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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![I '55 ] In canvaffing the opinion of Dr. Welk; I have only made ufe of that Hberty to which all have a claim in treating philofophical fubjedls; and I truft, that while producing a dirert oppofite opinion, I haVe not, any where, exprelTed myfelf in terms which can with reafon give the flighteft degree of of- fence to that Writer. It remains to ftate the evidence we have for confidering the united appearance of ob- jedls feen by both eyes to be the confe- quence of an united impreffion or fenfation; this will be the fubjed: of the following Seftion*. * Before I proceed to the ntfxt Section I wifh to make a few remarks on a certain phenomenon of vifion which is mentioned by Dr. Wells in a note in the 105th page of his Eflay, for which I have not been able to find a place before, as the principles concerned here are very different from thofe we have been confidering. The experiment is this: If a fmall hole be made in a card and held near to the eye and fome opaque body, as a needle, be pafled between the eye and the hole, there will be feen two objeds, one the needle itfelf paffing in one direftion over the hole, the other a Ikadow of the needle paifmg in aeon-](https://iiif.wellcomecollection.org/image/b21175408_0177.jp2/full/800%2C/0/default.jpg)
