•f3*J*«- ' . •■'■i'lMuA' rjlf*_^l. 
 
r\^s 
 
 -OL-OOA 
 
NEW ELUCIDATION 
 
 OF 
 
 COLOURS, 
 
 ORIGINAL PRISMATIC, ^nd MATERIAL; 
 
 SHOWING 
 
 THEIR CONCORDANCE IN THREE PRIMITIVES, 
 
 YELLOIF, RED, and BLUE; 
 
 AND- 
 
 THE MEANS OF PRODUCING, MEASURING, 
 AND MIXING THEM: 
 
 WITH 
 
 SOME OBSERVATIONS on THE ACCURACY of SIR ISAAC NEWTON, 
 
 Who "From tlie whitening uiulistingiiislied lilaze 
 
 Collecting every ray into its kind. 
 
 To the charmed eye educed the gorgeous train 
 
 Of Parent Colours." 
 
 Thomson . 
 
 By JAMES SOWERBY, F.L.S. &c. 
 
 Designer of English Botany, and Exotic Botany; Author of English Fungi, British Miupralogy, 
 British MisccUaDy, the Botanical Drasving Book, &c.— No. '2, Me.id PKicp, Lambc h, Surrey. 
 
 Hoution: 
 
 Printed by Richard Taylor and Co. .Shoe-Lane. 
 
 MDCCC-IX. 
 
TO THE MEMORY OF 
 THE GREAT SIR ISAAC NEWTON 
 
 I indulge an incUnatmi with much humility to dedicate 
 this gift of Nature, as a part belonging to the foundation of 
 light and colours, first laid by his penetrating genius ; presum- 
 ing that collecting, measuring, and arranging them is a ne- 
 cessary if not an. essential appendage. I had dedicated this 
 more naturally, it might be thought, to the Honourable Presi- 
 dent, Sir Joseph Banks, Bart, and to the Fellows of the Royal 
 Society. The Dedication to the Memory of Sir Isaac Newton 
 being admitted, the latter follows of course, as every thing re- 
 lating to the philosophical scheynes of that great man naturally 
 comes under their cognizance ; and they, like his heirs, under 
 such circumstances I hope will he pleased to accept it, 
 
 JAMES SOWERBY. 
 
 London. 
 
INTRODUCTION. 
 
 When I first proposed to publish on Colours, it was merely with 
 an intent of simplifying the means of mixing them, and that chiefly 
 with regard to such as are used for painting in water or oil, with a 
 particular desire to show a means of agreement and ready reference 
 among naturalists and others, as to their identity. This led me to 
 inquire for some permanent and constant means of comparison, from 
 some original source that might always be consulted, and leave no 
 room for doubt. Observing a sort of originality in the prismatic 
 tints of stones, and that I could trace their order, I began with 
 them ; but, after all, finding them too fixed as it were for some 
 purposes, and that it would be desirable to mix or unmix the 
 original prismatic tints with the same order as common colours, and 
 perceiving a strange want of agreement in this particular among 
 philosophers, &c., I was the more anxious, especially as to the ob- 
 taining the same three primitives as were pretty universally allowed 
 to common colours, viz. Yellow, Red and Blue ; for should Nature 
 agree in this, which seemed to me a desideratum, I might then find 
 a means of producing them so as to mix them perfectly, and be able 
 to come to some fair conclusion. I made a few inquiries upon the 
 subject, but to no purpose, as it was generally thought impossible: 
 and having a further desire to measure them, it seemed to be consi- 
 dered as a vanity. I was however satisfied, that as there was some- 
 thing wanted to make the desired agreement, so it might possibly 
 
 B 
 
2 INTRODUCTION. 
 
 be found out. I therefore determined, if in my power, to find it 
 oat ; and was much sooner favoured with the discovery than I ex- 
 pected, and that too to a nicety that surprised me much, especially 
 as it was so easy and likely to be brought to perfection, not only to 
 correct former errors, but to serve as a firm basis for future inquiries. 
 Indeed, it may seem a wonder, in the present rapidly improving 
 age, that any thing remained to be done towards the elucidation of 
 colours, either evanescent or natural. I presume, however, that this 
 work in its present form is likely to fill up some important desi- 
 derata ; and if it is not established as a book of reference, which is 
 much wanted, I hope it will help at least to call one forth, as such 
 a book may be of infinite service in many departments of science, 
 for the subject promises already to branch into many divisions for 
 different purposes. One truth established helps another ; and it 
 may give a hint even to the astronomer Dr. Herschel, who has 
 paid so much attention to the subject of prismatic colours, that 
 strong opposites, such as light and dark, may not be proper in the 
 use of telescopes, as when they are next each other, in particular, 
 they may produce the most brilliant prismatic tints by the help of 
 the angle of a lens*. Thus a middle tint I should presume best 
 for lining telescopes. I find a middle tint in my schemes best to 
 neutralize colours (black I believe is in general use for telescopes 
 kc. but 1 do not know what Dr. Herschel uses). 
 
 Again, calculation by means of a prism has been used to assist 
 in examining some of the constellations ; if the sun's width at a 
 known distance is such as to show a white space when viewed in a 
 prism, it must be broader or nearer than those constellations that do 
 not show a white space: — thus the smaller objects of our hemisphere 
 show only the four colours of Dr. Wollaston's narrow ray of light, 
 or C. A. Prieur's white thread or silk, which will be understood in 
 the sequel. It is somewhat curious, that the middle tints brought in 
 contact by smallness or narrowness exclude light or white, and be- 
 
 * Dr. Herschel probably broke his coloured glasses by some such contrast. 
 
INTRODUCTION. 3 
 
 come green, from yellower green to darker and bluer green. May 
 green be reckoned the inicklle tint in Nature, as grass: it seems 
 suited to our vision. It is not a little remarkable, that many 
 subjects partake of the prismatic order of the colours of the sun 
 or other luminaries, especially hemispherical ones, surrounded in 
 a dark or perhaps aerial medium. Thus the evanescent tints be- 
 come in effect realized in an admirable manner to our senses, taking 
 due place in Nature to the fullest extent. 
 
 I have only hinted at these things, that they may be enlarged 
 upon if it should seem useful. Certainly, some fruits, such as 
 peaches, pears, &c., have, occasionally, nearly if not all the tints 
 allowed to the prism in due order upon them : thus the upper part, 
 or the next under the leaf or stalk, is a full or crimson red, and 
 this is often softened into orange ; yellow or yellowish succeeds ; 
 then yellowish green ; then bluer, till the dull or under side par- 
 takes of violet, especially if the warmer rays of an evening sun glow 
 aslant on its downy coat, or help by their reflexion. Artists are 
 generally aware of this in their paintings, and keep the warmer co- 
 lours above and the colder ones below: even the warmer tints in 
 Man, who walks erect and looks on Heaven, are seen most conspi- 
 cuously in the upper part of his features. Indeed many artists con- 
 sider the general light and warmer tints with the cold and shady 
 sides (if I may so call them) of the rainbow, as a sort of rule to 
 go by: the lighter side, to blend the colours of the lighter side of 
 the subject, when the softening into the back ground would form a 
 violet; a warm or reddish tint would come next, which would be 
 blended by yellowish orange into the local tint, when the heightening 
 would succeed ; next something of the local tint which would be- 
 gin to recede into the yellowish and shade forming a grayish green ; 
 then would succeed a darker shade with a violet tinge, and the rest 
 would depend upon reflexion. Now these tints being judiciously 
 managed, give a richness that is only understood by the artist who 
 practises with such ideas. I have introduced the peach as an 
 
 B 2 
 
4 INTRODUCTION. 
 
 example ; and I remember, when a young student at the Royal 
 Academy, to have painted from the hfe with nearly such a lesson 
 from a worthy and most esteemed artist, who was at that time the 
 visiting academician. It would therefore seem that light or shade 
 on convex or concave subjects, or where shadow is, is also accom- 
 panied with colours ; the smallest shade being compounded not 
 only of light and shade, or black and white, but of many tints de- 
 pending on the nature of that light; for mere black and white would 
 give an unartist-like manner and coldness, which would be con- 
 demned in general, even by the least discerning, although perhaps 
 without knowing why. Light and shade or shades will be shown 
 hereafter to have a greater effect than is usually understood, with 
 regard to colours, and will, I have no doubt, be found useful in 
 ' many other respects. Light and dark, as a contrast, and for effect, is 
 very ancient, and sufficiently attracted Laban's flocks under the care 
 of Jacob*. 
 
 Light is essential in colouring some things and bleaching others; 
 and it was once a valuable secret, that to get the brightest carmine 
 it should in the process of making be dried in the sun. Many 
 chemical substances are changed by exposure to light ; oils become 
 whiter. Perhaps even this effect may be assisted with the help of a 
 contrasting shade, that the actions may be more forcibly directed on 
 the object. Light, on an object when seen refracted by the prism, 
 shows its colours ; which however do not affect the general local tint 
 of the object which seems to reflect it, but rather depend upon the 
 darks or shadows ; and broad flat masses of any coloured object do 
 not appear changed excepting at the extremities, or where dark or 
 shade seems to help to collect the coloured radii : thus it may be 
 possible to make broad tints or narrow ones with such proportions of 
 dark or shade as may be suited for many purposes of the utmost 
 utility in tlie arts^ manufactures, agriculture, &c. 
 
 * Genesis XXX. 37 to 41. 
 
INTRODUCTION. 
 
 That philosophers and artists liavc long wished for some never- 
 fading colours to fix their ideas and universalize them, is in every 
 age anij)ly verified ; and as coloured substances, like all other sublu- 
 nary things, are liable to a certain decay, so it has been but weakly 
 attempted lately; besides, the dilVicuIty of finding a means of agree- 
 ment in the modifying and arranging them has been a desideratum, 
 as late works have abundantly, showed. Enamel, perhaps, is as 
 durable as any substance, and has with much jiropriety been pro- 
 posed; but the uncertainty of an ability to procure an equality 
 throughout a single tint, puts us nearly in the same predicament as 
 with other coloured schemes. This vve shall find true in our attempt, 
 as will be too evidently seen in the present examples. We presume 
 our method of arranging will much assist both the colours and the 
 mind, and even this scheme might be desirable in enamel or glass 
 for the sake of durability; but 1 may question even if the best ena- 
 meling artists can place colours so well, (which in no way degrades 
 their greater merit,) as it is seldom they have occasion for the ex- 
 perience of an object so trifling to the best of such ailists*. 
 
 Upon the whole, the necessity of supplying this desideratum 
 need not be dwelt upon, as the numerous attempts to do it are a 
 suflicient acknowledgement, and argue much for its utility. In my 
 researches it has luckily fallen to my lot to find one resource or 
 monitor in Nature, which is as constant as the light from which it is 
 deduced, and the regularity or certainty depends upon very simple 
 materials. 
 
 The use of a true original for colours, and a regularity of arrange- 
 ment, is almost infinite; for to the artist in any line it will be a 
 solid satisfaction to know when he treads on a sure foundation, laid 
 by unerring Nature. The mineralogist, the botanist and the zo- 
 ologist may in future agree in their descriptions and ideas, so as to 
 identify them to all parts of the world, and the remotest ages. 
 
 * Perhaps it may succeed somewhat in transparent oil, but water colours are most 
 convenient for a book. 
 
6 INTRODUCTION. 
 
 It was observed to me by a very good friend, " that as the seven 
 tints were permanent, that was an evidence of tlieir sufficiency as 
 primitives and their original derivation, and that water was perfect 
 in itself, although it was found to consist of hydrogen and oxygen." 
 The latter was once thought a pure element, and led to wrong con- 
 clusions. The former being thought perfect, it will be evident, has 
 also caused wrong conclusions; and as water is not necessary to be 
 formed to produce one of its original parts, hydrogen or oxygen, so, 
 it will be less necessary to mix yellow and red and yellow and blue* 
 to make a yellow ! when yellow is originally and necessarily so, to 
 form the very ingredients so unhappily combined, and leading into 
 continued and self-proving errors. Thus water does not form hy- 
 drogen and oxygen, but hydrogen and oxygen form water. Yellow, 
 red, and blue, I presume, therefore, will more properly form the re- 
 mainder of the seven prismatic tints, than either two or more of the 
 seven will form a single primary colour. I would not have insisted 
 so much on this subject, but that the present improving state of 
 natural science seems to demand a concordance of the primitives of 
 prismatic tints and substantial colours, which appear so much to 
 depend on each other ; and it has been understood by many, from 
 the time of sir Isaac Newton, that the prismatic tints may be imi- 
 tated by what I would consider as simple primitives, viz. yellow, 
 red, and blue. 
 
 Now to me it seems that, if these are allowed to be the proper 
 primitives of the prismatic tints or colours, there will be a perfect 
 concordance on the most permanent footing. 
 
 I should not have set about this work without a confidence of its 
 utilit)', although I had not intended or expected to carry it quite so 
 far. I therefore may not have arranged it so regularly as I wish, 
 
 * It has been, by some, a long mistaken notion, that as yellow is placed between 
 «range and green among the seven tints, it was a natural result from them, when the 
 ■contrary is so naturally and truly the case, as is proved by the very first hypothesis, 
 seeing that yellow and red make orange, &c. 
 
INTRODUCTION. 
 
 as every thing did not present itself to me at once, like an old sub- 
 ject, but rather as a new. I therefore hope some allowance will be 
 made by the discerning, more especially in the philosophical jjart ; 
 as the intention is, to generalize the subject : and the author does 
 not jjretend to be either a great philosopher or artist ; for, if he had 
 been the first, he probably would have wanted enough of the latter 
 to answer the peculiarities of the present intention, and vice versa. 
 
A NEW 
 
 ELUCIDATION OF COLOURS, 
 
 X. HERE may seem a want of order, in commencing this work with 
 showing rather a finished series than the beginning of one. I have, 
 however, in this instance thought it necessary to give general ideas, 
 and afterwards to begin in as simple a manner as I could ; and, by 
 descending to certain particulars, endeavour to lead to a natural re- 
 sult. I therefore show them even the first and the last series of 
 prismatic tints, viz. light colours and dark ones, as they are in their 
 nature of much consequence, having been very little if at all noticed 
 in natural order, especially the browns and other ternaries. Thus 
 we have, as it were, white as the first beginning of colours, and 
 brown to black the termination of them to our senses. We shall 
 find in the sequel that these include all colours, and that a certain 
 position or arrangement will make them evident, with the most 
 beautiful order and unerring regularity. I am pleased to find these 
 first examples in minerals, whose agency is no less conspicuous in 
 this department, than of the first necessity in most others, showing 
 us much of the nature of light and colours, from the most evanes- 
 cent* to the more solid or material. They help us much to judge 
 of their permanency, and seem the best vehicles to trace them in, 
 and from their first source ; for we may produce them at pleasure, 
 
 * Changeable, in many substances, according to the course of the light they are 
 viewed by. 
 
and make our general observations on them at any time. We 
 may press together or open tiie lamina; which have been j)artially 
 separated, of gyi)sum for instance, in order to produce the colours, 
 either concentrically or otherwise, and this may be repeated, or we 
 may allow them to be stationary for future use or practice, and to 
 serve as one of our resources for a natural proof or example, and we 
 may even measure with some accuracy the space allowed in jiUites 
 for the different tints. (See Dr. Young's excellent paper*.) Thus 
 Tab. \. a,b, c, d, e,f, are representations of colours, that are or may 
 be produced in the flaws of or betwixt the laminae of transparent 
 stones, such as the diamond, gypsum, or selenite, mica, carbonate 
 of lime, &c. (See Brit. Mn. tab. 2.) I have a specimen of mica 
 showing a minute opening or division of 'the laminae of about the 
 eighth of an inch in diameter, having a yellow centre, which I place 
 first; as it succeeds, in the increasing order of density, next to light. 
 It is surrounded by light blue, passing through purplish brown to 
 very dark, when, by degrees, it again passes into faint brown-}- wilh 
 a light margin, and then the stone appears to be close and solid sur- 
 rounding it; PL 1. a. In another part of the same specimen, I 
 have a red centre, to which succeeds the yellow, and the yellow is 
 succeeded by the blue, and the other rings succeed in due order as 
 the first ; PI. I. b. A third flaw has blue in the centre, as in c, with 
 the red, yellow, and the usual rings in the same succession. It is 
 not often that we can find one colour only shown in these sub- 
 stances, they being more commonly a succession of rings. I have 
 however met with dark brown with a lighter margin, passin"' to 
 light or white as at d, and e shows the stone grayish in the centre 
 with the white margin, surrounded by the brown and other rings, as 
 it were reversed in order: it is in fact the curved margin of the va- 
 rious and unequal divisions or fissures in the substance. In general 
 the external or extreme mai-gin finishes with brown, as most of 
 these, whether narrow or broad, do. The other more commonly 
 
 * Phil. Trans. 1802. 
 
 t Browns have scarcely, if at all, been considered by authors on this subject. 
 
 c 
 
10 
 
 concentrates with yellow, red, or blue, or a mixture depending upon 
 a natural and regular phaenomenon : (viz.) That as we have seen in 
 a, b, c, that blue is on the inner side of the dark circle, if there is 
 much proportional breadth, so commonly a white or light space suc- 
 ceeds, passing into yellow, orange, and red ; and sometimes the ar- 
 rano-ements in succession approach nearer and nearer, and the white 
 is obliterated, and yellow is facing or nearer the light blue : again, 
 the yellow and blue pass into each other in narrow or nearer circles, 
 and produce green very often at the expense of the marginal tints, 
 if I may so call the blue on one hand, and the red on the otlier. 
 Something like this, or duller and deeper, appears at fig. g, and the 
 semicircles surrounding show it more distinctly, although placed 
 here for a no less curious example. 
 
 I have perhaps enlarged too much on this subject here. I, how- 
 ever, thought it essential not only to begin with these general pre- 
 mises, but to show some common varieties in the arrangement of 
 prismatic colours, by which we ma^^ perceive that there is a perfect 
 rule for proportion in it, however unequal it may at first appear, 
 which seems to me to have been hitherto a desideratum ; and as I 
 expect to prove much from the nature of this particular appearance, 
 I have dwelt the longer upon it ; which is the more necessary, seeing 
 how orderly sir Isaac Newton produced certain colours by the pres- 
 sure of two glasses, and how naturally and truly he enumerated 
 them without quite attaining the leading and true cause or principle 
 of that arrangement, which he was so near discovering, and which 
 would imdoubtedly have been of the most essential consequence in 
 such good hands. The whole agrees so well with what is said of the 
 experiments of that great man, that, although it is well known, 
 I cannot forbear relating it here. Sir Isaac Newton himself had 
 observed, that as he was compressing two prisms hard together, in 
 order to make their sides (which happened to be a little convex) to 
 touch one ano'.her, in the place of contact they were both perfectly 
 tran' parent, as if they had been but one continued piece of glass. 
 Koimd the point of contact, where the glasses were a little separated 
 
II 
 
 from each other, rings of different colours appeared. To observe 
 more nicely the order of the colours produced in this manner, he 
 took two object-j>lasses ; one of them a plano-convex one belonging 
 to a fourteen-feet refracting telescope, and the other a large double 
 convex one for a telescope of about fifty feet; and laying the former 
 of them upon the latter with its plane side downwards, he pressed 
 them slowly together ; by which means the colours very soon 
 emerged, and appeared distinct to a considerable distance. Next to 
 the pellucid central spot, made by the contact of the glasses, suc- 
 ceeded blue, white, yellow and red. The blue was very little in 
 quantity, nor could he discern any violet in it ; but the yellow and 
 red were very copious, extending about as far as the white, and four 
 or five times as far as the blue. The next circuit immediately sur- 
 rounding these consisted of violet, blue, green, yellow and red : all 
 these were copious and vivid, except the green, which was very little 
 in quantity, and seemed more faint and dilute than the other colours: 
 of the other four, the violet or purple was the least in extent, and 
 the blue les.s than the yellow or red. The third circle of colours 
 was pur}>le, blue, green, yellow, and red : in this the purple seemed 
 more reddish than the violet in the former circle; and the green was 
 more conspicuous, being as brisk and copious as any of the former, 
 except the yellow; but the red began to be a little faded, inclining 
 much to purple. The fourth circle consisted of green and red ; and 
 of these the green was very copious, inclining on the one side to 
 blue, and on the other to yellow : but in this fourth circle there was 
 neither blue, violet, nor yellow, and the red was very imperiect 
 and dirty. All the succeeding colours grew more and more im- 
 perfect and dilute, till after three or four revolutions they ended in 
 perfect whiteness*. It is perhaps now to be wondered that sir Isaac 
 Newton did not take more particular notice of the fading of the 
 violet and red, or of their becoming more of a diluted cast, and of 
 
 * Probably brownish first. I have not the means of trying his glasses, but it seems a 
 general law that has been overlooked, as a sign of obscurity perhaps. 
 
 c 2 
 
12 
 
 the three primitive tints mixing as the circles became narrower, 
 which was the cause of the green in the third ring. As the colours 
 were found to vary according to difi'erent distances of the glass plates 
 from each other, our author showed that they proceeded from the 
 different thicknesses of the plates of air intercepted between the 
 glasses. But to return to the order in which he so naturally found 
 the colours in the circles. — First, the three primitives and the seven 
 prismatic tints naturally mixed from them, which I wish he had 
 been aware of, as it would have accounted for the other rings or re- 
 volutions. I have therefore produced an example of the order of 
 his tints in Plate 1. figures 1, 2, 3, &c. in which it will appear that 
 the rings which are called revolutions begin in a natural order, al- 
 though reverse to what I have begun with, viz. first blue, whereas 
 I have begun with yellow. This however is because his instruments 
 were reversed, two opposite convex surfaces producing them in his 
 scheme, and two concave opposites producing my past example. 
 Thus, No. 1 is Blue 
 
 2 — White* 
 
 3 — Yellow 
 
 4 — Red 
 
 5 — Violet 
 
 6 — Blue 
 
 7 — Green 
 
 8 — Yellow 
 
 9 — Red 
 
 10 — Purple 
 
 1 1 — Blue 
 
 12 — Green 
 
 13 — Yellow 
 
 1 4 — Red 
 
 15 — - Greenish 
 
 16 — Dirty ish Red, &c. 
 
 * White is light, dependent upon the distance of the rings or revolutions which begin 
 or end the series, as Red or Blue, which in these cases come back to back as it were, 
 
13 
 
 Blue, yellow, and red, omitting white as neuter, we find, are liis 
 three first colours ; and in the next range, we only want indigo to 
 begin or terminate the series after the red and orange, between the 
 yellow and red, to comj)lete tlie seven prismatic tints in tiie second 
 series ; which, if we observe the joining of tlie red and IjIlic by being 
 viewed at a certain distance, will seem very nearly to be the real 
 case: indeed, a proper softening of one into the other would make 
 it too nice for our discernment ; although, if the red is pure, it 
 ought to be only violet, which in a bad light will ap])ear as dull as 
 common indigo, as a deep purple is dulled by the yellower rays of 
 candle-light and lilac, and all purples ajjpear brightest by day-light. 
 The approach or nearer a})pearance of the two revolutions will also 
 in this instance be found to form green, where the white took place 
 before, as the yellow and blue join to form it ; and so it is with the 
 other rings or revolutions which approach nearer and nearer, next 
 losing the yellow as it were by mixing, and are both duller and paler 
 from want of that opposition to stronger light or darkness, which 
 probably towards the end became obscure, finishing in perfect white- 
 ness, or light reflected on the face of the glass. The middle tint, if 
 1 may so call it, at g, would not allow of a dark blue margin, as will 
 be understood more perfect! \' hereafter. 
 
 Having therefore produced the order of his tints, which without 
 more instruction than his words we are enabled to do very perfectly, 
 and as the tints come according to Nature, so we may conclude he 
 was right, as may always be ])roved by the order of the colours ; for 
 the prismatic tints, however irregular they may appear, or seem con- 
 founded, are most perfectly and unerringly regular in their order: 
 thus the rainbow, the colours in the flaws of stones, &c. follow the 
 same rule, even to the coal called peacock coal, for the colours of 
 which, see British Mineralogy, tab. 4Q. Thus if we look through the 
 prism, at a window or a multitude of objects, or any varied number 
 even of coloured things*, all will.be found to be reducible to certain 
 
 ♦ A print, with many objectSj coloured or uncoloured, may be convenient to examine. 
 
14 
 
 rules, as a given proportion of light or sliade produces proportionate 
 colours with as much certainty as any figure in arithmetic. 
 
 It may perhaps be convenient in this place to ask, whether it is 
 the lamina^ which cause the plates of air of a certain dimension to 
 reflect a particular tint or colour, or whether, like the rainbow, par- 
 helion, or halo, it may not be produced by the crystallized particles 
 of the suijstance acting as water, ice, or hail* ? 
 
 Iris-like tints are to be produced many ways, and sometimes with 
 very remarkable pha?nomena. At Weather-Cot Cave, in Yorkshire, 
 it is said that if, at certain seasons, a jDcrson placed at the mouth of 
 the cave look at the stream or fall of water that is precipitated from 
 above it, he will see six or more iris-like appearances. These are 
 probably governed by the shadow of the prominences of the rock, or 
 perhaps the disturbed undulations of the water: either repetition 
 seems to depend upon something analogous to the efi'ect of dark 
 lines, which will be seen in the present theory, and the same with 
 the repetitions in different substances, and when artifically contrived 
 by convex or plane glasses, &c. or perhaps in this latter it may 
 depend upon the grinding of the glass, which, however finely po- 
 lished and perfectly smooth to our perception, is nevertheless full of 
 the irregularities left by the tool of the workman in turning it to 
 grind or polish it ; and this would greatly agree with the idea of the 
 crystalline particles producing the colours in various minerals; and 
 it may seem that a double combination of the watery particles, or 
 mist and shadow, produced the circles around the shadows of the 
 heads of sir Joseph Banks and his companions, in the bason of the 
 boiling fountain of Geyer, when visiting Iceland in l/Tlj as Von 
 
 * As it seems somewhat doubted, what is the form of ice in its crystallization, we 
 can assure our readers that we have found snow in regular tetraedrons, Brit. Min. lai. 281, 
 and in hexaedtal pyramids, produced by truncation at the edges of the tetraedrons j 
 sometimes truncated at the top ; in hexaedral columns formed of plates curiously stel- 
 lated with spiculae; and hail in regular tetraedrons, somewhat plated with nuclei: I 
 have also found the tetraedron with rounded faces, somewhat like the sulphate of cop- 
 per, British Mineralogy, tab. //, but nearer round, like a drop of water. 
 
15 
 
 Troil says, thut each saw around the shadow of his own head, 
 though not around the shadows of the heads of others, a circle of 
 almost the same colours which compose the rainbow, and around 
 this another circle. There are many curious instances of such 
 pheenoniena. I have known boys to imitate the rainbow by simply 
 sjju-ting- water from their mouths, in the sunshine, &c. to imitate 
 fine rain, producing the rainbow tints extremely well. 
 
 Somethmg like this may account for the number of circles or seo^- 
 ments of circles in the various substances in which they happened 
 to form, even the common air. Thus we may conceive certain un- 
 dulations, not unaptly represented in the common crown glass of 
 our windows (which it appears is made by taking a largi>h ball of 
 metal* and spreading it by turning the instrument as when a mop 
 is whirled or trundled to dry it), when the arrangement of the par- 
 ticles of water in the air, like the rings in the glass, varying, gives 
 each a similar eH'ect, or forms circles Now it will be found that the 
 eye cannot see those circles, but by the proportion of light and shadow 
 with the reflexions : and betwixt every swelling, or other cause of light 
 and shadow, there always appear the coloured rings when looked at 
 in the sun, or when the sun shines upon the plate so formed, or 
 obliquely through it on a wall, &c. I'he eye is often so circum- 
 stanced, that things not at all forming real circles have yet the co- 
 loured appearance of them, as a shining waxed table, a greasy ap- 
 pearance on glass, or the almost imperceptible dust that may be on 
 some smooth surfaces, the most minute particles of damp^ breathin"- 
 on glass and copper, or the slime of snails, and many other objects 
 sufficiently well known, either requiring the prism to refract the 
 tints, or forming them to the unassisted eye. These colours fre- 
 quently obtain permanency, and we may trace them till they seem 
 to approach solidity in heated or oxidized steel or other metals, 
 which begin with yellow: this is followed bv orange, then the red, 
 passing to crimson or violet, and thence to blue, as the heat is con- 
 
 » In the glass fiarnace, the melted glass is called metal by the workmen-. 
 
16 
 
 tinued; and if it is still heated, fresh sets of colours are formed; which 
 is not only a proof of a sort of permanence of colours brought on 
 by heat, but of their regularity in successively forming rings, which 
 is rather universal vviiere colours are formed, especially as they de- 
 pend upon some sort of prismatic agency: but the yellow and red 
 are not very bright, as the steel does not reflect them so well as 
 many other substances, although the blue is generally beautifully 
 reflected. Nature, however, produces them all most brilliantly on 
 some iron ores and other oxides. 
 
 Having gone thus far, I found it might give much satisfaction if 
 I were to examine the light from the full sun's rays, as an original 
 source, in the open air. I therefore took the usual three-sided 
 prism, and was highly gratified by observing white in the refracted 
 reflexion of the sun, as seen of an oval form, light on the face of the 
 prism, and the three primitive tints, a fine yellow, a rich red, and 
 a light blue: (see Tab. 2. Jig. 1 and 2,) and I found, by turning 
 the prism, very beautiful phaenomena took place within it, scarcely, 
 if at all, before noticed in open light. The rays, as they become 
 more oblique, spread over each other, the yellow over the white to 
 the blue forms green, while the blue on tlie darker side is changed 
 into violet and indigo. The red, by the same motion, passes over 
 some of the yellow spreading into orange, and thus are formed the 
 regular seven prismatic tints or spectrum. At the same time as the 
 above, may be seen lefracted immediately from the sun's most bril- 
 liant rays, upon any object within a few inches, a fine image of the 
 prism bordered lengthwise, by the same three tints: {see Tab. 2, 
 fig. 3.) This shows the primitive tints on a larger scale, and will 
 therefore give a fuller exjjlanation of the whole. Thus the middle 
 I call white, as the more direct light, the yellow is below it, the red 
 lowest, and the blue on the uppermost or opposite side, blending 
 but a little with each other, and least so when most vivid, or when 
 the oval reflexion. Jig. 2, is nearest in form to a circle. When a 
 strip of white paper is seen through a prism, at a proper distance, on 
 a mahogany or dark table, blue will terminate one edge, and red 
 
another, with the same appearance as the above ; and the proper 
 motion of the prism or paper will produce tlie green, orange, indigo, 
 and violet, if the jjajjer is not too broad. We therefore find three 
 original primitive tints may be formed distinctly on white paper*. 
 
 Rich lights, or whites, and full or more perfect darkness opposing 
 each other, produce the more brilliant tints. The rich light of the 
 sun dispelling the darkness of the morning, or passing away in the 
 evening, produces more apparent colour than at noon when the 
 whole atmosphere is illuminated ; and a small candle in a large room, 
 surrounded as it were by much darkness, gives as great brilliancy 
 in the prism as the sun itself: and again, the prismatic rays col- 
 lected from the sun require a quantitj^ of shade to show them most 
 brilliantly: — thus they were generally refracted into a dark room. 
 Next to this we might consider convexity and concavity ; and it will 
 be found that they add to the brilliancy, as they allow a greater 
 strength of light and shade. Convexity and concavity amount, by 
 undulation, as it were, to nearly tiie same thing as light and shade 
 (by which artists have their imitative power) ; and any light with 
 shade will produce prismatic tints ; thus, as it were, reducing the ])ro- 
 duction of tints to light and shade, or white and black. We shall 
 find the means of illustrating this in every necessary example. Hence 
 it is found, that as the appearance of colour depends upon a certain 
 opposition of light and darkness, so much depends upon the pro- 
 portion of each for the colour they may produce, and the degree or 
 strength of it. I therefore look at the middle of a piece of dense 
 smooth black paper with the prism, and perceive no colour ; if I 
 produce a small dot, or ray of light, or streak of white, immediately 
 certain prismatic tints are produced, according to the proportion, from 
 
 * Dr. WoUaston, however, as an original in philosophy, examined a narrow ray of 
 light, :ind found what he considered as the four primitives ; and Dr. Young, a broader 
 ray, by which he determines seven primitives, inchiding white. I think it will be seen 
 that the breadth of the ray will naturally vary the appearance, as ill a broad ray, or a ray 
 of a certain proportion, they ellow and blue do not mix as in a n.irrow one, unless by turn- 
 ing llie prism. 
 
 D 
 
18 
 
 three to seven, like those of a rainbow *. As I admit more light, of 
 make tlie marks broader and larger, the colours become brighter 
 and more separated, till white is admitted in the broadest, when it 
 will appear that the white, with yellow, red and blue, only remain, 
 and perhaps a little mixture, between the bright red and yellow, of 
 orange-1-, and the yellow with the light or white, naturally blend 
 into each other, and the blue is also softened into the white termi- 
 nating at the lower edge. Having thus produced the coloured rays 
 by a little light and much black, it may be proper to try a contrary 
 process, by a little black and much white. We should therefore 
 look at the middle of a piece of white pajier, or any white object, 
 when if smooth, and free from spots or marks, we shall perceive no 
 colour; but if a fine stroke of black be produced, pale tints or colours 
 will be seen ; but if more black is added, the colours will be more 
 distinct in a certain proportion. The order of the colours will com- 
 mence as it were with the penumbra of the former experiment oa 
 light, as light blue above passing downwards into indigo and violet, 
 the white immediately beneath partaking of the red and yellow, as in 
 the upper part of the white line, and the blue will not recommence 
 till something terminates the space of white, as a wrinkle or shadow; 
 the margin of the paper or book, a stroke with a pen, &c. producing, 
 (and we have power of continuing) the same phaenomena at plea- 
 sure. It was just observed, that if we added more black the colours 
 would be more distinct in a certain proportion ; I may add, that they 
 will be more vivid and apparently more perfect. 
 
 Ultimate perfection not being in the power of mortals, it is well 
 if we are allowed to attain to a certain degree of it ; and it is surely 
 a hi<Th satisfaction to arrive at any certainty within our limited 
 spliere. If proportion therefore of black will naturally or artificially 
 discover the quality or quantity of the coloured rays, finding this 
 
 * The rainbow mostly shows the same set of tints more or less brilliant. 
 ■\ The three tints or colours may be made to mix and even to form browns, by turn- 
 hig the prism on its axis so much as to show a lengthened range of colours. 
 
»9 
 
 proportion constant we become capable of a certain accuracy : we are 
 furthermore led to reduce them to any proportion at pleasure, as we 
 can repeatedly produce them: (see Tab. 3. and 4.) 
 
 Seeinjif them produced in any place at pleasure, it will be found 
 that they may be brought or placed in contact with each other, and 
 be mixed : (see 7«Z'. 4. d. e. &,c.) Thus we are enabled to show, with 
 as much nicety and calculation as we think proper, w hat may be the 
 primitive rays ; and considering them as reduced to three, we can 
 produce by means of a few strokes properly placed any possible tint, 
 naturally and truly, without equivocation. In the present instance, 
 for simplicity' sake, I determine the proportion by the breadth of the 
 black. Thus a given tint may be represented by a given proportion 
 of black upon white, as in Jig. d. &c. We have therefore a very 
 simple means of operation for accomplishing what has long been 
 thought beyond our reach. 
 
 It appears that the primaries chiefly depend on the edges of the 
 white and black of a certain proportion in contact, and that orange 
 and green depend on the narrowness of the white between two black 
 edges : thus a broad light upon black efluses yellow, red and blue, 
 the red and blue always bordering more or less on the black back 
 ground, and the yellow appearing upon some part of the space of 
 light or white, whatever light it is, even the shining or gloss light 
 on any black or dark coloured surface ; and should the light be nar- 
 row, the blue on one side and the red on the other mix with the 
 yellow, independent of the motion of the prism * ; and that the 
 light being still narrower, the yellow is lost in green formed by 
 its mixing with the blue; and when the red reaches the blue 
 
 * I do not put a black page with white streaks as an example of this ; those who have 
 a mind to examine it with a prism may easily procure such. The light spaces in Tab. 3. 
 f. e. d. answer nearly the same purpose, showing the space of tlie lights producing the 
 tintSj which are put on the side for better explanation : the lights being left in these ex- 
 amples may be made use of, and will show the colours nearly as figured in the proper 
 places for comparison. As we intend to use a white ground as most convenient, the pro- 
 portion ofblack producuig the tints will chiefly be considered. 
 
 D 2 
 
20 
 
 side, it becomes purple, soon after which they may be lost in the 
 narrowness of the line. Thus a single light space may be contrived 
 to show with the prism white, yellow, red and blue ; and by mixture, 
 orange, green and purple. So that we have primaries and binary 
 compounds, but no ternary compounds or browns*. 
 
 Nature having dictated thus much, I presumed to look further, and 
 found that there wanted nothing to form browns, except the means 
 of bringing the proper proportion of colours together, something like 
 the mixing of material colours. It was therefore required to con- 
 trive that the yellow, red and blue rays should pass among each 
 other, for the production of browns or ternaries. I succeeded in 
 accomplishing this, as shall be shown presently. 
 
 Finding that artificial light and dark will, by means of the prism, 
 in common daylight, give all the original tints, it was thought 
 necessary to show that yellow, red and blue, artificially contrived or 
 placed, produce the three or more tints, and the tints so produced 
 partake of the colour of the yellow, red, or blue, that produce them ; 
 (see Tab. 3. a. h. c.) in which are instanced, first, the yellow, a. The 
 white space between the two yellows would produce a proportion of 
 white, 1 a proportion of yellow, 2 a proportion of red, and 3 a propor- 
 tion of blue. The yellow is pretty good, being produced by the prism 
 from yellow. The red being produced by the yellow partakes of it, and 
 forms an orange tint. The blue is pale and wants brilliancy, on 
 account of the yellow being the palest of colours, therefore a bad 
 substitute for black. The penumbra below the blue has a poor 
 reddish tint, partaking of the yellow, where violet would take place 
 if produced by black, and so of the rest. b. The two reds will be 
 seen to give an eflfect to the prismatic tints evidently depending upon 
 the red that produces them, and so of the blue. It is however re- 
 markable that the red c. 2 is more orange than when produced by 
 black, the seven prismatic tints beneath which having among them 
 more perfect yellow, red and blue. Thus, black or dark in this 
 
 * The motion of the prism, however, is to be left out of the question at present. 
 
St 
 
 case seems to liave the power of producing these tints in a sort of 
 neutral manner, as if it only relieved tliem in their utmost purity ; 
 {Tab. 3. g. It. /.) and thin or pale tints marked by dark, or black, 
 still give pale colours in proportion as they are pallid or less forcible 
 themselves. 
 
 COLOURS PRODUCED BY A CERTAIN BREADTH OF LIGHT ADMITTED 
 BETWEEN REGULiVR PROPORTIONS OF BLACK, 
 
 At 5 or 6 Inches Distance from the Prism. 
 
 Tab. 3./ is a proportion that may give a general idea of four 
 colours, red, blue, green and indigo ; the yellow being just seen at 
 the edge of the green. In many instances the dazzling richness of the 
 tints gives them more distinctness than perhaps belongs to them, (see 
 Dr. Wollaston, and Dr. Young's descriptions, with that of Prieur's,) 
 but I believe the tints in all cases blend a little as in our fioures, but 
 " \\\w can paint as Nature paints" must argue for the want of nicety 
 m them. Tab. 4. e. will perhaps convey a tolerable hint of the 
 wider proportion producing the usual idea of the seven prismatic 
 tints of sir Isaac Newton, and show how they mix : 
 
 No. 2. Red No. 4. Orange Red and Yellow. 
 
 No. 1. Yellow No. 5. Green Yellow and Blue, 
 
 No. 6. Indigo Blue and a little Red. 
 
 No. 3. Blue No. 7. Violet Blue and Red. 
 
 It is perhaps difficult to account for the rays that produce the two 
 last mixtures. We, however, always see them more or less perfectly. 
 I suspect that the penumbra or loose rays that always accompany a 
 beam of light, produce again by refraction the red, yellow, and 
 blue, in a fainter manner upon the dark ground outside the princij)al 
 spectrum. Thus the indigo No. 6. is found to consist of the blue 
 with a proportion of the pale edge of the red so produced, and the 
 violet No. r. has a portion of the stronger red in addition to the 
 blue. Tab. 3. g. h. i. show that a narrow line of black gives the 
 appearance of three tints chiefly, and those pale, as it were diluted 
 with white, or water, as it has been done by the artist in the ex- 
 
h 
 
 22 
 
 ample ; and it is a general rule of Nature, in diluting colours, to give 
 them a bluer cast to our senses, whether in prismatic or material 
 colours, as we shall find upon a fair trial. The broader line h. is less 
 pale, and has four colours more distinct, blending into each other a 
 little : i. shows five tints distinctly and vividly, although somewhat 
 blended. 
 
 fYellow 
 Thus g has < Red 
 
 LBlue. 
 
 fYellow 
 Red 
 Violet 
 
 .Blue. 
 
 'Yellow 
 Red 
 
 <; Violet 
 Indigo 
 
 [Blue. 
 The gradual blending or passage from one to another is generally 
 too indistinct for use, excepting on some occasions. The yellow and 
 blue, that give a broader appearance in colours than the black pro- 
 ducing them, have a share or partake of the white, as it must be 
 remembered that they depend on both. Thus it produces by means 
 of the light on one side two proportions of yellow, and on the other 
 one of blue. I have before shown that a given proportion of 
 light or dark produces a given quantity or force of tint or colour. 
 In the present scheme, in which the mixing is to be more perfectly 
 understood, I have endeavoured to place the black marks in such a 
 position, that it may be seen what tints become mixed with others 
 by leaving a portion of each unmixed, llie upper five figures, 
 Tab. 4. c. show the quantity of black that produces those colours 
 represented in the lower five figures Tab. 4. d. c. 1 *, therefore, by the 
 
 * It was thought convenient, to prevent confusion in exanainiog the subject with the 
 
2S 
 
 help of a prism, will appear like (/. 1, having the five prismatic tints, 
 as Tab. 3. /; d. 1 being distant like c. 1 from c. 2, it does not interfere 
 with d. 2, but c. 2 is so near c. 3, as to allow one portion of yellow, 
 as in d. 2, which does not diminish in breadth, to reach the blue of 
 c. 3, forming a green binary, that may be distinctly seen, without 
 mixing with the other colours ; and so of the rest, which by their 
 construction give deeper mixtures of greens; and finally they become 
 triple compounds, as may be seen at c. 4 and 5, the red of 4 being 
 mixed with the blue of 5, the j'ellow of which passes as it were over 
 the violet and purplish red of 5, causing blue, red, or yellow browns, 
 in many degrees, where it passes over the red, the browns becoming 
 warmer, &c. No. 5 is narrow, like Tab. 3. g. that it may as it were 
 admit of the colours produced from the black of 4 above it 
 being effective. Thus we have a means of producing browns, 
 and different proportions may be made use of for different pur- 
 poses of measure, &c., as these are portioned in divisions of about 
 the 10th of an inch in width, to show what is the proportion mixed 
 or causing the mixture. Thus the four examples of black, each about 
 -■Lths of an inch wide, approach nearer by -pirthj ^^ich producing, in 
 conjunction with its proportion of white, a broad set of colours, and 
 this is made distinct even in the narrow line, 5, which is only ^^^ths 
 of an inch wide, and ^'^th is left of white, (see c. 4 and 5, and d. 4 and 
 5,) which just allows of an almost imperceptible penumbra to join 
 the brown in the latter example. 
 
 OF GRADUATING TINTS, &c. BY WEDGES. 
 
 If two wedges are placed opposite each other, they may be so 
 arranged that the space between shall allow the colours produced to 
 form a green mixture, and the green thus formed will be blue green 
 
 prism, to put as few figures of reference as possible, as in such examination each figure 
 will give a certain quantity of colour. We therefore request the reader will understand 
 that c. 1 means the black mark nearest the letter c ; and d. 1 the first range of colours 
 nearest d, reckoning downwards cord. 1, 2, 3, 4, 5. 
 
S4 
 
 at one end and yellow green at the other end, at the same time it 
 will be very gradual, and so of the other tints, but there will be no 
 browns: see Tab. 4. e. 
 
 The outl'ne /. with the squares will show how any spot may be 
 measured by length and breadth, as well as show the usual division 
 of parts that constitute the best proportions for the most perfect 
 colours. 
 
 Some apology may here be necessary, on account of the difficulty 
 of colouring the examples. It however may be urged, as in all other 
 cases, that the most perfect artist, or the most perfect materials we 
 borrow from Nature, resemble every thing else borrowed from that 
 source, and we must refer to the Great Original alone for perfection. 
 The use of the prism therefore is advisable to all that can have an op- 
 portunity to jjrocure one ; and when I haveshown a means of forming a 
 long wedge as most appropriate for seeing a large variety (see 
 Tab. 7.) I shall proceed to explain it : and I may here observe, 
 that it will be a fund of amusement to practise the producing of 
 tints by these means, when perhaps something will be found out 
 to improve and make it more instructive: An apparatus for thus 
 measuring tints, or colours, I have called a Chromatometer. 
 
 Having thus far spoken chiefly of prismatic colours, it may not 
 be amiss to show the effect of mixing material colours which cor- 
 respond exactly. 
 
 Primary tints or colours I have considered as yellow, red and blue, 
 because I do not comprehend that there has been proposed any 
 way of compounding them from others, that I am not perfectly sure 
 is founded on some deception ; and finding that they are capable of 
 producing all others by mixture, in every method I have had oppor- 
 tunity of examining with the greatest certainty. Venturing this con- 
 sideration as conclusive, as well from the opinion of many that I con- 
 sider competent Judges, as my own, I proceed to say something 
 of the mixing them in two's or 
 
 Binaries. Tab. 4. a. Now yellow No. 1 passing among red No. 2, 
 
25 
 
 forms distinctly, when viewed at a moderate distance or from the 
 bottom of the j)hite, the orange binary ; and again, yellow No. 1 
 passing among blue No 3, forms the green binary ; and lastly, 
 red No. 2, at the bottom of letter a. passing among blue No. 3, 
 forms the violet or purple binary: the whole sum of the proper bi- 
 naries, excepting their being ligliter or darker. 
 
 I shall now consider them combined by threes, or in Ternaries, b. 
 iit the bottom of the same Tab. 4. thus; Nos. I and 3, yellow and 
 blue, pass into Nos, 2 and 3, red and blue, and the yellow and red 
 being inost prominent, the efTect becomes at a moderate distance, or 
 from the top of the plate, orange brown, as at the bottom half; and 
 where there is a double portion of blue as in the upper half, it is a 
 darker brown when seen at such a distance as that the effect may 
 unite the whole to our vision. We see therefore that independent 
 coloured rays may become so placed as to give the sense of a perfect 
 mixture, which would have been the case with these if the lines had 
 not been made visible, which, however, was absolutely necessary to 
 explain them to our purpose : fine dots of the primaries among each 
 other would produce binaries or ternaries with a similar effect, also 
 one transparent tint over another, &c. 
 
 CHROMATOMETER. 
 
 I now enter upon a curious subject ; and I presume that even after 
 what has been said and done, it will appear at first a sort of chimaera 
 for a parcel of dark unintelligible forms to give a most exact account 
 of the proportion of colours. Having in the preceding part shown 
 in what manner colours are produced by means of the proportions 
 of black upon a white ground, or white on a black ground, this is in- 
 tended to serve as a lasting means of proving the hypothesis, or as a 
 test for any particular tint, under whatever impression we wish to 
 form a comparison. 
 
 I shall here denominate the black forms productors, as they ap- 
 pear to produce the colours ; their proportions being told or mea-. 
 
 E 
 
s6 
 
 jured to identify them when examined with the prism at a certain 
 distance ; but this varies with the refractive power of the prism, 
 wherefore some index is necessary to determine it. 
 
 I considered that, as perfect red is equal in breadth to the 4th part 
 of its own productor, and is equal to the pale blue above any pro- 
 ductor, so an increase of width at one end of the wedge, of one fourth 
 part, will be equal to the width of the perfectest red or pale blue to 
 be expected from it, and it will be a regulator or index for the whole 
 of the instrument. 
 
 Thus when the person has the prism so placed, that the upper 
 edge of the light blue, above the first wedge, is in a right line from the 
 edge of this index, or the dark blue upon it, I expect a similar 
 breadth of scarlet will be at the bottom, adjoining an equal breadth 
 of red under the index, supposing the index formed at the top, for 
 it may be either at the top or bottom, but I prefer the top as being 
 least in the way, (see the left hand end of the upjier figure, Tab. 7.) 
 This wedge, at the beginning including the index, contains five, 
 divisions which is equal to a much broader black space, for perfect 
 red is given where it is four parts, and no greater width will give so 
 perfect a red, but will always give scarlet. It will be seen that this 
 proportion is observed in the examples of T«Z'. 3. and 4. In achro- 
 matometer it should not be forgotten, that as few lines as possible 
 should come in the way, and that at any rate extra horizontal lines, 
 from the construction which at present seems best, will be greatly 
 in the way, and even perpendicular ones will be a little so if not 
 drawn quite through the scheme ; but to avoid both, I have managed 
 that the productors in the lower figure shall so correspond with a 
 certain measure that it may be immediately understood. But to 
 proceed with a sketch of the upper wedge. As an inch and :|:th pro- 
 duces scarlet, when viewed at a foot or more, one inch produces red^ 
 and Aths produce lighter red approaching crimson : thus we may 
 pass from the upper portion of the wedge to the next, beginning im- 
 mediately where the above left oft', and consequently with the same 
 
27 
 
 tint, (which may be noted as a proof of the proper position of 
 the jjrisra it is viewed by,) this will become more and more dilute to 
 the end. The third j)art of the wedge begins where the second left 
 off, with the same proportion and colour, and so of the other two ; 
 as these diminish, the red diminishes, or becomes more and more 
 dilute, till lost at the end of the fifth or last line of the wedge. The 
 red, in the way I generally look at the prism, is at the bottom of these 
 productors, as I may perhaps call them ; at the same time the blue at 
 the top will diminish from full and perfect blue to the most dilute 
 immediately opposite to the reds, and the yellow will do the same 
 under the red, but is double the breadth, as represented in Tab. 4. 
 This wedge therefore produces an infinite variety of these three pri- 
 mitive tints, from the most full and perfect to the most dilute, which 
 may be measured precisely at pleasure in a very certain manner ; so 
 that every person may, in a common light, agree in pointing out a 
 precise tint, even at distant parts of the world, if a similar wedge or 
 chromatometer is used. Thus suppose the present to be a founda- 
 tion, and for sake of accuracy was in general use, I would say, the 
 red of Euphorbia Peplis for instance, (see English Botany, Tab. 
 2002.) is, or should be, equal to one inch, that is equal to the red 
 given by such a width of black on white paper ; and so of any tint 
 or colour of any subject; and thus we may make conclusive com- 
 parisons, and learn what was intended, though time had caused it 
 to fade. 
 
 CHROMATOMETER CONSIDERED SOMEWHAT ABSTRACTEDLY, 
 
 Hitherto it has been chiefly shown how the prism may be used 
 to produce colours in a book. It may now be necessary to show the 
 use of the Chromatometer as an independent instrument (something 
 like a barometer), as a useful and if we please an ornamental ap- 
 pendage in a parlour or study, with a more exact method of apply- 
 ing it. 
 
 It might therefore be flattened on a board and hung like a pic- 
 
 e2 
 
28 
 
 ture, decorated with a gold or other frame that does not overshadow 
 it, perhaps rather in the shady corner of a room to preserve it, and 
 when used, so placed that it may be nearly perpendicular so that the 
 beams of light in the room, may illuminate the face of it; when a 
 prism may be adjusted at a proper distance opposite to it. The 
 prism may also have been selected, and perhaps measured as to its 
 power of refraction, from which there may be a means of de- 
 termining the distance or angle to be subtended, &c., in which case 
 it will be most comjietent for use. 
 
 One angle of the prism should be directed towards it, and the 
 spectator should look in at the opposite face of the prism towards 
 the lower face, where the spectrum will appear in great beauty and 
 order. 
 
 The upper separated wedge should be looked at by itself, and the 
 lower one also. By use we may afterwards readily compare them, by 
 moving the prism. 
 
 The wedge or open chromatometer. Tab. "J. upper Jig. The 
 square at the beginning will indicate the proper distance, by giving 
 the spectator eight divisions or tints of regular and equal propor- 
 tions, viz. 
 
 1 Light Blue apparently above the black space. 
 
 2 Darker Blue 
 
 3 Violet 
 
 4 Blue Black \ upon the black space. 
 
 5 Black 
 
 6 Scarlet 
 
 \ below the black space. 
 8 Lighter YellowJ ^ 
 
 A broader square wiU not give more divisions of colours either 
 regular or otherwise, if observed either at the same or at a less 
 distance. 
 
 The commencement of the wedge should give two parts of blue, 
 one of indigo, one of violet, one of red, and two of yellow, nearly as 
 Tab. 3. i. or as Tab. A. d. The dark blue, indigo, and violet will 
 
29 
 
 continue as long as their respective parallels or breadths along the 
 productor: the red should be perfect and will become more dilute 
 and a})proach crimson, as it gets to the narrow end of the first seg- 
 ment, the yellow and blue will diminish in proportion, or appear 
 more dilute. The beginning of the second segment will have crim- 
 son in the place of the red, which will be paler at the end ; the yel- 
 lows and blues diminish of course. The third segment will have a 
 middle crimson or a crimson more dilute, as also the yellow and 
 blue. The fourth segment will have light crimson with light yel- 
 lows and blues. The fifth segment will have pinks or paler crim- 
 sons, yellows, and blues till they all fade into light, 
 
 THE UNIVERSAL CHROMATOMER, Tab. 7. lowerjig. 
 
 This is formed of segments of the wedge, parallelized in certain pro- 
 portions, and which may be called indicators and determinators *. 
 Tiiey are brought near to each other to mix and form the binaries 
 and ternaries. 
 
 The narrow end of the upper determinator gives the proportions 
 of yellows, reds, and blues, according to its respective width, and so 
 to the middle with some violet. The two next segments give also 
 the same proportions of colour as the upper wedge ; but, according 
 to the proportionate distance exemplified in Tab. 3. and 4., mix with 
 the next determinators immediately under them forming light to 
 darker greens. The second five segments form chiefly light blues 
 and light to denser crimsons. Between the second and -third sets 
 of determinators will be found verdigrease-Iike greens. The third 
 determinator will have light and dark browns ; between it and the 
 fourth will be light and dark grays at the broader end. The fourth 
 and fifth will produce pinks, light brownish orange to nearly orange 
 at the broadest end. As every determinator gives its exact propor- 
 
 * Indicators, when they are competent to show the tint or colour indicated by the 
 comparative proportions : thus, as sir Joshua Reynolds says, " Theory is the art of 
 knowing what is truly Nature." Determinators, when with the help of tlie prism we 
 can determine the proportions. 
 
30 
 
 tion of colours, so they must mix in these proportions, and I know 
 nothing more beautiful than to witness it ; yet like many other 
 things, it requires some practice to arrive at tolerable perfection. 
 This scheme is in its nature perfect, and calculation, measure, &c. 
 will prove it; but how far the limited powers of mankind will carry 
 it, remains a desideratum. One man can divide a micrometer into 
 25 million parts per square inch, in every line of which seems a 
 whole suit of colours ; but whether any can carry it much further 
 is not known. The chromatometer is capable of every degree of 
 extension or of the most minute division. I left off in the upper 
 chromatometer nearly in a point ; in the lower one at a determined 
 measure about ^d part of an inch. 
 
 OF THE MIXING OF MATERIAL COLOURS, OR THE CHROMATIC 
 
 SCALE. 
 
 The mixing of material colours is very simple, if we dwell upon 
 the idea of the three jjrimitives ; otherwise the very beginning is 
 absolute confusion, as will be seen in most preceding attempts ; it 
 is much easier to comprehend this figure than to mix the chroma- 
 tic tints, as the primitive colours are distinctly seen passing into 
 each other and forming orange, green, and purple, see 1, 2, 3. The 
 centre of the triangle and circle, Tab. 5. and 6. we consider as ana- 
 logous to light or white, represented as passing or spreading under 
 the triangle, gradually passing to a nearly distinct tint ; that is to 
 say, yellow, red, and blue when mixed or in union with certain pro- 
 portions of light or white, do not give positive ideas of yellow, red 
 and blue, the yellow having a grayer tinge, if I may use the ex- 
 pression, and the red rather a bluish tinge, the blue also losing its 
 beauty with a duller or grayish appearance *. To make short of it, I 
 shall call these the primitive colours diluted, which in the figure are, I 
 presume,yet sufficiently to be understood as far as the circle continues, 
 
 * These are analogous to the appearance of whorled mixtures, too often compareJ 
 to white, whorling being an aerial dilution of colours. 
 
31 
 
 but most so at the extremities where they are strongest ; and they 
 are put upon the paper in such a gradation that, however the space 
 is confined and the tints consequently innumerable, they may be 
 identified by the measures from the centre with the compasses ; and 
 so nearly do the different copies correspond with one another, that 
 they will pretty well accord with the nicest comparison of which we 
 can be sensible. 
 
 The inner triangle commences, as it were, with a tint darker than 
 the circumference of the circle above described, and the next or 
 middle portion shows the yellow, red, and blue still more determined, 
 and the outer triangle, perhaps, most perfect, or what I would wish 
 to consider as the fullest and most determined colours which I have 
 got pretty well represented. These three divisions are distinct, and 
 I call the innermost, light, the next, middle, and the outer, the full 
 tint, which may be compared to the upper wedge. Tab. 7. The full 
 red may be found at the beginning of the wedge, the middle red 
 at about the middle of the second line, and the pale red at the end 
 of the third line; when the whole is adjusted, portions of the vellovv 
 and blue in the same parts of the wedge will also accord. Thus 
 three degrees of the simple or primary tints. These, passing over 
 each other at the angles, form binaries ; being atone corner, orange ; 
 at another, green ; and at the other purple. Thus light yellow and 
 light red form light orange ; middle yellow, and middle red, form 
 middle orange : and full yellow, and full red, form full orange ; light 
 yellow, and middle red, forming reddish orange, &c. ; in all nine 
 distinct tints, and the same with the greens and purples ; for a fuller 
 description see the nomenclature to the chromatic scale. 
 
 Now these may form ternaries by adding to them the third co- 
 lours, — to the orange blue, to the green n^d, and to the purple yellow ; 
 thus are formed the different browns or ternaries, which must al- 
 ways consist of the three primaries as the cjiromatometer shows t 
 these are innumerable of course, as they may be lighter or darker, 
 orange, green, or purple browns, &c. 
 
 The lovver circle c, d. represents t\vo of the three principal browns. 
 
33 
 
 beginning at light, viz. yellowish browns, red brown, and bluish or 
 grayish brown, &c. 
 
 The three extra lozenged quadrangles are continued from the yel- 
 low and red forming orange, and the third tint blue is in the three 
 degrees passed over them. 
 
 The first or light blue forming chiefly orange browns; the second 
 or middle forming greener browns ; and the third or full blue form- 
 ing the darken or grayer and bluer browns. 
 
 CHROMATIC SCALE. 
 
 In order that the tints in the former plate 5 should not be blackened 
 by figures, I have annexed the following one, plate 6 to explain the 
 primaries, binaries, and ternaries, or form a list of tints in as simple 
 an arrangement as possible, selecting the usual terms or commonest 
 nomenclature, that it might be generally understood. I have ex- 
 pressed the yellow by dots, the red by undulating lines, and the 
 blue by straight lines. It may therefore be understood what colours 
 pass into each other to form the binaries and ternaries, with a precision 
 equal to that of a coloured example. These, in proper proportions, 
 may serve to practise on, in some measure like the lines in heraldry, 
 in the place of representing colours, upon many occasions, as in en- 
 graving, &c. I now proceed to my nomenclature ; and, as much in- 
 formation may be given by letters or figures, at present I shall 
 use small Italics for light tints, small Roman characters for middle 
 tints, and roman capitals for the full or perfect tints, as I have be- 
 fore termed them : 
 
 ij therefore may signify light yellow, 
 
 y ■ middle do. 
 
 Y full do., 
 
 and the same of the red and blue. 
 
 Binaries may therefore be explained by ?/. r., signifying light ycl- 
 /oH' and middle red ; and ternaries thus, ?/. r. i?., signifying light yel- 
 loiv, middle red, and full blue ; which will be easily understood by 
 
33 
 
 the chromatic scale and table*. Latin terms are added upon excel- 
 lent authority, with as much precision as possible. It appears that 
 they have been taken too indefinitely in general, and it is the less to 
 be wondered at, as there is so little agreement among authors with 
 regard to colours every where. 
 
 NOMENCLATURE FOR THE CHROMATIC SCALE, 
 Primaries. 
 Yellows. 
 
 1 Light yellow, Pallide flavus, .~..-----y. 
 
 2 Middle yellow, Flavus, ----------- y. 
 
 3 Full yellow, Saturate flavus, -.__--_- -y. 
 
 Reds. 
 
 4 Light red, Pallide ruber, _.-------- r. 
 
 5 Middle red. Ruber, -r. 
 
 6 Full red, Saturate ruber, ----------- R, 
 
 Blues. 
 
 7 Light blue, Pallide caeruleus, __------. i. 
 
 8 Middle blue, Ca;ruleus, ----------- b. 
 
 9 Full blue. Saturate caeruleus, --------- b. 
 
 Binaries. 
 
 10 Reddish yellow, Rubescente flavus, ------ Y. r. 
 
 11 Yellowish orange, Flavescente aurantiacus, - - - - y. r. 
 
 12 Full do. Saturate flavescente aurantiacus, - - - - y. r. 
 
 13 Light orange, Pallide aurantiacus, ------- y. r. 
 
 14 Middle orange, Aurantiacus, --------y. r. 
 
 15 Full orange, Saturate aurantiacus, -------y. R. 
 
 16 Reddish orange, Rubescente aurantiacus, - - - - - V-^' 
 
 * Should any of these methods of expressing colours be adopted, there will be a stan- 
 dard for any tint, as they may be identified by either mode of expression ; and the mea- 
 sure of any one, or all, may be referred to, whether primary, binary, or ternary, 
 
 Y 
 
34 
 
 17 Full orange. Saturate rubescente aurantiacus, - - - y. r. 
 
 18 Yellowish red, Flavescente ruber, -_-.-__ j/. r. 
 
 19 Bluish red, Caerulescente ruber, ------- ^i. r. 
 
 20 Reddish purple, Rubescente violaceus, - - - - - b. r. 
 
 21 Full do., Saturate rubescente violaceus, - - - b. R. 
 
 22 Light purple, Pallide violaceus, ------- -b.r. 
 
 23 Middle purple, Violaceus, --_--__-. b. r. 
 
 24 Full purple. Saturate violaceus, -------- b. r. 
 
 25 Bluish purple, Csrulescente violaceus, ----- b. r, 
 
 26 Full do.. Saturate csrulescente violaceus, - - - B. r. 
 
 27 Reddish blue, Rubescente caeruleus, ------ b. r, 
 
 28 Yellowish blue, Flavescente caeruleus, ----- b. 7/. 
 
 29 Bluish green, Caerulescente viridis, ------ b. ?/. 
 
 30 Full do.. Saturate cjerulescente viridis, - - - - r. y. 
 
 31 Light green, Pallide viridis, ------ ~ . - b. 1/. 
 
 i2 Middle green, Viridis, ---.-.---_ b. y. 
 
 33 Full green. Saturate viridis, -_-._--- b. Y. 
 
 34 Yellowish green, Flavescente viridis, ------ ^. y. 
 
 3 5 Full do., Saturate flavescente viridis, - - - b. Y. 
 
 36 Bluish yellow, Cferulescente flavus, ------ Z^. y. 
 
 Ternabies. 
 
 37 Full brownish yellow, Saturate brunnescente flavus, - b. r.Y. 
 
 38 Middle yellowish brown, Flavescente brunneus, - - b.r.y. 
 
 39 Yellow orange brown, Flavo aurantiaco brunneus, - b.r. y. 
 
 40 Light brown, Pallide brunneus, ------- b. r. t/. 
 
 41 Middle orange brown, Aurantiaco brunneus, - - - b.r.y. 
 
 42 Brownish orange, Brunnescente aurantiacus, - - - b.R.Y. 
 
 43 Reddish brown, Rubescente brunneus, - - - - - b. r. y. 
 
 44 Reddish orange brown, Rubescente aurantiaco brunneus, b. r. y. 
 
 45 Brownish red, Brunnescente ruber, - -=■ » - - b. R.y. 
 
 46 Brownish yellow green, Brunnescente flavo viridis, - y. r. b. 
 41 Middle greenish gray, Viridescente griseus, - - - y. r. h. 
 48 Full yellowish brown. Saturate flavescente brunneus, y. r. b. 
 
35 
 
 •49 Bluish gray, Caerulescente griseus, - - - - - - y. r.h. 
 
 50 Middle brown, Brunneus, - - ------ y. n b. 
 
 51 Full orange brown. Saturate aurantiaco brunneus, - y, r. b. 
 
 52 Purplish gray, Violascente griseus, - - - - - - y. r.h. 
 
 53 Full reddish brown. Saturate rubescente brunneus, - y. r. b, 
 
 54 Brownish purple, Brunnescente violaceus, - - - y. R. b. 
 
 55 Blackish green, Nigrescente viridis, ----- y. r. b. 
 
 56 Brownish blue, Brunnescente cyaneus, - - - - y. r. b. 
 
 57 Greenish black, Viridescente niger, - - - - - y. r. b. 
 
 58 Blackish blue, Nigro cyaneus, - -------?/. r. b. 
 
 59 Bluish black *, Caeruleo niger, - - - - - - - y. r. b« 
 
 60 Full brown, Saturate brunneus, ------- v. r. b. 
 
 61 Blackish blue purple, Nigro cyaneo violaceus, - - - ?/. r. b, 
 
 62 Purplish black, Violascente niger, ------ y. r. b. 
 
 63 Blackish purple, Nigro violaceus, --..__ y. r. p. 
 a Yellowish white, Flavescente albus. 
 
 b Reddish white, Rubescente albus. 
 
 c Bluish white, Cterulescente albus. 
 
 d Brownish white, Brunnescente albus. 
 
 e Grayish white, Canescente albus. 
 
 I intended to have had the light, middle, and full tints so as to 
 consider the latter or full colour, as giving no other idea than that of a 
 perfect yellow, red, and blue, so that the simple names flavus, ruber, 
 and caeruleus might correspond, which now stand for the middle 
 colours which are neither light nor strong, and must be considered 
 as tints that are exactly betwixt the extremes ; yellow, for example, 
 under these circumstances, is neither light nor full, and is not by any 
 means to partake of any tinge of red or blue. Thus light yellow is 
 yellow distinct, mixed with light or white in such a proportion that 
 it has not another tint, as a little more white would somewhat obli 
 terate or disguise it. The middle being a determined yellow, 
 neither light nor strong. The full may be conceived as such an ac- 
 
 * True black would be between this and brown, but nearest to bluish black. 
 
 F 2 
 
36 
 
 cumulation of mere yellow, that to add more would give an idea of 
 another colour bordering on orange. The same of red and blue. 
 Black is as it were a supersaturation of the darkest tints : thus full 
 brown or saturate brunneus with a supersaturate portion of blue will 
 be analogous to black. Grays may be made upon this principle by 
 adding a portion of blue to the light and middle browns. 
 
 Having reconciled the primitive of all tints, and colours, on the 
 most permanent basis, it becomes necessary to speak of the material 
 colours, it being one of the first objects of my intention to simplify 
 them. 
 
 MATERIAL COLOURS USEFUL TO ARTISTS. 
 
 The most perfect are those that have some transparency, as they 
 may be applied with greater variety, and as every object is seen 
 through a transparent medium, which helps to give an effect that 
 the artist is otherwise too often unable to accomplish, and for 
 which much pains is taken by glazing with the help of gum or 
 varnish assisted with asphaltum. I should think that, the fewer the in- 
 gredients the more perfectly they may be understood ; but, being 
 easily comprehended, perhaps they may be more casually passed 
 over ; yet it were better to understand a few things well, than to be 
 confounded with a multitude. 
 
 It happens that what are called material colours are not all so per- 
 manent as might be desirable, and the artists in oil or water colours, 
 and even in enamel, are often much troubled to accomplish their ends 
 on this account. Mineral colours for enamel are often so tender as 
 easily to be affected by a small difference of heat in fixing, and those 
 for oil or water colours often readily change by exposure to air. 
 Vegetable colours are more used in water or size colourings or paint- 
 ings, but are only fit to be kept in portfolios or books. Colours from 
 animal substances are least in use; and although Nature allows us ta 
 procure colours from either of these three great divisions for our dif- 
 ferent uses, they may all depend upon nearly the same bases ; which 
 however yet remains to be found out. I will now enumerate the 
 
37 
 
 most necessaiy or useful colours in the simple order of Yellow, Red, 
 and Blue, with some hint of their general properties. 
 
 White is only considered as a heightener ; white lead or carbonate 
 of lead serves in oil generally, and the oil partly preserves it; it 
 soon changes with water. Barytes white is now adapted to use 
 with water colours, and is very good ; whitening is used for ordinary 
 purposes. 
 
 Whites are naturally opaque, and I think conveniently so to give 
 solidity when occasion requires it: thus, scarce any thing is wanting 
 to a good artist : it is as it were a neutral, as well as black or dark, 
 upon which true colours depend. 
 
 PRIMARIES. 
 Yellows. 1, Gamboge is most perfect yellow, used in water colours. 
 
 2 Lake 
 
 3 King's, semimetallic, opaque^ 
 
 4 Naples 
 
 5 Patent 
 
 6 Ochre, earthy with oxide of iron, British Mineralogy, 
 
 tab. 253. 
 Reds, 1 Carmine, most perfect when good 
 
 2 Lake 
 
 3 Burnt ochre, called red ochre, not perfect red 
 
 4 Venetian red, commonly so called, rather a deep 
 
 rusty colour. 
 Blues. 1 Prussian or Berlin blue, most perfect 
 
 2 Antwerp blue, greenish blue 
 
 3 Indigo, dull, strong 
 
 4 Smalt, cobalt, purplish.1 
 
 BINARIES. 
 Yellow and red. Orange orpiment 
 Chromate of lead 
 Oxide of lead 
 Vermilion, scarlet. 
 
38 
 
 Yellow and blue. Verdigrise 
 
 Terre vert. 
 Purple or violet, or red and blue. 
 
 Cochineal 
 
 Logwood. 
 
 TERNARIES. 
 
 Yellow, red, and blue. 
 
 Terra Siennae, rather orange brown 
 Umbers, reddish brown 
 
 Terra Sepis, cuttle brown, nearly neutral, not in- 
 clining either to yellow, red, or blue. 
 Black. 
 No. 1 Gamboge, capable of solution in water or oil, from very 
 transparent dilute or light to a somewhat opaque 
 perfect yellow, but, if stronger, inclines to a reddish 
 cast. Most commonly used in water. Liable to fade 
 on exposure to light. Often makes good binaries : with 
 blue, green ; with red, orange ; or ternaries, with the 
 red and blue, as browns. 
 
 2 Yellow lake, used in oil, makes much the same binaries and ter- 
 
 naries as the above. 
 
 3 King's yellow, adapted to opaque Avater colours, but liable to 
 
 change slightly. 
 
 4 Naples yellow, (must not be rubbed with a metal palette knife,) a 
 
 bright durable yellow sometimes used in oil. 
 
 5 Patent yellow, when used in oil, is more durable than in water, 
 
 in which it is liable to change soon to a dark brown. 
 
 6 Yellow ochre, used most commonly in oil, gets more forcible, if 
 
 I may use the expression, and is afterwards durable ; it is 
 rather a brown yellow : see B. M. tab. 253, p. 104. 
 1 Carmine red, or Lake. The latter is rather adulterated carmine, 
 to make it seem cheaper and go further, and to serve in 
 oil. Carmine when properly prepared is perhaps the 
 
99 
 
 most perfect colour ; may be used in mixtures with the 
 same facility as gamboge, from thin, nearly transparent, 
 to strong, nearly opaque. 
 2 Vermilion, sometimes approaches this, but generally borders 
 on orange or scarlet, that is, having a little yellow mixed. 
 So we have but one perfect red. Those called red ochre 
 or Venetian red are comparatively yellow or brown reds ; 
 the first is useful in oil, the latter in water or size. 
 
 1 Prussian blue may be used in water or oil ; it is the most perfect 
 
 blue we know, but has a purplish tinge in some in- 
 stances. It is extremely useful in forming greens with 
 gamboge, and purples with reds, and ternaries or browns 
 with both. 
 
 2 Indigo blue, chiefly useful for fixing shades that are to be 
 
 worked over in water colours, is dull. 
 
 3 Smaltblue,most permanent, most rich vvitharedcast,difficulttouse. 
 The best yellows, reds and blues will form good binaries, as men- 
 tioned above. 
 
 The local binaries, if I may so call such as nature produces chemi- 
 cally, and as it were without apparent mixture, are : 
 
 1 Vermilion, sulphuret of quicksilver, used in oil or water, is li- 
 
 able to change on exposure to air; oil or varnish defends 
 it, which gum Arabic does somewhat as a water colour. 
 
 2 Orpiment, sometimes yellow, liable to change. 
 
 3 Orange or red lead, liable to change. 
 
 4 Chromate of lead, changes green with heat, has not been much 
 
 used in England. 
 
 1 Verdigrise, used in water or oil, very bright yellow or blue, 
 
 may have gamboge mixed with it, changes most in oil. 
 
 2 Terre-verte, used in oil, not bright but durable, probably used 
 
 by the ancients of the Venetian school : see Bril. Min. 
 tab. 272. 
 The three best primitives will make any ternaries, if well managed, 
 and even produce the blackest effect possible. 
 
40 
 
 "Terra Siennas, umber and Coulognes earth are cheaper. 
 
 Sepiae, the cuttle fish brown, commonly so called, is a sort of 
 
 neutral, as all browns are, being chiefly used for shades, 
 but should vary with the subject to be represented. 
 
 Those that may be used in oil may generally be used for printing 
 in colours, &c. 
 
 As perfect black is rather a desideratum in printing, I might ad- 
 vise transparent red or blue, which may be added to lamp or Franck- 
 fort black, to take from their dull opacity, — the red to the lamp black, 
 commonly called blue black ; and the blue to the other when too 
 brown. A discreet printer will know by a trifling hint what to do. 
 
 Painters of experience do not generally want the finest colours for 
 their works, as they can give a natural and fine effect by properly 
 contrasting them in chiar' oscuro, &c. : and it is not the best paint or 
 best tools that make the best artists : yet some hint may be of use 
 to judicious hands. No merit is of consequence without competent 
 judges. 
 
 I have used ordinary colours all through the present work, because 
 it will ehow the more general extent of common colours. The best 
 preparations might have seemed to have given a fuller effect, but 
 would perhaps mislead, as too much might have been attributed to 
 their gaiety, and not to their order : my list is therefore only as 
 follows. 
 
 Gamboge 
 Carmine 
 Prussian blue : 
 a few others as occasional auxiliaries may now and then be useful for 
 cheapness in back grounds, drapery, &c. 
 
 Among minerals, the three substances which approach nearest to 
 the colours of the three primitives are: 
 
 Yellow, orpiment, or sulpluiret of arsenic. 
 
 Red, realgar, or red sulj)liuret ofai-senic. 
 
 Blue, lapis lazuli. 
 
 Among vegetables, the petals of ranunculus, and the lemon peel- 
 
41 
 
 ing are yellow, as well as many other plants and parts of plants. 
 The fruit of Ribes rubrum, or red currant, and the fructification of 
 Lichen cocciferus are red. The flowers of Veronica saxatilis, E. B. 
 tab. 1027', and alpina, E. B. tab. 484, are blue; and those of \. 
 spicata, E. B. tab. 2, are full blue. 
 
 Binaries and Ternaries are more universal. 
 
 Colours are identically the same on any substance however re- 
 flected, whether mineral, as from earthy or metallic ones; vegetable, 
 as from flowers or fruit ; or animal, as from hair, feathers, &c. I'he 
 same colours may be reflected very dully and afterwards be mixed 
 by shade till lost in darkness, as may be readily understood if we 
 colour different substances with the same yellow, red, or blue, such 
 as paper, silk, velvet, or silver. 
 
 I once thought of making more references to the three primi- 
 tive colours in minerals, vegetables, and animals; liowever, as minerals 
 are chiefly used, so they come of course in their places as material 
 colours. Vegetables in Great Britain have good yellows, as most 
 Banunculuses ; perfect blues are more scarce, and perfect reds 
 also. I cannot find tliat we can refer to any British insect 
 for yellow, red, or blue. The Rev. W. Kirby, author of the 
 JVIonographia Apum Anglise, was so good as to point out some parts 
 of insects, including some foreign ones, that would identify these 
 colours very well, when the specimens are perfect ; but perhaps it 
 might be aggravating to make these references, as something might 
 be wrong. Birds and quadrupeds have the local colours in parts 
 occasionally very brilliant. The scarlet Ibis is universally allowed 
 to be so ; and D. Turner, Esq. in his Fuci, considers red as 
 between crimson and scailet ; which seems to me to be perfectly 
 correct. I need here say no more, but refer to the Chromatometer 
 as the instrument or more perfect instructor when duly attended 
 to ; and I have no doubt that by such attention reasonable ideas will 
 become more general, and lead to improvement in the hands of some 
 person who has a happy independent leisure, and abilities not only 
 
 G 
 
42 
 
 to add calculations for the more exact proportions and distances, but 
 to show what is the utmost extent of its utility. 
 
 The Rev. W. Kirby informs me that Lamarck is said by Latreille 
 to have given a chromatic scale of colours ; and from a sketch which he 
 was so kind as to give me, just as I was about to send this to the ])ress, 
 1 tind it was very conclusive as far as it went, and is truly ingeuiuu;'. 
 He observes tiiat the colours of the rainbow or prism are nut in the 
 natural order, but exhibit two reversed branches of that order joined 
 together, white and black being suppressed, v\ hich he affirms are the 
 extremities of the natural series of colours: by this reversion the 
 yellow is laid next to the blue, and from the mixture of yellow and 
 blue rays results green, observable in the rainbow. Yellow, red, and 
 blue, he considers as three principal points of coloration ; for the type 
 of these colours he takes the middle part of the yellow, red, and blue 
 bands of the rainbow. He observes that although it is very easy 
 to determine the colour of the middle part of the red band, because 
 that band has its full width, yet it is more difficult to determine 
 that of the blue and yellow bands, because these bands have half 
 their width taken up to form the green band. He then forms by 
 proportion binaries, and mixtures, of which he gives an instructive 
 table, and an arrangement which clearly points out the difficulties 
 that attend accuracy in this subject. It shows also that it is na- 
 tural to apply to the prismatic colours for an original source, and 
 by that application how various the ideas and modes of improve- 
 ment have been, while all have had a similar confidence of being 
 most perfect. 
 
 Perhaps there may have been ages of perfection in this subject, 
 which are lost, like other things that do not depend upon durable 
 materials ; as the statues of Praxiteles, which being handed down to 
 us give evident proofs of great perfection in those days. Indeed I 
 can scarce help thinking that I have seen something in antiquity that 
 belongs to a compounded wedge, such as I have constructed for a 
 measurer of colours : if so, it may help to unravel a mystery ; and I 
 
43 
 
 hope antiquaries will not forget to inquire into the subject, should 
 it ever come into their hands. 
 
 According to Dr. Young, " Dr. Wollaston has determined the di- 
 vision of the coloured image or spectrum in a more accurate manner 
 than had been done before: by looking through a prism at a narrow 
 line of light, he produces a more effectual separation of the colours 
 than can be obtained by the common method of throwing the sun's 
 image on a wall. The spectrum formed in this manner consists of 
 four colours only, viz. red, green, blue, and violet." 
 
 " The colours differ scarcely in their quality within their respec- 
 tive limits, but they differ in brightness; the greatest intensity of 
 light being in that part of the green that is nearest the red ; a narrow- 
 line of yellow is generally visible at the limits of the red and green, 
 but its breadth scarcely exceeds that of the aperture by which the 
 light is admitted; and Dr. Wollaston attributes it to the mixture of 
 the red with the green light, which is found to be the same, what- 
 ever refracting powers may have been used for its formation." 
 
 " If the breadth of the aperture viewed through a prism is in- 
 creased, the space occupied by each variety of light in the spectrum 
 IS augmented in the same proportion, and each portion encroaches 
 on the neighbouring colours and is mixed with them ; so that the 
 red is succeeded by orange, yellow, yellowish green, and on the other 
 side by violet, and it is in this state the prismatic spectrum is com- 
 monly exhibited." Thus there are five colours to this specimen of 
 Dr. Young's common prismatic spectrum, four positive ones to 
 Dr. Wollastou's, and five doubtful ; but seven to Sir Isaac Newton's. 
 
 The doctor proceeds to observe, that " when a beam of light is so 
 much enlarged as to exceed the angular magnitude of the spectrum, 
 it retains its whiteness in the centre, and is terminated by two difl^er- 
 ent series of different colours at the different ends. These series are 
 still divided by well marked lines ; on the one hand, the red remains 
 unmixed; the space belonging to the green and blue becomes a 
 greenish yellow nearly uniform throughoiit, and here the appearance 
 of the colour ends, the place of the violet being scarcely distinguish- 
 
 G 2 
 
44 
 
 able from the neighbouring white light." If Dr. Young had had a 
 jjerfect line of light, viz. with an equal appearance of centre and sides 
 altogether resembling white, the three primitive tints would pro- 
 bably have presented themselves to him as in my Tab. 2, Jig. 3. 
 Therefore he was near seeing what might, in such hands, have proved 
 useful. 
 
 It is further observed that "the effect of white light on the sense 
 of sight might be imitated by a mixture of colours taken from dif- 
 ferent parts of the spectrum, notwithstanding the omission of some 
 of the rays naturally belonging to white light. Thus, if we intercept 
 one iialf of each of the principal portions into which the spectrum 
 is divided, the remaining halves, when mixed together, will still 
 preserve the appearance of whiteness ; so that it is probable that the 
 different parts of these portions of the spectrum which appear of one 
 colour, have precisely the same effect in the eye. It is certain that 
 the perfect sensations of yellow and blue are produced respectively, 
 by mixture of red and green and of green and violet light, and there 
 is reason to suspect that those sensations are always compounded of 
 the separate sensations combined ; at least this supposition simpli- 
 fies the theory of colours. It may therefore be adopted with advan- 
 tage until it be found inconsistent with any of the phenomena; 
 and we may consider the white light as composed of a mixture of 
 red, green, and violet only, in the proportions of two parts of red, 
 four of green, and one of violet, with respect to the quantity or in- 
 tensity of the sensations produced." Again: "From these three 
 simple sensations with their combinations we obtain seven primitive 
 distinctions of colours * ; but the different proportions, in which they 
 may be combined, afford a variety of tints beyond all calculation. 
 The three simple sensations being red, green, and violet, the three 
 binary combinations are yellow, consisting of red and green ; crim- 
 son, of red and violet ; and blue, of green and violet ; and the seventh 
 in order is white light composed of all three united; but the blue 
 
 * Thus we have seven colours diffeving from Sir Isaac Newton's. 
 
45 
 
 thus produced by combining the whole of the green and violet rays 
 is not the blue of the spectrum : four parts of green and one of 
 violet make a blue, diH'ering very Utile from green ; while the blue 
 of the spectrum appears to contain as much violet as green, and it is 
 for this reason that red and blue usually make a purple, deriving its 
 hue from the predominance of the violet." 
 
 The doctor says, " It would be possible to exhibit at once to the 
 eye the combinations of any three colours in all imaginable vari- 
 eties; two might be laid down on a revolving surface, in form of 
 triangles placed in opposite directions, and the third on projections 
 perpendicular to the surface, which, while the eye remains at rest in 
 any one point, obliquely situated, would exhibit more or less of their 
 jndntefl sides, as they passed tiieir diti'erent angular positions; and 
 the only further alteration that could be produced in any of the 
 tints, would be derived from the dilFerent degrees of light only. The 
 same effect may also be exhibited by mixing colours in different 
 proportions by means of the pencil, beginning from the equidistant 
 jioints or centres." 
 
 This, I think, seems a conclusive argument of the ntility of the 
 knowledge of the three primitives, viz. yellow, red, and blue; for it is 
 impossible for the compound sensations, as I would call the green and 
 violet, with or without the red, to produce yellow in any part of the 
 triangle ; and this is confessed in the following explanation of Dr. 
 Young's^?"-. 427 : "A triangular figure exhibiting in theory all pos- 
 sible shades of colours; the red, green, and wiiite are single in their 
 respective angles, and are generally shaded off towards the opposite 
 sides ; a little j/e//o2<; and blue only are added in their places in order 
 to supply the want of brilliancy in the colours which ought to com- 
 pose them. The centre is gray, and the light of any two colours 
 which are found at equal distances on opposite sides of it, would 
 always very nearly make up together white light, as yellow and 
 violet, greenish blue and red, or blue and orange." 
 
 This triangle of Dr. Young's will only make a variety of light or 
 dark browns, which any three colours, simple or mixed, would, if 
 
46 
 
 i)assed from the three corners over each other to the opposite sides, 
 as he places them. If this would make "all possible colours," there 
 would be no occasion for yelloiu and blue, which were wanted, and 
 which he has been obliged to put in : here it is plain that simj)Ie 
 yellow and blue must answer for themselves, even under the dulling 
 influence of the general mixture *. 
 
 There are many phamomena attending the iris like colours, which 
 will now easily be reduced to some jihilosophical order for descrip- 
 tion, and prevent that vague and confused uncertainty that prevails 
 in many works, and which I did not dare to quote, however curious, 
 as in some parts they might be above my abilities to comprehend. 
 
 Before printing this little essay, 1 thought it proper to look at one 
 ■or two more works, perhaps to supersede my taking any more trouble 
 about the matter; but finding nearly the same difficulties arise, I ven- 
 tured to proceed. I-ndeed I was pleased that Jameson, in the eight 
 fundamental colours of Werner, admits, if I take the meaning right, 
 of Yellow, which he compares to ripe lemons. Blue, which he calls 
 Berlin blue, commonly called Prussian blue, and Red, which is 
 carmine. 
 
 These agree with my ideas, and are exact, as I have shown ; and it 
 may be universally known that these three are not naturally com- 
 pounded of others, or made of mixtures, but are the bases of all possi- 
 ble tints. Their not being used as such makes most of his compounds 
 unnatural and absurd, as a few examples will easily show. The 
 common appellations may be good, such as " snow white;" but sim- 
 ply " white" might have been better, as it could properly have no 
 other meaning. 
 
 Ash gray is very indeterminate. 
 
 Velvet black is misleading. Black must be the same on any sub- 
 
 * It will be fuund that we can represent the primaries, yellow, red, and blue, and their 
 binaries, orange, greens, and violet, in every possiblejvariety, passing among each other in 
 a sketch without motions ; but we cannot represent ail the ternaries, or browns, grays 
 and darks, without the motion of one of the primitives. I have got three triangles and 
 quadrangles, prepared simply to show all mixtures, which will prove this. 
 
^7 
 
 stance. Velvet has various appearances, from its construction, distinct 
 from colour. 
 
 Emerald green is good ; but f;reen is very properly a comj)ound, 
 and the emerald may be more or less perfect, thick or thin, &c. 
 
 " Reddish white" might do very well without the explanation, which 
 makes it quite absurd: it is "snow white with a little crimson and 
 ash gray." If any philosopher or other person were to endeavour to 
 compound this confounded mess, they will see no natural means of 
 doing it. First, they must have, I suppose, a j)erfect white, for snow 
 white; then some white mixed with black for ash gray; and lastly, 
 some "carmine red with a considerable proportion of blue, for 
 crimson. If 1 can guess at the sequel, it will prove a very muddy 
 affair. " White with a little red" would have done better, and would 
 have been both natural and simple. 
 
 'I'his I think a sufficient example* It might be deemed invidious to 
 point out more, and the whole speaks for itself. I have done thus 
 much as a duty; others may take the task of judging and cri- 
 ticizing. What I have done v\ill show them that thej^ may pro- 
 duce any variety of tints, even beyond all calculation, if the three 
 simple primitives, as I call them, are used. I am only aiming at simpli- 
 city, the foundation of every thing natural. 
 
 When I wished to have concluded, which I should have done Ion"" 
 since on the original plan, I happened occasionally to meet with 
 something which many persons might think should not be passed 
 over. However, as I might seem negligent if I did not make, some 
 ajjplicable observations, I say a few words on the Decomposition of 
 Light, by C. A. Prieur*. 
 
 He observes that " the disk of the moon, when far from the horizon, 
 with a single prism displays upon her lengthened image several 
 circles, which indicate separations of colours perfectly unblended." I 
 take the liberty of observing, that the more the image is lengthened, 
 
 * Annales de Chimie, torn, lix. p. 227. Phil. Mag. vol. p. 162. 
 
48 
 
 the more the colours are blended : they, however, are never perfectly 
 unblended, if I understand the term right. 
 
 "Examine also with the prism the coloured fringes of a white 
 rectangular bod}', a little large, and well illuminated, you will remark 
 on one side a red stripe, falling into the yellow abruptly, which, in 
 its turn, loses itself in the white; and on the other hand some blue, 
 distinctly enough between the white and a violet stripe* ; from this 
 it would follow that there are only four sorts of colours." 
 
 "Again, if we look at a white and narrow body, placed upon a 
 black ground, such as a strijj of paper, a thread of silk, or a metallic 
 needle, there will only appear, for one of these objects, if we are 
 properly placed, three colours, red, green and violet, and scarcely 
 can we perceive, either on the one or the other, any softening of the 
 shades." See my Tab. 4. These answer in a great measure to a narrow 
 line of light of Dr. Wollaston, which had blue and a little yellow. 
 See Tab. 4. d. betwixt 3 and -1. 
 
 Thus much resembles my Tab. 2. Jig. 3. made narrower, and the 
 violet is more or less perceptible, as it is more or less relieved by a 
 strong light or a dark back ground, especially if widened by the 
 prism .And, upon examination, it will be found to be a mixture of 
 binary tints, and accords well with Tab. 4, d. The lower part, if at 
 all relieved or shining, will, according to precise laws, show brighter 
 tints ; and 1 have further to observe that this is a mixture of the red, 
 from the nature of the black ground above, with the blue and yellow 
 of the lower black back ground : thus the red is purplish, and the 
 yellow below the red, mixing with the other portion of the blue, 
 forms the green &,c. It is not a little curious that C. A. Prieur, having 
 so nearly hit upon the true mixture, should have let it pass. The con- 
 cordance of my descriptions with his would almost look like a pla- 
 giarism, as well with regard to him as with some parts of other de- 
 
 * The '. !ue side of the white rectangular body was relieve 1 by some darkness, else no 
 distinct violet stripe. How near to the true order of colours ! 
 
49 
 
 scriptions; which is the less a wonder, as everyone endeavouring at the 
 same effect hits on tliu same causes : but a trifling mistake in conjec- 
 ture, liowever, keeps us in that darkness which time alone disperses 
 to show true light and colours, 
 
 C. A. Prieur says, " I remarked that, under certain circumstances, 
 the colours exhibited by refraction were almost wholly these three, 
 red, green, and violet; that sometimes yellow appeared to arise from 
 a mixture of red and green ; and blue from a mixture of green and 
 violet." This is, in my opinion, really unmixing what were previously 
 mixed ; or, properly, substituting a broader light, naturally or arthi- 
 cially, instead of a narrow one: see it partly expressed in (ab. 4. c. d. 
 
 He in another place observes, " How is it that the rays, when taken 
 in pairs from the extremities of every diameter of the dial, that is, 
 from any two opposite points, shall always form the same white ? 
 A certain red with a green gives white; and an orange with a bhie, 
 the same ; and a violet with a yellow, also." It will be found that it 
 is easy to make either or all of them produce white, if it is proper to 
 call it white, which will depend much upon the velocity, or something 
 else ; and in material colours they may be more simply termed, and all 
 formed of yellow, red, and blue. 
 
 First, Red with green, which is formed of yellow and blue, give 
 white. 
 
 Second, Orange, which is formed of red and yellow, and blue, 
 which mixing with the yellow of the orange make a green like the 
 first, so that orange and blue are tantamount to red and green. 
 
 Third, A violet with a yellow. Red and blue form violet, the 
 blue of which mixed with the yellow are green; and therefore each 
 being in the same proportion, when mixed, form the same colour. 
 This is so distinct and simple, that it is amazing that there should 
 appear any ditHculty to so discerning a gentleman. 
 
 I must further observe that each mixture would be a light or 
 darker grayish, brownish or blackish white, depending upon the 
 
 H 
 
50 
 
 most prominent colour ; but if at regular distances, which is probably 
 meant, it is gray or darkish white. 
 
 " I liad therefore," he observes, " a problem to solve, the com- 
 plicated data of which, at first, seemed not to promise a simple solu- 
 tion ; yet, after various attempts, 1 obtained my object, as will be seen. 
 First, I considered that both the nature and quantity of red, green 
 and violent rays, which I suppose to be the sole element of light, are 
 absolutely unknown ; but I could likewise conceive them trans- 
 formed into coloured matters of such intensity or condensation, that 
 the mixture of an equal quantity of each should produce exactly 
 white." I will take the liberty to say that it will be whitest when 
 most spread as common light, and darkest when most condensed : 
 thus they are naturally lost, either way, to our senses, and my 
 figures will show what is meant. 
 
 In another place it is observed, that " a pencil of very decided 
 blue, being well formed, on white cloth, a green phial was placed be- 
 fore the hole, when the light of the spot was immediately much 
 weakened, and its colour changed to green." Certainly a very na- 
 tural result, as green passed over blue, or mixed with it, makes it yel- 
 lowish or bluish green, according to the quantity of either yellow or 
 blue in the combination, as in material colours : see the triangle, 
 &c. The yellow would be green with a blue phial, and orange with 
 a red one, and blue and red would become violet or purple. 
 
 C. A. PRIEUR'S RECAPITULATION. 
 
 " Thus our system of colours appears to me reduced to these few 
 data : three sorts of luminous rays of a particular unknown nature ; 
 red, green, and violet. Combined by two's, the red and green produce 
 yellow ; the green and violet produce blue ; the violet and red, 
 purple ; and the three together produce white. 
 
 " The first and second propositions seem most contradictory, and 
 by no means to agree with the mixing of material colours. We 
 
51 
 
 however find, that it is agreeable to the tenets of other philosophers, 
 and of such authority that only what is truly Nature can prevail." 
 
 With regard to Mons. Rochon's experiments on the fixed stars, 
 it will be found by the chromatometer, &c., that a proportional 
 smallness and distance may readily be calculated; and it is depen- 
 dent on these, whether they have white in the centre like the figure 
 of the sun, or are like the star Sirius as it were composed of the 
 three colours, viz., red, green, and violet, with a feeble shade of 
 yellow or not, exactly like Dr. Wollaston's small ray of light, so that 
 its measure when observed by Mons. Rochon was equal, or nearly 
 so, to the diameter of that ray in the star Sirius, and that were he 
 nearer the star, or the star larger, the tints would be proportionally 
 different. Thus Sirius is comparatively as a thread or narrow ray 
 of light, the planets are in their proportions and distances broader, 
 and the sun broadest, (to our Earth) from whose glorious light are 
 derived the three perfect primitive prismatic colours, naturally the 
 parents of all others by mixing and forming binaries, and ternaries, 
 in due order, till lost in night or darkness, when with a new re- 
 turning morn it again renovates the system. 
 
 I need say nothing on the ingenious Dr, Herschel's paper in the 
 Philosophical Transactions, as he knows how to appreciate truth 
 while he is searching for her, and is so nearly on the brink of dis- 
 covery. 
 
 THE END. 
 
 PRINTED BY RICHARD TAYLOR AND CO. 
 SHOE lANE, LONDON. 
 
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SHORTLY WILL BE PUBLISHED, 
 
 A. CONCISE PRODKOMUS of the British Minerals in Mr. Sowerby's 
 Cabinet, as a Sort of Essay towards a New, Natural, and Easy Ar- 
 rangement, v\ith References to the Author's BRITISH MINERALOGY, 
 made for the Use of those who will find British Mineralogy more useful for a 
 Library than a Travelling Book. Mr. Sowerby having found no consistent 
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 cernment. In his more extensive Application, Mr. Sowerby thinks a good 
 Arrangement may much facilitate this useful Foundation of every Branch of 
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 I-reland ; comprehending the Combustibles, Earths, and Metals, in Coloured 
 Figures, with Descriptions from the Primitive Crystals to their Amorphous 
 States, as either for Ornaments, Agriculture, or other useful and scientific 
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 2. SOWERBY'S ENGLISH BOTANY, or Coloured Figures of all the 
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 British Isles, and chiefly in Possession of the Author, James Sowerby. 
 \ 2 Numbers. Price, in Numbers, 2l. 7s. 6d. 
 
4. EXOTIC BOTANY, or Coloured Figures of new, beauiiful and rare 
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 Number. 
 
 5. CRYSTALLOGRAPHY; Parts I and II, with Models, 105. 6d. each ; 
 without Models, is. each — Intended to explain the Nature of the Crystal- 
 lization of different Mineral Substances. The First Part on Coals, the 
 Second on Diamond. 
 
 6. ENGLISH FUNGI, or Coloured Figures of English Fungi or Mush- 
 rooms. By James Sovverby, F. L. S. &c. In 28 Numbers, loZ. 6s. 6d. 
 No- 28 being the First of the Supplement, of which the Second is in the Press, 
 and will be published July 1, I8O9. 
 
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 Finishing ; with a concise Description of Transparent and Opaque or Body 
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 from Light to Full Yellow, Red, and Bhie, being the proper Primitives, may be 
 passed over each other to show the Binaries and Ternaries very distinctly : 
 thus showing all possible Mixtures from Light to Dark. 35. the Set. 
 
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 be accommodated at their own time, at five guineas the party, not exceeding 12 
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 up some of the desiderata of British information with the best intent. Their 
 utility is sufficiently evinced by the publicity they have obtained without the 
 usual aid of continual advertisement. 
 
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 SHOE lANE, LONDON, 
 
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