Let us consider in the first place the balance between straight lines and curves.  The richer and fuller the curves, the more severe should be the straight lines that balance them, if perfect repose is desired.  But if the subject demands excess of movement and life, of course there will be less necessity for the balancing influence of straight lines.  And on the other hand, if the subject demands an excess of repose and contemplation, the bias will be on the side of straight lines.  But a picture composed entirely of rich, rolling curves is too disquieting a thing to contemplate, and would become very irritating.  Of the two extremes, one composed entirely of straight lines would be preferable to one with no squareness to relieve the richness of the curves.  For straight lines are significant of the deeper and more permanent things of life, of the powers that govern and restrain, and of infinity; while the rich curves (that is, curves the farthest removed from the straight line) seem to be expressive of uncontrolled energy and the more exuberant joys of life.  Vice may be excess in any direction, but asceticism has generally been accepted as a nobler vice than voluptuousness.  The rococo art of the eighteenth century is an instance of the excessive use of curved forms, and, like all excesses in the joys of life, it is vicious and is the favourite style of decoration in vulgar places of entertainment.  The excessive use of straight lines and square forms may be seen in some ancient Egyptian architecture, but this severity was originally, no doubt, softened by the use of colour, and in any case it is nobler and finer than the vicious cleverness of rococo art.

We have seen how the Greeks balanced the straight lines of their architectural forms with the rich lines of the sculpture which they used so lavishly on their temples.  But the balance was always kept on the side of the square forms and never on the side of undue roundness.  And it is on this side that the balance would seem to be in the finest art.  Even the finest curves are those that approach the straight line rather than the circle, that err on the side of flatnesses rather than roundnesses.

[Sidenote:  Between Flat and Gradated Tones]

What has been said about the balance of straight lines and curves applies equally well to tones, if for straight lines you substitute flat tones, and for curved lines gradated tones.  The deeper, more permanent things find expression in the wider, flatter tones, while an excess of gradations makes for prettiness, if not for the gross roundnesses of vicious modelling.