Another fundamental element of decorative form is rhythmic repetition. Technical activities in which regularly repeated movements are employed lead to rhythmic repetition in the direction in which the movement proceeds. The rhythm of time appears here translated into space. In flaking, adzing, hammering, in the regular turning and pressing required in the making of coiled pottery, in weaving, regularity of form and rhythmic repetition of the same movement are necessarily connected. These rhythmic movements always produce the same series of forms. Examples of rhythmic surface forms determined by perfect control of a technique are found in many industries and in all parts of the world. Exquisite regularity of flaking is found in the Egyptian flint knives (see fig. 5, p. 21). It is not so frequent in the flaking of American Indians. The adzed boards of the Indians of the North Pacific Coast bear chipping marks of great regularity that give the appearance of a pattern (figs. 6, p. 23 and 18, p. 30). On surfaces that are to be painted these marks are often polished off with grit-stone or shark skin, while on unpainted parts they are kept, presumably on account of their artistic effect. In Oriental metal work the strokes of the hammer are so regular that patterns consisting of flat surfaces originate. Other examples of the artistic effect of the regularity of movement are found in the prehistoric corrugated pottery of the North American South West. The coils are indented by pressure of the fingers and a series of indentations form a regular pattern on the surface (fig. 35). The effect of automatic control is seen nowhere more clearly than in basketry, matting and weaving. It has been pointed out before (p. 20) that evenness of surface results from regularity of movement. The rhythmic repetition of the movement leads also to rhythmic repetition of pattern. This is most beautifully illustrated by the best examples of California basketry. The virtuoso who varies the monotony of his movements and enjoys his ability to perform a more complex action, produces at the same time a more complex rhythm. This happens particularly in weaving and related industries such as braiding and wrapping with twine. Skipping of strands,—that is twilling (see fig. 17, p. 30) is the source of many rhythmic forms and twilling is undertaken by the virtuoso who plays with his technique and enjoys the overcoming of increased difficulties. [Illustration: Fig. 36. Necklace of Thompson Indians.] In many cases rhythmic complexity is clearly the result of careful planning. I have referred before to the rhythmical arrangement on fringes of the Thompson Indians of British Columbia, (p. 29). Another good example (fig. 36) is a double necklace in which the rhythmic series is— black, red, yellow, green, blue, green, both in the inner and outer lines while the connecting links have the order black, red, yellow, green, red, blue.[29]