A rationale of the laws of cerebral vision : comprising the laws of single and of erect vision, deduced upon the principles of dioptrics / by John Fearn.

  • Fearn, John, 1768-1837.
Date:
[1830]
Catalogue details

Licence: Public Domain Mark

Credit: A rationale of the laws of cerebral vision : comprising the laws of single and of erect vision, deduced upon the principles of dioptrics / by John Fearn. Source: Wellcome Collection.

Provider: This material has been provided by UCL Library Services. The original may be consulted at UCL (University College London)

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    and important phenomena of the double pin's heads sink into trifles in comparison. And here, the grand fact of the re-crossing of images within the head is, in the most unexpected manner, de- monstrated : because, it must be manifest to all persons that our real external nose must be seen,—its right side with the right eye, and its left side with the left eye: and therefore it is confirmed, most certainly, that the two noses which we see are NOT the two sides of our real external nose. i: If farther proof could make the fact in question appear stronger; we are to observe that, the two seen noses do not join, as the two halves of our real external nose join; but they appear an inch and a half asunder. Now the reason, they do so, is plain ; it being because each seen nose is seen in consequence of an impression in the eye ; and the different retinal impressions fall upon parts that are not calculated to produce a junction of visual objects behind the eyes ; but they make the seen noses stand apart, on the same principle as two arrows, marked out an inch and a half asun- der, and one of them seen by each eye, would ap- pear an inch and a half asunder. To what has now been said, is to be added the momentous consideration, that, in the case of Vision without External Objects, we have thrown away our eye-tubes ; and, with them, have thrown away, or excluded, also the External World : And we now contemplate only those Visual Objects and their Crossings, ivhich form the figured World of our own Mental Mo- difications.