NOTE ON TWO RECENT THEORIES OF COLOUR. HERING has lately proposed a theory of colour which is quite different from that of Young. According to the new theory, the retina is provided with three visual substances, and the fundamental sensations are not three but six Black and White. Red and Green. Blue and Yellow. Each of these three pairs corresponds to an assimilation or diassimilation process in one of the visual substances; thus red light acts on the redgreen substance in exactly the opposite way from green light, and when both kinds of light are present in suitable proportions a balance is effected, and both sensations, red and green, vanish. Furthermore, according to this theory, all the colours of the spectrum also affect the black and white substance in the same way that white light does; for example, red light affects the red-green substance and produces the sensation of red, but it also acts on the white-black substance, and the sensation of red is mingled with that of white-to a large degree. Consequently, according to this theory, the white which is produced by mixtures of red and green light ought to have a less intensity than the sum of the separate components; but according to the experiments of the author this is not the case.* For further details the reader is referred to the original paper, “Lehre vom Lichtsinne,” Vienna, 1878. In 1876 F. Boll discovered that the retina contained a red or purple substance that quickly disappeared on exposure to light. Boll and Kühre have both studied the effect of monochromatic light on this coloured substance, and it was found that red light intensified the hue at first and afterward caused it to fade slowly. The action of yellow light was siow; green, blue, and violet light acted more quickly. On observations of this charac "American Journal of Science and Arts," October, 1877. ter Kühne has constructed a theory of vision. He supposes that the waves of light give rise in the retina to different compounds according to their length, and thus produce the different colour-sensations. If three such compounds are thus produced, giving rise to the sensations red, green, and violet, then this new theory is identical with that of Young; if there are five such compounds, furnishing the sensations red, yellow, green, blue, violet, then the apparatus for yellow and blue has been duplicated in the retina, since it can be shown that a mixture of the sensations red and green gives that of yellow, a mixture of green and violet that of blue. Good reasons can also be adduced to render probable the idea that yellow and blue are not fundamental sensations, but mixtures (compare the observations of Bezold in Chapter XII.). For additional information the reader is referred to the papers of Kühne published in the "Verhandlungen des Naturhistorische-medicinischen Vereins zu Heidelberg, 1877-'79." INDEX. Abnormal perception of colour, 92. Absorption of light by stained glass, 65. Airy opposed to Brewster's theory, 109. All pigments reflect some white light, 76. Aubert on mixtures of blue and white, 196; B Bert, observations of on chameleon, 101; Bezold, prismatic colours change with their Bierstadt, experiments of in colour-photog- Blake, Eli, his mode of recomposing white Blue, complement of, 177. Bokowa, Maria, artificial colour-blindness Brewster, Sir David, colour theory of, 108; C Calculation of number of visible tints, 40. Chameleon, its power of imitating colours, Charts, colour, 218, 220. Colour, abnormal perception of, 92; appar. Colour and wave-length do not change Colour-blindness, 95, 96; of artists, 100; Colour-chart, Chevreul's, 222; of Du Fay, 233. weights, 218; mixture of by binocular Colours, complementary, 161, explained by Complementary colours, by gas-light, 173; Contrast, 235-278; experiment with shad- Cross and rings produced by polarized light, 47. Cross, C., experiments of in colour-photog- Curves for action of red, green, and violet D Dalton, colour-blindness of, 97. Gas-light, effects of, on colours, 154. Glass under strain, colour of by polarized D'Arcy on duration of impression on retina, Gold used in painting, 85. 203. Dichrooscope. Dove's, 187. Diffraction grating, 23; Rutherfurd's, ib. Disks, complementary, 170; Maxwell's, Dispersion, production of colour by, 17. Gradation of colour, 276; rapid, often un- H Harris, colour-blindness of, 99. Helmholtz and Young, colour theory of, 113. Helmholtz's spiral disk for after-images, 93. Huddart, remarkable case of colour-blind- | Niepce de Saint-Victor's experiments on ness, 99. Hue, 86. I Melloni opposed to Brewster's theory, 109. Mile, his mode of mixing colours, 189. Monochromatic illumination, 102. Morton, H., thallene described by, 68. N Newton's diagram for the colour-blind, 105; photographing colours, 86. Nitrate of potash, colours of, in polarized Nobert, diffraction grating of, 23. Normal spectrum, 24, 25; appearance of, 122. P Painting, first practice, 818. Painting and decoration divergent in aim, Painting and drawing, connecting links, 814. Pfaff, experiment of on optic nerve with Phosphorescence, colours of, 64. Photography, coloured, thus far a failure, 86. Pigments, action of light on, 88; appear- Platino-cyanide of barium used for fluores- Polarization, production of colour by, 48. Pouchet, observations of on colour of floun- Preyer on colour-blindness, 97, 98. Purity of colour, 82. Purkinje, relative luminosity of warm and Purple, how produced, 28. |