The directions of the apparent vertical and horizontal meridians of the retina and their modification from physiological and pathological causes : with a description of the clinoscope / by George T. Stevens.

  • Stevens, George T. (George Thomas), 1832-1921.
Date:
[1897]
Catalogue details

Licence: Public Domain Mark

Credit: The directions of the apparent vertical and horizontal meridians of the retina and their modification from physiological and pathological causes : with a description of the clinoscope / by George T. Stevens. Source: Wellcome Collection.

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

    22/24 (page 202)
    holding the horizontal lines approximately so in order to unite the two images, a very considerable latitude is per- mitted in respect to the position of the vertical lines, and the torsional act may overcome an important normal deviation. The principle holds in stereoscopic vision, that the visual recognition of form and of the third dimension is not the direct result of an instantaneous image formed on each retina, but the result directly, or indirectly, of a series of muscular adjustments. That both form and depth may be perceived instantaneously is true, but doubtless in such instantaneous realizations of the actual dimensions of objects there is a mental acceptance of the phenomena which experience has taught to be the result of impressions received upon the two retinas, provided time is allowed for the usual rapid ocular movements. The fact of difference in torsion for horizontal and vertical lines has its practical application in many directions. A single example may be introduced here as an illustration of this important principle. The question of the form and pro- portions of printed type, in order to produce the most per- fectly legible characters and a page which can be read with greatest ease, has long interested those who are interested in the progress of the art of printing in its relation to the preser- vation of the functions of the eyes. Experience has, indepen- dent of any theory, taught practical men engaged in the art of typography, that the height of letters must be considerably greater than their breadth. In the ordinary type used in America and England the Vertical length of all the letters of a line aggregates rather more than thirty millimetres to - every twenty millimetres of breadth of letters. In the French typography the height of the letters is still greater. A little examination of different styles of typography will convince a careful investigator that broad, low letters are less easily held in perfect binocular union than the form more nearly approaching the gothic style. In what precedes I have gone over a number of somewhat closely related subjects more with the view of indicating the directions in which exact investigations are to be made