AUTHOR'S NOTE.
My sincerest thanks are due first to the fifty students who made this research possible by devoting to it so much time upon which other demands were heavy, and to Professor James Rowland Angell, of the University of Chicago, who suggested the problem, furthered the work in the laboratory in every way, and assisted throughout by his kindly criticism and counsel. I wish also to make a grateful acknowledgement to Dr. Edwin Campbell Woolley, of Ohio Wesleyan University, to whose careful revision of the manuscript and reading of the proof the book is chiefly indebted for whatever excellence of form it may possess; to Miss Jeanette A. Marks, of Mount Holyoke College, for reading and criticising the manuscript; to Miss Eleanor Lauder Jones, for her assistance in making out the questions on personality and general information; to Dr. Paul Gerhardt Woolley, of McGill University, for suggesting and making the apparatus used in the fifth test on ingenuity, and to Miss Alice Rollins Little, of Mount Holyoke College, for her help in enlarging the drawings.
Chicago, July 12, 1092.
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