A D V E N T U R E S in C Y B E R S O U N DAlhazen (Abu Ali Hasan Ibn al-Haitham) : 965 - 1039
Alhazen, Arabic (Abu Ali Hasan Ibn al-Haitham) (b. c.965, Basra, Iraq d. 1039, Cairo), mathematician and physicist who made the first significant contributions to optical theory since the time of Ptolemy (flourished 2nd century). In his treatise on optics, translated into Latin in 1270 as Opticae thesaurus Alhazeni libri vii, Alhazen published theories on refraction, reflection, binocular vision, focussing with lenses, the rainbow, parabolic and spherical mirrors, spherical aberration, atmospheric refraction, and the apparent increase in size of planetary bodies near the Earth's horizon. He was first to give an accurate account of vision, correctly stating that light comes from the object seen to the eye.
The ancient Greek studies of mathematics, philosophy, the arts and science would have been lost to us forever if the Arabs had not preserved and collected this legacy for all. In addition, through their annotations and studies they added to our knowledge. One of the most famous of these Arab scholars was Alhazen (Abu Ali Hasan Ibn al-Haitham). His studies included contributions to physics, especially optics and mathematics. Added to the Greek observation that incident and reflected light makes the same angle to the normal, the "Law of Reflection", the idea that both of these angles lie in the same plane. Also, disproved through experiment the notion suggested by Ptolemy that the ratio of the angles of the incident and refracted light is constant, but did not suggest a "Law of Refraction". Alhazen also suggested stars are self-luminous, that is they give of their own light, rather than merely reflecting light from the sun. He contributed to our ideas about sight. His study of the eye resulted in a description of its parts whose translation to English we use today, e.g. retina, cornea, vitreous humor and aqueous humor. His observations led him to support the suggestions of Democritus and Aristotle that the eye collects light and is not the source of light as had been suggested by Euclid and the Platonists.
Abu Ali Hasan Ibn al-Haitham Alhazen 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 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 travelled 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 colours. His book Kitab-al-Manadhir was translated into Latin in the Middle Ages, as also his book dealing with the colours 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 Bacon and Kepler. It brought about a great progress in experimental methods. His research in catoptrics centred 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 norrnal 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.
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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 A.D. 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. 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. Al-Hazen'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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