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. The Appendix to the Introduction differs very materially from the corresponding portion of Dr. Grou''s book. There as else where I have been constantly advised and as constantly enlight ened by my kind friend and former teacher, Professor W. W. Goodwin. But this list of my creditors must necessarily remain incomplete, for I cannot mention those who have helped me most, nor can I record here the names of all my pupils, past and pres ent, whose needs have been my guide and my impulse in pre paring this book.