53a. Form of selenium cell used by Bell and Tainter 110

54. Diagram showing construction of modern cell 111

55. Resistance curve of selenium cell 111

55a. Actual curve of selenium cell 112

56. Diagram of Professor Korn's method for counteracting inertia 113

57. Arrangement of plate sheath and line screen 117

58. Details of clips to hold line screen 118

59. Arrangement of apparatus for copying 119

60. Drawing showing method of arranging camera and copying stand for
adjustment 119

61. Photograph of line screen and metal print }
} _facing page_ 124
62. Photograph of sketch drawn upon metal foil }

63. Method of marking out copying board 124

64. Diagram illustrating law of refraction 127

65. Forms of lenses 128

66. Action of light passed through a prism 129

67. Diagram illustrating action of a lens 130

68. Formation of principal focus of a lens 130

69. Formation of conjugate foci of a lens 131

70. Apparatus illustrating principle of camera 132

71. Formation of an image by a lens 133

72. Diagram illustrating apparent magnitude 134

73. Formation of virtual image by a convex lens 137

74. Formation of virtual image by a concave lens 138

75. Diagram showing spherical aberration 139

76. Combination of plano-convex lenses 139

77. Combination of meniscus and convex lenses 139

* * * * *

{1}

RADIO-PHOTOGRAPHY

CHAPTER I

INTRODUCTORY

Those who desire to experiment on radio-photography, _i.e._ transmitting
photographs, drawings, etc., from one place to another without the aid of
artificial conductors, must cultivate at least an elementary knowledge of
optics, chemistry, mec