Needless to add that in so large and inexhaustible a field a bibliography will only have practical value for the readers for whom this series is intended if it represents a selection out of the great mass. With few exceptions I have read and consulted the works, monographs, and articles enumerated, and recom mend them therefore from personal knowledge of their contents. With a view of presenting the Bibliography in a more systematic fashion, it has been divided up into sections corresponding so far as possible to the main divisions of the book itself. The preference has been given to publications in English, though of course German, French, and Dutch works come in for a large share. My very dear and esteemed friend, Mrs. Caspar Wister, has placed me under lasting obligations by kindly undertaking to read one proof of the entire work; and as I go over the pages for the last time, I find everywhere traces of her most skilful revision. The index has been prepared by Miss Katherine S. Leiper, and I wish to take this opportunity of thanking her for the intelligent care and painstaking accuracy with which she has carried out what was necessarily an arduous task.