PREFACE 



I have now only to thank the various editors and pro- 

 prietors of periodicals (or books) in which the articles or 

 parts of them first appeared, for permission to reprint 

 them. 



I have also to express my thanks to the numerous 

 friends, the scientific societies and the publishers and 

 authors of illustrated works, for the various photographs or 

 engravings I have been permitted to make use of for these 

 volumes. As regard both text and illustrations full 

 acknowledgment is made in the table of contents, and 

 sometimes, where it seemed specially needed, in the body 

 of the work. 



A. R. W. 



July, 1900. 



