Visual Repetition: An alternating series must end on the heavy unit, but since one does not look at series from left to right any more than from right to left, a heavy unit must be at both ends, not on one alone. In auditory rhythm, this final pause is not a function of any of the intervals of the period, for it comes at the end, when the sounds are no more present. But in visual repetition, after feeling the series rhythmically, it is still in the field, either as an unending series, or as a whole, in which each part is equally related to all the others. The final pause of a series that ends must be at _each_ end, and the series perfect from either point of view. It therefore fulfils the demands of symmetry as well as rhythm, but since symmetry in its strict sense has no meaning for sound-series, this double finality of visual repetition cannot be analogued in auditory rhythm. (9) I have found no recorded experiments of rhythms of sounds of different timbre and pitch, _i. e._, a regular rhythm of a bell with a violin, a piano with a whistle, etc. It would seem, however, that such a succession would produce the same irritation as a visual repetition of incongruous elements; as a circle introduced into the Greek fret, or a series of Renaissance columns and Egyptian monoliths. In both cases, the whole set of adjustments for each element would be thrown into confusion by encountering the next one, which would require a different attitude. Such a readjustment would be impossible in the space necessary for the perception of any rhythm, hence there must be congruity in elements, either auditory or visual, to be in a series at all. (10) Auditory Rhythm: "If every alternate element of a temporally uniform sound-series receive increased stress, the interval which succeeds the unaccented sound will appear of greater duration."[97] Visual Repetition: The distance between unit groups with a strongly accented centre appeared shorter than between rhythmic groups where the movement was not restrained at the centre, but went from edge to edge. The principles which explain these similarities are, however, different. In the auditory rhythm, the stronger accented beat excites a greater response than the unaccented. This lasts over longer in consciousness, and for that reason the interval after the accent seems shorter. In visual rhythm, however, the symmetrically rhythmic group drives the attention in toward the centre, and whatever excursion it makes to either side, it returns finally to the centre. In the even-number rhythmic group, there is no such central line to restrain it, and as one goes across it one has less check at the edge, the rhythm does not wholly finish, and the space is thereby overestimated. The _overestimation_ is due to the rhythmic activity in the group which oversteps its limit.