and their comparative lengths and directions, we shall treat the uninteresting white extensions as a _blank,_ a gap, as that which separates the objects of our active interest, and takes what existence it has for our mind only from its relation of separating those interesting actively measured and compared lines. Thus the difference between our _active perception_ and our merely _passive sensation_ accounts for the fact that every visible shape is composed of lines (or bands) measured and compared with reference to our own ocular adjustments and our axis and centre; lines existing, as we express it, in _blank space,_ that is to say space not similarly measured; lines, moreover, _enclosing_ between each other more of this blank space, which is not measured in itself but subjected to the measurement of its enclosing lines. And similarly, every _audible_ Shape consists not merely of sounds enclosing _silence,_ but of heard tones between which we are aware of the intervening _blank interval_ which _might have been_ occupied by the intermediary tones and semitones. In other words, visible and audible Shape is composed of alternations between _active,_ that is _moving,_ measuring, referring, comparing, attention; and _passive,_ that is comparatively sluggish _reception_ of mere sensation. This fact implies another and very important one, which I have indeed already hinted at. If perceiving shape means comparing lines (they may _be bands,_ but we will call them _lines),_ and the lines are measured only by consecutive eye movements, then the act of comparison evidently includes the co-operation, however infinitesimally brief, of _memory._ The two halves of this Chippendale chair-back exist simultaneously in front of my eyes, but I cannot take stock simultaneously of the lengths and orientation of the curves to the right and the curves of the left. I must hold over the image of one half, and unite it, somewhere in what we call "the mind"--with the other; nay, I must do this even with the separate curves constituting the patterns each of which is measured by a sweep of the glance, even as I should measure them successively by applying a tape and then remembering and comparing their various lengths, although the ocular process may stand to the tape-process as a minute of our time to several hundreds of years. This comes to saying that the perception of visible shapes, even like that of audible ones, takes place _in time,_ and requires therefore the co-operation of _memory._ Now memory, paradoxical as it may sound, practically implies _expectation:_ the use of the past, to so speak, is to become that visionary thing we call the _future._ Hence, while we are measuring the extension and direction of one line, we are not only _remembering_ the extent and direction of another previously measured line, but we are also _expecting_ a similar, or somewhat similar, act of measurement of the _next_ line; even as in "following