A case of vivid after-images explained on Hering's theory / by David Fraser Harris.

  • Fraser-Harris, David Fraser, 1867-1937.
Date:
1900
Catalogue details

Licence: In copyright

Credit: A case of vivid after-images explained on Hering's theory / by David Fraser Harris. Source: Wellcome Collection.

Provider: This material has been provided by The University of Glasgow Library. The original may be consulted at The University of Glasgow Library.

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    A CASE OF VIVID AFTER-IMAGES EXPLAINED ON HEEING'S THEORY. , . BY DAVID FBASBR HARRIS, M.D., B.SC.(LOND). Lecturer on Physiology in the University of St. Andrews. The phenomena recorded and analysed below were ex- perienced by myself when I was occupied in estimating the principal focal lengths of one or two convex lenses. While focussing the sun's rays at noon upon a sheet of white paper, and without at the moment thinking of the probable effect on the retina, I stared at the dazzlingly white spot for some time, until roused by noticing that the paper was on the point of being set on fire. On turning my eyes towards the least well-lighted corner of the white-walled room, I noticed a most pronounced black after-image, which persisted for about thirty seconds. Had this merely faded away and given place to normal colour-vision, there would have been nothing more to be experienced than the famihar sensation of being Winded as after gazing at the sun itself; but the black patch was followed by two coloured images of such brilliance and, pro t&m.., apparently so persistent, that a record of them may be pardoned. The first was a beautiful rose-pink patch, referable to the part of the retina concerned in direct vision; it lasted about three minutes; it was replaced by a brilliant canary- yellow patch of rather larger size, persisting for about twice as long. Before this last had faded I had to leave the building, and so experienced the very unusual sensatioia of seeing, almost as through a piece of yellow glass, all objects projected on the central portion of the retina ; while at the same time their colours seemed less changed than if yellow glass had really been used. It seems to me that Bering's theory of colour-vision accounts for the colours of these after-images, and for their order of succession. The theory virtually involves the following (for light of ordinary intensities) :—