Table of contents

Following a resolution by the Physics and Mathematics Division U.S.S.R. Academy of Sciences, the present issue is devoted to the memory of the outstanding Soviet theoretical physicist Yakov ll'ich Frenkel. The editors

Introduction 292 1. Basic Information 294 2. Two Theories 297 3. Vertical Structure of Field, Conductivity, and Current in "Good Weather" 299 4. Distribution of Space Charge in the Atmosphere 302 5. Time Variation of Field and Potential at High Altitudes 303 6. Description of Electric Processes in Regions of Good Weather 305 7. Electricity of Stratified Clouds 307 8. Electricity of Cumulus and Cumulus Congestus Clouds 311 9. Structure of Shower and Thunderstorm Clouds 313 10. Accumulation of Charges in Thunderstorm Clouds 316 References 320

Introduction 323 1. Complex Dielectric Tensor _ij(ω, k) and Normal Waves in the Medium 328 a) The Tensor _ij(ω, k) and Its Properties 328 b) Normal Electromagnetic Waves in a Medium. Transverse and Longitudinal Waves. "Fictitious" Longitudinal Waves and "Polarization Waves" 331 c) Energy and Other Relations for Waves in an Anisotropic Medium 334 2. The Tensor _ij(ω, k) in Crystals 337 a) The Concept of the Tensor _ij(ω, k) for Crystals 337 b) The Case of Weak Spatial Dispersion (a/λ ≪ 1) 339 Cited Literature, Part I 345 3. Crystal optics with allowance for spatial dispersion, a) New wave near absorption line in gyrotropic crystals, b) New waves in non-gyrotropic crystals, c) Optical anisotropy of cubic crystals. Quadrupole absorption lines, d) Effect of mechanical stresses and external electric and magnetic fields, e) The problem of boundary conditions, f) Experimental investigations of effects of spatial dispersion in crystal optics. 4. Quantum mechanical calculation of the tensor _ij(ω, k). a) Quantum mechanical expression for _ij(ω, k). b) Mechanical excitons and the tensor _ij(ω, k) in molecular crystals and in the case of the classical oscillator model, c) Absorption mechanism and calculations. Concluding remarks. Cited literature, part II.