e thirty feet and the other three hundred feet distant. We note
that the nearer tree shows the _detail_ of the bark and leaves, while
the more distant one lacks this detail. The nearer tree also reflects
more _light_ and _color_ than the one farther away. These minute
differences, registered as they are on the retinal image, come to stand
for so much of distance.

The ear also learns to perceive distance through differences in the
quality and the intensity of sound. Auditory perception of distance is,
however, never very accurate.

THE PERCEIVING OF DIRECTION.--The motor senses probably give us our
first perception of direction, as they do of distance. The child has to
reach this way or that way for his rattle; turn the eyes or head so far
in order to see an interesting object; twist the body, crawl or walk to
one side or the other to secure his bottle. In these experiences he is
gaining his first knowledge of direction.

Along with these muscle-joint experiences, the eye is also being
trained. The position of the image on the retina comes to stand for
direction, and the eye finally develops so remarkable a power of
perceiving direction that a picture hung a half inch out of plumb is a
source of annoyance. The ear develops some skill in the perception of
direction, but is less dependable than the eye.

4. THE PERCEPTION OF TIME

The philosophers and psychologists agree little better about our sense
of time than they do about our sense of space. Of this much, however, we
may be certain, our perception of time is subject to development and
training.

NATURE OF THE TIME SENSE.--How we perceive time is not so well
understood as our perception of space. It is evident, however, that our
idea of time is simpler than our idea of space--it has less of content,
less that we can describe. Probably the most fundamental part of our
idea of time is _progression_, or change, without which it is difficult
to think of time at all. The question then becomes, how do we perceive
change, or succession?

If one looks in upon his thought stream he finds that the movement of
consciousness is not uniformly continuous, but that his thought moves in
pulses, or short rushes, so to speak. When we are seeking for some fact
or conclusion, there is a moment of expectancy, or poising, and then the
leap forward to the desired point, or conclusion, from which an
immediate start is taken for the next objective point of our thinking.
It is proba