te experience. From this standpoint it may be assumed that, in a
state of waking reverie, the attention is so scattered that no
impression is made to stand out clearly in consciousness. On the other
hand, as soon as the mind focuses itself on a certain impression, for
example, the report of a gun, the relation of two angles, or the image
of a centaur, this stands out so clearly that it occupies the whole
foreground of consciousness, while all other impressions hide themselves
in the background. This single focal state of consciousness is,
therefore, pre-eminently a state of attention while the former state of
reverie, on account of its diffuse character, may be said to be
relatively devoid of attention.

=Physical Illustrations of Attention.=--To furnish a physical
illustration of the working of attention, some writers describe the
stream of our conscious life as presenting a series of waves, the
successive waves representing the impressions or ideas upon which
attention is focused at successive moments. When attention is in a
diffuse state, consciousness is likened to a comparatively level stream.
The focusing of attention upon particular impressions and thus making
them stand out as distinct states of consciousness is said to break the
surface of the stream into waves. This may be illustrated as follows:

[Illustration: FIG. 1--Consciousness in a state of passive reverie.

FIG. 2--Active consciousness. Attention focussed on the
definite experiences _a, b, c, d, e, f, g_.]

By others, consciousness is described as a field of vision, in which the
centre of vision represents the focal point of attention. For instance,
if the student intent upon his problem in analysis does not notice the
flickering light, the playing of the piano, or the smell of the burning
meat breaking in upon him, it is because this problem occupies the
centre of the attentive field. The other impressions, on the contrary,
lie so far on the outside of the field that they fail to stand out in
consciousness. This may be represented by the following diagram:

[Illustration: P represents the problem on which attention is fixed. A,
B, C, D, E, represent impressions which, though stimulating the
organism, do not attract definite attention.]

It must be understood, however, that these are merely mechanical devices
to illustrate the fact that when the mind selects, or attends to, any
impression, this impression is made to stand out clearly as an object