The general background of this monograph and the aim of it is described
in detail in Chapter I. As stated in 1.7 it is written according to the
principle that "when rigour appears to conflict with simplicity,
simplicity is given preference", which means that it is intended for a
rather broad public. Not only graduate students but also advanced
undergraduates should be able to understand at least most of it. This
monograph is the result of many years of inspiring discussions with a
number of colleagues, for which I want to thank them very much.
Especially I should mention the groups in Stockholm and La Jolla: in
Stockholm, Dr Carl-Gunne Flilthammar and many of his collaborators,
including Drs Lars Block, Per Carlqvist, Lennart lindberg, Michael
Raadu, Staffan Torven, Miroslav Babic, and Itlgvar Axniis, and further,
Drs Bo Lehnert and Bjorn Bonnevier, all at the Royal Institute of
Technology. Of other col- leagues in Sweden, I should mention Dr Bertel
Laurent, Stockholm University, Dr Aina Elvius, The Stockholm
Observatory, and Dr Bengt Hultqvist, Kiruna. In La Jolla my thanks go
first of all to Dr Gustaf Arrhenius, who once invited me to La Jolla,
which was the start of a most interesting collaboration; further, to Dr
W. B.