the ocular harpsichord of louis-bertrand castel - Gewina

Castel's ocular harpsichord 37
Castel's harpsichord in France.
Shortly before Castel's death, however, the ocular harpsichord had been
introduced into England by an unknown associate of Castel. In 1757 this man
published a leaflet, entitled Explanation of the ocidar harpsichord, in which he
recorded some of the history of the instrument and also his own solution to the
problem.*^ The description he gives of his instrument is quite detailed: it
consisted of a rectangular box of about 170 by 100 by 60 cm, placed on top of a
normal harpsichord. In the front it had fifty elliptic windows of transparent
enamel, which were ht from behind by some 500 candles. When a key was
pressed, the window with the corresponding colour would glow up, but how this
was achieved the author did not say, although he did indicate that even the
difference in propagation velocity between light and sound had been taken into
account! The author, however, had taken one crucial step away from Castel's
theory, in adopting Newton's "minor scale", connecting the colour violet with the
note D. But did this author succeed where Castel had failed? There is much
reason to doubt it. The copy of the Explanation in the British Library has a
written comment of its original owner, saying: "The Idea of this Instrument is
something very extraordinary, not to say Extravagant; I was admitted among a
select Party to a sight of it at the Great Concert Room in Soho Square; but to a
sight only of the instrument, for nothing was then performed nor afterwards, as
ever I heard, neither did I ever know why.""
More daring was an adaption of Castel's project which had been proposed
already quite early in Germany. In 1743 Johann Gottlob Krijger, a professor at
the university of Halle, published a paper entitled "On a new kind of music,
enjoyed by the eyes,"** in which he severely criticized Castel's views on colour
music. For Castel's ocular harpsichord, as Kriiger knew it showing, at the
pressing of a key, a strip of coloured silk lit from behind by candles, could
imitate the melodic aspect of music but not the harmonic aspect. There was no
convincing analogue of a chord. This is not to say that Kruger rejected the idea
of colour music in itself; according to him it was clear "that our mind, in judging
the pleasure or displeasure of the things that reach our eyes, follows the same
laws and rules that are followed in distinguishing musical consonance from
dissonance".*' This fact, however, could not be explained by any physical
Explanation, pp. 17-22. The leaflet was reviewed in the Memoires de Trevoux, January 1759,
pp. 342-357.
^ British Library, shelf nr. 1041.h.4.(l.)
Kruger, "De novo musices."
Ibid., p. 352: "animum nostrum in diiudicanda obiectorum, quae oculum afficiunt, suavitate &
molestia, easdem observare leges, easdemque regulas, quibus in distinguendis consonanttis a
dissonantiis musicis uti consuevimus".