CONTENTS. 



MAGNIFYING GLASSES. 



PACE 



1. Magnifiers intermediate between spectacle -glasses and microscopes. 

 2. Variously mounted. 3. Extensive use in the arts. 4. 

 Their magnifying power explained. 5. Visual magnitude. 6. 

 Standard of visual magnitude. 7. Distance of most distinct 

 vision. 8. Visual magnitude at ten-inch distance. 9. Magnify- 

 ing 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 ma- 

 terials. 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 Superseded nevertheless by the improvement of compound 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. Supports for these. 25. Pocket magnifiers. 26. Coddington 

 lens. 27. Doublets. 28. Their optical effects. 29. Their ad- 

 vantages 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 97 



INSTINCT AND INTELLIGENCE. 



CHAP. I. 1. Instinct defined. 2. Independent of experience or prac- 

 tice. 3. Sometimes directed by appetite. 4. A simple faculty 

 independent of memory. 5. Instinctive distinguished from intelli- 

 gent acts. 6. Instinct and intelligence always co-exist. 7. The 

 proportion of instinct to intelligence increases as we descend in the 

 organic chain. 8. Opinions of Descartes and Buffon. Character 

 of the dog. 9. Researches and observations of Frederic Cuvier. 

 10. Causes of the errors of Descartes, Buffon, Leroy, and Condil- 

 lac. 11. Degrees of intelligence observed in different orders of 

 animals. 12. Accordance of this with their cerebral develop- 

 ment. 13. Opposition between intelligence and instinct. 14. 

 Consequences of defining their limits. 15. Example of instinct 

 in ducklings. 16. In the construction of honeycomb. 17. The 

 snares of the ant-lion. 18. Their mode of construction and use. 

 19. Spiders' nets. 20. Fishes catching insects. 21. Provi- 

 dent economy of the squirrel. 22. Haymaking by the Siberian 

 lagomys. 23. Habitations constructed by animals. 24. The 

 house of the hamster. 25. The habitation of the mygale, with 

 its door. 26. Habitations of caterpillars. 27. Clothing of the 

 larva of the moth. 28. Dwellings of animals whichare torpid at 

 certain seasons. 29. The Alpine marmot curious structure of 

 their habitations. 30. Method of constructing them. 31. Sin- 

 gular habits of these animals. 32. Instincts of migration. 33. 

 Irregular and occasional migration. 34. General assembly pre- 

 paratory to migration. 35. Occasional migration of monkeys . 113 



