xii PREFACE TO THE FIRST EDITION. 



unquestionable phenomena of the human mind and feel- 

 ings. 



It is approximately certain that in freely employing 

 illustrations drawn from many different sciences, I have 

 frequently fallen into errors of detail. In this respect I 

 must throw myself upon the indulgence of the reader, 

 who will bear in mind, as I hope, that the scientific facts 

 are generally mentioned purely for the purpose of illus- 

 tration, so that inaccuracies of detail will not in the 

 majority if cases affect the truth of the general principles 

 illustrated. 



December 15, 1875. 



