the causes and consequences of human migration, comprehensive in scope and thorough in detail, can be developed only by co-operative efforts, such as the committees of the National Research Council and the Social Science Research Council are promoting. Many intensive investigations of specific issues, like the present report, must be made before we can attain the well-rounded knowledge needed as a basis for private opinion and public policy regarding migration. In accordance with the established procedure of the National Bureau, Dr. Jerome's present monograph was submitted in manuscript to our Board of Directors. Criticisms made by members of the Board have resulted in various improvements upon the original draft. This process of criticism and betterment through which the National Bureau's reports pass before publication involves much labor upon the part of the Directors;-labor which is mostly selfeffacing, for almost all the suggestions are incorporated in the text before publication. It is but just to state that this volume, like its predecessors, owes much more than appears to the acumen, the wide and varied experience, of the Directors. WESLEY C. MITCHELL. Sources, Terminology, and Comprehensiveness of Migration Statistics Pertinent Features of Migration to and from the United States Other Available Monthly Statistics. Previous Studies in Employment Fluctuations Indexes of Factory Employment, by Months, 1889-1923 133 . 136 Immigration and the State of the Labor Market Cyclical Movements in Male Emigration The Comparative Volume of Migration and Changes in Employment in the De- |