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ABU ALI HASAN IBN AL-HAITHAM (ALHAZEN) (965 - 1040
C.E.)
Al-Haitham, known in the West as Alhazen, is considered
as the father of modern Optics. Abu Ali Hasan Ibn al-Haitham
was one of the most eminent physicists, whose contributions
to optics and the scientific methods are outstanding.
Ibn al-Haitham was born in 965 C.E. in Basrah (present
Iraq), and received his education in Basrah and Baghdad.
He traveled to Egypt and Spain. He spent most of his
life in Spain, where conducted research in optics, mathematics,
physics, medicine and development of scientific methods.
Al-Haitham conducted experiments on the propagation
of light and colors, optic illusions and reflections.
He examined the refraction of light rays through transparent
medium (air, water) and discovered the laws of refraction.
He also carried out the first experiments on the dispersion
of light into its constituent colors. In detailing his
experiment with spherical segments (glass vessels filled
with water), he came very close to discovering the theory
of magnifying lenses which was developed in Italy three
centuries later. It took another three centuries before
the law of sines was proposed by Snell and Descartes.
His book Kitab-al-Manazir was translated into Latin
in the Middle Ages, as also his book dealing with the
colors of sunset. He dealt at length with the theory
of various physical phenomena such as the rainbow, shadows,
eclipses, and speculated on the physical nature of light.
Roger Bacon (thirteenth century), Pole Witelo (Vitellio)
and all Medieval Western writers on Optics base their
optical work primarily on Al-Haitham's 'Opticae Thesaurus.'
His work also influenced Leonardo da Vinci and Johann
Kepler. His approach to optics generated fresh ideas
and resulted in great progress in experimental methods.
Al-Haitham was the first to describe accurately the
various parts of the eye and gave a scientific explanation
of the process of vision. He contradicted Ptolemy's
and Euclid's theory of vision that the eye sends out
visual rays to the object of the vision; according to
him the rays originate in the object of vision and not
in the eye. He also attempted to explain binocular vision,
and gave a correct explanation of the apparent increase
in size of the sun and the moon when near the horizon.
He is known for the earliest use of the Camera obscura.
Through these extensive researches on optics, he has
been considered as the father of modern Optics.
In Al-Haitham's writings, one finds a clear explanation
of the development of scientific methods as developed
and applied by the Muslims, the systematic observation
of physical phenomena and their relationship to a scientific
theory. This was a major breakthrough in scientific
methodology, as distinct from guess work, and placed
scientific study on a sound foundation comprising systematic
relationship between observation, hypothesis and verification.
His research in catoptrics focused on spherical and
parabolic mirrors and spherical aberration. He made
the important observation that the ratio between the
angle of incidence and refraction does not remain constant
and investigated the magnifying power of a lens. His
catoptrics contains the important problem known as Alhazen's
problem. It comprises drawing lines from two points
in the plane of a circle meeting at a point on the circumference
and making equal angles with the normal at that point.
This leads to an equation of the fourth degree. He also
solved the shape of an aplantic surface for reflection.
In his book Mizan al-Hikmah, Al-Haitham has discussed
the density of the atmosphere and developed a relation
between it and the height. He also studied atmospheric
refraction. He discovered that the twilight only ceases
or begins when the sun is 19o below the horizon and
attempted to measure the height of the atmosphere on
that basis. He deduced the height of homogeneous atmosphere
to be fifty-five miles.
Al-Haitham's contribution to mathematics and physics
is extensive. In mathematics, he developed analytical
geometry by establishing linkage between algebra and
geometry. In Physics, he studied the mechanics of motion
of a body and was the first to propose that a body moves
perpetually unless an external force stops it or changes
its direction of motion. This is strikingly similar
to the first law of motion. He has also discussed the
theories of attraction between masses, and it appears
that he was aware of the magnitude of acceleration due
to gravity.
Al-Haitham wrote more than two hundred books, very
few of which have survived. His monumental treatise
on optics has survived through its Latin translation.
During the Middle Ages his books on cosmology were translated
into Latin, Hebrew and other European languages. Also,
he wrote a book on the subject of evolution; the ideas
contained in that book are worth reading and useful
even today.
Al-Haitham's influence on physical sciences in general,
and optics in particular, has been held in high esteem
and his ideas heralded in a new era in both the theoretical
and experimental optical research. He wrote commentaries
on Aristotle, Galen, Euclid and Ptolemy. Beer and Medler
in their famous work Der Mond (1837) mention one of
the surface features of the moon after Alhazen. It is
the name of a ring-shaped plain to the west of the hypothetical
Mare Crisium in Section No. 12.
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