The Philosophical Review/Volume 1/Summary: Helmholtz - Versuch das psychophysische Gesetz auf die Farbenunterschiede trichromatischer Augen anzuwenden
In the second volume of the above periodical H. had tried to formulate the psychophysic law so as to embrace more than one variable, e.g. the three variables in the determinations of the color sensations of trichromatic eyes. In the present article H. shows there is a close correspondence between the curve for color differences experimentally found by König, and the curve calculated from the extended pp. formula on the assumption of the three elementary fundamental colors. This verification of the formula gives a basis for the determination of the fundamental colors which are found to be provisionally, carmine red, ultra marine blue, and yellowish green. The relation of these colors to the spectral colors is shown by the position of the latter within a color triangle of which the apices are the fundamental colors, and the gravity centre, white. According to this construction, spectral red, for instance, would be a whitish and yellowish modification of the fundamental carmine red. Moreover, the curve of the spectral colors shows that all the fundamental colors affect, with but little difference in intensity, all the nerve elements of the trichromatic eye, sensitive to light, simultaneously. It can be shown that the disagreement between the lacking color of dichromatic systems and any one of the given fundamental colors does not give rise to an insoluble contradiction. Newton's law of color mixing is applicable to the colors of the dichromatic system, and colored lights which appear like to normal eyes appear also like to dichromic eyes. The close agreement between sensitiveness to differences of color and differences of brightness corresponds to the author's supposition that perception of differences of color rests originally on perception of differences of brightness.