appears to have a purely physical basis. We know that the agreeableness of simultaneous tones depends partly on the relative frequency of recurring correspondences of the vibrations producing them, and partly on the relative infrequency of beats, and we may suspect that there is a kindred cause for the agreeableness of successive tones; since the auditory apparatus which has been at one instant vibrating in a particular manner, will take up certain succeeding vibrations more readily than others. Evidently it is a question of the degree of congruity; for the most congruous vibrations, those of the octaves, yield less pleasure when heard in succession than those of which the congruity is not so great. To obtain the greatest pleasure in this and other things, there requires both likeness and difference. Recognition of this fact introduces us to the next element of sensational pleasure—that due to contrast; including contrast of pitch, of loudness, and of timbre. In this case, as in other cases, the disagreeableness caused by frequent repetition of the same sensation (here literally called "monotony") results from the exhaustion which any single nervous agent undergoes from perpetual stimulation; and contrast gives pleasure because it implies action of an agent which has had rest. It follows that much of the sensational pleasure to be obtained from music depends on such adjustments of sounds as bring into play, without conflict, many nervous elements: exercising all and not overexerting any. We must not overlook a concomitant effect. With the agreeable sensation is joined a faint emotion of an agreeable kind. Beyond the simple definite pleasure yielded by a sweet tone, there is a vague, diffused pleasure. As indicated in the Principles of Psychology, § 537, each nervous excitation produces reverberation throughout the nervous system at large; and probably this indefinite emotional pleasure is a consequence. Doubtless some shape is given to it by association. But after observing how much there is in common between the diffused feeling aroused by smelling a deliriously scented flower and that aroused by listening to a sweet tone, it will, I think, be perceived that the more general cause predominates.
The division between the sensational effects and the perceptional effects is of course indefinite. As above implied, part of the sensational pleasure depends on the relation between each tone and the succeeding tones; and hence this pleasure gradually merges into that which arises from perceiving the structural connections between the phrases and between the larger parts of musical compositions. Much of the gratification given by a melody consists in the consciousness of the relations between each group of sounds heard and the groups of sounds held in memory as having just passed, as well as those represented as about to come. In many cases the passage listened to would not be regarded as hav-