ACKNOWLEDGMENTS 



THE writer is indebted, above all, to Professor J. McKeen Cattell 

 for suggesting the problem, and for helpful criticism and encourage- 

 ment throughout the experiment. In the preparation of the manu- 

 script, and in the evaluation of the statistical material, thanks are 

 also due to Professors Robert S. Woodworth, Edward L. Thorndike 

 and Henry A. Ruger. 



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