L-3L 



CONTENTS. 



%* As this book is not paged, the figures in the Table of Contents refer to 

 Paragraphs, and not to Pages. 



OPTICAL IMAGES. 



CHAP. I. 1. Great importance of the 

 subject in relation to all the effects 

 of vision. 2. Explanation of how 

 an object is seen with the naked eye. 

 3. Images produced by plane re- 

 flectors. 4. How rays are reflected 

 from such surfaces. 5. Experimen- 

 tal verifications of this. 6. Image 

 of a point in a plane reflecting sur- 

 face. 7. Image of an object in the 

 same. 8. Real and imaginary images. 

 9. Images produced by spherical 

 reflectors. 10. By a concave re- 

 flector. 11. Experimental verifica- 

 tion. 12. Variation of position, and 

 magnitude of image. 13. Images 

 in convex reflectors. 14. Images 

 produced by transparent bodies. 

 15. Refraction. 16. Cases in which 

 light will not enter a transparent 

 body. 17. Reflection of objects in 

 water. 18. The fallacy of the fable 

 of "the Dog and the Shadow." 

 19. Objects seen at the bottom of a 

 transparent body. 20. Case of 

 water and glass. 21. Broken ap- 

 pearance of a rod immersed in water. 

 22. Cases in which rays cannot 

 emerge from a transparent body. j 

 23. Experimental verification. 24. I 

 Reflection by a rectangular Prism . I 



25. Images produced by lenses. 



26. Six kinds of lenses. 27. The 

 axis of a lens. 28. Example of, 

 each kind of lens. 29. Optical image I 

 produced by a con vex lens. 30. Re- j 

 lative position of the object and image. | 



CHAP. II. 31. Experimental verifica- 

 tion. 32. Variation of the magni- 

 tude of the image. 33. Principal 

 focus and focal length. 34. Varia- 

 tion of position, and magnitude of 

 image. 35. When images real, and 

 when imaginary. 36. Images pro- 

 duced by concave lenses. 37. Focal 

 length varies with refracting power. 

 38. Refracting power depends on 

 material of lens. 39. Spherical 

 aberration. 40. Images produced 

 by lenses not absolutely clear and 

 distinct. 41. Series of images. 

 42. Nebulous and confused effect. 

 43. Spherical aberration greater 

 near' the borders. 44. Increases 

 with the curvature. 45. And with 

 the magnifying power. 46. Sphe- 

 rical distortion. 47. Curved images. 

 48. How to diminish spherical 

 aberration. 49. Lenses made from 

 diamonds and other precious stones. 

 50. Ineffectual attempts at im- 

 provement by this means. 51. 

 Methods of diminishing spherical 

 aberration by proper adaptation of 

 curvatures. 52. Aplanatic lenses. 

 53. Chromatic aberration. 54. 

 White light compound. 55. Co- 

 loured lights sometimes compound. 

 56. Images produced by homogeneous 

 lights. 57. Images produced by 

 compound light. 58. Lenses always 

 produce several images of a natural 

 object. 59. Why they are not al- 

 ways so confused as to be useless for 



