Artists' Colors and Newton's Colors

Artists' Colors and Newton's ColorsAuthor(s): Alan E. ShapiroSource: Isis, Vol. 85, No. 4 (Dec., 1994), pp. 600-630Published by: The University of Chicago Press on behalf of The History of Science SocietyStable URL: http://www.jstor.org/stable/235280 .

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Artists' Colors

and Newton's Colors

By Alan E. Shapiro*

N THE RENAISSANCE artists developed a new approach to color, and in the seventeenth century Newton proposed a new theory of light and color. These events

have not hitherto been considered to be related, but I shall suggest that there is a unity to the study of color in the early modem era that has previously gone unnoted. The common painters' practice of mixing pigments emerged gradually in the late Middle Ages and did not become widely adopted until the Renaissance, when painters freely experimented with mixed pigments. By the beginning of the seventeenth century the quest to provide a modem foundation for painting culminated in the discovery that color mixing was governed by a simple law: all colors may be made from just three, the painters' primaries-red, yellow, and blue-together with white and black.' About half a century later Newton discovered that sunlight is not simple, as had hitherto been believed, but is a mixture of all the simple or "primary" spectral colors, an infinite number of them. When he first proposed his theory in 1672 these two discoveries appeared to clash, and Newton's critics asked why nature should require an infinite number of "primary" colors when humble artists could work with just three, or perhaps even two. Despite this conflict, by the time he published the Opticks in 1704 Newton had constructed a synthesis between his new view of white light and color and the artists' view.

Artists and scientists in the early modem era shared much common ground, and I intend to show how much Newton and other seventeenth-century scientists had drawn from artists. Newton framed his theory of white light and color in the modem language of color mixing, and his contemporaries understood it to be, at least in part, a color-mixing theory. Newton's choice of language plays an important part in my story. It made his theory more immediately accessible and ultimately assisted its acceptance, but it also engendered confusion that persisted through the eighteenth

* Program in History of Science and Technology, University of Minnesota, 116 Church Street SE, Minneapolis, Minnesota 55455.

This paper was initially prepared as one of my F. E. L. Priestley Memorial Lectures in the History of Ideas, delivered at University College, University of Toronto, in March 1993. I appreciate the thought- ful comments from Charles Parkhurst and an Isis referee.

' What I call "painters' primaries" (red, yellow, and blue) are often called "subtractive primaries," which implies the existence of "additive primaries" (green, red, and violet) and the whole conceptual apparatus of modem color theory. Such terminology distorts our understanding of an earlier era, when there was only one set of primaries, and begs the significant historical question of the development of these distinctions.

Isis, 1994, 85: 600-630 ?1994 by The History of Science Society. All rights reserved. 0021-1753/94/8401-0001$01.00

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ALAN E. SHAPIRO

century, since his concept of a "primary," "primitive," or "simple" color differed fundamentally from the artists' concept. Newton's theory took its starting point from the idea that white and black are different from the chromatic colors and could not generate them. This was perhaps the most radical fruit of Renaissance revisions of the concept of color. Since antiquity these contraries had dominated the realm of color, and now they were cast out and placed with the grays. Newton's theory not only advanced the new conception of white and black, but their separation from the chromatic colors in turn helped to advance his theory by weakening modification theories of color, the principal rival to his own. In traditional modification theories, colors arise from a mixture of light with darkness, that is, white and black. Thus, the artists' new ideas about color mixing and black and white were gradually adopted by natural philosophers in the seventeenth century, and Newton constructed his new theory of light and color upon this common ground. If my claims that Newton and his contemporaries drew much from the artists' tradition and that he cast his theory in the language of pigment mixing are valid, then they readily render two puzzling features of eighteenth-century color theory understandable by putting them in their proper historical context: namely, why it was widely believed that according to New- ton there are only seven primary colors in sunlight, and why no distinctions were made between mixtures of pigments and of lights.

The study of the relation of art and science in the Scientific Revolution is not a new one. The invention of linear perspective by Brunelleschi and Alberti around 1425 and its subsequent development by artists and scientists is well known.2 Both art and science in this era had the goal of naturalistically portraying the visible world, and both were dynamic forces transforming early modern culture. Linear perspective allowed the artist to depict a three-dimensional world on the flat, two-dimensional surface of canvas or drawing paper and consequently to create a more realistic representation of nature. An understanding of color, an inherent characteristic of our perceived world, was equally essential for depicting and describing the natural world. What should be surprising, then, is not my claim that Newton and his predecessors adopted many of the innovations of the Renaissance reconceptualization of color but, rather, a claim that they remained unaffected by it. The interaction of the fine arts and natural philosophy with respect to color forms part of a common pattern in which scientists drew from the arts knowledge about the natural world that had been ac- cumulated over centuries. To cite only some notable examples: from engineering the sciences acquired knowledge of projectile motion, from hydraulics of hydrostatics, and from glass working of the telescope.

Since I am attempting to characterize certain ideas about color over many centuries, I can perforce offer only a rough sketch and shall focus on the relation between artists' and natural philosophers' knowledge in the early modern era rather than on the knowledge of either group.3 This means that I shall slight medieval

2 The literature on perspective is immense, but see Martin Kemp, The Science of Art: Optical Themes in Western Art from Brunelleschi to Seurat (New Haven, Conn.: Yale Univ. Press, 1990), Pt. 1, for a recent, judicious introduction to the subject and a bibliography. 3 In the last few decades historians of art and of science have made major strides in understanding color in the early modern era, and I shall freely build upon their contributions. The work of Charles Parkhurst on the painters' primaries and black and white has been especially crucial for my thinking about color, as has his work, together with that of John Gage, on color mixing. See Charles Parkhurst, "Aguilonius' Optics and Rubens' Color," Nederlands Kunsthistorisch Jaarboek, 1961, 12:35-49; Park- hurst, "A Color Theory from Prague: Anselm de Boodt, 1609," Allen Memorial Art Museum Bulletin,

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ARTISTS' COLORS AND NEWTON'S COLORS

developments, which began at least with Giotto and Roger Bacon and can legiti- mately be seen as leading to the Renaissance developments that concern me.4 Before turning to color and the arts, we should recall that the early modern revolution in the sciences occurred about a century after that in the arts: in the midst of the high Renaissance in art, around 1500, at the time of Raphael, Leonardo, Diirer, and Mi- chelangelo, Copernicus was still a student in Italian universities; his De revolution- ibus would not appear until 1543.

* * *

To appreciate the history of color in the early modern era, we must first briefly look at the ancient and medieval heritage. I shall focus on Aristotle, because a few central ideas from his writings were nearly universally adopted in the Middle Ages, and they still dominated thinking about color well into the seventeenth century. Aristotle and his collaborator Theophrastus culminated a long line of natural philosophers concerned with color and color mixing that extended from Empedocles through De- mocritus to Plato. Let us begin with white and black, which are the two fundamental colors not only in Aristotle's color theory but in all theories before the early moder era. Aristotle held that all the chromatic colors, like red, green, and blue, derive from various mixtures of white and black. In his most extensive discussion of color mixing, in De sensu, he describes the various ways in which white and black can be mixed to produce the colors of bodies: by a juxtaposition of minute white and black parts that are separately imperceptible; by an overlay or superposition, as when a painter applies a wash over a darker color; and by true interpenetration of the parts, as in a chemical compound. Aristotle believed that the colors of bodies come from a true mixture, but he indicated that all three kinds of mixture give the same result.5 The equivalence of all methods of color mixing would not be questioned until the late eighteenth century.

1971, 29:3-10; Parkhurst, "Louis Savot's 'Nova-antiqua' Color Theory, 1609," in Album Amicorum J. G. van Gelder, ed. J. Bruyn et al. (The Hague: Martinus Nijhoff, 1973), pp. 242-247; Parkhurst, "Leon Battista Alberti's Place in the History of Color Theory," in Color and Technique in Renaissance Painting: Italy and the North, ed. Marcia B. Hall (Locust Valley, N.Y.: Augustin, 1987), pp. 161- 204; John Gage, "Colour in History: Relative and Absolute," Art History, 1978, 1:104-130; and Gage, "A 'Locus Classicus' of Colour Theory: The Fortunes of Apelles," Journal of the Warburg and Cour- tauld Institutes, 1981, 44:1-26. Gage's valuable Colour and Culture: Practice and Meaning from An- tiquity to Abstraction (London: Thames & Hudson, 1993) appeared after this article was submitted, but it is essential. For eighteenth-century color science see David Hargreave, "Thomas Young's Theory of Color Vision: Its Roots, Development, and Acceptance by the British Scientific Community" (Ph.D. diss., Univ. Wisconsin, 1973). Martin Kemp's two chapters on color in The Science of Art treat the influence of science on art and thus complement my concern, the influence of art on science. For scientific color theories in the early modem era see J. Mac Lean, "Geschiedenis van de Kleurentheorie in de zestiende Eeuw," Scientiarum Historia, 1967, 9:23-39; Mac Lean, "Kleurentheorie in de Periode 1600-1635," ibid., pp. 126-147; Mac Lean, "De Kleurentheorie van de Aristotelianen en de Opvat- tingen van de la Chambre, Duhamel en Vossius in de Periode 1640-1670," ibid., 1968, 10:208-225; and Mac Lean, "De Kleurenleer van de Aanhangers der Corpusculartheorie," ibid., 1970, 12:1-22.

4 See Charles Parkhurst, "Roger Bacon on Color: Sources, Theories, and Influence," in The Verbal and the Visual: Essays in Honor of William Sebastain Heckscher, ed. Karl-Ludwig Selig and Elizabeth Sears (New York: Italica, 1990), pp. 151-201; and Gage, Colour and Culture.

5 Aristotle, De sensu, 3.440b 13-23. According to modern theories of color mixing, interpenetration- understood as pigment mixing and not as a chemical transformation-and superposition are both subtractive processes. Juxtaposition as a pointillist or mosaic technique is an additive process and often yields different results from the other two. If juxtaposition is understood to be like the mixing of grains of sand of two different colors, it will generally be subtractive. These complexities were not generally understood until the nineteenth century.

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ALAN E. SHAPIRO

YELLO VIOLET) LGREENU) BLUE ) (BLACK

Figure 1. Aristotelian arrangement of colors, ordered by inherent tone or brightness from white to black.

Aristotle does not explain why a mixture of white and black should produce colors other than to assert that "this product can appear neither white nor black, but, since it must have some colour and can have neither of the above two, it must be a sort of compound and a fresh kind of tint. In this way, then, we may conceive that numbers of colours over and above black and white may be produced, and that their multiplicity is due to differences in the proportion of their composition." If the proportions of white and black are simple ratios such as 3:2 or 3:4, the most pleasant colors will arise, "exactly as is the case in harmonies"; but if the ratios are incom- mensurable, the other colors will result. Pursuing his musical analogy, he declared that there are just seven species of color, and between the extreme colors white and black he placed yellow, crimson or red, violet, green, and deep blue; gray is considered to be a variety of black (Figure 1). "All other colours are got by combining these." This is a classification of colors by tonal value or inherent brightness. The names of the hues simply indicate a position on a linear scale between white and black. Yellow, for example, is intrinsically bright and so contains mostly white with little black and is placed closest to white; whereas blue is dark and contains little white and is placed closest to black. Lightness and darkness, or whiteness and blackness, are the fundamental concepts in ancient and medieval color theory and not, as we take for granted, color or hue.6 The transformation of the classification of color from brightness or tonal value to hue is one of the most fundamental changes in color theory that emerged in the early modem era.

Aristotle's explanation of the origin of the radiant colors of the rainbow in the Meteorologica differs in fundamental ways from the account given in De sensu. He declares that there are three colors in the rainbow-red, green, and violet-which "are almost the only colours which painters cannot manufacture," for "three com- pletes the series of colours (as we find three does in most other things)." Aristotle invokes two principles to explain the origin of the colors in the bow, namely, that when bright light is seen on or through a black medium it appears red, and that weakened light or sight makes things appear blacker. When light is reflected from a dark cloud it is gradually weakened and darkened, and the three colors of the bow-red, green, and violet-are successively generated.7 Aristotle's explanation

6 Aristotle, De sensu, 439b23-28, 439b34, 442a27, in Aristotle, De sensu and de memoria, trans. G. R. T. Ross (Cambridge: Cambridge Univ. Press, 1906), pp. 57, 59, 69. The preeminence of white (XEVK6v) and black (!LEXav) is more understandable if we recognize that these terms initially had a broader meaning than simply white and black. They are best translated as "light" and "dark," with the former encompassing such light things as snow, ivory, sand, water, and blond hair and the latter freshly plowed earth, the sea, wine, and blood. Though the terms XEVK6V and E.eXoav became more restricted by the time of Plato and Aristotle, they still connoted more than white and black. See Maurice Platnauer, "Greek Colour-Perception," Classical Quarterly, 1921, 15:153-162.

7 Aristotle, Meteorologica, 372a6, 374b31-33, trans. E. W. Webster, in The Complete Works of Aristotle: The Revised Oxford Translation, ed. Jonathan Barnes, 2 vols. (Princeton, N.J.: Princeton Univ. Press, 1984), Vol. 1, pp. 600, 603. See, further, ibid., 374b10-33, p. 603.

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of the radiant colors of the bow was important for the arts tradition in offering an alternative to his seven-color scale.

Natural philosophers from Empedocles to Aristotle and Theophrastus were en- deavoring to find the rules underlying painters' practice of mixing different colors by various methods to produce a new one. Yet, if we are to judge by their testimony, much of this mixing was with white and black. In the first century A.D. Pliny in his Natural History (35.50) related that Apelles and other artists of the fourth century B.C. used only four colors: white, yellow, red, and black. There is also evidence from later antiquity that the mixing of pigments was frowned upon. Plutarch in his Moralia (ca. 100 A.D.) reported an objection to color mixing in the course of explaining that sailors draw water from the Nile at night because during the day it becomes so roiled and mixed that it goes bad: "Mixing produces conflict, conflict produces change, and putrefaction is a kind of change. This is why painters call a blending of colours a 'deflowering' and Homer calls dyeing 'tainting,' and common usage regards the unmixed and pure as virgin and undefiled." Two centuries later, Alexander of Aphrodisias reiterated the view that "artificial" or mixed colors are "far inferior to the natural colors."8

From the limited number of colored art works extant from antiquity, John Gage has argued that painters' practice also followed a prohibition against pigment mixing. Not that color mixing did not occur; but they preferred to use washes and glazes and mosaic or pointillist techniques.9 Whether or not the practice and especially the views of late antiquity influenced medieval practice, analysis of surviving art works from the Middle Ages shows that pigments were infrequently mixed, except with white and black or when a naturally occurring alternative was unavailable. Medieval artists preferred fully saturated colors, and mixing desaturates colors. Sometime in the late Middle Ages, apparently in the fourteenth century, the restriction against mixed colors began to be relaxed, and by 1400 color mixing was more common. The painter's palette, the tool for preparing mixed colors, made its first appearance about 1400. Thus, all the evidence indicates that the mixing of pigments did not enter general artistic practice in Western Europe until the beginning of the early modem era, cor- responding to the increasing use of oil techniques, and so the problem of color mixing became a genuinely modern one.10

* * *

Alberti's De pictura (On Painting) presented the first modern theory of that art and played an important part in the process of raising painting from a craft to a part of learned, humanistic culture."1 It reflected the innovative practices of Alberti's Flor-

8 Plutarch, Plutarch's Moralia, Table Talk (Quaestiones convivales), 8.5.725, trans. Edwin L. Minar, Jr., F. H. Sandbach, and W. C. Helmbold, Vol. 9 (London: Heinemann, 1961), pp. 155-157; and Gage, "'Locus Classicus' of Colour Theory" (cit. n. 3), p. 9 (from Alexander's commentary on Aris- totle's Meteorologica, which was translated into Latin by William of Moerbeke in the thirteenth century). 9

Gage, "Colour in History" (cit. n. 3), p. 119; and Gage, "'Locus Classicus' of Colour Theory." 0o Parkhurst, "Alberti's Place in History of Color Theory" (cit. n. 3), p. 174; Gage, "Colour in His-

tory," p. 119 (both also give examples of late medieval pigment mixing); and Marcia B. Hall, "From Modeling Techniques to Color Modes," in Color and Technique in Renaissance Painting, ed. Hall (cit. n. 3), pp. 1-29, esp. p. 2. On oil paints and pigment mixing see Gage, Colour and Culture (cit. n. 3), pp. 131-132.

1 Alberti apparently composed De pictura in 1435 and translated it into Italian the following year. The Latin version was printed in 1540 and the Italian in 1547; five more editions appeared in the next hundred years, including a French translation. My account of Alberti depends on Parkhurst, "Alberti's Place in History of Color Theory"; see also Samuel Y. Edgerton, Jr., "Alberti's Colour Theory: A Medieval Bottle without Renaissance Wine," J. Warburg Courtauld Inst., 1969, 32:109-134.

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entine contemporaries Brunelleschi, Donatello, Ghiberti, and Masaccio, who, like Alberti himself, aimed at a naturalistic art. De pictura is most celebrated for the first mathematical description of linear perspective, but it also contained a pioneering account of color. Alberti stressed that he was writing as a painter, not as a philosopher, but he had studied natural philosophy at the University of Bologna, and his innovations marked a sharp break with Aristotelian color theory. Their full impli- cation would take a few centuries to unfold. Alberti rejected the idea, held for millennia, that black and white were the fundamental colors, or that they were even colors at all. "The painter," he wrote, "may be assured that white and black are not true colours but, one might say, moderators [alteratores] of colours." Alberti had broken with Aristotle's linear arrangement of colors and separated black and white from the chromatic colors. Since the chromatic colors were no longer to be derived from black and white, he now proposed as an alternative that the "almost infinite" variety of colors could be derived from four primaries or "genera," red, green, blue, and yellow, together with the "moderators," white and black.12 When the different genera are mixed with one another or with black and white, different species of color arise. The search for a small number of chromatic primaries, from which all other colors could be derived, was under way.

If perspective allowed artists to present space in a naturalistic way, the naturalistic representation of color was less tractable. Painters had to learn how to represent colors in true light and gain command of a modeling that was consistent with perspective. Fourteenth-century painters, for example, rendered the least illuminated areas of an object with the most saturated colors and diluted the more illuminated areas with white, a modeling technique that makes shadowed areas appear to advance and illuminated ones recede, contrary to what one actually sees with real objects in natural illumination.13 Theory, including Alberti's, provided little assistance in re- solving these problems, and in the following centuries artists experimented on their canvases. Leonardo's chiaroscuro is no doubt the best example of innovation in treating light, color, and shadow.

Leonardo approached the problem of understanding and naturalistically rendering light and color both as an artist and as an experimental natural philosopher. He left voluminous notes for a treatise "On Painting," which, like all his literary projects, remained unfinished. It was widely circulated in manuscript, and in 1651 Italian and French editions were published simultaneously. Perhaps because he studied the elu- sive phenomena of color mixing so intensively-for example, by superposing colored glass plates, mixing pigments, and reflecting colored lights-Leonardo was unable to make up his mind as to exactly which colors were primary or "simple."

12 Leon Battista Alberti, On Painting and on Sculpture: The Latin Texts of "De pictura" and "De statua," ed. and trans. Cecil Grayson (New York: Phaidon, 1972), pp. 46-47. Alberti's "yellow," cinereum colorem, has long caused scholars difficulty, since it is usually means "ash colored" or "gray." Since he rejected white and black as generators of colors, one would expect a chromatic color here. Jonas Gavel, Colour: A Study of Its Position in the Art Theory of the Quattro- and Cinquecento (Stock- holm: Almqvist & Wiksell, 1979), pp. 47-52, has identified Alberti's cinereum colorem as a grayish dark yellow; see also Parkhurst, "Alberti's Place in History of Color Theory," pp. 162-163, which supports this identification, and Gage, Colour and Culture (cit. n. 3), pp. 118-119, which rejects it.

13 On color modeling and naturalistic representation in the fifteenth century see John Shearman, "Leonardo's Colour and Chiaroscuro," Zeitschriftfiir Kunstgeschichte, 1962, 25:13-47; James S. Ack- erman, "On Early Renaissance Color Theory and Practice," in Studies in Italian Art and Architecture, Fifteenth through Eighteenth Centuries, ed. Henry A. Millon (Cambridge, Mass.: MIT Press, 1980), pp. 11-40; and Hall, "Modeling Techniques to Color Modes" (cit. n. 10).

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At one point he chose six, including Alberti's four chromatic colors, and at another eight; both sets also included black and white. Leonardo accepted Alberti's still- novel idea that black and white "are not included among the colors, because one is darkness and the other is light," but he included them with his simple colors "because they are the principal ones used in painting, as painting is composed of shadows and lights, that is, of lightness and darkness." 14

In color theory, as with so many endeavors in the sixteenth century, many were rebelling against Aristotle's ideas, though the basic framework of their thought was still essentially Aristotelian. While most still ordered colors on a scale from black to white, there was no longer agreement as to the number and choice of chromatic primaries. For example, the architect and sculptor Antonio Filarete in about 1460 chose Alberti's four, the physician Camillo Leonardi in his 1502 work on gems chose three-red, yellow, and green-and in the latter part of the sixteenth century Giu- seppe Arcimboldo, court painter to Rudolf II in Prague, adopted five-red, yellow, blue, green, and brown. 15 By the beginning of the seventeenth century-nearly two centuries after Alberti-much practical experience in working with oil paints and mixing colors by glazing, by layering, and by mixing paints and pigments had ac- cumulated in an effort to develop naturalistic representation. Books on art were largely written by amateurs and humanists who were unlikely to be abreast of the latest developments in technique. Few artists devoted themselves to writing treatises on art theory and practice as Alberti and Leonardo did. Natural philosophers too were at least one step removed from contemporary practice until the latter part of the sixteenth century, when they became more intimately involved with the arts. These factors help to explain why it took so long to recognize the three artists' primaries and why they did not appear until the beginning of the seventeenth century.

As Charles Parkhurst and John Gage have found, in the early seventeenth century four scholars-Guido Antonio Scarmiglioni in 1601, Louis Savot and Anselm Bo- ethius de Boodt in 1609, and Franqois d'Aguilon in 1613-independently announced the discovery of the three painters' primaries-red, yellow, and blue-from which (together with white and black) all other colors could be derived, and which could not themselves be derived from any others. Scarmiglioni was professor of medicine in Vienna and familiar with painters' practice. The Flemish physician de Boodt served in the court of Rudolf II and was a naturalist and a talented watercolorist. De Boodt's book on gems, in which he set forth his color theory, was widely known, particularly in England, where Robert Boyle sang its praises and Robert Hooke and Newton owned copies. Savot was just completing his medical studies at the University of Paris when his book on color appeared. He drew on the knowledge of "dyers, painters, glass makers, and such other artisans who work with colors," but he seems to have been especially familiar with the practice of dyeing.16 Aguilon was a teacher

14 Leonardo, Treatise on Painting, ed. and trans. Amos Philip McMahon, 2 vols. (Princeton, N.J.: Princeton Univ. Press, 1956), Vol. 1, p. 82 (Urb fol. 68v); I have altered the translation somewhat. On four and six chromatic primaries see pp. 81, 83 (Urb fols. 75v, 68v).

'5 Antonio Filarete, Filarete's Treatise on Architecture: Being the Treatise by Antonio di Piero Av- erlino, Known as Filarete, trans. John R. Spencer, 2 vols. (New Haven, Conn.: Yale Univ. Press, 1965), Vol. 1, pp. 309-310. On Leonardi see Parkhurst, "Camillo Leonardi and the Green-Blue Shift in Sixteenth-Century Painting," in Intuition und Kunstwissenschaft: Festschrift fur Hans Swarzenski, ed. Peter Bloch et al. (Berlin: Mann, 1973), pp. 419-425; and on Arcimboldo see Kemp, Science of Art (cit. n. 2), pp. 273-274.

16 Anselm Boethius de Boodt, Gemmarum et lapidum historia (Hanau, 1609), went through three editions and was translated into French and English. For Boyle's accolade see Robert Boyle, A Short

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of mathematics at the Jesuit college in Antwerp. Thus, all brought the outlook of the natural sciences to bear on their knowledge of the arts.17

Aguilon most clearly formulated the idea of three primaries, and his work was the most influential, in large part because the Jesuits were the leading science teach- ers of the seventeenth century. He was a friend of the artist Peter Paul Rubens, who designed the title page and six of the illustrations of Aguilon's Opticorum and also wrote a lost treatise on color. His painting Juno and Argus, which was completed by 1611 (the same year that Aguilon completed his book), celebrates the three-color theory with the red of Juno's costume, the yellow of her chariot, and the blue of Iris's robe, which are repeated, together with the composites orange, green, and violet, in the rainbow accompanying Iris.'1

Aguilon presented his color-mixing rule in Book 1, proposition 39-"There are five species of simple colors, and three compound"-as a general one applying to colors as visible qualities and not to pigments, such as cinnabar, indigo, and ceruse, "which painters lay on pictures." Although he illustrated his rule with mixtures of pigments, he also warned that the results may not always turn out as expected since many painters' pigments are not simple but contain other colors. Red lake, for example, contains some blue and so inclines to purple, whereas minium has some yellow and inclines to orange. Again stressing the generality of his rule, Aguilon invoked Aristotle's three kinds of mixing-juxtaposition, overlay, and true mixture-which he called, "notional," "intentional," and "real composition." He illustrated his rules with what is probably the first published color-mixing diagram (Fig- ure 2). The three "intermediate" colors, yellow, red, and blue (flavus, rubeus, caeruleus), when mixed pairwise produce gold, purple, and green (aureus, purpu- reus, viridis). A mixture of all three produces an "unpleasant color, livid, lurid, and even cadaverous." Mixing white and black with the three primary and three secondary colors does not change their species, only their intensity. "Consequently, some will perhaps judge that whiteness and blackness are not true colors but only certain degrees of color, by which the individual colors vary by more or less." The "almost infinite variety of color" comes from mixing the six chromatic colors with black and white. "But," Aguilon concluded, "nobody knows these things so pre-

Account of Some Observations Made by Mr. Boyle about a Diamond that Shines in the Dark, appended to his Experiments and Considerations Touching Colours (1664; rpt., New York: Johnson, 1964) (hereafter cited as Boyle, Touching Colours), p. 396. Hooke owned copies of the 1609 and 1636 editions of the Gemmarum; see Leona Rostenberg, The Library of Robert Hooke (Santa Monica, Calif.: Modoc, 1989), pp. 174, 207. Newton owned the 1636 edition; see John Harrison, The Library of Isaac Newton (Cambridge: Cambridge Univ. Press, 1978), no. 245, p. 106. Louis Savot, Nova, seu verius nova- antiqua de causis colorum sententia (Paris, 1609), fol. 6v.

17 See Parkhurst, "Aguilonius' Optics and Rubens' Color," "Color Theory from Prague," and "Savot's 'Nova-antiqua' " (all cit. n. 3); and on Scarmiglioni see Gage, Colour and Culture (cit. n. 3), pp. 153- 154, 230. Aguilon alone set the number of chromatic primaries and compounds unequivocally at three each. Scarmiglioni posited three primaries, yellow, blue (hyacinthinus), and red (ruber), and only two compounds, red or orange (puniceus) and green, apparently to maintain the Aristotelian seven colors; see Guido Antonio Scarmiglioni, De coloribus, libri duo (Marburg, 1601), pp. 111-112, 116-117. Moreover, his primaries were themselves derived from black and white. Savot initially admitted only two primaries, red and blue, but then divided red into a red and a yellow; while de Boodt started with three, but then divided the red into two sorts, miniatus and ruber. I have yet to find a reference to Scarmiglioni's work in the seventeenth century.

18 On Aguilon see Parkhurst, "Aguilonius' Optics and Rubens' Color"; August Ziggelaar, Francois de Aguil6n S.J. (1567-1617): Scientist and Architect (Rome: Institutum Historicum, 1983); and Kemp, Science of Art (cit. n. 2), pp. 274-277.

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WHITE YELLOW RED BLUE BLACK

\OLD PURPLE

GREEN

Figure 2. Aguilon's color-mixing diagram translated into English; based on Aguilon, Opticorum, p. 40.

cisely as painters."19 While Aguilon distinguished the intermediate chromatic colors from the extremes, white and black, he still ordered his colors in the Aristotelian manner between white and black rather than by hue. Newton's spectrum would soon provide a new, natural ordering.

Perhaps because he was a Jesuit, Aguilon did not wish decisively to reject the Aristotelian idea that black and white are "true colors" and simply suggested that "some" might conclude this. De Boodt and Savot rejected that idea as unequivocally as Alberti had. De Boodt tells us that those who consider the intermediate or chromatic colors to derive from a mixture of black and white are deceived, because nothing but gray (cinereum) will arise. In holding that when more white is added to such a mixture a brighter gray results, and that when less is added a darker one results, he established a separate white-black scale. Savot too proposed that mixtures of white and black form their own "genus," and he commended Julius Caesar Scal- iger for arguing (in 1557) that mixing white and black yields no other colors than gray.20

By the beginning of the seventeenth century the idea that white and black are not chromatic colors and could not produce them by mixture was gradually gaining adherents.21 Already, a century earlier, Leonardo had noted that black and white were

'9 Francois d'Aguilon, Opticorum libri sex philosophis juxtd ac mathematicis utiles (Antwerp, 1613), pp. 38, 41, 39-40, 40-41 (here and elsewhere, all translations into English are mine unless otherwise indicated).

20 Boodt, Gemmarum (cit. n. 16), p. 25; Savot, Nova-antiqua (cit. n. 16), fol. 7r; and Julius Caesar Scaliger, Exotericarum exercitationum, Liber XV: De subtilitate, a D. Hieronymum Cardanum (Leyden, 1615), exercitatio 325, sect. 9, p. 823.

21 Kemp, in contrast, sees the rejection of black and white as chromatic colors as occurring in France in the mid-seventeenth century; see Kemp, Science of Art (cit. n. 2), p. 281.

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not considered to be colors. In Appendix 1 I have listed those who rejected the idea that white and black are colors or that they could generate colors, and one can see how supporters of this modern view rapidly increased in the seventeenth century. This table does not represent the fruits of a systematic search (especially before 1600), and I am sure that the list of such supporters could be readily multiplied with a careful study of the literature. One should not assume that everyone who encountered the painters' primaries or the idea that white and black cannot generate colors immediately adopted them. At almost the same time that Newton learned of and accepted both these new ideas, the young Leibniz rejected them. In Dissertatio de arte combinatoria (1666) he recounted that Georg Philipp Harsdorffer had "assumed these five primary colors: white, yellow, red, blue, and black." "Yet," Leibniz responded, "I suggest that the assumed, so to speak, primaries themselves are not primaries; but all arise from a mixture of white and black, or light and shadow."22

Since I want to show how changes in artistic theory and practice caused a more widespread change in thinking about color, I must, at least briefly, indicate how these new ideas and techniques were gradually diffused through European culture. Beginning in the sixteenth century, drawing and painting with watercolors and oils became a popular pastime, and manuals or handbooks started to appear. The move- ment of Renaissance artists to raise the social status of painting from a manual art to a liberal art worthy of ladies and gentleman had succeeded: Galileo had studied at the Accademia del Disegno in Florence, and even the nobility-Rudolf II and England's King Charles I, for instance-were engaged in drawing and painting. Publication of how-to-do-it books increased greatly during the course of the seventeenth century.23 By mid century even a country boy like Newton was reading books on how to draw and paint. Sometime shortly after 1659, when he was in his late teens, he got a copy of John Bate's The Mysteries of Nature and Art, which taught boys how to make kites, watermills, and other delights. Part of the book was devoted to drawing and painting, and Newton took extensive notes on that section. To give just a few examples: he copied out that "a bras colour . . . is made of Masticot, & umber" (massicot is a yellow pigment and umber a brown one); and also to make "a colour for gold[.] Take Lake[,] umber[,] red lead & Masticot" (which combines two reds, a brown, and a yellow); and finally under "a marble or ash colour," that is, gray, he entered "This is black & white."24

22 Gottfried Wilhelm Leibniz, Sdmtliche Schriften und Briefe (Preussischen Akademie der Wissen- schaften, Ser. 6, Vol. 1) (Darmstadt: Otto Reichl, 1930), p. 204; and Georg Philipp Harsdorffer, Delitiae philosophicae et mathematica: Dritter Theil (Nuremberg, 1653), Pt. 3, question 16, pp. 233-236. On Leonardo's rejection of black and white as colors see Leonardo, Treatise on Painting, ed. and trans. McMahon (cit. n. 14), Vol. 1, p. 82.

23 On Galileo see Samuel Y. Edgerton, Jr., The Heritage of Giotto's Geometry: Art and Science on the Eve of the Scientific Revolution (Ithaca, N.Y.: Cornell Univ. Press, 1991), Ch. 7; on Charles I see Allan Ellenius, De arte pingendi: Latin Art Literature in Seventeenth-Century Sweden and Its Interna- tional Background (Uppsala: Almqvist & Wiksells, 1960), p. 42, and also Pt. B, Ch. 6; and on Rudolf II see Thomas DaCosta Kaufmann, The School of Prague: Painting at the Court of Rudolf II (Chicago: Univ. Chicago Press, 1988), p. 42. On the proliferation of how-to-do-it books see R. D. Harley, Artists' Pigments, c. 1600-1835: A Study in English Documentary Sources (London: Butterworth Scientific, 1982), pp. 5-7; and Henry V. S. Ogden and Margaret S. Ogden, "A Bibliography of Seventeenth- Century Writings on the Pictorial Arts in English," Art Bulletin, 1947, 29:196-201.

24 David Eugene Smith, "Two Unpublished Documents of Sir Isaac Newton," in Isaac Newton, 1642- 1727: A Memorial Volume Edited for the Mathematical Association, ed. W. J. Greenstreet (London: G. Bell, 1927), pp. 16-34, on pp. 20-21. E. N. da Costa Andrade showed that Newton used the third edition of Bate (London, 1654); see E. N. da Costa Andrade, "Newton's Early Notebook," Nature, 1935, 135:360.

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Clearly, color mixing, which was unsystematic before 1400, had become com- monplace. By the latter part of the sixteenth century natural philosophers were citing the artists' practice of pigment mixing, something that was unheard of in preceding centuries; and by the seventeenth century references to pigments and pigment mixtures had become a standard part of their repertory. At a number of points in his writings Newton referred to painters, especially for their knowledge of harmonious color combinations, and he frequently used painters' powders in his experiments and observations.25 When he arrived at Cambridge in 1661, Newton still had not been exposed to the idea of the painters' three primaries. That idea was relatively new and was becoming more widely known just as he was beginning his scientific studies. Before describing the diffusion of the painters' primaries and their influence on the scientific community, let me briefly sketch how natural philosophers explained color.

* * *

The half century before Newton was a period of rapid transition from Aristotelian natural philosophy to the new mechanical philosophy. Although Aristotelian natural philosophy was revitalized in the sixteenth and seventeenth centuries, its account of color had not fundamentally changed since the Middle Ages. A distinction had been introduced between the "apparent" colors of light seen in such transient phenomena as the rainbow and the prismatic spectrum and the "real," permanent colors of bodies. The permanent colors of bodies were considered to be inherent qualities of bodies that were exhibited by light. Medieval scholars explained the apparent colors of the rainbow and the prism by elaborating upon Aristotle's explanation of the rainbow, according to which color arises from a weakening or darkening of visual or light rays; that is, it is some modification of pure, uniform sunlight. In these theories, colors do not exist independently prior to some modification.

In the seventeenth century the mechanical philosophers cast out the idea that bodies possess sensible secondary qualities such as color, sweetness, and weight, and along with it the distinction between real and apparent colors. They held that color- whatever its source, be it a rainbow or a body-is a sensation excited by light in the brain and that different colors arise from different properties of light. Conse- quently, to study color, only colored light need be investigated. This program led

25 Newton invoked painters twice in the second version of his "Optical Lectures," which was com-

posed in the winter of 1671-1672; these passages are quoted later in the text (see notes 38 and 45). In a version of his "Hypothesis" from 1672 he referred to "the harmony and discord . . . wca the more skilfull Painters observe in colours," and in a draft proposition 12 for the Opticks he again cited painters' knowledge of color harmonies; see Isaac Newton, The Optical Papers of Isaac Newton, ed. Alan E. Shapiro, Vol. 1: The Optical Lectures, 1670-1672 (Cambridge: Cambridge Univ. Press, 1984) (hereafter cited as Newton, Optical Papers, ed. Shapiro), p. 546, nn. 27, 28. For references to painters' "powders" in the published Opticks see Isaac Newton, Opticks: or, A Treatise of the Reflexions, Refractions, Inflexions, and Colours of Light (London, 1704; rpt., Brussels: Culture et Civilisation, 1966) (hereafter cited as Newton, Opticks), Bk. 1, Pt. 2, prop. 5, exp. 15, pp. 110, 111, prop. 6, p. 117. Giovanni Battista della Porta, in De refractione optices parte libri nonum (Naples, 1593), pp. 195, 197, 199, was one of the first natural philosophers to cite painters (pictores) and pigment mixing. For references to painters and pigment mixing in the seventeenth century see, e.g., Boyle, Touching Colours, Pt. 2, exp. 14, p. 225, Pt. 3, exp. 12, pp. 219-220, exp. 17, pp. 232, 238-239; Robert Hooke, Micrographia: or, Some Physiological Descriptions of Minute Bodies Made by Magnifying Glasses with Observations and Inquiries Thereupon (London, 1665; rpt., Brussels: Culture et Civilisation, 1966), p. 58; Edme Mariotte, De la nature des couleurs (1st ed., 1681), in Oeuvres de Mariotte, 2 vols., new ed. (The Hague, 1740), Vol. 1, p. 208; and Walter Charleton, Physiologia Epicuro-Gassendo-Charltoniana (Lon- don, 1654; rpt., New York: Johnson, 1966), p. 196. These passages are quoted later in the text (see notes 34, 51, 54).

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directly to Newton's work later in the century. If the moderns rejected the idea of color as a real, essential property of bodies, they carried over the medieval explanation of apparent colors by extending it to all colors, whether from bodies or light. Virtually all natural philosophers in the seventeenth century-be they Aristotelians or mechanical philosophers-both before and after Newton adopted a modification theory of color. There was, however, no consensus as to the nature of the modification. Aristotelians, and some modems, still adhered to the idea that colors derive from a mixture of white and black, or light and shadow, though they often refor- mulated the notion-for example, by attributing color to a mixture of light with the opacity or the shadows of the corpuscles composing a prism or raindrop.

A new sort of modification theory was also proposed, a modem one that offered a genuine alternative to the idea that color came from a mixture of white and black. Rene Descartes, for example, believed that color is caused by various rotations in the little round corpuscles that compose the fine matter or aether that transmits light. When a beam of sunlight falls upon the surface of a glass prism, the balls at rest in the unilluminated part of the aether on each edge of the beam cause the rotation of the light corpuscles to change: direct sunlight consists of corpuscles whose rotation is almost equal to their motion in a straight line, while red and blue light, which are generated at opposite edges of the beam, consist of corpuscles that rotate more quickly or slowly than the corpuscles of white light. Hooke's theory of color was more complex and ambitious than Descartes's, but he too abandoned the idea that color arises from light and shadow and made it depend on the relative strength of suc- cessive light pulses or waves.26 Only one historian, to my knowledge, has recognized that a fundamentally different kind of modification theory had been proposed in the seventeenth century, and he offered no explanation for it.27 This fundamental shift away from white and black, or light and shadow, I am quite confident, reflects the artists' discovery that white and black are not true colors and cannot by their mixture generate chromatic colors. By the early seventeenth century (see Appendix 1) the idea that mixing white and black could produce nothing but gray was increasingly being adopted by both artists and natural philosophers.

* * *

As an undergraduate Newton immersed himself in the new philosophy, carefully reading the works of Descartes, Boyle, and Hooke, among others. Newton's work rests solidly within this scientific tradition and developed out of it, but it was also informed by the innovations in color theory that derived from the artistic tradition. We have already seen that in his teens he studied color mixing, and I shall show how it entered into the very formulation of his new theory of light and color. I shall

26 Ren6 Descartes, Les meteores (Leyden, 1637), in Oeuvres de Descartes, ed. Charles Adam and Paul Tannery, new ed., Vol. 6 (Paris: Librairie Philosophique J. Vrin, 1965), discours 8, pp. 331-333; and Hooke, Micrographia, pp. 59, 62-63. Despite Descartes's and Hooke's attempts to abandon the traditional view, it was still incorporated in their explanations of prismatic colors. In Descartes's theory, for example, after light is refracted colors are generated at the edges of the beam, or, as Newton noted, from a mixture of light and shadow; see Newton, Optical Papers, ed. Shapiro, Vol. 1, pp. 105, 161, 307. This was not, however, an intrinsic feature of their theories, as can be seen from their accounts of the colors of bodies. According to Descartes (La dioptrique, discours 1), a body appears of a particular color, suppose red, because the entire beam-not just the edges-acquires a rotation that causes the sensation of red.

27 Hideto Nakajima, "Two Kinds of Modification Theory of Light: Some New Observations on the Newton-Hooke Controversy of 1672 Concerning the Nature of Light," Annals of Science, 1984, 41:261- 278.

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Aa

C K T

Figure 3. Newton's basic experiment, in which a spectrum is cast on a distant wall after a narrow beam of sunlight is refracted symmetrically by a prism; based on Newton, Optical Papers, ed. Shapiro, Vol. 1, p. 50.

also show how the idea that white and black are achromatic colors whose mixture cannot produce the chromatic colors served as a starting point for him. Newton de- vised his theory of light and color in 1666, while still a student at the University of

Cambridge, and continued to develop it through the early 1670s, especially in the

"Optical Lectures" he delivered as Lucasian Professor of Mathematics at Cambridge between 1670 and 1672. Only in early 1672 did he decide to make his theory public, submitting to the Royal Society a brief paper, "A New Theory about Light and

Colors," that was afterward published in the Philosophical Transactions. After a series of acrimonious exchanges over his theory, which was not at all well received, Newton chose silence. In 1704 he finally published the Opticks, which contained a

thoroughly argued account of his theory. This time it was accepted relatively rapidly. In presenting Newton's ideas on color and color mixing, I shall follow his published work and draw upon his unpublished papers and the "Optical Lectures" as they serve to illuminate his sources and show his connections to the artists' tradition.28

The foundation of Newton's theory was a simple experiment with light rays-not pigments-upon which he then performed an abundance of variants (Figure 3). He

28 Isaac Newton to Henry Oldenburg, 6 Feb. 1671/72, in The Correspondence of Isaac Newton, ed. H. W. Turnbull, J. F. Scott, A. R. Hall, and Laura Tilling, 7 vols. (Cambridge: Cambridge Univ. Press, 1959-1977) (hereafter cited as Newton, Correspondence, ed. Turnbull et al.), Vol. 1, pp. 92-102. Oldenburg published a slightly edited version of this letter, "A Letter of Mr. Isaac Newton . . . Con- taining His New Theory about Light and Colors," Philosophical Transactions, 1671/72, 7(80):3075- 3087. See Richard S. Westfall, Never at Rest: A Biography of Isaac Newton (Cambridge: Cambridge Univ. Press, 1980); Westfall, "The Development of Newton's Theory of Color," Isis, 1962, 53:339- 358; Maurizio Mamiani, Isaac Newton filosofo dell natura: Le lezioni giovanili di ottica e la genesi del metodo newtoniano (Florence: Nuova Italia Editrice, 1976); and Alan E. Shapiro, "The Evolving Struc- ture of Newton's Theory of White Light and Color," Isis, 1980, 71:211-235.

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passed a narrow beam of sunlight OF through a hole in his window shutter and then through a glass prism ABCa3K and cast the colored image onto the wall. Instead of a round image in the shape of the sun, as predicted by the law of refraction, he found an elongated spectrum PT. From his observations and measurements of the spectrum he was able to demonstrate that sunlight consists of different sorts of rays, each of which possesses a different degree of refrangibility, or is bent a different amount. This experiment lies at the foundation of Newton's theory, according to which refraction separates or decomposes sunlight into rays that are originally of different colors but does not create them.

Newton then showed that to each degree of refrangibility there corresponds a unique color (and vice versa), that is, the rays that are bent the most are always violet, those bent the least red, and so on. "Nor are there only Rays proper and particular to the more eminent colours, but even to all their intermediate gradations." Since the spectrum is continuous, there must be innumerable degrees of refrangibility and, cor- responding to them, just as many gradations of spectral colors, that is, there are innumerable spectral colors: "And so to all the intermediate colours in a continued series belong intermediate degrees of refrangibility."29 It is important to recognize that the seven spectral colors that Newton enumerated and that are so closely as- sociated with his name-red, orange, yellow, green, blue, indigo, and violet-are simply the most prominent colors and not the only ones, a misunderstanding that, as we shall see, Newton himself later encouraged.

No matter how Newton tried to alter the color of any particular sort of light ray- by refraction, reflection, or whatever-he found that it was immutable. This fundamental property leads directly to the problem of color mixing, for when rays of different colors are "mix't and blended together," such as blue and yellow, the color does appear to change to a green. Such transformations, Newton insists, are only "apparent" and not "real." When rays are mixed to make a new color and are then separated from one another, "they will exhibit the very same colours, which they did before they entered the composition; as you see, Blew and Yellow powders, when finely mixed, appear to the naked eye Green, and yet the colours of the Com- ponent corpuscles are not thereby really transmuted, but only blended. For, when viewed with a good Microscope, they still appear Blew and Yellow interspersedly."30

Newton now introduces one of the most fundamental concepts in his theory, the distinction between simple and compound colors:

There are therefore two sorts of colours. The one original and simple, the other compounded of these. The Original or primary colours are, Red, Yellow, Green, Blew, and a Violet-purple, together with Orange, Indico, and an indefinite variety of Intermediate gradations.

He also found that "the same colours in Specie with these Primary ones may be also produced by composition: For, a mixture of Yellow and Blew makes Green; of Red and Yellow makes Orange . . .,,31

We are now at the climax of the theory: "But the most surprising and wonderful composition was that of Whiteness. There is no one sort of Rays which alone can

29 Newton, Correspondence, ed. Turnbull et al., p. 97. 30 Ibid., p. 98. The microscopic observation derives from Boyle, Touching Colours, Pt. 3, exp. 17,

pp. 238-239. 31 Newton, Correspondence, ed. Turnbull et al., p. 98 (italics added, except to "Specie").

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exhibit this. 'Tis ever compounded, and to its composition are requisite all the afore- said primary Colours, mixed in a due proportion." This was by far the most revo- lutionary of Newton's claims and the one most resisted. Four years later Newton recalled that this "seemed the most Paradoxicall of all my assertions, & met with the most universall & obstinate Prejudice."32 For millennia it had been assumed that sunlight was pure, simple, and homogeneous. So much of Western religious and literary imagery used sunlight as a symbol of purity and simplicity, and the sun's radiance was virtually identified with the divine. Newton turned all this upside down with his claim that it was the colors that were simple and homogeneous, while the whiteness of sunlight was the most compound of all colors.

Perhaps because it is so "obvious," it is easy to overlook how much of Newton's theory is cast in the framework of color mixing: sunlight is a mixture of rays, each of which is a different simple or primary color; and when rays of different color are mixed and blended, the compound is a new color. Newton often drew an analogy between the mixing of pigments and the mixing of colored lights; he did so in the "New Theory," and his contemporaries understood it to be a theory about color mixing. At this point it is imperative to bear in mind that in this era no one distinguished between additive and subtractive color mixing-all mixing was the same. To be sure, Newton's contemporaries also understood his theory to be about the physical composition of light and its properties, but it is not my purpose to examine that well-studied aspect of his theory.

While he was a student at Cambridge, Newton learned of the discovery of the three painters' primaries, which in the 1660s were just becoming widely adopted in England. In 1662 William Petty explained dyers' use of the three primaries, which Newton accurately summarized in his notes: "All ye materialls (wch of themselves doe colour) are Red yellow & blew, from wch (wth fundamentall white) ariseth yt

greate variety wee see in dyed stuffs." Newton also owned the 1636 edition of de Boodt's Gemmarum, but we do not know when he purchased it.33 In his Experiments and Considerations Touching Colours Boyle too explained the primaries, and New- ton took extensive notes on it shortly after it appeared in 1664. Newton drew his color-mixing terminology from Boyle. Appealing to the practice of "Painters, Dyers and other Artificers," Boyle announced

that there are but few Simple and Primary Colours (if I may so call them) from whose Various Compositions all the rest do as it were Result. For though Painters can imitate the Hues . . . of those almost Numberless differing Colours that are to be met with in the Works of Nature, and of Art, I have not yet found that to exhibit this strange Variety they need imploy any more than White, and Black, and Red, and Blew, and Yellow.

A few pages later he reiterated that "'tis of advantage to the contemplative Naturalist, to know how many and which Colours are Primitive (if I may so call them) and Simple, because it . . . eases his Labour by confining his most sollicitious Enquiry to a small Number of Colours upon which the rest depend." All of Newton's terms

32 Ibid. (italics added); and Newton to Oldenburg, 7 Dec. 1675, "Observations," ibid., p. 385 (this passage was later struck out).

33 Isaac Newton, Cambridge University Library (CUL), Add. MS 3958, fol. 7v; he summarizes Wil- liam Petty, "An Apparatus to the History of the Common Practices of Dying," read 7 May 1662, printed in Thomas Sprat, History of the Royal Society (London, 1667), ed. Jackson I. Cope and Harold Whit- more Jones (St. Louis: Washington Univ. Press, 1959), pp. 284-306, on p. 302. On Newton's own- ership of the Gemmarum see Harrison, Library of Isaac Newton (cit. n. 16), no. 245, p. 106.

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to describe color mixing, except for original, were used by Boyle to describe "the Painters Art"; and in his "Optical Lectures" Newton often used the term primitive. The terms simple, primary, and primitive and their cognates were used for pigments in French, English, and Latin.34

* * *

Before looking a little more closely at Newton's use of the primaries, we should examine his concept of whiteness and blackness and its relation to the arts tradition. It should already be clear that, like the artists, he considered white to be a different sort of color from the chromatic colors. Even before he came upon his theory, when he had just taken up natural philosophy, he had already accepted the idea that white and black are not true colors and presented evidence for it. In a notebook from this period, Questiones quaedam philosophicae, in which Newton entered his reading notes and his own thoughts, he recorded in a new entry "Of Colours" various pro- posals for the origin of colors: "Colours arise either from shaddows intermixed wth

light, or ... stronger & weaker reflection. or parts of ye body mixed wth & carried

away by light." He first rejected the idea that strength of reflection could be the cause of color and then turned to the first proposal:

No colour will arise out of ye mixture of pure black & white, for yn pictures drawne wth inke would be coloured[,] or printed would seeme coloured at a distance[,] & ye verges of shadows would be coloured. & lamb black & spanish whiteing would produce colours[.] whence they [colours] cannot arise from more or lesse reflection of light or shadows mixed wth light.35

When "Of Colours" resumed on a new page, Newton recorded the first prismatic experiments that started him on his path to his new theory of color.

In noting that the pigments lamp black and Spanish whiting or chalk do not make colors, Newton is appealing to his own experience with color mixing. Few artists since the time of Leonardo would have quarreled with his claims, though few natural philosophers identified white and black with light and shadow as unequivocally as Newton. The idea that white and black differed from the chromatic colors and could not generate them was an important starting point for Newton. It allowed him to eliminate a priori the oldest and largest class of modification theories for the origin of color, while most of his contemporaries were still in some measure dependent on the traditional black and white or light and shadow.36

34 Boyle, Touching Colours, Pt. 3, exp. 12, pp. 219-220, exp. 17, p. 232 (Boyle's italics on color names); for Newton's notes-which are none too accurate-see "Of Colours," sect. 12, in J. E. McGuire and Martin Tamny, Certain Philosophical Questions: Newton's Trinity Notebook (Cambridge: Cam- bridge Univ. Press, 1983), p. 440. For Newton's use of primitive see Newton, Optical Papers, ed. Shapiro, Vol. 1, pp. 462-463, 506-507, esp. "Optical Lectures," prop. 4, p. 507 (this proposition is quoted at note 42); and Newton, "New Theory," prop. 6, in Correspondence, ed. Tumbull et al., Vol. 1, p. 98. Through most of the seventeenth century simple was the most common term for the primaries (see, e.g., Aguilon, Opticorum [cit. n. 19], p. 38), but by the turn of the century primary and primitive were becoming more prevalent, particularly on the Continent; see the later discussion of Malebranche's acceptance of Newton's theory and the references on that topic cited in note 57.

35 McGuire and Tamny, Certain Philosophical Questions, p. 388. My account of Newton's development differs significantly from that of Nakajima, "Two Kinds of Modification Theory of Light" (cit. n. 27). He sees Newton as initially accepting the idea that colors derive from black and white, failing to recognize that Newton's statement and refutation of that idea are in a single paragraph that gives every indication of having been written at one time.

36 Boyle held that white and black could not generate colors but suggested that in refraction light and shadow might generate them; see Boyle, Touching Colours, Pt. 1, Ch. 5, p. 87.

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Although Newton's treatment of white, insofar as it differs from the chromatic colors, agreed with the artists' and thus helped to buttress his theory, his claim that it is a mixture of all colors appeared to be in direct conflict with the evidence of pigment mixing, according to which a dark, obscure color should result. In the first published criticism of Newton's "New Theory," the French Jesuit Ignace Gaston Pardies made precisely this point. Since, he wrote Henry Oldenburg, a mixture of pigments gives the same result as a mixture of rays of the same color-and he cor- rectly included Newton among those supporting this principle-Newton's theory is contradicted by simple experience. In his reply Newton explained why his views were not at all in conflict with the results of pigment mixing:

To me white, black, and all the intermediate grays that can be compounded from mixing white and black seem not to differ as to species of color but only in the quantity of light. And since in a mixture of pigments the individual corpuscles reflect only their own proper color, so that the greater part of the incident light is suppressed and retained, the reflected light becomes dark and as it were mixed with shadow, so that it ought exhibit not an intense whiteness, but such as is mixed with blackness, that is, a gray.

By explaining that white, black, and grays form one species of color that differs only in the amount of light reflected and that there is a separate white-gray-black scale in addition to the chromatic scale of colors, Newton showed that his theory agreed with contemporary artistic theory. With this explanation he succeeded in turning criticism into an implicit and ultimately successful appeal for support from the artists' tradition. In the Opticks he expanded this explanation and illustrated it with experiments with "the coloured Powders which Painters use," whereupon it became well known.37

* * *

After the discovery and publication of the three painters' primaries between 1601 and 1613, knowledge of them spread slowly until 1646, when the Jesuit polymath Athanasius Kircher published an account of the primaries in his popular book The Art of Light and Shadow (see Appendix 2). Word of the primaries spread most rapidly in France and England, which is not surprising since they were then the two leading scientific nations. I have found four advocates of the painters' primaries in France and six in England between 1660 and 1681. It should be recalled that Newton published his theory in 1672, in the midst of this period. In the "Optical Lectures" Newton himself had invoked the artists' primaries in a passage that clearly shows his knowledge of the artists' tradition and its new conceptions of color mixing and the nature of white, black, and gray. He had devoted virtually all of proposition 3- "The colors white and black together with intermediate ashens and grays are gen-

37 Ignace Gaston Pardies to Oldenburg for Newton, 13 Apr. 1672, in Newton, Correspondence, ed. Turnbull et al., Vol. 1, p. 133 (where the letter is misdated). Oldenburg published this letter in Philo- sophical Transactions, 1672, 7(84):4087-4090. A few months earlier Hooke had raised the same criticism: Robert Hooke to Oldenburg, 16 Feb. 1671/72, in Newton, Correspondence, ed. Turnbull et al., Vol. 1, p. 114. Pardies approvingly cited Newton's example of mixing yellow and blue pigments (see note 30). Newton to Oldenburg for Pardies, 13 Apr. 1672, ibid., pp. 141-142, which was published in Philosophical Transactions, 7(84):4091-4093; and Newton, Opticks, Bk. 1, Pt. 2, prop. 5, exp. 15, p. 110. Newton had described this experiment in his "Optical Lectures"; see Newton, Optical Papers, ed. Shapiro, Vol. 1, pp. 111-113. The problems Newton encountered in mixing colored powders are described at note 62.

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erated from rays of every sort confusedly mixed"-to proving the compound nature of white. He then concluded by observing that "concerning gray and other nonprimitive colors, the proposition is evident, since painters have known that grays are compounded from white and black and all the others from red, yellow, and blue."38

From Appendix 2 we can see that in the last three decades of the century the primaries were gradually diffused throughout Europe. Although this table greatly increases our knowledge of the diffusion of the painters' primaries, it is not comprehensive. Not only have I not examined every treatise on natural philosophy or every artist's manual, I have barely looked at treatises in natural history and medicine, which are also concerned with color. It should cause no surprise that I found that the three primaries were more quickly adopted by scientists than by artists; it was, after all, the scientist's business to find universal laws of nature, and here was a nice simple one. To artists the primaries had very limited practical value, and in the debate on the relative importance of design and color that ran through the century many even argued that color was not a very important aspect of art. Nonetheless, by the beginning of the eighteenth century artists generally adopted them too. In the same period published supporters of Newton's theory numbered at best two or three scientists versus fourteen who favored the three primaries.39 Thus, from its initial espousal Newton's proposal of an infinite number of primaries had to contend with the simpler idea of three primaries and was resisted. From the perspective of the latter part of the seventeenth century it can fairly be characterized as a rival theory.

Newton's choice of color-mixing terminology for his new theory was, I am sure, an unconscious though quite natural one that readily provided familiar language and concepts for his new ideas. While this allowed his theory to be more readily grasped, his concept of a primary color was in fact very different from that of the painters, and it initially encountered resistance and caused confusion. In his referee's report on the "New Theory" Hooke questioned Newton's ideas on the nature and number of primary colors: ,"yt there are an indefinite variety of primary or originall colours, amongst which are yellow, green, violet, purple, orange, &c and an indefinite number of intermediat gradations; I cannot assent thereunto, as supposing it wholy useless to multiply entities without necessity: since I have elsewhere shewn, that all the varietys of colours in the world may be made by the help of two."40 In his Micro- graphia Hooke had proposed that all colors derive from yellow and red, which he took to be varieties of one color, and blue. We may consider this scheme to be a variant of the painters' primaries in order to focus on the fundamental issues, the

38 Newton, Optical Papers, ed. Shapiro, Vol. 1, pp. 462-463, 506-507. This passage also shows how much Newton's concept of a primary or primitive spectral color differs from that of the artists. His "nonprimitive colors" are those that are not one of the spectral colors, whereas for painters nonprimitive colors (i.e., compound colors) are all colors except the three primaries and so constitute a far larger class than Newton's.

39 I count only Nathaniel Fairfax, A Treatise of the Bulk and Selvedge of the World (London, 1674), p. 51; William Molyneux, Dioptrica nova: A Treatise of Dioptricks, in Two Parts (London, 1692), pp. 4-5; and Edmond Halley, "De iride, sive de arcu coelesti, dissertatio geometrica . .. ," Philosophical Transactions, 1700-1701, 22:714-725, on p. 720, as clearly supporting Newton's theory in print. A number of scholars privately backed his theory to varying degrees. Even counting all of them, their number was clearly less than that of the published supporters of the painters' primaries in this same period. See Kemp, Science of Art (cit. n. 2), pp. 283-284, for a brief account of the so-called color- design debate.

40 Hooke to Oldenburg, 15 Feb. 1671/72, in Newton, Correspondence, ed. Turnbull et al., Vol. 1, p. 113.

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concept of primary colors and whether their number is finite and small or indefinitely large.

Newton responded to Hooke by more clearly defining his concepts of simple and compound colors strictly in terms of the refrangibility of light rays: "That colour is primary or originall wch cannot by any art be changed, & whose rays are all alike refrangible; & that compounded which is changeable into other colours, & whose rays are not alike refrangible." Thus, to determine whether a color is simple or compound one need only pass its rays through a prism to see whether they are all refracted alike. To take Newton's own example: though two beams of green light may appear to the naked eye to be the same color, if one of them is decomposed by a prism into beams of different color, such as yellow and blue, while the other passes through unchanged, then "I suppose these two Greens will in both cases be granted of a different origine & constitution. "41 The former will be a compound green and the latter a simple one. Despite their sensible identity, the two colors differ in their physical composition.

We can now see, as Newton himself came to recognize fully, that by "primary" he means the physically irreducible, elementary components of light, which are separated by their physical property of refrangibility. This concept of "primary" differs from that of Hooke and those in the arts tradition of pigment mixing, where the primary colors are those elements out of which all other colors can be made and which cannot themselves be made from any others. Since Newton took the method of physical decomposition by refraction as his principal conceptual tool, he was not- at least at this time-bothered by nature's profligate use of an infinite number of colors when three would apparently suffice. Not so Hooke, who considered it "wholy useless to multiply entities without necessity." Moreover, colors identical with New- ton's primaries, in contrast to the painters', could be made by mixing other primaries, as he had demonstrated himself. Christiaan Huygens pursued Hooke's criticism, and he compelled Newton to clarify and reformulate his theory in a more rigorous and elegant form and to propose new definitions and terms. Newton elim- inated the misleading terms primary and primitive and substituted the more neutral terms simple or homogeneal, which he drew from his mathematical theory of color.42

* * *

If the story were to end here it would seem as if Newton had distanced himself from the artists' pigment-mixing approach, and we would have yet another tale of the separation of the arts and sciences. Over thirty years later, however, the story took a new turn with the publication of the Opticks, which was one of the most widely read treatises on natural philosophy in the eighteenth century and certainly the most influential optical treatise. Although Newton for the most part stuck to his decision to abandon the color-mixing term primary, he reintroduced it in a definition at the beginning of the Opticks and also in two propositions. One of the propositions, that

41 Newton to Oldenburg, 11 June 1672, ibid., pp. 180-181. 42 Newton, "New Theory," prop. 6, ibid., p. 98. See also "Optical Lectures," prop. 4: "Primitive

colors can be exhibited by the composition of the neighboring colors on each side of them"; Newton, Optical Papers, ed. Shapiro, Vol. 1, p. 507 (see note 38). For the changes prompted by Huygens see Newton to Oldenburg, 23 June 1673, in Newton, Correspondence, ed. Turnbull et al., Vol. 1, pp. 292- 293; see also Shapiro, "Evolving Structure of Newton's Theory" (cit. n. 28), pp. 221-228. The term simple also referred to primaries, but Newton seems to have been sensitive to changing usage, for primary and primitive were becoming more common terms (see note 34).

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"the whiteness of the Sun's Light is compounded of all the primary Colours," was the most fundamental of his theory, and so most readers saw it; the other was on color mixing and was consequently of great interest to all those in the arts.43 The reintroduction of the term primary was, I claim, part of an attempt on Newton's part to bridge the gap between his innumerable spectral colors and the painters' three primaries. In drafts and the manuscript of the Opticks he made changes that encouraged thinking of his colors as if they were the same as the artists'. For example, in his earlier writings, after naming the principal colors of the spectrum, he invari- ably added some such phrase as "with their innumerable intermediate gradations," but in the Opticks he explicitly omitted that amplification in all but a single passage.44

Newton imagined that colors formed harmonies just as musical tones do, and so he divided the spectrum into seven segments that were proportional to a string sound- ing the seven notes of the octave in the just diatonic scale. This of course required that there be seven colors. Before he introduced the musical division of the spectrum in his revision of the "Optical Lectures" in the winter of 1671-1672, Newton worked with only five principal colors. To get the requisite seven he added orange between red and yellow and indigo between blue and violet. In the "Optical Lectures" Newton conceded that he could not "so precisely observe and define" the boundaries of the colors and that the spectrum could be divided "somewhat differently." Nonetheless, he declared his preference for the musical division "because it perhaps involves something about the harmonies of colors (such as painters well know, but which I myself have not yet sufficiently studied) perhaps analogous to the concordance of sounds."45 As we saw, this analogy went back at least as far as Aristotle, who ar- ranged the colors musically on the basis of the proportions of white and black that each color contained. Newton's spectrum provided a modern ordering of colors, using the natural sequence of the solar spectrum, while eliminating black and white, which were now generally considered not to belong with the chromatic colors. This natural ordering of color was one of the more significant consequences of his theory, especially for the arts, and culminated changes that had been under way for nearly three centuries. Newton's musical division of the spectrum exercised the eighteenth- century imagination and was largely responsible for the widespread belief that there were only seven spectral colors. In his exposition of this division of the spectrum in Book 1, Part 2, proposition 3, of the Opticks, however, Newton did not inform his readers of its somewhat arbitrary nature as he had in the earlier "Optical Lec- tures." Now that he stressed seven rather than innumerable colors, the gap between his primaries and the painters' three was no longer a substantial one.46

Newton introduced a color-mixing rule that made his theory appear still closer to

43 Newton, Opticks, def. 8, p. 3, and Bk. 1, Pt. 2, prop. 5, p. 98 (italics added). Prop. 6 is discussed below.

44 See the passage quoted at note 31 and Shapiro, "Evolving Structure of Newton's Theory," p. 235, n. 77. For other changes in the manuscript see notes 46, 47.

45 Newton, Optical Papers, ed. Shapiro, Vol. 1, pp. 545-547; for the use of five colors see pp. 51, 87.

46 In the manuscript of the Opticks Newton revised the statement of the proposition-"To define the refrangibility of the several sorts of homogeneal Light answering to the several Colours"-to stress the "several" colors. It originally read, "To define the refrangibility of homogeneal light answering to the single colours"; that is, he added "the several sorts" and replaced "single" by "several": CUL, Add. MS 3970, fol. 96r; cf. Opticks, Bk. 1, Pt. 2, prop. 3, p. 91 (italics added to illuminate Newton's changes). For one attempt to bridge the gap between Newton's colors and the painters' primaries see the caption to the cover illustration of this issue of Isis.

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Figure 4. Newton's color-mixing circle; from Newton, Opticks (1704), Bk. 1, Pt. 2, prop. 6, Plate 3, Fig. 11.

the painters' in the Opticks, Book 1, Part 2, proposition 6: "In a mixture of primary Colours, the quantity and quality of each being given, to know the Colour of the compound." Newton's rule contains deep insights into the nature of color mixing, but I need only sketch its basic structure (Figure 4). The circumference of a circle is divided into arcs proportional to the lengths of the seven spectral colors, that is, in a musical proportion; and at the center of each arc is placed a small circle whose size or "weight" is proportional to the number of rays of that particular color. Each arc contains all the "degrees" of that color. The center O of the circle represents white and the circumference pure, unsaturated hues without any admixture of white. The common center of gravity Z of all the little circles indicates the color compounded from a mixture of any seven "primary" colors. In the example illustrated Z is an unsaturated orange that results from a mixture of seven colors in which red, orange, and yellow predominate, but Newton tells us that it could be imitated by mixing orange and white painters' "powders."

By including the degrees of each color with that color, an approach that he used elsewhere in the Opticks, Newton was able to bridge the gap between his innumerable colors and the painters' three primaries. The colors at the centers of the arcs will not in general be simple, homogeneous, or "primary" colors in Newton's sense, since they represent all the degrees of that color. It is perhaps for this reason that in the manuscript of the Opticks he added a concluding caveat that the rule is "accurate enough for practise, though not Mathematically accurate." His original formulation of the proposition more accurately stated the aim of the rule: "A mixture of rays being given, to know the colour of the light." The changes he then made clearly indicated that it applied as much to mixing pigments-"powders"-as to lights. Newton's color-mixing circle was an important vehicle for the diffusion of his theory and was rapidly absorbed into the artists' pigment-mixing tradition, where it served as the foundation for most color-mixing schemes proposed in the eighteenth century. Brook Taylor's popular and influential treatise New Principles of Linear

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Perspective devoted an appendix to elucidating Newton's color-mixing circle because "Knowledge of this Theory may be of great use in Painting."47

Newton's theory of color has long been understood as a theory about colored light, and indeed most of his experiments were with spectral colors and not pigments. Yet Taylor's application of it to pigments was sanctioned by both Newton's writings and his practice, as we have just seen. The equivalence of mixing pigments and mixing lights came as close as any principle of seventeenth-century color theory to being a universally accepted axiom.48 In 1852 Hermann von Helmholtz finally discovered that different rules apply to the mixing of pigments and of lights, which are now known as subtractive and additive color-mixing processes, respectively. There were, however, many good theoretical and experimental reasons for Newton and his contemporaries to accept the equivalence of mixing pigments and lights, and none that I know of for doubting it. To Aristotelians like Aguilon the color-mixing rules were universal rules that referred to qualities and not substances, and Aristotle had asserted the equivalence of all types of color mixing. To mechanical philosophers like Boyle and Newton color was a property of light, and the source of the colored light, whether a body or a prism, should not alter its properties. The experimental evidence continued to accumulate. In Touching Colours Boyle had mixed yellow and blue nine different ways-including mixing pigments, passing light through superposed glass plates, mixing spectral lights, and reflecting yellow light from a blue body-and all yielded green. Boyle was extremely sensitive to sources of experimental error and problems of replication and reported that the experiments could easily go awry, "yet when all necessary Circumstances were duely observ'd, the Event was answerable to our Expectation and Desire."49 Boyle and Hooke found that when mixtures of colored powders were viewed through a microscope, the individual particles main- tained their own color, even though the compound was of a new color. Newton interpreted this to mean that each particle reflected rays of its own color, just as if prismatic rays of those colors were mixed.50 Finally, the very sequence of the spectral

47 CUL, Add. MS 3970, fol. 114r; and Newton, Opticks, p. 117. Cf. CUL, Add. MS 3970, fol. 11 lr. Brook Taylor, New Principles of Linear Perspective (London, 1719), Appendix 2, "A new theory for mixing of colours, taken from Sir Isaac Newton's Opticks," pp. 62-70, on p. 67. Taylor's work was well known. Two more editions appeared in the eighteenth century, as well as Italian (1755) and French (1757, 1759) translations. On Newton's color-mixing circle in eighteenth-century color-mixing schemes see Kemp, Science of Art (cit. n. 2), Ch. 7; and Charles Parkhurst and Robert L. Feller, "Who Invented the Color Wheel?" Color Research and Application, 1982, 7:217-230.

48 Francesco Maria Grimaldi, for example, confidently asserted that "we prove that the same color results from a mixture of two colors whether only rays of apparently colored light coincide, or two pigments are mixed that are colored with those colors that are exhibited by the rays individually": Gri- maldi, Physico-mathesis de lumine, coloribus, et iride, alijsque adnexis libri duo (Bologna, 1665), prop. 60, sect. 22, p. 291.

49 Boyle, Touching Colours, Pt. 3, exp. 14, p. 225 (italics added); see also p. 227. He summarized his observations in exp. 27, pp. 231-236. Newton took notes on these experiments in "Of Colours," sects. 11, 12, 23, 24, in McGuire and Tamny, Certain Philosophical Questions (cit. n. 34), pp. 440, 454. On Helmholtz's distinction between additive and subtractive color mixing see Hermann von Helm- holtz, "Uber die Theorie der zusammengesetzten Farben," Annalen der Physik und Chemie, 1852, Ser. 2, 87:45-66, which was translated as "On the Theory of Compound Colors," Philosophical Magazine, 1852, Ser. 4, 4:519-535.

50 Newton, Optical Papers, ed. Shapiro, Vol. 1, p. 109. See Boyle, Touching Colours, Pt. 3, exp. 17, pp. 238-239; Newton cited this observation in the "New Theory" (see note 30). Hooke mixed vermilion and bice to make purple; see Hooke, Micrographia (cit. n. 25), p. 78. Newton understood the difference between additive and subtractive color mixing (Optical Papers, ed. Shapiro, Vol. 1, p. 513, n. 16, p. 519, n. 19), but with the support of these observations by Boyle and Hooke he believed pigment mixing to be an additive process.

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colors seemed to support the equivalence of mixing pigments and mixing lights, what with orange falling between red and yellow, and green between yellow and blue.5' Despite all this evidence, when, some two hundred years later, Helmholtz mixed yellow and blue lights under very carefully controlled conditions using instruments and glass incomparably better than what was available in the seventeenth century, he got white, not green.

An obvious question to ask is how experimental and observational anomalies were treated when they were encountered. The historical evidence suggests that differences between mixing pigments and mixing lights were not as striking as modem color science would lead one to believe. Carefully controlled experiments were not common for much of the eighteenth century, so that the principle of equivalence was not initially put to any severe tests. Experiments with color are very delicate, and the results can change quite dramatically with small changes in the experimental arrangement, as Boyle recognized. Sometime after the mid-eighteenth century more extensive experiments on mixing colored lights began to be carried out with prismatic colors and colored tops, and even pigment-mixing experiments were more carefully executed.52

When discordant results between different kinds of mixing appeared, the initial response was simply to call attention to the difference. Color science, however, like all sciences, developed a set of plausible explanations to account for apparently divergent results. One, which goes back at least as far as Aguilon, attributed anomalies to impurities in the colors. Newton extended this explanation from pigments to prismatic colors and described methods for preparing pure or homogeneous spectral colors. The second principal way to explain differences resulting from mixing pigments and mixing lights was to attribute them to a loss of light. Newton adopted this approach when he explained that a black or a gray, rather than a white, arises from a mixture of diversely colored pigments because most of the incident light is absorbed.53 Though some did deny the principle of equivalence, by the turn of the century these explanations were incorporated into color science.

* * *

But let me return to the early eighteenth century, well before the anomalies in New- ton's synthesis of his new theory with the fruits of the artists' tradition became apparent, and show why I believe that his synthesis assisted in the acceptance of his new theory of light and color. The idea, initially proposed by Alberti, that white and black are not colors but form their own scale of intensities was an important starting point for Newton. He subsequently further developed the uniqueness of white and thereby accelerated the historical trend that was differentiating it from the chro-

51 Boyle (Touching Colours, Pt. 2, exp. 14, p. 225), Hooke (Micrographia, p. 58), and Mariotte (Nature des couleurs [cit. n. 25], Vol. 1, p. 208) held that spectral green is a compound of yellow and blue, and Mariotte even added that "painters and dyers also make green by mixing blue with yellow." For still more adherents to this view see Newton, Optical Papers, ed. Shapiro, Vol. 1, p. 110, n. 31.

52 For colored tops see, e.g., Giovanni Antonio Scopoli, Entomologia carniolica (Vienna, 1763); for prismatic colors see Christian Ernst Wiinsch, Versuche und Beobachtungen iiber die Farben des Lichtes (Leipzig, 1792); and for pigment mixing see Johann Heinrich Lambert, Beschreibung einer mit Ca- lauschen Wachse ausgemalten Farbenpyramide (Berlin, 1772). 53 Lambert mixed red and green pigments and got a dark, brownish-gray red color, whereas he got a somewhat brownish orange when he mixed spectral red and green; he was able to get a dark brown by inserting a gray paper in the beam of light to lessen the intensity in imitation of pigment mixing. See Lambert, Farbenpyramide, pp. 10, 21.

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matic colors. This long-term trend was also weakening modification theories, the principal alternative to Newton's account of the origin of color. Discrediting the most venerable of them, that colors derive from a mixture of white and black, meant that all modification theories became less plausible, even the modem mechanical ones, like that of Descartes. This historical process helps to explain why, when Newton proposed his theory anew in the Opticks, he met far less opposition based on a defense of modification theories than he had a generation earlier.

The changing views of Walter Charleton, whose Physiologia Newton studied in his student days, serve to illustrate how the old modification theories based on black and white were being abandoned independently of Newton. Despite his atomistic natural philosophy, Charleton's explanation of color in his Physiologia was essentially Aristotelian, as he still derived the chromatic, intermediate colors from the extremes. After treating "the Two Extreme and Ground Colours, White and Black," he claimed that "there can be no great difficulty remaining concerning the Genealogy of all other INTERMEDIATE ones, since they are but the off-spring of the Extreme, arising from the intermission of Light and shadow, in various proportions." Later in the same chapter he avoided details about the origin of compound colors (which "are as Generally, as rightly praesumed to be only the multiplied removes of Light and Darkness"), since they are treated by the painters, "especially . . . those ex- cellent Rules of that Modern Apelles, Albertus Durerus, praescribed in his Art of Limning." The Art of Limning, which was a very popular work erroneously attributed to Diirer, did not adopt the three primaries but utilized an Aristotelian scale with five chromatic colors (red, yellow, blue, green, and brown) in addition to white and black.54 This is yet another indication of how common it was by the mid-seventeenth century for natural philosophers to draw upon the arts.

Nearly twenty-five years later, in an appendix, "On the Names and Differences of Colors, and on the Colors of Fur and Feathers," to Exercises on the Differences and Names of Animals, Charleton entered the modem world of color theory. He rejected the idea that white and black are the generators of the chromatic colors and adopted the painters' primaries. To explain the origin of color he appealed to "some modification of light, but clearly a different sort from those modifications that cor- respond to whiteness and blackness," and suggested that the modification derives from either reflection or refraction (infractione). Charleton's work appeared five years after Newton's "New Theory," but he gives no indication that he was influenced by Newton. Rather, his source was Francis Glisson, whose writings on color he quotes extensively. While Charleton, and Glisson, still supported a modification theory, the idea that the modification arose from reflection or refraction alone, independent of light and shadow, was a significant step toward making Newton's theory more ac- ceptable.55

54 Charleton, Physiologia Epicuro-Gassendo-Charltoniana (cit. n. 25), pp. 191-192, 196. According to Ogden and Ogden, "Bibliography" (cit. n. 23), p. 197, the Art of Limning is the same work as [Thomas Jenner], Drawing, Limning, Washing, or Colouring of Maps and Prints (London, 1652), which went through numerous editions and was also published as Albert Durer Revived: or, A Book of Drawing, Limning, Washing, or Colouring of Maps and Prints. ....

55 Charleton, "Appendicula de colorum differentiis & nominibus; deque pilorum plumarumque coloribus," in Exercitationes de differentiis & nominibus animalium, 2nd ed. (Oxford, 1677), pp. 61-78 (third pagination), on pp. 64-65; and Francis Glisson, Tractatus de ventriculo et intestinis, (London, 1677), Ch. 9, "De coloribus pilorum," pp. 50-65, on pp. 51-53. Boyle held a similar position on the nature of modification (see note 36).

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The discovery of the painters' primaries was the most important discovery in color before Newton's own theory, and by the end of the seventeenth century it was far more widely adopted than his. When he first formulated his theory in the early 1670s, Newton naturally drew upon the developed language and concepts of the color-mixing tradition, although his critics made him recognize that his concept of a primary color was a fundamentally different one. Later, by reintroducing the term primary in the Opticks and stressing the seven primaries, he attempted to lessen the tension between the three primaries and the innumerable simple colors he had posited. In this he succeeded, for most adherents to his theory in the first half of the eighteenth century believed that there were only seven simple spectral colors and identified them as "primaries" or "primitives."56

Nicolas Malebranche was the first advocate of Newton's theory in France, and his circle of followers were its principal supporters in the first two decades of the eighteenth century. Before Malebranche could adopt Newton's theory of color, he first had to give up his own modification theory. In the 1700 edition of his Recherche de la verite he had assumed that white light was simple and that colors were some modification of it, but he gave this view a modern twist. He proposed that only three "primitive" colors-red, yellow, and blue-resulted from the modification of white light (a change in frequency) and that all other colors were compounded of these. In the 1712 revision of Recherche de la verite he dropped his theory in favor of Newton's and adopted Newton's synthesis with color-mixing ideas by now declaring that there are only seven "simple, homogeneous, or primitive" colors in sunlight. As would soon become common, Malebranche explicitly defined the seven colors as homogeneous, or possessing a single, immutable degree of refrangibility: "there are only a fixed number [nombre determine'] of simple rays, which always preserve the same promptitude in their vibrations, and always undergo the same quantity of refraction; this is certain from the experiments of Mr. Newton."57

In 1743 George-Louis Leclerc, comte de Buffon, delivered a paper to the Acad- emy of Sciences in Paris that thoughtfully blurred the distinction between Newton's and the painters' primaries. Buffon recognized, as few did, that the spectrum consists of rays of an infinite number of colors and degrees of refrangibility, but he then proceeded to justify dividing the spectrum into only seven intervals containing seven colors with their various degrees. "Each of these intervals," he explained, "contains

56 See Hargreave, "Young's Theory of Color Vision" (cit. n. 3), pp. 60-74, 477-495. 57 Nicolas Malebranche, Oeuvres de Malebranche, ed. Andre Robinet, 20 vols. in 21 (Paris: Librairie

Philosophique J. Vrin, 1958-1970), Vol. 3, pp. 258, 301. Cf. Henry Guerlac, Newton on the Continent (Ithaca, N.Y.: Cornell Univ. Press, 1981), pp. 63-108. Malebranche mostly used the term simple for Newton's seven spectral colors, but in the early eighteenth century primitive was becoming the standard French term for primary, both in the painters' and in Newton's sense; cf. note 34. See, e.g., Traite de la peinture en mignature . . . auquel on a ajoute un petit traite de la peinture au pastel, avec la methode de composer les pastels, new ed. (The Hague, 1708), p. 152; and Charles Francois de Cisternay Dufay, "Observations physiques sur le melange de quelques couleurs dans la teinture," Memoires de IAcadcemie Royale des Sciences, 1737, pp. 253-268, on p. 267. On the authorship of the Traite de la peinture, as well as that of the new section on pastels, which was added to this edition and contains a description of the primaries, see Parkhurst and Feller, "Who Invented the Color Wheel?" (cit. n. 47), pp. 220- 223. Malebranche read the Latin translation of the Opticks, where Newton's primaries was rendered "primarios": Optice: Sive de reflexionibus, refractionibus, inflexionibus & coloribus lucis libri tres, trans. Samuel Clarke (London, 1706), p. 4. In the French translation it became "primitives": Traite d'optique, trans. Pierre Coste, 2nd ed. (Paris, 1722; rpt., Paris: Gauthier-Villars, 1955), p. 5. On Malebranche, his circle, and the acceptance of Newton's theory of color in France see Guerlac, Newton on the Continent, pp. 54-73, 106-114.

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colors that, although taken together, are not decomposable by a prism or any other means, which has given them the name primitive colors." If, Buffon argued, the spectrum were divided into fewer intervals, the colors would no longer be immutable; and if it were divided into more intervals, it would be fruitless, since there would be intervals containing the identical color but in each case it would be called by a different name. Newton, however, showed that such broad expanses of the spectrum are not simple and homogeneous but a mixture, and in the Opticks, Book 1, Part 1, proposition 4, he gave detailed descriptions for preparing rays of immutable color. Buffon's approach violates the one-to-one correspondence between refrangibility and color that Newton had established. Indeed, Newton's statement of this principle in the Opticks contains its one explicit assertion on the innumerable spectral colors. When he observed the spectrum after separating the rays by the methods described in Book 1, Part 1, proposition 4, he found the seven colors "together with all their intermediate degrees in a continual succession perpetually varying: So that there appeared as many degrees of Colours, as there were sorts of rays differing in refrangibility."58 Nonetheless, Buffon's interpretation of Newton's theory was precisely the sort of misreading that Newton had encouraged.

Buffon did not mention the painters' three primaries, but Willem 's Gravesande, whose interpretation of Newton's theory was similar to Buffon's, warned about con- fusing Newton's primaries with the painters': "these three Colours, red, yellow, blue being given, we may imitate all the Rest; but we ought not from thence to infer, that there are only three primary Colours, since we really discover seven." I could easily multiply references to show how widespread were the belief that there are only seven primary colors in the spectrum and their conflation with the painters' primaries or primitives, but Buffon, 's Gravesande, and his countryman Pieter van Musschenbroek were astute and extremely influential natural philosophers, and I need not describe all the interpretations of Newton's theory.59 It is important to recognize that virtually all those who claimed that there were seven, or even three, rather than innumerable colors in sunlight had adopted the most fundamental principles of Newton's theory, namely, that colors are innate to sunlight and not some modification of it and that white is a mixture of colors and not simple. By mid century, whatever disagreements there were as to the number of primaries, modification theories had largely been rejected.60 It is equally important to recognize that

58 George-Louis Leclerc, comte de Buffon, "Dissertation sur les couleurs accidentelles," Mem. Acad. Roy. Sci., 1743, pp. 147-158, on pp. 148-149; and Newton, Opticks, Bk. 1, Pt. 2, prop. 2, p. 88. See Newton's Latin gloss on this passage quoted later in this essay and the reference at note 62.

59 Willem 's Gravesande, Mathematical Elements of Natural Philosophy, Confirm'd by Experiments: or, An Introduction to Sir Isaac Newton's Philosophy, trans. J. T. Desaguliers, 2 vols., 6th ed., Vol. 2 (London, 1747), sect. 3573, p. 259. The French translation refers to "couleurs primitives": Elemens de physique demontrez mathematiquement, et confirmez par des experiences: Ou introduction d la philosophie Newtonienne, trans. Elie de Joncourt, 2 vols. (Leyden, 1746), Vol. 2, p. 304. Pieter van Musschenbroek, Cours de physique experimentale et mathematique, trans. Sigaud de La Fond, 3 vols., Vol. 2 (Paris, 1769), sects. 1804, 1815, pp. 482, 487.

60 Tobias Mayer was among those who asserted that sunlight consists of just three colors-red, yellow, and blue; see Mayer, "Treatise on the Relationship of Colours," in Tobias Mayer's "Opera Inedita": The First Translation of the Lichtenberg Edition of 1775, ed. Eric G. Forbes (New York: American Elsevier, 1971), pp. 81-91. Supporters of trichromatic theories have either been dismissed for failing to understand Newton's theory of color or hailed as forerunners of the trichromatic theory of color vision; see, e.g., R. A. Weale, "Trichromatic Ideas in the Seventeenth and Eighteenth Centuries," Nature, 1957, 179:648-651. Neither judgment is appropriate. This tradition was in the mainstream of eighteenth- century color theory, albeit at an extreme edge of it because of its nearly total conflation of optical and pigment-mixing concepts.

625




underlying the seven-color misinterpretation of Newton's theory was the universal belief in the equivalence of mixing pigments and mixing lights. Yet, as common as this misinterpretation was, one should not assume that it was ubiquitous. William Porterfield and Jean Le Rond d'Alembert, for instance, recognized that there were infinitely many primaries in Newton's sense.6'

Was Newton simply being an opportunist in hitching his theory to the rising star of the three primaries? Not particularly: I believe that in returning to the word primary he was attempting to appeal to a more familiar, accepted idea; but in regard to their number I believe that he was genuinely trying to synthesize two valid discoveries-his own, on the compound nature of sunlight, and that of the painters. In an important passage that is only in the Latin editions of the Opticks, and thus was not seen by the many readers of the English and French editions, Newton explained that the designation of seven primary colors is just a convention. Although we see a continual succession of innumerable colors in the spectrum, "yet all of them may be comprehended under the species and names of the seven aforementioned principal colors, even if their degrees may be innumerable." Newton, at the end of his career, had arrived at a stalemate. He knew that sunlight consisted of innumerable degrees of color. He had chosen seven principal-later, primary-colors solely because of the musical analogy. Likewise, he knew that painters could work with just a few colors, though I am certain that he was no longer convinced that they were working with just three primaries. He had determined that "the coloured Powders which Painters use, " and indeed all colored bodies, possessed compound colors, so that painters were actually working with more than three. In the Opticks he described mixtures of two, three, and four pigments that gave a gray or dun color, whereas his theory required that it be composed of all the colors. He explained that he was able to succeed with just two pigments (red lead and viride aeris) because "these two Col- ours were severally so compounded of others, that in both together were a mixture of all Colours."62 This factor would explain why Newton did not even mention the painters' primaries in the Opticks as he had earlier in his "Optical Lectures."

The problem of the number of colors required to compose white light went back to the debate over the "New Theory." Newton had consistently insisted that the sun's white light was a mixture of innumerable colors until Huygens suggested in a letter to him in 1673 that white could be compounded from just two colors, yellow and blue. Newton rejected Huygens's claim as it applied to sunlight, but he did essentially concede that white light sensibly-though not physically-like sunlight could be made from fewer colors.63 In the Opticks Newton returned to this issue in his proposition on color mixing. If two colors opposite one another on the color-mixing circle are mixed (see Figure 4), then according to the diagram white should result,

61 William Porterfield, A Treatise on the Eye, the Manner and Phaenomena of Vision, 2 vols. (Edin- burgh, 1759), Vol. 1, pp. 326, 329; and Jean Le Rond d'Alembert, Opuscles mathematiques, Vol. 3 (Paris, 1764), pp. 392-393. For Robert Smith and Joseph Priestley see Hargreave, "Young's Theory of Color Vision" (cit. n. 3), pp. 483-484, 486.

62 Newton, Optice (cit. n. 57), "Errata, Corrigenda, & Addenda," p. [viii], referring to Bk. 1, Pt. 2, prop. 2, p. 100; and Newton, Opticks, Bk. 1, Pt. 2, prop. 5, exp. 15, pp. 110, 111. Viride aeris is verdigris, which is green.

63 Newton, Correspondence, ed. Turnbull et al., Vol. 1, pp. 255-256, 265, 291-292; see also Sha- piro, "Evolving Structure of Newton's Theory" (cit. n. 28), pp. 223-225. I there attributed Newton's emphasis on seven colors to his discovery that white could be made with a small number of colors, but I now recognize that that was just one manifestation of the tension in his theory between innumerable and a small number of colors.

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ALAN E. SHAPIRO

since the center O represents white. Newton admitted this deduction but denied that a "perfectly white" color would actually arise. He always found just "some faint anonymous Colour." Thus he denied the existence of complementary colors, as such pairs are called. "Whether," Newton asked, white "may be compounded of a mixture of three taken at equal distances in the circumference I do not know, but of four or five I do not much question but it may." Such a white, however, would be an unnatural "curiosity," since all whites in nature are a mixture of all sorts of rays.64 Exactly how many colors are required to compound white light, even if an unnatural one, Newton could not say. Nor was it clear how many colors painters actually use. It was clear, though, that the phenomena of nature could be imitated with a small number of colors. And, finally, it was demonstrably true that sunlight consisted of innumerable colors. All that Newton could do at this stage of his career was to create a loose synthesis of these divergent conclusions. However, he did it so skillfully that it took nearly a century for it to begin to unravel.

The changes in artistic thinking and practice about color that burst forth about 1400 had, 300 years later, dramatically altered the science of color. The widespread use of color mixing culminated in the early seventeenth century in the disclosure of the painters' primaries, and henceforth the painters' trinity would play a fundamental role in color theory, though it would take another 250 years for its true significance to be recognized. A transformation had also occurred in the very conception of what a color is, with the shift from a tonal classification based on black and white to a chromatic one based on hue and a separate black-gray-white scale. While artists' new ideas about color fundamentally altered scientific concepts of color in the seventeenth century, in the eighteenth century artists encountered some difficulty in coming to terms with the essential elements of the Newtonian synthesis. As it turned out, they were unable to apply Newton's theory to practice, and in the eighteenth century art and science largely went their own ways. If the first revolution in color mixing that I have described here had largely run its course with the publication of Newton's Opticks, art and science came together once again in a second revolution in the mid-nineteenth century, with the development of the trichromatic theory of color vision and Impressionism; but that is another, better-known story.65

64 Newton, Opticks, Bk. 1, Pt. 2, prop. 6, p. 116. 65 Kemp, Science of Art (cit. n. 2), Ch. 7, "Newton and After" (on science and art in the eighteenth

century), esp. pp. 306-319 (which includes references to the literature on Impressionism).

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APPENDIX 1 REJECTION OF BLACK AND WHITE AS COLORS

CHROMATIC COLORS OR GENERATORS OF

Name

1. Theodoric of Freiberg

2. Leon Battista Alberti*

3. Leonardo da Vinci* 4. Julius Caesar

Scaliger

5. Anselm de Boodt

6. Louis Savot

7. Franqois d'Aguilon 8. Marin Cureau de La

Chambre

9. Pierre Gassendi

10. Robert Boyle

11. Robert Hooke

12. Andr6 Felibien*

13. Johannes Scheffer*

14. Isaac Newton

15. Walter Charleton

16. Francis Glisson

17. Edme Mariotte

18. Filippo Buonanni

19. Willem Beurs*

20. Gerard de Lairesse*

Year

ca. 1305

1435

ca. 1500 1557

1609

1609

1613 1650

1658

1664

1665

1666

1669

1672

1677

1677

1681

1684

1692

1707

Views on Black and White

Not generators of colors

Not colors or generators of colors

Not colors Not colors or

generators of colors



Not colors Not generators of

colors




Not colors


Not generators of colors, but composed of all colors



Not colors


Not colors

Not colors

Source

De iride 2.3 (unpublished)a

De pictura (published 1540)b

"On Painting" (published 1651)c Exotericarum exercitationum

(1615), ex. 325, sect. 9, p. 823d

Gemmarum et lapidum historia, p. 25d

Nova-antiqua, fol. 7rd

Opticorum, p. 40 Nouvelles observations et

coniectures sur l'iris (Paris, 1650), p. 163

Syntagma philosophicum, in Opera omnia, Vol. 1 (Lyons, 1658), p. 440

Touching Colours, Pt. 1, Ch. 5, p. 87'

Micrographia, pp. 75, 78

Entretiens sur les vies et sur les ouvrages des plus excellens peintres, 2nd ed., Vol. 2 (Paris, 1685), pp. 624-625

Graphice: Id est, de arte pingende (Nuremberg, 1669), pp. 158-162

Philosophical Transactions, 1672, 7(84):4091-4093f

Appendix to Exercitationes de differentiis & nominibus animalium, 2nd ed., pp. 61-78 (third pagination)g

Tractatus, pp. 51-52

De la nature des couleurs, Vol. 1, pp. 298-299

Recreatio mentis, et oculi in observatione animalium testaceorum (Rome, 1684), p. 60

De Groote Waereld in't kleen geschildert (Amsterdam, 1692), p. 4

The Art of Painting in All Its Branches, trans. John Frederick Fritsch, 2nd ed. (London, 1778), p. 119; trans. of Heet Groot Schilderboek (1707)

628



ALAN E. SHAPIRO

21. Anonymous*h 1708 Not colors Traite de la peinture en mignature, p. 152

NOTE.-This table is intended to illustrate the gradual separation of black and white from the chromatic colors and is not comprehensive.

*Indicates a member of the arts community; all others are natural philosophers, naturalists, or phy- sicians.

aJoseph Wiirschmidt, ed., Dietrich von Freiberg tiber den Regenbogen und die durch Strahlen er- zeugten Eindriicke, in Beitrdge zur Geschichte der Philosophie des Mittelalters, 1912, 12(5-6):66-67. See also Parkhurst, "Alberti's Place in History of Color Theory" (cit. n. 3), pp. 174-176.

bDiscussed in the text at note 12. CDiscussed in the text at note 14. dDiscussed in the text at note 20. eDiscussed in note 36. fQuoted in the text at note 37. See also note 35. gDiscussed in the text at note 55. hOn the authorship see note 57.

APPENDIX 2 DIFFUSION OF THE PAINTERS' PRIMARIES IN THE SEVENTEENTH CENTURY

Name Year Nationality* Source

1. Guido Scarmiglioni 1601 Austrian De coloribus, libri duo, pp. 111-112, 116-117a

2. Anselm de Boodt 1609 Flemish Gemmarum et lapidum historia, p. 25 3. Louis Savot 1609 French Nova-antiqua, fols. 6r, 7r-8v 4. Francois d'Aguilont 1613 Flemish Opticorum, p. 38b 5. Jean Leurechon 1622 French Selectae propositiones in tota sparsim

mathematica, 2nd ed. (Pont-a-Mousson, 1629), p. 30

6. Athanasius Kirchert 1646 Italian Ars magna lucis et umbre, Bk. 1, Pt. 2, cap. 2, p. 67

7. Marin Cureau de La 1650 French Nouvelles observations et coniectures sur Chambre l'iris, p. 160

8. Georg Harsd6rffer 1653 German Delitiae philosophicae et mathematica: Dritter Theil, Pt. 3, question 16, pp. 233-236c

9. John Tradescant 1656 English Musaeum Tradescantianumd

10. Jean Baptiste 1660 French Astronomia physica, in Operum Duhamel philosophicum, Vol. 1 (Nuremberg,

1681), pp. 38-40 11. William Petty 1662 English "Apparatus to the History of the Common

Practices of Dying"e 12. Robert Boyle 1664 English Touching Colours, Pt. 3, exps. 12, 17f 13. Andrd Felibien* 1666 French Entretiens sur les vies et sur les ouvrages

des plus excellens peintres, 2nd ed., Vol. 2 (1685), pp. 624-625

14. Johannes Scheffer* 1669 Swedish Graphice: Id est, de arte pingende, p. 158

15. Honor6 Fabrit 1671 French Phvsica, id est, scientia rerum

16. Isaac Newton 17. William Salmon

ca. 1671 English 1672 English

18. Zacharia Trabert 1675

corporearum, Vol. 2 (Lyons, 1671), pp. 64-80

"Optical Lectures," prop. 3g Polygraphice; or, The Art of Drawing,

Engraving, Etching, Limning, Painting, Washing, Varnishing, Colouring, and Dying (London, 1672), p. 229h

Nervus opticus (Vienna, 1690), pp. 16-17

629

Austrian




19. Walter Charleton 1677 English Appendix to Exercitationes de differentiis & nominibus animalium, 2nd ed., pp. 61-78 (third pagination)i

20. Francis Glisson 1677 English Tractatus, p. 52

21. Elias Brenner* 1680 Swedish Nomenclatura et species colorum miniatiae picturae (Stockholm, 1680)

22. Edme Mariotte 1681 French De la nature des couleurs, Vol. 1, p. 282 23. Filippo Buonanni 1684 Italian Recreatio mentis, et oculi in observatione

animalium testaceorum, pp. 59-60 24. Johannes Zahn 1685 German Oculis artificialis teledioptricus sive

telescopium (Wiirzburg, 1685), p. 113 25. Richard Waller 1686 English "Catalogue of Simple and Mixt Colours,"

Philosophical Transactions, 1686, 16:24-32, on p. 24

26. Georg Albrecht 1689 German Dissertatio optica de coloribus, Hamberger respondent C. F. Fischer (Jena, 1699),

p. 9

27. Willem Beurst 1692 Dutch De Groote Waereld in't kleen geschildert, p. 4

28. Nicolas Hartsoeker 1694 Dutch/French Essay de dioptrique, p. 44 29. Nicolas 1699 French Recherche de la verite (1712), in

Malebranche Oeuvres, ed. Andre Robinet, Vol. 3, p. 258j

30. Gerard de Lairesse* 1707 Dutch The Art of Painting in All Its Branches, 2nd ed. (1778), p. 119; trans. of Heet Groot Schilderboek (1707)

31. Anonymous*k 1708 French Traite de la peinture en mignature, pp. 152-153

NOTE.-This table indicates those who adopted the painters' primaries; no attempt was made to dis- tinguish the significance of their support. From 1650 horizontal rules separate decades.

*Represents the country of activity rather than birthplace. 'Indicates a Jesuit; Jesuits played a relatively large role in diffusing the primaries on the Continent. *Indicates a member of the arts community; all others are natural philosophers, naturalists, or phy-

sicians. aDiscussed in note 17. bDiscussed in the text at note 19. CDiscussed in the text at note 22. dReprinted in Mea Allen, The Tradescants: Their Plants, Gardens, and Museum, 1570-1662 (London:

Michael Joseph, 1964), p. 263. eQuoted in the text at note 33. fQuoted in the text at note 34. gQuoted in the text at note 38. Newton's "Optical Lectures" were published in 1728 and 1729, but

they were available in the Cambridge University Library from 1674. hWhile Salmon is following Boyle here, earlier in the Polygraphice (p. 124) he reported five chromatic

primaries. 'Discussed in the text at note 55. jDiscussed in the text at note 57. kOn the authorship see note 57.

630

