vi PREFACE 



due to many colleagues and friends for suggestions and criti- 

 cisms concerning the organization or selection of the material, and 

 to President Kenyon L. Butterfield for his interest and encour- 

 agement in its publication. To my wife, Ida Densmore Phelan, 

 I am indebted for assistance in the abridgement of selections. 

 the reading of the proof and the preparation of the index. 



JOHN PIIELAN. 



Massachusetts Agricultural College, 



Amherst, Massachusetts, 



1920. 



