Whilst the greatest effort has been made to ensure the quality of this text, due to the historical nature of this content, in some rare cases there may be minor issues with legibility. Much valuable aid given to the author requires grateful acknowledgment. Most especially must I express my thanks to two helpers. To the compiler of the index - the fourth' and the largest which has been constructed for' books of mine by the same kindly hands - and to my friend Mr. C. H. Turner, Fellow of Magdalen College, who read the whole of the proofs, and furnished me with a great number of corrections and improve~ ments.