the ocular harpsichord of louis-bertrand castel - Gewina

gcxDdbye to melody and harmony.
Castel's ocular harpsichord 51
Diderot was convinced that "to solve this problem, one needs only a very small
part of the sagacity which the invention of the harpsichord supposes".'* Indeed,
Castel had remarked repeatedly that all that was needed was the resignation that
one inevitably had to become used to colour music gradually. Had the French
public not encountered similar difficulties in accepting Italian music?
Although Diderot had visited Castel's workshop and seen a model harpsichord
demonstrated, he did not say anything on the technical realization of the
instrument. Neither did he promise a drawing of it in the Recueil des planches,
as he did for other inventions described in the same volume (for instance a
curious mechanical calendar mentioned under "Chronologique, machine"). He
only admitted that "the fabrication of this instrument is so extraordinary that
only a little enlighted public will complain that it is constantly made and never
finished", and that it needed a "rare engineer" to do it.*^
Apart from the ocular harpsichord, Diderot was also impressed by the
coloured ribbons that Ca.stel had made in the course of his colour experiments
during the years 1734-1740. By taking silken threads dyed in the twelve colours
of the chromatic scale and twining them into yarn in different combinations, he
had manufactured ribbons that showed a certain colour passing by imperceptible
changes through all the chiaroscuro shades from almost black to almost white,
or others showing a complete octave in which all the different colours imperceptibly
changed into the next one until the root colour was regained."'*' When the
first volume of the Encyclopedic appeared Diderot wrote to Jaucourt: "Here is
our Encyclopedic. In it I have rendered homage to Father Castel at several
occasions; and 1 will seize the opportunity to do so again in the following
volumes.""" One of these occasions was the article "Animal", in the introduction
of which Diderot mentioned Castel's ribbons as a metaphor for the "great
Idem: "il faudroit trouver quelque expedient qui liat les couleurs.