rhythm of the breath; but these are, for the most part, unfelt; and moreover, they would hardly explain the predominance of rhythms quite other than the physiological ones. Another theory, closely allied, connects rhythm with the conditions of activity in general, but attaches itself rather to the effect of rhythm than to its cause. Thus we are reminded of the "heightened sense of expansion, or life, connected with the augmentation of muscular movements induced by the more extensive nervous discharges following rhythmic stimulation."1 But why should it be just rhythmic stimulation that produces this effect? We are finally thrown back on physiology for the answer that in rhythmical stimulation there are involved recurrent activities of organs refreshed by immediately preceding periods of repose. Here again, however, we must ask, why on this hypothesis the periods themselves must be exactly equal. For within the periods the greatest variety obtains. One measure of a single note may be succeeded by another containing eight; within the periods, that is, the minor moments of activity and repose are quite unequal.

Last of all, we must note the view of rhythm as a phenomenon of expectation (Wundt). But while we can undoubtedly describe rhythm in terms of expectation and its satisfaction, rhythm is rhythm just through its difference from other kinds of expectation.

1 H. R. Marshall, Pain, Pleasure, and Esthetics.

All these explanations seem either merely to describe the facts we seek to explain, or to fail to notice the peculiar intimate nature of the rhythmical experience. But if it could be shown not only that in all stimulation there must be involved an alternation of activity and repose, but also that an equality of such periods was highly favorable to the organism, we should have the conditions for a physiological theory of rhythm. Now the important psychological facts of so-called subjective rhythmizing seem to supply just this need.

It has been shown 1 that we can neither receive objectively equal sense-stimuli, nor produce regular movements, without injecting into these a rhythmical element. A series of objectively equal soundstimuli the ticking of a clock, for instance - is heard in groups, within each of which one element is of greater intensity. A series of movements are never objectively equal, but grouped in the same way. Now this subjective rhythm, sensory and motor, is explained as follows from the general physiological basis of attention.

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Attention itself is ultimately a motor phenomenon. Thus the sensory aspect of attention is vividness, and vividness is explained physiologically as a brain-state of readiness for motor discharge; 2 in

1 T. L. Bolton, Amer. Jour. of Psychol., vol. vi. The classical historical study of theories of rhythm remains that of Meumann, Phil. Studien, vol. x.

2 Münsterberg, Grundzüge d. Psychologie, 1902, p. 525.

the case of a visual stimulus, for instance, a state of readiness to carry out movements of adjustment to the object; in short, the motor path is open. Now attention, or vividness, is found to fluctuate periodically, so that in a series of objectively equal stimuli, certain ones, regularly recurring, would be more vividly sensed. This is exemplified in the well-known facts of the fluctuation of the threshold of sensation, of the so-called retinal rivalry, and of the subjective rhythmizing of auditory stimuli, already mentioned. There is a natural rhythm of vividness. Here, therefore, in the very conditions of consciousness itself, we have the conditions of rhythm too. The case of subjective motor rhythm would be still clearer, since vividness is only the psychical side of readiness for motor discharge; in other words, increased readiness for motor discharge occurs periodically, giving motor rhythm.

It has been said1 that this periodicity of the brain-wave cannot furnish the necessary condition for rhythm, inasmuch as it is itself a constant, and could at most be applied to a series which was adapted to its own time. But this objection does not fit the facts. The "brain-wave," or "vividness," or attention period, is not a constant, but attaches itself to the contents of consciousness. In other words, it does not function without material. It is itself conditioned by its occasion. In the case

1 J. B. Miner, "Motor, Visual, and Applied Rhythms," Psychol. Rev., Mon. Suppl., No. 21.

of a regularly repeated stimulus, it is simply adjusted to what is there, and out of the series chooses, as it were, one at regular periods.1

Closely connected with these facts, perhaps only a somewhat different aspect of them, is the phenomenon of motor mechanization. Any movement repeated tends to become a circular reaction, as it is called; that is, the end of one repetition serves as a cue for the beginning of the next. Now, in regularly recurring stimuli, giving rise, as will be later shown, to motor reactions, which are differentiated through the natural periodicity of the attention (physiologically the tendency to motor discharge), we have the best condition for this mechanization. In other words, a rhythmical grouping once set up naturally tends to persist. The organism prepares itself for shocks at definite times, and shocks coming at those times are pleasant because they fulfill a need. Moreover, every further stimulus reinforces the original activity; so that rhythmical grouping tends not only to persist, but to grow more distinct, -as, indeed, all the facts of introspection show.

All this, however, is true of the repetition of objectively equal stimuli. It shows how an impulse to rhythm would arise and persist subjectively, but

1 Facts, too technical for reproduction here, quoted by R. H. Stetson (Harvard Psychol. Studies, vol. i., 1902) from Cleghorn's and Hofbauer's experiments seem to be in harmony with this view.

does not of itself explain the pleasure in the experience of objective rhythm. It may be said in general, however, that changes which would occur naturally in an objectively undifferentiated content give direct pleasure when they are artificially introduced, when, that is, the natural disposition is satisfied. This we have seen to be true in the case of color contrast; and it is perhaps even more valid in the realm of motor activity. Whatever in sense stimulation gives the condition for, helps, furthers, enhances the natural function, is felt both as pleasing and as furthering the particular activity in question. Now, the objective stress in rhythm is but emphasis on a stress that would be in any case to some degree subjectively supplied. Rhythm in music, abstracting from all other pleasure-giving factors, is then pleasurable because it is in every sense a favorable stimulation.

In accordance with the principle that complete explanation of psychical facts is possible only through the physiological substrate, we have so far kept rather to that field in dealing with the foundations of our pleasure in rhythm. But further description of the rhythmical experience is most natural in psychological terms. There seems, indeed, on principle no ground for the current antithesis, so much emphasized of late, of "psychical and "motor" theories of rhythm. Attention and expectation are not "psychical psychical" as opposed to "motor." Granting, as no doubt most psychologists