Preface to the First Edition The book is aimed at advanced students of physics and related disciplines, and it is hoped that some sections will also serve to augment the teaching material already available. This book stems from lectures given regularly by the author at the Tech- nical Uni rsity Munich Many and co assisted in the t:Ms.I Wefers,Ms.E.Jorg-Mille Schwier Schenk,M. .alM.nd Wb.Maier. Wefers Feuchter A.Wonhas.The problems were conceived with the help of E.Frey and W.Gasser.Dr.Gasser also read through the entire manuscript and made many valuable suggestions.I am indebted to Dr.A.Lahee for supplying the initial English version of this difficult text,and my special thanks go to Dr.Roginald Hilton for his perceptive revision that has ensured the fidelity of the fi nal rendition Toall those mentioned here,and to the ues who gave their】 Hans-Jiirgen Kolsch of Munich,March 1999 F.SchwablX Preface to the First Edition The book is aimed at advanced students of physics and related disciplines, and it is hoped that some sections will also serve to augment the teaching material already available. This book stems from lectures given regularly by the author at the Tech￾nical University Munich. Many colleagues and coworkers assisted in the pro￾duction and correction of the manuscript: Ms. I. Wefers, Ms. E. J¨org-M¨uller, Ms. C. Schwierz, A. Vilfan, S. Clar, K. Schenk, M. Hummel, E. Wefers, B. Kaufmann, M. Bulenda, J. Wilhelm, K. Kroy, P. Maier, C. Feuchter, A. Wonhas. The problems were conceived with the help of E. Frey and W. Gasser. Dr. Gasser also read through the entire manuscript and made many valuable suggestions. I am indebted to Dr. A. Lahee for supplying the initial English version of this difficult text, and my special thanks go to Dr. Roginald Hilton for his perceptive revision that has ensured the fidelity of the final rendition. To all those mentioned here, and to the numerous other colleagues who gave their help so generously, as well as to Dr. Hans-J¨urgen K¨olsch of Springer-Verlag, I wish to express my sincere gratitude. Munich, March 1999 F. Schwabl