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- > - > Abu 'Ali Al-Hasan bin Al-Haytham (965-1040 C.E.)
was one of the most eminent physicists, whose contributions to optics
and scientific methods are outstanding. Known in the West as Alhazen,
Ibn Al-Haytham was born in 965 CE in Basrah, and was educated in
Basrah and Baghdad.Thereafter, he went to Egypt, where he was asked to
find ways of controlling the flood of the Nile.
After failing in his attempt to regulate the flow of the Nile, Ibn
Al-Haytham feared that al-Hakim would punish him. To avoid punishment,
he pretended to be insane until al-Hakim's death. He also traveled to
Spain and during this period, he had ample time for his scientific
pursuits, which included optics, mathematics, physics, medicine and
development of scientific methods -- on each of which he has left
several outstanding books.
He made a thorough examinationof the passage of light through various
media and discovered thelaws of refraction. He also carriedout the
first experiments on the dispersion of light into its constituent
colors. His book Kitaab-al-Manaadhir was translated into Latin in the
MiddleAges, as also his book dealing with the colors of sunset. He
dealt at length with the theory ofvarious physical phenomena like
shadows, eclipses, the rainbow and speculated on the physical nature
of light.
Ibn Al-Haytham is the first to accurately describe the various parts
of the eye and give a scientific explanation of the process of vision.
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 . He contradicted Ptolemy's and Euclid's theory of vision,
that objects are seen by rays of light emanating from the eyes;
according to him the rays originate in the object of vision and not in
the eye. Through theseextensive researches on optics, he has been
considered as the Father of Modern Optics.
The Latin translation of his main work, Kitaab-al-Manaadhir , exerted
a great influence upon Western science, for example on the work of
Roger Bacon and Kepler. It brought about great progress in
experimental methods. His research in catoptrics centered on spherical
and parabolic mirrors and spherical aberration. He made theimportant
observation that the ratio between the angle of incidence and
refraction does notremain constant and investigatedthe 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.
In his book Meezaan al-Hikmah , Ibn Al-Haytham has discussed
thedensity of the atmosphere and developed a relation between it and
the elevation. He also studiedatmospheric refraction. He discovered
that the twilight only ceases or begins when the sun is 19° below the
horizon and attempted to measure the heightof the atmosphere on that
basis. He has also discussed the theories of attraction between
masses, and it seems that he wasaware of the magnitude of acceleration
due to gravity.
Ibn Al-Haytham's contribution to mathematics and physics was
extensive. In mathematics, he developed analytical geometry
byestablishing a link between algebra and geometry. He studiedthe
mechanics of motion of a body, and was the first to maintain that a
body moves perpetually unless an external force stops it or changes
its direction of motion. This would seem equivalent to the first law
of motion.
The list of his books runs to 200 or so, very few of which have
survived. Even his monumental treatise on optics survived through its
Latin translation. During the middle Ages, his books on cosmology were
translated into Latin, Hebrew andother languages. He has also written
on the subject of evolution, a book that deserves serious attention
even today.
In his writing, one can see clear development of the scientific
methods as developed and applied by the Muslims, comprising the
systematic observation of physical phenomena and their linking
together into a scientific theory. This was a major breakthrough
inscientific methodology, making itdistinct from guess-work and
conjecture, and placed scientific pursuits on a sound foundation
comprising systematic relationship between observation, hypothesis and
verification.
Ibn Al-Haytham's influence on physical sciences in general and optics
in particular, has been heldin high esteem and, in fact, it ushered in
a new era in optical research, both in theory and practice.
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