surface decoration, any arrangement of forms, as at A., consisting only of straight lines, is monotonous, and affords but imperfect pleasure; but, introduce lines which tend to carry the eye towards the angles, as at B., and you have at once an additional pleasure.
“Then add lines giving a circular tendency, as at C., and you have now complete harmony: in this case the square is the leading form or tonic; the angular and curved are subordinate.
“We may produce the same result in adopting an angular composition, as at D., add the lines as at E., and we at once correct the tendency to follow only the angular direction of the inclined lines; but, unite these by circles as at F., and we have harmony still more nearly perfect, i.e., repose, for the eye has now no longer any want that could be supplied.”
Still, compositions distributed in equal lines or divisions will be less beautiful than those which require a greater mental effort to appreciate them: proportions the most difficult for the eye to detect will be the most agreeable.
In surface decoration by the Moors, lines flow from a parent stem: every ornament, however distant, can be traced to its branch and root; they have the happy art of so adapting the ornament to the surface decorated, that the ornament as often appears to have suggested the general form as to have been suggested by it. In all cases we find the foliage flowing out of a parent stem, and we are never offended, as in modern practice, by the random introduction of an ornament set down without a reason for its existence. However irregular the space they have to fill, they always commence by dividing it into equal areas, and round these trunk lines they fill in their detail, but invariably return to their parent stem.
The Moors also followed another principle, that of radiation from the parent stem, as we may see exemplified in nature by the human hand, or in a chestnut leaf. When style becomes debased, neither of these laws is followed; as in Elizabethan ornament, where nothing is continuous, nothing radiates, all is haphazard.
All junctions of curved lines with curved, or of curved with straight, should be tangential to each other. The Oriental practice always accords with this principle. Many of their ornaments are on the principle which is observable in the lines of a feather and in the articulations of a leaf; and to this is due that additional charm found in all perfect ornamentation, which is called “the graceful.”