COMPLEMENTARY COLOURS. 29 



but regarded them both as discs. The solid cube was now placed in a 

 somewhat oblique position before the eye, and close beside it a figure 

 cut out of pasteboard, representing a plain outline prospect of the cube 

 when in this position. Both objects he took to be somewhat like flat 

 quadrates. A pyramid placed before him, with one of its sides towards 

 his eye, he saw as a plain triangle. This object was now turned a little, 

 so as to present two of its sides to view, but rather more of one side than 

 of the other : after considering and examining it for a long time, he said 

 that this was a very extraordinary figure ; it was neither a triangle, -nor 

 a quadrangle, nor a circle : he had no idea of it, and could not describe it : 

 ' in fact,' he said, ' I must give it up.' " An example of the close as- 

 sociation which exists between the sense of touch and that of sight in 

 enabling the mind to form a correct idea of an object, is afforded in the 

 statement of this patient, that, although, by the sense of sight he could 

 detect a difference in the cube and sphere, and perceive that they were not 

 drawings, yet he could not form from them the idea of a square and a 

 disc, " until he perceived a sensation of what he saw in the points of his 

 fingers, as if he really touched the objects." When he took the sphere, 

 cube, and pyramid, into his hand, he was astonished that he had not 

 recognized them as such by sight, being well acquainted with them by 

 touch. 



When the patient first acquired the faculty of sight, all objects ap- 

 peared much nearer to him than they really were, and much larger than 

 he had supposed them to be from the idea obtained by his sense of touch. 

 He also saw everything perfectly flat : and, by the sense of sight alone, 

 could obtain no correct idea of a solid or projecting body. When, by the 

 division of the internal rectus muscle of both eyes, effected about two 

 months after the operation for cataract, the strabismus was cured, all 

 objects were, for a considerable time afterwards, seen much to the right 

 of their real position. These various circumstances shew how large a 

 share is taken by the operations of the mind in association with the im- 

 pressions received on the retina, in forming a correct estimate of the 

 form, size, distance, arid position of an object presented to the sight, and 

 how difficult it is in the case of the educated eye to say " what belongs 

 to mere sensation, and what to the influence of the mind," * 



Physiological colours produced by contrast. Some interesting observa- 

 tions with respect to the formation of complementary colours, have been 

 published by Dr. Tourtual.f On moving rapidly to and fro a pen-knife in 

 front of the white glass shade of a burning lamp, Dr. Tourtual observed 

 that it assumed a beautiful blue colour, the distinctness of which was in 

 direct proportion to the rapidity of the movements. On the cessation of 

 these movements the colour changed into black. The introduction of a 



* Muller's Physiology, p. 1166. t Canstatt's Jahresbericht, 1845, p. 208. 



