The stereoscope : its history, theory, and construction, with its application to the fine and useful arts and to education / by Sir David Brewster.

  • Brewster, David, 1781-1868.
Date:
1856
Catalogue details

Licence: Public Domain Mark

Credit: The stereoscope : its history, theory, and construction, with its application to the fine and useful arts and to education / by Sir David Brewster. Source: Wellcome Collection.

Provider: This material has been provided by King’s College London. The original may be consulted at King’s College London.

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    point, cannot be doubted; and it is also true that the objects there obscurely seen are frequently doubled. In ordinary vision, it may be said, this indistinctness and duplicity are not attended to, because the eyes shifting continually from point to point, every part of the object is successively rendered distinct, and the perception of the object is not the consequence of a single glance, during which a small jyart of it omly is seen distinctly^ but is formed from a comparison of all the pictures successively seen, while the eyes were changing from one point of an object to another. All this is IN SOME DECREE tmte^ hit were it eMirely so no appearance of relief should present itself when the eyes remain intently fixed on one point of a binocular image in the stereoscope. But in performing the experiment care- fully, it will be found, provided the picture do not extend far beyond the centres of distinct vision, that the image is still seen single, and in relief, when in this condition.”^ In this passage the author makes a distinction between ordinary binocular vision, and binocular vision through the stereoscope, whereas in reality there is none. The theory of both is exactly the same. The muscles of the two eyes unite the two dissimilar pictures, and exhibit the solid, in ordinary vision; whereas in stereoscopic vision the images are united by reflexion or refraction, the eyes in both cases obtaining the vision of different distances by rapid and successive convergences of the optical axes. Mr. Wheat- stone notices the degree of indistinctness in the parts of the picture to which the eyes are not immediately directed ; but he does not notice the “ confusion and incongruity^'* which