For the Binet tests and some results obtained by their use, see Louis M. Terman, The Measurement of Intelligence, 1916.

The group tests used in the American Army during the War are described in detail In Vol. 15 of the Memoirs of the National Academy of Sciences, 1921, edited by Robert M. Yerkes. This large book describes the work of preparing and standardizing the tests, and also gives some results bearing on the Intelligence of different sections of the population. Some of the interesting results appear on pp. 507, 522, 528, 537, 693, 697, 705, 732, 743, 799, 815, 819, 829, 856 and 869.

For briefer treatments of the subject, see Walter S. Hunter's General Psychology, 1919, pp. 36-58, and W. B. Pillsbury's Essentials of Psychology, 2nd edition, 1920, pp. 388-407.

For the poor results obtained in attempting to judge intelligence from photographs, see an illustrated article by Rudolph Pintner, in the Psychological Review for 1918, Vol. 25, pp. 286-296.

For a study of one of the special aptitudes, see C. E. Seashore's Psychology of Musical Talent, 1919.

For a comprehensive survey of test methods and results, see the two volumes of Whipple's Manual of Mental and Physical Tests, 2nd edition, 1914, 1915.

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CHAPTER XIII
LEARNING AND HABIT FORMATION