perceive the object, not as
diminished in size, but as far away. The painter colors his near hills
green, his distant ones blue, and washes out all detail in the
latter--"aerial perspective", he calls this. His distant hill peeks
from behind his nearer one, being partially covered by it. His shadows
fall in a way to indicate the relief of the landscape. These signs of
distance also affect the single resting eye and are responded to by
appropriate spatial perceptions.

Now let the single eye move, with the head, from side to side: an
index of the distance of objects is thus obtained, additional to all
the painter has at his disposal, for the distant objects in the field
of view now seem to move with the eye, while the nearer objects slide
in the opposite direction. How much this sign is ordinarily made use
of in perceiving distance is not known; it is believed not to be used
very much, and yet it is the most delicate of all the signs of
distance. The reason why it may not be much used by two-eyed people is
that another index almost as delicate and handier to use is afforded
by binocular vision.

When both eyes are open, we have a sign of distance that the painter
does not use, though it is used in stereoscope slides. The right and
left eyes get somewhat different views of the same solid object, the
right eye seeing a little further around the object to the right, and
the left eye to the left. The disparity between the two retinal
images, due to the different angles at which they view the object, is
greatest when the object is close at hand, and diminishes to
practically zero when it is a few hundred feet away. This disparity
between the two retinal images is responded to by perception of the
distance and relief of the object.

It will be recalled [Footnote: See pp. 253-254.] that when two utterly
inconsistent {443} views are presented to the two eyes, as a red field
to one and a green field to the other, the visual apparatus balks and
refuses to see more than one at a time--the binocular rivalry
phenomenon. But when the disparate views are such as are presented to
the two eyes by the same solid object, the visual apparatus (following
the law of combination) responds to the double stimulation by getting
a single view of an object in three dimensions.

Esthetic Perception

Beauty, humor, pathos and sublimity can be perceived by the senses,
though we might debate a long time over the question whether these
charact