An essay upon single vision with two eyes : together with experiments and observations on several other subjects in optics / by William Charles Wells, M.D.

  • Wells, William Charles, 1757-1817.
Date:
1792
Catalogue details

Licence: Public Domain Mark

Credit: An essay upon single vision with two eyes : together with experiments and observations on several other subjects in optics / by William Charles Wells, M.D. Source: Wellcome Collection.

Provider: This material has been provided by University of Bristol Library. The original may be consulted at University of Bristol Library.

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    which an object feems to either eye to pof- fefs, manifeftly depends both upon its ap- parent diftance, and its apparent direction from that eye, if vifible place be, in the language of Dr. Smith, only an idea of real or tangible place, vifible direction muft bear the fame relation to tangible direction ; a confequence of which is, that we can never have a more accurate knowledge of the di- rection, in which an object may lie from any part of our bodies, by fight than by toucn. Facts however prove the contrary. Let any perfon, for inftance, taking a pin in his hand, endeavour, without looking, to bring its head upon a level with either of his eyes ; and there are many chances to one but he will fail in the attempt, of which fight will inform him, when he turns his eye to the object. This to me is a con- vincing argument, that external bodies are not feen in certain directions, becaufe they have been previoufly felt in them ; and confequently, that vifible place, of which vifible direction is a component part, is not merely a reprefentative of the place per- ceived