THE PERCEPTION OF SIGHT. 245 



in accordance with experiments by Fechner, 1 Yolkmann, 2 and 

 myself, which prove that even the fully developed eye of an 

 adult can only accurately compare the size of those lines or 

 angles in the field of vision, the images of which can be thrown 

 one after another upon precisely the same spot of the retina by 

 means of the ordinary movements of the eye. 



Moreover, we may convince ourselves by a simple experi- 

 ment that the harmonious results of the perceptions of feeling 

 and of sight depend, even in the adult, upon a constant com- 

 parison of the two, by means of the retinal pictures of our hands 

 as they move. If we put on a pair of spectacles with prismatic 

 glasses, the two flat surfaces of which converge towards the 

 right, all objects appear to be moved over to the right. If we 

 now try to touch anything we see, taking care to shut the eyes 

 before the hand appears in sight, it passes to the right of the 

 object ; but if we follow the movement of the hand with the 

 eye, we are able to touch what we intend, by bringing the retinal 

 image of the hand up to that of the object. Again, if we handle 

 the object for one or two minutes, watching it all the time, a 

 fresh correspondence is formed between the eye and the hand, in 

 spite of the deceptive glass, so that we are now able to touch 

 the object with perfect certainty, even when the eyes are shut. 

 And we can even do the same with the other hand without see- 

 ing it, which proves that it is not the perception of touch which 

 has been rectified by comparison with the false retinal images, 

 but, on the contrary, the perception of sight, which has been 

 corrected by that of touch. But, again, if, after trying this ex- 

 periment several times, we take off the spectacles and then look 

 at any object, taking care not to bring our hands into the field of 

 vision, and now try to touch it with our eyes shut, the hand 

 will pass beyond it on the opposite side that is. to the left. 

 The new harmony which wag established between the percep- 



1 Gustav Theodor Fechner, author of Elemente tier Psyclwphytik, I860 ; also 

 known as a satirist. Tn. 



2 Alfred Wilhelm Volkmann, successively Professor of Physiology at Leipzig, 

 Dorpat, and Halle ; author of Phys'wlogische Untr.rsucliungen im Gebiete dtr 

 Optik, 1864, &c. TK. 



