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.

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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