THE PERCEPTION OF SIGHT. 271 



within reach, at once as to resistance, volume, and weight; 

 but the range of touch is Hmited, and the distinction it 

 can make between small distances is not nearly so accu- 

 rate as that of sight. Yet the sense of touch is sufficient, 

 as experiments upon persons born blind have proved, to 

 develop complete notions of space. This proves that the 

 possession of sight is not necessary for the formation of 

 these conceptions, and we shall soon see that we are con- 

 tinually controlling and correcting the notions of locality 

 derived from the eye by the help of the sense of touch, 

 and always accept the impressions on the latter sense as 

 decisive. The two senses, which really have the same 

 task, though with very different means of accomplishing 

 it, happily supply each other's deficiencies. Touch is a 

 trustworthy and experienced servant, but enjoys only a 

 limited range, while sight rivals the boldest flights of 

 fancy in penetrating to illimitable distances. 



This combination of the two senses is of great im- 

 portance for our present task ; for, since we have heie 

 only to do with vision, and since touch is sufficient to 

 produce complete conceptions of locality, we may assume 

 these conceptions to be already complete, at least in their 

 general outline, and may, accordingly, confine our in- 

 vestigation to ascertaining the common point of agree- 

 ment between the visual and tactile perceptions of space. 

 The question how it is possible for any conception of 

 locality to arise from either or both of these sensations, 

 we will leave till last. 



It is obvious, from a consideration of well-known facts, 

 that the distribution of our sensations among nervous 

 structures separated from one another does not at all 

 necessarily bring with it the conception that the causes of 

 these sensations are locally separate. For example, we 

 may have sensations of light, of warmth, of various notes 

 of music, and also perhaps of an odour, in the same room, 



