On Negative After-Images, and Their Relation to Certain other Visual Phenomena . te compounded from Bed and Blue-green.—Such a white always gavea pink pulsative image—a fact which confirms the inference derivedfrom previously described observations that the blue-green sensationis, after an interval of repose, more readily fatigued than the redsensation. White compounded from Yellow and Blue.—A white colour-patch wasformed by combining a blue of A 4530 to A 4710 with a yellow of A 5650to A 5860. The colour of the pulsative image was rather doubtful, butan artist (who did not know what to expect
On Negative After-Images, and Their Relation to Certain other Visual Phenomena . te compounded from Bed and Blue-green.—Such a white always gavea pink pulsative image—a fact which confirms the inference derivedfrom previously described observations that the blue-green sensationis, after an interval of repose, more readily fatigued than the redsensation. White compounded from Yellow and Blue.—A white colour-patch wasformed by combining a blue of A 4530 to A 4710 with a yellow of A 5650to A 5860. The colour of the pulsative image was rather doubtful, butan artist (who did not know what to expect) unhesitatingly . pro-nounced it to be yellow. Since the Young-Helmholtz theory supposesthat yellow excites the green sensation, this result was unexpected. Itis also opposed to the usually received opinion that the sensation ofyellow is more readily exhausted than that of blue.* V. Pulsative Images of Complete Spectrum. The spectrum was projected upon a screen covered with white card-board, which was put in the place of the slit-screen, as shown in fig. 8. Jb iG-. 8». The beam of intermittent white light was reflected upon the screen bymeans of a mirror and formed an oblong bright patch upon the site ofthe spectrum. The upper part of the mirror was covered by a screen,so arranged that the site of the spectrum was longitudinally dividedinto two equal parts, the lower of which was exposed to intermittent * Foster, loc cit. 276 Dr. S. Bid well. On Negative After-images, and white light, while the upper was not. Thus the spectrum and itspulsative image could be seen together, the one above the other. Atfirst sight the pulsative image appeared to contain only two colours—blue-green corresponding to the spectral red and orange, and purple-pink corresponding to the green. Closer inspection revealed a palegrey band between the blue-green and the purple, and a feeble tint oflavender corresponding to the blue of the spectrum. Nothing at allcould be seen beneath the violet and
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