the
effectiveness of design, but more than half the efficiency of practical
life, is due to our establishing such imaginary lines. We are
inevitably and perpetually dividing visual space (and something of
the sort happens also with "musical space") by objectively
non-existent lines answering to our own bodily orientation. Every course,
every trajectory, is of this sort. And every drawing executed by an
artist, every landscape, offered us by "Nature," is felt, because it is
measured, with reference to a set of imaginary horizontals or
perpendiculars. While, as I remember the late Mr G. F. Watts
showing me, every curve which we look at is _felt as being_ part of
an imaginary circle into which it could be prolonged. Our sum of
measuring and comparing activities, and also our dramas of
remembrance and expectation, are therefore multiplied by these
imaginary lines, whether they connect, constellation-wise, a few
isolated colour indications, or whether they are established as
standards of reference (horizontals, verticals, etc.) for other really
existing lines; or whether again they be thought of, like those circles,
as _wholes_ of which objectively perceived series of colour patches
might possibly be _parts._ In all these cases imaginary lines are
_felt,_ as existing, inasmuch as we feel the movement by which we
bring them into existence, and even feel that such a movement might
be made by us when it is not.

So far, however, I have dealt with these imaginary lines only as an
additional proof that shape-perception is an establishment of two
dimensional relationships, through our own activities, and an active
remembering, foreseeing and combining thereof.

CHAPTER VII

FACILITY AND DIFFICULTY OF GRASPING

OF this we get further proof when we proceed to another and less
elementary relationship implied in the perception of shape: the
relation of Whole and Parts.

In dealing with the _ground_ upon which we perceive our red and
black patches to be extended, I have already pointed out that our
operations of measuring and comparing are not applied to all the
patches of colour which we actually see, but only to such as we
_look at_; an observation equally applicable to sounds. In other
words our attention selects certain sensations, and limits to these all
that establishing of relations, all that measuring and comparing, all
that remembering and expecting; the other sensations being
excluded. Now, while whatever is thus