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Optical
Illusions
In year of 1922 Matthew Luckiesh
wrote an optical illusions book
titled: Visual Illusions: Their
Causes, Characteristics and
Applications. It was I believe,
the first book to comprehensively
cover the topic of Optical
Illusions or as they were called
in his time: Visual
Illusions.
The Greeks were one of the first
to use optical illusions. For
nearly 2,500 years the Parthenon
on the Acropolis at Athens,
Greece, has been one of Western
civilization's ideals of
architectural beauty. The eye
delights especially in the
simplicity of its extremely
straight lines. Yet in reality
the Parthenon contains no
straight lines. Wisely, the
architects Ictinus and
Callicrates made its columns,
which taper toward the top, with
a slightly convex or bulging
curve, a distension called
entasis. They also made its
seemingly horizontal lines curve
almost imperceptibly according to
a very careful mathematical
scheme. They knew that the eye
deceives that straight lines
viewed from a distance appear
curved, so they curved the lines
of the temple in a manner to make
them appear straight.
In the course of history, people
have encountered illusions in
hundreds of ways. A good example
of such an illusion, occurred
when L. Herman was reading a book
on sound, written by John
Tyndall. He saw gray smudge spots
in the intersections of spaces
among the figures that Tyndall
had arranged in a matrix. The
same intensity of light is
reflected all the way along the
white spaces in the grid, but the
intersections appear gray. See:
Images that Cause the Mind to
Create Additional Images
above.
The optical illusions that occur
in our everyday lives have become
the subject of study by many
psychologists and sociologists.
This field involves even aspects
of the fine arts, entertainment,
architecture and modern physics.
The study of illusion reflects
both how we perceive what is
around us and also how we project
our own concepts onto what we
see.
The way the eye sees an object is
by detecting the light rays that
bounce off the object. Some
visual illusions result from the
refraction, or bending, of that
light as it passes from one
substance to another. Thus a
stick dipped part way into water
appears to have broken at the
point it passes from air into
water.
Another illusion that depends on
refraction is the vision of a
pool of water in a mirage. Cool
layers of air refract the sun's
rays at different angles than do
less dense layers of heated air.
When the rays pass through both
layers at the right angle, they
create what appears to be
water.
Not all illusions are related to
the eye. For example, if fairly
hot water is run over one hand
and cold water over the other for
some time, then both are plunged
into lukewarm water, the cold
hand will feel very warm and the
hot one will feel cold?
Today we see optical illusions
everywhere, even when we are
watching television. The picture
on the screen is not really
moving in realtime. It is
actually many pictures moving so
fast that our mind cannot
comprehend each individual
picture. The same is true with
magazines and newsprint, we see
beautiful colored images, but
actually it is thousands of dots
colored red, green, and blue. If
you take a magnifying glass and
look very closely at your TV
screen or at the ads in your
newspaper, the dots will become
very apparent.
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