CH. XIV] 



577 



LENSES AND THEIR ACTION 



FIG. 314. THE OPTIC CENTER AND THE PRINCIPAL OPTIC Axis OF VARIOUS 



FORMS OF LENSES. 



(From The Microscope) 



c c' Centers of curvature of the different lenses. 



As shown in all the figures each curved face of the lens is a part of a sphere 

 of greater or less size. 



c.l Optic center of the lens. 



r Radius of the sphere from which the lens is derived. (Radius of curva- 

 ture). 



1 . Double-convex lens, the two faces having different curvatures. 



2. Double- concave lens, the two faces of different curvatures. 



3. Plano-convex lens. 



4. 5, 6. The same showing the optic center (cl). 



7. Plano-concave lens showing optic center (cl). 



8. Converging, meniscus lens. The optic center (cl) is outside the lens, 

 on the convex side. 



9. Diverging meniscus lens with the optic center (cl) outside the lens, and 

 on the concave side. 



