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.