the ocular harpsichord of louis-bertrand castel - Gewina

Castel's ocular harpsichord 43
indication at all that the rates of vibration of the various colours had any such
simple ratios. The only indication of what the physical properties of the different
colour rays were, be it their vibration rate or any other property that determined
the impact of the ray on, for instance, our eye, was their refractibility, which was
the only thing in which they could be said to differ. Mairan then assumed that
for each ray the ratio of the angles of incidence and refraction was the right
measure of this physical property, let's say its rate of vibration. But the maximal
ratio of the different values of this property, for the colours red and violet, was
77:78, as Newton had so laboriously measured. The conclusion had to be that no
pleasure could be expected of colour harmonies.''*
Second, as had been remarked earlier by the "Philosophe Gascon", the
organs of hearing and sight were so different in their anatomy, the one hard and
dry, the other soft and humid, that it was inconceivable that the impressions they
transmitted to the soul were commensurable. In fact, the pleasure we feel with
simple frequency ratios of tones can be seen to be grounded in the anatomy of
the ear: "The immediate organ of hearing is in fact, so to say, a real musical
instrument, ... it is a kind of harpsichord, [containing] an infinity of strings, which
by their different lenghts and their different tensions are capable of taking care
of the relations and the vibrations of all possible tones."'' For the eye there was
no indication of a similar mechanism. Then there were other problems, such as
the fact that two colours mix to a new colour, while two tones mbc to a chord,
something quite different from a single tone; the fact that we enjoy the slowly
fading of one colour into another but loathe the tuning of a string such that one
tone changes into another; and finally the fact that colours are absolute, whereas
with tones only the intervals are absolute, and any tone can be the root of any
interval.*
To summarize, Mairan stated:
There is no relation between these sensations [of hearing and sight] but in their intensity or
magnitude; no other relation, neither as to their nature nor as to the idea we have of them. If
there would be the least such a relation, it would not be impossible to give someone bom blind
but not mute some idea of what colour and painting are, and conversely a mute who is not
Mairan, "Discours," pp. 29-30.
79
Ibid., pp. 37-38 resp. 10: "L'organe immediat de I'ouie est en effet, on le peut dire, un
veritable Instrument de Mu.sique ... c'est une sorte de Clavecin, [conlenant] une infinite de cordes,
qui par leurs differentes longueurs, & par leurs differentes tensions, sont en ^tat de foumir aux
rapports, & aux vibrations de tous les tons possibles."
^ Ibid., pp. 39-42.