Abu
Ali Hasan Ibn al-Haitham was one of the most eminent physicists, whose
contributions to optics and the scientific methods are outstanding.
Known in the West as Alhazen, Ibn al-Haitham was born in 965 C.E. 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. Being unsuccessful in this, he feigned madness until the death
of Caliph al-Hakim. 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 examination of the passage of light through various
media and discovered the laws of refraction. He also carried out the
first experiments on the dispersion of light into its constituent
colors. His book Kitab-al-Manadhir 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 like
shadows, eclipses, the rainbow, and speculated on the physical nature
of light. He is the first to describe accurately 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 these extensive researches on optics, he has been considered
as the father of modern Optics.
The
Latin translation of his main work, Kitab-al-Manadhir, exerted a great
influence upon Western science e.g. on the work of Roger Bacon and
Kepler. It brought about a great progress in experimental methods. His
research in catoptrics centered 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
contain 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 Mizan al-Hikmah Ibn 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 19° below the horizon and
attempted to measure the height of the atmosphere on that basis. He
has also discussed the theories of attraction between masses, and it
seems that he was aware of the magnitude of acceleration due to
gravity.
His
contribution to mathematics and physics was extensive. In mathematics,
he developed analytical geometry by establishing linkage between
algebra and geometry. He studied the 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 and other languages. He has also written
on the subject of evolution a book that deserves serious attention
even today.
In
his writing, one can see a clear development of the scientific methods
as developed and applied by the Muslims and comprising the systematic
observation of physical phenomena and their linking together into a
scientific theory. This was a major breakthrough in scientific
methodology, as distinct from guess and gesture, and placed scientific
pursuits on a sound foundation comprising systematic relationship
between observation, hypothesis and verification.
Ibn
al-Haitham's influence on physical sciences in general, and optics in
particular, has been held in high esteem and, in fact, it ushered in a
new era in optical research, both in theory and practice.
