Locke on discrimination. Martineau _ditto_. Simultaneous sensations originally fuse into one object. The principle of mediate comparison. Not all differences are differences of composition. The conditions of discrimination. The sensation of difference. The transcendentalist theory of the perception of differences uncalled for. The process of analysis. The process of abstraction. The improvement of discrimination by practice. Its two causes. Practical interests limit our discrimination. Reaction-time after discrimination. The perception of likeness, 528. The magnitude of differences. The measurement of discriminative sensibility: Weber's law. Fechner's interpretation of this as the psycho-physic law. Criticism thereof. CHAPTER XIV. ASSOCIATION The problem of the connection of our thoughts. It depends on mechanical conditions. Association is of objects thought of, not of 'ideas'. The rapidity of association. The 'law of contiguity'. The elementary law of association. Impartial redintegration. Ordinary or mixed association. The law of interest. Association by similarity. Elementary expression of the difference between the three kinds of association. Association in voluntary thought. Similarity no elementary law. History of the doctrine of association. CHAPTER XV. THE PERCEPTION OF TIME, 605 The sensible present. Its duration is the primitive time-perception. Accuracy of our estimate of short durations. We have no sense for empty time. Variations of our time-estimate. The feeling of past time is a present feeling. Its cerebral process. CHAPTER XVI. MEMORY Primary memory. Analysis of the phenomenon of memory. Retention and reproduction are both caused by paths of association in the brain. The conditions of goodness in memory. Native retentiveness is unchangeable. All improvement of memory consists in better _thinking_. Other conditions of good memory. Recognition, or the sense of familiarity. Exact measurements of memory. Forgetting. Pathological cases. Professor Ladd criticised. INDEX. PSYCHOLOGY. CHAPTER I. THE SCOPE OF PSYCHOLOGY.