Observations on the nature and theory of vision : with an inquiry into the cause of the single appearance of objects seen by both eyes / by John Crisp, F.R.S.
- Crisp, John
- Date:
- MDCCXCVI [1796]
Licence: Public Domain Mark
Credit: Observations on the nature and theory of vision : with an inquiry into the cause of the single appearance of objects seen by both eyes / by John Crisp, F.R.S. Source: Wellcome Collection.
Provider: This material has been provided by the Francis A. Countway Library of Medicine, through the Medical Heritage Library. The original may be consulted at the Francis A. Countway Library of Medicine, Harvard Medical School.
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![This (jueftion will be confidered hereafter: at prefent we have only to do wath the faft. And it is here to be noted, that though the pi6tures which fall on correfponding points of the retinae appear fingle, the vifible objed is compofed of the two projections. It is eafy to conceive, that if two plane figures perfedlly fimilar and equal in magni- tude (liould be applied one over the other, the outlines of the two muft coincide and form one figure. The efFed: of viewing objeds through two tubes, one appHed to each eye, is well known ; if fuch tubes are properly applied, and two fimilar objeds, as two guineas, placed one in the axis of each tube, the projedions will fall on correfpond- ing points of the retinae, when the axes of the tubes and the axes of the eyes coincide, and the two guineas will be feen under one outline and become undifl:inguilhab]e. This efFed is fimilar to what occurs in the ordi- nary ufe of the eyes; the two projedions arc](https://iiif.wellcomecollection.org/image/b21175408_0088.jp2/full/800%2C/0/default.jpg)
