PHYSIOLOGICAL PARADOXES. 



line of the left eye, and on the left-hand side 

 of the vision line of the right eye. In the two 

 eyes looking at P, it appears in opposite parts 

 of the field of vision. And as the brain recog- 

 nises only one field of vision at a time, that 

 is for one position of the eyes, images in oppo- 

 site parts of the field must necessarily look 

 like different objects. Hence it is that when 

 the eyes are looking at the door-knob P, the 

 finger S 2 is seen as two fingers, one visible to 

 each eye. 



Similarly, if the eyes are directed to the 

 nearer object S 2 , their lines of vision run from 

 L to S 2 , and from R to S 2 . Then the more 

 distant object P appears to the right eye on 

 the right-hand side of the central vision line, 

 and on its left-hand side to the left eye. Each 

 eye perceives it in a different part of its own- 

 field of vision. Consequently, the brain once 

 more, when the eyes are looking at the finger 

 S 2 , sees the door-knob P as two door-knobs. 



Readers will remember how the poet of 

 Caledonia, after an evening which put him 

 in a position to say 



" I was na fou', but just had plenty " 



on his belated return to his humble home, 

 diverted his mind from the thought of the 

 reception awaiting him there by turning his 

 attention, poet-like, to the study of Nature. 

 He studied the moon, and speedily found him- 



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