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PREFACE TO THE SIXTH EDITION.
IN preparing this edition I have not thought it necessary to alter in any material respect the general arrangement of the book. Care, however, has been taken to adapt the illustrations, as far as possible, to the circumstances of the present time.
I cannot place too high a value upon the assistance which I have derived from my wife. In the course of revising the book, she has made many most valuable suggestions, and she has also prepared an Index which I believe will be found very useful by the reader.
I also desire to thank my private secretary, Mr. F. J. Dryhurst, for having carefully revised the proofs as they passed through the press.
August, 1883.
