EDUCATIONAL PSYCHOLOGY. VOLUME III. MENTAL WORK AND FATIGUE AND INDIVIDUAL DIFFERENCES AND THEIR CAUSES by EDWARD L. THORNDIKE. Originally published in 1914. PREFACE: This third volume presents the results of psychological studies of mental work and fatigue in Part I, and of indi vidual differences and their causes in Part II. Part II is a revision of a book, Educational Psychology, which appeared in 1903 and, in revised form, in 1910. Part I is entirely new. The same procedure of introducing topics by means of re ports of typical investigations, presenting instructive evidence as well as conclusions, and discussing the important principles of quantitative treatment in each case adopted in the earlier volumes is maintained. Teachers College, Columbia University, November, 1913. Contents include: I. MENTAL WORK AND FATIGUE DEFINITIONS AND PROBLEMS i Mental Work versus Bodily Work Mental Work versus Play and Mere Activity The Concept of Mental Fatigue II. THE DECREASE IN EFFICIENCY OF A SINGLE FUNCTION UNDER CONTINUOUS EXERCISE 13 A Sample Experiment The Amount and Rate of Fatigue of a Single Function III. THE CURVE OF WORK 45 Initial Spurt End Spurt Spurt after Fatigue and Spurt after Disturbance Rhythm of Attention Other Rhythmical Fluctuations Warming Up Adaptation Summary Speculative Analyses of the Cunre of Work The Curve of Satisfyingness IV. THE INFLUENCE OF CONTINUOUS MENTAL WORK, SPECIAL OR GENERAL, UPON GENERAL ABILITY 79 Experimental Results The Symptoms of Mental Fatigue The Relations of Muscular Work and Fatigue to Mental Wprk and Fatigue Vlii V. GENERAL THEORIES OF MENTAL WORK AND FATIGUE m Definitions Dodges Theory of Mental Work The Mechanical or Energy Theory and the Biological or Response Theory VI. THE HYGIENE OF MENTAL WORK 126 Means of Increasing Mental Efficiency Means of Preventing Injury frqm Over-work PART II VII. INTRODUCTION TO PART II 142 The Problems of Individual Differences A Concrete Illustration of the Problems of Individual Differences VIH. THE MEASUREMENT OF INDIVIDUAL DIFFERENCES 152 Simple and Compound Differences Units and Scales for Measuring Mental Differ ences The Variability of a Mental Measurement Tables of Frequency or Distribution IX. THE INFLUENCE OF SEX . 169 Sex Differences in Ability . Sex Differences in Variability Sex Differences in Traits Not Measured Ob jectively - X. THE INFLUENCE OF REMOTE ANCESTRY OR RACE 206 A Sample Study of Racial Differences The Results, of Measurements of Racial Mental Differences The Interpretation of - the Differences between One Race and Another in AchievementE XI. THE INFLUENCE OF IMMEDIATE ANCESTRY OR FAMILY 225 The Variability of Individuals, of the Same Sex and Ancestry Methods of Measuring Resemblance Measurements of Resemblance in Related In dividuals The Specialization of the Influence of Near Ancestry The Analysis erf Mental Inheritance THE INFLUENCE OF MATURITY 270 Changes in Mental Traits with Age The Difficulties in Inferring Changes in In dividuals with Age from Differences be tween Old and Young Individuals XIII. THE INFLUENCE OF THE ENVIRONMENT 281 Difficulties in Estimating the Amount of In fluence of the Environment Measurements of the Influence of the Environ ment The Method of Action of Differences in En vironment The Relative Importance of Original Nature and Environment XIV. THE NATURE AND AMOUNT OF INDIVIDUAL DIF FERENCES IN SINGLE TRAITS 315 The Amounts of Difference in Different Traits The Continuity of Mental Variations The Relative Frequencies of Different Amounts of Difference The Chance or Probability Distribution in the case of Single Mental Traits X. THE RELATIONS BETWEEN THE AMOUNTS OF DIFFERENT TRAITS IN THE SAME INDIVIDUAL 347 The Measurement of Relations between Mental Traits The Relations between the Amounts of Dif ferent Traits in the Same Individual XVI...