AUTHOR'S PREFACE 



It is an agreeable duty for me to convey to Professor J. Arthur 

 Thomson the expression of my warmest gratitude for his very 

 great kindness and courtesy in revising the first part of my work, 

 and also for the invaluable assistance which he has rendered me 

 throughout. I would like, also, to take this opportunity of 

 expressing my hearty thanks to Mr. Benjamin Kidd, to whom 

 I am indebted for many helpful suggestions and for much valu- 

 able criticism ; to Dr. J. W. Slaughter, to whose never-failing 

 courtesy 1 owe the avoidance of considerable material difficulty 

 caused by my absence from England ; and to my friend Dr. 

 Maurice de Pleury. 



G. C.-H. 



