Acknowledgments Chapter 1: Introduction: From Propagation Studies to Active Sensors From Propagation Studies to Active Sensing: Experiment and Theory Field Experiments and Direct Evidence Epistemic Status of Theories Where This Book Fits In Outline of Chapters A Note on Units PART I: Conceiving Long-Range Propagation, 1901-19 Chapter 2: Theorizing Transatlantic Wireless with Surface Diffraction European Theoretical Physicists and Wave Propagation Surface Diffraction Theory in Britain and France Macdonald''s Initiative Rayleigh''s Coup Poincaré''s Formula Nicholson''s Numbers Surface Diffraction Theory in Germany Antenna Directivity and Zenneck''s Surface Waves Sommerfeld''s Refinement of Surface Waves Chapter 3: The U.S. Navy and the Austin-Cohen Formula A Naval Wireless Laboratory The Experiment The Formula Chapter 4: Synthesis with Atmospheric Reflection Surface Diffraction after Austin-Cohen The German Story A New Experiment The British Response Atmospheric Reflection Theory Kennelly-Heaviside Layer Eccles''s Ionic Refraction Watson''s Synthesis and Its Acceptance The 1918 and 1919 Papers Consolidating the Watson-Austin-Cohen Paradigm PART II: Discovering the Ionosphere, 1920-26 Chapter 5: Radio Amateurs Launch the Short-Wave Era American Radio Amateurs in the Early Twentieth Century Fading Experiments Standard Experimental Procedure and Data Format Setting the Stage for Transatlantic Experiments Transatlantic Experiments The First Trial The Second Trial The Third Trial The Two-Way Test and the Fourth Trial Chapter 6: From the Skip Zone to Magneto-Ionic Refraction Discovering the Skip Zone and Short-Wave Data Albert Hoyt Taylor and the U.S. Naval Research Laboratory Discovery of the Skip Zone More Comprehensive Range Data at High Frequencies Magneto-Ionic Theory for Short Waves Eccles''s Ionic Refraction Theory Larmor''s Ionic Refraction Theory Effects of Geomagnetism: Nichols, Schelleng, and Appleton Explaining the Skip Zone: Taylor and Hulburt Chapter 7: British Radio Research and the Moments of Discovery Direct Evidence, Sounding-Echo Experiments, Operational Realism A British System of Radio Ionospheric Research Direction Finding, Wave Polarization, and the Ionosphere Loop Direction Finders and Their Problems Thomas Eckersley''s Work on Polarization National Physical Laboratory, Radio Research Board, and Reginald Leslie Smith-Rose Smith-Rose and Barfield''s Experiment Frequency-Change Experiments and Discovering the Ionosphere Edward Victor Appleton The Frequency-Change Experiment Smith-Rose and Barfield Try Again Improving Direction Finding as a By-product Chapter 8: Pulse Echo, CIW, and Radio Probing of the Ionosphere Pulse-Echo Experiments in the United States Carnegie Institution of Washington, Gregory Breit, Merle Tuve Pulsed Radio Sounding of the Ionosphere The Meaning of Height The Ionosphere has a Structure Appleton''s Program of Ionospheric Sounding The Discovery of the F Layer PART III: Theory Matters, 1926-35 Chapter 9: Consolidating a General Magneto-Ionic Theory Generalizing the Magneto-Ionic Theory Appleton and Altar''s Derivation Lassen''s Derivation Goldstein''s Derivation Measuring Polarization in Both Hemispheres A Polarimetric Experiment More Polarization Research in Both Hemispheres A Mathematical Inquiry into the General Magneto-Ionic Theory Chapter 10: Handling Microphysics The Lorentz Correction Origin of the Concept Douglas Hartree and the Lorentz Correction in Ionic Refraction A Microphysical Controversy without Microphysics Where Was the Empirical Evidence? The Quasi-Elastic Force Measuring the Dielectric Constant of Ionized Air A Propagation Theory from Tabletop Experiments Anatomy of a Debate Death of a Theory PART IV: Conclusion Chapter 11: A New Way of Seeing the World From Wave Propagation Studies to Ionosphere Probing A Case History for Active Sensing Bibliography Index.