Had the other sense of the term been used, examples might have been multiplied without limit, of slightly varying repeated units, and unvarying alternate blank spaces. But it was felt that such accumulation of illustration was unnecessary, and that what was true in a stricter sense of the term would be recognized as true for the larger number of cases that might be cited with a wider meaning. If the minor units had a definite enclosing outline, they were counted even though they were blank within, but without an enclosing outline, that is, if they were mere spaces, they were not considered, although the fact that there is such universal use of this type of decoration shows only more conclusively how the necessity of the invariability of alternates is taken for granted as an axiom of design. Another type of alternate repetition was not included in the illustrations, _i. e._, when two sets of units alternated, _without variation in either one_. To this class belong all the conventionalized designs used so much in all kinds of decoration, and of which a very full account is given in Owen Jones's Grammar of Ornament. These, to be sure, illustrate the negative points, viz., that size and shape are unalterable for rhythmic repetition; that distances must be equal and invariable; and that alternate units must not vary. But since the principal units do not vary either, it seemed needless to give them as examples of the point in question. A mention of this class of alternating repetitions, of which there is such a great number, is enough to show that they fall within the theory. But one example is as good as a thousand, and their inclusion among the illustrations for rhythmic alternates will be taken for granted without further mention. We are left, then, to the consideration of those alternating repetitions alone, where both have a definite outline, and one or both varies to a greater or lesser extent. The effort will be to show that the unit which for some reason is of principal importance in the rhythm, is the one chosen to vary, and if not that the repetition suffers thereby. 125 EXAMPLES A. Variations in Principal Unit alone: 87. I. Content alone: a. Metopes and Tryglyphs in Friezes: 9. b. Arches and Columns: 2. c. Statues in niches alternating with supports: 37. d. Windows alternating with supports or decorations: 12. e. Paintings or mosaics: 7. f. Carved designs in screens or ceilings: 17. II. Size and Content. a. Doors, paintings and reliefs on façades. Vary in size to emphasize symmetry: 4. b. Statues or shields over arcades. Vary in size to complicate rhythm: 1. B. Variations in Principal Unit AND Alternate: 37. I. Content alone: