Ocular harpsichord. This instrument with keys is similar to an auricular harpsichord, and is composed of as many color octaves per tone and per half-tone as the auricular harpsichord has sounds per tone and half-tone. It aims at offering the soul, through the eyes, the same agreeable sensations of melody and harmony in colors, that the ordinary harpsichord transmits to the ears, through the melody and harmony of sounds.

What is required for an ordinary harpsichord? Strings that are tuned with a diapason according to a particular musical system, and the means to have these strings resonate. What is required for an ocular harpsichord ? Colors tuned just like the strings, and the means to produce them to the eyes: but one harpsichord is as possible as the other.

To the five sound tonics - C , D , E , G , and A - correspond five color tonics - blue, green, yellow, red, and purple; to the seven diatonic sounds - C , D , E , F , G , A , B , and C - correspond the seven diatonic colors blue, green, yellow, light pink, purple, dark blue, light blue; to the twelve chromatic or semi-diatonic sounds, correspond the twelve chromatic or semi-diatonic colors blue, pale green, green, olive, yellow, light pink, orange, red, dark red, purple, agate [1], blue, etc. Through this process, one sees via colors all we can hear via sounds; major and minor modes; diatonic, chromatic, enharmonic, tones; modulation arrangements; consonances, dissonances, melody, harmony, so that if one were to master the basics in auricular music, like M. d'Alembert, and were one to substitute everywhere the word sound for the word color , one would obtain the complete elements of ocular music: colored pieces in several parts, a fundamental bass, a continual bass, numbers and concords of all kinds, even through supposition and suspension, a rule of association, harmonic inversion, etc.

The rules of auricular music all have as a basis the natural and primitive production of the perfect concord through any sound-producing object: if this object is C tuned, then it resonates C , G , and E , to which will correspond the colors blue, red, and yellow - colors that several artists and physicians consider the three primary colors. Ocular music, thus, has in its principles a basis similar to auricular music. See Color.

What is entailed in the act of playing? For the ordinary harpsichord, it means to sound and remain silent, to appear and disappear to the ear. What would it be for an ocular harpsichord ? To show or to keep hidden, or to appear and disappear to the eye: and since auricular music has twenty or thirty ways to produce sounds, through strings, tubes, voices, violins, basses, lyres, guitars, harpsichords, spinets, oboes, recorders, fifes, flageolets, [2] bassoons, bass horns, trumpets, organs, etc., ocular music will have as many corresponding ways to produce colors, boxes, fans, suns, stars, paintings, natural and artificial lights, etc. Here is the plan.

The objections that were raised against ocular music and ocular instruments are so self-evident that it is useless to reproduce them here; we shall only assume that they have been well answered, if not rendered moot, through the comparison of both types of music, so that now there are no more experiments left to be done that would settle the question.

The only essential difference between the two harpsichords that struck us, is that, despite the large interval between the first and the last key on an ordinary harpsichord, the ear perceives no discontinuity between the sounds; to the ear, these sounds are linked as if the keys were neighbors; whereas colors will differ a lot and appear distinct. To remedy this shortcoming in ocular melody and harmony, one should find some method that would link the colors, and which would create continuation among them for the eye; otherwise, in the midst of an extremely lively musical piece, the eye, unaware of the interval of color that the player plays, will fail to notice, after having seen one tone, where it should look for the next tone, and would thus only grasp a few disjointed notes from a colored tune in a battery of colors; or one would strain himself so much to grasp them all that he/she would soon start seeing things; from then on, you may forget any melody and harmony. One could further add that when the colors are grasped, it would be impossible to ever retain them, and that one has a memory for color tunes, as one has for sound tunes.

It seems that the colors of an ocular harpsichord should be placed on one single strip, vertical and parallel to the musician's body height; whereas the strings of an auricular harpsichord are placed horizontally and parallel to the musician's body breadth.

Whatever the case, I do not assume to give this objection more value than it has: to resolve it, one would require but a small fragment of the sagacity that the invention of the ocular harpsichord itself requires.

One cannot picture such a machine without being well versed in Music and Optics; one would not build it successfully without being an exceptional worker.

P. Castel, the famous Jesuit, is its inventor; he made it public in 1725. The workmanship required for this instrument is so extraordinary that only a poorly enlightened public would complain that it is still being built, and not yet near completion.

Notes

1. Agate is a silica-based mineral used in several industries for its hardness. Once polished, it can be used for jewelry (as it was in Antiquity). However, agate has an array of possible colors, and it remains problematic to identify the one meant by Diderot here.

2. A type of flute.