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 aiad 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 Superseded nevertheless 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 4kat 
purpose.—38. Mechanism to make 
