PLATE XII. [PAGE 168.] 

 OPTICAL PRINCIPLES. 



Fig. 



1. Refraction through a glass plate. 



2. Law of refraction. 



3. Reflexion from a plane surface. 



4. Reflexion from a concave mirror. 



5. Refraction at a curved surface. 



6. A doubly convex lens. 



7. A plano-convex lens. 



8. A doubly concave lens. 



9. A plano-concave lens. 



10. A concavo-convex lens, or me- 



niscus. 



11. Refraction through a convex lens. 



12. Relation of a convex lens to 



prisms. 



13. Relation of a concave lens to 



prisms. 



14. Refraction of parallel rays through 



a convex lens. 



15. Refraction of converging rays 



through a convex lens. 



Fig. 



16. Refraction of diverging rays 



through a convex lens. 



17. Refraction of parallel rays through 



a concave lens. 



18. Spherical aberration. 



19. Dispersion and formation of a 



spectrum. 



20. Chromatic aberration. 



21. Formation of images in the eye. 



22. Angle of vision. 



23. Objects too near the eye. 



24. Action of convex lens in vision. 



25. Aplanatism. 



26. Aberration produced by cover. 



27. Course of rays through the mi- 



croscope. 



28. Achromatism. 



29. Waves of light conspiring (a, b), 



and interfering (b, c). 



30. Polarization: ^tourmaline; d, cry- 



stal j s, crystal of calcareous spar. 



