On the photochemistry of the retina and on visual purple / translated from the German of W. Kühne ; edited, with notes, by Michael Foster.

  • Kuhne, W, 1851-1930.
Date:
1878
Catalogue details

Licence: Public Domain Mark

Credit: On the photochemistry of the retina and on visual purple / translated from the German of W. Kühne ; edited, with notes, by Michael Foster. Source: Wellcome Collection.

Provider: This material has been provided by UCL Library Services. The original may be consulted at UCL (University College London)

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    The action was here so much greater than in the previously described blue-green spectrum, that it could be recognized within 16 minutes, and in 54 minutes the purple had become changed into the palest yellow. The experiment was conducted on the 10th of March, between 12.30 and 1.30 p.m., the sky, although cloudless, not being entirely free from haze, somewhat whitish-blue in fact, and the less intensity of the sunlight on this day, compared with that of the following day (see above), manifested itself even in the first spectrum in the much greater length of time required for the total bleaching. Slight as appears to be the influence especially of the red, but also of the violet and ultra-violet rays, it is nevertheless certainly not entirely absent, and is probably sufficient to ex- plain the fact that our sense of light can be excited by these, colours. That portions of the blue and violet, although they are a long time in bleaching, in the end do so all the more completely, deserves special notice. It would, I think, be un- profitable if I were to attempt to carry out any further deduc- tions from the facts which have j ust been established; these indeed will readily suggest themselves to every one. I rather turn to the less thankful but more necessary task of attempting to fill up the gaps in our knowledge of the facts in the almost boundless region thus opened out to us. Want of sunlight and of the necessary refractive quartz apparatus, has hitherto prevented my taking properly in hand any decisive experiments upon the ultra-violet rays, desirable as these would be in refer- ence to the observations of Helmholtz and Setschenow on the fluorescence of the retina, and especially to the fact proved by Helmholtz, that the eye can directly perceive the most re- frangible solar rays. In company with Mr A. Ewald, who has assisted me in the foregoing investigations in the most active and generous manner, I hope to be able soon to communicate further results, on this as well as on other points in the doctrine of visual purple\ Meanwhile the foregoing experi- ments may suffice to shew that in the visual purple there exist qualities which one would expect to find in a body serving as the means of producing vision by chemical stimulation.