Researches in colour vision : and the trichromatic theory / by William de W. Abney.

  • Abney, William de Wiveleslie, Sir, 1843-1920.
Date:
1913
Catalogue details

Licence: In copyright

Credit: Researches in colour vision : and the trichromatic theory / by William de W. Abney. Source: Wellcome Collection.

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

    29/448 (page 13)
    the cones become more numerous. The total number of cones has been calculated as being more than three millions. The macula lutea, or yellow spot, is oval, subtending an angle of about 6° in its longest axis, and 4° in the shortest. As its more common name indicates, it is distinguished from the rest of the retina by its yellowish brown colour. At its edges, the oval is slightly thickened, but in the centre it becomes very thin, and is there termed the fovea centralis, and is about *3 mm. in diameter. The general character of the layers in the macula are pretty much the same as in the rest of the retina, except that the cones are more numerous than outside. The rods diminish in number as they approach the fovea centralis, where they are altogether absent. The colour is due to a pigment staining one or more of the layers, but is said to be absent at the fovea. The yellow spot we shall have to take into account in our experiments. It is a continual source of difficulty in making measures, more particularly as the amount of colouring matter often varies in different observers. Zone of Distinct Vision. Another feature of the optical arrangements and the retina is that there is a zone of distinct vision near and around the axis of the eye. When we look at a small point of light, such as a star, the image falls on the fovea centralis. When two points of light subtend an angle less than about one minute of arc, the two images are blended one into the other, and the separation is not noticed. Calculating the distance apart on the retina on which the two images fall, it is found that they are about xoIjo °f a millimetre apart. In the human eye the