41 



Describe the image as above Negative After Image, 

 (c) Colour. Using the coloured squares supplied study the 

 after images as in (a) and (6). 



VIII. How far does our Visual Perception give us a true 

 Knowledge of our Surroundings ? 



Modified Visual Perceptions. 



METHODS. 1. Two squares of equal size are fixed upon 

 paper : one is white placed upon a black ground, and one 

 black placed upon a white ground. Which appears larger, 

 and why ? 



2. Place three equidistant dots in a straight line on a piece 

 of paper and subdivide one division by a. series of dots. Which 

 part appears longer, and why ? 



3. (a) A red square is placed on a white ground and another 

 on a green ground. Which appears redder in colour ? 



(6) A red paper is placed on the table with a grey one a 

 foot away on one side and a green one a similar distance away 

 on the other. 



Does the red appear redder after looking at the grey or at 

 the green sheet ? 



4. Rule a square with parallel diagonal lines, and place 

 short vertical and horizontal lines upon the alternate dia- 

 gonals. Do the latter now appear parallel ? If not, w r hy 

 not ? 



From these experiments draw your CONCLUSIONS as to the 

 necessary accuracy of the knowledge gained by vision. 



C. Vision with Two Eyes. 

 I. What are the Advantages ? 



1. Extent of Field of Vision. 



With the perimeter investigate the field of vision in the 

 horizontal plane first for the right eye, then for the left eye, 



