270 THE SPECIAL SENSES 



Apply in front of magnifying glass the proper spectacle lens 

 to bring focus to screen. 



7) Far-sight: Place candle, glass and screen as in 6), for 

 focusing on screen. Move screen toward lens until image is 

 blurred, to imitate the focal condition of far-sight. 



Apply in front of magnifying glass the proper spectacle lens 

 to bring focus to screen. 



8) Sharpness of vision: a) Determine farthest distance at 

 which white thread on black card can be seen, using one eye; 

 using both eyes. 



b) Determine farthest distance when card is 10 and 20 

 from line of vision. 



9) Change in iris (2 working together) : a) Have subject 

 sit facing window; cover one eye with hand for 1 min. 

 Quickly uncover eye and note changes in pupil. 



b) Compare size of pupil when looking at distant object 

 with that when looking at object 6 in. away. 



10) Blind spot: Determine distance from eye at which large 

 spot on p. 263 disappears when one looks at cross with right 

 eye. 



11) Accommodation: Determine greatest and least distances 

 at which objects can be seen clearly with left eye; with right 

 eye. 



12) Binocular vision: a) Hold 2 pencils vertically in front 

 of eyes, one at distance of 1 ft., other at 2 ft. When you look 

 at either one with both eyes open, what is appearance of other, 

 and why? Show by diagram. 



b) Under what conditions do you see "single" when using 

 both eyes? 



13) Determine movements of eyes in changing from far to 

 near vision. 



14) Test visual judgment of 



a) Sizes of disks of equal diameters but of different colors 

 (black on white, white on black, red on white, etc.). 



b) Lengths of vertical and horizontal lines which appear of 

 same length. 



c) Two halves of a line, one of which is crossed by several 

 short lines. 



15) Fatigue of color sense: a) Place a piece of bright red 

 paper upon sheet of white paper and gaze at it steadily for 



