The Origins of Modern Color Science - University of Cambridge

1

CHAPTER CONTENTS

The Origins of ModernColor Science

J. D. MollonDepartment of Experimental PsychologyUniversity of Cambridge, Downing Street, Cambridge CB2 3EB, UK

1

Jove’s wondrous bow, of three celestial dyes,Placed as a sign to man amid the skies

Pope, Iliad, xi: 37

1.1 Newton 2

1.2 The trichromacy of color mixture 41.2.1 Trichromacy and the development of

three-color reproduction 61.2.2 Trichromacy in opposition to Newtonian

optics 81.2.3 The missing concept of a sensory

transducer 91.2.3.1 George Palmer 101.2.3.2 John Elliot MD 121.2.3.3 Thomas Young 13

1.3 Interference colors 14

1.4 The ultra-violet, the infra-red, and thespectral sensitivity of the eye 16

1.5 Color constancy, color contrast, andcolor harmony 19

1.6 Color deficiency 221.6.1 Inherited color deficiency 221.6.2 Acquired deficiencies of color perception 251.7 The golden age (1850–1931) 261.7.1 Color mixture 261.7.2 The spectral sensitivities of the receptors 291.7.3 Anomalous trichromacy 311.7.4 Tests for color deficiency 321.7.5 Color and evolution 341.8 Nerves and sensations 35

Further reading 35

References 36

The Science of Color Copyright © 2003 Elsevier LtdISBN 0–444–512–519 All rights of reproduction in any form reserved

Each newcomer to the mysteries of color sciencemust pass through a series of conceptualinsights. In this, he or she recapitulates the his-tory of the subject. For the history of color sci-ence is as much the history of misconception andinsight as it is of experimental refinement. Theerrors that have held back our field have mostoften been category errors, that is, errors withregard to the domain of knowledge withinwhich a given observation is to be explained. Forover a century, for example, the results of mix-ing colored lights were explained in terms ofphysics rather than in terms of the properties ofhuman photoreceptors. Similarly, in our owntime, we remain uncertain whether the phe-nomenological purity of certain hues should beexplained in terms of hard-wired properties ofour visual system or in terms of properties of theworld in which we live.

1.1 NEWTON

Modern color science finds its birth in the sev-enteenth century. Before that time, it was com-monly thought that white light representedlight in its pure form and that colors were mod-ifications of white light. It was already wellknown that colors could be produced by pass-ing white light through triangular glass prisms,and indeed the long thin prisms sold at fairshad knobs on the end so that they could besuspended close to a source of light. In hisfirst published account of his ‘New Theory ofColors,’ Isaac Newton describes how he boughta prism ‘to try therewith the celebratedPhaenomena of colours’ (Newton, 1671). In theseventeenth century, one of the great trade fairsof Europe was held annually on StourbridgeCommon, near the head of navigation of theriver Cam. The fair was only two kilometersfrom Trinity College, Cambridge, where Newtonwas a student and later, a Fellow. In his old age,Newton told John Conduitt that he had boughthis first prism at Stourbridge Fair in 1665 andhad to wait until the next fair to buy a secondprism to prove his ‘Hypothesis of colours’.Whatever the accuracy of this account and itsdates – the fair in fact was cancelled in 1665 and1666, owing to the plague (Hall, 1992) – thestory emphasizes that Newton did not discover

the prismatic spectrum: His contribution lies inhis analytic use of further prisms.

Allowing sunlight to enter a small round holein the window shutters of his darkened chamber,Newton placed a prism at the aperture andrefracted the beam on to the opposite wall. Aspectrum of vivid and lively colors was pro-duced. He observed, however, that the coloredspectrum was not circular as he expected fromthe received laws of refraction, but was oblong,with semi-circular ends.

Once equipped with a second prism, Newtonwas led to what he was to call his ExperimentumCrucis. As before, he allowed sunlight to enterthe chamber through a hole in the shutter andfall on a triangular prism. He took two boards,each pierced by a small hole. He placed oneimmediately behind the prism, so its aperturepassed a narrow beam; and he placed the secondabout 4 meters beyond, in a position thatallowed him to pass a selected portion of thespectrum through its aperture. Behind the sec-ond aperture, he placed a second prism, so thatthe beam was refracted a second time before itreached the wall (Figure 1.1). By rotating thefirst prism around its long axis, Newton was ableto pass different portions of the spectrumthrough the second aperture. What he observedwas that the part of the beam that was morerefracted by the first prism was also morerefracted by the second prism.

Moreover, a particular hue was associated witheach degree of refrangibility: The least refrangiblerays exhibited a red color and the most refrangi-ble exhibited a deep violet color. Between these

■ THE SCIENCE OF COLOR

2

Figure 1.1 An eighteenth-century representation ofNewton’s Experimentum crucis.As the left-hand prismis rotated around its long axis, the beam selected bythe two diaphragms is constant in its angle ofincidence at the second prism.Yet the beam isrefracted to different degrees at the second prismaccording to the degree to which it is refracted at thefirst. (From Nollet’s Leçons de Physique Expérimentale).

two extremes, there was a continuous series ofintermediate colors corresponding to rays ofintermediate refrangibility. Once a ray of a partic-ular refrangibility has been isolated in variants ofthe Experimentum Crucis, there was no experimen-tal manipulation that would then change itsrefrangibility or its color: Newton tried refractingthe ray with further prisms, reflecting it from var-ious colored surfaces, and transmitting it throughcolored mediums, but such operations neverchanged its hue. Today we should call such abeam ‘monochromatic’: It contains only a narrowband of wavelengths – but that was not to beknown until the nineteenth century.

Yet there was no individual ray, no singlerefrangibility, corresponding to white. White lightis not homogeneous, Newton argued, but is a‘Heterogeneous mixture of differently refrangibleRays.’ The prism does not modify sunlight to yieldcolors: Rather it separates out the rays of differentrefrangibility that are promiscuously intermin-gled in the white light of a source such as the sun.If the rays of the spectrum are subsequentlyrecombined, then a white is again produced.

In ordinary discourse, we most often use theword ‘color’ to refer to the hues of natural sur-faces. The color of a natural body, Newtonargued, is merely its disposition to reflect lightsof some refrangibilities more than others. Todaywe should speak of the ‘spectral reflectance’ of asurface – the proportion of the incident light thatis reflected at each wavelength. As Newtonobserved, an object that normally appears red inbroadband, white light will appear blue if it isilluminated by blue light, that is, by light fromthe more refrangible end of the spectrum.

The mixing of colors, however, presentedNewton with problems that he never fullyresolved. Even in his first published paper, hehad to allow that a mixture of two rays of differ-ent refrangibility could match the color pro-duced by homogeneous light, light of a singlerefrangibility. Thus a mixture of red and yellowmake orange; orange and yellowish green makeyellow; and mixtures of other pairs of spectralcolors will similarly match an intermediate color,provided that the components of the pair are nottoo separated in the spectrum. ‘For in such mix-tures, the component colours appear not, but, bytheir mutual allaying each other, constitute amidling colour’(Newton, 1671). So colors that

looked the same to the eye might be ‘originaland simple’ or might be compound, and the onlyway to distinguish them was to resolve themwith a prism. Needless to say, this complicationwas to give difficulties for his contemporariesand successors (Shapiro, 1980).

White presented an especial difficulty. In hisfirst paper, Newton wrote of white: ‘There is noone sort of Rays which alone can exhibit this. ‘Tisever compounded, and to its composition are req-uisite all the aforesaid primary colours’ (Newton,1671). The last part of this claim was quickly chal-lenged by Christian Huygens, who suggested thattwo colors alone (yellow and blue) might be suf-ficient to yield white (Huygens, 1673). There do,in fact, exist pairs of monochromatic lights thatcan be mixed to match white (they are now called‘complementary wavelengths’), but their exis-tence was not securely established until the nine-teenth century (see section 1.7.1). Newtonhimself always denied that two colors were suffi-cient, but the exchange with Huygens obligedhim to modify his position and to allow that whitecould be compounded from a small number ofcomponents.

In his Opticks, first published in 1704, Newtonintroduces a forerunner of many later ‘chro-maticity diagrams,’ diagrams that show quantita-tively the results of mixing specific colors(Chapters 3 and 7). On the circumference of acircle (Figure 1.2) he represents each of theseven principal colors of the spectrum. At thecenter of gravity of each, he draws a small circleproportional to ‘the number of rays of that sortin the mixture under consideration.’ Z is thenthe center of gravity of all the small circles andrepresents the color of the mixture. If two sepa-rate mixtures of lights have a common center ofgravity, then the two mixtures will match. If, forexample, all seven of the principal spectral colorsare mixed in the proportions in which they arepresent in sunlight, then Z will fall in the centerof the diagram, and the mixture will match apure white. Colors that lie on the circumferenceare the most saturated (‘intense and florid in thehighest degree’). Colors that lie on a line con-necting the center with a point on the circum-ference will all exhibit the same hue but willvary in saturation.

This brilliant invention is a product ofNewton’s mature years: It apparently has no

THE ORIGINS OF MODERN COLOR SCIENCE ■

3

antecedent in his published or unpublishedwritings (Shapiro, 1980). However, as a chro-maticity diagram it is imperfect in several ways.First, Newton spaced his primary colors on thecircumference according to a fanciful analogywith the musical scale, rather than according toany colorimetric measurements. Secondly, thetwo ends of the spectrum are apparently madeto meet, and thus there is no way to representthe large gamut of distinguishable purples thatare constructed by mixing violet and red light(although in the text, Newton does refer tosuch purple mixtures as lying near the line ODand indeed declares them ‘more bright andmore fiery’ than the uncompounded violet).Thirdly, the circular form of Newton’s diagramforbids a good match between, say, a spectralorange and a mixture of spectral red and spec-tral yellow – a match that normal observers canin fact make.

And in his text, Newton continues to deny onecritical set of matches that his diagram doesallow. The color circle implies that white couldbe matched by mixing colors that lie oppositeone another on the circumference, but he writes:

if only two of the primary Colours which in thecircle are opposite to one another be mixed inan equal proportion, the point Z shall fall uponthe centre O, and yet the Colour compounded

of these two shall not be perfectly white, butsome faint anonymous Colour. For I could neveryet by mixing only two primary Colours producea perfect white. Whether it may be compoundedof a mixture of three taken at equal distances inthe circumference, I do not know, but of four orfive I do not much question but it may. Butthese are Curiosities of little or no moment tothe understanding the Phaenomena of Nature.For in all whites produced by Nature, there usesto be a mixture of all sorts of Rays, and byconsequence a composition of all Colours.

(Newton, 1730)

In this unsatisfactory state, Newton left the prob-lem of color mixing. To understand better hisdilemma, and to understand the confusions ofhis successors, we must take a moment to con-sider the modern theory of color mixture. Forthe historian of science must enjoy a conceptualadvantage over his subjects.

1.2 THE TRICHROMACY OFCOLOR MIXTURE

The most fundamental property of human colorvision is trichromacy. Given three different col-ored lights of variable intensities, it is possible tomix them so as to match any other test light ofany color. Needless to say, this statement comeswith some small print attached. First, the mix-ture and the test light should be in the same con-text: If the mixture were in a dark surround andthe test had a light surround, it might be impos-sible to equate their appearances (see Chapter4). Two further limitations are (a) it should notbe possible to mix two of the three variable lightsto match the third, and (b) the experimentershould be free to mix one of the three variablelights with the test light.

There are no additional limitations on the col-ors that are to be used as the variable lights, andthey may be either monochromatic or them-selves broadband mixtures of wavelengths.Nevertheless, the three variable lights are tradi-tionally called ‘primaries’; and much of the his-torical confusion in color science arose because aclear distinction was not made between the pri-maries used in color mixing experiments and thecolors that are primary in our phenomenologicalexperience. Thus, colors such as red and yellow


4

Figure 1.2 Newton’s color circle, introduced in hisOpticks of 1704.

are often called ‘primary’ because we recognizein them only one subjective quality, whereasmost people would recognize in orange the qual-ities of both redness and yellowness.

The trichromacy of color mixture in fact arisesbecause there are just three types of cone recep-tor cell in the normal retina. They are known aslong-wave, middle-wave and short-wave cones,although each is broadly tuned and their sensi-tivities overlap in the spectrum (Chapter 3).Each type of cone signals only the total numberof photons that it is absorbing per unit time – itsrate of ‘quantum catch.’ So to achieve a matchbetween two adjacent patches of light, theexperimenter needs only to equate the tripletsof quantum catches in the two adjacent areas ofthe observer’s retina. This, in essence, is thetrichromatic theory of color vision, and it should

be distinguished from the fact of trichromacy.The latter was recognized, in a simplified form,during Newton’s lifetime. But for more than acentury before the three-receptor theory wasintroduced, trichromacy was taken to belong toa different domain of science. It was taken as aphysical property of light rather than as a fact ofphysiology. This category error held back theunderstanding of physical optics more than hasbeen recognized.

The basic notion of trichromacy emerged inthe seventeenth century. Already in 1686,Wallerpublished in the Philosophical Transactions of theRoyal Society a small color atlas with three pri-mary or simple colors. A rather clear statement isfound at the beginning of the eighteenth centuryin the 1708 edition of an anonymous treatise onminiature painting (Figure 1.3):


5

Figure 1.3 An early statement of trichromacy, from an anonymous treatise on miniature painting, publishedat The Hague in 1708.

Strictly speaking there are only three primitivecolors, that cannot themselves be constructedfrom other colors, but from which all others canbe constructed. The three colors are yellow, redand blue, for white and black are not truly colors,white being nothing else but the representationof light, and black the absence of this same light.

(Anonymous, 1708)

1.2.1 TRICHROMACY AND THEDEVELOPMENT OF THREE-COLORREPRODUCTION

It is trichromacy – a property of ourselves – thatmakes possible relatively cheap color reproduc-tion, by color printing, for example, and by colortelevisions and computer monitors (see Chapter8). Three-color printing was developed nearly acentury before the true nature of trichromacywas grasped. It was invented – and brought to ahigh level of perfection at its very birth – byJacques Christophe Le Blon. This remarkableman was born in 1667 in Frankfurt am Main. Itis interesting that Le Blon was working as aminiature painter in Amsterdam in 1708, whenthe anonymous edition of the Traité de la Peintureen Mignature was published at the Hague; andwe know from unpublished correspondence,between the connoisseur Ten Kate and thepainter van Limborch, that Le Blon was experi-menting on color mixture during the years1708–12 (Lilien, 1985).

In 1719, Le Blon was in London and he theresecured a patent from George I to exploit hisinvention, which he called ‘printing paintings.’Some account of his technique is given byMortimer (1731) and Dossie (1758). To prepareeach of his three printing plates, Le Blon usedthe technique of mezzotint engraving: a coppersheet was uniformly roughened with the finelyserrated edge of a burring tool, and local regionswere then polished, to varying degrees, in orderto control the amount of ink that they were tohold. Much of Le Blon’s development work wentinto securing three colored inks of suitable trans-parency; but his especial skill lay in his abilitymentally to analyze into its components thecolor that was to be reproduced. Sometimes heused a fourth plate, carrying black ink. Thismanoeuvre, often adopted in modern colorprinting, allows the use of thinner layers of

colored ink, so reducing costs and acceleratingdrying (Lilien, 1985).

In 1721, a company, The Picture Office, wasformed in London to mass-produce color printsby Le Blon’s method. Shares were issued at tenpounds and were soon selling at a premium of150%, but Le Blon proved a poor manager andthe enterprise failed. In 1725, however, he pub-lished a slender volume entitled Coloritto, inwhich he sets out the principle of trichromaticcolor mixing (Figure 1.4). It is interesting that hegives the same primaries in the same order(Yellow, Red, and Blue) as does the anonymousauthor of the 1708 text, and uses the same termfor them, Couleurs primitives.

Notice that Le Blon distinguishes between theresults of superposing lights and of mixing pig-ments. Today we should call the former ‘additivecolor mixture’ and the latter, ‘subtractive colormixture.’ Pigments typically absorb light predom-inantly at some wavelengths and reflect or trans-mit light at other wavelengths. Where Le Blonsuperposes two different colored inks, the lightreaching the eye is dominated by those wave-lengths that happen not to be absorbed by eitherof the inks. It was not until the nineteenth cen-tury that there was a widespread recognition that


6

Figure 1.4 From J.C. Le Blon’s Coloritto published inLondon in 1725.

additive and subtractive mixture differ not only inthe lightness or darkness of the product but alsoin the hue that may result (see section 1.7.1).

Le Blon himself explored a form of additivemixture. In his patent method of weaving tapes-tries, he juxtaposed threads of the primitive col-ors to achieve intermediate colors. An account isgiven by Cromwell Mortimer (1731):

Thus Yellow and Red produce an Orange, Yellowand Blue a Green, Etc. which seems to be con-firmed by placing two Pieces of Silk neartogether; viz. Yellow and Blue: When by inter-mixing of their reflected Rays, the Yellow willappear of a light Green, and the Blue of a darkGreen; which deserves the farther Considerationof the Curious.

The phenomenon that Mortimer describes hereis probably the same as the ‘optical mixture’ or‘assimilation’ later exploited by Signac and theneo-impressionists (Rood, 1879; Mollon, 1992);and it still exercises the Curious (see Chapter 4).Some neural channels in our retina integrateover larger areas than do others, and this may bewhy, at a certain distance from a tapestry, we cansee the spatial detail of individual threads whileyet we pool the colors of adjacent threads. FromMortimer’s account, it seems that Le Blonthought that the mixing was optical, and thiswill certainly be the case when the tapestry isviewed from a greater distance. However, anaturally-lit tapestry consisting of red, yellow,and blue threads can never simulate a white. Foreach of the threads necessarily absorbs someportion of the incident light, and in convention-ally lit scenes we perceive as white only a surfacethat reflects almost all the visible radiation inci-dent on it. In his weaving enterprise, Le Blon didnot have the advantage of a white vehicle for hiscolors, such as he had when printing on paper.The best that he was able to achieve from adja-cent red, yellow, and blue threads was a ‘LightCinnamon’. Similarly, since the three threadsalways reflect some light, it is impossible to sim-ulate a true black within the tapestry. So Le Blonwas obliged to use white and black threads inaddition. And – Mortimer adds – ‘tho’ he foundhe was able to imitate any Picture with these fiveColours, yet for Cheapness and Expedition, andto add a Brightness where it was required, hefound it more convenient to make use of severalintermediate Degrees of Colours.’

Sadly, Le Blon’s weaving project did not pros-per any better than the Picture Office. He was,however, still vigorous – at the age of 68 hefathered a daughter – and in 1737, Louis XVgave him an exclusive privilege to establish colorprinting in France. He died in 1741, but hisprinting technique was carried on by JaquesGautier D’Agoty, who had briefly worked forhim and who was later to claim falsely to be theinventor of the four-color method of printing,using three colors and black. Figure 1.5 – thefirst representation of the spectrum to be printedin color – was published by Gautier D’Agoty in1752.

Le Blon himself did not acknowledge any con-tradiction between his practical trichromacy andNewtonian optics; but his successor, GautierD’Agoty, was vehemently anti-Newtonian. Heheld that rays of light are not intrinsically col-ored or colorific. The antagonistic interactions of


7

Figure 1.5 The first representation of Newton’sspectrum to be printed in color. From theObservations sur l’Histoire Naturelle of GautierD’Agoty, 1752.

light and dark (‘Les seules oppositions de l’ombre &de la lumiere, & leur transparence’) produce threesecondary colors, blue, yellow, and red, andfrom these, the remaining colors can be derived(Gautier D’Agoty, 1752).

1.2.2 TRICHROMACY IN OPPOSITIONTO NEWTONIAN OPTICS

As the eighteenth century progressed, increas-ingly sophisticated statements of trichromacywere published, but their authors invariablyfound themselves in explicit or implicit opposi-tion to the Newtonian account, in which thereare seven primary colors or an infinity.

The anti-Newtonian Jesuit Louis BertrandCastel (1688–1757) identified blue, yellow, andred as the three primitive colors from which allothers could be derived. In his Optique desCouleurs of 1740, he gives systematic details ofthe intermediate colors produced by mixing theprimaries. Father Castel was aware that phe-nomenologically there are more distinguishablehues between pure red and pure blue thanbetween blue and yellow or between yellow andred – as is clear in the later Munsell system. Byinformal experiments he established a color cir-cle of twelve equally spaced hues: Blue, celadon(sea-green), green, olive, yellow, fallow, nacarat(orange-red), red, crimson, purple, agate, pur-ple-blue (Castel, 1740). These he mapped on tothe musical scale, taking blue as the keynote,yellow as the third, and red as the fifth.

In his time, Castel was most celebrated for hisscheme for a clavecin oculaire – the first colororgan. For many years, the clavecin oculaire was astrictly theoretical entity, for Père Castel insistedthat he was a philosophe and not an artisan.Nevertheless, there was much debate as towhether there could be a visual analogue ofmusic. Tellemann wrote approvingly of the colororgan, but Rousseau was critical, arguing thatmusic is an intrinsically sequential art whereascolors should be stable to be enjoyed.Eventually, practical attempts seem to have beenmade to build a clavecin oculaire (Mason, 1958). Aversion exhibited in London in 1757 wasreported to comprise a box with a typical harpsi-chord keyboard in front, and about 500 lampsbehind a series of 50 colored glass shields, whichfaced back towards the player and viewer. The

idea has often been revived in the history ofcolor theory (Rimington, 1912).

One of the most distinguished trichromatistsof the eighteenth century was Tobias Mayer, theGöttingen astronomer. He read his paper ‘On therelationship of colors’ to the Göttingen scientificsociety in 1758, but only after his death was itpublished, by G.C. Lichtenberg (Forbes, 1971;Mayer, 1775; Lee, 2001). He argued that thereare only three primary colors (Haupfarben), notthe seven of the Newtonian spectrum. TheHaupfarben can be seen in good isolation, if onelooks through a prism at a rod held against thesky: On one side you will see a blue strip and onthe other a yellow and a red strip, without anymixed colors such as green (Forbes, 1970). HereMayer, like many other eighteenth-centurycommentators, neglects Newton’s distinctionbetween colors that look simple and colorsthat contain light of only one refrangibility.For an analysis of the ‘boundary colors’ observedby Mayer and later by Goethe, see Bouma(1947).

Mayer introduced a color triangle, with thefamiliar red, yellow, and blue primaries at itscorners. Along the sides, between any twoHaupfarben, were 11 intermediate colors, eachbeing described quantitatively by the amountsof the two primaries needed to produce them.Mayer chose this number because he believedthat it represented the maximum number of dis-tinct hues that could be discerned between twoprimaries. By mixing all three primary colors,Mayer obtained a total of 91 colors, with grayin the middle. By adding black and white, heextended his color triangle to form a three-dimensional color solid, having the form of adouble pyramid. White is at the upper apex andblack at the lower.

A difficulty for Mayer was that he was offeringboth a chromaticity diagram and a ‘color-ordersystem.’ The conceptual distinction betweenthese two kinds of color space had not yet beenmade. A chromaticity diagram tells us only whatlights or mixtures of lights will match each other.Equal distances in a chromaticity diagram do notnecessarily correspond to equal perceptual dis-tances. A color-order system, on the other hand,attempts to arrange colors so that they are uni-formly spaced in phenomenological experience(see Chapters 3, 4 and 7).


8

One advance came quickly from J.H. Lambert,the astronomer and photometrist, who realizedthat the chosen primary colors might not beequal in their coloring powers (la gravité spécifiquedes couleurs) and would need to be given differentweightings in the equations (Lambert, 1770). Heproduced his own color pyramid (Figure 1.6),realized in practice by mixing pigments with wax(Lambert,1772). The apex of the pyramid waswhite. The triangular base had red, yellow, andblue primaries at its apices, but black in the mid-dle, for Lambert’s system was a system of sub-tractive color mixture (section 1.7.1). He wasexplicit about this, suggesting that each of hisprimary pigments gained its color by absorbinglight corresponding to the other two primaries.He made an analogy with colored glasses: If ared, a yellow, and a blue glass were placed inseries, no light was transmitted.

Other eighteenth-century trichromatists wereMarat (1780) and Wünsch (1792). Particularlyanti-Newtonian was J.P. Marat, who, rejected bythe Académie des Sciences, became a prominent

figure in the French Revolution. He had the sat-isfaction of seeing several académiciens go to theguillotine, before he himself died at the hand ofCharlotte Corday.

1.2.3 THE MISSING CONCEPT OF ASENSORY TRANSDUCER

It has been said (Brindley, 1970) that trichro-macy of color mixing is implicit in Newton’s owncolor circle and center-of-gravity rule (see Figure1.2). Yet this is not really so. If you choose asprimaries any three points on the circumference,you can match only colors that fall within theinner triangle. To account for all colors, youmust have imaginary primaries that lie outside thecircle. And for Newton such imaginary primarieswould have no meaning.

The reason is that Newton, and most of hiseighteenth-century successors, lacked the con-cept of a tuned transducer, that is a receptortuned to only part of the physical spectrum. Itwas generally supposed that the vibrations occa-sioned by a ray of light were directly communi-cated to the sensory nerves, and thencetransmitted to the sensorium. Here are two char-acteristic passages from the Queries at the end ofNewton’s Opticks:

Qu 12. Do not the Rays of Light in falling uponthe bottom of the Eye excite Vibrations in theTunica Retina? Which Vibrations, being propa-gated along the solid Fibres of the optick Nervesinto the Brain, cause the Sense of seeing . . .

Qu. 14. May not the harmony and discord ofColours arise from the proportions of theVibrations propagated through the Fibres of theoptick Nerves into the Brain, as the harmony anddiscord of Sounds arise from the proportions ofthe Vibrations of the Air? For some Colours, ifthey be view’d together are agreeable to oneanother, as those of Gold and Indigo, and othersdisagree . . .

(Newton, 1730)

This was an almost universal eighteenth-centuryview: The vibrations occasioned by light weredirectly transmitted along the nerves. Since suchvibrations could vary continuously in frequency,there was nothing in the visual system thatcould impose trichromacy. So the explanation oftrichromacy was sought in the physics of theworld.


9

Figure 1.6 The Farbenpyramide of J.H. Lambert(1772). Reproduced with permission of J.D. Mollon.

Sometimes indeed, there was a recognition ofthe problem of impedance matching. Here is arather telling passage from Gautier D’Agoty,written in commentary on his anatomical printsof the sense organs:

The emitted and reflected ray is a fluid body,whose movement stimulates the nerves of theretina, and would end its action there, withoutcausing us any sensation, if on the retina therewere not nerves for receiving and communicat-ing its movement and its various vibrations asfar as our sense; but for this to happen, a nervethat receives the action of a ray composed offluid matter (as is that of the fire that composesthe ray) must also itself be permeated with thesame matter, in order to receive the same mod-ulation; for if the nerve were only like a rod, orlike a cord, as some suppose, this luminousmodulation would be reflected and could neveraccommodate itself to a compact and solidthread of matter . . .

(Gautier D’Agoty, 1775)

An early hint of the existence of specific recep-tors can be found in a paper given to the StPetersburg Imperial Academy in July 1756 byMikhail Vasil’evich Lomonosov. Both a poet anda scientist, Lomonosov established a factory thatmade mosaics and so he had practical experienceof the preparation of colored glasses (Leicester,1970). His paper concentrates on his physicaltheory of light. Space is permeated by an etherthat consists of three kinds of spherical particle,of very different sizes. Picture to yourself, hesuggests, a space packed with cannon balls. Theinterstices between the cannon balls can bepacked with fusilier bullets, and the spacesbetween those with small shot. The first size ofether particle corresponds to salt and to red light;the second to mercury and to yellow light; andthe third to sulfur and to blue light. Light of agiven color consists in a gyratory motion of agiven type of particle, the motion being com-municated from one particle to another. Inpassing, Lomonosov suggests a physiologicaltrichromacy to complement his physical trichro-macy: the three kinds of particle are present inthe ‘black membrane at the bottom of the eye’and are set in motion by the corresponding rays(Lomonosov, 1757; Weale, 1957).

In the Essai de Psychologie of Charles Bonnet(1755) we find the idea of retinal resonators

combined with a conventionally Newtonianaccount of light. Bonnet, however, supposedthat for every degree of refrangibility there mustbe a resonator, just as – he suggested – the earcontains many different fibers that correspond todifferent tones. So each local region of the retinais innervated by fascicles, which consist of sevenprincipal fibers (corresponding to Newton’s prin-cipal colors); the latter fibers are in turn made upof bundles of fibrillae, each fibrilla being specificfor an intermediate nuance of color. Bonnet wasnot troubled that this arrangement might beincompatible with our excellent spatial resolu-tion in central vision.

In the last quarter of the eighteenth century,the elements of the modern trichromatic theoryemerge. Indeed, all the critical concepts werepresent in the works of two colorful men, wholived within a kilometer of each other in theLondon of the 1780s. Each held a complemen-tary part of the solution, but neither they northeir contemporaries ever quite put the partstogether.

1.2.3.1 George PalmerOne of these two men was George Palmer.Gordon Walls (1956), in an engaging essay,described his fruitless search for the identity ofthis man. It was Walls’ essay that first promptedmy own interest in the history of color theory. Infact, Palmer was a prosperous glass-seller and,like Lomonosov, a specialist in stained glass(Mollon, 1985, 1993). He was born in London in1740 and died there in 1795. His business wasbased in St Martin’s Lane, but for a time in the1780s he was also selling colored glass in Paris.His father, Thomas, had supplied stained glass forHorace Walpole’s gothick villa at Strawberry Hilland enjoys a walk-on part in Walpole’s letters(Cunningham, 1857).

George Palmer represents an intermediatestage in the understanding of trichromacy, for hewas, like Lomonosov, both a physical and aphysiological trichromatist. In a pamphlet pub-lished in 1777 and now extremely rare, he sup-poses that there are three physical kinds of lightand three corresponding particles in the retina(Palmer, 1777b). In later references, he speaks ofthree kinds of ‘molecule’ or ‘membrane’. Theuniform motion of the three types of particleproduces a sensation of white (Figure 1.7). His


10

1777 essay attracted little support in Britain. Theonly review of this proto-trichromatic theorywas one line in the Monthly Review: ‘A visionarytheory without colour of truth or probability.’ Inthe French-speaking world, however, his ideaswere better received: A translation of the pam-phlet (Palmer, 1777a) attracted an extravagantreview in the Journal Encyclopédie.

Once equipped with the idea of a specificreceptor, Palmer ran with it. In 1781 in aGerman science magazine, his explanation ofcolor blindness is discussed, although his name isthere given mysteriously as ‘Giros von Gentilly’while ‘Palmer’ is said to be a pseudonym (Voigt,1781). He is reported to say that color blindnessarises if one or two of the three kinds of mole-cules are inactive or are constitutively active(Mollon, 1997). In a later pamphlet published

in Paris under his own name (Palmer, 1786),Palmer suggests that complementary color after-effects arise when the three kinds of fiber aredifferentially adapted – an explanation that hasbeen dominant ever since. To explain the ‘flightof colors,’ the sequence of hues seen in the after-image of a bright white light, Palmer proposesthat the different fibers have different time con-stants of recovery. And to explain the Eigenlicht,the faint light that we see in total darkness, heinvokes residual activity in the fibers.

Another modern concept introduced byGeorge Palmer is that of artificial daylight. In1784, the Genevan physicist Ami Argand intro-duced his improved oil-burning lamp (Heyer,1864; Schrøder, 1969). In its day, the Argandlamp revolutionized lighting. It is difficult for ustoday to appreciate how industry, commerce,


11

Figure 1.7 George Palmer’s proposal that the retina contains three classes of receptor, in his Theory ofColours and Vision of 1777. Only four copies of this monograph are known to survive.

entertainment, and domestic life were restrictedby the illuminants available until the late eigh-teenth century. Argand increased the brillianceof the oil lamp by increasing the flow of air pastthe wick. He achieved this by two devices. First,he made the wick circular so that air could passthrough its center, and second, he mountedabove it a glass chimney. Unable, however, tosecure suitable heat-resistant glass in France, hewent to England in search of the flint glass thatwas an English specialty at the time. While hewas gone, the lamp was pirated in Paris by anapothecary called Quinquet, who was so suc-cessful a publicist that his name became aneponym for the lamps. For a time, however,Quinquet had a partner, no other than GeorgePalmer – and Palmer’s contribution was clever:He substituted blue glass for Argand’s clear glass,so turning the yellowish oil light into artificialdaylight. Characteristically, this novel idea wasset out in a pamphlet given away to customers(Palmer, 1785). The selling line was that artisansin trades concerned with color could buy theQuinquet–Palmer lamp, work long into thenight, and so outdo their competitors. Palmereven proposed a pocket version that would allowphysicians correctly to judge the color of bloodor urine during the hours of darkness. The con-cept of artificial daylight appears again in amonograph by G. Parrot (1791).

George Palmer never took the final step ofrealizing that the physical variable is a continu-ous one. Living only streets away from him in1780 was another tradesman, John Elliot, whopostulated transducers sensitive to restrictedregions of a continuous physical spectrum – butwho never restricted the number of transducersto three (Mollon, 1987; in press).

1.2.3.2 John Elliot MDElliot was a man of a melancholic disposition,the opposite of the outgoing entrepreneur,George Palmer. It was said of him that he wasof a sallow complexion and had the appearanceof a foreigner, although he was born in Chardin Somerset in 1747. At the age of 14, hewas bound apprentice to an apothecary inSpitalfields, London. At the expiry of his time, hebecame assistant in Chandler’s practice inCheapside and – if we are to believe the Narrativeof the Life and Death of John Elliot MD

(Anonymous, 1787) – it was during this periodthat he first established a romantic attachment toMiss Mary Boydell, whose many attractionsincluded an Expectation – to be precise, anexpectation of £30 000 on the death of heruncle, Alderman Boydell. Miss Boydell encour-aged and then rejected the clever young apothe-cary. By 1780, Elliot was in business on his own,first in Carnaby Market and then, as he pros-pered, in Great Marlborough Street (Partingtonand McKie, 1941).

In his Philosophical Observations on the Senses(Elliot, 1780), he described simple experimentsin which he mechanically stimulated his owneyes and ears, and was led to an anticipation ofJohannes Mueller’s ‘Doctrine of Specific NerveEnergies’ (Müller, 1840). Our sense organs,Elliot argued, must contain resonators – trans-ducers – that are normally stimulated by theirappropriate stimulus but can also be excitedmechanically:

there are in the retina different times of vibra-tion liable to be excited, answerable to the timeof vibration of different sorts of rays. That anyone sort of rays, falling on the eye, excite thosevibrations, and those only which are in unisonwith them . . . And that in a mixture of severalsorts of rays, falling on the eye, each sort excitesonly its unison vibrations, whence the propercompound colour results from a mixture of thewhole.

(Elliot, 1780)

He develops his ideas in his Elements of NaturalPhilosophy, a work intended for medical students,which was first published in 1792 and then in asecond edition in 1796. So modern is Elliot’saccount that it deserves quoting at length:

The different colours, like notes of sound, may beconsidered as so many gradations of tone; forthey are caused by vibrations of the rays of lightbeating on the eye, in like manner as sounds arecaused by vibrations or pulses of the air beatingon the ear. Red is produced by the slowest vibra-tions of the rays, and violet by the quickest . . .

If the red-making rays fall on the eye, theyexcite the red-making vibrations in that part ofthe retina whereon they impinge, but do notexcite the others because they are not in unisonwith them . . . From hence it may be understoodthat the rays of light do not cause colours in theeye any otherwise than by the mediations of the


12

vibrations or colours liable to be excited in theretina; the colours are occasioned by the latter;the rays of light only serve to excite them intoaction. So likewise if blue- and yellow-makingrays fall together on the same part of the retina,they excite the blue- and yellow-making vibra-tions respectively, but because they are so closetogether as not be distinguished apart, they areperceived as a mixed colour, or green; the same aswould be caused by the rays in the midwaybetween the blue- and yellow-making ones. Andif all sorts of rays fall promiscuously on the eye,they excite all the different sorts of vibrations; andas they are not distinguishable separately, themixed colour perceived is white; and so of othermixtures.

We are therefore perhaps to consider each ofthese vibrations or colours in the retina, as con-nected with a fibril of the optic nerve. That thevibration being excited, the pulses thereof arecommunicated to the nervous fibril, and by thatconveyed to the sensory, or mind, where it occa-sions, by its action, the respective colour to beperceived . . .

(Elliot, 1786)

Elliot suggests that each of the several types of res-onator is multiplied many times over, throughoutthe retina, the different types being completelyintermingled. As we shall see later, his physiolog-ical insight was to lead him to the important phys-ical insight that there might exist frequencies forwhich we have no resonators. Yet his life was tobe brought to its unhappy end before he couldmake the final step of suggesting that there wereonly three classes of resonator in the retina.

The year 1787 found Elliot again obsessedwith Miss Boydell and increasingly disturbed inhis behavior. He bought two brace of pistols. Hefilled one pair with shot, and the other withblanks – or so the Defense claimed at the trial.On 9 July he came up behind Miss Boydell,who was arm in arm with her new companion,George Nichol. Elliot fired at Miss Boydell, butwas seized by Nichol before he could shoothimself, as he apparently intended. By 16 Julyhe was on trial at the Old Bailey. The prosecu-tion insisted that the pistols had been loadedand that Miss Boydell had been saved onlyby her whalebone stays. The Jury found Elliotnot guilty, but the Judge committed him toNewgate Gaol nevertheless, to be tried forassault (Hodgson, 1787). He died there on 22July 1787.

1.2.3.3 Thomas YoungWe have seen that all the conceptual elements ofthe trichromatic theory were available in the lastquarter of the eighteenth century. However, thefinal synthesis was achieved only in 1801, byThomas Young.

Young was born in Somerset in 1773, the eld-est of ten children of a prosperous Quaker(Wood, 1954). His first scientific paper was onthe mechanism of visual accommodation, apaper that secured his election to the RoyalSociety at the early age of 21. There is no evi-dence that Young himself ever performed sys-tematic experiments on color mixing, but we doknow that he was familiar with the evidence fortrichromacy that had accumulated by the end ofthe eighteenth century. Intent on a medicalcareer, he spent the academic year of 1795–96 atthe scientifically most distinguished university inthe realms of George III, the Georg-AugustUniversity in Göttingen. We know from his ownrecords that he there attended the physics lec-tures of G.C. Lichtenberg at 2 p.m. each day(Peacock, 1855); and from a transcript of theselectures got out by Gamauf (1811), we knowthat Young would have heard about the color-mixing experiments of Tobias Mayer, about thecolor triangle and the double pyramid formedfrom it, as well as about colored after-images andsimultaneous color contrast.

After leaving Göttingen, Young spent a periodat Emmanuel College, Cambridge, but by 1800he was resident in London, having inherited thehouse and fortune of a wealthy uncle. In 1801,in a lecture to the Royal Society, he put forwardthe trichromatic theory of vision in a recogniza-ble form. Adopting a wave theory of light, hegrasped that the physical variable was wave-length and was continuous, whereas the trichro-macy of color matching was imposed by thephysiology of our visual system. The retina mustcontain just three types of sensor or resonator.Each resonator has its peak in a different part ofthe spectrum, but is broadly tuned, respondingto a range of wavelengths.

Now, as it is almost impossible to conceive eachsensitive point of the retina to contain an infinitenumber of particles, each capable of vibrating inperfect unison with every possible undulation,it becomes necessary to suppose the number


13

limited, for instance, to the three principalcolours, red, yellow, and blue, of which theundulations are related in magnitude nearly asthe numbers 8, 7, and 6; and that each of theparticles is capable of being put in motion less ormore forcibly, by undulations differing less ormore from a perfect unison; for instance, theundulations of green light being nearly in theratio of 61⁄2, will affect equally the particles in uni-son with yellow and blue, and produce the sameeffect as a light composed of those two species:and each sensitive filament of the nerve mayconsist of three portions, one for each principalcolour . . .

(Young, 1802a)

Notice that in this first account Young does notrefer explicitly to the trichromacy of color mix-ture; and he remains hesitant about the numberof resonators. Later, in his article ‘Chromatics’for Encyclopaedia Britannica (Young, 1817) he isfirmer, now taking the three distinct ‘sensations’to be red, green, and violet. The rays occupyingintermediate places in the Newtonian spectrumexcite mixed ‘sensations,’ so monochromaticyellow light excites both the red and green ‘sen-sations’ and monochromatic blue light excitesthe violet and the green ‘sensations.’ He is dis-tinguishing here between the excitations of thenerves (‘sensations of the fibres’) and phenom-enological experience: ‘the mixed excitationproducing in this case, as well as in that ofmixed light, a simple idea only.’ He realized –and it took others a long time to follow – thatwe cannot assume that the phenomenologicallysimplest hues (say, red, yellow, blue) necessarilycorrespond to the peak sensitivities of thereceptors.

Thomas Young did not accurately know thespectral sensitivities of the three receptors, buthe had overcome the category error that hadheld back color science since Newton. ClerkMaxwell was later to say, in a lecture to theRoyal Institution: ‘So far as I know, ThomasYoung was the first who, starting from the well-known fact that there are three primary colours,sought for the answer to this fact, not in thenature of light, but in the constitution of man’(Maxwell, 1871).

1.3 INTERFERENCE COLORS

Yet Thomas Young’s insight into sensory physiol-ogy was secondary to his contribution to colorphysics. Of his several legacies to modern sci-ence, none has been more significant than hisgeneralized concept of interference. The colors ofthin plates – the colors observed in soap bubblesand films of oil – had intrigued Hooke and Boyleand were measured systematically by Newton.But Newton, although he applied the concept ofinterference to explain the anomaly of tides inthe Gulf of Tonking (Newton, 1688), andalthough he knew that the colors of thin filmswere periodic in character, did not make the leapthat Thomas Young was to make a century later.

In order to quantify the conditions that gaverise to the colors of thin films, Newton pressed aconvex lens of long focal length against a glassplate (Figure 1.8). Knowing the curvature of theconvex surface, he could estimate accurately thethickness of the air film at a given distance fromthe point of contact. When white light was


14

Figure 1.8 Newton’s representation of the colors seen when a convex lens is pressed against a glass plate.

allowed to fall normally on the air film, Newtonobserved several series of concentric rings ofcolor. If observations were made of light that hadpassed through both the lens and the plate, thencolored rings were again seen, but these werecomplementary in hue to those seen by reflec-tion from the plate. If light from only one part ofthe spectrum were used, then isolated brightbands were seen at certain distances from thecentral point. Newton supposed that each of theconstituent colors of white light produced itsown system of rings and that the colors seenwith a white illuminant were due to the over-lapping of the individual components. Whenusing light of one color only, he could measureabout 30 successive rings; and he found that inmoving from one ring to the next, the corre-sponding thickness of the air film alwaysincreased by the same amount (Newton, 1730).Newton’s own explanation was in terms of ‘fitsof easy reflection’ and ‘fits of easy transmis-sion.’ He supposed that a ray of light in arefracting medium alternates between twostates (‘fits’). In one state, the light is disposedto be reflected, in the other it is disposed to betransmitted. The rate of alternation betweenthe two states varied with the color of the light(Shapiro, 1993).

Thomas Young was led to the concept of inter-ference by his study of acoustics (Mollon, 2002).At Göttingen in 1796, to satisfy one of therequirements for his degree, he gave a lecture onthe human voice (Peacock, 1855). Proceeding toEmmanuel College, Cambridge, he planned toprepare a paper on this subject, but ‘found him-self at a loss for a perfect conception of whatsound was’ and so set about collecting all theinformation he could, from books and fromexperiment (Young, 1804). A contemporary atEmmanuel wrote of him ‘His rooms had all theappearance of belonging to an idle man . . . Ionce found him blowing smoke through longtubes.’ He was soon to use the concept of inter-ference to explain auditory beats – the waxingand waning of loudness that is heard as twotones of very similar pitch drift in and out ofphase (Young, 1800).

Legend holds that Young was prompted tothink about interference by observing the ripplesgenerated by a pair of swans on the pond inEmmanuel College, and certainly he explicitly

sets out such a lacustrine model in the pamphlethe wrote to defend his theory against thecriticisms of Henry Brougham:

Suppose a number of equal waves of water tomove upon the surface of a stagnant lake, with acertain constant velocity, and to enter a narrowchannel leading out of the lake. Suppose thenanother similar cause to have excited anotherequal series of waves, which arrive at the samechannel at the same time, with the same velocity,and at the same time as the first. Neither series ofwaves will destroy the other, but their effects willbe combined: if they enter the channel in such amanner that the elevations of one series coincidewith those of the other, they must together pro-duce a series of greater joint elevations; but if theelevations of one series are so situated as to cor-respond to the depressions of the other, theymust exactly fill up those depressions, and thesurface of the water must remain smooth; at leastI can discover no alternative, either from theoryor from experiment.

(Young, 1804)

By his own account, it was only in May 1801 thatYoung realized that interference could explainthe colors of thin plates. He supposed that lightconsisted of waves in an all-pervading ether.Different wavelengths corresponded to differenthues, the shortest wavelengths appearing violet,the longest, red. In his initial model, however, theundulations were longitudinal – that is, along theline of the ray – rather than transverse, as Fresnelwas later to show them to be.

In his Bakerian Lecture of November 1801,Young proposed that the colors of thin filmsdepended on constructive and destructive inter-ference between light reflected at the first sur-face and light reflected at the second: When thepeak of one wave coincides with the trough ofanother, the two will cancel, but when the pathlength of the second ray is such that the peakscoincide for a given wavelength, then the huecorresponding to that wavelength will be seen(Young, 1802a). The first published account is inthe Syllabus of his Royal Institution lectures:

When two portions of the same light arrive at theeye by different routes, either exactly or verynearly in the same direction, the appearance ordisappearance of various colours is determined bythe greater or less difference in the lengths of thepaths: the same colour recurring, when the inter-vals are multiples of a length, which, in the same


15

medium, is constant, but in different mediums,varies directly as the sine of refraction.

(Young, 1802b)

By applying his interference hypothesis toNewton’s measurements of the colors of thinfilms, Young achieved the first accurate map-ping of colors to the underlying physical vari-able. Figure 1.9 reproduces his table of thewavelengths that correspond to particular hues(Young, 1802a). Once converted from fractionsof an inch to nanometers, the estimates closelyresemble modern values. Particularly striking isthe wavelength given for yellow, since it is inthis region of the spectrum that hue changesmost rapidly with wavelength. Young’s valueconverts to 576 nm and this is within ananometer of modern estimates of the wave-length that appears ‘unique’ yellow, the yellowthat looks neither reddish nor greenish to anaverage eye in a neutral state of adaptation(Ayama et al., 1987). His values for orange,green, and violet are very reasonable. The valuefor blue, 497 nm, is a longer wavelength thanwould be taken as the exemplar of blue today,but Newton’s ‘blew,’ in a spectrum that had toaccommodate indigo, may have been close tocyan, resembling the modern Russian golyboi.Indeed, we may have here an interesting expla-nation for Newton’s statement that a mixture ofspectral yellow and spectral blue makes green(Newton, 1671), a statement that has exercisedhistorians of science (Shapiro, 1980).

It is in the same Bakerian lecture that Youngmade the first suggestion that interference also

accounts for the colors seen when light falls onstriated surfaces (Young, 1802a). Young notedthe systematic variation in hue as he rotated apair of finely ruled lines at different angles to anincident beam, so anticipating the diffractiongratings that are today widely used in mono-chromators and spectroradiometers (Chapter 7).

As far as I am aware, the earlier literatureholds no approximations to the Table of Figure1.9. Thomas Young reached modern values inone leap. Yet it is important to realize that hisaccuracy is a tribute to the precision of Newton’smeasurements, made in the seventeenth cen-tury. Although Young’s two-slit demonstrationof optical interference (Young, 1807) has proba-bly been even more influential in modernphysics than Newton’s prismatic experiments, ithas to be said that Young was not by inclinationan experimentalist. His first biographer, HudsonGurney records:

he was afterwards accustomed to say, that at noperiod of his life was he particularly fond ofrepeating experiments or even of very frequentlyattempting to originate new ones; consideringthat, however necessary to the advancement ofscience, they demanded a great sacrifice of time,and that when the fact was once established, thattime was better employed in considering thepurposes to which it might be applied, or theprinciples which it might tend to elucidate.

(Gurney, 1831)

1.4 THE ULTRA-VIOLET, THEINFRA-RED, AND THESPECTRAL SENSITIVITY OFTHE EYE

Something else was clear to Thomas Young in1801 and that was the continuity of visible andinfra-red radiation. He writes: ‘it seems highlylikely that light differs from heat only in thefrequency of its radiations’ (Young, 1802a).

For most of the eighteenth century, there waslittle suspicion that radiation existed outside thevisible spectrum. In part, we can attribute thisinnocence to the anthropocentric world-view thatstill prevailed: the Creator would not have filledspace with radiation that Man could not perceive.A more specific explanation, however, is the


16

Figure 1.9 Thomas Young’s table of the wavelengthscorresponding to particular hues. Conversions tonanometers have been added to the right. (From hisBakerian Lecture published in 1802.)

absence – discussed above – of the physiologicalconcept of a tuned transducer: If all frequenciesare directly communicated to the nerves, then weshould perceive all frequencies that exist.

Historians of science often attribute to JamesHutton in 1794 the first suggestion of theexistence of invisible rays beyond the red end ofthe spectrum. The first empirical demonstrationwas by William Herschel, the astronomer, theyear before Thomas Young’s Bakerian lecture(Herschel, 1800a). Figure 1.10 shows one of hisexperiments. He used a glass prism to form a

solar spectrum on a graduated surface, andplaced a thermometer with a blackened bulb atdifferent positions within and beyond the spec-trum, noting the rise of temperature. He placedfurther thermometers to one side of the spec-trum to control for any change in ambient tem-perature (Herschel, 1800b). He systematicallyshowed that the invisible rays are reflected,refracted and absorbed by different media, muchas are the visible ones. Yet he concluded that thetwo kinds of ray are quite different in nature. Hewas misled by a category error.


17

Figure 1.10 An experimental arrangement used by Herschel to investigate the infra-red. A rise intemperature is recorded by a thermometer placed beyond the visible spectrum.

Figure 1.11 shows Herschel’s representation ofthe spectral efficiencies of the two types of ray.Certainly, he does deserve some credit for thisplot. The very idea of a graph was still unusual in1800; and this one may be the earliest ancestorof Vk, the standard curve that represents thephotopic sensitivity of the human eye (Chapter3). The abscissa of Herschel’s graph is refrangibil-ity and will be dependent on the dispersiveproperties of the glass of the prism, as will thepositions of the actual peaks. Notice that there isno ordinate for either of the two curves. For thethermal curve, it is the heating power as meas-ured by the thermometer. To obtain the visualcurve, Herschel scaled different colors by an acu-ity criterion, judging their ability to support thediscrimination of spatial detail when light of dif-ferent colors illuminated various objects under amicroscope.

If he offered the second curve as a visual sensi-tivity curve, it would be rather impressive. But hedoesn’t. He offers it as a curve of the relative radi-ances of lights of different refrangibility, a spectralpower distribution, and he offers a distinct curve

for the calorific rays, which he supposes to be of aquite different quality. Operating with the wrongmodel of sensory transduction, Herschel is unableto grasp that the visible and invisible parts of thephysical spectrum are continuous.

Yet the insight William Herschel lacked, hadbeen provided in a work published 15 years ear-lier (Anonymous, 1786). The author of the latterwork advances a vibratory theory of heat, andwe can be sure of his identity, since it wasprinted with another essay that was rejected bythe Royal Society. That careful body still retainsthe manuscripts that its referees rejected in theeighteenth century and hence we know that theauthor was John Elliot. And in a telling passage,Elliot writes:

A writer on this subject has shewn (PhilosophicalObservations on the Senses, Etc) that colours may beexcited in the eye, by irritating that organ, whichdo not at all depend on the rays of light . . . Hetherefore suggests that the rays of light excitecolours in us only by the mediation of theseinternal colours. From whence it would follow,that if there are rays of light which have no


18

Figure 1.11 Herschel’s representation of the spectral efficiencies of what he supposed were two kinds of ray.R corresponds to visible radiation and S to the heat-making rays.

answerable colours in the eye, those rays cannotbe visible; that is, they cannot excite in us anysensation of colour.

Thus it was the concept of a tuned transducerthat allowed Elliot to envisage the possibility ofnonvisible radiation. There might be opticalvibrations for which we have no answering res-onators, as there may be acoustic vibrations thatare too high or too low for us to hear. And downthe side of one page, Elliot explicitly representsthe visible spectrum extended in two directions,with only a limited space devoted to the sevenNewtonian colors ROYGBIV (Figure 1.12). Hisdiagram has had many successors.

Elliot also deserves credit as the father of spec-troscopy, and he was the first to hint at the radi-ant spectrum of a black body and the conceptof color temperature. He observed through a

prism the spectrum of bodies as they wereheated or allowed to cool. During cooling, forexample, the peak of the band of radiation sinksdownwards through from the blue to the red inthe visible spectrum and out into the infra-red:

As the body in the third experiment cooled, itwas pleasant to observe how, by degrees, the vio-let first, and then the indigo, blue, and the otherinferior colours, vanished in succession, as if thespectrum were contracting itself towards its infe-rior part; and how the centre of the rangeseemed gradually to move from orange to red,and at length beneath it, as it sunk into theinsensible part below R in the scheme, the supe-rior part following it, till the whole range was outof sight, vanishing with red . . .

1.5 COLOR CONSTANCY,COLOR CONTRAST, ANDCOLOR HARMONY

When a given object is viewed in different illu-minants, its apparent color changes much lessthan might be expected from the change in thespectral composition of the light that it reflects toour eye. The latter – the spectral flux reachingthe eye – depends on both (a) the spectral com-position of the illumination and (b) the object’sspectral reflectance, its disposition to reflectsome wavelengths more than others. It is thesecond of these that is of biological importanceto us in recognizing the objects of our world; andthe visual system appears able to discover, andcompensate for, the color of the illumination inorder to recover the surface property of theobject. This relative stability of our color percep-tion is called ‘color constancy’ (Chapter 4).

Color constancy cannot be accounted for by asimple model of three receptors and three corre-sponding nerves that each evoke particular sen-sations in the sensorium. Modern textbookssometimes attribute such a model to Young, andso it is instructive to note that he was fully awareof color constancy. In his Lectures he writes:

when a room is illuminated either by the yellowlight of a candle, or by the red light of a fire, a sheetofwritingpaper still appears to retain itswhiteness;and if from the light of the candle we take awaysome of the abundant yellow light, and leave orsubstitute a portion actually white, the effect is


19

Figure 1.12 The first representation of a spectrumthat includes the ultra-violet and infra-red as well asthe visible region. From John Elliot’s Experiments andobservations on light and colours of 1786. Elliotpublished the monograph anonymously.

nearly the same as if we took away the yellow lightfrom white, and substituted the indigo whichwould be left: and we observe accordingly that incomparison with the light of a candle, the commondaylight appears of a purplish hue.

(Young, 1807)

In this compressed passage, Young not onlydescribes color constancy, but also links it – as ithas often been linked since – to the simultane-ous contrast of color. An earlier passage fromYoung’s Syllabus is equally telling:

Other causes, probably connected with some gen-eral laws of sensation, produce the imaginarycolours of shadows, which have been elegantlyinvestigated and explained by Count Rumford.When a general colour prevails over the wholefield of vision, excepting a part comparativelysmall, the apparent colour of that part is nearlythe same as if the light falling on the whole fieldhad been white, and the rays of the prevalentcolour only had been intercepted at one particularpart, the other rays being suffered to proceed.

(Young, 1802b)

Young, however, was neither the first to observecolor constancy nor the first to relate it to colorcontrast. The phenomenon itself was alreadydescribed by the geometer Philippe De La Hire in1694 in his monograph Sur les diférens accidens dela Vuë. We do not commonly realize, he says,that we see colors differently by daylight andby candlelight. For in a given illumination, wejudge the array of colors as a whole (l’on comparetoutes les couleurs ensemble). To appreciate the dif-ference between objects illuminated by candle-light and those illuminated by daylight, whatone must do is close the shutters of a roomtightly during daylight hours and illuminate thisroom with candle light.

. . . passing then into another place illuminatedby sunlight, if one looks through the door of theroom, the objects that are lit by candlelight willappear tinted reddish-yellow in comparison withthose lit by the sun and seen concurrently. Onecannot appreciate this when he is in the candle-lit chamber.

(De La Hire, 1694/1730)

La Hire’s monograph was published under theaegis of the Royal Academy of Sciences of Paris.A century later, the same Academy was to hearthe most brilliant paper ever delivered on color

constancy. The lecture was delivered in thespring of 1789, only weeks before the revolutionbegan, and the author was another distinguishedgeometer, Gaspard Monge (Figure 1.13). It is amark of the genius of this man that he held highoffice under administrations as diverse as theancien régime, the Comité de Salut Publique, and theFirst Empire, owing no doubt to his skills as amilitary technologist.

To illustrate his lecture, Monge had hung a redcloth on the wall of a house opposite the west-facing windows of the meeting room of theAcademy. He invited his fellow académiciens toview the red cloth through a red glass. Theappearance of the cloth was counter-intuitive.Seen through a filter that transmitted predomi-nantly red light, it might have been expected tocontinue to look a saturated red. But no, itlooked pale, even whitish. The same was truewhen the assembled company inspected one oftheir fellows who happened that day to be wear-ing a red outfit. A yellow-tinted paper examinedthrough a yellow glass looked absolutely white.Monge was aware that his illusion (we may call itthe Paradox of Monge) was strongest when thescene was brightly lit and when there was an arrayof variously colored objects present in the scene,including objects that one knew to be naturallywhite. When all that was visible through the redglass was a red surface, the effect was abolished.

Monge related his illusion to a second phe-nomenon, that of colored shadows. In his day,colored shadows were already a familiar andantique phenomenon. They were brieflydescribed, for example, in 1672 by Otto von


20

Figure 1.13 A critical passage from Gaspard Monge(1789), in which he insists on the relative nature of ourcolor perception.

Guericke of Magdeburg, the inventor of thevacuum pump. At the end of the eighteenthcentury, however, commentators were stilluncertain as to whether they were perceptualphenomenon or had a physical basis. VonGuericke himself had supposed that they arosefrom the interaction of light and dark (‘. . .sicutgutta lactis & gutta atramenti ad invicem positae, inloco conjunctionis intermedio, coeruleum efficiunt col-orem’). Monge described how colored shadowscan be seen in the morning of a fine day if oneopens a window to allow diffuse skylight toenter a room and fall on a sheet of paper that isalso illuminated by the light of a nearby candle.The shadow of a small object – where the paperis illuminated only by skylight – will look a richblue. And yet if the candle is suddenly extin-guished, the paper will look uniformly white,even though the region of the shadow has notphysically changed. Very similar is an illusioncommunicated to Monge by Meusnier: If a roomis illuminated by sunlight passing through a redcurtain and if there is a small hole in the curtainthat allows a beam of sunlight to fall on a sheetof white paper, then the patch of sunlight willnot look white but rather will look ‘a very beau-tiful green’ (Monge, 1789).

To explain such illusions, and to explain theparadox of the red cloth, Monge suggested thatour sensations of color do not depend simply onthe physical light that reaches our eye from agiven surface. Rather, we reinterpret this stimu-lus in terms of what we judge to be the illumi-nant falling on the scene: If we judge theilluminant to be reddish, then we shall perceiveas greenish an object that physically deliverswhite light to the eye, since such an object is notdelivering the excess of red light that a whitesurface ought to reflect in a reddish illuminant.Similarly, a red object in red illumination willlook whitish to us because it delivers light of thesame composition as the estimated illuminant.

In 1789, Thomas Young’s Bakerian Lecturewas more than a decade in the future, andMonge did not know what the physical variablewas that distinguished the hues of theNewtonian spectrum, but he was clear that ourperceptions of color in a complex scene do notdepend only on that physical variable. In a pas-sage that would be echoed two centuries later byEdwin Land, he wrote:

So the judgements that we hold about the col-ors of objects seem not to depend uniquely onthe absolute nature of the rays of light thatpaint the picture of the objects on the retina;our judgements can be changed by the sur-roundings, and it is probable that we areinfluenced more by the ratio of some of theproperties of the light rays than by the prop-erties themselves, considered in an absolutemanner.

Monge is describing the process that today weshould call ‘color constancy,’ the process thatworks largely unnoticed to allow us to judge theconstant properties of surfaces in varying illumi-nants. Monge asked the question that hasremained at the heart of studies of color con-stancy: How do we estimate the color of the illu-minant in order to reinterpret the spectralstimulus reaching us from a given object? Hisanswer reflects his primary interest in geometry.All surfaces reflect to our eye some light of theunmodified illuminant as well as light of thecharacteristic color of the object, the color thatresults from the object’s absorption properties.At one extreme, a glossy object, like a stick ofsealing wax, will exhibit highlights, regions ofspecular reflectance where the illuminant colorpredominates. Other regions of any object,whether glossy or not, will reflect varying pro-portions of illuminant and object colors, the pro-portions varying with the viewing angle and theindentations and protrusions of the surface.Here, Monge anticipates the theory of constancyadvanced by Lee (1986): In a chromaticity dia-gram, the colors of each surface will lie along aline connecting the object color to the illumi-nant, and the illuminant chromaticity is definedby the intersection of such lines. Hurlbert (1998)has called this the ‘chromaticity convergence’theory.

One of the first Americans to study color wasBenjamin Thompson, Count Rumford. Writingto the Royal Society of London from Munich inApril 1793, he described his experiments on col-ored shadows, experiments to which ThomasYoung refers in the passage cited at the begin-ning of this section. He set up two matchedArgand lamps (see section 1.2.3.1), ‘welltrimmed, and which were both made to burnwith the greatest possible brilliancy.’ The lightthey emitted was of the same color, for when


21

they both illuminated a sheet of white paper anda small cylinder was interposed between thelamps and the paper, the two shadows of thecylinder were identical and colorless. Rumfordmounted a blackened tube so that he could viewin isolation the shadow cast by one of the twolamp beams. An assistant then introduced a yel-low glass in front of this lamp. Observed throughthe tube, the shadow remained colorless, andindeed Count Rumford could not tell when theassistant passed the yellow glass in and out of thebeam. Yet when he looked freely at the paper,the shadow was of a beautiful blue color, whilethe other was yellow. Here was uncontestableevidence that the cause of the colored shadowswas not physical (Thompson, 1794). One otherthing struck Rumford very forcibly in theseexperiments: Although the colors of the twoshadows varied as the colors of the two illumi-nants were varied, there was always a perfectand very pleasing harmony between the colorsof the paired shadows. Nowadays, we wouldnote that the two colors are physical comple-mentaries with respect to the light falling on thesurrounding white paper: Each of the two shad-ows lacks part of the total illumination of thescene, and the missing part is present in thefellow shadow.

1.6 COLOR DEFICIENCY

1.6.1 INHERITED COLOR DEFICIENCY

We have seen that the normal human observerrequires only three variables in a color-matchingexperiment (section 1.2). The common forms ofinherited color deficiency are defined in terms ofhow they depart from standard color-matchingbehavior: ‘Dichromats’ can match all colors bymixing two primary lights, whereas ‘anomaloustrichromats’ resemble normals in requiring threeprimaries in a color match but differ from thenormal in the matches that they make. Theseinherited forms of color blindness are surpris-ingly frequent, affecting 8% of male Caucasianpopulations.

Yet the historical recognition of color defi-ciency came very late. This may reflect theimprecision of our common coinage of colorwords, and also the fact that the color blind

seldom regret what they never have enjoyed,even reaching adulthood before an occupationaltest brings recognition. Robert Boyle, in his‘Uncommon Observations about Vitiated Sight’of 1688, described a ‘Mathematician, Eminentfor his skill in Opticks and therefore a very com-petent Relator of Phaenomena.’ This subject madeexcellent use of his eyes in astronomical obser-vations, but confused colors that appeared quitedissimilar to other men. Frustratingly Boyle doesnot tell us the particular colors that his subjectconfounded, but we may speculate on the iden-tity of this mathematician and optician. Couldwe relate Boyle’s brief description to Newton’sremark that ‘my own eyes are not very critical indistinguishing colours’ (Newton, 1675/1757)?

Further cases of color deficiency weredescribed with increasing detail in the Englishand French literature of the 1770s. JosephHuddart (1777) gave an account of the shoe-maker Harris, from a Quaker family of Maryportin Cumberland. Harris had good discriminationof form but poor color discrimination, a defectthat he shared with his brother, a sea captain.Huddart writes of Harris:

He observed also that, when young, other chil-dren could discern cherries on a tree by somepretended difference of colour, though he couldonly distinguish them from the leaves by theirdifference of size and shape. He observed also,that by means of this difference of colour theycould see the cherries at a greater distance thanhe could, though he could see other objects at asgreat a distance as they; that is, where the sightwas not assisted by the colour. Large objects hecould see as well as other persons; and even thesmaller ones if they were not enveloped in otherthings, as in the case of cherries among theleaves.

This is a telling passage, for it reveals the condi-tions under which we need color vision in thenatural world. When a stationary target objectis embedded in a background that varies ran-domly in form and lightness, it is visible only toan observer who can distinguish colors – thatis, an observer who can discriminate surfacesby differences in their spectral reflectances(Mollon, 1989). As we shall see, the naturaltask of finding fruit in foliage was later to findits analogue in artificial tests for color deficiency(see section 1.7.4).


22

As the second half of the eighteenth centuryprogressed, a wider public became aware that noteveryone’s perceptions of color were the same. In1760 Oliver Goldsmith, who may himself havebeen color deficient, wrote of the inappropriate-ness of recommending the contemplation ofpaintings ‘to one who had lost the power of distin-guishing colors’ (MacLennan, 1975). And by the1780s color blindness was well enough known tobe remarked on at the English court. FannyBurney recounts in her journal an uncomfortableconversation with George III:

He still, however, kept me in talk, and still uponmusic. ‘To me,’ said he, ‘it appears quite asstrange to meet with people who have no ear formusic and cannot distinguish one air fromanother, as to meet with people who are dumb. . . There are people who have no eye for differ-ence of colour. The Duke of Marlborough actu-ally cannot tell scarlet from green!’ He then toldme an anecdote of his mistaking one of those col-ors for another, which was very laughable, but Ido not remember it clearly enough to write it.How unfortunate for true virtuosi that such aneye should possess objects worthy of the mostdiscerning – the treasures of Blenheim!’

(Barrett, 1904)

So the existence of color deficiency was alreadywell established when in 1794 the young JohnDalton gave an account of his own dichromacyto the Manchester Literary and PhilosophicalSociety. But Dalton’s account was more analyticthan anything that had gone before, and hislater fame as a chemist meant that ‘daltonism’became the term for color deficiency in manylanguages, including French, Spanish, andRussian. For him, the solar spectrum had twomain divisions, which he called ‘blue’ and ‘yel-low.’ ‘My yellow,’ he wrote, ‘comprehends thered, orange, yellow and green of others’ (Dalton,1798). The red of sealing wax and the green ofthe outer face of a laurel leaf looked much thesame to him, but scarlet and pink – which sharea common quality for the normal observer –were quite different colors for Dalton, falling onopposite sides of neutral. In daylight the pinkflowers of clover (Trifolium pratense) and of thered campion (Lychnis dioica) resembled the lightblue of sky. What first prompted him to investi-gate his own vision was his observation that theflowers of the cranesbill, Pelargonium zonale

(Figure 1.14), looked sky-blue by daylight butyellowish by candlelight (Lonsdale, 1874). Ofhis immediate acquaintances, only his ownbrother experienced this striking change. Onfurther enquiry, however, he discovered that hisdefect of color perception was not so very rare:in one class of 25 pupils, he found two whoagreed with him. He never, however, ‘heard ofone female subject to this peculiarity,’ so givingthe first indication that color deficiency is asex-linked characteristic. We now know thatit affects fewer than half of one percent ofwomen.

John Dalton himself thought that his defectarose from a blue-colored medium within hiseye. Since there was nothing odd to be seen byexternal observation of the anterior parts of hiseye, he thought that it was likely be his vitreoushumor that was blue, absorbing disproportion-ately the red and orange parts of the spectrum.To allow a test of this hypothesis, he directedthat his eyes should be examined on his death.


23

Figure 1.14 The pink geranium or cranesbill,Pelargonium zonale.To John Dalton and his brother, theflower looked sky-blue by daylight but yellowish bycandlelight. (Copyright: Department of ExperimentalPsychology, University of Cambridge, reproduced withpermission.)

He died aged 78 on 27 July 1844, and on the fol-lowing day an autopsy was done by his medicalattendant, Joseph Ransome. Ransome collectedthe humors of one eye into watch glasses andfound them to be ‘perfectly pellucid’, the lensitself exhibiting the yellowness expected insomeone of Dalton’s age. He shrewdly left thesecond eye almost intact, slicing off the posteriorpole and noting that scarlet and green objectswere not distorted in color when seen throughthe eye (Wilson, 1845; Henry, 1854).

In fact, as we have seen (section 1.2.3.1), thecorrect explanation of most forms of inheriteddichromacy had already been advanced byGeorge Palmer (Voigt, 1781), when Dalton wasonly 15 years old. Palmer’s suggestion was takenup in 1807 by Thomas Young. Listing Dalton’spaper in the bibliography of his Lectures on NaturalPhilosophy, he remarks: ‘He [Dalton] thinks itprobable that the vitreous humour is of deep bluetinge: but this has never been observed byanatomists, and it is much more simple to sup-pose the absence or paralysis of those fibres of theretina, which are calculated to perceive red.’

Many distinguished commentators (e.g. Abney,1913; Wright, 1967) have followed Young inassuming that it was the long-wavelength recep-tor that Dalton lacked. It is instructive to considerwhy this view was so persistent. First, in an often-cited phrase, Dalton described the red end of thesolar spectrum as ‘little more than a shade ordefect of light.’ Second, he saw no redness in pinksand crimsons, matching them to blues.

Let us take the two observations in turn. Inthe type of color blindness called ‘protanopia,’where the long-wavelength cone is absent, aprominent sign is the foreshortening of the redend of the spectrum. In fact, the physicists SirDavid Brewster and Sir John Herschel both ques-tioned Dalton directly and both reported that hedid not see the spectrum as foreshortened at longwavelengths (Brewster, 1842; Henry, 1854). Infact, even a deuteranope – someone lacking themiddle-wave pigment – might speak of the long-wave end of the spectrum as dim, for the long-wave pigment in fact peaks in the yellow-green,and for a dichromat the long-wave end of thespectrum does not offer the Farbenglut, the extrabrightness of saturated colors, that enhances thered end of the spectrum for the normal observer(Kohlrausch, 1923).

But what of the absence of redness inDalton’s experience of surfaces that the normalwould call pink or scarlet? Does that mean helacked long-wavelength cones? The trichro-matic theory has historically often been com-bined with a primitive form of Mueller’sDoctrine of Specific Nerve Energies: There arethree receptors and three corresponding nerves,and centrally the nerves secrete red, yellow, andblue sensations or red, green, and blue sensa-tions. It took a very long time for color sciencefully to free itself from this notion, and to thisday generations of undergraduates are misledby lecturers and textbooks that speak of ‘red,’‘green,’ and ‘blue’ cones. Dalton helpfully spec-ified several crimson and pink flowers thatappeared blue to him. I have measured theseflowers spectroradiometrically and have plottedtheir chromaticities in Figure 1.15. The twostraight lines passing through the chromaticity ofthe daylight illuminant represent sets of chro-maticities that match daylight for protanopesand deuteranopes respectively. Chromaticitiesthat lie above the line will have the hue qualitythat the dichromat associates with long wave-lengths, and chromaticities that lie below theline will have the quality that the dichromatassociates with short wavelengths. For bothtypes of dichromat the several pink and crimsonflowers lie below the line and should have thesame hue quality as blue sky. So Dalton’s failureto see redness in these flowers is no basis forplacing him in one category of dichromat or theother.

Shriveled fragments of Dalton’s eye, pre-served only in air, survive to this day in thepossession of the Manchester Literary andPhilosophical Society (Brockbank, 1944). In the1990s the Society gave permission for smallsamples to be examined using the polymerasechain reaction, which allows the amplificationof short stretches of DNA defined by primersequences specific to particular genes. This exer-cise in molecular biography yielded only copiesof the gene that encodes the long-wave pho-topigment of the retina and never the gene thatencodes the middle-wave photopigment (Huntet al., 1995; Mollon et al., 1997). So Daltonappears to have been a deuteranope, and notthe protanope lacking ‘red’ cones, as so oftensupposed.


24

1.6.2 ACQUIRED DEFICIENCIES OFCOLOR PERCEPTION

Color discrimination can deteriorate during a per-son’s lifetime, owing to ocular diseases (such asglaucoma), or to systemic conditions that affectthe eye and optic pathways (such as diabetes andmultiple sclerosis), or to strokes, cerebral inflam-mations, and head injuries. What one loses, onenotices and regrets. So it might be expected thatacquired deficiencies would have been recordedhistorically before the inherited deficiencies.

Certainly, a self-report of altered color visionoccurs as early as 1671 in the Traité de Physique of

Jacques Rohault (Figure 1.16). Since it leads himto suspect the existence of congenital coloranomalies, the passage is worth translating in full:

Yet I would venture to insist that just as it oftenhappens that the same food tastes quite differentto two different people, similarly it can be thattwo men have very different sensations whenlooking at the same object in the same way; andI am the more convinced of this because I havean experience of it that is wholly personal to me:For it happening once that my right eye wasweakened and injured, by looking for more thantwelve hours through a telescope at the contestof two armies, which was going on a leagueaway; I now find my vision so affected that whenI look at yellow objects with my right eye, theydo not appear to me as they used to do, nor asthey now appear when I observe them with theleft. And what is remarkable is that I do notnotice the same variation in all colors but only insome, as for example in green, which appears tocome close to blue when I observe it with theright eye. This experience of mine makes mebelieve that there are perhaps some men who areborn with, and retain all their life, the dispositionthat I currently have in one of my eyes, and thatthere perhaps are others who have the disposi-tion that I enjoy in the other: However, it isimpossible for them or anyone else to be awareof this, because each is accustomed to call thesensation that a certain object produces in him bythe name that is already in use; but which, beingcommon to everyone’s different sensations, isnonetheless ambiguous.

Rohault’s textbook was widely circulated inseveral editions, and so it may not be coinci-dence that the following decade brought a flurryof case reports – of varying sophistication.Stephan Blankaart, in a Dutch collection ofmedical reports, briefly described a woman who,after suffering a miscarriage, ‘saw objects asblack’ but later recovered (Blankaart, 1680). In1684 ‘the great and experienced Oculist’Dawbenry Turbervile wrote from Salisbury tothe Royal Society: ‘A Maid, two or three andtwenty years old, came to me from Banbury,who could see very well, but no colour besideBlack and White’ (Turbervile, 1684). ButTurbervile then spoils his already slight reportby adopting an emissive theory of vision: ‘Shehad such Scintillations by night (with theappearances of Bulls, Bears Etc.) as terrified her


25

y

x

0.8

0.6

0.4

0.2

0

–0.20 0.2 0.6 0.8 1 1.20.4

1

CIE(1931)

550 nm

500 nm

C 600 nm

400 nm

Laurel leaf

Sealing wax

Protan confusion point

Deutan confusion point

Blue skyPelargonium

zonaleRed campion

Ragged robin

•

••

•••

•

Figure 1.15 The CIE (1931) chromaticity diagram(see section 1.7.1 and Chapter 3). Plotted in thediagram are several flowers that looked blue toDalton: the cranesbill (Pelargonium zonale), redcampion (Lychnis dioica) and ragged robin (Lychnisfloscuculi). Also plotted are sealing wax and the upperside of a laurel leaf, which Dalton judged to be verysimilar in color. The open square in the center of thediagram represents Illuminant C, a standardapproximation to daylight. Passing through this pointare two lines, one (a ‘protan confusion line’)representing the set of chromaticities that would beconfused with white by a dichromat who lacks thelong-wave cones, and the other (a ‘deutan confusionline’) representing the set of chromaticities thatwould be confused with white by a dichromat wholacks the middle-wave cones. For both kinds ofdichromat, the pink flowers lie on the blue side of theneutral line, whereas sealing wax will have theopposite quality. Dalton (1798) himself wrote ‘Redand scarlet form a genus with me totally different frompink’.

very much; she could see to read sometimesin the great darkness for almost a quarter ofan hour.’ He is implying that the ‘Scintillations’– the subjective sensations of light that nowwould be called ‘phosphenes’ – correspondedto actual light. This misinterpretation of phos-phenes lingered until the nineteenth centuryand was one of the factors that prompted theyoung Johannes Mueller to develop his‘Doctrine of Specific Nerve Energies.’

Whatever we make of Turbervile’s Maid fromBanbury, we can only admire Robert Boyle’saccount of a suspiciously similar case, publishedin his Vitiated Sight of 1688. The subject was agentlewoman ‘about 18 or twenty years old’when Boyle had examined her. After an uniden-tified illness treated with blisters, she had losther sight entirely. Slowly light sensation andthen form vision returned, but color perceptionremained impaired. Like the Maid from Banbury‘she is not unfrequently troubled with flashes ofLightning, that seem to issue out like Flamesabout the External Angle of her Eye, whichoften make her start, and put her into Frights

and Melancholy Thoughts’ (Boyle, 1688). Withmaterials that came to hand, Boyle establishedthat she could read and had good acuity, but wasunable to identify reds, greens or blues. He adds– in a passage both poetic and insightful – ‘whenshe had a mind to gather Violets, tho’ shekneel’d in that Place where they grew, she wasnot able to distinguish them by the Colour fromthe neighbouring Grass, but only by the Shape,or by feeling them.’ Banbury is but 25 km fromBoyle’s home in Oxford; and Boyle, always trou-bled by poor eyesight, himself consultedTurbervile. Almost certainly, Boyle and Tuberviledescribe the same case, but Boyle’s is much thebetter account.

1.7 THE GOLDEN AGE(1850–1931)

Our survey has shown that many of the conceptsof modern color science were in place by themiddle of the nineteenth century. The followingdecades saw a golden era, when colorimetryemerged as a quantitative science and whencolor perception held a more prominent place inscientific discussion and in public debate than ithas held before or since.

1.7.1 COLOR MIXTURE

When Hermann Helmholtz published his firstpapers on color in 1852, he was already cele-brated for his essay on the conservation offorce, his measurements of the speed of neuralconduction, and his invention of the ophthal-moscope. Born in Potsdam in 1821, he hadbecome professor at Königsberg in 1849. Oneof his first contributions to color science was toclarify the distinction between the subtractivemixture of pigments and the additive mixtureof colored lights (Helmholtz, 1852). He conceivedof a pigment as a series of semi-transparentlayers of particles acting as filters to light thatis reflected from the underlying layers.Consider a mixture of yellow and blue pig-ments. A bright yellow pigment will reflect red,yellow, and green light, whereas a blue pigmentwill reflect green, blue, and violet. Some light,Helmholtz suggested, will be reflected by parti-cles at the surface, and this component will


26

Figure 1.16 The treatise of physics of Jacques Rohault(1671), in which he describes an acquired disturbanceof his own color vision.

include a large range of wavelengths and willbe close to white in its composition. Light thatis reflected from deeper layers, however, will besubject to absorption by both blue and yellowparticles; and so the light that is returned tothe eye will be dominated by wavelengths thatare not absorbed by either component – in thiscase, wavelengths from the green region of thespectrum.

Helmholtz offered a striking illustration of thedifference between additive and subtractive mix-ture. He painted the center of a disk with a mix-ture of yellow and blue pigment, but in the outerpart of the disk he painted separate sectors withthe same individual component pigments. Whenthe disk was spun, the center looked dark green,as painterly tradition required, but the circum-ference looked lighter and grayish. In the formercase, the perceived color depends on residualrays that are reflected after the physical mixtureof pigments. In the latter case, the two broad-band components are effectively combined atthe retina, owing to the temporal integration ofsuccessive stimuli within the visual system.

It is reassuring, however, and instructive, tosee a genius err. And so we can note thatHelmholtz’s 1852 paper contains an empiricalerror and a conceptual error. He reports hisresults for the additive mixture of spectral, nar-row-band, colors. He formed two prismatic spec-tra that overlay each other at 90�, so that allcombinations of monochromatic lights werepresent in the array; and he then viewed smallregions of the array in isolation. His empiricalerror was to conclude that there was only onepair of spectral colors, yellow and indigo-blue,that were complementaries in that they wouldmix additively to form a pure white; from othercombinations, the best that he could achieve wasa pale flesh color or a pale green – a report thatrecalls Newton’s phrase ‘some faint anonymousColour.’ The failure of Helmholtz to identifymore than one pair of complementaries maymerely reflect difficulty in isolating the appropri-ate small regions of the array. But his conceptualerror in the 1852 paper is instructive. By mixingred and a mid-green, he was unable to match amonochromatic yellow in saturation. This resultis correct and the reason for it is that a mid-greenlight stimulates all three cones, whereas a mono-chromatic yellow stimulates only the long- and

middle-wave cones. Helmholtz was led, however,explicitly to reject what he understood to beYoung’s trichromatic theory. If yellow is the colorseen when red and green sensations are concur-rently excited, he argued, then exactly the samecolor should be produced by the simultaneousaction of red and green rays. Because green is aphenomenologically simple hue, he does notentertain the possibility that monochromaticgreen light excites more than one class of fiber.

The failure of Helmholtz to find more thanone pair of complementaries drew a responsefrom the mathematician Hermann Grassmann.Grassmann (1853) began with the assumptionthat color experience is three-dimensional, beingfully described by the attributes of hue, bright-ness, and saturation. These three attributes ofsensation correspond, he suggested, to the threephysical variables of wavelength (or frequency),intensity (or amount of light), and purity (theratio of white to monochromatic white in a mix-ture). By assuming from the start that vision wasthree-dimensional and by adding the assump-tion that phenomenological experience neverchanged discontinuously as one of the physicalvariables was changed, Grassmann was able toshow that each point on the color circle ought tohave a complementary. Helmholtz now adopteda better method of mixing spectral lights andfound that the range of wavelengths betweenred and greenish-yellow had complementaries inthe range between greenish-blue and violet(Helmholtz, 1855; Figure 1.17). A range ofgreens, however, do not have complementariesthat lie within the spectrum: Their complemen-taries are purples, i.e. mixtures of lights drawnfrom the red and violet ends of the spectrum.Moreover, complementary lights of equal bright-ness do not necessarily mix to yield white: Theratio needed in the mixture may be veryunequal. For example, in the mixture of yellow-green and violet that matches white, the violetcomponent will be of much lower brightnessthan the yellow-green component. If the center-of-gravity principle for mixing is to be preservedand if the weightings of the component lights areto be in terms of subjective luminosity, then achromaticity diagram like that of Figure 1.18 isrequired. The range of purples is represented bya straight line connecting the two ends of thelocus of spectral colors.


27

In the same year, 1855, the 24-year-old JamesClerk Maxwell took Young’s theory several stepsfurther (Maxwell, 1855a, 1855b). He made hisexperiments on additive mixture by means of aspinning top that carried superposed disks(Figure 1.19). The disks, cut from colored papers,were slit along a radius, so that Clerk Maxwellcould expose a chosen amount of a given colorby slipping one disk over another. He used twosets of disks, one set of twice the diameter of theother. The inner disks were typically formed bywhite and black and, when spun, they exhibiteda gray corresponding to how much of each paperwas exposed. In the outer ring, he typically usedsectors of three different colors. Clerk Maxwellexperimentally adjusted the proportions of thethree colors of the outer ring until, being spun,they gave a gray that was equivalent to the gray

seen in the inner area. Once the match wasachieved, Clerk Maxwell used the perimeterscale to read off the space occupied by eachpaper in hundredths of a full circle. Suppose theouter colors were vermilion (V), ultramarine(U), and emerald green (EG), and the centerpapers snow white (SW) and black (Bk). Thenhe would write an equation of the followingform:

.37 V � .27 U � .36 EG � .28 SW � .72 Bk

Suppose that we take the three outer colors asour standard colors. By replacing one of theouter colors by some test color, Clerk Maxwellcould obtain a series of equations that containedtwo of the standard colors and the test color.Then, by bringing the test color to the left-handside of the equation, and bringing the threestandard colors to the right, he could representthe test color as the center of gravity of threemasses, whose weights are taken as the numberof degrees of each of the standard colors.

By 1860 Clerk Maxwell had constructed adevice that allowed him to match daylight withmixtures of three monochromatic lights(Maxwell, 1860). This allowed him to expressthe spectrum in terms of three primaries and toplot against wavelength the amounts of thethree primaries required to match any givenwavelength (Figure 1.20). The latter curvesare the forerunners of later ‘color matching


28

Figure 1.17 Helmholtz’s graph of the wavelengthsthat are complementaries, i.e., the wavelengths thatwill form white when mixed in a suitable ratio.

Figure 1.18 The first chromaticity diagram to havea modern form, prepared by Helmholtz on the basis ofhis measurements of complementaries.

Figure 1.19 The color-mixing top of James ClerkMaxwell. The instrument survived in the collection ofthe Cavendish Laboratory, Cambridge. Thisphotograph was taken in 1982. (Copyright:Department of Experimental Psychology, CambridgeUniversity, reproduced with permission.)

functions.’ In the same paper, Clerk Maxwellnoted that the matches he made with centralvision did not hold when he observed them indi-rectly. This discrepancy, and also the discrepancybetween his central matches and those of hiswife, he attributed to the yellow spot of the cen-tral retina, which selectively absorbs light in thewavelength range 430–90 nm.

Fresh determinations of the color matchingfunctions were made in the 1920s by Guild,using a filter instrument, and by Wright, usingmonochromatic stimuli. When the two sets ofresults were expressed in terms of a common set

of primaries, they were found to agree extremelywell, and they were taken as the basis for a stan-dard chromaticity diagram adopted by theCommission Internationale d’Éclairage (CIE) in1931. This CIE system has remained the princi-pal means of specifying colors for trade andcommerce (Chapter 3). W.D. Wright has left usa personal account of its origins, in an Appendixto Kaiser and Boynton (1996).

1.7.2 THE SPECTRAL SENSITIVITIES OFTHE RECEPTORS

We have seen that a chromaticity diagram allowsany light to be specified in terms of three arbi-trary primary lights: All that we need to know isthe relative amount of each primary that isrequired to match the test light. It is thenstraightforward to re-express the chromaticity ofthe test light in terms of a new set of primarylights, since we know how much of each of theold primaries is required to match each of thenew primaries. But somewhere in the diagramthere should be a set of three points that have aspecial status: These would be the lights – if theyexisted – that stimulated only one individualclass of Young’s receptors. Clerk Maxwell in1855 was firm in saying that such lights do notexist in the real world. He draws a version ofNewton’s color circle within a larger triangle andwrites:

Though the homogeneous rays of the prismaticspectrum are absolutely pure in themselves, yetthey do not give rise to the ‘pure sensations’ ofwhich we are speaking. Every ray of the spec-trum gives rise to all three sensations, though indifferent proportions; hence the position of thecolours of the spectrum is not at the boundary ofthe triangle, but in some curve CRYGBV consid-erably within the triangle . . . All natural coloursmust be within this curve, and all ordinary pig-ments do in fact lie very much within it.

(Maxwell, 1855b)

Clerk Maxwell himself proposed how it might bepossible experimentally to establish the positionsof the individual receptors in a chromaticity dia-gram – and thus to express each wavelength ofthe spectrum in terms of the relative excitation itproduces in the three receptors. It is necessary toassume that the color blind retain two of thenormal receptors and lack a third. In 1855 Clerk


29

Figure 1.20 The first empirical color-matchingfunctions.The data shown are for Clerk Maxwell’swife, Katherine.The lower plot represents theproportions of the red, green and blue primariesneeded to match a given wavelength.The spectrumruns from red on the left to violet on the right.Theupper plot is a chromaticity diagram based on thesame color-matching data.The locus of the spectralcolors is expressed in terms of the proportions of thethree primaries used in the experiment.

Maxwell was aware of only one class of colorblind subjects, those he thought to lack the long-wave receptor. Using his technique of spinningdisks, he showed that these dichromatic subjectsneeded only four colors (including black) in theirequations (Maxwell, 1855a). With the red, green,and blue standard colors of Figure 1.21, forexample, a dichromat generated the equation

.19G � .05B � .76 Bk � 1.00 R,

that is, a full red was equivalent to a dark blue-green mixture. Along the line Redb (see Figure1.21), the subject can match all chromaticitiesmerely by varying the amount of black in themixture: In other words, provided we equate thedifferent chromaticities in lightness, he cannotdiscriminate among them. Such a line wouldtoday be called a ‘dichromatic confusion line.’ Todistinguish chromaticities on this line, the nor-mal must be using the receptor that the dichro-mat lacks. All that varies along the line is thedegree of excitation of the receptor that is miss-ing in the color blind. If we establish a secondconfusion line (e.g. cd in the diagram), then thepoint D, where Redb and cd intersect, gives theposition in the chromaticity diagram of the miss-ing receptor. Physical lights can then be re-expressed in terms of the relative excitations ofthe three receptors.

This approach, which Clerk Maxwell pro-posed in 1855, has remained a prominentpsychophysical method for estimating thespectral sensitivities of the retinal receptors.Arthur König (Figure 1.22), a colleague ofHelmholtz, obtained color-matching functionsfor normals, protanopes and deuteranopes, andderived the sensitivities shown in Figure 1.23(König and Dieterici, 1892). Notice that thepeak of König’s long-wave receptor lies in theyellow region of the spectrum. Twentieth-century color-matching functions allowed freshestimates of the receptor sensitivities (e.g.Nuberg and Yustova, 1955; Wyszecki and Stiles,1967). An important advance came from precisemeasurements of the confusion lines of tri-tanopes, those rare dichromats who lack theshort-wave receptor (Wright, 1952). However,even amongst those who favored a trichromatictheory, receptor sensitivities derived by ClerkMaxwell’s method did not secure universalacceptance until late in the twentieth century.Convergent evidence came from the work ofW.S. Stiles, who measured thresholds for mono-chromatic increments on monochromatic fields.By varying systematically either the wavelengthof the test flash or that of the adapting field, hewas able to show that the sensitivity of an indi-vidual cone channel is primarily determined by


30

Figure 1.21 Clerk Maxwell’s diagram showing howthe position in the chromaticity diagram of one of theretinal receptors can be estimated from theconfusions made by a dichromat.

Figure 1.22 Arthur König (1856–1901), a protégé ofHelmholtz. König suffered from a progressive andpainful deformity of the spine.

the photons absorbed by that channel alone; andthus he was able to estimate the spectral sensitiv-ities of the cones, estimates that resembled thoseobtained by Clerk Maxwell’s method (Stiles,1939). Objective measurements of the cone pig-ments were later obtained by the method ofreflection densitometry (Rushton, 1965) andby direct microspectrophotometric and electro-physiological measurements of single cones.

1.7.3 ANOMALOUS TRICHROMACY

Clerk Maxwell died of cancer in 1879, when stillonly forty-eight. His successor in the Cavendishchair of physics at Cambridge was BaronRayleigh, who took the post only because theagricultural depression had temporarily spoiledhis plans of maintaining a large private labora-tory on his family estate at Terling Place (Strutt,1924). In 1881, Lord Rayleigh described how hehad discovered that three of his wife’s brothers– including Arthur Balfour, later British PrimeMinister and author of the ‘Balfour Declaration’– differed from him in matching monochromaticyellow light with a mixture of red and green.The mixture set by Rayleigh himself looked‘almost as red as red sealing wax’ to his brothers-in-law, who set a match with only half as muchred in it. A fourth brother was normal, as werethe three sisters. Others in Rayleigh’s circle,

including J.J. Thompson (his successor asCavendish Professor), similarly required a muchsmaller ratio of red to green in the match thandid the normal observer, while two furtherobservers required more red in the match, in theratio 2.6 to 1 relative to the normal. Yet severalof these deviant observers had fine discrimina-tion in the red–green range and could not beconventionally described as color blind(Rayleigh, 1881).

The class of observers identified by Rayleighwere soon being called ‘anomalous trichro-mats’(König and Dieterici, 1886). Rayleigh him-self suggested that they were very common, andwe now know that they constitute some 6% ofthe male population. However, the distinguishedDutch ophthalmologist Donders showed that theanomalous observers with good discrimination(such as the Balfour brothers) were relativelyuncommon, and that an anomalous match wasmore often associated with reduced discrimina-tion of color (Donders, 1884). He also obtained‘Rayleigh equations’ for a population of over 50normal observers and noted the large variationin their individual matches.

Donders standardized the wavelengths usedfor the Rayleigh equation: The red and greencomponents of the mixture were provided bythe lithium line at 670 nm and the thallium lineat 535 nm, and this mixture was to be matched


31

Figure 1.23 The first realistic estimates of the sensitivities of the retinal receptors.The spectrum is plottedwith long wavelengths to the left.The solid and dashed curves show the estimates of the receptors of normalobservers. (From König and Dieterici, 1892.)

to the orange light of the sodium line at 589 nm.Remarkably, Donders’ red and orange wave-lengths have been retained to this day as stan-dards for the Rayleigh equation (e.g. Germanstandard DIN 6160). The green component waslater moved to the mercury line at 546 nm, sincethis gives a mixture that is closer to the orange insaturation.

1.7.4 TESTS FOR COLOR DEFICIENCY

There is never any end to the invention of newcolor tests, but nearly all the main principlesemerged in the period 1870–1930. The introduc-tion of tests for mass screening was prompted bythe use of color signaling on the rapidly expand-ing railroads (Wilson, 1855; Jennings, 1896). AtLagerlunda in Sweden, in the early hours of 15November 1875, nine people died when twoexpress trains collided on a single-line track(Nettleship, 1913). The engineer of the late-running northbound express apparently did notrecognize a red light waved by the stationmasterat Bankeberg station, for he slowed and thenrestarted forwards without the stationmaster’sorder. A lineman ran with a red lamp after thetrain, but a carriage oiler, in the front van, is saidto have called out to the engineer that he saw the‘line-clear’ signal. Two or three minutes later, as itsteamed up the incline to the bridge over the

Lagerlund river, the train met the southboundexpress (Figure 1.24). The engineer and the oilerof the northbound train were among the dead,but Professor F. Holmgren of Upsala raised thepossibility that one or other had been color blind.He campaigned for the screening of all railwayemployees. The superintendent of the Upsala–Gefle line provided Holmgren with a private railcar and he proceeded down the line, halting ateach station and gatekeeper’s house to test everyemployee. Some 4.8% of the personnel, includ-ing a stationmaster and an engineer, were foundto be color-deficient (Holmgren, 1877).

Holmgren sought a test that did not require thenaming of colors, since the daltonian’s use ofcolor terms will often disguise an inability to dis-criminate. Instead, Holmgren required the sort-ing of colored wools: ‘it is necessary to leave tothe activity of the hands the task of revealing thenature of sensation.’ The examiner places on thetable a sample skein, green for the first test andpurple for the second. Nearby, is a jumbled pile ofskeins of varying color and lightness. The subjectis asked to pick from the pile the skeins that havethe same hue. Daltonians quickly reveal them-selves by picking from the pile not only the skeinsthat a normal would pick, but also ‘confusioncolors’ characteristic of this form of deficiency.

Concurrently, in Germany, Stilling introducedthe first ‘pseudoisochromatic plates,’ which pres-


32

Figure 1.24 The fatal consequence of color blindness? The scene after the Lagerlunda collision of November1875. (Reproduced by permission of Sveriges Järnvägsmuseum.)

ent a target digit or letter of one color embeddedin a background of another color. Initially, anattempt was made to print solid figures of onechromaticity on an equally light background of asecond chromaticity, the chromaticities beingones confused by the color blind. It was quicklyfound, however, that it was impossible to printfigure and ground in such a way as to eliminateall edge artifacts. Moreover, a figure and groundthat were equally light for one daltonian werenot necessarily so for another. Stilling solvedthese problems by two ingenious manoeuvres(Stilling, 1877). First, he broke the target and thefield into many small patches, each with its owncontour; and secondly, instead of attempting toequate the lightness of target and field, he variedthe lightness of the individual patches (Figure1.25). So neither edge artifacts nor luminancedifferences could be used as cues to discriminatethe target from the background. The target canbe detected only by color discrimination, and thetask resembles the natural task that challengesthe color blind, that of finding fruit amongstdappled foliage.

Stilling’s pseudoisochromatic plates are all ofthe ‘disappearing’ type, so called because the tar-

get becomes invisible for a particular type of color-deficient observer. A clever later variant was the‘transformation plate’, where the normal and thecolor-deficient give alternative readings. This isachieved by linking the elements of the array byone neural signal for the normal and by a differ-ent one for the daltonian: For example, on anorange background, the normal might link bluish-green elements with yellow-green elements,whereas, for the daltonian, the more salient link-age might be between the bluish-green elementsand plum-colored ones, or between elements ofsimilar lightness. Early examples of transforma-tion plates dating from 1916 are seen in the test ofPodestà, who was Marine-Generaloberarzt of theGermany Navy. This test has passed into thegraveyard that accommodates many forgottencolor tests, but it is the most baroque set ofplates ever produced, and it is particularly cleverbecause some of the alternative readings are alsoantonyms (Figure 1.26). The following year, theJapanese ophthalmologist Ishihara published thefirst edition of a set of plates that included dis-appearing and transformation plates, as well asplates in which the daltonian sees a digit that ismasked for the normal by random color varia-tion (Ishihara, 1917). Despite many rivals, thepseudoisochromatic plates of Ishihara became –and remain today – the dominant instrument forroutine screening of color vision. They readilydetect dichromats and all but a tiny minority ofanomalous trichromats. In part, this sensitivity isachieved not by testing color discrimination butby pitting one perceptual organization against asecond.

Whereas the Ishihara plates are used forscreening, the classification of color deficiencydepends on another instrument introduced earlyin the twentieth century: the anomaloscope ofNagel (1907). This optical device is essentially areverse spectroscope: Lights from three slits passthrough a prism, and an ocular lens focusesthem on the subject’s pupil. In the standardmodel, the slits isolate the wavelengths chosenby Donders for the Rayleigh equation (see sec-tion 1.7.3). The subject sees a field subtending2 degrees: One half-field is illuminated byorange light and the second by the red-greenmixture. One control varies the ratio of red togreen light in the mixture, and a second adjuststhe luminance of the orange light. Dichromats


33

Figure 1.25 An example of a pseudoisochromatictest for color deficiency. (From Stilling, 1877.)

reveal themselves by matching the orange fieldwith any mixture of red and green, and pro-tanopes and deuteranopes can be distinguishedby the amounts of orange lights they require tomatch different red-green mixtures. Anomaloustrichromats are classified by their Rayleigh equa-tions as ‘protanomalous’ (requiring excess red)or ‘deuteranomalous’ (requiring excess green).Their power of discrimination (and that of thosewith normal equations) can be gauged by therange of matches that they accept.

An insight into the early days of color testingcan be had by reading the entertaining history ofMr Trattles, a British seaman who was denied hisFirst Mate’s certificate after earlier passing theHolmgren test (Boltz, 1952). His case was dis-cussed in both Houses of Parliament, andWinston Churchill, then President of the Boardof Trade, defended Holmgren’s test (Hansard,1909). On the basis of spectral luminosity meas-urements at Imperial College, the physicistWilliam Abney declared Trattles a protanope.Trattles finally secured his certificate after he hadbeen taken down the Thames one winter’s nighton a steamer and had successfully identified nav-igation lights in the presence of witnesses. Hewas probably protanomalous, but there is norecord that he was ever tested with Nagel’s newinvention. The Trattles case well illustrates theintense public interest in color perception in theperiod before the First World War.

1.7.5 COLOR AND EVOLUTION

The Origin of Species was published in 1859, andin the following decades, Darwinism spread toall branches of biology. The father of visual ecol-ogy is undoubtedly a Canadian, Grant Allen,later infamous for his feminist novel The WomanWho Did. In 1879 he argued systematically thatcolor perception in animals had co-evolvedwith color signals in plants. His own summarycannot be bettered:

Insects produce flowers. Flowers produce thecolour-sense in insects. The colour-sense pro-duces a taste for colour. The taste for colour pro-duces butterflies and brilliant beetles. Birds andmammals produce fruits. Fruits produce a tastefor colour in birds and mammals. The taste forcolour produces the external hues of humming-birds, parrots, and monkeys. Man’s frugivorousancestry produces in him a similar taste; and thattaste produces the various final results of thechromatic arts.

(Allen, 1879)

Donders (1883) explicitly suggested that humantrichromacy evolved from an earlier dichromaticstate and had appeared first in females. The basisof the evolution was the successive differentia-tion of a visual molecule. The American psychol-ogist Christine Ladd-Franklin (Figure 1.27)made evolution central to her own theory ofcolor perception. She proposed:


34

Figure 1.26 A transformation plate from the test of Podestà (1916).The normal reads ‘Armee’ but thedichromat reads the antonym,‘Zivil’.

that the substance which in its primitive condi-tion excites the sensation of grey becomes in thefirst place differentiated into two substances, theexciters of yellow and blue respectively, and thatat a later stage of development the exciter of thesensation of yellow becomes again separated intotwo substances which produce respectively thesensations of red and green.

(Ladd-Franklin, 1892)

Mrs Ladd-Franklin’s chemistry is of its time, andshe assumes too close a link between her recep-tor molecules and sensations. But her sequenceanticipates the modern view of the evolution ofprimate photopigments: Molecular genetics sug-gest that the long- and middle-wave pigmentsbecame differentiated relatively recently in pri-mate evolution, whereas the common ancestorof these molecules diverged from the short-wavepigment at a much earlier, pre-mammalian stage(Nathans et al., 1986).

1.8 NERVES AND SENSATIONS

The work of Helmholtz, Clerk Maxwell andKönig did not secure universal acceptance of athree-receptor theory. A prominent opponentwas the physiologist Ewald Hering, who took hisstart from color sensations. There are four huesin our experience – red, green, yellow, and blue– that look phenomenologically simple, whereasother hues, such as orange or purple, look to usmixed in quality. We can see the redness and theblueness in a purple, whereas we cannot men-tally dissect a pure red or a pure blue. Moreover,the simple hues are organized into two antago-nistic pairs (Gegenfarben): red and green, and yel-low and blue. The qualities of a given pair areones that do not normally occur together. Heringproposed that each pair of Gegenfarben was asso-ciated with the dissimilation or assimilation ofa specific visual substance in the eye or visualsystem (Hering, 1878).

For much of its history, the trichromatic the-ory had the disadvantage of being tied to a sim-ple Müllerian doctrine in which there were threetypes of visual nerve corresponding to the threereceptors. Granted, as early as 1869 J.J.Chisholm, a physician from Charleston, SouthCarolina, suggested that ‘there are special nervefibres, for the recognition of special colours,independent of those used in the clear definitionof objects’(Chisholm, 1869). And the same sus-picion was expressed by Thomas Laycock(1869), who wrote: ‘the optic nerve may sub-serve to at least three differentiations – namely,form, colour, and as a nerve of touch simply’.Only in the twentieth century, however, did theidea emerge that some nerve fibers might beexcited by one type of photoreceptor and inhib-ited by others (Adams, 1923). A nerve that sig-naled the ratio of quantum catches in differentclasses of cone would be directly signaling chro-maticity, rather than signaling the absolute levelof quantum catch in one class of photoreceptors.The cones themselves are color blind (section1.2), responding with a signal of the same sign toa broad spectral band; but a nerve that respondsto the ratio of cone excitations does representchromaticity as such.

In the 1960s, by micro-electrode recordingfrom the lateral geniculate nucleus (LGN) of theprimate visual system, neurons were revealed


35

Figure 1.27 Christine Ladd-Franklin (1847–1930).A graduate of Vassar, Ladd-Franklin studied vision inGöttingen and Berlin, and developed an evolutionaryaccount of color perception (Copyright:Vassar CollegeLibrary, reproduced with permission).

that did draw inputs of opposite sign from differ-ent classes of cone (De Valois et al., 1967). Suchcells gave an excitatory response to one part ofthe spectrum and an inhibitory response toanother part. Moreover, the cells appeared to fallinto four classes, on the basis of (a) whethertheir excitatory response was at short wave-lengths or at long and (b) where in the spectrumthe excitatory response crossed over to inhibi-tion. Many commentators were ready to identifythese spectrally antagonistic cells with the yel-low–blue and red–green opponent processes ofHering. Brindley (1970) was one of very fewskeptics. In textbooks it became a commonplaceto say that that theory of Helmholtz held at thelevel of receptors while the theory of Heringapplied at a post-receptoral level. In fact, thereturned out to be little correspondence between:(a) the directions in color space that uniquelystimulate individual types of chromaticallyantagonistic cells in the primate LGN, and (b) thered–green and blue–yellow axes of phenomeno-logical color space (Derrington et al., 1984).

In surveying the history of color science, wehave seen that confusion arose when informa-tion from one domain was used to constrainmodels in a different domain. The properties ofour subjective color space still remain to taunt ustoday. We do not know the status that should begiven to the phenomenological observations ofHering and we do not know how to incorporatethem into a complete account of color science.

FURTHER READING

The following works are recommended:

Crone, R.A. (1999) A History of Color. Dordrecht:Kluwer Academic.

Gage, J. A. (1993) Colour and Culture. London: Thamesand Hudson.

MacAdam, D. (1970) Sources of Color Science.Cambridge, MA: MIT Press.

Turner, R.S. (1994) In the Eye’s Mind: Vision and theHelmholtz–Hering Controversy. Princeton, NJ:Princeton University Press.

The following analytic bibliographies are valuable:

Bell, J. (1926) Colour-blindness. Eugenics LaboratoryMemoirs, XXIII. Cambridge: Cambridge UniversityPress.

Helmholtz, H. von (1896) Handbuch der PhysiologischenOptik, 2nd edn. Hamburg: Voss.

Plateau, J. (1877) Bibliographie analytique des prin-cipaux phénomènes subjectifs de la vision.Mémoires de l’Académie royale des sciences, des lettres etdes beaux-arts de Belgique, volume 42.

Sutcliffe, J.H. (1932) British Optical Association Libraryand Museum Catalogue. London: BOA.

A chronological bibliography of color is maintainedby the Grupo Argentino del Color at the web site:http://www.fadu.uba.ar/sicyt/color/bib.htm

REFERENCES

Abney, W. (1913) Researches in Colour Vision and theTrichromatic Theory. London: Longmans, Green Co.

Adams, E.Q. (1923) A theory of color vision.Psychological Review, 30, 56–76.

Allen, G. (1879) The Colour-Sense: Its Origin andDevelopment. London: Trübner & Co.

Anonymous (1708) Traité de la peinture en mignature.La Haye (The Hague): van Dole.

Anonymous (1786) Experiments and observations onlight and colours: to which is prefixed the analogy betweenheat and motion. London: J. Johnson.

Anonymous (1787) A Narrative of the Life and Death ofJohn Elliot M.D. containing an account of the rise,progress, and catastrophe of his unhappy passion for MissMary Boydell; a review of his writings. Together with anApology, written by himself. London: Ridgway.

Ayama, M., Nakatsue, T., and Kaiser, P.K. (1987)Constant hue loci of unique and binary balancedhues at 10, 100, and 100 Td. Journal of the OpticalSociety of America A, 4, 1136–44.

Barrett, C. (ed.) (1904) Diary and Letters of MadameD’Arblay. London: Macmillan.

Blankaart, S. (1680) Collectanea Medico-Physica oftHollands Jaar-Register Der Genes- en Natuur-kundigeAanmerkingen van gantsch Europa. Amsterdam:Johan ten Hoorn.

Boltz, C.L. (1952) A Statue to Mr. Trattles. London:Butterworths.

Bonnet, C. (1755) Essai de psychologie; ou considérationssur les opérations de l’âme, sur l’habitude et sur l’educa-tion. London.

Bouma, P.J. (1947) Physical Aspects of Colour.Eindhoven: Philips.

Boyle, R. (1688) Some Uncommon Observations aboutVitiated Sight. London: J. Taylor.

Brewster, D. (1842) Letters on Natural Magic, addressedto Sir Walter Scott, Bart. London: J. Murray.

Brindley, G. S. (1970) Physiology of the Retina and VisualPathway. London: Arnold.

Brockbank, E.M. (1944) John Dalton. Manchester:Manchester University Press.

Castel, L. (1740) L’Optique des couleurs. Paris:Briasson.

Chisholm, J.J. (1869) Colour blindness, an effect ofneuritis. Ophthalmic Hospital Reports, pp. 214–15.

Cunningham, P. (ed.) (1857) The Letters of HoraceWalpole, Earl of Orford. London: Richard Bentley.


36

Dalton, J. (1798) Extraordinary facts relating to thevision of colours. Memoirs of the Literary andPhilosophical Society of Manchester, 5, 28–43.

De La Hire, P. (1694) Dissertation sur les différensaccidens de la vuë. Mémoires de l’Académie Royale desSciences, 9, 530–634.

De Valois, R.L., Abramov, I., and Jacobs, G.H. (1967)Analysis of response patterns of LGN cells. Journal ofthe Optical Society of America, 56, 966–77.

Derrington, A.M., Krauskopf, J., and Lennie, P. (1984)Chromatic mechanisms in lateral geniculatenucleus of macaque. Journal of Physiology (London),357, 241–65.

Donders, F.C. (1883) Nog eens: de kleurstelsels, naar aan-leiding van Hering’s kritiek. Utrecht: G. Metzelaar.

Donders, F.C. (1884) Equations de couleurs spectralessimples et de leurs mélanges binaires, dans les sys-tèmes normal (polychromatique) et anormaux(dichromatiques). Archives Néerlandaises des sciencesexactes et naturelles, 19, 303–46.

Dossie, R. (1758) The Handmaid to the Arts. London: J.Nourse.

Elliot, J. (1780) Philosophical Observations on the Sensesof Vision and Hearing. London: J. Murray.

Elliot, J. (1786) Elements of the Branches of NaturalPhilosophy Connected with Medicine. London: J.Johnson.

Forbes, E.G. (1970) Tobias Mayer’s theory of colour-mixing and its application to artistic reproductions.Annals of Science, 26, 95–114.

Forbes, E.G. (1971) Tobias Mayer’s Opera Inedita.London: Macmillan.

Gamauf, G. (1811) Lichtenberg über Luft und Licht nachseinen Vorlesungen herausgegeben. Erinnerungen ausLichtenbergs Vorlesungen über Erxlebens Anfangsgründeder Naturlehre. Vienna and Trieste: Geistinger.

Gautier D’Agoty, J.F. (1752) Observations sur l’HistoireNaturelle, sur la Physique et sur la Peinture, avec desPlanches imprimées en couleur. Paris: Delaguette.

Gautier D’Agoty, J.F. (1775) Exposition anatomique desorganes des sens, jointe a la névrologie entiere du corpshumain et conjecture sur l’électricité animale. Paris:Demonville.

Grassmann, H.G. (1853) Zur Theorie derFarbenmischung. Annalen der Physik, 89, 69–84.

Guericke, O. v. (1672) Experimenta Nova (ut vocantur)Madeburgica de Vacuo Spatio. Amstelodami:Janssonium.

Gurney, H. (1831) Memoir of the Life of Thomas Young,M.D., F.R.S. London: John and Arthur Arch.

Guyot, G.-G. (1769) Nouvelles récréations physiques etmathématiques. Paris: Gueffier.

Hall, A.R. (1992) Isaac Newton. Oxford: Blackwell.Hansard (1909) The Parliamentary Debates of the United

Kingdom. London: HMSO.Helmholtz, H. (1852) Über die Theorie der zusam-

mengesetzten Farben. Annalen der Physik, 87, 45–66.Helmholtz, H. (1855) Über die Zusammensetzung von

Spectralfarben. Annalen der Physik, 94, 1–28.Henry, W.C. (1854) Memoirs of the life and scientific

researches of John Dalton. London: Cavendish Society.

Hering, E. (1878) Zur Lehre vom Lichtsinne. SechsMittheilungen an die Kaiserliche Akademie derWissenschaften in Wien. Vienna: Carl Gerold’s Sohn.

Herschel, W. (1800a) Investigation of the Powers ofthe prismatic Colours to heat and illuminateObjects; with remarks that prove the differentRefrangibility of radiant Heat. To which is added, anInquiry into the Method of viewing the Sun advan-tageously with Telescopes of large Apertures andhigh magnifying Powers. Philosophical Transactions ofthe Royal Society, 90, 255–83.

Herschel, W. (1800b) Experiments on the Refrangi-bility of the Invisible Rays of the Sun. PhilosophicalTransactions of the Royal Society, 90, 284–92.

Heyer, T. (1864) Ami Argand. Geneva: Gruaz.Hodgson, E. (1787) The Trial of Doctor John Elliot, for

Feloniously Shooting at Miss Mary Boydell. London:Hodgson.

Holmgren, F. (1877) Color-blindness in its Relation toAccidents by Rail and Sea. Washington: SmithsonianInstitute.

Huddart, J. (1777) An account of Persons who couldnot distinguish Colours. Philosophical Transactions ofthe Royal Society, 67, 260–5.

Hunt, D.M., Dulai, K.S., Bowmaker, J.K., and Mollon,J.D. (1995) The chemistry of John Dalton’s colorblindness. Science, 267, 984–8.

Hurlbert, A.C. (1998) Computational models of colourconstancy. In V. Walsh and J. Kulikowski (eds),Perceptual Constancy: Why Things Look as They Do.Cambridge: Cambridge University Press.

Hutton, J. (1794) A Dissertation upon the Philosophy ofLight, Heat and Fire. Edinburgh.

Huygens,C. (1673) AnExtractofaLetterLatelyWrittenby an Ingenious Person from Paris, Containing SomeConsiderationsuponMr.NewtonsDoctrineofColors,as Also upon the Effects of the Different Refractionsof the Rays in Telescopical Glasses. PhilosophicalTransactions of the Royal Society, 8, 6086–7.

Ishihara, S. (1917) Series of Plates Designed as Tests forColour-blindness. Tokyo.

Jennings, J.E. (1896) Color-Vision and Color-Blindness. APractical Manual for Railroad Surgeons. Philadelphia:F.A. Davis.

Kaiser, P.K. and Boynton, R.M. (1996) Human ColorVision. Washington, DC: Optical Society of America.

Kohlrausch, A. (1923) Theoretisches und Praktischeszur heterochromen Photometrie. Pflügers Arch.Gesamte Physiol. Menschen Tiere, 200, 216–19.

König, A. and Dieterici, C. (1886) Die Grundempfind-gungen und ihre Intensitätsvertheilung im Spec-trum. Sitzungsberichte Preuss. Akad. Wissenschaften,Berlin, pp. 805–29.

König, A. and Dieterici, C. (1892) DieGrundempfindungen in normalen und anomalenFarbensystemen und ihre Intensitätsverteilung imSpektrum. Zeitschrift für Psychologie, 4, 241–347.

Ladd-Franklin, C. (1892) A new theory of light sensa-tion. International Congress of Psychology, 2nd Congress.London, Kraus Reprint, 1974.


37

Lambert, J.H. (1770) Mémoire sur la PartiePhotométrique de l’Art du Peintre. Histoire deL’Académie Royale des Sciences et Belles-Lettres. AnnéeMDCCLXVIII, 24, 80–108.

Lambert, J.H. (1772) Beschreibung einer mit demCalauschen Waschse ausgemalten Farbenpyramide, wo dieMischung jeder Farbe aus Weiss und drey Grundfarbenangeordnet, dargelegt und derselben Berechnung undvielfacher Gebrauch angewiesen wird durch J. H. Lambert.Berlin: Hande and Spener.

Laycock, T. (1869) Mind and Brain. New York:Appleton.

Lee, B.B. (2001) Colour science in Göttingen in the 18thCentury. Color Research and Application, 26, S25–S31.

Lee, H.-C. (1986) Method for computing the scene-illuminant chromaticity from specular highlights.Journal of Optical Society of America, A3, 1694–9.

Leicester, H.M. (1970) Mikhail Vasil’evich Lomonosov onthe Corpuscular Theory. Cambridge, MA: HarvardUniversity Press.

Lilien, O.M. (1985) Jacob Christoph Le Blon. Stuttgart:Anton Hiersemann.

Lomonosov, M.V. (1757) Oratio de origine lucis.Petropoli: Typis Academiae Scientiarum.

Lonsdale, H. (1874) The Worthies of Cumberland. Volume5. John Dalton. London: Routledge.

MacLennan, M. (1975) The Secret of Oliver Goldsmith.New York: Vantage Press.

Marat, J.P. (1780) Découvertes de M. Marat sur laLumière; Constatées par une suite d’Expériences nou-velles. Paris: Jombert.

Mason, W. (1958) Father Castel and his color clavecin.Journal of Aesthetics and Art Criticism, 17, 103–16.

Maxwell, J.C. (1855a) Experiments on Colour, asperceived by the Eye, with remarks on Colour-blindness. Transactions of the Royal Society ofEdinburgh, 21, 275–98.

Maxwell, J.C. (1855b) On the theory of colours inrelation to colour-blindness. Researches on colour-blindness. G. Wilson, pp. 153–9.

Maxwell, J.C. (1860) On the theory of the compoundcolours and the relations of the colours in the spec-trum. Philosophical Transactions of the Royal Society,150, 57–84.

Maxwell, J.C. (1871) On colour vision. Proceedings ofthe Royal Institution of London, pp. 260–71.

Mayer, T. (1775) Opera Inedita. Göttingen: J.C.Dieterich.

Mollon, J. D. (1985) L’Auteur énigmatique de lathéorie trichromatique. Actes du 5eme Congrès. Paris,Association Internationale de la Couleur.

Mollon, J.D. (1987) John Elliot MD (1747–87).Nature, 329, 19–20.

Mollon, J.D. (1989) ‘Tho’ she kneel’d in that Placewhere they grew ...’. Journal of Experimental Biology,146, 21–38.

Mollon, J.D. (1992) Signac’s secret. Nature, 358,379–80.

Mollon, J.D. (1993) George Palmer. The Dictionary ofNational Biography (ed. C. S. Nicholls). Oxford:Oxford University Press, pp. 509–10.

Mollon, J.D. (1997) ‘..aus dreyerley Arten vonMembranen oder Molekülen’: George Palmer’slegacy. Colour Vision Deficiencies XIII (ed. C.R.Cavonius). Dordrecht: Kluwer.

Mollon, J.D. (2002) The origins of the concept ofinterference. Philosophical Transactions of the RoyalSociety A, 360, 1–13.

Mollon, J.D. (in press) John Elliot (1747–87). NewDictionary of National Biography (ed. H.C.G.Matthew). Oxford: Oxford University Press.

Mollon, J.D., Dulai, K.S., and Hunt, D.M. (1997)Dalton’s colour blindness: an essay in molecularbiography. John Dalton’s Colour Vision Legacy (eds C.Dickinson, I. Murray and D. Carden). London:Taylor and Francis, pp. 15–33.

Monge, G. (1789) Mémoire sur quelques phénomènesde la vision. Annales de Chimie, 3, 131–47.

Mortimer, C. (1731) An Account of Mr. James-Christopher Le Blon’s Principles of Printing, inImitation of Painting and of Weaving Tapestry, inthe same manner as Brocades. PhilosophicalTransactions of the Royal Society, 37, 101–7.

Müller, J. (1840) Handbuch der Physiologie des Menschen.Coblenz: H. Ischer.

Nagel, W.A. (1907) Zwei Apparate für dieAugenärzliche Funktionsprüfung. Adaptometerund kleines Spektralphotometer (Anomaloskop).Zeitschrift für Augenheilkunde, 17, 201–22.

Nathans, J., Thomas, D., and Hogness, D.S. (1986)Molecular genetics of human color vision: Thegenes encoding blue, green, and red pigments.Science, 232, 193–202.

Nettleship, E. (1913) On Cases of Accident to Shipping andon Railways due to Defects of Sight. London: Adlard andSon.

Newton, I. (1671) A Letter of Mr. Isaac Newton,Professor of the Mathematicks in the University ofCambridge; Containing His New Theory about Lightand Colors: Sent by the Author to the Publisherfrom Cambridge, Febr. 6. 1671/72; In Order to beCommunicated to the R. Society. PhilosophicalTransactions of the Royal Society, 6, 3075–87.

Newton, I. (1675/1757) Newton’s second paper oncolor and light, read at the Royal Society in 1675/6.History of the Royal Society of London. T. Birch. London,Millar, vol. 3, pp. 247–305.

Newton, I. (1688) Philosophiae Naturalis PrincipiaMathematica. London: Joseph Streater.

Newton, I. (1730) Opticks, or a Treatise of the Reflections,Refractions, Inflections & Colours of Light. London: Wm.Innys.

Nuberg, N.D. and Yustova, E.N. (1955) Issledovaniecvetovogo zrenija dikhromatov. TrudyGosudarstvennogo Opticheskogo Instituta, 24, 33–93.

Palmer, G. (1777a) Théorie des couleurs et de la Vision.Paris: Prault.

Palmer, G. (1777b) Theory of colours and vision. London:S. Leacroft.

Palmer, G. (1785) Lettre sur les moyens de produire, lanuit, une lumière pareille à celle du jour. Paris: ‘Chezl’Auteur, rue Meslé, No. 18’.


38

Palmer, G. (1786) Théorie de la Lumière, applicable auxarts, et principalement à la peinture. Paris: Hardouin etGattey.

Parrot, G.F. (1791) Traité contenant la manière de changernotre lumière artificielle de toute espèce en une lumièresemblable à celle du jour. Strasbourg: J.G. Treuttel.

Partington, J.R. and McKie, D. (1941) Sir John Eliot,Bart. (1736–86), and John Elliot (1747–87). Annalsof Science, 6, 262–7.

Peacock, G. (1855) Life of Thomas Young MD, FRS.London: John Murray.

Podestà, H. (1916) Wandtafeln zur Prüfung desFarbensinnes und Erkennung der Farbensinnstörungen.Hamburg: Friederischsen.

Rayleigh, L. (1881) Experiments on colour. Nature, 25,64–6.

Rimington, A.W. (1912) Colour-music. The Art of MobileColour. London: Hutchinson.

Rood, O.N. (1879) Modern Chromatics with Applicationsto Art and Industry. London: Kegan Paul.

Rushton, W.A.H. (1965) Chemical basis of colourvision and colour blindness. Nature, 206, 1087–91.

Schrøder, M. (1969) The Argand Burner. Odense:Odense University Press.

Shapiro, A.E. (1980) The evolving structure ofNewton’s theory of white light and color. Isis, 71,211–35.

Shapiro, A.E. (1993) Fits, Passions and Paroxysms.Cambridge: CUP.

Stiles, W.S. (1939) The directional sensitivity of theretina and the spectral sensitivities of the rods andcones. Proceedings of the Royal Society B 127, pp.64–105.

Stilling, J. (1877) Die Prüfung des Farbensinnes beimEisenbahn- und Marine-personal. Cassel: TheodorFischer.

Strutt, R.J. (1924) John William Strutt: Third BaronRayleigh. London: Edward Arnold.

Thompson, B. (1794) An Account of someExperiments upon coloured Shadows. ByLieutenant-General Sir Benjamin Thomson, Countof Rumford, F.R.S. In a Letter to Sir Joseph Banks,Bart. P.R.S. Philosophical Transactions of the RoyalSociety, 84, 107–18.

Turbervile, D. (1684) Two Letters from the great, andexperienced Oculist, Dr. Turbervile of Salisbury, to

Mr. William Musgrave S.P.S. of Oxon, containingseveral remarkable cases in Physick, relating chieflyto the Eyes. Philosophical Transactions of the RoyalSociety, 14, 736–7.

Voigt, J.H. (1781) Des herrn Giros von GentillyMuthmassungen über die Gesichtsfehler beyUntersuchung der Farben. Magazin für das Neuesteaus der Physik und Naturgeschichte (Gotha), 1, 57–61.

Walls, G.L. (1956) The G. Palmer Story. Journal of theHistory of Medicine, 11, 66–96.

Weale, R.A. (1957) Trichromatic ideas in the seven-teenth and eighteenth centuries. Nature, 179,648–51.

Wilson, G. (1845) The life and discoveries of Dalton.British Quarterly Review, 1, 157–98.

Wilson, G. (1855) Researches on colour-blindness, with asupplement on the danger attending the present system ofrailway and marine coloured signals. Edinburgh:Sutherland & Knox.

Wood, A. (1954) Thomas Young, Natural Philosopher1773–1829. Cambridge: Cambridge UniversityPress.

Wright, W.D. (1952) The characteristics of tritanopia.Journal of the Optical Society of America, 42, 509–21.

Wright, W.D. (1967) The Rays are not Coloured. London:Hilger.

Wünsch, C. E. (1792) Versuch und Beobachtungen überdie Farben des Lichts. Leipzig: Breitkopf.

Wyszecki, G. and Stiles, W.S. (1967) Color Science. NewYork: Wiley.

Young, T. (1800) Outlines of experiments andinquiries respecting sound and light. PhilosophicalTransactions of the Royal Society, 90, 106–50.

Young, T. (1802a) The Bakerian Lecture. On theTheory of Light and Colours. PhilosophicalTransactions of the Royal Society of London, 92, 12–48.

Young, T. (1802b) A syllabus of a course of lectures on nat-ural and experimental philosophy. London: RoyalInstitution.

Young, T. (1804) Reply to the animadversions of theEdinburgh reviewers on some papers published in thePhilosophical Transactions. London: Longman & Co.

Young, T. (1807) A course of lectures on natural philoso-phy and the mechanical arts. London: J. Johnson.

Young, T. (1817) Chromatics. Supplement to theEncyclopaedia Britannica, 3, 141–63.


39

The Origins of Modern Color Science - University of Cambridge

Documents

Transcript of The Origins of Modern Color Science - University of Cambridge