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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![E^XPEKIMENT II. I PROVIDED a piece of pafteboard of about one foot in breadth and two in length; one end I cut fo as to adapt it to the profile of my face, in fuch mannev, that when ap- phed to it in a vertical poiition perpendicu- lar to the plane of the face, the rays which came to one eye w^ere intercepted from the other. I then placed a fhcet of white paper perpendicularly againft a wall to which a not that which mig^it have been previoufly expe6]:ed from the compoiition of the two. And 1 apprehend that Dr. Wells, in the experiment he mentions, has been apt to confound imagination with fenfe; for I conceive it to be impofiible to fee one colour through another. Wken we lock at an objecl: of known colour through a flaincd glafs of any other colour, we are apt to think we perceive two colours at ^he fame tim.e; but it is probsbl© that in this cafe the im^agination is em.ployed at the fame time with fenfation; that is, from knowing the colour of the ob- ject we conceive it to be of one colour, while Ave fee it of another; and I apprehend it m.ay be laid down as a maxim in vifion that the fEjne individual point cannot appear at the fame time to have two different colours. This is not a pro- pofition to be proved by argument; it is a firll principle; if we attempt to conceive the contrary, we find it impoflible. ftrong](https://iiif.wellcomecollection.org/image/b21175408_0190.jp2/full/800%2C/0/default.jpg)
