It is hard to appreciate but nevertheless true that Michael John Seaton, known internationally for the enthusiasm and skill with which he pursues his research in atomic physics and astrophysics, will be sixty years old on the 16th of January 1983. To mark this occasion some of his colleagues and former students have prepared this volume. It contains articles that de­ scribe some of the topics that have attracted his attention since he first started his research work at University College London so many years ago. Seaton's association with University College London has now stretched over a period of some 37 years, first as an undergraduate student, then as a research student, and then, successively, as Assistant Lecturer, Lecturer, Reader, and Professor. Seaton arrived at University College London in 1946 to become an undergraduate in the Physics Department, having just left the Royal Air Force in which he had served as a navigator in the Pathfinder Force of Bomber Command. There are a number of stories of how his skill with instruments and the precision of his calcula­ tions, later to be so evident in his research, saved his crew from enemy action, and on one occasion, on a flight through the Alps, from a collision with Mount Blanc that at the time was shrouded in clouds.

Table of Contents:
1. Low-Energy Electron Collisions with Complex Atoms and Ions.- 1. Introduction.- 2. Theory of Electron Collisions with Atoms and Ions.- 3. Numerical Solution of the Coupled Integro-Differential Equations.- 4. Computer Program Packages.- References.- 2. Numerical Methods for Asymptotic Solutions of Scattering Equations.- 1. Introduction.- 2. Specification of Asymptotic Forms.- 3. Travels in Intermedia.- 4. At the Border of Asymptopia.- 5. Concluding Remarks.- References.- 3. Collisions between Charged Particles and Highly Excited Atoms.- 1. Introduction.- 2. The Impact Parameter (IP) Method.- 3. The Sudden Approximation.- 4. Transitions between Levels with Quantum Defects.- 5. Transitions within the Degenerate Sea.- References.- 4. Proton Impact Excitation of Positive Ions.- 1. Introduction.- 2. Excitation of Fine-Structure Transitions.- 3. Excitation of Metastable Transitions.- 4. Charge-Transfer Ionization.- References.- 5. Long-Range Interactions in Atoms and Diatomic Molecules.- 1. Introduction.- 2. General Form of the Model Hamiltonian.- 3. Form of the Model Potential for Atomic Systems.- 4. Form of the Model Potential for Diatomic Systems.- 5. Addition Theorems for Solid Harmonics.- References.- 6. Applications of Quantum Defect Theory.- 1. Historical Survey.- 2. Mathematical Background to Quantum Defect Theory.- 3. Single-Channel Quantum Defect Methods: General Formulas in the Independent-Particle Approximation.- 4. Applications to Simple Multichannel Problems.- 4.2. Bound States of Complex Ions by Extrapolation of Calculated Scattering Parameters: Configurations 1s22s22pqnl.- 5. Extrapolation of the Generalized Reactance Matrix.- 6. Conclusions.- References.- 7. Electron-Ion Processes in Hot Plasmas.- 1. Introduction.- 2. Line Intensities.- 3. Electron-Ion Processes.- 4. Conclusion.- References.- 8. The University College Computer Package for the Calculation of Atomic Data: Aspects of Development and Application.- 1. Introduction.- 2. The Growth of Astronomical Observations.- 3. Some Aspects of the Genesis of the Programs.- 4. The C III Challenge.- References.- 9. Planetary Nebulae.- 1. Introduction.- 2. Observations.- 3. Models: Atomic Data.- References.- 10. Forbidden Atomic Lines in Auroral Spectra.- 1. Introduction.- 2. Beginnings.- 3. Seaton’s Work.- 4. Refinement of Classical Theory.- 5. Advent of In Situ Measurements.- 6. N2(A3?u+)—O Excitation Transfer.- 7. Quenching.- 8. Coordinated Rocket and Satellite Measurements.- 9. ?3466 and ?10,400 of N I.- References.