THE PERCEPTION OF SIGHT. 275 



difference. If it were not so, it would be impossible to 

 distinguish any local difference in the field of vision. The 

 sensation of red, when it falls upon the right side of the 

 retina, must in some way be different from the sensation 

 of the same red when it affects the left side ; and, more- 

 over, this difference between the two sensations must be 

 of another kind from that which we recognise when the 

 same spot in the retina is successively affected by two 

 different shades of red. Lotze ^ has named this difference 

 between the sensations which the same colour excites 

 when it affects different parts of the retina, the local sign 

 of the sensation. We are for the present ignorant of the 

 nature of this difference, but I adopt the name given by 

 Lotze as a convenient expression. While it would be 

 premature to form any further hypothesis as to the 

 nature of these * local signs,' there can be no doubt 

 of their existence, for it follows from the fact that we 

 are able to distinguish local differences in the field of 

 vision. 



The difference, therefore, between the two opposing 

 views is as follows. The Empirical Theory regards the 

 local signs (whatever they really may be) as signs the 

 signification of which must be learnt, and is actually 

 learnt, in order to arrive at a knowledge of the external 

 world. It is not at all necessary to suppose any kind of 

 correspondence between these local signs and the actual 

 differences of locality which they signify. The Innate 

 Theory, on the other hand, supposes that the local signs 

 are nothing else than direct conceptions of differences 

 in space as such, both in their nature and their magni- 

 tude. 



' Eudolf Hermann Lotze, Professor in the University of Gottingen, 

 originally a disciple of Herbart (v. supra), author of Allgemeine Fhysiologie 

 des menschlichen Korpers, 1851. — Te. 



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