214 PSYCHOLOGY. 



height and length in the mountain-chains that bound it to 

 our view. But as aforesaid, let us not consider the ques- 

 tion of absolute size now, — it must later be taken up in a 

 thorough way. Let us confine ourselves to the way in 

 which the three dimensions which are seen, get their values 

 fixed relatively to each other. 



Eeid, in his Inquiry into the Human Mind, has a section 

 * Of the Geometry of Visibles,' in which he assumes to 

 trace what the perceptions would be of a race of ' Idome- 

 nians ' reduced to the sole sense of sight. Agreeing with 

 Berkeley that sight alone can give no knowledge of the third 

 dimension, he humorously deduces various ingenious ab- 

 surdities in their interpretations of the material appear- 

 ances before their eyes. 



Now I firmly believe, on the contrary, that one of Beid's 

 Idomenians would frame precisely the same conception of 

 the external world that we do, if he had our intellectual 

 powers.* Even were his very eyeballs fixed and not mov- 

 able like ours, that would only retard, not frustrate, his 

 education. For the sa7ne object, by alternately covering in 

 its lateral movements different parts of his retina, would 

 determine the mutual equivalencies of the first two dimen- 

 sions of the field of view ; and by exciting the physiological 

 cause of his percejjtion of depth in various degrees, it would 

 establish a scale of equivalency between the first two and 

 the third. 



First of all, one of the sensations given by the object 

 is chosen to represent its * real ' size and shape, in accord- 

 ance with the principles laid down on pp. 178 and 179. 

 One sensation measures the ' thing ' present, and the ' thing ' then 

 measures the other sensations. The peripheral parts of the 

 retina are equated with the central by receiving the image 

 of the same object. This needs no elucidation in case the 



* " In Froriep's Notizen (1838, July), No. 133, is to be found a detailed 

 account, with a picture, of an Esthonian girl, Eva Lauk, then fourteen 

 years old, born with neither arms nor legs, which concludes with the 

 following words : 'According to the mother, her intellect developed quite 

 as fast as that of her brother and sisters ; in particular, she came as quickly 

 to a right judgment of the size and distance of visible objects, although, 

 of course, she had no use of hands.' " (Schopenhauer, Welt als Wille, n 

 *4.) 



