Preface, 1 5 



vestigatlon of their own complex powers, so that 

 our relations to the world shall be better under- 

 stood, they will subserve the purpose for which 

 they were written. 



WiLLIAMSTOWN, MASS., 

 November i, 1871. 



SECO]^D EDITIOI^. 



The first edition of this work was soon ex- 

 hausted, and the author promised himself and the 

 publishers to embody in a new edition the results 

 reached by other investigators, as well as additions 

 to the discussion as here presented. The pressure 

 of ofificial duties caused delay, and the material 

 constantly increasing and giving rise to many im- 

 portant questions demands separate treatment, 

 which the writer hopes soon to give it. He finds 

 no occasion, however, in the new facts recorded by 

 investigators to essentially modify the statements 

 of facts and principles here made. The work has 

 passed under the review of those whose studies 

 and investigations fitted them specially for pass- 

 ing judgment upon these intricate questions, which 

 all careful students admit to be of most difificult 

 solution. The author is under great obligation to 



