Colour vision : a discussion of the leading phenomena and their physical laws / by W. Peddie.

  • William Peddie
Date:
1922
Catalogue details

Licence: In copyright

Credit: Colour vision : a discussion of the leading phenomena and their physical laws / by W. Peddie. Source: Wellcome Collection.

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    theory, with its associated dichromatic theory, seem to indicate entire ignorance of the possibilities. It is well therefore to give his words. “ The mode of explanation adopted by Th. Young and most of the workers at the theory, and formerly taken up by myself, by E. Hering, A. Konig, and C. Dieterici, that in dichromasy one of the fundamental excitations simply does not exist is contradictory to the result mentioned [yellow-blue vision]. But there is a general theory possible regarding the nature of dichromasy, in which it ceases to be necessary that the failing colour should be a fundamental colour, and yet the rule remains that all pairs of colours which seem identical to the normal trichromatic eye also seem identical to the dichromatic eye. “ To make this clear by a simple example, assume that the action of light which otherwise excites the perception of green does not excite the green perception nerve, but affects the red and blue perceptions in a definite fixed ratio. All perceptions of such an eye would seem to be compounded of red and blue ; it would be dichromatic. But the colours which in the colour diagram lie on that straight line which is drawn through the position of the green perception, would in general not seem alike, as would be the case under the older assumption where simple lapse of the green sensation was assumed. For, instead of the varying amount of green in the trichromatic eye, a varying amount of a definite purple colour would here be added to the already present different mixed purple, and would alter it in the majority of cases. In fact, the intersection point of those lines of the dichromatic field which contain like seeming colours, would lie outside the colour triangle beyond the green corner. “ This condition remains unaltered if we yet further assume that each excitation of the red, even that just considered, excites also the green perceptive parts of the nerve in a definite proportion, and so would bring a definite kind of yellow into perception, and each excitation of the blue similarly a definite kind of green-blue. Then all perceptions of such an eye would be compounded of yellow and green-blue, whilst the inter¬ section point of the dichromatic lines of like appearance would not thereby be changed.“ The conditions referred to are illustrated in projection in
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