CH. XV] 



DEMONSTRATIONS OF NORMAL VISION 



655 



Kepler, Retinal Image, 



Accommo- 

 dation 



1604 



Presbyopia 



Astigmia. 1800-1825 



Effect of the Pupil 



Hyperopia 



Two Eyes Different 



FIG. 382. OUTLINES OF THE TRIAL LENSES NEEDED FOR SIMPLE 

 EXPERIMENTS IN NORMAL AND DEFECTIVE VISION. 



(About one-third size) 



/ A 3 diopter convex lens (+3). For diopter see 356a. 



2 A3 and a 4 diopter convex lens (+3, +4). 



j A 4 diopter convex lens (+4), and a i diopter concave lens ( i). 



4 A 2 diopter and a i diopter convex lens (+2, +i). 



5 A3 diopter and a i diopter convex lens (+3, +!) 



6 A 4 diopter convex lens (+4), a 0.5 convex cylinder, (+0.5 cyl.) and a 

 0.5 concave cylinder, ( 0.5 cyl.). 



7 A 4 diopter convex lens (+4), and a 0.5 convex or concave cylinder 

 (0.5 cyl.). 



