The responses were as follows: Five said it did more violence to the series to have the alternate varied than the major unit; it was more confusing. Three preferred it, giving as their reason that it made the elements more different from each other than before, hence more easily distinguished. The preponderance of evidence was, therefore, that, although any variation from symmetry in a unit was likely to be detrimental to the repetition, it was more likely to be tolerable in the major unit than in the alternate space. In either case it was demanded that the two units be distinctly different, and it depended on the individual subject, whether in this experiment the variation of one unit or the other brought out this distinction more obviously. Aside from this consideration, however, it appeared that the alternate spaces as such required equilibrium more than the principal unit. Also, variation of symmetry in the major unit, while it made it more prominent in the way of eccentricity, also made the symmetrical minor unit more prominent in the way of interest. As one subject expressed it, "Since the others vary, the attention requires something which does not vary, and forces prominence on the minor unit, because it remains symmetrical"; and "The minor unit is too small to merit such prominence as it gets by lack of symmetry. It is distorted, and has not enough content to bear it."

These introspections from temporal and spatial subject alike, all point to the fact of a certain value attached to the alternating units in a series. (1) The units must not be too much alike in interest, or they rival each other. (2) They must not have more prominence given them as regards the whole than they have interest to sustain. (3) There must be a congruity between the two elements so that one shall not be noticeable in one way, and one in another, thus carrying the attention in two different directions.

One more thing was suggested by this experiment: (4) The subjects who had invariably grouped their different elements in other series found it very difficult to do so in this, or wholly impossible. None of them did so when taking the series naturally, but moved on from one to the next just as the rhythmic type did. They felt "forced to move on," "no place to rest," while one in whom the rhythmic feeling was weakest was much fatigued by this movement, and insisted on having something stable to rest upon if he was to gain any pleasure at all.

Next the series was varied by making both units unsymmetrical; first with the balance tipping the same, and second in opposite ways.

Those who preferred this gave essentially the same reason. They agreed that the unity of both elements was broken up by this change, and they did not stand out distinctly from each other; but all felt a certain congruity in having both major and minor units follow the same scheme in composition. They were not distinctly an alternating series, but harmonized better as lines. The two spatial subjects, who disliked this arrangement more than the other, gave the same reason: the unity of the elements was spoiled, they did not "hang together." Their dislike was similar in kind to that of the others, only the congruity which made up for it with the former failed to satisfy these. With the symmetry broken and the balance tipping in different ways, the feeling was not strong in either direction. They still criticised it in the same terms of congruity and distinctness, with no especial change on account of this modification.

These experiments all pointed to the fact that (1) a certain amount of congruity and equality was necessary between elements of a series (although it did not establish what were the essential features of such a harmony). (2) It is more pleasant, as a rule, to have the elements symmetrical, although symmetry was not a necessity for an agreeable series. (3) Provided the change in the symmetry of the units was not enough to shift the whole order of the series, changing the major to minor units (and vice versa), any varying of the symmetry of a minor unit was more disturbing to the repetition than of the major, while varying their symmetrical position, as regards the unit on either side, was absolutely destructive to the order.

The next experiment dealt with a different side of the question. Since the unit of a repeated series may be a group with repetitions inside itself, does the repetition of lines or figures inside the group differ from the repetition of the groups as a whole? If so, how? That is, in the enjoyment of a series of groups with repeated lines in the group, in what respect does our apperception of the repetition differ in the two cases? Or does it in reality differ at all?

To test this, the strings were arranged in the following way. 10 groups of five strings were hung 100 mm. wide and 100 mm. apart. Each unit had, then, five repetitions within it.

The arrangement was pleasant to all the subjects, and they described the effect of the experience, falling at once into the spatial and temporal types as before (this was wholly naïve, for the same questions were asked of each, and they had no idea of being grouped in types). The introspection of both types must be taken in some detail, to fully analyze the experience.

Spatial: J. felt he took in all groups at once. Each unit seemed like a rich experience in itself, but he could not detect any rhythm in it, nor in the whole series. The pleasure consisted in getting a number of similar objects in the field at once, and enjoying the combination of them all, feeling that they stretched away in each direction. H. and U. grouped several unit-groups into a larger unity and enjoyed the cluster as a whole. They did not group them in any particular system, nor could they detect the slightest pleasure in moving from one such group to the next. One found his enjoyment solely in the contrast effects in each, while the other laid it to the space relations of each independently. The pleasure only came when each group of groups was spread before him. Those outside the immediate field meant nothing to him, and the movement between them had absolutely no conscious interest for him. S. said that enjoyment stopped altogether during motion of any kind, and the experience was pleasant only during total repose, on whatever happened to be in his field at once.

With the temporal type came a marked difference in apperception.

B. affirmed the pleasure to consist in going from one cluster to another, and to begin just at the point where he meets the next stimulation and feels it is going to be the same as the one previous. It is the expectation, rather than the verification recurring at intervals, which makes up the pleasure; not the actual movement, or subsequent contemplation of a group. The pleasure came in pulses; in knowing by seeing from the side of the eyes that the experience is to be repeated, and on reaching the edge of a new group, in the feeling that the experience is just about to begin.

R. felt that she "wriggled around" in each group of lines, and that a certain feeling came from "wriggling" among the lines in a particular fashion.

The pleasure consisted in having this feeling recur at regular intervals. The repetitions inside the group and of the group as a whole differed in this respect: For the separate unit-group, it apparently consisted in repeated short irregular movements, back and forth, enough to bring about a certain feeling which seemed pleasant and sufficient unto itself. Repetition of the groups as a whole meant movement across the field in one direction, for the purpose of meeting another group, and getting the required feeling from it again. The pleasure was not in the movement or in any repose (she could detect no repose at all), but in experiencing the group again, feeling that it had been so before, and would be again.

L. (the most extreme of the temporal type) agreed with R. that the lines inside the group were perceived and enjoyed temporally, as well as the groups as a whole. There was no experiencing the groups at once. He felt that he moved regularly across the field encountering five lines, one after the other, then an empty space, then five lines more. The only meaning which the group as such had for him was the five accents which came near one another in time. He could feel no unity whatever apart from this. He was even certain that his pleasure would be identical if in some mechanical way the same figure could be pushed forward, so that the same amount of time and movement would be necessary to reach it that was required to move from one figure to the next on the field. The experience was in every way analogous to auditory rhythm with him, and he was unable to express himself in other than temporal terms. Immediate perception, repose on the object, or groupings, had no significance for him.

The other two subjects were links between the extremes already described. They could feel each group, and sometimes even the whole series at once apparently, and yet were all the time conscious of a certain rhythm in going from one to the next. The whole experience seemed immediate at first, but on reflection a certain alternate rhythm was felt to be present, which was too rapid to take any considerable time, but yet had to be included as a factor in the experience. These introspections I believe to throw light on the nature of the whole experience of repetition. Since there are two methods of apperception so extreme, but moreover certain subjects partake of the characteristics of both, it might seem that both types represent but one side of the experience. Since both are enjoying the same objective series, but in their description of their feeling in face of it emphasize such different sides (leaving at the same time the other side unaccounted for), and since certain subjects share the experience of both, it might be that the sum of both methods of apperception was necessary to the fullest appreciation of the repetition in question, only in certain subjects one aspect of it was so much stronger that the other possible factors in the experience were overlooked.

It would tend to bear out this view, that when it was suggested to those of the temporal type (always excepting L.) that according to their description the other groups remaining in the field, after having performed their part in a temporal series, ought to have no further influence in the repetition, whereas they did in reality, they admitted the fact, but could not account for it. Moreover, those of the spatial type admitted that their enjoyment in having spaces equal, and in having repeated objects exactly like one another, had a certain character which no other experience possessed. This did not seem accounted for by any description they could give of its effect on them, although they could not detect what this other elusive factor might be.

These introspections, therefore, and the confessions on the part of both that there was a feeling of something more which they could not hold long enough to describe, suggested that both types were but opposite ends of a series of possible apperceptive types, and that in both cases certain essential features were emphasized at the expense of the others.

After these experiments, the next step was to find how a series of groups was apperceived when the lines in each group were arranged symmetrically about a centre, as distinguished from their arrangement at invariable distances apart. The same number and size of groups were taken, but the arrangement of lines in each varied as stated above.

Spatial subjects: J. felt a different kind of pleasure from that felt with Fig. 19. Here the enjoyment was in each unit for itself, a certain repose in its symmetry. Although he fixated on the centre of the groups, and in going across the field moved from centre to centre, there was no feeling of rhythm whatever, merely enjoyment of the unit itself. Moreover, although he had detected no rhythm in the previous experience, this one seemed distinctly different in having lost a feature that the other had. He felt by comparison that the other had had a temporal character, some movement in the groups, which was wholly lacking in this. This was more beautiful and restful, the other more exciting and rich.

H. and S. both enjoyed this series better on account of possibility of greater repose in the unit-groups. The pleasure was solely in each unit for itself, not in their repetition, so the group which offered most balance and equilibrium in itself was pleasantest. S. also found enjoyment in slight variations in the groups (trifling difference in distance, different light effect, etc.). It is noticeable that when repetition alone was the main feature of the series, any variation was either ignored or found unpleasant. But when the unit for itself is the object of enjoyment, variation if slight is another element of pleasure.

There is also pleasure in the mere repeating of symmetrical groups, although, when the attention is turned to this feature, the feeling of symmetry is less felt. Even when attending chiefly to the repetition of the groups, the symmetry of each is felt somewhat, which makes the whole experience better than Fig. 19, but the two attitudes seem to hinder, rather than help each other.

This introspection was suggestive, giving rise to two more questions: (1) When is variation allowable, and when not? Is it adapted only to objects when taken, as ends-in-themselves, and not when considered as means to something else, i. e., as means to make a series or border, or anything which takes attention from themselves as unities with individual meaning? (2) Is a distinctly symmetrical group as adapted to repetition, as such, as one with merely equal divisions? Does it not tend more to repose in itself, instead of to the motion necessary for the apperception of a repeated series? These questions will be considered later.

Temporal type: R. felt a difference in the movement across, in that in Fig. 20 it was from the centre of one unit to the next, while in Fig. 19 there was no regularity in the movement.

L. felt the difference between the two apperceptions very strongly. In Fig. 20 the movements seemed organized. He felt as if his attention (if not his eyes) went back and forth from edge to edge of the unit, finally settling in the centre; while in Fig. 19 the very essence of the apperception was that every line was compared with every other, meaning a great number of movements in both directions, not stopping in the centre. If he did rest finally in the centre, in the unit of Fig. 19, instead of seeming evenly repeated, it too became symmetrically perceived, but the usual way to get from one such unit to the next was to move from and to any point in the next adjacent, other than the central one. In either case the pleasure came in identification of the second figure with the first, and the feeling, "I have seen it before." The pleasure lay in the process of recurrence of sameness.

V. also, who had not felt much motion in Fig. 19 at first, felt it strongly now in comparison with Fig. 20. He said in the former, although he did not make actual movements across (in fact his eyes were plainly at rest), he was sure he felt "dispositions to do so" which were lacking in Fig. 20. The pleasure came in the first moment of repose after finding the new unit was the same as the old.

After we had investigated the different methods of apperceiving groups of repeated lines, and compared the effects of different groupings, and studied the feeling of one unit alternating with another, another question arose.

These questions had all referred to the alternation of two units; either a unit with an empty space, or with a space of different filling. How did the apperception differ when three repeated units alternated with each other? To test this, three spaces were taken equally wide (110 mm.) and equally distant from each other (150 mm.), but with three different designs within them. These designs were of the same general character and importance although different, and repeated themselves regularly.

The subjects were asked as before to describe their reaction on the series. Not one of all the number was able to feel the repetition of the three units; what pleasure they got from the series (if indeed they got any) was from other sources. The general type of answer was formulated more fully by L. He saw 1, then looked for 2 and found it different, but could have included it in the series if it were not for 3. That being still different sent 1 and 2 out of mind, so that he could not feel any repetition of 1 when he met it again. He felt a certain sense of repetition in that the spacing and general motifs were the same, but there was no pleasure in that. What pleasure he got was wholly intellectual, not immediate, except for a slight pleasure in their uniformity of position. In him the rhythmic feeling had always been of the strongest, but he found in this experience none whatever. It was simply impossible to keep the three units going at once. Another temporal subject tried to group 2 and 3 as one element, with one as an alternate, thus reducing it to a rhythm of twos. This process was labored, but otherwise no enjoyment was possible. The spatial subjects derived what pleasure they could, either from the units separately, with no regard to their repetition, or from some method of grouping, by which their difference could be overlooked. One expressed his pleasure solely in terms of contrast of the white strings against a black ground. Any immediate feeling for the repetition was impossible for either type. It will be noticed that the feeling of the repetition is quite different from the knowing it is there. They were all perfectly conscious that 1 was repeated again after 3, but could not feel it, while repeated simply after 2, they could feel it.

Next, the series was varied again. The size of the blocks, instead of being alike, was varied three ways, while the designs remained similar.

The interspaces were 150 mm. in every case, but 1 was 150 mm. wide; 2 = 110 mm.; 3 = 70 mm. All the spatial subjects found Fig. 22 worse than Fig. 21. The irregularity and general disorder was more pronounced. Although the rhythm had never consciously given them pleasure, and, when not violated, was never noticed, still the threefold difference in size violates some feeling which they can only express in rhythmic terms. Some tried to group the three units into a larger group, but this being unsymmetrical displeased them. Others picked out the most satisfactorily proportioned unit and ignored the others, but any possible apperception was irritating. The temporal subjects found it equally poor. They felt the continual dissatisfaction of having their expectation, that the adjacent unit should be the same, disappointed. They all said that they could carry the feeling of repetition over one dissimilar unit (i. e., in an alternating series of two different units), but that the third difference completely upset the scheme. When only the filling varied as in Fig. 21, it could be partially ignored, but difference in size could not be ignored, and only the equal distances apart kept them from being a heap. They could not feel the evenness of the empty interspaces, however. They were not consciously present in the experience at all, they merely knew they must be even. There was no feeling-tone whatever to the empty alternates.

Only one subject preferred Fig. 22 to Fig. 21, and the reason was obvious. 1, 2, and 3 appeared as the same unit where variation in size was apperceived as due to perspective. Thus, instead of appearing as three units repeated, they were one set which progressed by means of "pulsations" or regular intervals of perspective. This gave an added richness to the rhythm, and was very pleasant. As three separate units of different size, there was no meaning in the series whatever.

It is evident from these introspections that, although the likes and dislikes may vary, the principles on which they are based have much in common.

The points on which they agreed unanimously were the following:

(1) There is no feeling of repetition for three separate units. The series may be enjoyed by means of subjective grouping of one kind or another, but as separate elements, the feeling of repetition is broken by adding the third.

(2) There is a distinction between perceiving or knowing a repetition, and feeling it. Even though a subject is equally conscious that elements are repeated according to some scheme in two different cases, he may feel it in one case and not in the other.

(3) The empty spaces between the elements have no conscious part to play in the experience. Even when there is a figure in the alternate space, it comes very little into consciousness as part of the repetition, yet it is alterations in these alternates which make or mar the feeling of repetition. A series may not be beautiful in itself, but if the alternates are regular, it feels repeated. Vice versa, the units may be enjoyable in themselves, but they do not feel repeated unless the alternates are regular and conform to certain requirements. In the units lies the meaning of the repetition, in the regular alternates the possibility of its expression.

(4) The rhythmic character of repetition is not felt by a certain type of subject, when it goes smoothly. When a variation is made which would destroy any possible rhythm, its lack is felt, and its violation finds expression only in rhythmic terms.

(5) More violation is done to a series to have the size of units varied than the filling. (This corroborates previous experiments.)

(6) A certain amount of ignoring and regrouping can be done by the subject. The series is not taken exactly as given, but with selective attention.

(7) In a series of different elements alternating, the most prominent one is chosen for the major unit, and the others for alternates. This prominence is more influenced by size than any other factor, but may be due to intrinsic interest of any kind.

(8) The major and minor elements must have a certain difference from each other, both in appearance and interest, and they must be different enough for the difference to be easily perceived, but not enough to be incongruous. They must differ in interest enough, so that one is easily more prominent than the other, or may be made subservient to the other, in the apperception.

(9) Variations are pleasant in the principal unit repeated, but not in the alternating figure unless very slight indeed, or affecting only secondary parts of the figure, not the main lines.

(10) Not the time actually spent on a unit makes it more or less prominent, but the feeling of more or less "energy" expended on it.

Ends: In an alternating repetition, must the series end on a light or heavy beat? That is, must the major or minor unit be on the end?

To test this a series of strings was hung in which a group of three alternated with a single string.

The subjects were asked to look at it with the three-groups on the end, and with the single string. In every case the three-group ending was emphatically declared the best. What reasons were given were much the same, although most of them could give no explanation at all. S. said the minor space on the end left him "hanging in mid-air, it needs the heavy beat to land me again." Others said it was "ragged" unless the three-group ended the series. R. said anything interesting would do on the end, as well as the larger-sized unit, it simply needed something of sufficient interest to stop the rhythmic process and keep one from going on.

It was impossible to describe the experience except in rhythmic terms, and those in whom this sense was not strong could give no account whatever for the difference in their feeling for end.

It will be remembered that some experiments were previously described relating to the difference in apperception of a group of lines equally distant from one another, and a group averaged at equal distances each side of a middle point, but unequally from each, to emphasize the bilateral symmetry. Two such series were now taken to find if there were any difference necessary in appropriate endings. Since the two types of groups differed so much in apperception, did that difference so extend to the whole series that a different space was needed at the end to finish them off?

The method of experiment was the following: Two series of repeated groups were hung (100 mm. wide and 100 mm. between) with the design of the groups varied as described. At the end of each a strip of cardboard was hung, which the subject was asked to move so that it bounded the amount of space at the end, necessary to finish the series adequately.

Thus b is the cardboard strip, and a the space which was to be varied according to his taste. The same experiment was tried with each series, with the following results:

In the case of every one but J. the subjects preferred a longer end space with I than with II. J. was, however, of the extreme spatial type who gave as his explanation that with II, when the central line was prominent, the end (a) must equal just the distance to another middle line, while with I it must harmonize with the shorter distances in the group, but not exactly equal them, for that would make it too narrow.

It would mean, then, that the apperception of the repeated group in I (if it accords with the subject's own introspection) consists in repeated fluctuations of attention over the five strings, with no repose on any one more than another. The movement is back and forth from edge to edge, and hence needs more of an end to finish it than in a series of symmetrical units where the movement is not back and forth, but balanced and resting on the central point. In other words, in Group I there is a rhythm of movement within the group itself, as well as of the whole, while in II it is balanced and coördinated from the centre of each group, out and back, so that a longer, or at least more important end of some description is necessary to break the rhythm, and stop the series in I than in II.

It is noticeable also that H. and S. thought in both cases they were making the end spaces equal to the interspaces; but after Series I, a was made 102 and 109; and after Series II 95 and 104 respectively. This naturally raised another question: Does a series of groups, with repetitions within each, tend to make one overestimate distances between or at the end, or at least does one overestimate these distances in comparison with a series of symmetrical units?

The subjects were so unanimous in preferring a larger "embankment" after Series I than II, that it was useless to test them further on that point, and the experiment was changed to the other question according to the suggestion above.

A series of eight cards was prepared (125 mm. wide) on four of which five heavy black strips were drawn equally distant from each other, and on the others a much wider strip in the centre with another on each side near the edges. Of the two series just made, one was composed of what we have called "rhythmic units" and the other of "symmetrical units."

The subjects were asked to arrange the two separate series so that the interspaces should be exactly equal to the units. It will be observed that the rhythmic unit had a black strip on each edge, thereby apparently decreasing its size, while the edge of the symmetrical unit was white. In this respect the comparison was hardly fair, but the result was the following. The figures represent an average of two trials, and stand for the size estimate of the interspaces for each subjects respectively, in the two series.

Average difference of estimate of both series = 2.64. Mean variation = 1.37.

It might be contended, however, that Series I is an example of optical illusion, that the card was overestimated for that reason, and the interspaces necessarily made wider. To avoid this difficulty another series was made. Two sets of cards (125 mm. wide) were prepared; one with five black strips at equal distances apart as before (excepting that the strips were made heavier), the other with six strips. The card with an odd number of strips had thereby a strip in the middle upon which the attention could centre,—possessed a kind of balance. The card with an even number of strips had, moreover, no such central line but only a space, thus preventing repose of attention, and making the unit more pronouncedly rhythmic. (It will be noticed in the foregoing table that one subject, V, made narrower interspaces in I than in II. He said he felt the units as centring around the group of three lines in the centre, not as proceeding equally to the edge. The unit became thus for him symmetrical instead of rhythmic, which could easily account for the difference in estimation.)

The results in the present case are an average of three trials:

Average difference in estimate of both series = 6.1. Mean variation = 2.1.

Since both these figures represent an effect usually explained by optical illusion, that factor may be counted out, and the difference in the estimate be accounted for by the difference in the rhythm of the units. The difference in estimation between the two rhythmic units, differing only in odd and even number of strips, is greater than between the rhythmic and more strictly symmetrical, and yet the two were more comparable in construction. It would seem, then, that the greater overestimation of II is due to the rhythmic movement which is not limited or driven back to a central line as in I, but, by continuing over the limits, produces a greater feeling of breadth.

The same question was experimented on in another way. Smaller strips of cardboard all 50 mm. wide, but with different designs, were hung behind the narrow window previously used. Four of each set were hung at a time behind the window, and subjects arranged them so that the interspaces appeared to equal the strips. These designs were to illustrate different points in question. The difference in estimation for an empty card, and a filled one; the difference according to the strongly centred, or rhythmic, or slant lines of the filling. These experiments were not so complete as the former ones, since the subjects were scattered; hence they represent only one trial or an average of two. But the results conform with what we have been led to expect.

These results point to the fact that there is a tendency to overestimate the strips unless there is a strong central accent, which draws the attention back to the middle of the strip, in which case it is slightly underestimated. This would seem to be contradicted in I, where the centre is strongly marked by slant lines coming toward it. But the subjects, instead of taking the lines as pointing towards the centre, in almost every case felt them as leading away from it, and the oblique lines gave an appearance of greater breadth, which result was carried out by the greater overestimation of II. In this case, in addition to slant lines, there was no central accent, and the overestimation was proportionately large. III and IV were intended to illustrate the difference in estimate of rhythmic and symmetrical units, but although a slight difference is apparent, the subjects did not feel III as strongly rhythmic, because the black lines on the ends of the strip were ignored against the black background, and only the two central lines were taken. This made it more a balanced than a rhythmic unit, so it is not a fair type of the point in question.

We may say, in conclusion, that oblique lines (which involve a more complex muscular adjustment to perceive them) give an impression of greater distance traversed, hence are overestimated; of two rhythmic groups, the one containing an even number is more overestimated than the odd, since the movement across is unchecked, and not balanced around a central line; a series of strongly centred groups is more correctly estimated as to its interspacing, and even slightly underestimated, because of the check imposed by the centre of fixation in each group. Although these results are very uniform, a more complete series of experiments should be done on this subject, to make the conclusions thoroughly valid.

Another question was suggested by these results: Is it more agreeable to have a series of repeated space forms nearer or farther apart when a design is within? Does the design, by drawing attention to itself (especially if it be markedly central), make the objects demand narrower or wider interspacing? To test this question, four blank strips of cardboard were hung behind the narrow window, and the subjects arranged them at the distance apart which suited them best. Then two other sets of cards, of the same size, but of different designs, were hung successively the same way, and these arranged also at the most agreeable distances. One decorated card had a circle within a rectangle, the other a triangle of gilt stars. The judgments were made in pairs, i. e. the blank cards and the one with the circular design were arranged twice in succession; then the blank cards and the star design. This gives three judgments for the blank cards, two for the circular, and one for the star design, and the judgments are given in full, since an average would disguise the point in question.

Although the favorite arrangements varied somewhat on the different days, the filled cards were with only four exceptions preferred nearer together than the empty ones at any one trial, and two of these put them equal. (The choice of V. was affected by the fact that the circular designs produced such strong after-images that he was obliged to put them farther apart, to avoid confusion with the real design.) The reason suggested by the subjects for a narrower interspacing with decorated cards was that, when they attended to the design, they paid no attention to the actual edge of the card, but the card ended so far as its interest was concerned with the design. Therefore they had to be nearer together to bring the designs, not the whole field of the cards, into a series. If, then, the design extended over all the card, and its interest was no more in the centre than the ends, would this difference in interspacing cease to be demanded?

Another series of cards was hung with a design of oblique lines over the whole field, and these arranged as the others were, at the most agreeable distances.

If, for the sake of comparison, the average be taken of the favorite arrangements of the four blank cards, and they compared with the interspacing of the oblique line design, it will be seen they approach each other closely, except in the case of W.

These experiments would seem to show that an empty space, or one completely covered with decoration, is taken in its entirety when repeated in the series. But when decorated, especially toward the centre, the design, instead of the whole including space, is taken as the repeated unit, and for this reason the different units must approach each other to make a satisfactory series.

To what extent does change in level and plane affect the units of a series? To test this, a series of diamond shapes was hung on the same level and at equal distances, and the subjects enjoyed them as a repeated series.

Then another row was hung above them, and halfway between.

The subjects grouped them either in twos or threes, thus transforming them into one series of similar group-units of triplets and pairs. They were asked if they could take them up and down, one after the other without grouping, as they would have done when on the same level. With a little practice two of them succeeded, but they found the series tiresome when taken in this way, and deprived of much of its pleasure.

The series was then changed by hanging a smaller diamond between the others, at the same level.