Sir Isaac Newton (1643-1727), in his examination of the dispersion of white light into its spectral components, categorized the spectrum into seven distinct colours: violet, indigo, blue, green, yellow, orange, and red. He arranged these colors in a circular manner, calling it a colour circle, which he utilized to illustrate the outcomes of combining spectral lights, including their complementary nature where certain combinations cancel out to produce white, gray, or black. Each segment's size varied based on Newton's calculations of its wavelength, the seven musical tones or intervals, and its corresponding width in the spectrum.
The decision to opt for seven colours stemmed from a belief, rooted in ancient Greek philosophy, that colours, celestial bodies, musical notes, and even the days of the week shared connections. This belief likely influenced the inclusion of indigo as an intermediary hue between blue and violet. However, some argue that in Newton’s arrangement, what he termed "indigo" would correspond to what we now identify as blue, while his "blue" would align with cyan.
Newton also proposed a method to gauge the saturation of combined colours on the circle, based on the distance of each colour's center of gravity from whiteness. While lacking nonspectral colours, the colour circle served as an early representation of what later evolved into the chromaticity diagram. Newton's arrangement, connecting violet to red, omitted a wide range of purples.
Painters later adopted a version of Newton’s colour circle (without including the indigo blue) to describe complementary colours. Nonetheless, this circular diagram served as a model for various colour systems throughout the eighteenth and nineteenth centuries.♪
The clavecin oculaire, also known as the "ocular harpsichord," was an invention of Louis-Bertrand Castel (1688-1757), a French Jesuit priest and philosopher, in the early 18th century. This device consisted of a harpsichord with colored glass panels mounted above each key, which would change colour as the keys were played. Castel's initial premise was to interpret the analogy between the tone scale and the colour scale quite literally. Within the range of tones forming an octave, there exists a spectrum of potential vibration rates, yet we perceive only a finite number of distinct tones, categorizing any arbitrary tone as one of the twelve notes in the chromatic scale. Similarly, Castel posited that our perception of colours follows a similar principle; despite colours blending seamlessly into one another, we recognize only a limited set of distinct colors. Hence, if Newton's sequence of colours—violet, indigo, blue, green, yellow, orange, red—represented the true counterpart to the diatonic scale, the transition from blue to green would equate to the smallest possible interval, E-F, suggesting that there exists no distinct colour between blue and green. Castel argued otherwise, asserting the presence of celadon between blue and green. (It's worth noting that Castel mistakenly assumes Newton's colours align with the C major scale, while Newton had actually compared them with the scale in D minor.)♪
Castel embarked on a quest to establish an analogy between sound and light phenomena, as well as between tones and colours. His premise was that just as various tones could be arranged to create artistic effects appreciated through sound, it should also be feasible to achieve similar artistic expression by arranging different colours. This notion proposed the emergence of an entirely new art form—a "music of colours."
Castel justified the analogy between sound and light on the basis that both were vibrational phenomena. This supposition formed the foundation for his exploration into the relationship between the auditory and visual realms, suggesting that similar principles governed both sound and light. Athanasius Kircher's (1602-1680) observations revealed striking similarities between sound and light: both reflect off flat surfaces, pass through denser materials and refract, and can be concentrated by concave mirrors. His invention, the speaking trumpet, resembled a telescope, reinforcing the connections between sound and light. ♪
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 has a very strong power to excite the affects of the mind.♪
Based on Kircher's findings, Castel suggested that if sound and light shared underlying physical processes, there would likely be parallels between the art forms of music and colour.
This method of comparing the internal relationships among colours to tone intervals provided the key to constructing the authentic chromatic color scale. Identifying red, yellow, and blue as essential components of this scale, it became necessary to ascertain the number of distinct colours between red and yellow, red and blue, and yellow and blue. Remarkably, it was found that there were precisely twelve distinct colours: blue, celadon, green, olive, yellow, fallow, nacarat, red, carmine, violet, agate, and violaceous forming a direct parallel to the chromatic scale in music.
However, Castel's subsequent approach diverged from music. Rather than allowing every colour to potentially serve as the root tone of a major or minor scale, he sought an absolute colour tonic, contending that this position was held by blue—the fundamental base of nature. According to Castel, all colours in nature are perceived against the backdrop of the blue sky.♪ It seems like Castel was interested in synaesthetic experiences that combined listening to music (the twelve tones) with other senses. Castel’s viewpoint stemmed from the philosophy of mechanism, which posits that external objects can only induce regular or irregular vibrations or undulations in our body's membranes. Following this line of thought, he formulated the "Principal proposition": all our sensory pleasures and displeasures arise from similar vibrations, specifically those in harmonic proportion. He reasoned that colour harmony must indeed exist because, without it, nothing would please us, likening it to the displeasure caused by completely dissonant music. Castel's proposition implied that harmony could extend beyond colour to include other senses, such as taste, smell, and touch—a notion he wholeheartedly embraced.♪