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...

This monograph is based on four papers which have been published in Astrophysics and Space Sciences 1970--1974. They contain the results of our joint work started in 1968 at the University of California, San Diego, in La Jolla. The work was based on the belief that the complicated processes by which our solar system was formed can only be clarified by close collaboration between representatives of the physical and chemical sciences. Our investigations have also been strongly supported by work at other institu tions, especially by a group at the Royal Institute of Technology, Stockholm, where...