This book is a revised and partially rewritten version of a dissertation of the same title submitted for the degree of PhD at the University of Cambridge in 1976. In bringing the work to its present state I owe much – including the original suggestion of the topic – to Professor Walter Ullmann. His constant enthusiasm and interest have been a great encouragement over the years. Professor Howard Kaminsky of the Florida International University and Dr Margaret Harvey of the University of Durham have both offered advice and debated various matters with me, the former also generously allowing me to consult unpublished material. Professor Barrie Dobson of the University of York read through a preliminary draft of the book and offered constructive and valuable criticism. Responsibility for the final product, and for any errors it may contain, remains entirely my own.

My debt to the libraries which allowed me to consult material in their keeping, particularly manuscripts, will emerge clearly from the notes and quotations, and the inclusion of a full list here would be both lengthy and tedious. Nevertheless, I would like to express my thanks to them for their ready assistance. I have received much stimulus from my contemporaries as research students at Cambridge, and during the final preparation of the book have been greatly encouraged by my colleagues at the University of York.