Notes on physiological optics. III and IV / by W. LeConte Stevens.

  • Stevens, Walter LeConte.
Date:
1882
Catalogue details

Licence: Public Domain Mark

Credit: Notes on physiological optics. III and IV / by W. LeConte Stevens. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

    6/34 (page 292)
    rating it in refutation of Brewster’s theory, was probably due to the fact that the fallacy and popularity of the latter, in its application to the stereoscope, had not been brought especially to his attention. 2. Relation between Different Elements of Binocular Perspective. The fact that in all stereoscopic vision there is necessarily an interruption of the usual relation between the axial and focal adjustments of the eyes was first noticed by Professor W. B. Rogers, who makes however no reference to the production of any disturbance of perspective, as noticed by myself. In the articles already published it has been shown that even when the stereograph is so constructed as to exclude to the utmost the ordinary elements of perspective, there are left still three to consider. These are— I. The optic angle, positive or negative, enclosed by the visual lines and interpreted through the sensation of contraction or relaxation in the rectus muscles of the eyeballs. II. The focal adjustment, interpreted through the sensation of contraction or relaxation in the ciliary muscle encircling the crystalline lens. III. The visual angle, subtended by the diameter of the ob- ject regarded, and interpreted by recognition of the retinal area impressed but instantly and unconsciously referred to the external object. With a view to finding, if possible, what relation these three elements bear to each other in abnormal vision like that in the stereoscope, I constructed a modification of the instrument originally devised by Wheatstone. Upon a cubical block, l. (fig. 1) two plane mirrors, m and m', were cemented, and a pair of arms were attached to carry the conjugate pictures. A and