1886.] NATURAL SCIENCES OF PHILADELPHIA. 30? 



while used in touch, is inverted. Hence, the notion is evidently absurd, 

 that infants at first see objects upside down, and learn to see things in their 

 proper positions, by comparing the erroneous information acquired by sight 

 with the accurate information acquired by touch. Many of the lower 

 animals manifest a perception of the true position of objects by means of 

 the sense of sight from the very first, and before any experience derivable 

 from touch can have had time to operate. To some philosophers, then, 

 there appears no difiiculty respecting erect vision, so long as all things 

 equally, and not some objects only, are seen by means of impressions coin- 

 cident with inverted images." He further says : "The mind neither views 

 the images on the retina, nor is in any way conscious of their existence." 



This theory is so identical with the one we have given, as to render the 

 latter, in a considerable sense, a repetition. Yet Mackenzie's views do not 

 seem well known, and are worth restating. Moreover, his theory is far 

 from being fully argued out, and no theoretical views can be held as in any 

 sense substantiated until they have been shown to be logically defensible. 

 This we have attempted to do. The hypothesis we have given of the prin- 

 ciple through which nerve impressions are mentally localized in position 

 has, we believe, not been previously advanced, but is here first presented. 



