The clinical use of prisms : and the decentering of lenses / by Ernest E. Maddox.

  • Maddox, Ernest E. (Ernest Edmund), 1860-1933.
Date:
1893
Catalogue details

Licence: Public Domain Mark

Credit: The clinical use of prisms : and the decentering of lenses / by Ernest E. Maddox. Source: Wellcome Collection.

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

    61/200 (page 45)
    enter the eye in one plane, for the smaller triangle ade is, just as much a plane as the whole triangle was at first. What, then, is the explanation ? It is this, that the distances a d and a e being greater than the distance ag, \h& gradient is less, as even a horse knows who prefers to descend a hill obliquely. A fly walking down e a would not have so steep a walk as one walking down g a. The paper, there- fore, does not represent the course of the rays through a prism, for a prism imparts equal gradients (that is, equal steepness) to all the rays. For the rays d a and e a therefore to possess the same gradient as g a, they must traverse the prism higher up, just as a long hill is higher than a short one of equal steepness. If we took a triangle of elastic material, and stiffened the base of the triangle, and then bent it at over a curved edge^ with its con- cavity upwards, we would then represent the course of the rays of light, and show why the line appears curved. So far we have only spoken of prisms held before one eye, the other being closed. Bin- ocular distortion results when both eyes are fitted with prisms, and has received its partial explana- tion, I believe, from Wadsworth, to whose paper* I would refer those interested, since it is difficult to give a just account of it without reproducing Trans. Amer. Oph. Soc, 1883.