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ingrained
prejudices of previous centuries. The
greatest scientists of Newton's day could
not accept his theory of colors, a theory
that we in the twentieth century, with
three hundred years of hindsight, regard
as self-evident. Newton's seemingly
simple idea was that the colors produced
when sunlight passes through a prism are
caused by the separation of the sunlight,
which contains all colors, into its
constituent parts by refraction. Ibn
al-Haytham demonstrated that the prism
made the colors visible by bending rays
of different colors in varying amounts,
thus producing the familiar spectrum.
lbn al-Haytham's
explanation of how a lens worked required
a similar leap of intellect. He contended
that magnification was due to the
bending, or refraction, of light rays at
the glass-to-air boundary and not, as was
thought, to something in the glass. He
correctly deduced that the curvature of
the glass, or lens, produced the
magnification;
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thus, the
magnifying effect takes place at the
surface of the lens rather than within
it.
This distinction
is, of course, critical to the design of
lenses, and without the ability to design
lenses, we would have no cameras, movies,
television sets, satellites, eyeglasses,
contact lenses, telescopes, or
microscopes-life would be very different
for the human race.
Although he did not build a telescope, it
is known that Ibn al-Haytham did
construct parabolic mirrors. Incoming
parallel rays of light, such as those
from the stars, are focused at a point so
that such mirrors can be used to obtain
unblurred images of celestial bodies and
remote objects on the earth. Today, these
are used in the world's great telescopes.
Like
Newton, Ibn al-Haytham was interested in
vision. Three Greeks, Galen in
particular, did pioneering work on the
anatomy of the eye and its connections to
the brain, but did not produce a
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