PREFACE TO THE SECOND 

 EDITION 



MY thanks are due to a number of friends for pointing 

 out to me various misprints and other errors or 

 omissions which had passed unnoticed in the first 

 edition. Professor Howes in particular has furnished 

 the titles of several scientific memoirs, the identifica- 

 tion of which is due to his careful research in the 

 journals of the learned societies. 



Of the fresh material which has come into my 

 hands recently, I have printed two or three letters. 

 In one or two passages, also, I have altered the word- 

 ing slightly in deference to Mr. Herbert Spencer, 

 who thought that despite the definite statement 

 quoted from a letter of his on ii. 442, the public 

 would receive the impression that my father's reading 

 of his proofs had extended to all his works. As a 

 matter of fact, to quote the substance of my subse- 

 quent letter to the Athenaeum, that reading was 

 restricted to MY. Spencer's biological writings, the 



