the ocular harpsichord of louis-bertrand castel - Gewina

THE OCULAR HARPSICHORD 

OF LOUIS-BERTRAND CASTEL 

The Science and Aesthetics 

of an Eighteentii-Century Cause Celibre 

Maarten Franssen 

Introduction 

Some inventions need never leave the drawing board and materialize in order to 

leave their marks on the cultural environment. The ocular harpsichord of Louis- 

Bertrand Castel (1688-1757), designed to produce a music of colours, certainly 

seems to have been such an invention. But although a number of studies have 

been dedicated to the instrument,' it has never been undertaken to systematically 

trace the extent of its impact on contemporary thought and to follow its 

appreciation in the world of science and as part of the gradual evolution of 

eighteenth-century aesthetics towards early Romanticism. The instrument has 

mostly been treated as the isolated invention of a crank. Only very rarely has it 

been recognized that, during the greater part of the eighteenth century following 

its announcement, the idea occupied the minds of many more people than just 

its inventor. An early and not very well known example is the work of the 

historian of literature Von Erhardt-Siebold, whose extensive study of the sudden 

emergence of synaesthetic imagery in early Romantic English poetry led her to 

surmise a wide diffusion of Castel's ideas on colour harmony. Although she had 

not read any of Castel's own writings, she stated: "I see the ocular harpsichord 

' Weliek, "Farbenharmonie und Farbenklavier"; Schier, Castel; Chouillet-Roche, "Le clavecin 

oculaire." Neither Scliier nor Chouillet-Roche knew the articles by Weliek, although it is from his 

work that one learns the most about the repercussions throughout Europe of the harpsichord. 

Schier, on the other hand, seriously misjudged the situation. His book, although very informative on 

Castel's life, is of little value as regards the ocular harpsichord. Chouillet-Roche concentrates on the 

outfit of Castel's instrument. Needless to say, I owe source references to all three of them. 

Tractrix 3, 1991, pp. 15-77

16 Maarten Franssen 

as the direct stimulus of the use of synaesthetic imagery in literature."^ Such a 

hypothesis is, of course, extremely difficult to prove. What I intend to do in this 

study is rather to chart the responses to the ocular harpsichord throughout the 

eighteenth century, and thereby discover what support there is for another 

conjectural assertion of Von Erhardt-Siebold, that "the ocular harpsichord 

counted as an invention that one had to come to terms with, and even while it 

was mostly rejected, even by the Romantics, as a practical instrument, there was 

wide recognition of the basic ideas behind it".' First, however, it is important to 

consider how scientific and aesthetic arguments intermingled in Castel's own 

defense of his instrument and, even, whether there ever was an ocular harpsichord. 

Castel's professional career* 

The history of Castel's ocular harpsichord 

When Louis-Bertrand Castel announced his "invention" of the ocular harpsichord 

in 1725 he was by no means a unknown man. Born in MontpcUier, he had 

entered the Jesuit Order when he was fifteen years old, and after finishing the 

fecole Saint-Stanislas in Toulouse he had taught for some time at various Jesuit 

colleges in the south of France. He developed a keen interest in mathematics 

and physics, and some of his writings on these subjects were read in Paris by 

Fontenelle, then secretary of the Academic Royale des Sciences, and by 

Tournemine, editor of the Memoires pour I'Hisloire des Sciences el des Beaux 

Arts, which was meant as a Jesuit counterpart to the Gallican Journal des 

Sqavans. Its title was universally abbreviated to Memoires de Trevoux or Journal 

de Trevoux, because it was published in Trevoux, capital of the formally 

independent principality of Dombes, near Lyon, to avoid the royal monopoly on 

journals. Both Fontenelle and Tournemine persuaded the general of the Jesuit 

Order to have Castel sent to Paris, where he became a teacher at the Coll6ge 

Louis-le-Grand in a wide range of subjects, including mathematics, mechanics, 

optics, pyrotechnics, "I'horlogerie" and civil and military architecture. In addition, 

he took place in the team of editors of the Memoires de Trevoux, where he 

remained the sole expert in mathematics and physics from 1720 until his 

resignation in 1746, when the journal was ordered to embark on a more 

Von Erhardt-Siebold, "Synasthesien," p. 51. 

'/bid., p. 44. 

Most facts about Castel's early career come from his eloge in the Memoires dc Trh'oiix, 

reprinted in Esprits, saillies et singularites, pp. v-xxxii. I"or Ostel's life in general, see Schier, Castel.

Castel's ocular harpsichord 17 

outspoken anti-Enlightenment course by its Jesuit superiors. 

It is not very clear to what extent Fontenelle really was involved in fetching 

Castel to Paris. Maybe he thought that Castel could come up with some new 

arguments against the increasingly popular Newtonian philosophy, which 

Fontenelle, as a follower of Cartesian physics, opposed. One of Castel's feats 

seems to have been that he had struggled through Newton's Principia and copied 

it word for word. Castel's highly unorthodox views on mathematics and physics, 

however, estranged him from the fellows of the Academic des Sciences, and he 

lost contact with Fontenelle after 1730. Nevertheless, Fontenelle managed to 

introduce Castel into the high life of Paris, especially the salon of Madame de 

Tcncin, whose lover Fontenelle had been for some time. Apparently la vie 

mondaine was not lost on Castel, as he became the one to introduce Rousseau 

to Madame de Bezenval and Madame Dupin on his arrival in Paris in 1742. 

After Castel's breach with Fontenelle the role of his protector was taken over by 

Montesquieu, whose son was Castel's pupil at Louis-le-Grand. Partly through 

Montesquieu's influence Castel became a foreign member of the Royal Society 

in 1730 and later a member of some French provincial academies. His relationship 

with Montesquieu was so close that the latter sent for Castel in his dying 

hour, after being asked whom it was he trusted most. It gave Castel enormous 

satisfaction to have been able to save Montesquieu's soul. 

In 1724 Castel's interest in physics had resulted in his first book, the monumental 

Traite de physique sur la pesanteur universelle des corps. It attracted 

much attention, especially as it was thought at that time that the cause of gravity 

remained the main mystery in physical science, and it was reviewed rather 

friendlily in the Journal des Sqavans, although the reviewer clearly did not quite 

know what to make of Castel's exuberant style of writing. From this book one 

gets already a clear picture of Castel's scientific opinions, which he did not 

change for the rest of his life: he had no trouble with the doctrines of mechanicism, 

that the physical processes in the world are just matter acting directly on 

matter. It was only the free will of man that formed no part of the mechanical 

universe (but, and that was Castel's own peculiar solution to the problem of 

gravity, he gave free human action an enormous physical efficacy). What he 

totally rejected, however, was the core of the Newtonian achievement: the direct 

application of mathematics to physics. He certainly acknowledged that Newton 

was a briUiant mathematician, but just that made him a bad physicist. It was 

Castel's opinion that 

physics in itself is simple, natural and easy, that is, easy to understand. Its terms are known, its 

objects are known. We observe and prove the majority of things naturally ... Everyone is to 

some extent a physicist ... Geometry, on the other hand, is all abstract and mysterious as to its


objects, its methods, and even its terms. With Newton, this order is reversed.^ 

This view is not wholly different from the general outlook of mechanicism, which 

can be said to make the ontology of everday life into the ontology of the physical 

imiverse, but with Castel it was very outspoken and even had some religious 

overtones. In a review of the French edition of Nieuwentijt's book Het regt 

gebruik der wereltbeschouwingen [Tfte right use of contemplating the works of the 

Creator] Castel remarked: "It is in the simple and naive account of nature as 

everyone knows it, that one has to look for demonstrations of the existence of 

God. Nature shows enough marvels to the eyes of all kinds of people, and there 

is no need to borrow ambiguous traits from Descartes or Newton to embellish 

the work of God."*" This way of thinking, keeping as much as possible to the 

surface of things, pervades all Castel's writings, including his ideas on colour 

music. 

Although Castel was the science editor for the Memoires de Trevoux, his 

first article on the ocular harpsichord appeared in another journal, the Mercure 

de France, which was more or less the official cultural magazine of France. It 

also published extensively on scientific subjects, however, - a clear indication of 

the swiftly rising popularity of science in the eighteenth century. It published a 

long debate on the cause of the tides, induced by Castel's La theorie de physique 

sur la pesanteur universelle, but also a laudatory letter on the book from Joly, 

avocat to the parliament of Paris, of no less than 47 pages.^ The Mercure always 

remained very friendly towards Castel, and called his 1743 critical book on 

Newton, for instance, "the work of a genius".* This attitude that probably 

mirrored the personal opinion of Antoine de La Roque, its editor in chief from 

1721 to 1744. 

Castel, Lf \rai systeme, p. 6: "L.a Physique est de soi simple, naturelle & facile, je dis facile a 

entendre. On en sait les termes, on en connoit les objets. Naturellement nous observons. & nous 

^prouvons la plupart des choses ... Tout le monde est un peu Ph>'sicien ... Au lieu que la 

Geometrie est tout abstraite & mysterieuse dans son objet, dans ses faqons, jusque dans ses termes. 

Chez Newton, cet ordre est renversc." 

Memoires de Trivowc. April 1726, pp. 607-608: "C'est dans I'histoire simple & naive de la 

nature telle que tout le monde la rcconnoit, qu'on doit puiser des demonstrations dc I'existence de 

Dieu. La Nature etale assez de merveilles aux yeux de toutes sortes de gens, sans etre oblige 

d'emprunter de Descartes ou de Newton des traits equivoques pour embellir I'ouvrage de Dieu." 

''Mercure de France, April 1725, 669-695; May 1725. 857-876. 

Mercure de France. November 1743, p. 2444. ITie book meant is Le vrai systeme de physique 

generate de M. Isaac Newton.

The first announcement of the ocular harpsichord 


It was in this context that there appeared in the Mercure de France of November 

1725 a letter from Castel directed to the otherwise unknown Monsieur Decourt 

of Amiens, entitled "Clavecin pour les yeux, avec Part de peindre les sons, et 

toutes sortes de pieces de musique.""* In this letter, Castel set out to prove that 

there was an analogy between the phenomena of sound and light, and between 

tones and colours, such that what had up till then been performed only with 

sound, that is, arranging different tones in such a way that we appreciate the 

effect as a form of art, should be equally possible by arranging different colours, 

so that a whole new form of art would emerge, a music of colours. 

Castel motivated the analogy between .sound and light by the supposition that 

both were vibrational phenomena. By way of a rhetorical question he wondered 

whether "sound and light do not equally consist in the insensible wigglings of the 

sonorous and luminous bodies, and of the media that transmit them to our ears 

[and to our eyes]?"'" And as tones are modifications of sound and colours are 

modifications of light, this implied an analogy between tones and colours. For 

arguments for this view he did not refer to one of the then current light theories 

of Newton, Malebranche or Descartes, but to the work of his Jesuit predecessor 

Athanasius Kircher, whom Castel on a later occasion called "my true, my first, 

and as it were my only master"." From Kircher Castel derived a number of 

observational analogies between sound and light: they both are reflected by 

plane surfaces; both can penetrate into denser media and are refracted in the 

process; and both can be concentrated in a focus by a hollow mirror. Moreover, 

the speaking trumpet or ear trumpet, Kircher's own invention, seemed the 

perfect analogue of the telescope. These observations sufficiently supported the 

hypothesis that sound and light were manifestations of the same kind of physical 

process. 

It was already Kircher who had concluded that, if this were true, there had to 

be an analogy between the art forms of tone and colour. According to Kircher: 

"If, when a musical instruments sounds, someone would perceive the finest 

movements of the air, he certainly would see nothing but a painting with an 

extraordinary variety of colours." And again: "The colours also have their 

harmony, which pleases no less than music, and this analogous harmony even 

"* Mercure dc France, November 1725, pp. 2552-2577. 

Ibid., p. 2557: "le son & la lumiere ne consistent-ils pas egalement dans les tremou-ssemens 

insensibles des corps sonores & lumineux. & du milieu qui les transmet jusqu'a nos oreilles?" 

Memoires de Trewtix. October 17.35, p. 2033: "mon veritable, mon premier, & comme mon 

unique Maitre".


has a very strong power to excite the affects of the mind."'^ Castel cited these 

passages with delight, and added examples of his own of how painters talked 

about colour tones and dissonances of colours and musicians about the design of 

a composition and the figures of a song. 

Apart from Kircher, Ca.stel mentioned a second authority for his cherished 

analogy: the Opticks of Newton, the French translation of which he had recently 

reviewed for the Memoires de Trevoux}^ As is well known, Newton had 

distinguished seven distinct colours in the spectrum, i.e. red, orange, yellow, 

green, blue, indigo and violet, and in Proposition III of Part II of Book One he 

recorded his measurements of the space that each colour occupied in the 

spectrum. He then mentioned that these relative widths corresponded exactly 

with the differences in the length of a string when it sounded the succesive notes 

of the diatonic scale. Newton, however, gave no clue whatsoever to what was to 

be concluded from this correspondence. Castel could not fail to notice this: 

"Here is all the analogy that this great geometrist has managed to find between 

the tones and the colours; where does this analogy lead to, where does it come 

from? I do not get any the wiser about it."'^ Nevertheless, it was clear that any 

colour music needed a colour-musical scale, and Castel was quick to adopt 

Newton's succession of colours as a scale with violet as its fundamental tone.'' 

That Newton had explicitly rejected any physical analogy between light and 

sound, mainly because he thought that treating light as vibrations of a medium 

was incompatible with the rectilinear propagation of light, seems not to have 

bothered Castel. 

Of course, Castel admitted that the analogy between tones and colours was 

not perfect. A tone is in practice a fleeting thing, while a colour is something 

Kircher, Musurgia, vol. 2, p. 240 rcsp. 223: "si enim quispiam subtilissimas aeris motiones, 

dum aliquod instrumentum musicum resonat, cerncret; certe is nihil aliud, quam picturam 

aliquam insigni colorum varietate adumbratam viderel"; "r.st enim & coloribus sua harmonia, quae 

non minus quam Musica recreat atque haec harmoniarum analogia maximam in concitandis animi 

affectibus vim possidet." 

Memoires de Trevoux, August 1723, pp. 1428-1450. 

Castel, Optique des couleurs, p. 162: "Voila loute lanalogie que ce grand Geometre a jamais 

trouvee entre les sons & les couleurs; a quoi va cettc analogic, & d'ou vient-elle? je n'cn sâis 

rien." It has always remained something of a mystery why Newton decided on exactly these seven 

colours; in other parts of the Opticks he mentions a division into only five. In an interesting article. 

David Topper has argued that Newlon introduced two extra colours for aesthetic reasons, to obtain 

a more even distribution of the colours. The analogy with the musical scale later strengthened him 

in this decision. See Topper, "Newton," 

' Mercure de France, July 1726, pp. 1542-1543. Câstcl didn't notice that Newton compared his 

colours to a minor scale, whereas he himself suppo.sed a major scale. It is interesting that Kircher 

already had compared the twelve tones of the chromatic scale with twelve colours, but Castel never 

referred to this solution. See Musurgia, vol. 1, p. 5f)8. Maybe this is because Kircher's correspondences 

are obviously inconsistent; see Weliek, "Renaissance- und Barock-Synasthesie," pp. 549-559.


permanent. Moreover, in a musical piece the different tones merge into one 

whole, while in a painting the different colours stay clearly separated. But this 

difficulty could easily be overcome: admittedly it was impossible to make tones 

permanent, but colours could be made transient. Although this would diminish 

the perfectness of colours as such, it would increase the perfection of the works 

of art which were produced by the use of colours.'* To achieve this, Castel 

proposed to take an ordinary harpsichord, but to change the mechanism so that 

"the pressing of the keys would bring out the colours with their combinations 

and their chords; in one word, with all their harmony, which would correspond 

exactly to that of any kind of music"." 

Perhaps some sceptics would question whether it would be in any way 

agreable to look at the succession of these single colours or combinations of 

colours. Castel, however, was convinced that we would enjoy colour music even 

more than we did ordinary music. For we do not particularly enjoy hearing a 

single tone, but we indeed enjoy the ensemble of many different tones. On the 

other hand, we certainly do enjoy the sight of one single colour, so how much 

more would we enjoy the interplay of many different colours! It is pre-eminently 

the continuous change of impressions that gives us the most enjoyment, according 

to Castel, and that is why we enjoy a piece of music more than a painting. 

The ocular harpsichord would, then, elevate the art of colour to the same level 

of enjoyment as music gives us: "The principal advantage of this new harpsichord 

is thus to give to the colours, apart from their harmonic order, a certain vivacity 

and lightness which on an immobile and inanimate canvas they never have."" 

But even when we discard the element of time, we could conceive of a specific 

painting as a complete analogue of a certain musical composition, reflecting its 

tonality, its harmonies and its structure and design, so that all these aspects of 

the composition could be contemplated at leisure: 

And be convinced that these emotive spots, these main harmonic lines, these inexpected 

changes of tone, which at any time cause detachments, yearnings, emotions and a thousand 

different transitions in the soul that abandons itself to them, change nothing of their force and 

their energy when passing from the ears to the eyes and from music to painting, which can thus 

Mercure de France, November 1725, pp. 2562-2565. 

Ibid., p. 2568: "le mouvement des touches fasse paroitre les couleurs avec leurs combinaisons 

& leurs accords; en un mot, avec toute leur harmonic, qui corresponde prccisement a celle de 

toute sorte de Musique." 

Ibid., p. 2573: "Le principal avantagc de cc nouvcau Clavecin, est done de donner aux 

couleurs, outre I'ordre hamionique, une certaine pointc de vivacite & de legerete qu'elles n'ont 

jamais sur une toile immobile & inanimee."


rightly be called, by a better name than it has carried so far, a mute music. 

In a follow-up article some months later, Castel tried to establish the principles 

of his colour music more geoinetrico^ It was generally accepted that the 

•vibrations of the air that constitute the different tones of music cause vibrations 

in our ear, and that, when different tones combine, our soul experiences 

pleasure if the ratios of the rates of vibrations of the different tones are simple 

rational numbers. For instance, in an octave the two notes vibrate with a ratio of 

2:1, and in a fifth with a ratio of 3:2. Castel argued that this was how all our 

senses functioned. According to him it was a consequence of the philosophy of 

mechanicism that external objects can only cause regular or irregular vibrations 

or undulations in the membranes of our body. Following this line of argument, 

he arrived at the following "Principal proposition. So the pleasure and displeasure 

of all our senses consists in the same sort of vibrations, that is, in vibrations in 

harmonic proportion." Evidently, colour harmony had to be a fact, because 

"without it, nothing could please us, and evcrvlhing would be very unpleasant to 

us, just as a completely dissonant music."^' This meant, of course, that there 

could also be a music of flavours, a music of scents and a music of touches. 

Castel acknowledged this wholeheartedly: 

p. Take some forty scent bottles filled with different perfumes, cover them with valves, and 

arrange them .so that the pressing of the key^ open these valves: there you are for the nose. 2". 

On a board arrange objects that can make different impressions on the hand, and then let the 

hand come down on each of them: there you arc for the touch. 3°. Arrange likewise some 

objects that taste fine, interspersed with bitter objects. But am I talking to people who have to 

be told everything?^ 

Ibid., pp. 2575-2576: "lit croyez-vous que ccs endroils pathetiques. ces grands traits d'harmonie, 

ces changemens inesperez de tons, qui cau.sent a tous momens des suspensions, des langueurs, 

des emotions, & mille sortes de peripcties dans I'ame qui s'y abandonne, perdent rien de leur 

force & de leur energie en pas.sant des oreilles aux yeux, & de la Musique a la Peinture, qui 

desormais pourra etre appellee a bien plus juste titre qu'clle ne I'a 6t6 jusqu'ici, une Musique 

mucilc". 

Mercure de France, February 1726, pp. 277-292. 

Ibid., pp. 286-287: 'Propos. principa/e. Done Ic plaisir & le dcplaisir de tous nos sens consiste 

dans la mcme espece de vibrations, c'est-a-dire, dans des \ibrations & [sic] proportion hamionique. 

... sans elle rien ne pourroit nous plaire, & tout nous seroit tres-desagreable. autant qu'une 

musique toute dissonante." 

Mercure de France. March 1726, p. 459: "1". Mctlez de suite une quarantaine de cassoletes 

pleines de divers parfums, couvrez-les de soupapcs, & faitcs en.sorte que le mouvement des touches 

ouvre ces soupapes: voila pour le nez. 2'\ Sur une planche, rangcz tout de suite, avec une certaine 

distribution, des corps capables de fairc divcrses impressions sur la main, & puis faites-la couler 

uniment sur ces corps: voila pour le toucher. 3°. Rangcz de mcme des corps agrâbles au gout, 

entremclez de quelque amertume. Mais paHai-je a des gens a qui il faille tout dire'.'" In 1755 

Polycarpe Poncelet published his botik Chimic du goui ci dc I'odorat, in which he proposed a


From a modern point of view it is interesting that Castel also argued for the 

possibility of an "auricular prism", which would be able to separate the different 

notes of a musical chord, and which he fruitlessly tried to construct for some 

time.^'' 

Castel's proposal of a colour music and an ocular harpsichord was greeted 

enthusiastically in the Mercure de France by a M. Rondct, who gave some 

concrete ad'vise concerning the actual construction of the harpsichord. He 

suggested that one make as many coloured windows in the case of the instrument 

as il had keys and place a strong light in the case. Normally the windows 

would be covered by a screen, but when a key was pressed, the corresponding 

screen would swing over and the lighted window would become visible. If 

desired, all kinds of mirrors could increase the effect.^ (Rondct's enthusiasm 

for the whole idea seems to have been so great that he was still defending the 

instrument in 1755.^^) It is less clear how seriously Castel himself took the 

problem of constructing a real ocular harpsichord. In his first article he wrote 

that he wanted "in the style of Socrates, the demonstration to precede the 

proposition and the construction of the thing ... since it is not as an artisan but 

as a philosopher that I set out to demonstrate you this new art."^ Much later, 

he remarked on this original period: "It was only an idea, and I had no intention 

of executing it."" And indeed, just the effect of the prism seemed enough to 

satisfy his chromatic appetite: 

One day, when the sun was shining brightly, having shut all windows of a room and having 

placed four or five prisms in front of some holes that I had made in the shutters, making them 

turn incessantly, I watched on the opposite wall a moving tapestry which, without any other 

concert of harmony, presented me with the most agreeable spectacle that I could remember 

having ever seen or heard.^ 

harmony of flavours along Castel's lines. His major diatonic scale was: sour, bland, sweet, bitter, 

sweet-and-sour, tart, hot. For scents he failed for want of a sufficiently refined terminology. See 

Chouillet-Roche. "Clavecin oculaire", p. 165. 

"/ft/rf., p. 463. 

Mercure dc France. April 1726, pp. 650-660. 

^"^ Ibid., April 1755, pp. ir>0-163. 

//)((/., .November 1725, pp. 2554, 2561: "Je veux mcme, en stile de Socrate, que la demonstration 

precede la proposition & la construction de la chose ... car ce n'est pas en artisan, mais en 

Philosophc que j'ai entrcpris de vous dcmontrer ce nouvel art". 

Ibid., July 1755, p. 147: "ce n'etoit en effel qu'une idee, & je n'avois nulle intention de 

Texccuter." 

Ibid., March 1726, p. 461: "Un jour ayant ferme toutes les fenctres d'une chambre que le 

Soleil eclairoit. & mis aux trous que j'avois fails dans les volets quatre ou cinq prismes qu'on 

faisoit tourner sans cesse, je vis sur la muraille opposee une tapisserie mouvante, qui sans autre 

concert d'harmonic. me donna le plus agreable spectacle que je me souvienne d'avoir jamais vu ni


77ie resumption of the project 

So it is perhaps not strange that nothing more was heard of the ocular harpsichord 

for ten years. Nevertheless, the instrument kept haunting Castel. When he 

was reading Felibien's Entretiens sur la vie et les ouvrages des plus excellents 

peintres anciens et tnodemes and noticed the author's complaint that the theory 

of painting lagged far behind the theory of music, and his remark that the 

painter Poussin had also thought about "I'art harmonique des couleurs", he 

decided to elaborate his invention. There was also the fact, however, that he had 

increasing doubts on the Newtonian colour scale. It seemed implausible that 

violet could play the role of fundamental tone, since this colour was in practice 

always produced by mixing red and blue. Therefore he set out in 1734 to 

perform a number of systematic experiments on colours, with the assistance of a 

painter friend. He published his conclusions from these experiments in a 321- 

page article in the Menioires de Trevoux, in the form of a letter to Montesquieu, 

who had urged him to make his new ideas public.^ 

Castel's starting point was to take the analogy between the tone scale and the 

colour scale as literal as possible. Between the two tones that together form an 

octave, there is a continuum of possible vibration rates, but we discern only a 

limited number of distinct notes, that is, we intcrprete any arbitrary tone as one 

of the twelve notes of the chromatic scale. According to Castel, our observation 

of colours is subject to the same rule; although all colours continuously merge 

into each other, we di.scern only a limited number of distinct colours. Then, if 

the Newtonian colour scale violet-indigo-blue-green-yellow-orange-red were the 

true analogue of the diatonic scale, the transition blue-green would correspond 

to the smallest possible interval E-F, which would imply that we do not discern a 

separate colour between blue and green. And this, according to Castel, is simply 

false; between blue and green is celadon. (Observe that Castel here made the 

mistake of taking the Newtonian colours for the scale in C major, although 

Newton had compared it with the scale in D minor.) This way of comparing the 

internal relations of the colours with the tone intervals was the clue to the 

construction of the true chromatic colour scale. Because red, yellow and blue 

would surely be part of this scale, it sufficed to determine how many distinct 

colours there were between red and yellow, between red and blue, and between 

yellow and blue. 

Miraculously, there turned out to be exactly twelve distinct colours: blueentendu." 

"Nouvelles experiences d'optique et d'acoustiquc," Memoires de Trewttx, August 1735. pp. 

1444-1482; August 1735, 2me partie, pp. 1619-1666; September 1735, pp. 1807-1839; October 1735, 

pp. 2018-2053; November 1735, pp. 2335-2372; December 1735, pp. 2642-2768.


celadon-green-olive-yellow-fallow-nacarat-red-carmine-violet-agate-violaceous, 

representing a direct analogue of the chromatic scale in music.^ Castel's next 

step meant a departure from music, however. Instead of permitting every colour 

to be the possible root tone of a major or minor scale, he wanted an absolute 

colour-tonic, and argued that this place was occupied by blue, the basse fondamentale 

of nature, because we see all colours in nature against the background 

of the blue sky." To make the departure from music seem less radical, 

however, Castel argued that in music there is also an absolute tonic, fixed by the 

range of the human voice, and this tonic was the standard C. Again miraculously, 

making blue the absolute key-colour resulted in the most perfect analogy 

possible: the three most important notes in the scale - tonic, dominant or fifth, 

and third - were now... blue, red and yellow. It was known that all colours could 

indeed be produced by mixing blue, red and yellow. And was not red indeed the 

dominant colour of nature, and had not the note G "something of the warrior, of 

anger, something bloody, something flamboyant"?'^ And was not, on the other 

hand, the interval F-B the most difficult to sing, and the corresponding colour 

interval fallow-violaceous a combination of "colours that are very undetermined 

and difficult to grasp"?'' 

Even this perfection did not yet satisfy Castel. Five years later, in his Optique 

des couleurs, he combined this colour scale with the chiaroscuro to solve the 

problems of different octaves. Just as all tones are posited between the silence 

below the lowest tone and the silence above the highest tone, so all colours are 

between the two "colourless colours" black and white. By adding the chiaroscuro, 

we can think of the colours as moving from black to white, in the sequence of 

the colour scale, such that when we have completed one octave the octave 

colour is one "chiaroscuro unit" lighter than the prime. By a similar process as 

had been used to discover the number of distinct colours in the scale, Castel 

established that there were exactly twelve full octaves of different chiaroscuro 

shades between black and white. This meant that the ocular harpsichord needed 

a keyboard of 144 or 145 keys. But the introduction of chiaroscuro also served 

another purpose for Castel: as blue is always the darkest colour of any three 

equally dark red, yellow and blue, according to Castel, and as the darkest blue is 

darker still than the darkest red or the darkest yellow, we can be extra sure that 

The French names used by Castel are bleu-CLiadon-verd-olive-jaune-fauve-nacarat-rougecramoisi-violct-agathe-violani. 

For violani Castel sometimes put gris-bleu. 

Memoires de Trevoux, August 1735, 2me partie, p. 1663. 

32 

Ibid., September 1735, p. 1830: "quelque chose de guerrier, de colere. de sanglant, de 

flamboyant". 

Ibid., August 1735, pp. 1474-1475: "des couleurs fort indccises & fort difficiles a attraper, 

aussi difficiles que le/a si triton dissonant est difficile a sentir & a entonner."

26 Maarten Frans.sen 

blue is the absolute fundamental tone of the colour scale. 

Obviously, this solution to the scale problem of colour harmony meant a 

complete breach with the Newtonian theory of equivalent primary colours. As 

Castel was quick to admit, "if the system of Mr Newton is true, mine will be 

turned on its head, there is no ocular music, harmony or harpsichord: and 

everything I have said so far is nothing but a beautiful chimaera".'^ Up till then, 

Castel's criticisms of Newtonian optics, as he voiced them for instance in his 

review of Newton's book in the Menunres dc Tri-vtuix^^, were in line with his 

rejection of the mathematization of nature. He scorned, for instance, Newton's 

introduction of the term "refrangibility", as a concept that explained nothing. 

After 1735, however, he was forced to reject Newton's experimental results as 

well. The solution to this problem presented itself in 1739, when a letter directed 

to him was published in the Metnoires de Trevoux which suggested where 

Newton had gone wrong. In fact, it happens to be identical to the later critique 

of Goethe. Newton had not looked well enough at his spectrum, argued this 

anonymous amateur physicist. The green in the spectrum is only visible at some 

distance from the prism; when you observe the outcoming rays directly behind 

the prism, the middle of the spectrum is not green but white. His suggestion was 

that the colours only arise at the edge of the white ray when it passes through 

the prism: in the shorter passage arise red and yellow, in the longer passage blue 

and violet. The yellow from the upper end and the blue from the lower end 

converge, and so produce green at some distance from the prism.'* 

Castel enthusiastically declared this solution to be the obvious and right 

one.'^ If no suspicious questions were asked about the violet (it was just the 

result of the overflow of some red), the result was that the prism did in fact only 

produce the three desired main colours blue, red and yellow. A load had been 

taken off Castel's mind: 

Ibid., October 17.35, p. 2033: "si le sisteme de M. Newton a lieu, tout le mien est renversfi de 

fond en comble, il n'y a ni musique, ni harmonic, ni clavecin de couleurs: & tout ce que j'en ai dil 

jusqu'ici n'est qu'une belle chimere". 

'^ Ibid., zXugust 1723, 1428-1450. 

The letter was reprinted in Castel's Optique des couleurs, pp. 353-369. The whole proposal is 

completely identical with Goethe's later one. The cause of all this confusion is, of course, that if 

one makes the beam of white light that enters the prism tcx) wide, or if one fails to make an 

incoming diverging beam converge by interposing a len.se (as Newton was careful to do), there will 

be an overlap of different spectra beyond the prism, causing white in the middle and leaving 

prismatic colours only at the edges. Note also that Newton himself had already pointed out that, for 

instance, primitive green light, or rather "greenmaking" ra>'s, is something different from the 

mixture of primitive blue and yellow causing the sensation of green, and that a prism can always tell 

the one from the other. See the Oplicks, Book One, Part 11, Propositions IV and VIII. 

• See Castel's reaction to the anonymous writer in Optique des couleurs, pp, 370^6.


... the great Newton, how could he have been so deeply wrong, and with that apparatus and that 

fuss that impresses the wise and keeps the universe in admiration and as it were enslaved by its 

brilliant spectrum of seven colours, no more, no less'.' ... I had challenged the prism and its 

fantastic spectrum ... I regarded it with terror, as if it were a reef signaled by the wreckage of a 

famous ship, followed by a thousand ships that had come to share its disaster, while collecting 

its debris.'* 

In his later book on Newtonian physics in general, Castel tried to give a theoretical 

foundation to his critique of Newton's optics.** He presented some objections 

against the emission theory of light (he had never discussed it before). For 

instance, it could not explain how objects could have a blue colour; if the surface 

of an object absorbs the larger and heavier red light-particles, it will surely also 

absorb the smaller blue light-particles, instead of reflecting them. Referring to 

Malcbranche's theoiy, in which light is a sequence of pulses, or a vibration, in a 

special medium, the aether, Castel argued that both white and coloured light arc 

vibrational phenomena. White light is a single, longitudinal vibration, and 

coloured light results when a second transverse vibration is added to the 

vibration of white light. In such a model, where coloured light is a modification 

of white light, it is conceivable that the light that passes through a prism gets 

coloured only at the edges; in the middle of the beam the transverse vibrations 

annihilate each other, while they can survive at the edges.'*" 

Castel's attempts actually to build an ocular harpsichord 

In neither the "Nouvelles experiences" nor the Optique des couleurs did Castel 

seriously discuss the actual construction of an ocular harpsichord. In his 1735 

article he ended with an enormously elaborate extension of his earlier proof 

more geometrico of the po.ssibility of colour music, building it into a complete 

"logique du gout" with eight principal propositions and 73 theorems, and finally 

lost himself in a delirious enumeration of all possible kinds of colour enjoyment. 

Nevertheless, from some occasional remarks it becomes clear that Castel had 

Ibid., pp. 373-374, 376-377: "le grand Newton, pourquoi & comment a-t-il pu s'y tromper 

solemnellement. & avec cet appareil & ce fracas qui impose aux sages, & tient tout I'univers dans 

I'admiration & prcsque dans I'esclavage de son spectre essentiellement brillant de 7 couleurs, ni plus 

ni moins? ... Je me defiois du prisme & de son spectre fantastique ... Je le regardois avec terreur, 

comme un ecueil signale par le naufrage d'un vaisseaux fameux, suivi de mille vaisseaux, qui 

venoient a I'envi partager .son desastre, en recueillant ses debris." 

39 

Castel, Le vrai systeme, pp. 421-500. 

40 

Ibid., pp. 501-507. Malebranche had included the first version of his theory in the 1700 edition 

of his De la recherche de la verite, but presented a slightly but significantly changed version in the 

1712 edition, to make it compatible with Newton's prism experiments. See Hakfoort, Optica, pp. 60- 

63. Castel apparently had read, or digested, only the 1700 version.


worked, reluctantly, to construct at least a model for the harpsichord. Addressing 

Montesquieu, he wrote: "I was forced to make the first model, which you 

have seen." It was completed in 1734, on 21 December, 

the fete of Saint Thomas, to whom I have dedicated it, under the motto nisi videro, non credam 

... The sound movement consists in striking a tone during a certain time, and then silencing it 

to strike a second tone, and then a third tone, etc. The colour movement consists in making 

appear and disappear, by placing the fingers on the keyboard, a colour, any colour, and any 

series of colours sought for. This has been thought out. done, and will soon be perfect. There 

have been a thousand witnesses.'' 

This description does not give us much information on the exact mechanism that 

Castel had in mind, except that he now wanted it to be an ordinary and an 

ocular instrument in one. 

The history of Ca.sters ocular harpsichord after 1735 has to be painstakingly 

reconstructed from different sources.''' From them a picture emerges of a man 

gradually worn out completely by his own invention, although he kept believing 

in it to the last. In 1739 a letter was published in Hamburg by the composer 

Georg Philipp Telcmann, in which he sang praises of Castel's invention, which 

he had admired while on a visit to Paris. In his letter Telemann gave a relatively 

precise description, suggesting that the instrument was complete: 

To have it sound a tone, one touches a key with a finger and presses it, and thereby a valve is 

opened that produces the chosen tone ... At the same time, when the key opens the valve to 

produce the tone. Father Castel has fitted silken threads or iron wires or wooden levers, which 

by push or pull uncover a coloured box, or a ditto panel, or a painting, or a painted lantern, 

such that at the same moment when a tone is heard, a colour is seen. 

Memoires de Tre\'oiLX, pp. 2645, 2722-2723: "il m'en a fallu faire le premier modele que vous 

avez vu ... jour memorable de Saint Thomas Apotre, a qui je I'ai consacr^, sous le devise nisi 

videro, non credam ... l£ mouvement des sons consiste, a faire entendre un son pendant un instant 

plus ou moins long. & puis a le faire taire pour laisser entendre un nouveau son; & apres celuila 

un troisicme, &c. Ije mouvement des couleurs consiste a faire paroitre & disparottre, au gre 

des doigts poses sur un clavier, une couleur, & telle suite de couleur qu'on veut. Or cela est 

trouve, fait & bien-tot parfait. II y en a mille tcmoins." 

And not all sources are equally reliable. The story in the anonymous English leaflet 

Explanation of the ocular harpsichord from 1757, for instance (cf. Schier, Castel, p. 183). although its 

author claims to have been a close associate of Castel. is completely wrong in asserting that Castel 

did not work on the harpsichord at all between 1734 and 1754. 

' Telemann. Heschreibung. p. 264-265: "Um einen Klang horen zulassen leget man die Finger 

auf die Claviertaste, man tricket sie nieder, und indem sie sich vorn hinein sencket, Oder hinten 

aufhebet, offnet sie ein Ventil, das den begehrten Klang mittheilet ... Zu gleicher Zeit, wenn die 

Taste, um einen Klang zu haben. das Ventil aufmachet, hat der P. Castel seidene Schniire, oder 

eiseme Drater, oder holtzeme Abstracten angebracht, die durch zichen oder stoBen ein farbigtes 

Kastgen, oder einen dergleichen Facher. txler eine Schildercy, ixler eine helle bemahlte Lateme, 

entdecken, also daB, indem man einen Klang hciret, zugleich eine I'arbe gesehen wird."


Basically, it has all the features of the 1734 model. All the various alternatives 

that Telemann mentioned for his one instrument nevertheless make clear that 

Castel was still considering different possibilities, to be applied in a definitive 

version of the instrument. A letter from Castel to Montesquieu written in 1739, 

published in the Memoires de Trevoux, is evidence that Castel was indeed 

experimenting with lanterns: "You have seen my lanterns, tuned by colour 

degrees and light [chiaroscuro?] degrees ... With lanterns wonderful effects can 

be produced using glasses, horn, nettings, taffetas, oiled or rather varnished 

sheets of paper, especially when the lanterns are made as mobile as mine 

are."^ 

Still in the same year the Mercure de France published a poem by a certain 

Mr. Descazeaux, "Stances sur le mervcilleux Clavecin Oculair", containing such 

lines as: "What rapid course of shades! What accord in their differences! For my 

charmed eyes what a voice!"^' As four years had pa.ssed since Castel had last 

published on the harpsichord, it is implausible that Descazeaux would have sent 

his poem to the Mercure if he had not recently seen it, be it only a model, and 

been impressed by it. 

Again some years later, in July 1741, Georg Wolfgang Krafft, a member of 

the Imperial Academy of St Petersburg, received a letter from Paris, informing 

him of Castel's theory. The correspondent mentioned that Castel was busy 

building his harpsichord and had promised its completion before the end of 

1740. The design seemed to be suffering further changes, as it was reported that 

the original plan was to show coloured strips, but that Castel had replaced them 

by a painting containing coloured crystals, realizing the instrument "in modo 

theatri comici".'** The report from Paris, for that matter, induced Krafft to 

dedicate an official meeting of the academy to Castel's colour music, where he 

did away with the whole idea, as will be shown in the next section. 

Castel clearly did not hold to his promise for the end of 1740, but his 

optimism held ground. In 1745 the Englishman Alban Butler, visiting Paris in 

the retinue of his employer, the earl of Shrewsbury, saw the "famous instrument" 

in Castel's workshop, and his account makes evident that Castel was still far 

from his goal: "This instrument is not finished, and gives only three colours." 

Butler added circumspectly: "The father pretends to entertain hopes of making it 

Memoires de Trevoux, August 1739, pp. 1676, 1677-1678: "Vous avez vu mes Lantemes 

diapasonnces par les degrcs des couleurs & de lumieres ... Par mes lantemes sur-tout on peut 

faire des merveilles avec des verres, des comes, des gazes, des taffetas, des papiers memes huil^s 

ou plGtot vemis: sur-tout si Ton donnoit a ces I.antemes la mobilite qu'ont les miennes." 

Mercure de France, April 1739, pp. 768-769: "Quel rapide cours de nuances! / Quel accord 

dans leurs differences! / Pour mes yeux charmes quelle voix!" 

Weliek, "Farbenharmonie und Farbenklavier," p. 358.


complete."''^ In entertaining these hopes Castel even tried to make up with the 

members of the Academic des Sciences, with whom he had embroiled himself 

some twenty years earlier. As he wrote to Montesquieu in 1748: 

I wanted to appease them concerning ... my harpsichord, that I am making for real without 

money, without workers, without leisure, but which I am making anyway piano, sano. (It is quite 

true, this harpsichord; ... the preliminaries have already convinced some unbelievers; I will defy 

them all without much ado three or four months from now; not only is it possible, this 

harpsichord, but easy as well). 

In a PS he added: "I will not leave my room any more until I have perfected my 

harpsichord."^* In this letter we find the first mention of an obvious problem: 

money. 

The last phase of Castel's desperate attempts to complete the harpsichord is 

recorded in his manuscript "Historical and demonstrative journal of the practical 

execution of the ocular harpsichord", perhaps meant to be published just as the 

"Nouvelles experiences" had been published in 1735. The "Journal" is written as 

a series of letters to the Comte de Maillebois, who had been his pupil at Louisle-Grand 

and to whom he had finally run for rescue in 1751. The "Journal" can 

be dated to 1752. It shows a Castel who is now at the end of his wits; in the 

drafts there are up to eleven new starts of his account of the history of his 

invention, and intermittently he varies the story of his triumphs and complaints 

with fragments of poetry. Some passages breath an atmosphere of utter failure: 

The nature of things is diminished, agitated, inadequate. The whole game of the universe, just 

as that of the rainbow and of music, is in a minor key ... in violet, in black, or in semi-black. All 

of nature, all our arts, all our organs, all our senses, all our faculties are in mourning for their 

initial perfection. Everything is dcximed in our hands and around us, everything is in discord 

and in di.ssonance.'" 

Butler, Trawls, p. 65. Butler's cryptical description of the harpsichord says that "when you 

touch a string or key, to produce a particular note, the whole instrument evidently assumes the 

colour that corresponds to it by analog)". 

Montesquieu, Oeuvres, vol. 3, pp. 1157, 1158: "j'ai voulu les amadouer vis-a-vis ... de mon 

clavecin, que je fais dans le vrai sans argent, sans ouvriers, sans loisir, mais que je fais pourtant 

piano, sano. (II est bien vrai, ce clavecin; ... mes seuls apprcts ont deja convaincu quelques 

incredules; je les defie tous sans faôn dans trois ou quatre mois d'ici; non seulement il est 

possible, ce clavecin, mais desormais facile) ... Je ne sors plus de ma chambre depuis que je fais 

tout bon mon clacecin." 

Brussels, Royal Library Albert I, manuscript collection nr. 15746, f. 53: "La nature des choses 

est diminuee, affoiblie, enervee, infirmee. Tout le jeu de I'univers comme celui de Tare en ciel et 

de la Musique est mont^ dans le mineur ... en violet, en noir, ou demi-noir. Toute la nature, tous 

nos arts, tous nos organes, tous nos sens, toutes nos facultcs portent le deuil de leur premiere 

perfection. Tout est maudit entre nos mains et autour de nous, tout est en discorde et en 

dissonance,"


Apparently Maillebois had offered to pay for the manufacture of the harpsichord. 

Castel had received some financial assistance earlier: according to the 

anonymous leaflet Explanation of the ocular harpsichord the duke of Huescar, 

the Spanish ambassador, had offered him 1000 crowns in 1735, but somewhat 

later Castel "refused being at the head of a company, who came to offer him ten 

thousand crowns to be the chief director of it, on communicating his secret and 

ideas, and obtaining an exclusive patent".^ The same source says that Maillebois 

furnished 2000 ecus, or 85 louis d'or, for the instrument.^' According to 

the "Journal", Castel had told Maillebois he needed 100 louis d'or. In a desperate 

begging-letter to the wife of Maillebois, a draft of which has been preserved with 

the "Journal", Castel wrote that he had indeed received some of the promised 

sum, but that it added up to no more than 20 of the needed 100 louis. It took 

him some time to come to the point, but finally he admitted: "Let me tell you 

quite frankly. I need 15 louis immediately to avoid going bankrupt for my 

harpsichord, that is to say, for my honour, and perhaps for [the honour of] M. le 

Comte."''^ If the sum of 85 louis d'or is indeed what Maillebois spent, the 

instrument cost in 1751-1752 alone several year's wages of a skilled worker in 

Paris. 

What becomes most clear from the "Journal" was that Castel felt he had 

fallen into a trap, and filled with rancour he blamed his readers, his "public", for 

this: "After this time [1735] my feet indeed slipped from underneath me: I was 

led to believe that I wanted to make, and little by little that I was making the 

harpsichord ... The public has taken it too seriously."^' All that was left of 

Ca.stel was an old man sitting between the remnants of his models, none of 

which was capable of coming anywhere near VNhat he had had in mind for the 

performance of his instrument; there was nothing left for him but to "adjust and 

readjust the debris of my harpsichord to the taste of the pubHc".^ From a 

report he gives of a demonstration it becomes clear how completely his con- 

' Explanation, pp. 7, 10. 

' In fact, the gift is ascribed to the Marquis de Maillebois, Marshall of France and father of 

the Comte de Maillebois, "some years after" 1735 {Explanaiion. p. 7). My suspicion is that this is a 

mistake, mixing up father and son, as there is no reference at all in the "Journal" to anything 

Maillebois' father might have done for the harpsichord. To be sure, Castel had discussed matters 

from the art of war with the Marquis de Maillebois. 

Brussels, Royal Library zMbert I, manuscript collection nr. 20754, f. 28r-29r; "Laisscs moi 

vous le dire franchement. il me faudroit tout a I'heure 15 Louis pour ne pas faire banqueroute a 

mon clavecin, c'est a dire a mon honncur, et peut etre a m^ le comte." 

Ibid., ff. 22r resp. 3A-: "Apres cc tems il est vrai que le pied me glissa: on me fit accroire que 

je voulois faire et peu a peu que je faisois le clavecin. ... le Public au bout a fait trop d'honneur a 

mon affaire, il I'a pris trop au serieuse". 

Ibid., f. 19v: "j'ajuste et je rajuste desormais les debris de mon clavecin au gout public."


fidence had left him: 

... before proceeding on the grand scale, I wanted to make an experiment, a test piece, a model 

which would demonstrate in a moment the entire potential of the harmonic play of colours. I 

arranged everything for this demonstration, and in order to seriously satisfy the audience I had 

prepared transparant sheets and candles, colours and light, screens and valves, even drums and 

rattles with hammers in the style of Pythagoras ... and I went on to perform this terrible 

experiment, terrible for me who would suffer all the embarrassment of it. 

In these circumstances, a few sceptical remarks from the audience were enough 

to make Castel lose control of himself: 

After these barely but audible words I was seized by a kind of picturesque enthusiasm, and 

throwing my pencil in the face of the horse that did not labour according to my wishes [sic], I 

exclaimed No, I am not going to do it, this fatal experiment, because I declare it done; I am not 

going to finish the harpsichord, because it is finished, and thereby demonstrated to be feasible, since 

it only needs perfecting. Well, in this way I addressed the 80 or 1(X) people present to see and 

judge, all mature and enlightened people, the majority of them not knowing what to think of it. 

Castel only dared to show this audience the things he was still proud of, the 

models and textiles that had resulted from his colour experiments in the 1730s 

but "were lying worthless, covered with dust and cobwebs, rusting en falling 

apart, and disheartening me, not daring to believe that they could be presented 

to gentlemen, intelligent people but not acquainted with the actual fabrication of 

the organ or harpsichord."^'^ Clearly, since 1735-1740 no progress at all had 

been achieved. 

Nevertheless, Castel managed to organize a last dignified colour concert, 

reporting to the Mercure de France that the ocular harpsichord had performed 

for fifty people, who demanded four encores, on the day of its patron saint, 

Ibid., ff. 37v-38v; "avant que d'y prcxreder tout a fait en grand, je voulois faire une experience, 

un essai, un modele qui demontreroit en peu de tems et d'un coup d'oeil I'entiere possibility du 

jeu harmonieux des couleurs. je m'arrangeois en effect pour cette Demonstration, et j'avois tout au 

serieux et au bon du Public prepare des transparents et des Bougies, des couleurs et des lustres, 

des Paravents et des soupapes, des tambours meme et des cresselles avec des ma[r]teaux a la faôn 

de Pythagore ... et j'allois proceder a cette terrible Experience, terrible pour moi qui devois en avoir 

tout I'embarras ... A ces mots a demi et trop entendus, saisi moi meme d'une sorte d'enthousiasme 

pittoresque, et jettant le Pinceaux au nes du cheval qui ne renifloit bien son ecume a mon gri non 

je ne le ferai point, ai je dit, cette experience fatale, car je la declare faite; non je ne ferai point le 

clcnecin, car il est fait, et par consequent demontre possible a faire, puisque ce n'est qu'a refaire et 

parfaire. Or j'ai dit cela a 80 ou 100 personnes assemblees pour voir et juger, tous gens murs et 

eclair6s, la pluspart ne sachant jusques la qu'en penser. ... elles restent la en non valeur dans des 

tas de poussiere, d'araignês, de rouille, de delabremcnt, de decouragement de ma part, n'osant 

pas croire avant vous [i.e., Maillebois] que cela meritail d'etre present^ a d'honnetes gens, a des 

gens d'esprit non au fait de la facture specifique de I'orgue ou du clavecin."


Saint Thomas, and even for 200 applauding people on the 1st of January 

1755.^ Again Castel gave no technical details, but the Explanation of the ocular 

harpsichord also contains a report on this performance, and there the instrument 

is said to have included coloured glass windows, illuminated from within by a 

hundred wax candles. However, as Castel was said to have exclaimed after the 

show "that this was not even a sketch, a beginning of it, so far was it from being 

perfect,"^ it probably still involved only a model. It was the harpsichord's swan 

song, as Castel died two years later. 

The author of Castel's eloge in the Memoires de Trevoux bluntly stated that 

Castel had fruitlessly spend the best part of his life trying to build the ocular 

harpsichord. There was no denying that in the theory of colours Castel had 

made "important discoveries from which the arts could profit," but the instrument 

which he had succeeded in constructing had "neither fulfilled the project of 

its author, nor satisfied the expectation of the public".^ 

Other harpsichord builders 

However, there are still some descriptions of the ocular harpsichord to be found 

after Castel's death, although they differ widely. In Saverien's Histoire des 

progres de I'esprit humain dans les sciences exactes et dans les arts qui en 

dependent, published in 1766, it says that the instrument "consists of a table on 

which is put up a kind of theatre complete with decorations. In front of the 

theatre is a keyboard, whose keys are connected with the decorations. When a 

key is pressed, no sound is heard but a colour is seen, in such a way that chords 

of colours are formed just like chords of notes."'^'* 

In 1769 the painter Lemierre, in his didactic poem La peinture, gave this 

versified description of the ocular harpsichord, built by "the industrious Castel, 

who today is not knovra any more": 

He [Castel] places on a buffet the silvery instrument, 

Where the ingenious art of a mobile hand 

Questions the ebony and harmonic ivory; 

Mercure de France, July 1755, pp. 144-145. 

Explanation, p. 13. 

Cited in Esprit, saillies et singularites, p. xx: "des decouvertes importantes dont les arts 

pourroient profiler ... n'a ni rempli le devis de I'auteur, ni satisfait I'attente du public". 

Saverien, Histoire, p. 275: "C'est un instrument forme par une table sur laquelle est 61ev£e 

une espece de theatre avec ses decorations. Sur le devant de cette table est un clavier, dont les 

touches repondent a ces decorations. Lorsqu'on louche sur le clavier, on n'entend pas des sons, 

mais on voit des couleurs; de sorte qu'on fait des accords de couleurs comme des accords de sons."


.Tctb-ula 171 

-V 

^j.II. 

\K. 

.T.if:rr,fch A ^ 

Figure 1 - Johann Gottlob Kriiger's design for an ocular harpsichord. From the Miscellanea 

Berolinensia, 1743 . (Courtesy Amsterdam University Library.)


At the end of each key a long elastic cord 

Answers to the ribbons, folded one over another, 

And as the hand, by varying the notes 

Knows how to compose the sounds coming from the strings, 

High above each strip opens up, unfolds, 

And purple, green, orange and blue, 

Return to the eye their movement and their play.**" 

Both descriptions suggest that Saverien and Lemierre actually saw the instrument 

they described, but we can only guess where and when they did. Nevertheless 

both descriptions can be connected with other ones: Savdrien's reminds 

one of the letter in which Krafft was informed that Castel wanted to realize his 

instrument "in modo theatri comici"; Lemierre's emphasis on the part of the 

ribbons will be encountered again with Diderot. 

Around the same time, in a book containing all kinds of "recreations" based 

on scientific experiments to amuse your family and friends (possibly the first 

example of this genre) the author, a certain Guyot, referring to Castel's Optique 

des couleurs, presented his own simplified version of an ocular instrument. It 

consisted of a cardbord cylinder, with a candle inside, placed in a square box 

having eight rectangular openings cut out in the front, corresponding to the eight 

notes of the diatonic scale, including the octave. The cylinder could be rotated 

by hand in such a way that it spiralled upwards at the same time. For a certain 

tune the cylinder could be provided with matching holes covered with coloured 

paper, such that, if the cylinder was turned round in measure with the melody, 

the right colours would be showing through the rectangular openings. The 

complete thing could even be purchased from Guyot himself; it was the most 

expensive item in the book. Guyot admitted that it was very simple compared 

with what Castel had looked for, but according to him the pleasure the instrument 

might be capable of would never be worth the costs. In fact, the experience 

with this simple model convinced Guyot "that it is far from the truth 

that the various chords and alternations of colours make any such impression as 

he [Castel] thought they did, and that there is no perceptible analogy between 

colours and sound".*' This small experiment was the last performance of 

lemierre, Peinture, p. 70: "II eleve en buffet I'instrument argentin / Ou Part ing^nieux 

d'une mobile main / Interroge I'ebene et I'yvoire harmonique; / Au bout de chaque louche un 

long fil elastique / R^pond a des rubans I'un sur I'autre plies, / Et selon que la main par des 

tons varies / Sait diriger les sons que la corde renvoye, / Plus haut chaque tissu s'entrouve, se 

d^ploye, / Et du pourpre, du verd, de I'orange, du bleu, / Fait retentir a I'oeil le passage & le 

jeu." 

Guyot, Recreations, vol. 3, recreation nr. 52, pp. 234-240: "qu'il s'en faut de beaucoup que 

ces differens changemens & accords de couleurs fassent une impression telle qu'il se Test imaging; 

qu'il n'y a aucune analogic sensible entre les couleurs & le son". For Guyot the whole idea was 

destroyed by the simple counterexample that two colours mix to a new colour, but that two notes


//.^j'SJoxs PE i/orr/tjiE .-imÂ^ :,3 

O" 


Castel's harpsichord in France. 

Shortly before Castel's death, however, the ocular harpsichord had been 

introduced into England by an unknown associate of Castel. In 1757 this man 

published a leaflet, entitled Explanation of the ocidar harpsichord, in which he 

recorded some of the history of the instrument and also his own solution to the 

problem.*^ The description he gives of his instrument is quite detailed: it 

consisted of a rectangular box of about 170 by 100 by 60 cm, placed on top of a 

normal harpsichord. In the front it had fifty elliptic windows of transparent 

enamel, which were ht from behind by some 500 candles. When a key was 

pressed, the window with the corresponding colour would glow up, but how this 

was achieved the author did not say, although he did indicate that even the 

difference in propagation velocity between light and sound had been taken into 

account! The author, however, had taken one crucial step away from Castel's 

theory, in adopting Newton's "minor scale", connecting the colour violet with the 

note D. But did this author succeed where Castel had failed? There is much 

reason to doubt it. The copy of the Explanation in the British Library has a 

written comment of its original owner, saying: "The Idea of this Instrument is 

something very extraordinary, not to say Extravagant; I was admitted among a 

select Party to a sight of it at the Great Concert Room in Soho Square; but to a 

sight only of the instrument, for nothing was then performed nor afterwards, as 

ever I heard, neither did I ever know why."" 

More daring was an adaption of Castel's project which had been proposed 

already quite early in Germany. In 1743 Johann Gottlob Krijger, a professor at 

the university of Halle, published a paper entitled "On a new kind of music, 

enjoyed by the eyes,"** in which he severely criticized Castel's views on colour 

music. For Castel's ocular harpsichord, as Kriiger knew it showing, at the 

pressing of a key, a strip of coloured silk lit from behind by candles, could 

imitate the melodic aspect of music but not the harmonic aspect. There was no 

convincing analogue of a chord. This is not to say that Kruger rejected the idea 

of colour music in itself; according to him it was clear "that our mind, in judging 

the pleasure or displeasure of the things that reach our eyes, follows the same 

laws and rules that are followed in distinguishing musical consonance from 

dissonance".*' This fact, however, could not be explained by any physical 

Explanation, pp. 17-22. The leaflet was reviewed in the Memoires de Trevoux, January 1759, 

pp. 342-357. 

^ British Library, shelf nr. 1041.h.4.(l.) 

Kruger, "De novo musices." 

Ibid., p. 352: "animum nostrum in diiudicanda obiectorum, quae oculum afficiunt, suavitate & 

molestia, easdem observare leges, easdemque regulas, quibus in distinguendis consonanttis a 

dissonantiis musicis uti consuevimus".


analogy between light and sound; it was simply a psychological phenomenon. 

This meant that there was no rationale for Castel's colour scale, nor was there 

any, for that matter, for Newton's casually presented analogy. Castel's scale 

could easily be proven to be defective: the combination of red and orange is not 

unpleasant, but the corresponding interval B-C is dissonant; similarly red and 

violet make a pleasant pair, whereas the major seventh D-C is dissonant; on the 

other hand red jars with green, while the corresponding interval G-C is a fourth 

and not dissonant. 

Acknowledging the possibility of colour music, Kruger set out to design an 

ocular harpsichord that would solve the problem of the missing chords, "an 

instrument radically different from Castel's, but in all respects fitter to make the 

eyes delight in colours".** He began by adopting an arbitrary colour scale, redorange-yellow-green-blue-purple-violet, 

to match the scale in C major, which 

amounted more or less to reversing the Newtonian spectral colours. Then he 

arranged a number of candles, each placed in the focus of a hollow mirror, in 

the form of a half-circle; the beams of light coming from the candles were each 

focused by a lens, such that all the beams projected into one point, the middle 

of the full circle, where a screen was set up. Each key of the instrument was not 

only triggering an ordinary harpsichord mechanism but was attached as well to a 

lever that normally screened off one of the beams, but when moved by pressing 

the key, pushed a circular window of coloured glass into the beam, resulting in 

the projection of a coloured circle onto the screen. The diameters of the 

windows decreased as the corresponding tones got lower, enabling the simultaneous 

projection of different coloured circles to visualize a colour chord, 

showing the root of the chord as a primary colour along the circumference of 

the projected circle and an array of increasingly superimposed colours towards 

the centre. 

Although Kruger added a blueprint of the instrument to his article, there is 

no indication that anyone ever tried to build it. He did, however, refer to it in 

the second and third edition of his Naturlehre, presenting it as completely his 

own invention and not even mentioning Castel as the originator of the whole 

idea: 

Anyone observing the beautiful colours that arise in the prism is easily led to the insight that it 

might be possible to delight the eye by the alternation and blending of the seven colours just as 

much as the ear by the seven tones. I have sketched such a machine ... which is not unworthy of 

Ibid., p. 353: "machinam a Castelliana diversissimam, quae omnino ad delectandos coloribus 

oculos aptior esse videtur".


the name of ocular harpsichord. 

As Kriiger wholeheartedly defended Newton's theory of optics in his Naturlehre, 

he might, especially in Germany, be partly responsible for the fact that in the 

latter half of the eighteenth century the idea of colour harmony was often 

thought to have been advocated by Newton himself. 

Initial reception: scientific scepsis and artistic affinity 

Scientific scepsis 

Castel's defence of his colour music was detailed enough to invite serious 

criticism. There was hardly any of it, however, after its first announcement in 

1725. Only one comment appeared in print, written by an anonymous "Philosophc 

Gascon", who accused Castel of confounding "two things which all philosophers 

distinguish, and which are indeed as apart as mind and body; you confound 

the sensations that the soul experiences with the occasional causes of 

these sensations".** Even if light and sound were both vibrational phenomena, 

the anatomical differences between eye and ear were sure to destroy any 

commensurability of optical and acoustical sensations. Castel never really 

answered this line of criticism, which would be voiced by later writers as well; 

apart from his mechanistic argument that all senses can only transmit the 

impulses they receive from outside into the sensorium, his simple conviction that 

colours delight the soul apparently counted sufficiently against it. 

It was only in 1735, after the publication of Castel's "Nouvelles expdriences 

d'optique et d'acoustiquc", that the ocular harpsichord fully entered the public 

arena. In the following five or ten years Castel must have been at the height of 

Kriiger, Naturlehre, 2nd ed.. vol. 1, p. 627; 3rd ed., vol. 1, pp. 684-685: "Wer die schonen 

Farben, welche durch das Prisma entstehen. bctrachtet, den kan man leicht auf den Einfall bringen, 

daU cs wohl eben so moglich sey, das Auge durch Abwechsclung und Vermischung der sieben 

Farben, als das Ohr durch die sieben Tone zu vergniigen. Ich habe daher eine solche Maschine 

angegeben ... welche des Namens eines Farbcnclavecj'mbels nicht unwiirdig ist." The last part of the 

sentence, calling the instrument an ocular harpsichord, was only added in the third edition. There 

were later posthumous editions up till 1777. In 1748 Kriiger published a description of his 

instrument in German, which did not contain anything new, except that it showed that Kriiger could 

be equally enthusiastic about colour music as Castel. What is interesting, however, is that Kriiger 

stated that he had previously worked as an organ builder. See Kruger, "Anmerkungen." 

Mercure de France, May 1726, p. 933: "vous confondez deux choses que tous les Philosophes 

distinguent, & qui sont effectivement aussi distinguees, que I'esprit I'est du corps; vous confondez 

les sensations que I'ame ^prouve avec les causes occasionnclles de ccs sensations".


his fame; even the Prince de Conti paid him a visit at his workshop,* and his 

1743 book on Newton's physics was a beautifully printed and expensive work. A 

clear indication of how Castel's reputation fared in these years can be found in 

two letters in the Mercure de France from 1754/1755. In one of them, Rondet, 

defender of Castel to the last, described the attitude of a certain Father Laugier 

in Castel's period of glory: 

You even spoke to me in raptures about the invention of the CKular harpsichord, and about the 

striking way in which its author had demonstrated the theory, undoubtedly after the letters that 

the Reverend Father had addressed to the illustrious President de Montesquieu in the 

Mercures [sic] of 1735. He had conquered the public, and even the most obstinate were 

convinced. 

But when, after twenty years, the harpsichord's music was still in the future, 

Laugier had changed his mind entirely, and he stated himself to be of the 

opinion "that the pleasure of sight has no connection at all with the pleasure of 

hearing, and that the idea of an ocular harpsichord could only arise in an 

imagination fertile of oddities but hardly a friend of the true and the solid".^' 

However, leaving aside what the general public may have thought about it in 

1735, there were quite a number of sceptical responses. Castel's "Nouvelles 

experiences" was immediately reviewed by the abbe Prevost in his journal Le 

Pour et Contre, and he rather sceptically remarked that 

if one strips from the theory all its ingenious researches and traits of the imagination with 

which the author has carefully adorned it, it only states that the colours, just like all other 

objects of sight and of the other senses, are linked by natural grounds of agreement and 

incompatibility, which cause that the connection and assemblage of these objects pleases us or 

shcKks us. On this the larger part of the arts and the sciences is based, and the principle 

stretches as far as the an de la cuisine ... 

But even granted this much, would Castel's application of the principle fulfil its 

promise of giving pleasure? Prevost did not believe it would, since a movement 

"so slight and still so sudden as has to be supposed in an ocular harpsichord or 

in any other instrument that answers to the ideas of Father Castel, will annoy 

and trouble the sight, to such a degree that this pretended music will instantly 

Brussels, Royal Library, ms. coll. nr. 15746, f. 13r-13v. 

Mercure de France, April 1755, pp. 160-161: "Vous me parliez meme avec extase de I'invention 

du clavecin oculaire, & de la maniere frappante dont I'auteur en avoit d^montr^ la theorie, sans 

doute apres les lettres que ce R.P. avoit ecrites a I'illustre President de Montesquieu, dans les 

Mercures de 1735. II avoit gagne le public, & les plus opiniatres etoient convaincus." 

Ibid., October 1754, pp. 37-38: "que le plaisir de la vue n'a aucun rapport avec celui de I'ouie, 

& que I'idee d'un clavecin oculaire ne peut trouver place que dans une imagination f€conde en 

singularites, mais peu amie du vrai & du solide."


become unbearable."^^ 

This scepsis was shared by Voltaire. While preparing his famous book on the 

Newtonian world view, Clemens de la philosophie de Neuton, Castel's ideas on 

colours were pointed out to him, and although he only exchanged some letters 

with Castel and never saw any instrument, he did enter the ocular harpsichord in 

his book, linking it with Newton's analogy between the widths of the various 

colours in the spectrum and the differences in string length for the notes of the 

minor scale. He fully accepted the analogy between tones and colours, and even 

thought it gave "reason to suspect that all things in nature have their hidden 

rapports, which perhaps some day will be discovered".^ The harpsichord itself, 

however, could not convince him: 

It is no doubt to be wished that this invention will not, like so many others, be an ingenious 

and useless effort; the rapid passage of various colours before the eyes may perhaps not fail to 

shock, dazzle and exhaust the sight; perhaps our eyes want some rest to be able to enjoy the 

agreement of the colours. It is not enough to propose us a pleasure, nature must have given us 

the capability to admit this pleasure: it is up to experience only to judge this invention.'"* 

Voltaire's initial benevolence, to be sure, could not for long withstand his 

malicious character. It seems that Voltaire had not appreciated Castel's review 

Le Pour et Contre 7 (1735), pp. 14 resp. 19: "si on la depouilloit de toutes les recherches 

ingenieuses, & de tous les traits d'imagination dont I'Auleur a pris soin de I'omer, elle signifieroit 

seulement qu'entre les couleurs comme entre tous les objets de la vue & des autres sens, il y a des 

fondemens naturels de convenance ou d'incompatibilite, qui font que la liaison & I'assemblage de 

ces objets nous plait ou nous choque. C'est la-dessus qu'est fondee la plus grande partie des Arts 

& des Sciences, & ce principe s'etend jusqu'a VArt de la Cuisine"; "aussi leger & aussi prompt 

qu'il faut les concevoir dans un Clavecin cKulaire ou dans tout autre Instrument qui r^ponde aux 

idees du R.P. Castel, la gene & trouble la vue. jusqu'a rcndre en un moment cette pr^tendue 

Musique insupportable." In 1739, however, Ix Fevre de Saint-Marc, who edited the journal in that 

year, published in Le Pour et Contre the integral translation of Telemann's Beschreibung der 

Augenorgel, commenting: 'On a d'abord traite I'idee de chimcrique, mais on commence a croire 

aujourd'hui qu'il n'est pas impossible de la realiser." (Vol. 18, p. 313.) 

Voltaire, Elemens, p. 184: "donnc lieu de soupônncr, que toutes les choses de la Nature 

ont des rapports caches, que peut-etre on decouvrira quelque jour." 

Ibid., p. 185: "II est a souhaiter sans doute, que cette invention ne soit pas, comme tant 

d'autres, un effort ingenieux & inutile: ce passage rapide de plusieurs couleurs devant les yeux 

semble peut-etre devoir etonner, eblouir, & fatiguer la vue; nos yeux veulent peut-etre du repos 

pour jouir de I'agrement des couleurs. Ce n'est pas assez de nous proposer un plaisir, il faut que la 

Nature nous ait rendus capable de recevoir ce plaisir: c'est a I'experience seule a justifier cette 

invention." It will come as no surprise that the harpsichord did not survive the many reprints of the 

Elemens for long. In 1741 Voltaire added the comment: "Au reste, cette idee n'a point encore 

it6 executee, et I'Auteur ne suivoit pas les decouvertes de Newlon." Starting from 1748 (the 

Dresden edition of the Oeuvres), the whole reference to the instrument was dropped. It just said: 

"A regard de I'analogie entre les sept couleurs primitives et les sept tons de la musique, c'est une 

ddcouverte qui n'est pas encore assez approfondie, ce qui ne peut encore mener a rien." See Part 

II, Ch. 13 of any edition.


of the Clemens in the Memoires de Trevoux. Poor Castel must have thought 

himself very polite indeed, copiously praising Voltaire's philosophical competence 

and not criticizing Newton's views for fear of giving the impression of 

criticizing the famous author himself. Voltaire, however, was mainly annoyed by 

Castel's remark that he, in writing on Newton's physics, "had switched from the 

frivolous to the solid", complaining that the writing of the Elemens had cost him 

only six months, while writing the Henriade had cost him six years,^ He took 

revenge by publishing an anonymous Lettre a Mr Rameau, taking a stand in a 

old and tedious quarrel between Castel and the composer Rameau. In this letter 

he ridiculed all of Castel's views, but most of all the ocular harpsichord: 

It paints minuets and nice sarabandes. All the deaf of Paris are invited to the concert that he 

promises them for twelve years ... With what goodness and obligingness towards humanity does 

he deign to demonstrate ... with lemmas, theorems and scholia, P. That people love pleasures, 

2°. That the art of painting is a pleasure. 3°. That yellow is different from red, and hundreds of 

other thorny questions of this kind.'* 

The most penetrating critique, however, came from the Acadcmie des Sciences. 

In 1737 Dortous de Mairan, to become the successor of Fontenelle as secretary 

of the Academic three years later, read a paper before the academy discussing 

the analogy between tones and colours, in which he listed a number of grave 

difficulties, many of which we in fact would still think valid today. Although he 

based himself solely on Newton's prism experiments and did not once mention 

Castel's harpsichord, 'Aitnessing the contempt Castel was still held in by the 

academicians, it can only have been the stir Castel's ideas had caused which 

motivated Mairan's extensive discussion. His arguments, however, according to 

Mairan, did not depend on the truth or falsity of Newton's theory of optics or of 

any such theory; indeed he himself was not a Newtonian.^ 

To start, it was of course accepted that the pleasure or displeasure of 

musical chords depends on the ratios of the rate of vibration of the constituent 

notes, the pleasure increasing as this ratio gets simpler. However, there was no 

Voltaire to d'Olivet, 20 October 1738, in Voltaire's Correspondence, vol. 7, p. 14. It seems not 

to have been just Voltaire's touchiness but a more general feeling; Desfontaines informed the poet 

Rousseau in August 1738: "All philosophers and geometers stumble ... over the corpse of the poor 

Newtonian; Father Castel has severely ridiculed him these days in the J. de Trevoux." Ibid., p. 322. 

I failed to get this impression from the review. 

In Voltaire, Correspondence, vol. 7, pp. 477^80: "II peint des Menuets, de belles Sarabandes. 

Tous les Sourds de Paris sont invites au Concert qu'il leur annonce depuis douze ans ... Avec 

quelle bonte, quelle condescendance pour le genre humain, daigne-t-il demontrer ... par Lemmes, 

Theoremes, Scholies, 1*. Que les hommes aiment le plaisir. 2° Que la Peinture est un plaisir. 3° 

Que le jaune est different du rouge, & cent autres questions epineuses de cette nature." 

See for Mairan's optical theory Hakfoort, Optica, pp. 43^8.


indication at all that the rates of vibration of the various colours had any such 

simple ratios. The only indication of what the physical properties of the different 

colour rays were, be it their vibration rate or any other property that determined 

the impact of the ray on, for instance, our eye, was their refractibility, which was 

the only thing in which they could be said to differ. Mairan then assumed that 

for each ray the ratio of the angles of incidence and refraction was the right 

measure of this physical property, let's say its rate of vibration. But the maximal 

ratio of the different values of this property, for the colours red and violet, was 

77:78, as Newton had so laboriously measured. The conclusion had to be that no 

pleasure could be expected of colour harmonies.''* 

Second, as had been remarked earlier by the "Philosophe Gascon", the 

organs of hearing and sight were so different in their anatomy, the one hard and 

dry, the other soft and humid, that it was inconceivable that the impressions they 

transmitted to the soul were commensurable. In fact, the pleasure we feel with 

simple frequency ratios of tones can be seen to be grounded in the anatomy of 

the ear: "The immediate organ of hearing is in fact, so to say, a real musical 

instrument, ... it is a kind of harpsichord, [containing] an infinity of strings, which 

by their different lenghts and their different tensions are capable of taking care 

of the relations and the vibrations of all possible tones."'' For the eye there was 

no indication of a similar mechanism. Then there were other problems, such as 

the fact that two colours mix to a new colour, while two tones mbc to a chord, 

something quite different from a single tone; the fact that we enjoy the slowly 

fading of one colour into another but loathe the tuning of a string such that one 

tone changes into another; and finally the fact that colours are absolute, whereas 

with tones only the intervals are absolute, and any tone can be the root of any 

interval.* 

To summarize, Mairan stated: 

There is no relation between these sensations [of hearing and sight] but in their intensity or 

magnitude; no other relation, neither as to their nature nor as to the idea we have of them. If 

there would be the least such a relation, it would not be impossible to give someone bom blind 

but not mute some idea of what colour and painting are, and conversely a mute who is not 

Mairan, "Discours," pp. 29-30. 

79 

Ibid., pp. 37-38 resp. 10: "L'organe immediat de I'ouie est en effet, on le peut dire, un 

veritable Instrument de Mu.sique ... c'est une sorte de Clavecin, [conlenant] une infinite de cordes, 

qui par leurs differentes longueurs, & par leurs differentes tensions, sont en ^tat de foumir aux 

rapports, & aux vibrations de tous les tons possibles." 

^ Ibid., pp. 39-42.


blind some idea of tones and music. 

Interestingly enough, some years later Diderot would turn Mairan's argument on 

its head, and conclude from his own observation that Castel's harpsichord had 

been able to give a blind man some idea of what colour was, that there was 

something to the harmony of the senses. 

The French academy stood not alone in its fierce critique. In 1742 the 

Imperial Academy of St Petersburg dedicated a similar session to Castel's ideas, 

after having been informed about them from Paris. There the physiologist 

Weitbrecht repeated the objection that the anatomical differences between eye 

and ear discredited any analogy between optical and acoustical sensations. The 

mathematician Krafft was even more radical, and argued that the existence of 

colour harmony and colour music depended completely on the question whether 

or not light was indeed a vibration of the aether. He himself thought this to be a 

false theory, which not only made Castel's views meaningless, but Newton's 

analogy just as well.*^ 

Although Castel had founded his colour harmony on the hypothesis that light 

was a vibrational phenomenon, the majority of scientists in the second quarter of 

the eighteenth century subscribed to Newton's emission theory. There were, of 

course, occasional defenders of Newton to whom the idea of colour harmony 

nevertheless appealed, not in the least while they thought they could find 

indications for it in Newton's own Opticks; Voltaire and Kruger are two examples. 

This situation changed in 1746, when Euler published a new vibration 

theory of light which was much more sophisticated than earlier ones, and one 

may rightly wonder whether adherents of this theory were more sympathetic to 

Castel's views. Euler himself certainly seems to have accepted the idea of colour 

harmony, as is shown by the reference to it in his Lettres d une Princesse 

d'Allemagne. In describing the refraction of white light into the spectral colours 

by a prism, he counted six colours, red-orange-yellow-green-blue-violet, although 

he admitted that actually the spectrum is a continuum of fading colour shades, 

causing the number of colours one discerns to depend on the number of 

available names and on the quality of one's retina. Indeed, some people said 

Ibid., pp. 35-36: "II n'y a de relation entre ces sentiments, que par I'intensite ou la grandeur; 

nulle relation d'ailleurs, ni dans leur nature, ni dans I'idee qui nous les represente. S'il y en avoit 

le moins du monde, il ne seroit pas impossible de donner a un Aveugle ne, qui n'est pas sourd, 

quelque idee des couleurs & de la peinture, & reciproquement a un Sourd qui n'est pas aveugle, 

quelque idee des Sons & de la Musique." 

See Schier, Castel, pp. 172-175 and Castel's own review of the transactions of the session, in 

the Memoires de Trevoux, May 1743, pp. 817-842. Castel muttered that the Russians were simply 

not informed well enough to judge; he was of the opinion that in his writings most of these 

objections had already been dealt with.


they could see a slight purple before the red. Next he introduced, out of the 

blue, a comparison between these colours and the musical scale in C major, 

"because the colours can be equally well expressed in numbers as the tones are". 

As the fundamental tone, however, he took purple and not red (which was a 

second above the root) since 

by raising the violet enough, one arives at a new purple, just like in rising along with the tones 

one gets from B to C which is an octave higher than the original C. And since in music this 

note is given the same name because of their ressemblance, it is the same with the colours, 

which, after having risen by the interval of an octave, recover the same names; or rather, two 

colours, just like two tones, one of which has exactly twice the number of vibrations as the 

other, are taken to be the same colour and carry the same name.*' 

Although no-one had succeeded in actually measuring the rates of vibrations of 

the various spectral colours, Euler thus not only supposed the rate for violet to 

be nearly twice as great as the rate for red, but believed as well, and in this he 

was wholly original, that there existed higher and lower octaves of the same 

colours.** 

It was on this principle, Euler said, that Castel had imagined a kind of music 

of colours and had deviced his ocular harpsichord, which he presumed the 

princess "had heard talked about on several occasions". It seems Euler in a way 

"rationally reconstructed" Castel's ideas within his own theory, discarding 

completely Castel's own chromatic scale. This did not, however, affect his 

appreciation of the performance of the harpsichord itself, since he doubted 

whether "showing various pieces of cloth dyed in different colours would be very 

agreeable". According to Euler it was painting "that to the eyes is the same thing 

as music is to the ears".^ Nevertheless, later German authors on natural 

philosophy who accepted Euler's theory rather than Newton's tended to bring in 

Cited in Euler, Lettres, vol. 11, p. 74 (Letter 31): "puisque les couleurs aussi bien que les sons 

se peuvent exprimer en nombres"; "haussant davantage le violet, on revient a un nouveau pourpre, 

tout comme en monlant dans les sons, on parvient au dcla de B au son c, qui est un octave audessus 

de C. Et comme dans la musique on donne a ce ton le meme nom a cause de leur 

ressemblance, il en est de meme dans les couleurs, qui apres avoir monte par I'intervalle d'une 

octave, recouvrent les memes noms: ou bien deux couleurs, comme deux tons dont le nombre de 

vibrations de I'une est precisement le double de I'autre, passent pour la meme couleur, et ont le 

meme nom." 

See Hakfoort, Optica, pp. 90-113, on Euler's theory. Of course the frequency of blue light is 

in fact roughly twice as great as the frequency of red light, but this is purely coincidental. 

Idem: "Pour moi je pense que c'est plutot la peinture, qui est par rapport aux yeux la meme 

chose que la Musique aux oreilles; et je doute fort qu'une representation de plusieurs morceaux de 

draps teints de diverses couleurs, puisse etre fort agreable." If he had not already learned about 

Castel's harpsichord, he would have from a letter by Krafft, discussing the St Petersburg Academy 

session of 1742. See A.P. Juskevii^ & E. Winter, ed.. Die Berliner und die Peiersburger Akademie der 

Wissenschafien im Briefwechsel Leonhard Eulers (Berlin [Ost], 1959-1976), vol. 3, pp. 137-138.


Castel's ocular music, while Newtonians mostly ignored him. An example of such 

an Eulerian is Boeckmann; in his Naturlehre from 1775 he mentioned how Euler 

connected the different colours with different rates of vibrations of the aether, 

and continued: "From this the famous geometer derives the further comparison 

of the colours with the tones, and adopts his colour octaves and his colour 

chords. Then a colour music cannot fail, which must be to the eye what the 

harmony of tones is to the ear. To this belongs the ocular harpsichord of Father 

Castel."^ Similarly, Erxleben mentioned the analogy between tones and colours 

in 1772 in his Anfangsgrimde der Naturlehre, although he rejected the existence of 

any colours beyond the red or the violet, and he summarized: "There was also 

the invention of a colour music, in which the eye would be pleased by a similar 

multiplicity of colours as the ear is by the multiplicity of tones in a piece of 

music; however, it was not a success."*" 

Artistic affinity 

Contrasting sharply with the negative responses from science was the reaction of 

theoreticians of art. In 1668 the painter Dufrcsnoy had started a tradition of 

didactic poetry on the art of painting with his De arte graphica, translated into 

French prose the same year by Roger de Piles. As Castel had already learned 

from Felibien, it was not uncommon to adopt the concept of harmony in 

painting as well, but it was only used in a rather general and non-committal way. 

The most far-reaching statement is to be found with the same Roger de Piles, 

who in his Idee du peintre parfait pronounced that "there is harmony and 

dissonance between the various colours and shades in the same way as there is 

in a musical composition", but for him the harmony in music was not just the 

harmony of the different tones but also of the different instruments, and in his 

last book on painting he applied the term harmony specifically to the "toutensemble", 

and for comparisons of colours spoke only in a general way of their 

accord and opposition or their amity and antipathy.** 

Boeckmann, Naturlehre, p. 322: "Ilieraus leitet dieser beriihmte Geometer die weitere 

Vergleichung der Farben mit den Tonen her, und nimmt .seine Farhen-Oclaven und Farben-Accorde 

an. Es kann also auch nicht an eincr Farben-Musik fehlen, die dcm Auge das seyn soil, was die 

Harmonic der Tone dem Ohr ist. Hicher gehoret das Farben-Clavic\Tnbel des Vater Castells.' 

Erx\^hci\, Anfangsgriinde. p. 315: "Man hat auch ein Farbcnmu.uk erfunden, wobey das Auge 

durch eben eine solche Mannichfaltigkeit von Farben ergotzt werden sollte, wie das Ohr bey einer 

Musik durch Mannichfaltigkeit der Tone; sie hat alier ihr Gliick nicht machen konnen." The editor 

Lichtenberg added as references Mendelssohn and Krijger. 

Piles, Idee. p. 40; Cours, pp. 334-342: "II y a une harmonic & une dissonance dans les especes 

de Couleurs, comme il y en a dans les tons de lumiere, de mcme que dans une Composition de 

Musique". The Idee is very commonly but mistakenly ascribed to Felibien; it is in fact the 

separately reprinted first book of Piles' Abrege dc la vie des peintres, originally published in 1699.


This terminology suddenly sharpened after 1735. In 1736 the abb6 Marsy 

published his Pictura, a didactic poem inspired by Dufresnoy. Marsy advised the 

aspiring painter to 

avoid intermingling inimical and incompatible colours; because, although we recommend 

varying the coloration, nevertheless there has to be an accord and a harmony among the colour 

tones, just as in a concert the art of the musician consists in according ill-matched notes and 

combining the dissonances of many voices. Is it but an pleasant reverie? Or might it be 

possible, at least to suit a poetic imagination, to combine the colour tones as we do sounds; to 

join them into a sort of concert, a kind of mute symphony, a sort of instrument without pipes, 

harmonious though lacking sound, that surprises and delights the eyes; in short, an ocular music 

that charms the senses of the .spectators?® 

The mention of accord and harmony prevailed in later works in this genre, 

although not always as extensively as with Marsy. In 1760 Watelet published his 

poem L'art de peindre; as a friend of d'Alembert (he wrote the article "Grace" 

for the Encyclopedic), he probable regarded the ocular harpsichord with 

scepticism, but it did not restrain him from using phrases like "the harmonious 

accord of the different shades" and "vary the harmony of his colouring", and 

pronounce that painting and music "both have their tones, their chords, their 

nuances, and these common terms mark their resemblances".'* Nine years later, 

however, the already mentioned Lemierre fully revived Castel in a similar 

didactic poem when he sang of the rainbow, 

Where by happy chords, the colour that glitters 

Has a tone it follows and a tone that follows it, 

Where by the effect of an invisible and supreme art 

This hue is no more and still seems the same, 

Where, displaying everywhere its imperceptible rapports, 

The contrast of tones appears only at both edges; 

In the meadows of the sky ocular harmony 

Cited from the French prose translation, in Watelet, L'art de peindre, pp. 283-285: "Gardezvous 

bien de meler ensemble des couleurs ennemis & incompatibles: car quoique nous recommandions 

de varier le coloris, il faut neansmoins qu'il y ait de I'accord & de I'hannonie dans les tons 

des couleurs; de meme dans un concert, l'art du Musicien sâit accorder des disparates, & marier 

ensemble les dissonances de plusieurs voix. N'est-ce qu'une agreable reverie? Ou seroit-il done 

possible, du moins au gri d'une imagination poetique, de combiner, comme on fait les sons, les 

modules & les tons des couleurs; d'en former une espece de concert, une sorte de simphonie 

muette, une maniere d'instrument organise sans tuyaux, & harmonieux sans rendre de sons, qui 

surpnl & enchantat les yeux; enfin une Musique Oculaire qui charmat les sens des Spectateurs?" In 

this edition from 1760 there is a note at the end saying: "Allusion au Clavecin oculaire du celebre 

Pere Castel, J^suite." 

90 

Watelet, L'an de peindre, pp. 22 resp. 29: "Des effets nuances I'accord harmonieux"; "Peut de 

son coloris varier Tharmonie."


Shows you the genius of the concert of colours. 

It was not only these French painter-theorists who were attracted to the reinforcement 

of the analogy between music and painting by the concept of colour 

harmony. In England the painter William Hogarth originally mentioned the 

ocular harpsichord in the manuscript of his famous The analysis of beauty, but 

deleted the reference before publication. From the small passage it is hardly 

possible to judge what he made of it, although he recognized that the idea only 

made sense if it is taken for granted "that colours and sound [are] of the same 

nature and that like dispositions of them both would answer the same purpose, 

i.e., that a jig in notes would be literally a jig in colours"."^ 

The observed adoption of the Castellian terminology of colour harmony in 

painting was not much more than the amplification of a manner of speaking 

which was already familiar. Moreover, these painters took Castel's complicated 

analogy as only an analogy between the already existing arts of painting and 

music. It did not have a lasting effect on the use of the concept of harmony in 

painting. In 1762 Christian Ludwig von Hagedorn placed the judgment of 

colours by harmony in opposition to the mechanical mixing of simple colours, 

stating that "the beautiful colours in itself do not make a colorist", and he 

applied the concept of harmony primarily with "the whole", just as Roger de 

Piles had done at the beginning of the century."^ 

On the other hand, there is one man standing apart in demonstrating a much 

more substantial affinity with Castel's ideas, namely Denis Diderot. The first 

evidence of an acquaintance of Diderot with Castel dates from 1751, when 

Diderot sought Castel's help in warding off the attacks of the Jesuits on the first 

volumes of the Encyclopedic. Already some years earlier there is an aside in 

one of Diderot's novels hinting that he knew Castel opposed the recently 

ordained crusade of the Jesuits against the unfolding Enlightenment.*" So it 

Lemierre, La peinture, p. 71: "Oii par d'heureux accords cette couleur qui luit / Tient du ton 

qu'elle quitte & du ton qui la suit, / Ou par I'effet d'un art invisible & supreme / Cette teinte 

n'est plus & semble encore la meme, / Ou laissant voir par tout d'insensible rapports / l.e 

contraste des tons ne paroit qu'aux deux bords, / Aux campagnes du ciel oculaire harmonic, / Du 

concert des couleurs te montre le genie." The 1770 edition has in the footnotes parallel passages 

from Watelet, including the phrases that were quoted above. 

92 

Hogarth, Analysis, p. 176. Like Prevost before him, his first association was to fantasize a 

concert of flavours. How Hogarth came to hear about the harpsichord is not clear. Castel was 

certainly known in England in the 1740s; see Von Erhardt-Siebold, "Inventions," p. 354 n. 2. 

'^ Hagedorn, Betrachiungen. pp. 688-689, 710-711. Hagedorn mentioned having studied 

Felibien, Marsy and Watelet (p. 64); he had also read Kriiger's Naturlehre (p. 711). 

See Diderot to Castel, March 1751, in Correspondance, vol. 1, pp. 115-116. The allusion to 

Castel is in IJ:S bijous indiscrets (1748): "C'etait un bon homme qui mettait de I'esprit a tout, et 

que les autres brames [Brahmins] noirs, ses confreres, firent mourir de chagrin." See Oeuvres


probably was in the late 1740s that Diderot paid a visit to Castel's workshop, as 

many others had done before him. The description of this visit Diderot included 

in his Lettre sur les sourds et muets, published in 1751. Diderot, however, had 

prepared himself better than the others, in bringing with him a deaf-mute: "I 

imagined that if there was anyone on earth who was to receive any pleasure 

from ocular music, and anyone who could judge it impartially, it was a deafmute 

by birth.""^ 

As is clear from his account, the reaction of the deaf-mute pleased Diderot 

and perhaps it played a part in winning him over to Castel's views. It was 

obvious, said Diderot, that there was no way of explaining to the deaf-mute 

anything about the nature and the marvelous properties of the harpsichord; since he had no 

idea of sound, what he understood of the ocular instrument assuredly had no relation to music, 

and the purpose of this machine was to him as incomprehensible as the use that we make of 

our speech organs. Then what did he think? And what basis was there for the admiration to 

which he succumbed when he saw the gamut of Father Castel? ... My deaf imagined that this 

inventor of genius was equally deaf and mute; that he used his harpsichord to communicate 

with other people; that each colour shade on the keyboard had the value of one of the letters 

of the alphabet; and that by way of the keys and the agility of his fingers, he combined these 

letters and formed words, phrases, indeed a whole conversation in colours. 

Now, suddenly, the deaf-mute believed himself to comprehend what music was: 

"He gathered that music was a special way of communicating thought, and that 

the instruments, the fiddles, the violins, the trumpets, were, in our hands, 

another type of speech organ." Diderot thought this very clever of the deaf-mute: 

"If he had perhaps not exactly chanced upon what [music] was, he had almost 

chanced upon what it should be."*' 

Given this appreciation, one would surely expect Diderot to say something 

completes, vol. 4, p. 203. 

Diderot, Oeuvres completes, vol. 1. pp. 356-357: "J'imaginai que s'il y avail un etre au monde 

qui dflt prendre quelque plaisir a la musique oculaire, et qui piit en juger sans prevention, c'etait 

un sourd el muet de naissance." 

Ibid., pp. 357-358; "qu'il n'etait pas possible de lui rien communiquer sur la nature et les 

propriit^s merveilleuses du clavecin; que n'ayant aucune idee du son, celles qu'il prenait de 

I'instrument oculaire n'^taient assurement pas relatives a la musique, et que la destination de 

cette machine lui itait tout aussi incomprehensible que I'usage que nous faisons des organes de la 

parole. Que pensait-il done? el quel etait le fondement de I'admiration dans laquelle il tomba, a 

I'aspect des 6ventails du Pere Castel? ... Mon sourd s'imagina que ce genie inventeur itait sourd 

et muet aussi; que son clavecin lui servait a converser avec les autres hommes; que chaque nuance 

avail sur le clavier la valeur d'une des lettres de I'alphabet; et qu'a I'aide des touches et de 

I'agilite des doigts, il combinait ces lettres, en formait des mots, des phrases; enfin, tout un 

discours en couleurs ... II crut que la musique etait une faôn particuliere de communiquer la 

pensê, et que les instruments, les vielles, les violons, les trompettes etaient, entre nos mains, 

d'autre organes de la paroles ... S'il ne rencontra pas exactement ce que c'itait, il rencontra 

presque ce que ce devrait etre."


about the ocular harpsichord in the recently initiated Encyclopedic. Indeed he 

gave it an article of its own in the third volume, published in 1753, under the 

heading "Clavecin oculaire (Musiq. et Opt.)". He described the instrument as 

"designed to give the soul through the eyes the same agreable sensations of 

melody and harmony of colours as the sensations of melody and harmony of 

sounds it receives by the ordinary harpsichord through the ear", and he readily 

followed Castel to the extremes of the analogy: 

... if one takes a nice rudimentary piece of auricular music, for instance the one of Mr. 

d'Alembert, and the word colour is everywhere substituted for the word tone, one will have the 

complete elements of ocular music, coloured songs of several voices, a fundamental bass, a 

thorough bass, chords of all kinds, even by supposition and suspension, a rule of connection, 

harmonic inversions, etc. 

He light-heartedly sidestepped the by now repeatedly raised difficulties: 

The objections which have been put forward against the ocular music and instrument are so 

obvious that it is useless to report them: we only venture to assure that they are perfectly, I will 

not say destroyed, but at least countered by the responses drawn from the comparison of the 

two musics, leaving now only experience to decide the question."" 

However, Diderot did discuss one particular problem, resembling the one that 

Voltaire had mentioned: the subjective jumps from one colour of the scale to 

the next are much greater than the corresponding jumps from one musical tone 

to the next. This meant that there had to be found 

some expedient to link the colours and rend them continuous to the eye; if not, the eye will, in 

very vivacious airs, not knowing what colour interval will come next, have no clue to where to 

expect the next tone, and will, out of a battery of colours, only seize some sparse tones, or will 

have to torment itself so much to seize all notes that il will be dazzled in no time; and then 

Encyclopedic, vol. 3, pp. 511-512: "destine a donner a I'ame par les yeux les memes 

sensations agriables de melodic & d'harmonie de couleurs, que celles de milodie & d'harmonic 

de sons que le clavecin ordinaire lui communique par I'oreille"; 'si Ton prend un bon rudiment de 

Musique auriculaire, tel que celui de M. d'Alembert, & qu'on substitue par-tout le mot couleur au 

mot son, on aura des Siemens complels de musique oculaire. des chants colores a plusieurs 

parties, une basse fondamentale, une basse continue, des chiffres, des accords de tout espece, meme 

par supposition & par suspension, une loi de liaison, des renversemens d'harmonie, &c"; "Les 

objections qu'on a faites contre la musique & I'instrument oculaires se presentent si naturellement, 

qu'il est inutile de les rapporter: nous osons seulement assurer qu'elles sont si parfaitement, sinon 

d^truites, au moins balancees par les reponses tirees dc la comparaison des deux musiques, qu'il 

n'y a plus que I'experience qui puisse decider la question." The authorship of Diderot was 

indicated by an asterisk. The article was left unchanged in the 1771-1776 quarto reprint of the 

Encyclopedic, in the octavo reprints of Neuchatel, 1777-1779, and Lausanne, 1778-1782, and even in 

Felice's adaptation of the Encyclopedic, the Dictionnaire universelle of 1770-1780.

gcxDdbye to melody and harmony. 


Diderot was convinced that "to solve this problem, one needs only a very small 

part of the sagacity which the invention of the harpsichord supposes".'* Indeed, 

Castel had remarked repeatedly that all that was needed was the resignation that 

one inevitably had to become used to colour music gradually. Had the French 

public not encountered similar difficulties in accepting Italian music? 

Although Diderot had visited Castel's workshop and seen a model harpsichord 

demonstrated, he did not say anything on the technical realization of the 

instrument. Neither did he promise a drawing of it in the Recueil des planches, 

as he did for other inventions described in the same volume (for instance a 

curious mechanical calendar mentioned under "Chronologique, machine"). He 

only admitted that "the fabrication of this instrument is so extraordinary that 

only a little enlighted public will complain that it is constantly made and never 

finished", and that it needed a "rare engineer" to do it.*^ 

Apart from the ocular harpsichord, Diderot was also impressed by the 

coloured ribbons that Ca.stel had made in the course of his colour experiments 

during the years 1734-1740. By taking silken threads dyed in the twelve colours 

of the chromatic scale and twining them into yarn in different combinations, he 

had manufactured ribbons that showed a certain colour passing by imperceptible 

changes through all the chiaroscuro shades from almost black to almost white, 

or others showing a complete octave in which all the different colours imperceptibly 

changed into the next one until the root colour was regained."'*' When the 

first volume of the Encyclopedic appeared Diderot wrote to Jaucourt: "Here is 

our Encyclopedic. In it I have rendered homage to Father Castel at several 

occasions; and 1 will seize the opportunity to do so again in the following 

volumes.""" One of these occasions was the article "Animal", in the introduction 

of which Diderot mentioned Castel's ribbons as a metaphor for the "great 

Idem: "il faudroit trouver quelque expedient qui liat les couleurs.


chain of being". He introduced them to the same purpose in his Rive de 

d'Alembert: "All beings circulate one inside the other, and so do all species... all 

is in perpetual flux... Every animal is more or less human; every mineral is more 

or less plant; every plant is more or less animal. There is nothing definite in 

nature... The ribbon of Father Castel... Yes, Father Castel, it is your ribbon and 

nothing else.""" 

For Diderot these ribbons were somehow the core of the ocular harpsichord, 

as becomes clear from a rather romantic letter written to either Sophie Volland 

or Madame de Maux, comparing his feelings towards living in Paris and in the 

countryside with the difference between music and colour: 

Do you know anything of the ocular harpsichord of Father Castel? Imagine small coloured 

ribbons that unfold as the fingers walk along the poignant keys of a pianoforte. Well, my friend, 

this instrument, it is me in the city and in the countryside. In the city, all the coloured ribbons 

unfold, and the poignant keys are silent. In the countryside, on the other hand (and from my 

comparison one can easily see that I am not there now), the coloured ribbons stay in their 

envelope and the harmonious and sombre kej'S of the instrument make themselves heard and 

the heart of my friend shivers with them."^ 

Colour harmony and the changing aesthetics of the later eighteenth century 

Diderot can be regarded as a key figure in the reception of the ocular harpsichord, 

in the sense that he did not simply accept, or reject, the concept of colour 

harmony and colour music as a scientific fact or by a mere artistic appeal, as 

most of the people discussed earlier had. Diderot's aesthetics was founded in the 

whole of internal relations of the work of art, that could be classified and 

studied scientifically instead of being obediently adopted from Antiquity or 

Cited in Oeuvres philosophiques, p. 311: "Tous les ctres circulent les uns dans les autres, par 

consequent toutes les especes... tout est en un flux perpetuel... Tout animal est plus ou moins 

homme; tout mineral est plus ou moins plante; toute plante est plus ou moins animal. II n'y a rien 

de precis en nature... Le ruban du pere Castel... Oui, pere Castel, c'est voire ruban et ce n'est 

que cela." The triptych Entretien entre d'Alembert et Diderot - Le re\'e de d'Alemben - Suite de 

I'entretien was written in 1769, but not published until 1830. 

Letter dated November 1769, in Correspondance. vol. 9, pp. 209-210: "Avez-vous quelque 

notion du clavecin oculaire du Pere Castel? Imaginez des pelits rubans coloris qui se diployent 

a mesure que les doigts se promenent sur les touches pathcliques d'un piano forte. Eh bien, mon 

amie, cet instrument, c'est moi a la ville et a la campagne. A la ville, tous les petits rubans 

colores se deployent, et les touches pathetiques sont muettes. A la campagne au contraire (et 

I'on voit bien a ma comparaison que je n'y suis pas) les petits rubans colores restent dans leur 

6tui, et les touches harmonieuses et sombres de rinslrument se font entendre et le coeur de mon 

amie en tressaillit." The passage is taken from the fragments that Naigeon copied out of the letters 

Diderot sent to Sophie Volland and to Madame de Maux, after which he destroyed the originals. 

Although the editors of the correspondence assume the letter which contained the cited passage 

was addressed to Madame de Maux, there is in this case really no way of telling.


remaining hidden behind a je ne sais quoi. In his article "Beau" in the Encyclopedic 

Diderot wrote: 

If, thus, nothing more enters in the concept of the beautiful ... than the notions of order, 

rapports, proportion, arrangement, symmetry, agreement, and disagreement, then, since these 

notions do not stem from any other source than do the notions of existence, number, length, 

size, depth, and an infinity of others that are not contested, one can, it seems to me, use the 

first set of notions in defining the beautiful without being accused of substituting one term for 

another and turning in a vicious circle.'"'' 

This would not have sounded completely alien to Ca.stel, who had started 

defending his colour music on the supposed fact that all pleasure is derived from 

harmonic proportion, and who in his later "logique du gout" (or even "sisteme 

physico-moral du gout") had called music "a simple agreement", be it one 

appreciated by the highest level of the mind, making it a pleasure of the 

understanding, the only pleasure humans do not share with animals.'"' 

It is, indeed, very interesting to examine the changing grounds for the 

appreciation of the idea of colour music as, in the course of the eighteenth 

century, the theories of aesthetics changed. The dominating view in the first 

decades of the eighteenth century was the ancient idea that all art should imitate 

nature; it was the "principle" to which the Batteux reduced art in 1746 in Les 

beaux arts redidts a un meme principe. For a long time it was held that the 

main change during the later eighteenth century and into the Romantic period 

was a replacement of imitation as the main criterion by expression. This was 

argued in 1958 by Abrams in his 77ie mirror and the lamp: during the greater 

part of the eighteenth century art was supposed to be a mirror which reflected 

nature to the audience, whereas in the Romantic conception art would be a 

lamp out of which streamed the light of the artist illuminating his audience. 

This view has recently been criticized in two books by Ncubauer and by 

Barry.'°* Ncubauer in particular shows how the idea of expression as a main 

characteristic of art was already defended by many people during the larger part 

of the eighteenth century, and both argue that the most important change in 

aesthetics at the end of the century was not a change from imitation to expression 

but from a representational to a non-representational conception of art. 

Cited in Diderot, Oemres estheiiqucs, p. 417: "S'il n'enlre done dans la notion de beau ... 

que les notions d'ordre, de rapports, dc proportion, d'arrangcment, de symctrie, de convenance, de 

disconvenance; ces notions ne decoulant pas d'une autre source que celles d'exislence, de nombre, 

de longueur, largeur, profondeur, el une infinites sur lesquelles on ne contesle point, on peut, ce 

me semble, employer les premieres dans une definition du beau, sans etre accuse de substituer 

un lerme a la place d'un autre, et de tourner dans un ccrclc vicieux." 

Memoires de Trevoux. November 1735, pp. 2342-2359. 

Ncubauer, Emancipation; Barry, Language.


Imitation and expression have in common that both are representational, in the 

sense that both take the work of art to have an encoded meaning, put in by the 

artist, that might be either a reference to the world outside, as in the case of 

imitation, or to the inner world of the artist, as in the case of expression. To 

enjoy a work of art was to grasp its meaning. At the end of the eighteenth 

century, however, people started to look upon art not as transmitting an encoded 

meaning, but as a structured whole which would, by triggering the imagination 

of the audience, evoke various associations of sensations and emotions, without 

these being necessarily put in first by the artist or without it being able to say 

that they were understood truthfully. Whereas Ncubauer defends this view of the 

aesthetic revolution towards the end of the eighteenth century primarily for the 

case of music, Barry argues that a similar change pervaded English poetry, 

changing from conveying messages to word play, and that it perhaps was 

considered even in painting, by the Englishman Alexander Cozens. 

Clearly, music was very important in this aesthetic revolution, since it had 

always been dominated at least in practice, regardlc.s.s of what theorists would 

claim for the ultimate meaning of music, by considerations of form and structure. 

The arguments by which Castel defended his colour music had no connection 

with the aesthetics of imitation; they suggested a complete parallel to 

formal, instrumental music (although he complicated this by his introduction of 

painting as a large scale analogue). In fact, il had been the composer Rameau, 

whom Ncubauer mentions as an important figure during the eighteenth century 

in keeping alive the view that music is nothing but a formally structured whole, 

without an encoded explicit meaning, - who had urged Castel to publish his first 

announcement of the ocular harpsichord. According to Castel, the idea had not 

surprised Rameau at all."'' Other compo.scrs did not react differently. In his 

Beschreibung der Augenorgel Telemann reported the many objections that were 

voiced against Castel's harpsichord, but he was not impressed by them. As he 

stated: 

ITie tones please only through a clear distinctness, through agiccmcnl and analogy. ITie colours 

are just as varied as the tones, and have certain agreements. Ilie eye can join them together, 

develop their analogies and experience their order and disorder. 'Phis experience causes the 

delight and stimulus in all things, and the real delight of music consists in perceiving such 

differences immediately or repeatedly during a short lime, lliis excites the soul, keeps il happy, 

and prevents it from falling into an inane monotony. In short: there is no doubt that this play 

of colours will please. For music is nothing but a pleasure. 

Memoires de Trex'owx. August 17,35, p. 1640. 

Telemann. Beschreibung, p. 266: "Die Klangc gefiillen nur durch eine deutliche Verschiedenheit. 

durch die Uebcreinstimmung und Vergleichung; Die Farben sind so mannigfaltig. als die 

Klange. und haben gewisse Ucbercinslimmungcn. Das Auge kan sie zusammenfijgen. ihre


Another author, closely related to the musical world of Castel's age, who 

discussed Castel's harpsichord was Francesco Algarotti. Voltaire had much 

admired his book // Newtonianismo per le dame from 1737, written in the form 

of a conversation between a teacher and his inquisitive pupil, a marquise, and it 

was quickly translated into French and into many other languages as well. 

Remarkably enough, considering the title of the book, in the part dealing with 

optics Algarotti defended the vibration theory of Malebranche, in the form 

Malebranche finally gave it to reconcile it with Newton's prism experiments. The 

marquise accepted this theory, as she said because "the fraternity between sound 

and light appeals to me", upon which her teacher answered: "I had expected, 

Madame, that this fraternity would please you, and I am convinced that the 

ocular harpsichord and its ocular music, which arc going to present you a new 

brilliance, will be successful with you." What follow are a lot of jokes, but it 

remains doubtful whether Algarotti wholly rejected the idea as such.'"^ 

The adoption of colour music as an art fully equal to music, interpreted as a 

wholly formal art, later was the choice of Immanuel Kant in his Kritik der 

Urteilskraft. Kant ordered the arts into three hierarchical pairs. First came 

rhetoric and poetry, both relating the Verstand or understanding with the 

imagination. Next came sculpture and painting, connected with the Sinnesanschauung 

or sensory apperception and leaving the imagination a much 

more modest role to play. Last came music and Farbenkunst, both acting purely 

on the level of the sensations and not involving anything more than different 

degrees of tension of the sense organs. Kant, in accordance with his acceptance 

of Euler's vibration theory of light in 1755, connected the sensations of each art 

with the velocity of the vibrations of the respective media. As he supposed the 

existence of both tone and colour scales, his Farbenkunst cannot have been 

anything else but Castel's colour music, but there is no explicit reference 

Vergleichungen entwickcln und ihre Ordnung und Unordnung empfinden. DiB Empfinden 

verursachet das Vergniigen und Anreilzen in alien Dingen, und das eigentliche Vergniigen der 

Musik beslehel in dem, solchen Unterschied augcnblicklich, und nach und nach in kurtzer Zeit 

mehrmals, zu bemercken. DiB erwecket die Scele, crhall sie beslandig munlcr, und vcrhindert. daO 

sie nicht auf einen albemen Glcichlaut verfalll. Kurtz: Es ist unstreiiig, daB dicB Farbenspiel 

ergetzen wird. Denn Musik ist nichts andcrs. als eine Ergetzlichkeit." 

Algarotti. Newtonianisme, p. 222: "la fratemite du Son & de la Lumiere me louche"; "J'ai 

bien juge, Madame, que cette fratemite vous plairoTt, & je ne desespere pas que le Clavecin des 

couleurs, & la .Musique des yeux qui vont lui donner un lustre nouveau, ne fasse fortune aupres de 

vous." Interestingly, the first extension the marquise thinks of is a "musique des ragouts", as did 

Prevost and Hogarth. At a certain moment, when .Algarotti became too frivolous, the translator 

defended Castel in a footnote! In the fully revised final edition of 1752 all references to Malebranche 

had disappeared, but Castel's harpsichord was still there. The only joke left - if il was a 

joke - was the statement that "on such an instrument the eyes enjoy arias by Pergolesi and 

Rameau: and thanks to it it will be possible to have copied on cloth some lines sung by Caffariello.' 

(Chapter 6 of any later edition.)


indicating the source of his knowledge of it. This is the more astonishing as Kant 

is the only theorist to have accepted the idea of colour music without any 

comment at all."" 

In Kant's ordering of the arts music is not thought to convey any meaning; it 

is only able to work on the senses according to its structure, and there was 

apparently no reason for Kant to deny the same effect to a similarly structured 

colour music. However, for many people experience told differently. During the 

second half of the eighteenth century it was increasingly emphasized that music 

had a stronger effect on us, was in a sense more inescapable, than any of the 

other arts, and few people did agree with Castel that colours could compete with 

sounds in this respect. Already Mairan ended his enumeration of objections 

against colour music with the observation that 

the impressions of pleasure and displeasure that the soul receives out of the presence and the 

various arrangements of colours are almost nothing compared to the impressions caused by 

sounds ... Sounds are sometimes able to excite or to calm the passions in an almost purely 

mechanical way by their arrangement and their movements. But sight, the most delicate and at 

the same time, if you please, the most peaceful of all our sen.scs, mechanically and by means of 

colours procures us only infinitely weak impressions.'" 

Diderot had wrestled with the same observation concerning his own aesthetics. 

As explained in his Lettre sur les sourds et muets, in any art the internal relations 

on which he placed so much emphasis were nevertheless to be used to convey 

ideas, be they imitative or expressive. In the Additions, written some months 

later, he tried to answer the objection of Madame de La Chaux that nearly 

everyone enjoys instrumental music, but that this music cannot be said to convey 

any ideas. Diderot started by repeating the standard response that these musical 

pieces "gratify your ears exactly like the rainbow delights your eyes, by a pure 

and simple pleasure of sensation". Genuine artistic delight depended on the 

presence of imitation or expression, which was why we find the stars painted on 

a canvas more beautiful than the real stars in a clear night sky. However, 

Diderot immediately seemed to realize the inadequacy of this answer: 

Painting shows the object itself, poetry describes it, music creates hardly an idea of it; it has no 

resources but the intervals and lengths of its tones. And what analogy do such pencils have with 

"" Kant, Urteilskraft, Section 51. For Kant and Euler, see Hakfoort, Optica, p. 118. 

Mairan, "Discours," pp. 43^t4; "les impressions de plaisir ou de peine que I'Ame revolt par la 

presence & par le divers assemblage des couleurs, nc sont presque rien en comparaison des 

impressions causees par les Sons ... Ixs sons par leur assemblage, & par leurs mouvements, vont 

cependant quelquefois jusqu'a exciter, ou a calmer les pa.ssions, & cela par une voye presque 

toute mechanique. Mais la viae, le plus delicat, & en mcme temps, s'il m'est permis de le dire, le 

plus paisible de tous nos sens, ne nous procure mcchaniquement, & par le moyen des couleurs, 

que des impressions infiniment foibles."


spring, darkness, solitude, etc., and with the majority of objects? How is it possible that out of 

three arts imitating nature, the most arbitrary and the least precise speaks the most forcefully 

to our soul? 

As a rare exception in eighteenth-century literary style, the question mark did 

not conclude a rhetorical question. One of his suggested answers clearly pointed 

to the later developments as described by Neubaucr and Barry: "Would it be 

that [music], by showing the objects to a lesser degree, leaves more room for 

our imagination ...?""^ 

Pointing out the exceptional ability of music to touch the human soul became 

a frequently used argument against Castel's colour music after 1750. One of its 

critics who used this argument was Rousseau. We can infer from a small remark 

in one of Castel's books that Rousseau had visited his workshop in 1742 or 1743 

and apparently had seen music in the instrument."'' Nevertheless, in his Essai 

sur I'origine des langues Rousseau confirmed to have seen "this famous harpsichord, 

on which it is pretended a mu.sic of colours can be played", but in the 

meantime he had developed many serious arguments again.st it, putting blatantly: 

There are no absurdities that physical observations have not given rise to considering the fine 

arts. In the analysis of sound the same relations have been discovered as were found by the 

analysis of light. Immediately this analogy has been seized upon, completely disregarding 

experience and reason. The esprit de sysli'me has confounded everything, and as one did not 

know how to paint for the ears, one has taken it into its head to sing to the eyes.'''' 

Rousseau not only called to mind the anatomical differences between eye and 

ear, but he pronounced the general difference between music and any art of 

colour, which Castel had thought open to manipulation, to be of the essence of 

All citations from Additions pour senir d'cclaircissement a quelques endroils de la Lettre sur 

les sourds et muets, in Diderot, Oemres completes, vol. 1, pp. 407^09: "ne flattcnt voire oreille que 

comme I'arc-en-ciel plait a vos yeux, d'un plaisir de sensation pur et simple"; "l.a peinture montre 

I'objet meme, la poesie le dccrit, la musique en excite a peine une idee; elle n'a de ressource que 

dans les intervalles et la duree des sons, lit quelle analogic y a-t-il entre cettc espece de crayons 

et le printemps, les tenebres, la solitude, etc., et la plupart des objets? Comment se fait-il done 

que des trois arts imitateurs de la nature, celui dont I'e.xprcssion est la plus arbitraire et la moins 

precise parle le plus fortement a I'ame? Serait-ce que, monlrant moins les objets, il laisse plus de 

carriere a notre imagination ...?" 

Castel, L'homme moral, p. 194, stating that "M. R[ousseau] ait cru autrefois voir de la 

Musique dans mon Clavessin oculaire." 

Rousseau, Essai, p. 169: "II n'y a sortes d'absurditcs auxquclles les observations physiques 

n'aient donne lieu dans la consideration des beaux-arts. On a trouve dans I'analyse du son les 

memes rapports que dans celle de la lumiere. Au.ssi-t6t on a saisi vivcmcnl cette analogic sans 

s'embarrasser de I'experience et de la raison. L'esprit de sisteme a tout confondu, et faute de 

savoir peindre aux oreilles on s'est avisc de chanter aux yeux. J'ai vii ce fameux clavecin sur lequel 

on pretendoit faire de la musique avec des couleurs". The &.«!/ was probably written between 1755 

and 1761, but only published in 1781, after Rousseau's death.


these arts: music consisted of the succession of tones in time, while colours had 

to be adjacent in space. Moreover, there was the difficulty of the absolute 

character of colours, compared to the relative nature of tones; this was an 

indication of the fact that "painting is closer to nature, while music is more of a 

human art". It was this last feature, that music was the essential human art, that 

made it the superior art: 

It is one of the great advantages of the musician that he can paint things that cannot he heard, 

whereas it is im[>ossible for a p


of music to animals."^ For Chabanon, music stood so much apart from the 

other arts that for this reason alone he judged Castel's colour music to be 

nonsense, calling the ocular harpsichord a "ridiculous invention" and an "absurd 

chimaera". The essence of melody consisted in the succession in time of the 

tones, and it was the ear that caught the internal connection of a melody; there 

was no indication at all that the eye could similarly appreciate a succession of 

colours."* 

Notwithstanding the opposing views of Rousseau and Chabanon regarding 

imitation, there is, of course, a striking difference in the way Rousseau and 

Chabanon looked at music, compared with the view of Rameau and Telemann. 

For the latter music was basically chords, i.e. harmony, while for the former it 

was above all song, i.e. melody. As Chabanon remarked: "The whole essence of 

music is thus contained in the single word song or nieiody."^'^ Rousseau 

compared the melody of a musical piece with the design of a painting and the 

chords with its colours, but he thought the harmonic part to be just a form 

prescribed by nature, while the melody of the music and the design of the 

painting made their products into works of art. If there was nothing more to 

painting and to music than combining colours and .sounds in ways agreeable to 

the eye and to the ear, then both would have to count as natural sciences and 

not as arts. "It is imitation alone which elevates them to that rank. And what is it 

that makes painting an imitative art? It is the design. What is it that makes 

music another one? It is the melody."'^ 

In Germany there was a similar development of an increasing emphasis on 

music as a privileged language of the soul. In 1755 Moses MendcKssohn, a typical 

Enlightenment theorist, seemed happy with the universality of harmony when he 

discussed the music of colours in his Briefe iiber die Empfindungen. Mendelssohn 

accorded that for the eye "a kind of harmony is reserved that is perhaps linked 

to no lesser delight than the harmony of tones is". He attributed the concept 

solely to Newton: 

It is you. great Newton, to whom humanity owes this discovery [of colour harmony], and you 

will be famous for it for many centuries. One has not yet succeeded in elevating this colour 

harmony to its true level and transform it into the mother of as many delights as the harmony 

'"Ibid., pp. 17-23. 

118 

Ibid., pp. 6-8: "invention ridicule"; 'absurde chimere". 

119 

Ibid., p. 15: Toute I'essence de la Musique est done renfermee dans ce seul mot chant ou 

melodic." 

Rousseau, Essai, p. 153: 'C'est I'imitation seule qui les eleve a ce rang. Or qu'est ce qui 

fait de la peinture un art d'imitation? C'est le dessein. Qu'est-ce qui de la musique en fait un autre? 

C'est la m^lcxlie."


of tones. The ocular harpsichords seem to promise more than they in fact are able to a- 

chieve.'^' 

Mendelssohn tested colour music against the three sources for pleasure he 

distinguished: "unity in mullipHcity, or beauty; the concord of the multiple, or 

intellectual perfection; and the improved state of the condition of our body, or 

sensual delight". He admitted that colour music would give pleasure of the third 

kind, and probably also of the first kind, although there was the problem of 

chords. Because of the fixedness of colours in space, Mendelssohn denied the 

possibility of colour chords similar to musical chords, but perhaps different 

colours could be joined to specific forms and then united. Without a solution 

along these lines, "either the disharmony [of the various colours] or the singularity 

of the forms will inevitably disturb the delight which is held out to us, if 

I may say so, by the euphonious colours." But this still left pleasure of the 

second kind, through intellectual perfection, that is, the imitation of human 

actions and emotions: "Can a colour melody give us this delight? The emotions 

are naturally expressed by certain tones, and therefore they can be re-enacted in 

our minds by the imitation of these tones. But what emotion has the least 

relation with a colour?"'^ 

Mendelssohn's book seems to have been the source from which the foremost 

German theorist of aesthetics. Herder, became acquainted with the idea of 

colour music.'^' The ocular harpsichord was a continuous presence in Herder's 

Cited in Mendelssohn, Schriften, vol. 2, p. 55: "fiir jeden Sinn ist eine Art von Harmonic 

bestimmt, die vielleicht mit nicht weniger Entziickung verkniipft ist, als die Harmonic der Tone ... 

Dir, grosser NcH'lonl hat das menschliche Geschlecht fiir dicsc Entdeckung verbunden sein sollen, 

und so viele Jahrhunderte mussten dir auch diesen unsterblichen Ruhm vorbehalten. Man ist aber 

noch so gliicklich nicht gewesen, diese Harmonic der Farben auf ihre wahre Stufe zu erheben, und 

zu der Mutter so vieler Ergotzlichkeiten zu machen, als die Harmonic der Tone. Die Farbenklaviere 

scheinen mehr zu versprechen, als sie in der That leisten." From the later added Anmerkungen it 

appears that he had read Kriiger's article, which explains why he spoke of harpsichords: he meant 

both Castel's and Kriiger's. He did mention Castel as "the first one to have sought to actually 

perform a colour melody" (p. 86). 

122 

Ibid., pp. 54, 56: "das Einerlei im Mannigfaltigen oder die Schonhcit, die Einhelligkeit des 

Mannigfaltigen oder die verstandliche Vollkommcnheit. und endlich der verbesserte Zustand 

unserer Ixibesbeschaffenheit oder die Sinnliche Lust"; "so mu.ss entweder die Disharmonie, oder 

das Einerlei der Figuren nothwendig die Lust storen, mit welchcr uns, wenn ich so redcn darf, die 

wohllautenden Farben zu erfreuen versprechen"; "Kann uns eine I'arbenmelodie mit diesem 

segnen? Die Leidenschaften werden natiirlicherweise durch gewisse Tone ausgedriickt, daher 

konnen sie durch die Nachahmung der Tone in unser Gedachtniss zuriickgebracht werden. Welche 

Leidenschaft aber hat die mindeste Verwandtschaft mit einer Farbe?" Inspired by the "line of 

beauty" from Hogarth's/4«a/yiis of beauty, Mendelssohn's proposal to combine specific colours with 

specific forms can be interpreted as suggesting a form of abstract painting not unlike Kandinsky's. 

In the Erstes Wdldchen of the Kritische Wdlder, Herder mentioned the possibility of a painted 

ocular harpsichord by combining colours with line forms, as had been discussed by Mendelssohn. 

See Werke, vol. 3, p. 139.


writings. His first mention of it was in 1765, his last in 1803. He not so much 

rejected the instrument as thought it already proven a failure, and referred to it 

in that way in arguments that very much resemble Rousseau's. Like Rousseau, 

he thought the juxtaposition of colours in space to be the essential aspect of 

pleasures for the eye and the succession of tones in time essential to the ear. If 

painting would try to use colours in a succession through time, "the essence of 

the art and all its effects would be lost. To this the ocular harpsichord gives 

testimony."'^" Like Rousseau, he rejected an art, be it an ordinary music or a 

colour music, that consisted only of harmonies, and he distrusted instrumental 

music. In his essay "Ob Malerei oder Tonkunst eine grosscrc Wirkung gewahre?", 

he made Music complain that 

the so-called educated world has become old and gray, and wants now partly to build with notes 

and juggle with them on a tightrope, instead of enjoving them. Tliey construct really enormous 

harmonious buildings, that fastly rise towards heaven and reason, as they cannot enter anymore 

into the sanctuary of the heart ... ITiis is just as foreign to my art, as when someone took it into 

his mind to invent an ocular harpsichord and then was astonished that this puppetry did not 

delight as an ordinary harpsichord did,'^'' 

Herder particularly cherished ideas similar to Rou.sseau's concerning the special 

power of music to affect the heart. The eye was to him "the coldest, most 

philosophical of the senses".'^ He thought the car to occupy a middling 

position between feeling (including touch, taste and smell) and "cold and 

detached" sight: "The former penetrates too deeply in us ... the latter stays to 

cool for us. [But] the tone of hearing enters so intimately into our soul ... Who 

would be able to watch an ocular harpsichord perform without being dazzled 

instantly? Whereas we can sustain listening much longer and can bear to listen 

Kritische Wdlder: Erstes Wdldchen (1769), in Werke, vol. 3, p. 1.36: "sonst gehet das Wesen 

und alle Wirkung der Kunst verlohren. Hieriiber ist das Farbenklavier zcuge." 

In Werke, vol. 15, p. 235: "diese so genannte gcbildete Welt ist alt und grau geworden, und 

will zum Theil jetzt stall Tone zu geniessen, mit Tone bauen txler Seiltanzcn und spielen. Sie bauen 

auch wirklich Wunderhohe harmonische Gebaude, die rasch zum Himmel, zum Verstande hinauf 

streben, da sie ins Heiligthum, zum Herzen nicht mehr kommen konnen ... Meiner Kunst ist dies so 

fremde, als da jemand auf den Gedanken kam, ein Farbenklavier zu erfinden, und sich wunderte, 

daB der Kinder-Jahrmarkt kein Vergniigen, wie das Klavier der Tone machte." The essay was first 

published in 1785. 

Kritische Wdlder: Viertes Wdldchen, in Werke, vol. 4, p. 77: "der kalteste, philosophischte der 

Sinne". The Viertes Wdldchen was written in 1769 but only published in 1846. Herder was much 

impressed by the English physician Chesselden's account, published in 1728, of the experiences of a 

boy who, by a new form of surgery, had been enabled to use his sight for the first time in his life. 

Herder reinterpreted the experiences of the boy as ex-pre.ssing primarily a feeling of disenchantment. 

See ibid., p. 82.


in almost any circumstances."'^^ This hierarchy of the senses gave music by far 

the most affective power of all arts: 

How often has the tone of a song, the simple movement of some heavenly notes, elevated a 

man from the deepest abyss of sorrow into heaven! How often does a simple melody cause 

tender, wistful tears to flow, cause people to suddenly find themselves with old feelings or 

places from childhood or in the unknown meadows of a blissful paradise, and how often does it 

completely resemble the magic tones of the original world, only more delicate ... Music has the 

magic wand of the essential action on the human heart within its immediate reach.'^ 

Strangely enough, at the end of his life, when Herder became more interested in 

natural science and he became acquainted with Euler's aether theory of light 

and fell under the spell of ihe idea of an all-pervading aether, he was inclined to 

accept the analogy of tone and colour scales (adopting the Newtonian colours), 

taking it to be, however, a question of an individual, not a universal psychology: 

Why could the colour scale not be compared with the tone scale? ... The range of both scales of 

such different senses seems miraculously the same in its relations, although irrationally ordered. 

The structure of our eye and ear, or rather of our seeing and hearing nerves, has to be 

analogous, which is not implausible ... It would also explain why each person likes certain tones, 

certain colours more than other ones; they are the ratio of the scales in which his organs finds 

pleasure, in that both scales order themselves most easily starting from this ratio ... But one 

cannot fix both scales by our harpsichord. Other nations have divided and divide the scales 

differently; they liked other intervals and other colours. 

This late conversion to the analogy notwithstanding, the distinction between the 

eye as the entrance to reason and the ear as the entrance to the soul was left 

intact. As Mendelssohn had argued before him. Herder made the action of light 

reach no further than inducing vibrations in the optical nerve and giving us, also 

by its warmth, a feeling of purely sensory pleasure. Sound affected "the organ 

whose function is to arouse emotions": "In harmony with the vibrating and 

sounding object, there rings in us a spiritual harpsichord and resounds with it. 

Abhandlung iiber den Vrsprung der Sprache (1772), in Werke, vol. 5, p. 66: "Das Gefuhl 

iiberwaltigt: das Gesicht ist zu kalt und gleichgiiltig; jenes dringt zu tief in uns ... dies bleibt zu 

ruhig fiir uns. Der Ton des Gehors dringt so innig in unsre Seele ... wer [kann] immer mit 

Aufmercksamkeit ein Farbenklavier begaffen, ohne nicht bald zu erblinden? Aber horen. gleichsam 

horend Worte denken, konnen wir langer und fast immer". 

"Ob Malerie oder Tonkunst...", in Werke, vol. 15, pp. 2.36 resp. 239: "Wie oft hat der Ton 

eines Gesanges, der simple Gang einigcr himnilischen Tone einen Men.schen aus dem tiefsten 

Abgmnde der Traurigkeit bis in den Himmel erhobeni Wie oft geschiehets, daB eine einfache 

Melodic zarte, wehmiithige Thranen rinnen macht, die Men.schen plotzlich in alte Empfindungen 

und Gegenden der Jugend, oder in unbekannte Auen eines seligen Paradieses verselzt, und voUig 

den Zaubertonen der ersten Welt, nur auf fcinere Art, gleich kommt ... Du Tonkunst hingegen hast 

den Zûberstab der eigentlichen Wirkung auf menschliche Herzen unmittelbar".


The tones are measured out to it, accounted to it, harmonically, melodically; an 

invisible, arousing Spirit talks with our feeling self in succession."'* 

The later writings of Herder seem to fit in with the then freshly blossoming 

German Romantic Naturphilosophie, in which the unity of nature and the 

connectedness of man with nature were much emphasized. One of the earliest 

books that made these ideas popular outside Germany was De TAllemagne, by 

Madame de Stael, who had spent most of the exile Napoleon had forced her 

into in Germany. In her book she brought back, unknowingly, the ocular 

harpsichord to France, as she described how 

the analogies of the various elements of physical nature together reveal the supreme law of 

creation, variety in unity and unity in variety. What is more astonishing than, for instance, the 

rapport between sounds and forms, between sounds and colours? ... a certain savant wanted to 

construct an ocular harpsichord which by the harmony of colours could imitate the delight that 

music gives. Incessantly we compare painting with music and music with painting, because the 

emotions we experience reveal to us analogies where cold observation discerns only differences. 

Each plant, each flower contains the whole system of the universe; a brief moment of life hides 

eternity in its bosom, the weakest atom is a worid and the world is perhaps but an atom.'^ 

It is not so much this sort of general programmatic statement that reveals an 

impact of colour music on Romanticism, however, as rather the use that early 

Romantic poets and novelists made of it. In 1781/1782, while travelling through 

Italy, Wilhelm Heinse read Mendelssohn's Briefe iiber die Empfindungen and 

commented on it in a notebook. He agreed with McndeLssohn that "it certainly is 

Fragment meant for Herder's journal Adrasiea (1801-1802), but finally not included by 

Herder. It was published posthumously in 1809. In Werke, vol. 24, pp. 436-440: "Warum sollte man 

nun die Farbenleiter nicht mit der Tonleiter vcrgleichen? ... Der Umfang beider Scalen so 

verschiedner Sinne ist wunderbarer Weise in seiner 'V'erhaltniBgliedern ahnlich. obgleich irrational 

geordnet. Die Structur unsres Auges und Ohrs, oder viclmehr unsres Seh- und Hornervs, muB eine 

Aehlichkeil gcben, die sehr denkbar ist ... Auch wiirde hieraus erklarlich, warum gewiBe Tone, 

gewiBe Farben Diesem und Jedem lieber sind als andre; sie sind das VerhiiltniB der Scala, bei 

welchem sein Organ das meiste Wohlbehagen findet, indem es von hieraus sich selbst die Scala aufs 

bequemste ordnet. ... nur darf man beide eben nach unserm Clavichord nicht fixieren. Andre 

Nationen theilten und theilcn die Scala anders; sie liebten andre Intervalle wie andre Farben"; 

"Harmonisch mit dem geschwungenen klingenden Korpcr klingt in uns ein geistiges Clavichord und 

tonet ihm nach. Zugemessen, zugezahlt werden ihm die Tone, harmonisch, melodisch; ein 

unsichtbarer, weekender Geist .spricht mit unserm fiihlcnden Ich in Succession." 

130 

Stael Holstein, De TAllemagne, vol. 3, pp. 149-150: "Les analogies des divers elements dc la 

nature physique entre eux servent a constater la supreme loi de la creation, la variete dans 

I'unite, et I'unite dans la variete. Qu'y a-t-il de plus etonnant, par exemple, que le rapport des 

sons et des formes, des sons et des couleurs? ... un savant a voulu faire un clavecin pour les yeux 

qui put imiter par I'harmonie des couleurs le plaisir qui cause la musique. Sans cesse nous 

comparons la peinture a la musique, et la musique a la peinture, parceque les emotions que nous 

eprouvons nous revelent des analogies ou I'observation froide ne verroit que des differences. 

Chaque plante, chaque fleur contient le systeme entier de I'univers; un instant de vie recele en 

son sein retemile, le plus foible atome est un monde, et le monde peut-etre n'est qu'un atome."


very difficult to create perfection and beauty and sensory pleasure with colours, 

since the air is a medium that acts far more powerfully on man than light. The 

emotions wholly disappear." He nevertheless thought he could see colour music, 

performed by nature itself, which made the ocular harpsichord fail by its limited 

capacity rather than by principle: 

And how far must any ocular harpsichord lag behind the evening and morning glow, the true 

beauties which indicate the perfection of light, of the sun? Nevertheless colour harmony 

certainly exists, and the beauty of colours, a fresh green, a healthy flesh tint, the red of flowers 

and all variations thereof certainly feed the imagination. Charm is not a mathematical nor a 

wavelike or flaming line of movement, but something alive approaching us lovingly, or a trace ... 

The Frenchman and Moses have not themselves felt what they wanted to explain.'^' 

Heinse was one of the first early Romantics to use synaesthetic imagery, 

although it still looked rather like a somewhat artificial application of his 

readings. In the diaries of his Italian journey he wrote phrases like: "In the 

Church delle Grazie [in Venice] there is a big masterpiece by Titian. The group 

in itself presents a fiery heroic colour music," and: "Titian was a great master in 

the music of light rays. Nature as well is infinitely rich in this," and: "The 12th of 

May -1 have never seen such a sweet transition from day into night. The 

harmony of light tones from saffron-red to a milk-white gleam."''^ In his novel 

Ardinghello, published in 1787, the reflection of his Italian travels, he wrote 

similarly: "What magic, what infinite melody of light and dark, of cloud forms 

and a merry blue!"'^^ 

In this, other Romantics followed suit. Ludwig Tieck, for example, was 

' ' In Heinse, Werke, vol. 8', pp. 455-456: "Vollkommcnheit und Schonhcit und sinnliche Lust 

mit Farben zu erregen zu wollen, ist gewiB sehr schwer, well die Luft ein well starker wirkend 

Medium auf den Menschen ist, als Licht. Die Ixidenschaften fallen ganz weg"; "Und wie weit muB 

jedes Farbenclavier nach Abend und Morgenrothen stehen? den wahrcn Schonheiten, die die 

Vollkommcnheit des Lichts, der Sonne anzeigen. Inzwischcn gibts gewiB eine Farbenharmonie, und 

Schonhcit in den Tinten, frisches Griin, gesunde Fleischfarbe, blumenroth mit alien Abwechslungen 

geben gewiB schon an und fiir sich der Phantasie zu schaffen. Reiz ist keinc mathematische weder 

Schlangen noch flammichte Linie der Bewegung, sondem etwas lieblich uns entgegen kommendes 

lebendiges cxier eine Spur ... Der Franzose und Moses haben nicht gefuhit, was sie erklaren 

wolllen." The "wavelike or flaming line of movement" referred, of course, to Mendelssohn's 

proposal to combine colours with forms; see n. 118. 

'^^ All in Heinse, Werke, resp. vol. 7, p. 233; vol. 8^ p. 245; vol. 8^, p. 35: "In der Kirche delle 

Grazie selbst ist ein hohes Meisterstiick von Tizian. Die Gruppe an und fiir sich selbst macht cine 

feurige heroische Farbenmusik"; "Tizian war ein grosser Meister in der Musik der Lichtstrahlen. 

Die Natur ist auch unendlich reich hierin"; 'Den 12. Mai. - Ich habe noch keinen siiBem tjbergang 

von Tag in Nacht gesehen. Die Harmonic der Lichttone vom Saffranrotlichen in milchweiBen 

Schimmer." These phrases were not published in Heinse's lifetime. 

Cited in Fischer, "Verbindung", p. 515: "Welch ein Zauber, welche unendliche Melodic von 

Licht und Dunkel, und Wolkenformen und heiterm Blau!"

Castel's oculcU" harpsichord 65 

greatly influenced by Heinse; he urged his friend Wackenroder to read Ardinghello.^^ 

In Tieck's work synaesthetic imagery appears in full bloom. In his 

poem Zerbino, written 1796-1798 and published in 1799, one reads: "What by 

order of the gods had been jealously separated, here the goddess Fantasy has 

united, having the sounds know their colours, causing sweet voices to shine 

through the leaves and making colour, scent and song call each other sisters.""' 

But in the Phantasien iiber die Kunst, which reads like a programme of 

a new Romantic aesthetics and was largely written by Wackenroder but expanded 

and published under his own name by Tieck, earlier objections against a 

full analogy between painting and music, raised earlier by, for instance, Rousseau, 

were taken up once again: painting cannot but imitate, and in this it is 

necessarily very close to nature, but at the same time it will always fall short of 

nature's own beauty. Music, on the other hand, is the essentially human, creative 

art. Therefore the evocative power of music is much greater than the power of 

colours.'^ Notwithstanding this asymmetry, however, Tieck engorged the 

sensory abundance of nature, agreeing with Castel that a even a single colour 

delights us, and he fully endorsed the use of synaesthetic imagery, although he 

did not justify it in any systematical way: 

The variety among flowers and shrubs is an arbitrary music in beautiful interplay, in sweet 

repetition: the songs of the birds, the gurgling of the water, the cries of the animals are in a 

sense at the same time an orchard or flower garden: the most charming love and friendship 

winds itself with glittering chains around all forms, colours and tones inseparable.'" 

'"" See ibid., p. 514. 

Cited in ibid., pp. 521-522: "Was neidsch sonst der Goiter SchluB getrennet, / Hat Gottin 

Phantasie allhier vereint, / So daB der Klang hier seine Farbe kennet, / Durch jedes Blatt die siiBe 

Stimme scheint, / Sich Farbe, Duft, Gesang, Geschwister nennet." 

'^ Tieck [and Wackenroder], Phantasien, esp. pp. 119-121, 240-245. 

137 

Ibid., p. 118: "Die Mannigfaltigkeit in Blumen und Gestrauchen ist eine willkiihrliche Musik 

im schonen Wechsel, in lieber Wiederholung: die Gesange der Vogel, der Klang der Gewasser, das 

Geschrey der Thiere ist gleichsam wieder ein Baum- und Blumengarten: die lieblichste Freundschaft 

und Liebe schlingt sich in glanzenden Fesseln um alle Gestalten, Farben und Tone unzertrennlich." 

Tieck did try to establish something of a formal analogy between colours and sounds, 

though. He rejected the elementary analogy of the ocular harpsichord as he had come to know it, 

but proposed instead an analogy not between single colours and tones but between the different 

shades of one colour and different tones. The single colours themselves had to be seen not as the 

analogues of single tones but of timbres or instruments. In this, Tieck repeated an interpretation 

that had been suggested already a couple of times before. The French printer Gauthier d'Agoty, 

one of the first printers to produce three-colour prints, had thought along these lines in 1753, and 

the German Hellwag had written an article about it in 1786 and even presented the idea to Kant. 

The one to have elaborated this idea the farthest was the German Johann Leonhard Hoffmann, in 

his book Versuch einer Geschicfue der mahlerischen Harmonic iiberhaupt und der Farbenharmonie 

insbesondere, published in 1786. Hoffmann even gave a list of all the different analogues of colours 

and instrument, coupling indigo to the violoncello, blue to the violin, green to the human voice,


Tieck, in his turn, was a dominating influence on E.TA. Hoffmann, one of the 

outstanding figures of German Romanticism, and it is in his writings that a last 

mention of the ocular harpsichord can be found in Germany. On the one hand, 

Hoffmann admitted that "tone is in music exactly what colour is in painting". On 

the other hand he rejected the kind of formal colour music the ocular harpsichord 

apparently performed. Melody and harmony in music could only be 

compared with the full bloom of nature itself: 

It is not the colour green, it is the wood with the graceful beauty of its foliage, that engenders 

the thrill and sweet melancholia in our breast. The deep blue of the sky will soon start to 

appear empty and sad to us when there are no clouds rising in myriads of changing images. 

Apply this to art and realize how soon you would be tired of seeing the most beautiful colours 

without any form, and how briefly sight would be tickled by them. Think of the silly ocular 

harpsichord of Father Castel! - And in music the same is true. The tone will only deeply affect 

the soul when it has formed itself into melody or harmony, in short, into music."* 

It is an indication of the aesthetic changes near the end of the eighteenth 

century as described by Neubauer and Barry, that Heinse and Tieck speak of 

fantasy and the imagination as the vehicle of artistic delight, and the Romantic 

synaesthetic imagery clearly has a primarily evocative function rather than a 

descriptive one. However, for all of these early Romantics, music is still standing 

very much apart; a harmony and melody of colours they find in nature itself, 

something they would not have deemed appropriate for music at all. 

Meanwhile, the word play of synaesthesia was developed and used especially 

yellow to the clarinet, scarlet to the trumpet, pink to the oboe, kermes to the flute, purple to the 

horn and violet to the basscxsn. Of course, the notion of a well-defined colour scale had at this 

stage of the historical development completely drifted out of the picture. See Gauthier d'Agoty, 

Observations, pp. 174-175; Hellwag, "Vergleichung," and his letter to Kant of December 1'790, in 

Kant, Briefwechsel, vol. 2, pp. 194-204. For Hoffmann, see Goethe's Malerialien zur Geschichle der 

Farbenlehre, pp. 395-399. Gauthier d'Agoty and Hoffmann developed their ideas in reaction to 

Castel's ocular harpsichord, which they rejected all the more vehemently for it. Tieck just as well 

called it a "kindische Spielwerk" (p. 243). A list of comparisons of colours with musical instruments 

similar to Hoffmann's, developed independently by the Englishman William Gardiner, was given in 

The lives of Haydn and Mozan (London, 1817), the English translation of the original French book 

by L.-A.-C. Bombet, a pseudonym of M.-H. Beyle, better known as Stendhal. See the note there on 

p. 255. 

' Hoffmann, "Ein Brief des Kapellmeisters Johannes Kreisler" (1819), in Werke, vol. 14, pp. 93- 

94; "Der Ton ist in der Musik ganz und gar dasselbe was in der Malerei die Farbe ... lis ist nicht 

die Farbung des Griinen, es ist der Wald mit der anmutigen Pracht seines Laubes, der in unserer 

Brust das Entziicken weckt und die siiBe Wehmut. Das tiefe Blau des Himmels diinkt uns bald ode 

und traurig, steigen nicht die Wolken auf in tausend wechselndcn Bildern: Wendet das auf die 

Kunst an und denkt Euch, Wiirdiger, wie bald es Euch ermiiden, oder was fiir einen momentanen 

Sinneskitzel es von Haus aus erregen wiirde, die schonsten Farben ohne Gestaltung zu schauen? - 

Denkt an das lappische Farbenklavier des Paters Castel! - Und nun i.st's ebenso in der Musik. Der 

Ton wird nur dann erst tief unser Gemiit ergreifen, wenn er sich zur Melodic oder Harmonie, kurz, 

eben zur Musik gestaltet."


in early Romantic England, and there, one person only seems to have passed on 

the Castellian notion of colour music. In the prose interludes of his famous 

poem The loves of the plants, first published in 1789, Erasmus Darwin mentioned 

Newton's "happy discovery" of the analogy of spectral colours and the 

minor scale proposal of deducing a luminous music from this analogy by Father 

Cassel [sic]. He accepted the conclusion that there was "a sisterhood of music 

and painting", and added that "hence they claim a right to borrow metaphors 

from each other; musicians to speak of the brilliancy of sounds, emd the light 

and shade of a concerto; and painters of the harmony of colours, and the tone 

of a picture.""' If Castel's colour music did play any role in English Romantic 

poetry, Darwin is a very likely source, since his poems had a great influence on 

the next generation of poets, particularly Shelley.''"' 

Interestingly enough, Darwin was the first to be able to defend colour 

harmony by a physiological argument, answering one of the most frequently 

raised objections against Castel, i.e. that the difference between the organs of 

hearing and sight was too great to support any analogy. Somewhere in the early 

1770's Darwin had discovered the phenomenon of the afterimage, which has a 

colour complementary to the colour of the object itself. In The love of the plants 

he proposed this as the physiological basis for colour harmony, in that on the 

retina the colour of the afterimage caused by the last object would interfere with 

the real colour of the next object. It is sad that this discovery came too late to 

be able to join the debate on colour music.'"' 

Conclusion 

It might seem strange that at the same moment when synaesthetic imagery 

became a frequently used stylistic device, the ocular harpsichord and the colour 

music it was supposed to play disappeared out of sight. However, with its 

entrance in poetry, the harmony of the senses became a thing of the imagination, 

to be treated in many kinds of ways, only not as a truthful description of 

Darwin, Love, 3rd Interlude, pp. 140-141. Darwin repeated all this almost verbatim in the 

"Additional notes" to his posthumous poem 77i* temple of nature (1803), under the heading "MelcxJy 

of colours". Darwin seems to have derived his knowledge of the ocular harpsichord from Guyot's 

Recreations'. 

140 

See Desmond King-Hele, Erasmus Darwin and the Romantic poets (London, 1986). For an 

extensive documentation on the emergence of synaesthetic imagery in poetry, see the writings of 

Von Erhardt-Siebold and Weliek. 

141 

Darwm, Love, p. 141. The existence of the afterimage vras announced by Erasmus' son 

Robert, the father of Charles Darwin, in the Philosophical Transactions of the Royal Society 76, 

1786, but the original discovery was almost certainly his father's. See Desmond King-Hele, Doctor of 

revolution: the life and genius of Erasmus Darwin (London, 1977), p. 177.


natural phenomena. The ocular harpsichord was in this respect essentially an 

eighteenth-century instrument, as this century seems to me to be pre-eminently 

dominated by problems of sensory perception. Philosophical empiricism is 

largely a product of the eighteenth century, developed and articulated by 

philosophers like Berkeley, Hume, Condillac, and others. The eighteenth century 

also saw the birth of aesthetics as an empirical theory of art, as distinct from the 

earlier theories of art which mostly consisted of prescriptive rules. Especially 

Diderot and Herder tried to base their aesthetics on a clear view of the nature 

of all the different senses. The evocative power of music emphasized by Rousseau 

and Herder was for them an experiential fact of human psychology, which 

any aesthetics had to incorporate. It is, then, I think, with respect to an empiricist 

aesthetics rather than to the emergence of synaesthesia in Romanticism 

that it seems undeniable that "the ocular harpsichord counted as an invention 

that one had to come to terms with", as Von Erhardt-Siebold wrote. Whether 

there indeed was "wide recognition of the facts behind it" is then perhaps not the 

most important question concerning it. 

With respect to the developments in late eighteenth-century aesthetics argued 

for by Neubauer and Barry, the way the ocular harpsichord was discussed 

testifies above all to the growing emphasis on the special problems that put 

music apart from the other arts. Of course this process cleared the ground for 

the changes of view concerning the place of representation in art, but the part 

the ocular harpsichord played in these later phases of the process, and especially 

its precise relation with the emergence of synaesthetic imagery, tends to be 

drowned in the polyphonic crescendo at the turn of the century.'"^ 

It is, on the other hand, remarkable that after the superficial enthusiasm of 

the theorists of painting in the first half of the century, the harpsichord was 

henceforth ignored by the visual arts. The early Romantic theorists of colour, 

like Runge, Friedrich and Turner, showed no interest in Castel, nor any knowledge 

of his ideas. If by anyone, they were influenced by Goethe, and although 

Goethe did praise Castel as a small champion of anti-Newtonianism in optics, 

his colour music left him cold. Nothing of Castel's views entered Goethe's own 

writings on the theory of colours.'"' This no doubt originated in the highly 

eclectic character of Castel's conception of colour music. The basic analogy 

Castel seemed to have believed in was that of colour music as a strict parallel to 

instrumental music. It was this analogy that necessitated an unambiguous and, 

Of course, Neubauer's and Barry's theses do not coincide, and in this study I can hardly do 

justice to their arguments. 

See Goethe's chapter on Castel in the Geschichle der Farbenlehre, pp. 328-333. In fact, 

Goethe had only read Castel's Optique des couleurs, and thought Castel had been a dyer! He also 

copied Kriiger's draft of an ocular harpsichord, but all without comment. See the Ergdniungen und 

Eriduterungen to the Geschichte der Farbenlehre, pp. 192, 199-203, 262, 286.


moreover, physically or psychologically "true" colour scale. On the other hand, 

Castel seemed to believe that the existing colour arts, not only painting but also 

dance and pantomime, were somehow parts of this as yet nonexistent colour 

music, or somehow subordinate to its rules. The suggested comparison of music 

with painting as these art forms existed in general was too vague, and already 

too often voiced in the past, to be able to convince painters that there was 

anything to be gained from studying it. 

On the whole one has to admit that Castel himself took no part in the 

adventures of his harpsichord. Both in his science and in his aesthetics Castel 

was looking backward rather than forward, although many passages in his 

writings seem to point to future developments. The groping way in which 

Wilhelm Heinse towards the end of the century tried to frame his experiences of 

the beauty of nature into the language of colour harmony are remarkably similar 

to the way Castel spoke about his colour music on some occasions: "I saw a 

garden dotted with flowers: a sweet zephyr blew, and singling out that moment, I 

saw the harpsichord. I saw a meadow strewn with rose drops; the sun rose, I 

moved my head a little, and my eye said to me: there is the harpsichord."'"" 

Epilogue 

With E.TA. Hoffmann, in 1819, the debate on the ocular harpsichord and on 

colour music in Germany finally died. The same year also saw its final flickering 

in England. In 1814 David Brewster had invented the kaleidoscope, an instrument 

of which in London and Paris together 200.000 copies were sold within 

three months. In 1819 Brewster wrote A treatise on the kaleidoscope, explaining 

its working, as so many bad ones were circulating. In his book he praised Castel 

as "the first person who attempted to supply the organ of vision with the luxuries 

of light and colour", criticizing him, however, for not having realized that colours 

can not please for long if they arc not combined with beautiful forms. After sixty 

years Brewster saw himself as having achieved what Castel had so vainly toiled 

at: 

Those who have been in the habit of using a correct Kaleidoscope, furnished with proper 

objects, will have no hesitation in admitting, that this instrument realizes, in the fullest manner, 

the formerly chimerical idea of an ocular harpsichord, llie combination of fine forms, and evervarying 

tints, which it presents, in succession, to the eye, have already been found, by ex- 

Memoires de Tre\oux, December 1735, p. 2699: "J'avois vii un Parterre jonche de fleurs: 

un doux Zcphire avoit soufle, & saisissant cet instant, j'avois vii le Clavecin. J'avois vu une Prairie 

semee de rosee; le Soleil s'etoit levc, j'avois fait un mouvement de tele. & mon oeil m'avoit dit, 

voila le Clavecin."


perience, to communicate to those who have a taste for this kind of beauty, a pleasure as 

intense and as permanent as that which the finest ear derives from musical sounds.'*^ 

In France, on the other hand, Castel's name was already completely forgotten at 

the begiiming of the 19th century. In his review of the Salon of 1846, Baudelaire 

suddenly argued for an analogy between colours and sounds, in apparently 

complete ignorance of its history. In fact, he almost sounded like Castel reincarnated: 

"In colour there are harmony, melody and counterpoint to be found ... 

Harmony is the basis of the theory of colour. Melody is the unity in colour, or 

coloiu" in general ... The colorists design from nature; their figures are naturally 

delimited by the harmonious struggle of harmonious masses," and he ended 

with: "I do not know whether any analogist has ever solidly established a 

complete scale of colours and feelings ..."'"* 

During the 19th century nothing more was said on the subject except by one 

or two isolated figures, until, from about the last decades of the 19th century, 

there suddenly emerged an enormous interest in the psychological phenomenon 

of synaesthesia. Weliek has listed some 800 titles on this subject for the period 

1880-1931.'"^ The phenomenon was considered a purely psychological one, a 

kind of automatic association of certain colours with certain sounds or smells, or 

combinations of such, which people reported actually to experience. There was 

no connection at all with the eighteenth-century discussion on colour music. In 

fact, the phenomenon of synaesthesia is hardly reported before the period it was 

so extensively studied. One of the first instances is a fragment of E.TA. Hoffmaim 

from 1814, in which he confessed to experience in the 

state of delirium that immediately precedes falling asleep, especially when I have listened a lot 

to music, an analogy of colours, tones and scents ... The smell of the dark red carnation has a 

strange magical force on me; inadvertently I sink into a dreamlike state and I hear, coming 

Brewster, Treatise, pp. 131, 134-135. The 200.000 copies are mentioned on p. 7. Note, 

moreover, with an eye on the theses of Neubauer and Barry, that Brewster's kaleidoscope did not 

show the abstract colour patterns of todays toy versions, but instead used the standard heroic 

human figures of academic painting. 

In Baudelaire, Oeuvres completes, vol. 2, pp. 423-426: "On trouve dans la couleur I'harmonie, 

la melodic et le contrepoint ... L'harmonie est la base de la theorie de la couleur. La 

melodic est I'unite dans la couleur, ou la couleur generale ... Les coloristes dessinent comme la 

nature; leurs figures sont naturellement delimitees par la lutte harmonieuse des masses colories 

... J'ignore si quelque analogiste a etabli solidement une gamme complete des couleurs et des 

sentiments". 

Weliek, "Synaesthesieforschung," pp. 369-373. In his other articles, Weliek discusses the 

ocular harpsichord as being part of the early history of synaesthesia. My study will have made clear, 

I hope, that this is not the right way to look at it.


from afar, crescendo and decrescendo, the deep tones of the basset horn 148 

Nevertheless, this phenomenon of synaesthesia soon made itself felt in contemporary 

music. Some colour instruments were built in Great Britain and in the 

United Sates; in Russia one Alexander Mozer tried to do the same on request 

of the composer Scriabin, who wrote a part for such an instrument in his 

symphonic poem Promethee, le poime du feu of 1908-1910. None of these 

instruments seem to have been based on any formal rules of harmony. The 

eighteenth-century debate remained a closed book. The only reminiscence was 

the article "Colour-music" (the contemporary version, of course) by Adrian B. 

Klein in the 14th edition of the Encyclopaedia Britannica, published in 1929, 

where Castel was mentioned as "the Giotto or Guido d'Arezzo of colour-music", 

although the author hardly knew anything about Castel's views. 

If one wonders whether since the eighteenth century anything has been 

achieved in keeping with Castel's ideas, perhaps one should say that the light 

and laser shows of the modern discotheque, though also lacking rules of 

harmony, come closest. Indeed, Castel himself already suggested that "by using 

carefully installed mirrors, or covering the walls of an appartment with mirrors, 

one can multiply the object and scatter it in all directions," or that the keys of 

his instrument could be coupled to centrally placed lights in casings of coloured 

glass, such that "the whole room would bath in light of a single colour which 

changes incessantly through the movements of the keys".'"^ 

Hoffmann, "Kreisleriana": "Hochst zerstreute Gedanken," in Werke, vol. 1, p. 56: "im Zustand 

des Delirierens, der dem Einschlafen vorhergeht, vorziiglich wenn ich viel Musik gehort habe, finde 

ich eine Ubereinkunft der Farben, Tone und Diifte ... Der Duft der dunkelrolcn Nelken wirkt mit 

sonderbarer magischer Gewalt auf mich: unwillkiirlich versinke ich in einen traumerischen Zustand 

und hore dann wie aus weiter Feme die anschwellenden und wieder verflicBenden tiefen Tone des 

Bassethoms." 

Mimoires de Trevoux, December 1735, p. 2746: "par des Miroirs places avec art, & en 

tapissant meme tout un appartement de Glaces, on peut multiplier I'objet & le semer de toutes 

parts"; "ensorte que tout un appartement soit colore d'une couleur mobile que le mouvement des 

touches fait changer a chaque instant."


Summary 

In the first part of this essay an overview is presented of Castel's theory of colour music and the 

ocular harpsichord. It is investigated to what extent he succeeded in building his harpsichord, 

concluding that various models have existed, none of which could perform up to Castel's expectations. 

Nor did anyone else succeed in this. In the second part of the essay contemporary 

comments (up till 1819) on the ocular harpsichord and on the idea of colour music are analysed. It 

is shown that these comments fit in with the search for a more empiricist aesthetics in the second 

half of the eighteenth century, and with an increasing emphasis on the special status of music that 

was a part of this development. 

Department of Philosophy 

University of Amsterdam 

Nieuwe Doelenstraat 15 

1012 CP Amsterdam 

The Netherlands


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A great number of manuscripts of Castel were acquired by the Royal Library in 

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SECONDARY LITERATURE 

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Jahrhundert," Archiv fiir die gesamte Psychologic 94, 1935, 347-375. 

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Literaturwissenschaft und Geistesgeschichte 14, 1936, 75-102.

the ocular harpsichord of louis-bertrand castel - Gewina

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