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

10b. View of image broken up by a "cross" screen
 facing page [21]
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]
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]
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

62. Photograph of sketch drawn upon metal foil
 facing page [124]
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]

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, mechanics, and electricity; photo-telegraphy calling for a knowledge of all these sciences. There are, no doubt, many wireless workers who are interested in this subject, but who are deterred from experimenting owing to a lack of knowledge regarding the direction developments are taking, besides which, information on this subject is very difficult to obtain, the science of photo-telegraphy being, at the present time, in a purely experimental stage.

The wireless transmission of photographs has, no doubt, a great commercial value, but for any system to be commercially practicable, it must be simple, rapid, and reliable, besides being able to work

in conjunction with the apparatus already installed for the purpose of ordinary wireless telegraphy.

As far back as 1847 experiments were carried out with a view to solving the problem of transmitting pictures and writing by electrical methods over artificial conductors, but no great incentive was held forth for development owing to lack of possible application; but owing to the great public demand for illustrated newspapers that has recently sprung into being, a large field has been opened up. During the last ten years, however, development has been very rapid, and some excellent results are now being obtained over a considerable length of line.