PREFACE vii 



or exact. I have not tried to escape from theory, nor 

 have I refrained from forming an hypothesis where it 

 has seemed to be justified by facts. The volumes of 

 reference at my disposal have been few ; and indeed 

 if my work has any merit, it must rest in the fact that 

 almost all it contains has been taken not from the 

 works of others but rather from what Nature in her 

 goodness has thought it fitting to disclose. 



THE AUTHOR. 



April 1920. 



