On negative after-images with pure spectral colours

In a paper “On Negative After-Images and Successive Contrast with Pure Spectral Colours,” by Mr. A. W. Porter, F. R. S., and Dr. F. W. Edridge-Green, the authors describe certain experiments, which they consider impossible of explanation on either the Hering or the Young-Helmholtz theory of colour vision. In justice to Thomas Young, it is only fair to point out a discrepancy between the title of the paper and the experimental conditions therein described, viz.: “The method adopted was as follows: In a dark room,in which, however, there was a certain amount of stray light , a horizontal spectrum, as pure as possible, was projected on a screen. A portion of the retina of one eye was then fatigued by rigidly gazing at a portion of another spectrum, isolated in the Edridge-Green colour-perception spectrometer. . . . After the fatiguing light had been viewed for about 20 seconds, the eye was turned to the screen, so that the after-image formed a band running right across the spectrum on the screen and occupying its centre.”