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could be expressed by six variables on whose relative proportion the
different colour qualities would depend. From this finding and Mach's
psychophysical maxim, Hering ( 1878 ) concluded that the correlated
material processes could be expressed similarly, and that the quality
of a colour directly correlated with the ratio of the magnitude of its
underlying material process to the sum of all colour-related material
processes operating simultaneously in the stimulated area. This sum,
in turn, correlated with the impressiveness of the colour sensation.
The green colour quality in a green-grey colour, for example, could
be specified as G /( G + W + B ), that is, the magnitude of the material
process underlying green relative to the sum of the material processes
underlying green, white and black, while the impressiveness of the
green-grey colour would correlate with the sum of the three different
material processes ( G + W + B ) (Hering, 1878 , pp. 82-85). His quantitative
analysis and mathematical treatment were rooted in what he termed
'das allgemeine psychophysische Grundgesetz' ('the common basic
psychophysical doctrine'), particularly the maxim that the purity,
plainness or clearness of a sensation depends on the ratio of the weight
of the sensation to the sum of the weights of all simultaneously
activated sensations (see Hering, 1878 , p. 84).
The phenomenological analysis of the visible spectrum
also revealed that there was no series of red-green or yellow-blue
intermediate hues. That is, no hue in the spectrum appeared simulta-
neously red and green, or yellow and blue (Hering, 1964 , p. 50). This
mutually exclusive character of red and green, and of yellow and blue
was also clearly displayed by binary colour mixtures where the two
chromatic components either cancelled each other out completely or
to the extent that only the dominant one was observed. Furthermore,
the phenomenological analysis of the white-grey-black colour series
revealed that white and black colour sensations were also opposed
to each other. Thus, Hering could point to the fact that when white
increased, black decreased and vice versa.
From these phenomenological analyses he concluded that the
material processes underlying red, yellow and white were antagonistic
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