The curves below represent the changes in the two opposing sets of muscles whose interaction brings about the movement cycle.  The contraction of the flexors, the positive muscle set, is represented by the curve above the base line.  It is obvious that during the contraction phase, the contraction in the positive muscle set is at its height; it continues at a maximum during the limiting sensation and then dies away during the relaxation phase.  The sensations from this positive muscle set have the principal place in consciousness during the rhythm experience.  The curve below the base line represents the contraction of the extensors, the negative muscle set.  The contraction of the negative muscles reaches its climax very soon after the maximum contraction of the positive muscles, in the contraction phase.  The sharp tension between the two opposing sets of muscles at the limiting sensation may be made very apparent if the finger beats the rhythm entirely in the air; in that case the limiting sensation consists entirely of the feeling of a sudden increase of tension between the positive and negative muscle sets.  During the relaxation phase the contraction of the negative muscles continues, but the tension between the two sets grows less and less, for the positive muscles are rapidly relaxing.  At the highest point in the movement either muscle set is exerting but very little strain; the condition is represented in the figure by the approach of either curve to the base-line; the amount of tension between the two sets is figured by the distance of the two curves from each other.

[Illustration:  FIG. 9.]

Assuming such a movement cycle, in which the tension between the two opposing sets never comes to zero until the close of the series, it is not difficult to arrange many of the facts of rhythmic perception under the motor theory.

1.  The feeling of rhythm is more definite as we proceed in a verse, or a series of simple sound sensations.  At first the cycle is not perfectly adjusted and complete automatism established.

2.  If an observer is listening to a series, and an unusually long pause is introduced between two beats, there is always a feeling of suspense or tension during the ‘lag.’  As long as the tensions are maintained there is a rhythmic continuity; the feeling of tension is the strain of opposition between the opposing muscle sets.

3.  The continuity of the rhythmic series, whereby all the beats of a period seem to belong to a single whole, is due to the continuity of the muscle sensations involved and the continuous feeling of slight tension between the positive and negative muscle sets; nowhere within the period does the feeling of strain die out.

4.  But at the close of the period we have a pause which is demonstrably not a function of any of the intervals of the period.  During this pause the tension between the two sets ‘dies out,’ and we have a feeling of finality.  This gradual dying out of the tension is clearly seen in the constant appearance of the cone-shaped final syllable at the end of each nonsense verse.