the ocular harpsichord of louis-bertrand castel - Gewina

Castel's ocular harpsichord 29
Basically, it has all the features of the 1734 model. All the various alternatives
that Telemann mentioned for his one instrument nevertheless make clear that
Castel was still considering different possibilities, to be applied in a definitive
version of the instrument. A letter from Castel to Montesquieu written in 1739,
published in the Memoires de Trevoux, is evidence that Castel was indeed
experimenting with lanterns: "You have seen my lanterns, tuned by colour
degrees and light [chiaroscuro?] degrees ... With lanterns wonderful effects can
be produced using glasses, horn, nettings, taffetas, oiled or rather varnished
sheets of paper, especially when the lanterns are made as mobile as mine
are."^
Still in the same year the Mercure de France published a poem by a certain
Mr. Descazeaux, "Stances sur le mervcilleux Clavecin Oculair", containing such
lines as: "What rapid course of shades! What accord in their differences! For my
charmed eyes what a voice!"^' As four years had pa.ssed since Castel had last
published on the harpsichord, it is implausible that Descazeaux would have sent
his poem to the Mercure if he had not recently seen it, be it only a model, and
been impressed by it.
Again some years later, in July 1741, Georg Wolfgang Krafft, a member of
the Imperial Academy of St Petersburg, received a letter from Paris, informing
him of Castel's theory. The correspondent mentioned that Castel was busy
building his harpsichord and had promised its completion before the end of
1740. The design seemed to be suffering further changes, as it was reported that
the original plan was to show coloured strips, but that Castel had replaced them
by a painting containing coloured crystals, realizing the instrument "in modo
theatri comici".'** The report from Paris, for that matter, induced Krafft to
dedicate an official meeting of the academy to Castel's colour music, where he
did away with the whole idea, as will be shown in the next section.
Castel clearly did not hold to his promise for the end of 1740, but his
optimism held ground. In 1745 the Englishman Alban Butler, visiting Paris in
the retinue of his employer, the earl of Shrewsbury, saw the "famous instrument"
in Castel's workshop, and his account makes evident that Castel was still far
from his goal: "This instrument is not finished, and gives only three colours."
Butler added circumspectly: "The father pretends to entertain hopes of making it
Memoires de Trevoux, August 1739, pp. 1676, 1677-1678: "Vous avez vu mes Lantemes
diapasonnces par les degrcs des couleurs & de lumieres ... Par mes lantemes sur-tout on peut
faire des merveilles avec des verres, des comes, des gazes, des taffetas, des papiers memes huil^s
ou plGtot vemis: sur-tout si Ton donnoit a ces I.antemes la mobilite qu'ont les miennes."
Mercure de France, April 1739, pp. 768-769: "Quel rapide cours de nuances! / Quel accord
dans leurs differences! / Pour mes yeux charmes quelle voix!"
Weliek, "Farbenharmonie und Farbenklavier," p. 358.