§ =3.= This common characteristic, however, requires to be defined somewhat more precisely. It is not merely succession of movements, but succession of different kinds of movement in a definite and recurring order. In the dance, the measure, or succession and alternation of quick and slow movements in regular and fixed order, is the essential point. This is also the foundation of music and poetry. But another elementary principle enters into these two arts. They are not founded, as dancing is, upon mere silent movements, but on movements of audible sounds, whether inarticulate, as in music, or articulate, as in poetry. These sounds are not all on a level in respect of their audibility, but vary in intensity: broadly speaking, they may be said to be either loud or soft. There is, it is true, something analogous to this in the movements of the dance; the steps differ in degree of intensity or force. Dancing indeed may be looked upon as the typical form and source of all rhythmic movement. Scherer brings this point out very well.[1] He says: 'Rhythm is produced by regular movements of the body. Walking becomes dancing by a definite relation of the steps to one another--of long and short in time or fast and slow in motion. A regular rhythm has never been reached by races among which irregular jumping, instead of walking, has been the original form of the dance. Each pair of steps forms a unity, and a repetition begins with the third step. This unity is the bar or measure. The physical difference between the comparative strength of the right foot and the weakness of the left foot is the origin of the distinction between elevation and depression, i.e. between relatively loud and soft, the "good" and the "bad" part of the measure.' Westphal[2] gives a similar explanation: 'That the stamp of the foot or the clap of the hands in beating time coincides with the strong part of the measure, and the raising of the foot or hand coincides with the weak part of it, originates, without doubt, in the ancient orchestic.' At the strong part of the bar the dancer puts his foot to the ground and raises it at the weak part. This is the meaning and original Greek usage of the terms 'arsis' and 'thesis', which are nowadays used in an exactly opposite sense. _Arsis_ in its ancient signification meant the raising of the foot or hand, to indicate the weak part of the measure; _thesis_ was the putting down of the foot, or the stamp, to mark the strong part of the measure. Now, however, it is almost the universal custom to use _arsis_ to indicate the syllable uttered with a raised or loud voice, and _thesis_ to indicate the syllable uttered with lower or soft voice. From the practice of beating time the term _ictus_ is also borrowed; it is commonly used to designate the increase of voice which occurs at the strong, or so-called rhythmical accent.