32. Horizontal section of the eyeball 66 33. Action of eye in formation of images 68 34. Action of a long-sighted eye 69 35. Diagram showing path of rays when viewing an object at an 70 easy distance 36. Action of short-sighted eye 71 37. Galilean telescope 73 38. Telescope 75 39. Diagram explaining the magnifying power of object-glass 76 40. Scheiner’s telescope 78 41. Dispersion of light by prism 80 42. Diagram showing the amount of colour produced by a lens 81 43. Decomposition and recomposition of light by two prisms 83 44. Diagram explaining the formation of an achromatic lens 84 45. Combination of flint- and crown-glass lenses in an achromatic 86 lens 46. Diagram illustrating the irrationality of the spectrum 87 47. Diagram illustrating the action of a reflecting surface 91 48. Experimental proof that the angle of incidence = angle of 92 reflection 49. Convergence of light by concave mirror 94 50. Conjugate foci of convex mirror 94 51. Formation of image of candle by reflection 95 52. Diagram explaining Fig. 51 96 53. Reflection of rays by convex mirror 98 54. Reflecting telescope (Gregorian) 101 55. Newton’s telescope 102 56. Reflecting telescope (Cassegrain) 103 57. Front view telescope (Herschel) 103 58. Diagram illustrating spherical aberration 105 59. Diagram showing the proper form of reflector to be an ellipse 106 60. Huyghens’ eyepiece 110 61. Diagram explaining the achromaticity of the Huyghenian 111 eyepiece 62. Ramsden’s eyepiece 112 63. Erecting or day eyepiece 113 64. Images of planet produced by short and long focus lenses, &c. 123 65. Showing in an exaggerated form how the edge of the speculum 128 is worn down by polishing 65*. Section of Lord Rosse’s polishing machine 131 66. Mr. Lassell’s polishing machine 132 67. Simple telescope tube, showing arrangement of object-glass 140 and eyepiece 68. Appearance of diffraction rings round a star when the 141 object-glass is properly adjusted