THE BLIND SPOT 



Reverse these processes, beginning with the 

 paper as near to the eyes as allows you to see 

 comfortably, and looking at R with the right 

 eye. L is seen, though not looked at. Remove 

 the paper to about six inches. L is not visible. 

 Remove it still further, and L is seen again. 

 The same phenomenon can be seen with the left 

 eye, closing the right eye with the right hand, 

 holding the paper in the left hand, and looking 

 at L. 



It thus appears that each eye has a blind spot. 



The explanation will be assisted by Fig. 

 46, which gives a plan corresponding to what 



FIG. 45.-DEVICE TO SHOW EXISTENCE OF BLIND SPOT IN EVERY 



EYE. 



would be seen if a section were taken horizon- 

 tally through the middle of the eyes and looked 

 at from above. R E and L E are the sections 

 through the right eye and left eye of a person 

 facing towards A, but looking towards B. C 

 represents an obstacle blocking the view of the 

 left eye. Automatically, however, the two 

 eyes converge in the direction of vision that is, 

 upon R. When the right eye is gazing at R, 

 that means it is so directed that the light from 

 R, passing through the pupil and lens, strikes 

 the retina at the back of the eye just at the 

 point marked by the end of the line from M L. 

 This point, the macula lutea, or yellow spot, 

 217 



