CHAPTER V

THE "TELEPHOGRAPH" 74

Author's System of Radio-Photography--Requirements--Advantages--Transmitting machine--Description of Differential Relay--Wireless Receiving Apparatus--Photo-Telegraphic Receiving Apparatus--Circuit Breaker--Friction Brake--Magnetic Clutch--Description of Isochroniser--Method of working--Types of Nernst Lamp--Action of Nernst Lamp--Comparison of Actinic Value--Inertia of Photographic Films--Choosing Films--Speed of Films--Standard of Speed--Comparative Film Speeds--Effects of Minimum Exposure--Effects of Maximum Exposure--Considerations in working and choosing Films.

APPENDIX A

SELENIUM CELLS 109

Nature of Selenium--Preparation of Selenium--Forms of Selenium Cells--Action of Selenium Cells--Characteristics of Selenium Cells--Effects of Inertia in Photo-Telegraphy--Methods of counteracting Inertia--Sensitiveness of Selenium to Light--Effect of Heat on Selenium.

APPENDIX B

PREPARING THE METAL PRINTS 115

Outline of Process--Line Screens--Choice of Camera--Fixing Line Screen in Camera--Lenses and Stops--Taking the Photograph--Copying Stands--Choice of Photographic Plates--Sources of Illumination--Metal Prints--Coating the {xi} Metal Sheets--Sensitising Solution--Printing Operations--Developing--Intensifying--Precautions to be observed in working--Preparing Sketches on Metal--Apparatus for Reducing or Enlarging--Improvements to Copying Board--Lenses for Copying--Formula for Copying.

APPENDIX C

LENSES 126

Action of Light--Law of Refraction--Lenses--Prisms--Action of Lenses--Focal Length of Lenses--Formation of Images--Apparent Magnitude of Objects--Real and Virtual Images--Formation of Virtual Images--Power of Magnification--Defects of Lenses--Aberration.

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{xiii}

ILLUSTRATIONS

FIG. PAGE

1. Diagram showing effects of capacity on an intermittent current 5

2. Bernochi's wireless apparatus 7

3. Knudsen's wireless apparatus 10

4. Wireless transmitting station 13

5. Diagram of experiment illustrating principle of line photograph 16

6. Drawing of transmitting machine 17

7. Drawing of transmitting machine 18

8. Drawing of stylus 18

9. Electrical connections of machine 19

10. Photograph of Author's experimental machine _Frontispiece_

10a. End view of Author's experimental machine } } _facing page_ 21 10b. View of image broken up by a "cross" screen}

11. Connections of complete transmitting apparatus 23

12. Drawing of ordinary type of spark-gap 27

13. Synchronous rotating spark-gap 28

14. Non-synchronous rotating spark-gap 28

15. Connections for complete wireless photographic station 30

16. Connections of Professor Korn's apparatus 31

17. Connections of Poulsen's photographic recorder 33

18. Author's photographic receiver 38

19. Enlarged drawing of cone 39

20. End view of Author's photographic receiver 39

21. Connections of decohering apparatus 41

22. Connections for complete photographic receiver 42

{xiv} 23. Arrangement of Einthoven galvanometer 45

24. Einthoven galvanometer arranged for receiving 46

25. Connection of telephone relay 49

26. Drawing of Author's improved photographic receiver 51

27. Diagram giving ratio of vibrating arm 51

28. Arrangement of polarisation receiver 53

29. Arrangement of kathode-ray receiver 54

30. Connections of electrolytic receiver 56

31. Drawing of improved stylus for receiving 58

32. Drawing of Hughes telegraph governor 66

33. Arrangement of simple speed regulator 68

34. Diagram of connections of simple speed regulator 68

35. Author's arrangement for complete radio-photographic station 77

36. Drawing of transmitting machine and circuit breaker 78

37. Drawing of special transmitting stylus showing adjusting arrangements 79

37a. End view of transmitting stylus 79

38. Connections of new type of relay designed by the Author 80

39. Arrangement of mercury containers and dipping rods for relay 82

40. Drawing of Author's receiver 84

41. Enlarged drawing of diaphragm and steel point 84

41a. Drawing showing arrangement of bush and counter-weight 84

42. Optical arrangements of receiver 85

43. Optical arrangements of receiver 86

44. Drawing of circuit breaker 88

45. Drawing of friction brake 89

46. Sectional drawing of magnetic clutch 90

47. Plan of magnetic clutch 90

48. Details of Isochroniser 92

49. Connections of Isochroniser 94

50. Dial of Isochroniser 94

51. Diagram of driving mechanism 96

{xv} 52. Diagram showing starting positions of machines 97

52a. Arrangement of small type Nernst lamp 99

52b. Ballasting resistances for Nernst lamps 100

52c. Arrangement of large type Nernst lamp 101

53. Connections of selenium cell elements 110

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

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RADIO-PHOTOGRAPHY