Page:Philosophical Review Volume 2.djvu/375

No. 3.] Hering's theory that the monochromatic ground-sensation is identical with the white-sensation of other color systems. (b) As regards dichromatic systems: the assumption holds, experimentally. That the calculative confirmation of it by the present results is only partial, is explicable. Hering assumes a similar relation between dichromates and trichromates, but regards the division of the former into two distinct types as secondary. Such a position is invalidated by this investigation. (c) As regards anomalous and normal tri- chromatic systems: it follows experimentally that they must so differ from one another, in the case of at least one ground-sensation, that this ground-sensation of the one group can in no way be represented as a homogeneous linear function of those of the other group. Calculation shows also that only two similar ground-sensations are possible; and that these are the two obtained in the comparison with dichromatic systems. § 23. The relations of the determined ground-sensations to the elementary-sensations; and their intensity-curves in the spectrum. One can explain the origin of the two investigated types of dichromatic systems from normal trichromatic systems by the absence of the ground-sensations R and G respectively. The third ground-sensation of anomalous trichromatic systems is different in its spectral distribution from the third in normal systems; and there is no possibility of expression in terms of homogeneous linear function. 24. The color-table, and the quality of the ground-sensa- tions. For the ground-sensations we obtain from the results of the research: for R a red, inclining a little from spectral red towards purple; for G a green of about 505 µµ wave-length; for B a blue of about 470 µµ, wave-length. It is clear from the triangle that B is most saturated, G least saturated, in the spectrum; and that spectral violet is more saturated than any mixture of spectral red and spectral blue. An anomalous trichromatic system is given, if the quality of G is retained, but the form of its intensity curve approximates to that of R. A dichromatic system of the first type is given, if the coinci- dence with R be complete. There remain the ground-sensations Blue (of about 470 µµ) and Yellow (of about 575 µµ); differently saturated. A similar explanation is possible in the case of the second dichromatic type.

If we draw a perpendicular through W of the normal color triangle, from the B angle to the opposite side, the sensations of the dichromate systems will be arranged on this perpendicular. The colors confused by dichromates lie on straight lines, which have a common point of intersection at the place of the absent sensation.