The stereoscopic manual / by W.I. Chadwick.

  • Chadwick, William Isaac.
Date:
[between 1890 and 1899?]
Catalogue details

Licence: Public Domain Mark

Credit: The stereoscopic manual / by W.I. Chadwick. Source: Wellcome Collection.

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    by a cord from the chandelier of a room with the interior of which we are not familiar. If we close one eye and enter the room with a pair of scissors in hand, and walk deliberately to cut the cord, the probability is that we shall not correctly estimate the true distance, and so fail on the first trial. Another simple experiment is to try to snuff a candle with one eye closed. When the two eyes are open there is no difficulty in performing either of these experiments, thus establishing the fact that a very imperfect idea of distance is obtained from the focussing arrangements of a single eye, but as has been said, and cannot be emphasised too strongly, that when two eyes are used, the optic axes converge to the single point, and inhere these axes meet the single image is seat. But this successive convergence is not necessary to the impression on the mind of solidity ; for the images which are outside the optic axes—double or indistinct—make us conscious of their presence, and the mind associates them with solidity or distance. If the number of the page on the left-hand corner of this book be intensely looked at, it will be quite distinct; at the same time, however, the number on the right-hand page cannot be distinctly recognised, nor can any other part of the book as it lies open before the reader, but he is nevertheless conscious of its presence, and the brain will associate the whole with a solid object of a certain size.
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