In itself, however, mere volume of space is no more aesthetic than mere bounding line or surface; in order to become beautiful, it must become alive. But how can space--the most abstract thing in the world--become alive? By having the activities which it incloses felt into it. Just as our bodies are felt to be alive because our activities express themselves there, so our rooms, because we live and move within them. As we enter a cathedral and look down the long aisle, the movement of our eyes inevitably suggests the movement of our bodies; or, as we look up and our eyes follow the ribs of the vaulting, it is as if we ourselves were borne aloft; in the imagination we move through the open spaces; and since we do not actually move, we locate our impulses to movement, not in our bodies, but in the space through which we take our imagined flight. Every object suggests movement to it, and we fill the intervening space with this imagined movement, provided only we stay our activities and give time for the imagination to work its will. Thus all space may become alive with the possibilities of movement which it offers. The aesthetic effects of volume vary chiefly according to size and shape. In order to be appreciated, these effects must in general be somewhat striking; otherwise they pass unnoticed, and we simply take the interiors of our buildings as matters of course. It is a curious fact that an impression of vastness can be secured by inclosing a relatively small space. A square, like the Place de la Concorde, or even the inside of a cathedral, produces a feeling of size almost, if not quite, as great as an open prairie or sea. The reason, I suppose, is that an inclosed space offers definite points as stimuli and goals for suggested movements. As we imaginatively reach out and touch these points, we seem to encompass their distance; and the volume of our own bodies seems to be magnified accordingly. The boundaries of the space become a second and greater integument. This is of decisive importance; for the aesthetic appreciation of size is relative to an appreciation of the size of our own bodies; in nature itself there is nothing either large or small. Along with the sense of vastness goes a sense of freedom; the one is the aesthetic experience resulting from the imaginative reaching of the goal of a movement, the other is the feeling of the imagined movement itself. When, on the other hand, an inclosure is small, as in the case of a cell, and especially when the ceiling or vault is low, as in a crypt, it feels cabined and confined, because our own possibilities of movement are restricted. In order to avoid this feeling, if a space is limited in one direction, it must be free in another; if narrow, it must be long; if small in plan, it must be high, as in a tower.