I wish to express my thanks to the Gifford Lectureship Committee for the invitation to deliver the Gifford Lectures at the University of Edinburgh during the academic year 1977–1978. My good friend Sir Hugh Robson, the Principal and Vice Chancellor, conveyed the invitation to me, and I was happily looking forward to a renewed association with him. Unfortunately he died unexpectedly a few weeks before the lectures were delivered. These lectures can be regarded as a memorial. I would like to thank especially Professor Tom Torrance who initiated the invitation and Miss Jean Ewan, Secretary of the Gifford Lectureship Committee, for so efficiently and kindly making all arrangements before and during the lectures. I need not name the many friends who made the stay in Edinburgh so memorable for my wife and myself. We greatly look forward to the next Giffords in April and May 1979.
Acknowledgements are given in the text for the many excellent illustrations that form an important part of such a wideranging scientifique presentation. My special thanks are due to Professor Rolf Hassler and Dr. Manfred Klee for so kindly arranging for the preparation of the illustrations which was carried out so well by Hedwig Thomas.
Again the staff of Springer-Verlag has given very personal service in the publishing of this book. Dr. Heinz Götze has been a very good friend throughout the whole publishing operation, and I wish particularly to thank Dr. Thomas Thiekötter for his dedication and efficiency and Silvia Osteen who also helped notably.