PHOTOGRAPHS
Reading edition
BY
MARCUS J. MARTIN
SECOND EDITION REVISED AND ENLARGED 1919
THE WIRELESS PRESS, LTD.
12-13 HENRIETTA STREET, STRAND
LONDON, W.C. 2
PREFACE TO SECOND EDITION
Although during the last few years very little, in common with other wireless work, has been possible in connection with the practical side of the wireless transmission of photographs, yet, now that the prospect of experimental work is once again occupying the minds of all wireless workers, advantage has been taken of a reprint of this little volume to amplify a few points that were insufficiently dealt with in the first edition, and also to add some fresh matter.
To Chapter V. has been added a short description of the Nernst lamp, and also some useful information regarding photographic films, and a few notes relating to enlarging included in the Appendix B.
A fresh appendix dealing with the principles of optical lenses has also been added. This is a subject that plays an important part in any system of wireless photography, and to those experimenters whose knowledge of optics is limited this section should prove useful.
To serious workers engaged on the problem of the wireless transmission of photographs, attention is called to a series of articles which are being published from time to time in the Wireless World, on the design and construction of wireless photographic apparatus.
M. J. M. Maidstone, 1919.
PREFACE
In these progressive times it is only reasonable to expect that some attempt would be made to utilise the ether-waves for other purposes than that of telegraphic communication, and already many clever minds are at work trying to solve the problems of the wireless control of torpedoes and airships, wireless telephony, and, last but not least, the wireless transmission of photographs.
It may seem rather premature to talk about the wireless transmission of photographs at a time when the ordinary systems are not fully developed; but the prospects of wireless photography are of a very encouraging nature, especially for long over-water distances, as there are great difficulties to be overcome in long-distance transmission over ordinary land lines and cables which will be entirely eliminated by wireless methods.
From a perusal of Chapter I. the reader will be able to understand something of the difficulties that are to be encountered in working over long distances, and he will also be able to appreciate something of the advantages that would be derived from a reliable wireless system. Apart from the value of such a system for transmitting news pictures, it would also be of great advantage to transmit to ships at sea photographs of criminals for identification purposes. In such a small volume as this it would be impossible to deal with the working of wireless apparatus and the many systems that have been devised for the transmission of photographs over metallic circuits. The Author has taken it for granted that other works have been studied in connection with these subjects, and will therefore only describe such apparatus as is likely to be of use in wireless transmission. At present the transmission of photographs by wireless methods is in a purely experimental stage, and this book will have served its purpose if it helps to put future experimenters on the right track and prevent them from making expensive and fruitless experiments, by showing them the right direction in which investigations are being carried out. As there is no claim to originality in respect of a good many pieces of apparatus, etc., described, I have not thought it necessary to state the various sources from which the information has been obtained.
M. J. M. Ashford, 1916.
CONTENTS
PAGE
Preface to Second Edition v
Preface vii
CHAPTER I
Introductory 1
Foreword—Early experiments—Advantages of Radio-Photography—Difficulties in Cable working—Bernochi's System—Knudsen's System.
CHAPTER II
Transmitting Apparatus 13
Wireless Apparatus—Preparing the Photographs—Transmitting Machines—Transmitting Apparatus—Effects of Arcing—Spark-Gaps—Contact Breakers—Complete Station—Professor Korn's Apparatus—Poulsen Company's Photographic Recorder—Comparison of various systems—Practical applications.
CHAPTER III
Receiving Apparatus 37
Methods of Receiving—Author's Photographic Receiver—Decohering Apparatus—Description of Einthoven Galvanometer—Use of Galvanometer in Receiving—Belin's Application of Blondel's Oscillograph—Description of Charbonelle's Receiver—Use of Telephone Relay—Description of Telephone Relay—Telephotographic Receiver—Polarisation Receiver—Kathode-Ray Receiver—Electrolytic Receiver—Atmospherics in Long-Distance working.
CHAPTER IV
Synchronising and Driving 63
Driving Motors—Isochronising the Electrolytic System—Professor Korn's method—Description of Hughes Governor—Author's Speed Regulator—Problem of Synchronising—Methods of Synchronising—Advances made in Radio-Photography.
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 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.
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 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