brations to which it is
attuned. Your mind is selective. It is discriminating. It seizes
upon those few sensory images that are related to your interests in
life and thrusts them forward to be consciously perceived and acted
upon. All others it diverts into a subconscious reservoir of
temporary oblivion._

[Sidenote: _In Tune with Life-Interest_]

You will have a clearer understanding of the sense-perceptive
processes and a more vital realization of the practical significance
of these facts when you consider how they affect your knowledge of
material things and your conception of the external world.

This subject possesses two distinct aspects.

One aspect has to do with the inability of the sense-organs to
record the facts of the outer world with perfect precision. These
organs are the result of untold ages of evolution, and, generally
speaking, have become wonderfully efficient, but they display
surprising inaccuracies. These inaccuracies are called Sensory
Illusions.

[Sidenote: _Practical Aspects of Perception Process_]

The other aspect of the Sense-Perceptive Process has to do with the
mental interpretation of environment.

Both these aspects are distinctly practical.

You should know something of the weaknesses and deficiencies of the
sense-perceptive organs, because all your efforts at influencing
other men are directed at their organs of sense.

You should understand the relationship between your mind and your
environment, since they are the two principal factors in your
working life.

CHAPTER III

SENSORY ILLUSIONS AND SUGGESTIONS FOR THEIR USE

[Sidenote: _Unreliability of Sense-Organs_]

Figure 1 shows two lines of equal length, yet the vertical line will
to most persons seem longer than the horizontal one.

[Illustration: FIG. 1.]

In Figure 2 the lines A and B are of the same length, yet the lower
seems much longer.

[Illustration: FIG. 2.]

Those things look smallest over which the eye moves with least
resistance.

In Figure 3, the distance from A to B looks longer than the distance
from B to C because of the time we involuntarily take to notice each
dot, yet the distances are equal.

[Illustration: FIG. 3.]

[Sidenote: _Being and Seeming_]

For the same reason, the hatchet line (A-B) appears longer than
the unbroken line (C-D) in Figure 4, and the lines E and F appear
longer than the space (G) between them, although all are of equal
length.

[Illustration: FIG. 4.