INTRODUCTION

My first impressions of Dennis Sciama came from a short introductory astrophysics course he gave to undergraduates in 1964. Then in 1966-7 I took his Cambridge Part III course in relativity, in which he charitably ignored my inadvertent use of Euclidean signature in the examination (an error I spotted just at the very end of the allowed time) and gave me a good mark. In both these courses he showed the qualities of enthusiasm and encouragement of students with which I was to become more familiar later in 1967 when I began as a research student. A project on stellar structure had taught me that I did not want to work on that, and I began under Dennis with the idea of looking at galaxy formation. However, by sharing an office with John Stewart I came to read John's paper with George Ellis (Stewart and Ellis, 1968) and its antecedent (Ellis, 1967) and developed an interest in relativistic cosmological models, which led to George becoming my second supervisor.

I was still in Sciama's group, and I learnt a lot from the tea-table conversations, which seemed to cover all of general relativity and astrophysics. Dennis taught us by example that the field should not be sub—divided into mathematics and physics, or cosmological and galactic and stellar, but that one needed to know about all those things to do really good work.