radiogalaxies like NGC 5128 and M 82, which may weIl be associated with the explosions of very massive objects. It is safe to say that from this growing field of study much still remains to be dis­ covered. The topics discussed in this volume will make clear to the reader the range and versatility of the subjects. F. HOYLE FOREWORD by THE PRINCIPAL The Symposium on Solid State Astrophysics held in July 1974 brought to University College Cardiff a large and very distinguished gathering of astronomers. It was the first time that such a collection of scholars, absorbed with the problem of the systems of outer space, had collected together in Wales, and so provided a splendid spring­ board for the researches of the newly founded group of astronomers in the Department of Applied Mathematics and Astronomy at University College.