ACKNOWLEDGMENT 
Among the sources to which I am indebted I wish to 
acknowledge, in particular, Mr. L. O. Pethick, whose in 
timate knowledge of industrial personnel problems con 
tributed immeasurably toward making these applications 
of psychology immediately practical. Among psycholo 
gists, I desire to express my thanks above all to Professors 
E. L. Thorndike, Roswell P. Angier, H. L. Holling- 
worth, and R. M. Elliott, who most generously gave me 
of their own experience and knowledge. For the index 
and other valued assistance I am indebted to Miss Sabina 
Connolly. Among the many friends and colleagues to 
whom I am grateful for very helpful cooperation are Mr. 
John L. Koehne, Miss Marion Gilbert, and Mr. J. H. J. 
Adams. In inscribing this book to my wife I am not only 
acknowledging a source of inspiration, but am faintly ex 
pressing my gratitude for her constant help in preparing 
the manuscript for publication. 
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