PREFACE AND INTRODUCTION vii 



the hypothetical nature of the thesis, they 

 did not appear to be justified. Repetition 

 has been avoided as much as possible, even 

 at the expense of forward reference, so that 

 the whole volume must be read in order that 

 a clear understanding may be obtained. The 

 volume is divided in the following manner : 

 Chapter I states the Theory; Chapters II, 

 III, and IV deal at length with some facts 

 on which the Theory rests ; the remaining 

 chapters exemplify the Theory. 



Exception will probably be taken to some 

 of the premises chosen, to some of the steps 

 in the arguments ; but entrance into this 

 most difficult subject is made only with great 

 diffidence. Nevertheless hope is entertained 

 that even if the Theory does not correlate a 

 good number of the facts to which it is applied, 

 it will at least explain a few. Even if it does 

 no more than lead other minds along new 

 lines of thought, the author will not be dis- 

 satisfied. 



