THE MICROSCOPE 



29 



entering the edges of a lens undergo greater refraction 

 than those entering nearer the optic axis (Fig. 13). 



A~--. 



B' 



Fig. 12. — Formation of Virtual Image by Convex Lens. 



1. Optic axis. 2. Focal points. A-B. Object within focal point (2). A'-B'. 

 Virtual image of object A-B. 



A' B' C 



Fig. 13. — Spherical Aberration. 



A-B-C. Light rays passing through different parts of the lens are brought to 

 different foci. A', B', C'. 



These differences in the amount of refraction cause the 

 rays entering the center of the lens to come to a focus 

 at a greater distance from the lens than those entering 



