A ..". 



p W 



Fig. 1. 



THE EYE. 



CHAPTER I. 



1. Pleasures and advantages of the power of vision. 2. Reasons why a 

 knowledge of the structure and functions of the eye is desirable. 

 3. Description of the eye. 4. Sclerotica and cornea. 5. Aqueous 

 humour, pupil, and iris. 6. Crystalline humour and ciliary processes. 

 7. 'Choroid. 8. Retina and vitreous humour. 9. Axis of the eye 

 and optic nerve. 10. Numerical data. 11. Limits of the play of 

 the eye. 12. Achromatism of the eye. 13-16. How vision is 

 caused. 17. Conditions of perfect vision. 18. Distinctness of the 

 image. 19. Parallel rays. 20, 21. Defects of vision and their 

 remedies. 22-24. Power of adaptation. 25-29. Limits of this 

 power. 30, 31. Causes of defective vision. 32. Magnitude of the 

 image on the retina. 33. Apparent magnitude denned. 34-37. 

 Nature of its variation. 38-40. Diminutiveness of the pictures on 

 the retina. 41. Sufficiency of illumination. 



1. Or all the organs of sense, that to which we are most 

 largely indebted is un questionably THE EYE. It opens to us the 

 widest and most varied range of observation. The pleasures and 

 advantages we derive from it directly and indirectly have neither 

 cessation nor bounds. It guides our steps through the world we 



LARDHER'S MUSEUM OF SCIENCE. E 49 



No. 54. 



