A rationale of the laws of cerebral vision : comprising the laws of single and of erect vision, deduced upon the principles of dioptrics / by John Fearn.

  • John Fearn
Date:
[1830]
Catalogue details

Licence: Public Domain Mark

Credit: A rationale of the laws of cerebral vision : comprising the laws of single and of erect vision, deduced upon the principles of dioptrics / by John Fearn. Source: Wellcome Collection.

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

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    Thirdly.—&Y Fig. 3, are represented the other principal phases of that extraordinary phenome- non—the re-crossed objects seen in consequence of varying the modifications of the pressure upon both eyes acting in concert. And here we have to contemplate the appearances immediately to be described. First—W]\e\i we press upon the upper part of each eye, any where on the inner side of EACH PUPIL; (always observing that a pressure by conthiuous lively impulsions, or, as steady pres- sure if at the same time we wink the closed eyes, is the most effectual,) we shall observe that the cor- respondent objects produced are occasioned, each one of them by its oiim eye: Which fact, not being a fact of re-crossing, does not require a Figure for illustration. SecondlyWhen we press upon the upper part of each eye, upon correspondent parts of the eyes about half way between the pupil and the extreme out- side of each eye; we may observe, from moving the pressing instruments up and down in contrary di- rections, that the object seen with the right eye has crossed over or changed its place horizontally, so that it now stands on the left hand of the object seen with the left eye, the two objects appearing at some distance from each other as represented by the letters L E i—R E i—in the present figure. From this result it is self-evident that, accord- ing to the increase of the distance between the pres- sures on the upper parts of the eyes, the seen crossed images must increase their distance between each other, until, by the time the pressure is on the Y