Colours of the Rainbow, tho' they be exactly represented on a piece of Paper that receives the said Rays. Then afterwards this Bottle being

removed out of this great and strong Light▪ into a more moderate or shaded Light, is turned into a curious and pleasant Green; because from the brightness of the Sun, which affords abundance of Light, the blue Colour, which the Wooden Vessel did produce, is changed into a green, which is compounded of a blue and a yellow. And last of all, when the Bottle is brought into a more shady place, the water appears of a deep or dark red; because the Redness is weakned by the decrease of the Light, and is changed into a kind of Rusty Colour.

XXVIII. Brazile Wood com∣municates a Red tin∣cture to water. In like manner we know, that Brazile Wood communicates a red Colour to the water wherein it is boiled; which being put into a Drinking glass, if a little distill'd Vinegar be added to it, it imme∣diately is turned into the colour of Straw or Amber▪ From which sudden change of Colours, we have good reason to conclude, that all Colours do arise from the various texture of the parts, and the different reflexion of the Light.

XXIX. Nephritick Wood yeilds a Golden, blue, and yellow Colour. There is also another kind of Wood, which hath taken its name of Nephritick Wood, from the great use it is of in curing the Gravel, the parts whereof being infused in water, and put into a Glass Vial, do after a few hours ••••••ge the water of a Golden Colour if the Vial be placed between the Eye and the Window, but if the Eye be placed between the Window and the Vial, it will appear of a blue Colour. For when the Rays of Light do enter into the Liquor, they become tinged with a yellow Colour; but the same represent a blue, when the Rays reflect from the Vial. And if you pour an Acid Liquor upon it, then the blue Colour will vanish, and the whole Liquor will appear of a Gold Colour.

The Reason of this is probably no other, than that of the foregoing: For it is evident, that this Wood doth consist of Tinging particles, which are easily resolved in the water, and so far seem to be much of the Nature of Salt; which particles entring the pores of the Water do so refract the Rays, that they appear tinged with a Gold Colour. And if you admit the Light of the Sun through some Hole, into a dark Room, and place the Vial full of the Infusion of this Nephritick Wood, partly within the Cone of Light, and partly with∣out it, you will observe a vast variety of Colours, caused by the various degrees of the Refraction of the Light. Now the Reason why, after that the blue Colour hath been extinguisht by an Acid Liquor, it should be restored by the Affusion of Oil of Tartar, or a Sulphureous Salt; and on the contrary why, when the Gold Colour is vanished, it is restored by the addition of an Acid Liquor, is, because Acid Salts do cut and slash the tinging particles into lesser divisions, or at least precipitate them, and so make the Colour to appear more weak and dilute.

Notes

• * 1.1

  Figure 13.