The visual arts and music already began to draw on one another in the nineteenth century, insofar as painters strove to depict movement, for example, while program music alluded to paintings. But it was only at the start of the twentieth century, in the course of the theoretical debate on a synthesis of the arts, that a transfer of structural modes of creative production took place. In the visual arts, this first became manifest in the integration of a temporal dimension derived from musical practice, then in an orientation based on rhythmic and harmonic relationships, and principles of composition and improvisation. Music, in turn, began to address color, surface, and artistic techniques.
Long before structural analogies between music and the visual arts became established in the twentieth century, the two genres made numerous references to one other throughout their respective histories: either at the theoretical level in the context of the paragone (the Renaissance debate on the rivalry between the arts), in the development of esthetics in the eighteenth century — which formulated common goals for the two genres — or at the practical level, in the choice of subject matter derived from the other art form.
Thus, the choice of musical themes such as the depiction of musicians or instruments was a long-standing tradition in painting before tone painting — which found expression even in literature, in numerous Künstlerromane — came to be propagated more forcefully as of the eighteenth century. Under the influence of musical esthetics, musical art became something of a role model for painting in the nineteenth century and, subsequently, structural principles were transferred gradually to the production of visual imagery, as illustrated by Philipp Otto Runge’s Die Zeiten (The Times of the Day; 1807). Because of the rise of photography, among other things, painting lost its monopoly on figurative reproduction and, in the course of its reorientation process, discovered in music a role model for an abstract approach to artistic material. To this attests a growing preference, manifest by the end of the nineteenth century, for musical titles for semiabstract or abstract paintings.
By the same token, mimetic representation of events in the real world was achieved in nineteenth-century music solely by recourse to tone painting. Imitations of natural phenomena such as birdsong, thunderstorms, idyllic landscapes (including a rushing stream and the blast of hunters’ horns), and a railway journey are just one example of this.
It is only with the proliferation of program music in the nineteenth century that one finds concrete references to works of fine art, as in Franz Liszt’s Années de pèlerinage (Years of Pilgrimage; 1839) and Hunnenschlacht (Battle of the Huns; 1857), and Modest Mussorgsky’s Kartinki s vystavki (Pictures at an Exhibition; 1874).
In these cases, correlations with the painterly template exist primarily as tertium comparationis, that is, through the use of identical adjectival ascriptions — monumental or static, for example — which had been transferred from the visual plane to music.
Since the early twentieth century, productive exchanges between visual art and music have ultimately intensified, either because of the synchronous activity of artist-musicians in the two genres, of endeavors to synthesize art forms — for example, in musical theater — or of the transfer of creative principles based on structural analogies.
Following the rise at the end of the nineteenth century of tendencies to graphically depict movements, such as those in dance — as in Henri Toulouse-Lautrec’s portrait Miss Loïe Fuller (1893) — aspirations to integrate a free, abstract approach to artistic material, modeled on music and including its temporal dimension, intensified in the early twentieth century.
This happened, first, within the two-dimensional static image, as illustrated by the caption Painting with Time noted on the back of a painting by Walter Ruttmann (Untitled; 1918).
Musical terms such as fugue, rhythm, dance, and triad were also frequently used in painting titles, such as František Kupka’s Amorfa - Dvoubarevná fuga (Amorpha: Fugue in Two Colors; 1912), which is based on sketches of movement made at a ball.
In a second step, painters such as Hans Richter and Viking Eggeling attempted to expand the canvas, which they considered too static and limited; first of all by exploring in their scroll drawings relationships between color and form in terms derived from the musical model, also with regard to a temporal sequence. Eggeling thus described Horizontal-Vertical Orchestra (1919), his first scroll, as creating evolutions and revolutions in the sphere of the purely artistic (abstract forms), analog somewhat to events in music with which our ear is already familiar. Ultimately, the concepts they had developed in painting led Eggeling, Richter, Ruttmann, and other painters to experiment with abstract film by the end of the 1910s.
However, painters were interested in music not solely because of its potential for shaping temporal sequences but also because of the finely regulated relationships between individual elements. Thus, as early as 1904, Adolf Hölzel had called for a counterpart in visual art to musical harmonics: I mean, similar to the counterpoint and harmonics that exist in music one must also endeavor in painting to create a specific theory regarding artistic contrasts of every kind and their harmonious equilibrium.
The break with the figurative at the end of the nineteenth century sparked reflection on and redefinition of the inherent value of the materials used in painting and, in the following decade, more concerted efforts at systematization: the principles of the proportionality of color and form were now formulated in analogy to musical art.
Robert Delaunay thus premised his visual idiom on simultaneous contrasts of color. By placing blocks of pure complementary color alongside one another he facilitated simultaneous perception of them, and hoped thereby to provoke an impression of movement in two or three dimensions. He manifested this concept in his series of window paintings (Fenêtres simultanées; 1912) and circular forms (Formes circulaires; as of 1912), and took it up again from 1930 onwards in his rhythm’ paintings (Rythmes). Synchromists Morgan Russell and Stanton MacDonald-Wright employed color rhythms based on color chords in paintings such as Synchromy No. 7 (1914–1915) and Creation Synchromy (1914).
In 1913–1914, Fernand Léger composed what he called form contrasts from cubic and cylindrical forms executed in primary colors. He considered contrast a powerful means of visual expression, analogous to dissonance in music. Franz Marc derived his concept of color dissonance directly from Schoenberg’s Theory of Harmony (1911) and combined it with an organization around the prism, as evident, for example, in Sonatine für Geige und Klavier (Sonata for Violin and Piano; 1913).
Johannes Itten regarded color as a vertical arrangement analogous to harmony and the development of the graphic line in the horizontal plane as analogous to melody. His deliberations on color drew on Adolf Hölzel’s contrast theory, yet he also went a step further by investigating, in particular, the effects of color on equilibrium, the proportions and degrees of saturation of colors, and their effects on light and space. This is evident in Itten’s Komposition aus zwei Formthemen (Composition of Two Form Themes; 1919), in which he used basic forms, the triangle and circle, to develop a complex interlocking visual structure in which the spectral colors run through the geometric construction in nuanced hues and thereby animate it. Form and color, and texture and depth create a multifaceted visual space. This multidimensional interconnectedness of the pictorial elements, for which Itten coined the term bandräumlich (spatially bound), keeps the viewer’s eye constantly moving.
In order to elucidate their concepts, and especially when it came to naming their works, visual artists referred frequently — mostly in metaphorical terms — to the musical forms and principles of Baroque, Classicism, and Romanticism as a means of communicating the systems that underpinned their compositions.
Yet others, including Itten, were drawn to contemporary forms such as the twelve-tone technique, a renunciation of traditional harmonics, or even to ragtime and the cakewalk. Léger created an ink drawing, Jazz (1930), in which the dissonant rhythms of jazz are expressed in the oblique pictorial structure and stark contrast of black and white tones. In his two similarly structured paintings, Broadway Boogie Woogie (1942–1943) and Victory Boogie Woogie (1942–1944), Piet Mondrian interpreted in form and color the syncopated rhythms of jazz and his experience of Manhattan’s bright, flickering lights and rectilinear street grid.
The definition of visual proportionality based on the musical model was accompanied at the beginning of the twentieth century by a transfer of the principles and structures of composition, whereby — thanks to great enthusiasm for Bach at that time — a polyphonic composition, the fugue, was predominant.
Generally, neither a specific fugue nor even the form of the fugue was taken as a model or starting point, rather the counterpoint as a musical principle, which may equally be described as countervoices or countermotifs. A horizontal arrangement of interreferential motifs is recognizable, and attention is drawn, therefore, not only to the temporal sequence of the piece but also to the motif’s ramifications within the fugue as a whole.
Eggeling thus began work in 1915 on a basso continuo of painting and, inspired by Futurist musician Ferruccio Busoni, became interested in musical counterpoint. From this ensued his concept of optical counterpoint, a theory of visual composition based on the polarity of pairs of opposites of abstract elements, such as he attempted to realize in his film Symphonie Diagonale (1924).
Itten also oriented himself to the contrapuntal method as a combinatorial principle. In Der Bachsänger (The Bach Singer; 1916), the figure of the Bach singer is employed symbolically in order to develop a pictorial structure whose complexity, transparency, and, above all, crystalline rigor were meant to reflect the polyphony of a Bach fugue. The musical correlative contrapuntality of colors rests on an elaborate pictorial construction proportioned so as to approximate the golden ratio.
Paul Klee’s concept of polyphonic painting made the most direct reference to Bach and the fugue. Klee borrowed the musical term polyphonic to describe a visual structure composed of several pictorial elements that permeate and overlay one another in constant flux, from which ensues simultaneous visual polyphony, a consonance of all the pictorial means employed. In Polyphon gefaßtes Weiß (White Framed Polyphonically; 1930), for example, he used circular layers of color that extend in all directions while the colored forms in Fuge in Rot (Fugue in Red; 1921) progress horizontally from dark towards light, overlaying one another like the voices in a fugue.
In 1917, Klee noted in his diary what it was about this method of musical composition that interested him: Polyphonic painting is superior to music insofar as the temporal is more spatial in this genre. The concept of simultaneity is even richer here.
Similar transfers of the fugue-style method of interweaving and developing different voices can be found in the work of Mikalojus Konstantinas Čiurlionis — Fuga (Fugue) from the diptych Preliudai ir fugos (Prelude and Fugue; 1907), Josef Albers — Fuge (Fugue; 1925), and others. Musical methodology based on permutations or mathematics was explored as a means of pictorial composition, in addition to the contrapuntal development of visual structures.
John and James Whitney, for example, thus drew on the compositional principles of twelve-tone music to create serial permutations of a set of geometric forms for their Five Film Exercises (1943–1944), a practice that John Whitney would later develop further using an analog computer. Mary Ellen Bute availed of Joseph Schillinger’s mathematically generated compositional system, while Peter Kubelka used arithmetical processes in musical scores to develop the structure of his metric films.
Improvisation, which in contrast to composition is not based on a fixed score but relies essentially on the spontaneous interaction of the musicians involved, gained significance in the twentieth century, also in the realm of visual arts, as a result of the liberation of artistic means from the object.
For Henri Matisse, improvisation in jazz corresponded to the technique of cutting up paper, which is why he named his famous album of colorful paper cutouts (papiers découpés) Jazz (1947). Despite their apparent simplicity, such paper cutouts can no more be copied than can a jazz musician’s completely new and original playing: the spirit of the cut or of the arrangement cannot be repeated.
Collaborative improvisation became common practice at the end of the 1950s also in a new genre, the light show. Groups with up to a dozen members accompanied concerts by creating improvised visual effects with a range of light instruments such as slide and film projectors, color wheels, liquid projections, and reflective objects. Similar equipment is employed in VJing and audiovisual live performance. Notable in this regard is the group 242.pilots, comprised of three video artists who have developed software that enables them to superimpose, contrast, blend, and otherwise transform images in real time, in improvised interaction that they see as comparable to free jazz.
In similar manner to how, at the start of the twentieth century, the visual arts adopted music as a model for the depiction of movement and temporality, music in the latter half of the century looked to the visual arts for inspiration regarding the execution of spatial structures. The ways in which pictorial space was structured and the relationships between various forms or visual levels of a work were now to be applied to the organization of audio material. As radically different types of work and artists served as a reference in this regard, radically different concepts were put into practice.
The systematic composition of Paul Klee’s painting Monument an der Grenze des Fruchtlandes (Monument on the Border of the Fertile Country; 1929) so fascinated Pierre Boulez, for example, that it served as a guideline for Structure Ia (1951), Boulez’s first serial work, a piece for two pianos. While Klee designed a systematic series of square planes by gradually reducing from left to right their horizontal pitch line and thereby expanding the planes, Boulez, in determining all the musical parameters, created an extremely rational form of music to which one might well apply the terms accuracy, rigor, and visible ordering principle, with which Boulez had described Klee’s painting. In his works for piano, Intermission 4 and Intermission 5 (1952), Morton Feldman adopted the all-over structure of Jackson Pollock’s paintings, which, as its name implies, was focused not on a central point but on the whole canvas, indeed, seemed even to extend beyond the latter’s edges. Accordingly, each note in Feldman’s compositions is of equal importance; the compositions have no center, no clear beginning, and no cadence.
Earle Brown, for his part, attempted in December 1952 to transpose to music the constantly shifting interrelationships of the individual elements of Alexander Calder’s mobiles. His score consists merely of a large number of horizontal and vertical black rectangles of varying height and width, spread out across a page. The basic structure of the score is unambiguous and unalterable, comparable to the individual components of a mobile. And yet, any one concrete performance of the piece is comparable to the incessant realignments of a mobile, for the various parts of the score can be interpreted freely.
The reference for Olga Neuwirth’s composition for ensemble with CD recording Hooloomooloo (1997) was the eponymous triptych from Frank Stella’s series Imaginary Places (1994). What inspired Neuwirth’s composition was the apparent three-dimensionality of the triptych’s three individual parts and the slight variations in their surface structure. She selected three variously composed ensembles, each located at a different point in a space. The alternation between the three gave rise to movement in space, analogous to the polarity of spatiality and surface in the painting. She also gave each ensemble its own harmonious potential by altering the scordatura tuning of the string instruments. In this way, analogies to the polarity of foreground and background in a picture emerged.
Musicians were also interested in the phenomenon of color and sought to transpose its multitude of hues and the interrelation of various shades of color to the composition of musical material. Arnold Schoenberg, who devoted himself increasingly to painting in the early twentieth century, undertook such an endeavor in Farben (Colors, 1909). The chords change so smoothly in this work that an emphasis on any individual instrument is imperceptible, except as a change in color (i.e., timbre). While Schoenberg raised the progression of minute intervals to the dominant principle of composition, György Ligeti went one step further in Lontano (1967), by increasing the number of voices and minute intervals to create clusters — noise like bunches of notes — in which the chord is replaced by a sound space, a process Ligeti describes as micropolyphony. The ensuing simultaneous processes at different speeds that shimmer through, overlay one another, and whose many types of break and reflection give rise to an imaginary perspective he compares with entering a dark room, in which colors and contours only slowly become visible.
Inspired by Barnett Newman’s monochrome paintings — which, due to several layers of paint applied with a coarse brush, not only acquire a particular intensity but also evince extremely fine nuances — Morton Feldman remained convinced that all elements of a potential differentiation are already contained in a sound and are able also to develop a luminosity comparable to that in Newman’s paintings. In order to bring these properties to light, he gave notes — in Intermission 5 (1952), for example — the chance to decay and thus to fully unfold all their latent sound potential.
Oliver Messiaen, in turn, oriented the structure of his work to the relationships between colors, although his approach as a whole remains obscure to the uninitiated. His own description of it appeared in 1963 in the foreword to the score of his orchestral work Couleurs de la cité céleste (Colors of the Celestial City; 1963): The form of this work is determined entirely by colors. The melodic or rhythmic themes and the tonal or timbral complexity evolve like colors. In their constantly renewed permutations one finds (by analogy) warm and cold colors, and complementary colors that influence their neighbors, shading down to white or toned down to black.
Procedures in visual arts were also a source of inspiration for composers. Thus, with the emergence of acoustic recording media, the collage technique was used to arrange sounds, whereby, as in the visual version, entirely disparate and often already existing material was combined. This procedure had a formative influence as of the 1940s, above all on musique concrète, whose initiator, Pierre Schaeffer, made magnetic tape recordings of individual notes and fragments of sound from his environment and existing musical works, then pasted them together to create new compositions. Iannis Xenakis, John Cage, and others also experimented in the 1950s with the new possibilities offered by sound recording. In William’s Mix (1952–1953), for example, Cage collaged such brief segments as to prevent associations with the origin of the notes and in such a way that the edit or cut takes center stage, in auditory terms, thereby establishing itself as a sound in its own right that lies neither above nor between the other sounds.
Other composers adopted for musical use the frottage technique first used by Max Ernst in 1925, which entailed placing a sheet of paper over an object and rubbing it, usually with graphite, to thus transfer to the paper an image of the object’s natural contours. Michael Denhoff used the first section of a Fantasy by Henry Purcell in this way as the basis for determining the notes of his sixth string quartet frottages op. 70 (1993). Denhoff tuned the lowest string of each of the four string instruments down so that the resulting sound corresponded to the four notes of the main motif of Purcell’s Fantasy: This motif, with consonances so uncommon for Purcell’s day, runs like a magic trace of ever new, resounding notes in the contrapuntal interweave of my score.
Andreas Dohmen also applied the frottage technique to his eponymous ensemble piece from 2000–2001, in his case as a point of contact for acoustic filtering and the discovery of present, yet hidden musical structures.
To conclude this account of potential structural analogies, mention must be made of several problematic aspects that arise when one examines this phenomenon. As unambiguous visual or acoustic evidence of structural analogies is only rarely available, and given the lack both in the musical sciences and the visual arts of sound or established methods with which such relationships might be systematically documented, analyzed, and then considered in relation to the respective genre-immanent techniques, such examinations tend to have to rely on composers’ and visual artists’ personal statements.
The fact that Franz Liszt’s Hunnenschlacht (Battle of the Huns; 1857) was based on the eponymous painting by Wilhelm von Kaulbach is not evident from its title alone. Similarly, had Modest Mussorgsky not commented on Victor Hartmann — a painter whose exhibition Mussorgsky visited and from among whose paintings he selected ten as inspiration for his piano cycle Pictures at an Exhibition (1874) — a reference to painting may have been presumed, yet one specific to this painter would have been impossible.
One might presume that to take the artists’ or musicians’ own title for a work would be an unambiguous indicator, yet on closer inspection this is revealed to be a relatively unreliable premise. Schoenberg’s Farben was at times called Der wechselnde Akkord (The Changing Chord). Probably nobody would have assumed the latter title had any connection to artists’ colors; and, had anyone done so, the interpretation would have been regarded as interesting, certainly, yet ultimately also as speculative. The title of a work may also be misleading. Alfred Schnittke’s Fünf Fragmente zu Bildern von Hieronymus Bosch nach Texten von Aischylos und Nicolaus Reusner (Five Fragments Based on Paintings by Hieronymus Bosch Inspired by Texts by Aeschylus and Nicolaus Reusner; 1994) was, despite its title, based not on paintings but on epigrams that Schnittke found in a volume of criticism of Bosch’s paintings and that reflect the painter’s intellectual and symbolic realms. Even though Schnittke was familiar with Bosch’s paintings, visual art was never a source of inspiration for his music. It is therefore often impossible to ascertain the extent to which different genres — music, visual art, or other disciplines — influence and overlap with one another.
Moreover, titles of artworks are often employed to metaphorical effect and may therefore lead to misinterpretations. A renowned example of this is František Kupka’s painting Amorfa - Dvoubarevná fuga (Amorpha: Fugue in Two Colors; 1912), which has prompted both music and art historians to try and explain where exactly the structures of a musical fugue may be found in the painting. Kupka personally explained the original arbitrary pairing of painting and title in a letter from 1923: I regret to this day the crazy notion that led me to name the painting ’Fugue’ — at the time it was an expedient; it seemed to me — quite conventionally — that I had to provide a figurative title. However, the point was solely the concept of space and time, and the potential to evoke such space-time associations.
In addition, a narrowing of the analytical perspective on the relationships between music and visual arts occurs whenever statements by the composer or visual artist in respect of this matter are available. In other words, an examination of structural analogies based on the titles of works or the statements of composers or visual artists lacks methodological credibility and the aforementioned examples are to be taken with reservation.
 Program music usually implies an independent instrumental piece based on a nonmusical theme to which the composer, as a rule, expressly alludes.
 Viking Eggeling, "Theoretische Präsentationen der Kunst der Bewegung," Ma (August 1, 1921); cited in Birgit Hein and Wulf Herzogenrath, eds., Film als Film: 1910 bis heute; Vom Animationsfilm der zwanziger zum Filmenvironment der siebziger Jahre, Kölnischer Kunstverein exhibition catalog (Cologne: Kölnischer Kunstverein, 1977), 45. — Trans. J. D.
 Adolf Hölzel, “Über die künstlerischen Ausdrucksmittel und deren Verhältnis zu Natur und Bild,” Kunst für Alle 20 (1904), 52.
 See Wolf Stadler, ed., Lexikon der Kunst in zwölf Bänden, vol. 1 (Erlangen: Müller, 1994), 17.
 Besides such transfers of principles, one also finds examples of precise visual transformations of individual musical works. Among these rank, for example, the works of Henrik Neugeboren (Bach-Monument; 1928/1968–1970), Robert Strübin (Musikbild J. S. Bach, Große Fuge g-Moll für Orgel; 1957), and Luigi Veronesi (Visualizzazione cromatica del Contrappunto n. 2 dell’Arte della Fuga di J. S. Bach; 1971), which transposed fugues to a visual medium. Such transfers are visual representations of descriptions of works as a preliminary stage of analysis. For Neugeboren it was not [a matter of] interpretations dependent on one’s personal mood but of scientifically executed transfers to another system. (Henrik Neugeboren, cited in Heinrich Poos, “Henrik Neugeborens Entwurf zu einem Bach-Monument (1928): Dokumentation und Kritik,” in Töne — Farben — Formen: Über Musik und die Bildenden Künste; Festschrift Elmar Budde, eds. Elisabeth Schmierer et al. (Laaber: Laaber, 1995), 45–57, esp. 48.) — Trans. J. D.
 Felix Klee, Tagebücher von Paul Klee 1898–1918 (Cologne: DuMont, 1957), 383, no. 1081.
 What struck me in particular at the time was the accuracy, the rigor of the division of the space into two more or less equal parts, which was varied very easily by means of a subtle invention, which (despite its variation being reduced to an absolute minimum) was versatile, thanks to a visible ordering principle. While in other paintings the visible ordering principle vanishes completely, it seems to me, here, that it has been purposely accentuated. That fit in well with my personal endeavors at that time. Cited in Günter Metken, Laut-Malereien: Grenzgänge zwischen Kunst und Musik (Frankfurt am Main: Campus, 1995), 126. — Trans. J. D.
 Besides such transfers of principles, one also finds examples of precise visual transformations of individual musical works. Among these rank, for example, the works of Henrik Neugeboren (Bach-Monument; 1928/1968–1970), Robert Strübin (Musikbild J. S. Bach, Große Fuge g-Moll für Orgel; 1957), and Luigi Veronesi (Visualizzazione cromatica del Contrappunto n. 2 dell’Arte della Fuga di J. S. Bach; 1971), which transposed fugues to a visual medium. Such transfers are visual representations of descriptions of works as a preliminary stage of analysis. For Neugeboren it was not [a matter of] interpretations dependent on one’s personal mood but of scientifically executed transfers to another system. (Henrik Neugeboren, cited in Heinrich Poos, “Henrik Neugeborens Entwurf zu einem Bach-Monument (1928): Dokumentation und Kritik”, in Töne — Farben — Formen: Über Musik und die Bildenden Künste; Festschrift Elmar Budde, eds. Elisabeth Schmierer et al. (Laaber: Laaber, 1995), 45–57, esp. 48.) — Trans. J. D. I restricted myself to one note (flattened Eβ) on the well-broken-in ondes Martenot (as a semielectronic instrument, it had a completely different sound quality than that of the traditional ensemble), which slowly changes timbre and progressively moves through various registers — that is, through the sound space — before returning to the overtoneless Eβ. Around this ’ground plan’ that runs through the whole piece, three ensembles comprised of different instruments move around, playing with foreground and background, analogous to the Hooloomooloo triptych. These three ensembles constitute three coequal variations. Each one of them somehow has its own independent statement and the same value as the others in relation to the ’ground plan,’ but only in its entirety is the version complete. (Olga Neuwirth, “Notizen zu Hooloomooloo, 1996/97”, in Olga Neuwirth: Zwischen den Stühlen — a Twilight Song auf der Suche nach dem fernen Klang, ed. Stefan Drees (Salzburg: Anton Pustet, 2008), 65f. — Trans. J. D.
 Cited in Ove Nordwall, György Ligeti. Eine Monographie, trans. Hanns Epstein, Ulrich Süsse, and Ove Nordwall (Mainz: Schott’s Söhne, 1971), 114. — Trans. J. D.
 Oliver Messiaen,Couleurs de la cité céleste (1963), Note de programme, http://brahms.ircam.fr/works/work/10588/ (accessed July 22, 2009). — Trans. J. D. Efforts were made, furthermore, to use analogies to transfer tones to colors and to make them visible with the aid of the light organ, for example, or, alternatively, to incorporate colors in the composition, as in Alexander Scriabin’s Prometheus (1910).
 See Antje Vowinckel, Collagen im Hörspiel: Die Entwicklung einer radiophonen Kunst (Würzburg: Königshausen und Neumann, 1994), 77.
 Michael Denhoff, Werkkommentare, http://www.denhoff.de/werkkommentare.htm (accessed June 17, 2009). — Trans. J. D.
 Stefan Drees, “Andreas Dohmen”, in Die Musik in Geschichte und Gegenwart, 2nd rev. ed. in 29 vols., ed. Ludwig Finscher (Kassel: Bärenreiter,1993–2008), supplement (ed. Schriftleitung) 2008, col. 160–161. — Trans. J. D.
 František Kupka, cited in Brigitte Léal, “Werkkommentar zu Kupkas Werken Nr. 67–69,” in František Kupka, 1871–1957: Eine Retrospektive, Friedemann Malsch (conception), (Paris: Centre Georges Pompidou, 2003), 75–77, here 75.