PREFACE TO SECOND EDITION. 



In preparing this edition we have made no change in the 

 original plan of the book. The text, however, has been care- 

 fully revised, and the results of the more recent researches 

 have been incorporated. Some parts have been condensed, 

 but, in consequence of the introduction of new subject-matter 

 and of additional illustrations, the size of the book as a whole 

 has been considerably increased. We trust that these altera- 

 tions will be found to be in the direction of improvement. 



May, 1899. 



