T. LIPPS, Raumaesthetik u. geometrisch-optische Tduschungen. 85 follow the law which Dr. Lipps has expounded elsewhere (in his Grundthatsachen) that experiences consolidate into a generalised law of mental working which serves us in fresh experiences which are only similar to the past ones. An excellent illustration of this " free movement " is given in the contrast between the unaesthetic effect of mere regularity as in a series of semicircles placed end to end with their concavities alternating in direction, and the beautiful smooth movement of the ordinary sinus-curve. But the aesthetic effect demands more than the free activity of mechanical forces. The forces must form a unity, and again we read this unity into the object from our own personality. Such unity may be either successive, as in the continuous impulse of movement in a column, or simultaneous as where a number of columns spring from the ground together (like an act of will comprehending many similar parts) or ' central ' where several activities radiate from the same point, as in a circle, and produce equilibrium. This last equilibrium is however only a special case in which the forces are in equilibrium to begin with. There is in a different sense an equilibrium in all beautiful forms which is of the last importance, for on it all the subsequent chapters depend. This is the equilibrium which grows out of the action of the forces engaged and is thus in any moment being reproduced. If the column rises it is also depressed by its weight, if the circle is com- pressed by the circumference it expands against it. Every force has in fact its counterforce, and in each case one of the two is primary and the other secondary, the one is described as ' force ' and the other as ' tendency '. But if there is always this equilibrium of force and tendency, how can illusion arise ? Dr. Lipps insists (section ii.) that illusion is not an error of perception (Wahrnehmung) but of judgment. A line is underestimated, where this is the case, not because we see it smaller but because we judge it smaller in comparison with a stand- ard of equal length brought in idea to compare with it. Only the judgment is so immediate and unreflective that it forces itself upon us as if it were an integral part of the perception. The illusion is an affair of ideas only. And we get geometrical illusions because of the forces we imagine working in the figure, and therefore altering the figure in idea in this direction. Thus if I imagine a line more compressed by its ends I judge it smaller than an equal line which does not suggest so much compression. The reason then why we can get such illusions in spite of the equilibrium of force and tendency is that we think of the one coming into play before the other, or we think of them as acting at different points of the figure. Hence, an enclosed space, e.g., a square, looks smaller than an equal space where the vertical sides are undrawn because com- pression by the vertical lines is primary. But a letter enclosed in a circle seems bigger than it is because the compressing force acts at the circumference, while the expansive force belongs to the whole included surface and is shared by the figure within.
