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XVIII. Contributions to the Physiology of F'ision. — Part the First. On some remark- 

 able, and hitherto unobserved. Phenomena of Binocular Vision. By Charles 

 Wheatstone, F.R.S., Professor of Experimental Philosophy in King's College, 

 London. 



Received and Read June 21, 1838. 



fV HEN an object is viewed at so great a distance that the optic axes of both eyes 

 are sensibly parallel when directed towards it, the perspective projections of it, seen 

 by each eye separately, are similar, and the appearance to the two eyes is precisely 

 the same as when the object is seen by one eye only. There is, in such case, no dif- 

 ference between the visual appearance of an object in relief and its perspective pro- 

 jection on a plane surface; and hence pictorial representations of distant objects, 

 when those circumstances which would prevent or disturb the illusion are carefully 

 excluded, may be rendered such perfect resemblances of the objects they are intended 

 to represent as to be mistaken for them ; the Diorama is an instance of this. But 

 this similarity no longer exists when the object is placed so near the eyes that to view 

 it the optic axes must converge ; under these conditions a different perspective pro- 

 jection of it is seen by each eye, and these perspectives are more dissimilar as the 

 convergence of the optic axes becomes greater. This fact may be easily verified by 

 placing any figure of three dimensions, an outline cube for instance, at a moderate 

 distance before the eyes, and while the head is kept perfectly steady, viewing it with 

 each eye successively while the other is closed. Plate XI. fig. 13. represents the two 

 perspective projections of a cube ; b is that seen by the right eye, and a that presented 

 to the left eye ; the figure being supposed to be placed about seven inches immediately 

 before the spectator. 



The appearances, which are by this simple experiment rendered so obvious, may 

 be easily inferred from the established laws of perspective ; for the same object in 

 relief is, when viewed by a different eye, seen from two points of sight at a distance 

 from each other equal to the line joining the two eyes. Yet they seem to have 

 escaped the attention of every philosopher and artist who has treated of the subjects 

 of vision and perspective. I can ascribe this inattention to a phenomenon leading 

 to the important and curious consequences, which will form the subject of the present 

 communication, only to this circumstance ; that the results being contrary to a prin- 

 ciple which was very generally maintained by optical writers, viz. that objects can 



3 b2 



