PREFACE 



but where the structuie needed repair, it seemed to 

 me due not only to the readers of the book but to 

 the memory of the author, that the repair should 

 be thorough, substantial, and simple. Such have 

 been the principles on which I have tried to carry 

 out my work. I have been greatly helped by 

 Mrs. Thacker, Fellow of Newnham College, who 

 has read through my proofs, and made valuable 

 suggestions. 



JOSEPH BARCROFT. 



King's College, Cambridge, 

 November 24, 1914. 



