CONTENTS. 



vision. 60. Dispersion. 61. Dis- 

 persion increases with refraction. 

 62. Dispersion different with dif- 

 ferent material. 



CHAP. III. 63. Experimental illustra- 

 tion. 64. Dispersive powers. 65. 



Dispersive power does not necessarily 

 increase with refractive power. 

 66. Example of the diamond. 67. 

 Achromatic lens. 68. Achromatic 

 combination of flint and crown-glass. 

 69. Form of the compound lens. 



MAGNIFYING GLASSES. 



1. Magnifiers intermediate between 

 spectacle -glasses and microscopes. 

 2. Variously mounted. 3. Exten- 

 sive use in the arts. 4. Their mag- 

 nifying power explained. 5. Visual 

 magnitude. 6. Standard of visual 

 magnitude. 7. Distance of most 

 distinct vision. 8. Visual magni- 

 tude at ten-inch distance. 9. Mag- 

 nifying power of a convex lens. 10. 

 Effect of the same lens with different 

 eyes. 11. Superficial and cubical 

 magnifying power. 12. The eye to 

 be placed close to the lens. 13. 

 Magnifying power depends on focal 

 length. 14. Focal length depends 

 on convexity and materials of lens. 

 15. Lenses of different materials. 

 16. Spherical aberration less with 



a greater refracting material. 17. 

 Diamond lens. 18. Magnitude of 

 lens greater with more refracting 

 material. 19. Advantages of gem 

 lenses. 20. Superseded nevertheless 

 by the improvement of compound 

 microscopes. 21. Magnifiers for 

 reading. 22. For miniature-painters 

 and engravers. 23. For watch- 

 makers, jewellers, &c. 24. Sup- 

 ports for these. 25. Pocket magni- 

 fiers. 26. Coddington lens. 27. 

 Doublets. 28. Their optical effects. 

 29. Their advantages over single 

 lenses. 30. Method of mounting 

 them ; triplets. 31. Mounting of 

 hand-doublets. 32. Method of 

 mounting doublets of high power for 

 dissection and similar purposes. 



THE MICROSCOPE. 



CHAP. I. 1. Origin of the term. 2. 

 Simple microscopes are magnifying 

 glasses. 3. Compound microscope. 

 4. Object-glass and eye-glass. 

 5 . General description of the instru- 

 ment. 6. Uses of the field-glass. 

 7. Reflecting microscopes. 8. Con- 

 ditions of distinct vision in the mi- 

 croscope. 9. Effects of different 

 magnifying powers. 10. Distinct- 

 ness of delineation necessary. 11. 

 Hence aberration must be effaced. 

 12. Achromatic object-lenses. 13. 

 Sufficient illumination necessary. 



14. Effects of angular aperture. 



15. Experiments of Dr. Goring. 



16. Method of determining the 

 angular aperture. 17. Mutual 

 chromatic and spherical correction 

 of the lenses. 



CHAP. II. Mutual chromatic and sphe- 

 rical correction of the lenses (con- 



tinued). 18. Centering. 19. Com- 

 pound object-pieces. 20. The eye- 

 piece. 21. Various magnifying 

 powers adapted to the same micro- 

 scope. 22. Actual dimensions of 

 the field of view. 23. Means of 

 moving and illuminating the object. 

 24. Focussing. 25. Preparation 

 of the object. 26. General descrip- 

 tion of the structure of a microscope. 

 27. The stage. 28. The illumi- 

 nators. 29. The diaphragms. 

 CHAP. III. 30. Oblique plane reflec- 

 tors. THE SUPPORT AND MOVEMENT 



OP THE OBJECT : 31. The stage. 

 32. Mechanism for focussing. 33. 

 Coarse adjustment. 34. Fine ad- 

 justment. 35. Method of deter- 

 mining the relief of an object. 36. 

 Difficulty of bringing the object into 

 the field. 37. Mechanism'' for that 

 purpose. 38. Mechanism to make 



