 Section 14 of Micrographia. This is a LibriVox recording. All LibriVox recordings are in the public domain. For more information or to volunteer, please visit LibriVox.org. Micrographia by Robert Hook. Observation 9, Part 2. Let us suppose, therefore, ABC in the second figure to represent a large chemical glass body about two foot long, filled with very fair water, as high as AB, and inclined in a convenient posture with B towards the Sun. Let us further suppose the top of it to be covered with an opacus body, all but the whole AB, through which the sunbeams are suffered to pass into the water, and are thereby refracted to CDEF, against which part, if a paper be expanded on the outside, there will appear all the colors of the rainbow. That is, there will be generated the two principal colors, scarlet and blue, and all the intermediate ones which arise from the composition and dilutings of these two. That is, CDEF shall exhibit a scarlet, which toward D is diluted into a yellow. This is the refraction of the ray IK, which comes from the underside of the sun, and the ray EF shall appear of a deep blue, which is gradually towards E, diluted into a pale-watchet blue. Between D and E the two diluted colors. Blue and yellow are mixed and compounded into a green, and this I imagine to be the reason why green is so acceptable a color to the eye, and that either of the two extremes are, if intense, rather a little offensive, namely the being placed in the middle between the two extremes and compounded out of both these, diluted also, or somewhat qualified, for the composition arising from the mixture of the two extremes undiluted makes a purple, which though it be a lovely color and pretty acceptable to the eye, it is yet nothing comparable to the ravishing pleasure with which a curious and well-tempered green affects the eye. If removing the paper, the eye be placed against CD, it will perceive the lower side of the sun, or a candle at night, which is much better because it offends not the eye and is more easily manageable, to be of a deep red, and if against EF, it will perceive the upper part of the luminous body to be of a deep blue, and these colors will appear deeper and deeper, according as the rays from the luminous body fall more obliquely on the surface of the water, and thereby suffer a greater refraction, and the more distinct the further CDEF is removed from the projecting hole. So that, upon the whole, we shall find that the reason of the phenomena seems to depend upon the obliquity of the orbicular pulse, to the lines of radiation, and in particular that the ray CD, which constitutes the scarlet, has its inner parts, namely those which are next to the middle of the luminous body, precedent to the outermost, which are contiguous to the dark and unradiating sky. And that the ray EF, which gives a blue, has its outward part, namely that which is contiguous to the dark side, precedent to the pulse from the innermost, which borders on the bright area of the luminous body. We may observe further that the cause of the diluting of the colors towards the middle, proceeds partly from the wideness of the hole through which the rays pass, whereby the rays from several parts of the luminous body fall upon many of the same parts between C and F, as is more manifest by the figure, and partly also from the nature of the refraction itself, for the vividness or strength of the two terminating colors arising chiefly as we have seen from the very great difference that is betwixt the outsides of these oblique undulations and the dark rays circumambient, and that disparity betwixt the approximate rays decaying gradually. The further inward toward the middle of the luminous body they are removed, the more must the color approach to a white or an undisturbed light. Upon the calculation of the refraction and reflection from a ball of water or glass, we have much the same phenomena, namely an obliquity of the undulation in the same manner as we have found it here, which, because it is very much to our present purpose and affords such an instantia crucis, as no one that I know has hitherto taken notice of, I shall further examine. For it does very plainly and positively distinguish and show which of the two hypotheses, either the Cartesian or this, is to be followed by affording a generation of all the colors in the rainbow where, according to the Cartesian principles, there should be none at all generated, and secondly by affording an instance that does more closely confine the cause of these phenomena of colors to this present hypothesis. And first, for the Cartesian, we have this to object against it, that whereas he says, Meteorum chapter 8, section 5, said Giudicabem Unicam, Refractione Saliset, et Minimu Rikiri, et quidum talum ut edjus effektus alia contraria refractione, non destruatur, non experientia doset sei superficies, n m and n p, nempe refrigerentis, parallele forend, radios tetundem por alterum iterum erectus quantum per unum frangerentur, nulos colores depicturos. This principle of his holds true indeed in a prism where the refracting surfaces are plain, but it is contradicted by the ball or cylinder, whether of water or glass, where the refracting surfaces are orbicular or cylindrical. For if we examine the passage of any globule or ray of the primary iris, we shall find it to pass out of the ball or cylinder again, with the same inclination and refraction that it entered in with all, and that that last refraction, by means of the intermediate reflection, shall be the same as if without any reflection at all the ray had been twice refracted by two parallel surfaces. And that this is true not only in one, but in every ray that goes to the constitution of the primary iris, nay in every ray that suffers only two refractions and one reflection by the surface of the round body, we shall presently see most evident if we repeat the Cartesian scheme mentioned in the tenth section of the eighth chapter of his meteors, where EFKNP in the third figure is one of the rays of the primary iris twice refracted at F and N, and once reflected at K by the surface of the water ball. For first it is evident that KF and KN are equal, because KN being the reflected part of KF, they have both the same inclination on the surface K, that is the angles FKT and NKV made by the two rays and the tangent of K are equal, which is evident by the laws of reflection. Once it will follow also that KN has the same inclination on the surface N, or the tangent of it XN, that the ray KF has to the surface F, or the tangent of it FY, once it must necessarily follow that the refractions at F and N are equal, that is, KFE and KNP are equal. Now that the surface N is by the reflection at K made parallel to the surface at F is evident from the principles of reflection. For a reflection being nothing but an inverting of the rays, if we re-invert the ray KNP and make the same inclinations below the line TKV that it has above, it will be most evident that KH the inverse of KN will be the continuation of the line FK, and that LHI the inverse of OX is parallel to FY. And HM the inverse of NP is parallel to EF, for the angle KHI is equal to KNO, which is equal to KFY, and the angle KHM is equal to KNP, which is equal to KFE, which was to be proved. So that according to the above mentioned Cartesian principles, there should be generated no color at all in a ball of water or glass by two refractions and one reflection, which does hold most true indeed if the surfaces be plain, as may be experimented with any kind of prism where the two refracting surfaces are equally inclined to the reflecting. But in this, the phenomena are quite otherwise. The cause therefore of the generation of color must not be what Descartes assigns, namely a certain rotation of the globuli etheriae, which are the particles which he supposes to constitute the pollucid medium, but somewhat else perhaps what we have lately supposed and shall by and by further prosecute and explain. But first I shall crave leave to propound some other difficulties of his, notwithstanding exceedingly ingenious hypothesis, which I plainly confess to me seem such, and those are, first, that if light be, as is affirmed, diopteryx chapter one section eight, not so properly a motion as an action or propension to motion, I cannot conceive how the eye can come to be sensible of the verticity of a globule, which is generated in a drop of rain, perhaps a mile off from it. For that globule is not carried to the eye according to his formerly recited principle, and if not so, I cannot conceive how it can communicate its rotation or circular motion to the line of the globules between the drop and the eye. It cannot be by means of everyones turning the next before him, for if so, then only all the globules that are in the odd places must be turned the same way with the first, namely the three, five, seven, nine, eleven, etc. But all the globules inter- posited between them in the even places, namely the two, four, six, eight, ten, etc., must be the quite contrary, when, according to the Cartesian hypothesis, there must be no distinct color generated but a confusion. Next, since the Cartesian globuli are supposed, Principiorum philosophy part three, section eighty-six, to be each of them continually in motion about their centers, I cannot conceive how the eye is able to distinguish this new generated motion from their former inherent one, if I may so call that other wherewith they are moved or terminated from some other cause than refraction. And thirdly, I cannot conceive how these motions should not happen sometimes to oppose each other, and then, instead of a rotation, there would be nothing but a direct motion generated, and consequently no color. And fourthly, I cannot conceive how by the Cartesian hypothesis it is possible to give any plausible reason of the nature of the colors generated in the thin laminy of these are microscopial observations. For in many of these, the refracting and reflecting surfaces are parallel to each other, and consequently no rotation can be generated, nor is there any necessity of a shadow or termination of the bright rays, such as is supposed, chapter eight, section five, at Preteria observavi umbram quoque, outlimitationum luminus racchiri, and chapter eight, section nine, to be necessary to the generation of any distinct colors. Besides that, here is oftentimes one color generated without any of the other appendent ones, which cannot be by the Cartesian hypothesis. There must be, therefore, some other propriety of refraction that causes color, and upon the examination of the thing, I cannot conceive any one more general, inseparable, and sufficient than that which I have before assigned. That we may therefore see how exactly our hypothesis agrees also with the phenomena of the refracting round body, whether globe or cylinder, we shall next subjoin our calculation or examine of it. And to this end, we will calculate any two rays, as, for instance, let EF be a ray cutting the radius CD, divided into twenty parts, in G, sixteen parts distant from C, and lowercase EF another ray, which cuts the same radius in lowercase G, seventeen parts distant. These will be refracted to K and lowercase K, and from thence reflected to N and lowercase N, and from thence refracted toward P and lowercase P. Therefore, the arch F lowercase F will be five degrees five minutes. The arch FK one hundred six degrees thirty minutes. The arch lowercase F lowercase K one hundred one degrees two minutes. The line FG six thousand and lowercase FG five thousand two hundred sixty seven. Therefore, lowercase HF seven hundred thirty three. Therefore, F lowercase C nine hundred eighty almost. The line FK sixteen thousand twenty four, and lowercase FK fifteen thousand four hundred thirty six. Therefore, N lowercase D one hundred ninety six, and lowercase NO one hundred forty seven almost. The line N lowercase N one thousand nineteen. The arch N lowercase N five degrees fifty one minutes. Therefore, the angle N lowercase N lowercase O is thirty four degrees forty three minutes. Therefore, the angle N lowercase O lowercase N is one hundred thirty nine degrees fifty six minutes, which is almost fifty degrees more than a right angle. It is evident therefore by this hypothesis that at the same time that lowercase EF touches lowercase F, EF is arrived at lowercase C. And by that time, lowercase EFKN is got to lowercase N. EFKN is got to lowercase D. And when it touches N, the pulse of the other ray is got to lowercase O and no farther, which is very short of the place it should have arrived to to make the ray lowercase NP to cut the orbicular pulse and lowercase O at right angles. Therefore, the angle N lowercase OP is an acute angle, but the quite contrary of this will happen if seventeen and eighteen be calculated instead of sixteen and seventeen, both which does most exactly agree with the phenomena. For if the sun or a candle, which is better, be placed about E lowercase E and the eye about P lowercase P, the rays EF lowercase EF at sixteen and seventeen will paint the side of the luminous object toward lowercase NP blue and towards uppercase NP red. But the quite contrary will happen when EF is seventeen and lowercase EF eighteen, for then towards NP shall be a blue and towards lowercase NP a red exactly according to the calculation. And there appears the blue of the rainbow where the two blue sides of the two images unite, and there the red where the two red sides unite, that is where the two images are just disappearing, which is when the rays EF and NP produced till they meet, like an angle of about forty one and a half. The like union is there of the two images in the production of the secondary iris, and the same causes as upon calculation may appear, only with this difference, that it is somewhat more faint by reason of the duplicate reflection, which does always weaken the impulse the oftener it is repeated. Now, though the second refraction made it N lowercase N be convenient, that is, do make the rays glance the more, yet is it not altogether requisite, for it is plain from the calculation that the pulse DN is sufficiently oblique to the rays KN and lowercase KN, as well as the pulse FC is oblique to the rays FK and lowercase FK. And therefore, if a piece of very fine paper be held close against NN, and the eye look on it either through the ball as from D, or from the other side as from B, there shall appear a rainbow or colored line painted on it with the part toward X appearing red, towards O blue. The same also shall happen if the paper be placed about KK, for towards T shall appear a red and towards V a blue, which does exactly agree with this my hypothesis, as upon the calculation of the progress of the pulse will most easily appear. Nor do these two observations of the colors appearing to the eye about P differing from what they appear on the paper at N contradict each other, but rather confirm and exactly agree with one another, as will be evident to him that examines the reasons set down by the ingenious Descartes in the 12th section of the 8th chapter of his meteors, where he gives the true reason why the colors appear of quite contrary order to the eye to what they appeared on the paper if the eye be placed instead of the paper, and as in the prism so also in the water drop or globe the phenomena and the reason are much the same. Having therefore shown that there is such a propriety in the prism and water globule whereby the pulses made oblique to the progressive and that so much the more by how much greater the refraction is, I shall in the next place consider how this conduces to the production of colors and what kind of impression it makes upon the bottom of the eye, and to this end it will be requisite to examine this hypothesis a little more particularly. First therefore if we consider the manner of the progress of the pulse, it will seem rational to conclude that that part or end of the pulse which precedes the other must necessarily be somewhat more obtunded or impeded by the resistance of the transparent medium than the other part or end of it which is subsequent whose ray is as it were prepared by the other, especially if the adjacent medium be not in the same manner enlightened or agitated. And therefore in the fourth figure of the sixth iconism the ray AAAHB will have its side HH more deadened by the resistance of the dark or quiet medium PPP, once there will be a kind of deadness super induced on the side HHH which will continually decrease from B and strike deeper and deeper into the ray by the line BR, when all the parts of the triangle RBHO will be of a dead blue color and so much the deeper by how much the nearer they lie to the line BHH which is most deaded or impeded and so much more dilute by how much the nearer it approaches the line BR. Next on the other side of the ray AAN, the end A of the pulse AH will be promoted or made stronger having its passage already prepared as twer by the other parts proceeding and so its impression will be stronger and because of its obliquity to the ray there will be propagated a kind of faint motion into QQ the adjacent dark or quiet medium which faint motion will spread further and further into QQ as the ray is propagated further and further from A, namely as far as the line MA, once all the triangle MAN will be tinged with a red and that red will be the deeper the nearer it approaches the line MA and the paler or yellower the nearer it is the line NA and if the ray be continued so that the lines AN and BR which are the bounds of the red and blue diluted do meet and cross each other there will be beyond that intersection generated all kinds of greens. Now these being the proprieties of every single refracted ray of light it will be easy enough to consider what must be the result of very many such rays collateral as if we suppose infinite such rays interjacent between AKSB and ANOB which are the terminating for in this case the ray AKSB will have its red triangle entire as lying next to the dark or quiet medium but the other side of it BS will have no blue because the medium adjacent to it SBO is moved or enlightened and consequently that light does destroy the color so likewise will the ray ANOB lose its red because the adjacent medium is moved or enlightened but the other side of the ray that is adjacent to the dark namely AHO will preserve its blue entire and these rays must be so far produced as till AN and BR cut each other before there will be any green produced from these proprieties well considered may be deduced to the reasons of all the phenomena of the prism and of the globules or drops of water which conduced to the production of the rainbow next for the impression they make on the retina we will further examine this hypothesis suppose therefore ABCDEF in the fifth figure to represent the ball of the eye on the cornea of which ABC to raise GACH and KCAI which are the terminating rays of a luminous body falling are by the refraction thereof collected or converged into two points at the bottom of the eye now because these terminating rays and all the intermediate ones which come from any part of the luminous body are supposed by some sufficient refraction before they enter the eye to have their pulses made oblique to their progression and consequently each rate to have potentially super induced two properties or colors that is a red on one side and a blue on the other not withstanding are never fully manifest but when this or that ray has one or the other side of it bordering on a dark or unmoved medium therefore as soon as these rays are entered into the eye and so have one side of each of them bordering on a dark part of the humors of the eye they will each of them equally exhibit some color therefore ADC in the production of GACH will exhibit a blue because the side CD is adjacent to the dark medium CQDC but nothing of a red because its side AD is adjacent to the enlightened medium ADFA and all the rays that from the points of the luminous body are collected on the parts of the retina between D and F shall have their blue so much the more diluted by how much the farther these points of collection are distant from D towards F and the ray AFC the production of KCAI will exhibit a red because the side AF is adjacent to the dark or quiet medium of the eye APFA but nothing of the blue because its side CF is adjacent to the enlightened medium CFDC and all the rays from the intermediate parts of the luminous body that are collected between F and D shall have their red so much the more diluted by how much the farther they are distant from F towards D now because by the refraction in the cornea and some other parts of the eye the sides of each ray which before were almost parallel are made to converge and meet in a point at the bottom of the eye therefore that side of the pulse which preceded before these refractions shall first touch the retina and the other side last and therefore according as this or that side or end of the pulse shall be impeded accordingly will the impressions on the retina be varied therefore the ray GACH refracted by the cornea to D there shall be on that point a stroke or impression confused whose weakest end namely that by the line CD shall proceed and the stronger namely that by the line AD shall follow and by the ray KCAI refracted to F there shall be on that part a confused stroke or impression whose strongest part namely that by the line CF shall proceed and those weakest or impeded namely that by the line AF shall follow and all the intermediate points between F and D shall receive impressions from the converged rays so much the more like the impressions on F and D by how much the nearer they approach that or this from the consideration of the proprieties of which impressions we may collect these short definitions of colors that blue is an impression on the retina of an oblique and confused pulse of light whose weakest part proceeds and whose strongest follows and that red is an impression on the retina of an oblique and confused pulse of light whose strongest part proceeds and whose weakest follows which proprieties as they have been already manifested in the prism and falling drops of rain to be the causes of the colors where generated may be easily found to be the efficiency also of the colors appearing in thin laminated transparent bodies for the explication of which all this has been promised and that this is so a little closer examination of the phenomena and the figure of the body by this hypothesis will make evident. For first as we have already observed the laminated body must be of a determinate thickness that is it must not be thinner than such a determinate quantity for I have always observed that near the edges of those which are exceeding thin the colors disappear and the part grows white nor must it be thicker than another determinate quantity for I have likewise observed that beyond such a thickness no colors appeared but the plate looked white between which two determinate thicknesses were all the colored rings of which in some substances I have found ten or twelve in others not have so many which I suppose depends much upon the transparency of the laminated body. Thus through the consecutions are the same in the scum or the skin on the top of metals. Yet in those consecutions in the same color is not so often repeated as the consecutions in thin glass or in soap water or any other transparent and glutinous liquor. For in these I have observed red, yellow, green, blue, purple, red, yellow, green, blue, purple, red, yellow, green, blue, purple, red, yellow, etc. to succeed each other ten or twelve times but in the other more opacious bodies the consecutions will not be half so many. And therefore secondly the laminated body must be transparent and this I argue from this that I have not been able to produce any color at all with an opacious body though never so thin. And this I have often tried by pressing small globule of mercury between two smooth plates of glass whereby I have reduced that body to a much greater thinness than was requisite to exhibit the colors with a transparent body. Thirdly there must be a considerable reflecting body adjacent to the under or further side of the lamina or plate. For this I always found that the greater that reflection was the more vivid were the appearing colors. From which observations is most evident that the reflection from the under or further side of the body is the principal cause of the production of these colors, which that it is so and how it conduces to that effect I shall further explain in the following figure, which is here described of a very great thickness as if it had been viewed through the microscope. And is indeed much thicker than any microscope I have yet used has been able to show me those colored plates of glass or Muscovy glass which I have not without much trouble viewed with it. For though I have endeavored to magnify them as much as the glasses were capable of, yet are they so exceeding thin that I have not hitherto been able positively to determine their thickness. This figure therefore I here represent is wholly hypothetical. Let ABCD HFE in the sixth figure be a frustum of Muscovy glass thinner toward the end AE and thicker towards DF. Let us first suppose the ray AGHB coming from the sun or some remote luminous object to fall obliquely on the thinner plate BAE. Part therefore is reflected back by CGHD, the first superficies, whereby the perpendicular pulse AB is after reflection propagated by CDCD, equally remote from each other with ABAB, so that AG plus GC or BH plus HD are either of them equal to AA as is also CC. But the body BAE being transparent, a part of the light of this ray is refracted in the surface AB and propagated by GIKH to the surface EF, once it is reflected and refracted again by the surface AB, so that after the two refractions and one reflection there is propagated a kind of fainter ray EMNF, whose pulse is not only weaker by reason of the two refractions in the surface AB, but by reason of the time spent in passing and repassing between the two surfaces AB and EF. EF, which is this fainter or weaker pulse, comes behind the pulse CD, so that hereby the surfaces AB and EF being so near together, so that the eye cannot discriminate them from one. This confused or duplicated pulse, whose strongest part precedes and whose weakest follows, does produce on the retina, or the optic nerve that covers the bottom of the eye, the sensation of a yellow. And secondly, this yellow will appear so much the deeper by how much the further back towards the middle between CD and CD, the spurious pulse EF is removed. As in two, where the surface BC being further removed from EF, the weaker pulse EF will be nearer to the middle and will make an impression on the eye of a red. But thirdly, if the two reflecting surfaces be yet further removed asunder, as in three CD and EF are, then will the weaker pulse be so far behind that it will be more than half the distance between CD and CD? And in this case, it will rather seem to precede the following stronger pulse than to follow the preceding one, and consequently a blue will be generated. And when the weaker pulse is just in the middle between two strong ones, then is a deep and lovely purple generated, but when the weaker pulse EF is very near to CD, then there is generated a green, which will be bluer or yellower according as the approximate weak pulse does precede or follow the stronger. Now fourthly, if the thicker plate chance to be cleft into two thinner plates, as CDFE is divided into two plates by the surface GH, then from the composition arising from the three reflections in the surfaces CD, GH, and EF, there will be generated several compounded or mixed colors, which will be very differing according as the proportion between the thicknesses of those two divided plates CDHG and GHFE are varied. And fifthly, if these surfaces CD and FE are further removed asunder, the weaker pulse will yet lag behind much further, and not only be coincident with the second CD, but lag behind that also, and that so much the more by how much the thicker the plate be, so that by degrees it will be coincident with the third CD backward also, and by degrees as the plate grows thicker with a fourth, and so onward to a fifth, sixth, seventh, or eighth, so that if there be a thin transparent body, that from the greatest thinness requisite to produce colors, does, in the manner of a wedge, by degrees grow to the greatest thickness that a plate can be of to exhibit a color by the reflection of light from such a body, there shall be generated several consecutions of colors, whose order from the thin end towards the thick shall be yellow, red, purple, blue, green, yellow, red, purple, blue, green, yellow, red, purple, blue, green, yellow, etc. And these so often repeated, as the weaker pulse does lose paces with its primary or first pulse, and its coincident with a second, third, fourth, fifth, sixth, etc., pulse behind the first. And this, as it is coincident or follows from the first hypothesis I took of colors, so upon experiment have I found it in multitudes of instances that seem to prove it. One thing which seems of the greatest concern in this hypothesis is to determine the greatest or least thicknesses requisite for these effects, which, though I have not been wanting in attempting, yet so exceeding thin are these colored plates, and so imperfect our microscope, that I have not been hitherto successful, though if my endeavors shall answer my expectations, I shall hope to gratify the curious reader with some things more removed beyond our reach hither too. Thus have I, with as much brevity as I was able, endeavored to explicate, hypothetically at least, the causes of the phenomena I formerly recited on the consideration of which I have been the more particular. First, because I think these I have newly given are capable of explicating all the phenomena of colors, not only of those appearing in the prism, water drop or rainbow, and in laminated or plated bodies, but of all that are in the world, whether they be fluid or solid bodies, whether in thick or thin, whether transparent or seemingly opatious, as I shall in the next observation further endeavored to show. And secondly, because this being one of the two ornaments of all bodies discoverable by the sight, whether looked on with or without a microscope, it seemed to deserve, somewhere in this tract, which contains a description of the figure and color of some minute bodies, to be somewhat the more intimately inquired into. End of Section 14. Made it probable that there are but two colors, and shown that the phantasm of color is caused by the sensation of the oblique, or uneven pulse of light, which is capable of no more varieties than two, that arise from the two sides of the oblique pulse, though each of those be capable of infinite gradations or degrees, each of them beginning from white and ending the one in the deepest scarlet or yellow, the other in the deepest blue, I shall in this section set down some observations which I have made of other colors, such as medalline powders, tinging or colored bodies, and several kinds of tinctures or tinged liqueurs, all which, together with those I treated of in the former observation, will, I suppose, comprise the several subjects in which color is observed to be inherent, and the several manners by which it inheres, or is apparent in them. And here I shall endeavor to show by what composition all kind of compound colors are made, and how there is no color in the world but may be made from the various degrees of these two colors, together with the intermixtures of black and white. And this being so, I shall in on show, it seems an evident argument to me that all colors whatsoever, whether in fluid or solid, whether in very transparent or seemingly opatious, have the same efficient cause. To it, some kind of refraction whereby the rays that proceed from such bodies have their pulse obligated or confused in the manner I explicated in the former section. That is, a red is caused by a duplicated or confused pulse whose strongest pulse precedes, and a weaker follows, and a blue is caused by a confused pulse where the weaker pulse precedes, and the stronger follows. And according, as these are more or less, or variously mixed and compounded, so are the sensations, and consequently the phantasms of colors diversified. To proceed, therefore, I suppose that all transparent colored bodies, whether fluid or solid, do consist at least of two parts, or two kinds of substances, the one of a substance of a somewhat differing refraction from the other, that one of these substances, which may be called the tinging substance, does consist of distinct parts, or particles of a determinate bigness, which are disseminated or dispersed all over the other. That these particles, if the body be equally and uniformly colored, are evenly ranged and dispersed over the other contiguous body, that where the body's deepest tinged, there these particles are ranged thickest, and where it is but faintly tinged, they are ranged much thinner, but uniformly, that by the mixture of another body that unites with either of these, which has a differing refraction from either of the other, quite differing effects will be produced. That is, the consequences of the confused pulses will be much of another kind, and consequently produce other sensations and phantasms of color, and from a red may turn to a blue, or from a blue to a red, etc. Now that this may be better understood, I shall endeavor to explain my meaning a little more sensible by a scheme. Suppose we therefore, in the seventh figure of the sixth scheme, that A B C D represents a vessel holding a tinged liquor. Let the group of eyes, etc., be the clear liquor, and let the tinging body that is mixed with it be double E, etc., double F, etc., double G, etc., double H, etc., whose particles, whether round or some other determinate figure is little to our purpose, are first of a determinate and equal bulk. Next they are ranged into the forms of quinconks, or equal lateral triangular order, which that probably they are so, and why they are so I shall elsewhere endeavor to show. Thirdly, they are of such a nature, as does either more easily or more difficultly transmit the rays of light than the liquor. If more easily, a blue is generated, and if more difficultly, a red or scarlet. And first, let us suppose the tinging particles to be of a substance that does more impede the rays of light. We shall find that the pulse or wave of light moved from AD to BC will proceed on through the containing medium by the pulses or waves double K, double L, double M, double N, double O. But because several of these rays that go to the constitution of these pulses will be slugged or stopped by the tinging particles, E, F, G, and H, therefore there shall be secondary and weak pulse that shall follow the ray, namely Pp, which will be the weaker. First, because it has suffered many refractions in the impeding body. Next, for that the rays will be a little dispersed or confused by reason of the refraction in each of the particles, whether round or angular, and this will be more evident if we a little more closely examine any one particular tinging globule. Suppose we therefore, AB in the eighth figure of the sixth scheme, to represent a tinging globule or particle which has a greater refraction than the liquor in which it is contained. Let CD be a part of the pulse of light which is propagated through the containing medium. This pulse will be a little stopped or impeded by the globule and so by that time the pulse is passed to E, F, that part of it which has been impeded by passing through the globule. We'll get but to L, M, and so that pulse which has been propagated through the globule to it L, M, N, O, P, Q will always come behind the pulses E, F, G, H, I, K, etc. Next, by reason of the greater impediment in AB and its globular figure, the rays that pass through it will be dispersed and very much scattered. Once C, A, and D, B, which before went direct and parallel will after the refraction in AB diverge and spread by A, P, and B, Q. So that as the rays do meet with more and more of these tinging particles in their way by so much the more will the pulse of light further lag behind the clearer pulse or that which has fewer refractions and thence the deeper will the color B and the fainter the light that is projected through it for not only many rays are reflected from the surfaces of A and B but those rays that get through it are very much disordered. By this hypothesis, there is no one experiment of color that I have yet met with, but may be, I conceive, very rationably solved, and perhaps had I time to examine several particulars requisite to the demonstration of it I might prove it more than probable for all the experiments about the changes in mixing of colors related in the treatise of colors published by the incomparable Mr. Boyle and multitudes of others which I have observed do so easily and naturally flow from those principles that I am very apt to think it probable that they own their production to no other secondary cause as to instance in two or three experiments. In the twentieth experiment, this noble author has shown that the deep bluish purple color of violets may be turned into a green by alkalazite salts and to a red by acid. That is, a purple consists of two colors, a deep red and a deep blue. When the blue is diluted or altered or destroyed by acid salts the red becomes predominant, but when the red is diluted by alkalazite and the blue heightened, there is generated a green. Four of a red diluted is made a yellow and yellow and blue make green. Now, because the spurious pulses which cause a red and a blue do the one follow the clear pulse and the other preceded it usually follows that those saline refracting bodies which do dilate the color of the one do deepen that of the other and this will be made manifest by almost all kinds of purples and many sorts of greens. Both these colors consisting of mixed colors for if we suppose A and A in the ninth figure to represent the two pulses of clear light which follow each other at a convenient distance A A each of which has a spurious pulse preceding it as B B which makes a blue and another following it as C C which makes a red the one caused by tinging particles that have a greater refraction the other by others that have a less refracting quality than the liquor or menstruum in which these are dissolved whatsoever liquor does not alter the refraction of the one without altering that of the other part of the tinged liquor must needs very much alter the color of the liquor for if the refraction of the dissolvent be increased and the refraction of the tinging particles not altered then will the preceding spurious pulse be shortened or stopped and not outrun the clear pulse so much so that B B will become E E and the blue be diluted whereas the other spurious pulse which follows will be made to lag much more and be further behind A A than before and C C will become F F and so the yellow or red will be heightened a saline liquor therefore mixed with another tinged liquor may alter the color of it several ways either by altering the refraction of the liquor in which the color swims or secondly by varying the refraction of the colored particles by uniting more intimately either with some particular corpuscles of the tinging body or with all of them according as it has a congruity to some more especially or to all alike or thirdly by uniting and interweaving itself with some other body that is already joined with the tinging particles with which substance it may have a congruity though it have very little with the particles themselves or fourthly it may alter the color of a tinged liquor by disjoining certain particles which were before united with the tinging particles which though they were somewhat congruous to these particles have yet a greater congruity with the newly infused saline menstruum it may likewise alter the color by further dissolving the tinging substance into smaller and smaller particles and so diluting the color or by uniting several particles together as in precipitations and so deepening it and some such other ways which many experiments and comparisons of differing trials together might easily inform one of From these principles applied may be made out all the varieties of colors observable either in liquors or any other tinged bodies with great ease and I hope intelligible enough there being nothing in the notion of color or in the supposed production but is very conceivable and may be possible The greatest difficulty that I find against this hypothesis is that there seems to be more distinct colors than two that is than yellow and blue this objection is grounded on this reason that there are several reds which diluted make not a saffron or pale yellow and therefore red or scarlet seems to be a third color distinct from a deep degree of yellow to which I answer that saffron affords us a deep scarlet tincture which may be diluted into as pale a yellow as any either by making a weak solution of the saffron by infusing a small parcel of it into a great quantity of liquor as in spirit of wine or else by looking through a very thin quantity of the tincture and which may be heightened into the loveliest scarlet by looking through a very thick body of this tincture or through a thinner parcel of it which is highly impregnated with the tinging body by having had a greater quantity of the saffron dissolved in a smaller parcel of the liquor now though there may be some particles of other tinging bodies that give a lovely scarlet also which though diluted never so much with liquor or looked on through never so thin a parcel of tinged liquor will not yet afford a pale yellow but only a kind of faint red yet this is no argument but that those tinged particles may have in them the faintest degree of yellow though we may be unable to make them exhibit it for that power of being diluted depending upon the divisibility of the tinged body if I am unable to make the tinging particles so thin as to exhibit that color it does not therefore follow that the thing is impossible to be done now the tinging particles of some bodies are of such a nature that unless there be found some way of comminuting them into less bulks than the liquor does dissolve them into all the rays that pass through them must necessarily receive a tincture so deep as their appropriate refractions and bulks compared with the proprieties of the dissolving liquor must necessarily dispose them to impress which may perhaps be a pretty deep yellow or pale red and that this is not gratis dictum I shall add one instance of this kind wherein the thing is most manifest if you take blue smalt you shall find that to afford the deepest blue which Cateris Paribus has the greatest particles or sands and if you further divide or grind those particles on a grindstone or periphery stone you may by comminuting the sands of it dilute the blue into as pale as one as you please which you cannot do by laying the color thin for where so ever any single particle is it exhibits as deep a blue as the whole mass now there are other blues which though never so much ground will not be diluted by grinding because consisting of very small particles very deeply tinged they cannot by grinding be actually separated into smaller particles than the operation of the fire or some other dissolving menstruum reduced them to already thus all kind of metalene colors whether precipitated, sublime, calcined or otherwise prepared are hardly changed by grinding as ultramarine is not more diluted nor is vermilion or red lead made of a more faint color by grinding for the smallest particles of these which I have viewed with my greatest magnifying glass if they be well enlightened appear very deeply tinged with their peculiar colors nor though have I magnified and enlightened the particles exceedingly could I in many of them perceive them to be transparent or to be whole particles but the smallest specks that I could find among the well ground vermilion and red lead seem to be a red mass compounded of a multitude of less and less motes which sticking together composed a bulk not one thousand thousandth part of the smallest viable sand or moat and this I find generally in most metalene colors that though they consist of parts so exceedingly small yet are they very deeply tinged they being so ponderous and having such a multitude of terrestrial particles thronged into a little room so that is difficult to find any particle transparent or resembling a precious stone though not impossible for I have observed divers shining and resplendent colors into mixed with the particles of cinnabar both natural and artificial before it have been ground and broken or flawed into vermilion as I have also in orpiment red lead and bice which makes me suppose that those metalene colors are by grinding not only broken and separated actually into smaller pieces but that they are also flawed and bruised whence they for the most part become opacious like flawed crystal or glass etc but for smalls and verdiatures I have been able with a microscope to perceive their particles very many of them transparent now that the others also may be transparent though they do not appear so to the microscope may be made probable by this experiment that if you take amel that is almost opacious and grind it very well on a porphyry or serpentine the small particles will by reason of their flaws appear perfectly opacious and that is the flaws that produce this opaciousness may be argued from this that particles of the same amel much thicker if unflawed will appear somewhat transparent even to the eye and from this also that the most transparent and clear crystal if heated in the fire and then suddenly quenched so that it be all over flawed will appear opacious and white and that the particles of metalene colors are transparent may be argued yet further from this that the crystals or vitriols of all metals are transparent which since they consist of metalene as well as saline particles those metalene ones must be transparent which is yet further confirmed from this that they have for the most part appropriate colors so the vitriol of gold is yellow of copper blue and sometimes green of iron green of tin and lead a pale white of silver a pale blue etc. and next the solution of all metals into menstruums are much the same with the vitriols or crystals it seems therefore very probable that those colors which are made by the precipitation of those particles out of the menstruums by transparent precipitating liquors should be transparent also thus gold precipitates with oil of tartar or spirit of urine into a brown yellow copper with spirit of urine into a mucus blue which retains its transparency a solution of sublimate as the same illustrious author I lately mentioned shows in his number 40 experiment precipitates with oil of tartar per deliquium into an orange colored precipitate nor is it less probable that the calcination of those vitriols by the fire should have their particles transparent thus saccharum Saturny or the vitriol of lead by calcination becomes a deep orange colored minimum which is a kind of precipitation of some salt which proceeds from the fire common vitriol calcine yields a deep brown red etc. a third argument that the particles of metals are transparent is that being calcined and melted with glass they tinged the glass with transparent colors thus the calcs of silver tinges the glass on which it is annealed with a lovely yellow or gold color etc. and that the parts of metals are transparent may be farther argued from the transparency of leaf gold which held against the light both to the naked eye and the microscope exhibits a deep green and though I have never seen the other metals laminated so thin that I was able to perceive them transparent yet for copper or brass if we had the same convenience for laminating them as we have for gold we might perhaps through such plates or leaves find very differing degrees of blue or green for it seems very probable that those rays that were bound from them tinged with the deep yellow or pale red as from copper or with a pale yellow as from brass have passed through them for I cannot conceive how by reflection alone those rays can receive a tincture taking any hypothesis extant so that we see there may be a sufficient reason be drawn from these instances why those colors which we are unable to dilute to the pale yellow or blue or green are not therefore to be concluded not to be a deeper degree of them for supposing we had a great company of small globular essence bottles or round glass bubbles about the bigness of a walnut filled each of them with a very deep mixture of saffron and that every one of them did appear of a deep scarlet color and all of them together did exhibit at a distance a deep dyed scarlet body it does not follow because after we have come nearer to this congeries or mass and divided it into its parts and examining each of its parts severally or apart we find them to have much the same color as the whole mattes it does not, I say, therefore follow that if we could break those globules smaller or any other ways come to see a smaller or thinner parcel of the tinged liquor that filled those bubbles that that tinged liquor must always appear red or of a scarlet hue since if experiment be made the quite contrary will ensue for it is capable of being diluted into the palest yellow now that I might avoid all the objections of this kind by exhibiting an experiment that might by ocular proof convince those whom other reasons would not prevail with I provided me a prismatical glass made hollow just in the form of a wedge such as is represented in the tenth figure of the sixth scheme the two parallelogram sides A B C D A B E F which met at a point were made of the clearest looking glass plates well ground and polished that I could get these were joined with hard cement to the triangular sides B C E A D F which were of wood the parallelogram base B C E F likewise was of wood joined on to the rest with hard cement and the whole prismatical box was exactly stopped everywhere but only a little hole near the base was left whereby the vessel could be filled with any liquor or emptied again at pleasure one of these boxes for I had two of them I filled with a pretty deep tincture of aloes drawn only with fair water and then stopped the hole with a piece of wax then by holding this wedge against the light and looking through it it was obvious enough to see the tincture of the liquor near the edge of the wedge where it was but very thin to be a pale but well colored yellow and further and further from the edge as the liquor grew thicker and thicker this tincture appeared deeper and deeper near the blunt end which was 7 inches from the edge and 3 inches and a half thick it was of a deep and well colored red now the clearer and pure this tincture be the more lovely will the deep scarlet be and the fowler the tincture be the more dirty will the red appear so that some dirty tinctures have afforded their deepest red much of the color of burnt ochre or Spanish brown others as lovely a color as vermilion and some much brighter but several others according as the tinctures were worse or more foul exhibited various kinds of red very differing degrees the other of these wedges I filled with a most lovely tincture of copper drawn from the fillings of it with spirit of urine and this wedge held as the former against the light afforded all manner of blues from the faintest to the deepest so that I was in good hope by these two to have produced all the varieties of colors imaginable for I thought by these means to have been able by placing the two parallelograms sides together and the edges contrary ways to have so moved them to and fro one by another as by looking through them in several places and through several thicknesses I should have compounded and consequently have seen all those colors which by other like compositions of colors would have ensued but instead of meeting with what I looked for I met with somewhat more admirable that was that I found myself utterly unable to see through them when placed both together though they were transparent enough when asunder and though I could see through twice the thickness when both of them were filled with the same colored liquors whether both with the yellow or both with the blue yet when one was filled with the yellow and the other with the blue and both looked through they both appeared dark only when the parts near the tops were looked through the exhibited greens and those a very great variety as I expected but the purples and other colors I could not by any means make whether I endeavored to look through them both against the sun or whether I placed them against the whole of a darkened room but to not withstanding this misguessing I proceeded on with my trial in a dark room and having two holes near one another I was able by placing my wedges against them to mix the tinged rays that passed through them and fell on a sheet of white paper held at a convenient distance from them as I pleased so that I can make the paper appear of what color I would by varying the thickness of the wedges and consequently the tincture of the rays that passed through the two holes and sometimes also by varying the paper that is, instead of a white paper holding a gray or a black piece of paper once I experimentally found what I had before imagined that all the varieties of colors imaginable are produced from several degrees of these two colors namely yellow and blue or the mixture of them with light and darkness that is white and black and all those almost infinite varieties limbers and painters are able to make by compounding those several colors they lay on their shells or pallids are nothing else but some compositeum made up of some one or more or all of these four now whereas it may here again be objected that neither can the reds be made out of the yellows added together or laid on in greater or lesser quantity nor can the yellows be made out of the reds though laid never so thin and as for the addition of white or black they do nothing but either whiten or darken the colors to which they are added and not at all make them of any other kind of color as for instance for million by being tempered with white lead does not at all grow more yellow but only there is made a whiter kind of red nor does yellow ochre though lead never so thick produce a color of vermilion nor though it be tempered with black does it at all make a red nay though it be tempered with white it will not afford a fainter kind of yellow such as masticut but only a whitened yellow nor will the blues be diluted or deepen after the manner I speak of as indigo will never afford so fine a blue as ultramarine or bice nor will it tempered with vermilion ever afford a green though each of them be never so much tempered with white to which I answer that there is a great difference between diluting a color and whitening of it for diluting a color is to make the colored parts more thin so that the tinged light which is made by projecting those tinged bodies does not receive so deep a tincture but whitening a color is only an intermixing of many clear reflections of light among the same tinged parts deepening also and darkening or blackening a color are very different for deepening a color is to make the light pass through a greater quantity of the same tinging body and darkening or blackening a color is only interposing a multitude of darker black spots among the same tinged parts or placing the color in a more faint light first therefore as to the former of these operations that is diluting and deepening most of the colors used by the limners and painters are incapable of to whit vermilion and red lead and ochre because the tinged parts are so exceeding small that the most curious grindstones we have are not able to separate them into parts actually divided so small as the tinged particles are for looking on the most curiously ground vermilion and ochre and red lead I could perceive that even those small corpuscles of the bodies they left were compounded of many pieces that is they seemed to be small pieces compounded of a multitude of lesser tinged parts each piece seeming almost like a piece of red glass or tinged crystal all flawed so that unless the grindstone could actually divide them into smaller pieces than those flawed particles were which compounded that tinged mode I could see with my microscope it would be impossible to dilute the color by grinding which because the finest we have will not reach to do in vermilion or ochre therefore they cannot at all or very hardly be diluted other colors indeed whose tinged particles are such as may be smaller by grinding their color may be diluted thus several of the blues may be diluted as smalt and bice and masticut which is yellow may be made more faint and even vermilion itself may by too much grinding be brought to the color of red lead which is but an orange color which is confessed by all to be very much upon the yellow now though perhaps somewhat of this diluting of vermilion by over much grinding may be attributed to the grindstone or molar for that some of their parts may be worn off and mixed with the color yet these seem not very much for I have done it on a serpentine stone with a molar made of a pebble and yet observed to the same effect follow and secondly as to the other of these operations on colors that is the deepening of them linearism painters colors are for the most part also uncapable for they being for the most part opacious and that opaciousness as I said before proceeding from the particles being very much flawed unless we are able to join and reunite those flawed particles again into one piece we shall not be able to deepen the color which since we are unable to do so with most of the colors which are by painters accounted opacious we are therefore unable to deepen them by adding more of the same kind but because all these opacious colors have two kinds of beams or rays reflected from them that is rays untinged which are only reflected from the outward surface without at all penetrating of the body and tinged rays which are reflected from the inward surfaces or flaws after they have suffered a two-fold refraction and because the transparent liquors mixed with such corpuscles do for the most part take off the former kind of reflection therefore these colors mixed with water or oil appear much deeper than when dry for most part of that white reflection from the outward surfaces removed nay some of these colors are very much deepened by the mixture and some transparent liquor and that because they may perhaps get between these two flaws and so consequently join two or more of those flawed pieces together but this happens but in a very few now to show that all this is not gratis dictum I shall set down some experiments which do manifest these things to be probable and likely which I have here delivered for first if you take any tinged liquor whatsoever especially if it be pretty deeply tinged and by any means work it into a froth the congeries of that froth shall seem an opatious body and appear of the same color but much whiter than that of the liquor out of which it is made for the abundance of reflections of the rays against those surfaces of the bubbles of which the froth consists does so often rebound the rays backwards that little or no light can pass through and consequently the froth appears opatious again if to any of these tinged liquors that will endure the boiling there be added a small quantity of fine flour the parts of which through the microscope are plainly enough to be perceived to consist of transparent corpuscles and suffer to boil till it thickens the liquor the mass of the liquor will appear opatious and tinged with the same color but very much whiten thus if you take a piece of transparent glass that is well colored and by heating it and then quenching it in water you flaw it all over it will become opatious and will exhibit the same color with which the piece is tinged but fainter and whiter or if you take a pipe of this transparent glass and in the flame of a lamp melt it and then blow it into very thin bubbles then break those bubbles and collect a good parcel of those laminate together in a paper you shall find that a small thickness of those plates will constitute an opatious body and that you may see through the mass of glass before it be thus laminated above four times the thickness and besides they will now afford a color by reflection as other opatious as they are called colors will but much fainter and whiter than that of the lump or pipe out of which they were made thus also if you take putty and melt it with any transparent colored glass it will make it become an opatious colored lump and to yield a paler and whiter color than the lump by reflection the same thing may be done by preparation of antimony as has been shown by the learned physician Dr. C. M. in his excellent observations and notes on Neri's art of glass and by this means all transparent colors become opatious or MLs and though by being ground they lose very much of their color growing much whiter by reason of the multitude of single reflections from their outward surface as I showed before yet the fire that in the kneeling or melting reunites them and so renews those spurious reflections removes all those whitenings of the color that proceed from them as for the other colors which painters use which are transparent and used to varnish over all other paintings it is well enough known that the laying of them thinner or thicker does very much dilute or deepen their color painters colors therefore consisting most of them of solid particles so small that they cannot be either reunited into thicker particles by any art yet known and consequently cannot be deepened or divided into particles so small as the flawed particles that exhibit that color much less into smaller and consequently cannot be diluted it is necessary that they which are to imitate all kinds of colors should have as many degrees of each color as can be procured and to this purpose both lemners and painters have a very great variety both of yellows and blues besides several other colored bodies that exhibit very compounded colors such as greens and purples and others that are compounded of several degrees of yellow or several degrees of blue sometimes unmixed and sometimes compounded with several other colored bodies the yellows from the palest to the deepest red or scarlet which has no intermixture of blue are pale and deep masticut or piment English ochre brown ochre red lead and vermilion burnt English ochre and burnt brown ochre which last have a mixture of dark or dirty parts with them etc. their blues are several kinds of smalts and vertitures and bice and ultramarine and indigo which last has many dirty or dark parts intermixed with it their compounded colored bodies as pink and vertigrees which are greens the one a pompongne the other a sea green then black which is a very lovely purple to which may be added their black and white which they also usually call colors of each of which they have several kinds such as bone black made of ivory burnt in a close vessel and blue black made of the small coal of willow or some other wood and Cullen's earth which is a kind of brown black etc. their usual whites are either artificial or natural white lead the last of which is the best they have yet and with the mixing and tempering of these colors together are they able to make an imitation of any color whatsoever their reds or deep yellows they can dilute by mixing pale yellows with them and deepen their pale by mixing deeper with them for it is not with opacious colors as it is with transparent whereby adding more yellow to yellow it is deepened but in opacious diluted they can whiten any color by mixing white with it and darken any color by mixing black or some dark and dirty color and any word most of the colors or colored bodies they use in limning and painting are such as the mixed with any other of their colors they preserve their own you and by being in such very small parts dispersed through the other colored bodies they both or altogether represent to the eye a compositum of all the eye being unable by reason of their smallness to distinguish the peculiarly colored particles but receives them as one entire compositum whereas in many of these the microscope can easily distinguish each of the compounding colors distinct and exhibiting its own color thus have I by gently mixing vermilium and bice dry produced a very fine purple or mixed color but looking on it with the microscope I could easily distinguish both the red and the blue particles which did not at all produce the phantasm of purple to sum up all therefore in a word I have not yet found any solid colored body that I have yet examined perfectly opatious but those that are at least transparent are metaline and mineral bodies whose particles generally seeming either to be very small or very much flawed or for the most part opatious though there are very few of them that I have looked on with a microscope that have not very plainly or circumstantially manifested themselves transparent and indeed there seems to be so few bodies in the world that are minimus opatious that I think one may make it a rational query whether there be any body absolutely thus opatious for I doubt not at all and I have taken notice of very many circumstances that make me of this mind that could we very much improve the microscope we might be able to see all those bodies very plainly transparent which we are now feign only to guess at by circumstances nay the object glasses we yet make use of are such that they make many transparent bodies to the eye seem opatious through them which if we widen the aperture a little and cast more light on the objects and not charge the glasses so deep will again disclose their transparency now as for all kinds of colors that are dissolvable in water or other liquors there is nothing so manifest is that all those tinged liquors are transparent and many of them are capable of being diluted and compounded or mixed with other colors and divers of them are capable of being very much changed and heightened and fixed with several kinds of saline minstrums others of them upon compounding destroy or vitiate each other's colors and precipitate or otherwise very much alter each other's tincture in the true ordering and diluting and deepening and mixing and fixing of each of which consists one of the greatest mysteries of the dyers of which particulars because our microscope affords this very little information I shall add nothing more at present but only that with a very few tinctures ordered and mixed after certain ways too long to be here sit down I have been able to make an appearance of all the various colors imaginable not at all using the help of salts or saline minstrums to vary them as for the mutation of colors by saline minstrums they have already been so fully and excellently handled by the lately mentioned incomparable author that I can add nothing but that of a multitude of trials that I made I have found them exactly to agree with his rules and theories and though there may be infinite instances yet may they be reduced under a few heads and comprised within a very few rules and generally I find that saline minstrums are most operative upon those colors that are purple or have some degree of purple in them and upon the other colors much less the spurious pulses that compose which being as I formally noted so very near the middle between the true ones that a small variation throws them both to one side or both to the other and so consequently must make a vast mutation in the formally appearing color end of section 15 section 16 of micrographia this is a LibriVox recording a LibriVox recordings are in the public domain for more information or to volunteer please visit LibriVox.org recording by Dion Giants Salt Lake City, Utah micrographia by Robert Hook section 16 observation 11 of figures observed in small sand sand generally seems to be nothing else but exceedingly small pebbles or at least some very small parcels of a bigger stone the whiter kind seems through the microscope to consist of small transparent pieces of some pollucid body each of them looking much like a piece of alum or salt gem and this kind of sand is angled for the most part irregularly without any certain shape and the granules of it are for the most part flawed though amongst many of them is not difficult to find some that are perfectly pollucid like a piece of clear crystal and divers likewise most curiously shaped much after the manner of the bigger of crystal or like the small diamonds I observed in certain flints of which I shall by and by relate which last particular seems to argue that this kind of sand is not made by the combination of greater transparent crystalline bodies but by the concretion or coagulation of water or some other fluid body there are other kinds of coarser sands which are browner and have their particles much bigger these viewed with a microscope seem much coarser and more opacious substances and most of them are irregularly rounded figures and they seem not so opacious as to the naked eye yet they seem very foul and cloudy but neither do these want curiously transparent no more than they do regularly figured and well colored particles as I have often found there are multitudes of other kinds of sands which in many particulars plainly enough coverable by the microscope differ both from these last mentioned kinds of sands and from one another there seeming to be as great variety of sands as there is of stones and as amongst stones some are called precious from their excellency so also are there sands which deserve the same epithite for their beauty for viewing a small parcel of East India sand which was given me by my highly honored friend Mr. Daniel Calwall and since that another parcel much of the same kind I found several of them both very transparent like precious stones and regularly figured like crystal Cornish diamonds some rubies etc and also tinged with very lively and deep colors rubies sapphires emeralds etc these kinds of granules I have often found also in English sand and it is easy to make such a counterfeit sand with deeply tinged glass enamels and painters colors it were endless to describe the multitudes of figures I have met with in these kind of minute bodies such as spherical oval middle, conical prismatical of each of which kinds I have taken notice but among many others I met with none more observable than this pretty shell described in the figure ten of the fifth scheme which though as it was lied on by chance deserved to have been omitted I being unable to direct anyone to find the like yet for its rarity was it not inconsiderable especially upon the account of the information it may afford us for by it we have a very good instance of the curiosity of nature in another kind of animals which are removed by reason of their minuteness beyond the reach of our eyes so that as there are several sorts of insects as mites and others as small as not yet to have had any names some of which I shall afterwards describe and small fishes as leeches in vinegar and small vegetables as moss and rose leaf plants and small mushrooms as mold so there are it seems small shellfish likewise nature showing her curiosity in every tribe of animals, vegetables and minerals I was trying several small and single magnifying glasses and casually viewing a parcel of white sand when I perceived one of the grains exactly shaped and wreathed like a shell but endeavoring to distinguish it with my naked eye it was so very small that I was feigned again to make use of the glass to find it then whilst I thus with a pin I separated all the rest of the granules of sand and found it afterwards to appear to the naked eye and exceeding small white spot no bigger than the point of a pin afterwards I viewed it every way with a better microscope and found it on both sides and edge ways to resemble the shell of a small water snail with a flat spiral shell it had 12 readings A, B, C, D, E, etc all very proportionably growing one less than another toward the middle or center of the shell where there was a very small round white spot I could not certainly discover whether the shell were hollow or not but it seemed filled with somewhat and it is probable that it might be petrified although large shells often are such as are mentioned in the 17th observation end of section 16 section 17 of micrographia this is a LibriVox recording a LibriVox recordings are in the public domain for more information or to volunteer please visit LibriVox.org recording by Dion Giants Salt Lake City, Utah by Robert Hook section 17 observation 12 of gravel in urine I have often observed the sand or gravel of urine which seems to be a tartarius substance generated out of a saline and a terrestrial substance crystallized together in the form of tartar sometimes sticking to the sides of the urinal the most part sinking to the bottom and they're lying in the form of coarse common sand these through the microscope appear to be a company of small bodies partly transparent and partly opatious some white some yellow some red others of more brown and dusky colors the figure of them is for the most part flat in the manner of slats or such like plated stones that is each of them seem to be made up of several other thinner plates much like muscovy glass or English spar to the last of which the white plated gravel seems most likely for they seem not only plated like that but their sides shaped also into roms rhomboids and sometimes interact angles and squares their bigness and figure may be seen in the second figure of the seventh plate which represents about a dozen of them lying upon a plate a b c d some of which as a b c d seemed more regular than the rest and e which was a small one sticking on the top of another was a perfect rhomboid on the top and had more rectangular sides the line e which was the measure of the microscope is one thirty second part of an English inch so that the greatest breadth of any of them exceeded not one one hundred twenty eighth part of an inch putting these into several liquors I found oil of vitriol spirit of urine and several other minstrums to dissolve them and the first of these in less than a minute without abolition water and several other liquors had no sudden operation upon them this I mention because those liquors that dissolve them first make them very white not vitiating but rather rectifying their figure and thereby make them afford a very pretty object of scope how great an advantage it would be to such as our troubled with the stone to find some minstrum might dissolve them without hurting the bladder is easily imagined since some injections made of such bodies might likewise dissolve the stone which seems much of the same nature it may therefore perhaps be worthy some physicians and query may not be something mixed with the urine in which the gravel or stone lies which may again make it dissolve it the first of which seems by its regular figures to have been sometimes crystallized out of it for whether this crystallization be made in the manner as alum Peter etc are crystallized out of a cooling liquor in which by boiling they have been dissolved or whether it be made in the manner of tartarum vitriolatum that is by the coalition of an acid and a sulfurous substance it seems not impossible but that the liquor it lies in may be again made a dissolvent of it but leaving these inquiries to physicians or chemists to whom it does more properly belong I shall proceed to the end of section 17