ABSTRACT
THE reason that comprehension of the vast mass of facts already well known regarding the chromatic sensations has made practically no progress since the days of Helmholtz is that these facts are somewhat equally distributed among three different sciences, and that consequently there is no one who is able (or, at least, willing) to hold them all in hand at once. (1) Important work by Hecht has been appearing in the last six volumes of the Journal of General Physiology, which makes it quite certain that the initial retinal process is a photo-chemical one, and that the light-sensitive substance concerned in the primitive white of the rods is the same substance (as shown by its subjective-intensity-distribution) as that in the cones. (But Hecht here overlooks the fact that the circumstance that the sensation is the same, that of whiteness—the basis of my colour theory—is already an irrefragable proof of this identity.) (2) Most important of all of these contributions is the fact that König determined (1892) the actual constituents of the tri-receptor retinal photo-chemical processes by means of establishing (after proper change of the independent variables) perfect coincidence between normal tetrachromatic vision and that of both of the two types of atavistic dichromatic vision. This is a fact, however, that, by a marvellous chain of accidents, has been overlooked by the physicists themselves. I have endeavoured to restore it to its proper significance in the Appendix which the Optical Society has permitted me to write to the English translation of Helmholtz. (3) The contribution of Psychology to this subject is (a) the laying down (1888) by G. E. Müller of the fundamental principles that must govern the formation of any theory concerning the neuro-psychic correlations, and (b) the work done by Hering during his fifty years of magnificent activity (aided by a large body of students both at Prag and at Leipzig) in showing successfully that the so-called theory of Helmholtz is no theory at all. His own theory, however, exists only by denying the great Helmholtz fact that the initial photo-chemical process is a tri-receptor process (I am much pleased to see that Howell, in the 9th edition of his Physiology, just out, has adopted all my terminology). In neglecting Hering’s theory, however, the physicist has unfortunately overlooked the fact which made it a necessity—the fact that both yellow and white are simple unitary sensations, no matter what their physical basis. In conclusion I permit myself to quote from a letter just received from M. Piéron of the Collège de France: “Il est certain que votre théorie concile le mieux les faits si complexes relatifs au fonctionnement lumineux et chromatique.”
