Abstract
THE perplexing illusion to which Mr. Bellamy refers (NATURE, vol. xx. p. 362) has long been known, and various explanations have been given of it by physicists. Sir Chas. Wheatstone, in 1838, showed clearly that it is a mental operation, while combating the idea of Prof. Necker, of Geneva, who attributed the alteration of appearance in geometrical figures, not to a mental operation, but to an involuntary change in the adjustment of the eye for obtaining distinct vision. Necker's experiment is substantially the same as that described by Mr. Bellamy. The solid angles at A and X being alternately looked at, sometimes one and sometimes the other appears the nearer, the entire figure at the same time changing in unison; and as Wheatstone points out, “the change of figure frequently occurs while the eye continues to look at the same angle.”
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ACKROYD, W. Change in Apparent Position of Geometrical Figures. Nature 21, 108 (1879). https://doi.org/10.1038/021108b0
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DOI: https://doi.org/10.1038/021108b0
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