much poorer without these academic exchanges and it is a great pleasure to be able to acknowledge the generous support of these organisations over many years. Last, but certainly not least, I am very grateful to Peter Sowden of Routledge who has skilfully steered the book though the production process with exactly the right combination of encouragement, fi rmness and tact. I am also grateful to the anonymous reviewers who have been both critical and constructive. The sole responsibility for any inaccuracies and omissions in the text rests, as it properly should, with the author.