LIST OF ILLUSTRATIONS. 



PIG. PAGE 



1. Section through the Human Eye z 



2. Illustration of Refraction 4 



3. Refraction by Prisms 5 



4. Refractions in Prisms of Different Angles 5 



5. Plano-convex Lens and its Principal Focus 6 



6. Course of Rays according to the Relation of a Luminous Point 



to the Principal Focus 7 



7. Formation of Image by Object outside Principal Focus 8 



8. " " " " " inside " " 9 



9. Leeuwenhoek's Microscope ii 



10. Hooke's Compound Microscope 12 



1 1. Course of Rays in Compound Microscope 13 



12. Chromatic Aberration 14 



13. Achromatic Objective. 15 



14. Effect of Homogeneous Immersion 16 



15. The Microscope 18 



16. Relation of Distance from Principal Focus to Size and Position 



of Image 21 



17. Proper Position for Observer 24 



18. Method oPInserting Objectives 26 



19. Abbe Condenser 28 



20. Refraction by Air-bubbles and Oil-drops , 30 



21. Disturbing Effect of the Cover-glass. 32 



22. Micrometer Calipers 33 



23. Curvature of the Field ; 35 



24. Turntable 42 



25. Thoma Microtome 48 



26. Camera Lucida 55 



27. Course of Rays in the Camera Lucida 56 



