the ocular harpsichord of louis-bertrand castel - Gewina

Castel's ocular harpsichord 35
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