a. Windows and decorations on façades. Alternates vary in design to emphasize symmetry: 4. b. Windows and turrets. Vary alternately in design to complicate rhythm: 2. c. Reliefs alternating with tablets; reliefs or statues and pillars: Alternates vary in design to give richer effect: 11. d. Alternate unit is human figure: 9. e. Alternate unit varies in design, but is on a different level: 3. f. Irregular variation in alternates (windows, shields, and railings): 3. II. Of Size of Alternate Unit. a. Windows and supports. Vary in size to emphasize symmetry: 1. b. Statues and pillars; windows and pilasters. Alternates vary in size to complicate rhythm: 3. c. Vary in size irregularly. Disorder: 1. C. Variation of Distance. Row of windows--Distance between first two is wider: 1. The 125 illustrations of alternating repetition which were taken at random among 5000 photographs show a decided compliance with the principles already laid down. But there are many divergences as well, which it is necessary to consider, to see whether they are really contrary in principle or fall under its wider application. Eighty-two accord exactly with the principles with which we started. The distances between each set of units are equal and invariable; one unit varies in content but not in size or including shape; the alternating unit is invariable. There is an interesting modification of this principle in the case of the metopes and triglyphs of the Greek friezes. Here the triglyphs are unquestionably the principal units structurally, and to many observers the principal beat of the rhythm when taken rhythmically. But the triglyphs never vary and the metopes do, which would seem at first to violate the rule that principal units alone, and not alternates, should vary. This difficulty is obviated in two ways. With the spatial type of observer, the triglyph is indeed the principal beat of the rhythm when the series is at such a distance that the difference in the metopes (if there is such) cannot be detected. When, however, the series is nearer at hand, there ceases to be any rhythm, but each carved relief is taken for itself without regard to the others. With the rhythmic type of observer, if the triglyph has been the principal unit before, the principal beat changes on nearer approach to the metope and the whole series shifts its accent. It is impossible for any observer to keep the triglyph as the principal unit of the rhythm, when so near that differences in the metope are easily perceived. There are still thirty-eight cases which vary from these rules, and many of them vary in more than one respect. These exceptions fall into several classes, quite distinctly marked off from one another, and will be taken up in turn.