Alhazen

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Alhazen Abu Ali al-Hasan Ibn Al-Haitham (also: Ibn al Haythen), (965-1040), was an Persian mathematician; he is sometimes called al-Basri, after his birthplace.

Life

Alhazen was born at Basra, then part of Buwayhid Persia, now part of Iraq (See [1] and [2]), and probably died in Cairo, Egypt.

One account of his career has him summoned to Egypt by the mercurial caliph Hakim to regulate the flooding of the Nile. After his field work made him aware of the impracticality of this scheme, and fearing the caliph's anger, he feigned madness. He was kept under house arrest until Hakim's death in 1021. During this time he wrote scores of important mathematical treatises.

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 aI-Hautham was born in 965 A. D. 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-at-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 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-at-Manazir, 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 19o 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.

Works

Alhazen was a pioneer in optics, engineering and astronomy. According to Giambattista della Porta, Alhazen was the first to explain the apparent increase in the size of the moon and sun when near the horizon, although Roger Bacon gives the credit of this discovery to Ptolemy. Alhazen also taught that vision does not result from the emission of rays from the eye, and wrote on the refraction of light, especially on atmospheric refraction, for example, the cause of morning and evening twilight. He solved the problem of finding the point on a convex mirror at which a ray coming from one point is reflected to another point.

Alhazen's extensive writings influenced many Western intellectuals such as Roger Bacon, John Pecham, Witelo, and Johannes Kepler.

Optics

His seven volume treatise on optics Kitab al-Manazir (Book of Optics) (written from 1015 to 1021) is possibly the earliest work to use the scientific method. The ancient Greeks believed that truth was determined by the logic and beauty of reasoning; experiment was used as a demonstration. Alhazen used the results of experiments to test theories. The "emission" theory of light had been supported by Euclid and Ptolemy. This theory postulated that sight worked by the eye emitting light. The second or "intromission" theory, supported by Aristotle had light entering the eye. Alhazen performed experiments to determine that the "intromission" theory was scientifically correct.

Optics was translated into Latin by Witelo in 1270. It was published by Friedrich Risner in 1572, with the title Oticae thesaurus Alhazeni libri VII., cum ejusdem libro de crepusculis et nubium ascensionibus. This work enjoyed a great reputation during the Middle Ages. Works by Alhazen on geometrical subjects were discovered in the Bibliothèque nationale in Paris in 1834 by E. A. Sedillot. Other manuscripts are preserved in the Bodleian Library at Oxford and in the library of Leiden.

Other Alhazens

There is another Alhazen who translated Ptolemy's Almagest in the 10th century.

Bibliography

Ibn al-Haytham's Optics: A Study of the Origins of Experimental Science, by Saleh Beshara Omar (Bibliotheca Islamica, 1977)

External links

See also

ar:ابن الهيثم de:Alhazen es:Alhazen fr:Alhazen gl:Alhazen ka:იბნ ალ-ჰაისამი ms:Abul Wafa Muhammad Al-Buzjani nl:Ibn al-Haytham no:Al-Haitham pl:Ibn al-Hajsam pt:Alhazen sl:Ibn al-Haitam