The relation of light perception to colour perception / by F.W. Edridge-Green.

  • Edridge-Green, F. W. (Frederick William), 1863-1953.
Date:
1910
Catalogue details

Licence: In copyright

Credit: The relation of light perception to colour perception / by F.W. Edridge-Green. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    to my notice with Eayleigh’s colour mixing apparatus, in addition to other .methods. In this apparatus a match is made between X 589 (sodium yellow) and a mixture of X 670 (lithium red) and X 535 (thallium green). The results obtained, however, seem to be quite independent of the power possessed by the individuals examined to appreciate differences in colour. In fact, by this apparatus we may obtain abnormal values in persons who have apparently no defect in hue perception, while others who are undoubtedly ■colour-blind may give results which correspond to that given by the average individual. The results seem to be determined not by varying power of appreciation of hue, but by slight variations in the luminosity curve of different parts of the spectrum in different individuals. Another important factor, probably the chief one, is the state of adaptation of the eye at the time of the observation. I All who have had practical acquaintance with colour-blindness are aware that all dichromics are not equally colour-blind ; one will be readily detected by almost any test, whilst another requires the greatest care to detect at all. I find that the cases of dichromic vision vary from almost total colour- blindness to cases bordering on those I have called the trichromic. I give below the monochromatic patches marked out by four dichromics with my spectrometer in similar conditions. The light was 180 meter-candles, the slit the same size in each, and the eyes light-adapted. The size of the patches is measured in micro-millimetres (/qa). No. 1 cannot see any difference between the cactus flower and its leaf, and does not see any difference between the red and green signal lights except at the moment when there is a change from one to the other. It is obvious that this case is much more colour-blind than the ordinary dichromic. On the other hand, a case bordering on the trichromic will see about eight definite patches in the spectrum ; make a normal match with Rayleigh’s apparatus; pass the Holmgren test with ease; and play pool regularly without on any occasion mistaking the coloured balls. Such a case, when examined with the spectrometer, has eight monochromatic patches instead of the normal eighteen; says that there are only two colours in the spectrum, red and violet, and has a very small neutral patch. It is quite easy to show that such a case is dichromic, as he will match spectral blue-green with a mixture of spectral red and violet: X 670 + X 470 = X 490. How could a defect in a light-perceiving substance have such varying results ? If we assume that in these cases there is a varying perception of colour difference, the facts are explained. It is stated in favour of the Young-Helmholtz theory that with three variables we can produce innumerable variations, the fact that on trial we