This book is now thirty years old. Published in 1957, it was as the original preface shows completed in Dunedin during 1954 and 1955,1 and the doctoral dissertation of which it is an outgrowth was written between 1948 and 1951, and accepted in 1952. A great deal has happened since then to enlarge our understanding of the history which it contains or implies, but the book has continued to enjoy readers and a certain standing.