the ocular harpsichord of louis-bertrand castel - Gewina

Castel's ocular harpsichord 25
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."