ORIGIN OF PHYSICAL CONCEPTS 25 



of the other distantial sensations. If sonorous un- 

 dulations excited vibration in every resistant 

 object of the environment they would undoubtedly 

 come to arrange themselves in an order resembling 

 the extensity suggested by Vision, though the 

 slower rate of transmission of sound would detract 

 from the practical simultaneity in the effect which, 

 as we have seen, largely accounts for the per- 

 ception of visual extensity. The universal diffusion 

 of sunlight is also a determining factor. 



The matter becomes still clearer when we contrast 

 the experience of vident men with what we have 

 been able to learn of the experiences of the blind. 

 Nowhere have we found this aspect of the question 

 discussed with the same clearness and ability as 

 by M. Pierre Villey in his recently published essay, 

 Le Monde des Aveugles Part III. 



The blind man, as he remarks, requires repre- 

 sentations in order to command his movements. We 

 must then penetrate the mind of the blind and 

 ascertain what are his representations. Are they, 

 he asks, muscular images combined by temporal 

 relations, or are they images of a spatial order ? 

 He replies without hesitation : Both, but, above 

 all, spatial images. It is clear, he says, that the 

 modalities of the action of the blind are explained 



