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File:Ibn haithem portrait.jpg

Ibn al-Haytham depicted in a 10000 Iraqi Dinar note.

Abū ‘Alī al-Haṣan ibn al-Haṣan ibn al-Haytham (965–1040) (Arabic: أبو علي الحسن بن الحسن بن الهيثم, Latinised: Alhacen or (deprecated) Alhazen), was an Islamic mathematician, astronomer, and physicist, who made significant contributions to the principles of optics and the use of scientific experiments. He is sometimes called al-Basri (Arabic: البصري), after his birthplace Basra, Iraq, then part of Buwayhids dynasty, Persia . He is considered the father of optics for his writings on and experiments with lenses, mirrors, refraction and reflection.

The Alhazen crater on the Moon was named in his honour.

Life

He was born in Basra, Iraq then part of Buwayhids Shia Muslim dynasty, Persia and probably died in Cairo, Egypt .

Abū ‘Alī al-Haṣan ibn al-Haṣan ibn al-Haytham was one of the most eminent physicists, whose contributions to optics and the scientific method are outstanding. Known in the West as Alhacen or Alhazen, Ibn al-Haytham was born in 965 A. D. in Basrah, and was educated there and in Baghdad. 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. He later 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 colours. His book Kitab al-Manazir (Book of Optics) 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-Manazir, exerted a great influence upon Western science e.g. on the work of Roger Bacon who cites him by name 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-Haytham has discussed the density of the atmosphere and related it to altitude. 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 maintained that a body moves perpetually unless an external force stops it or changes its direction of motion. This is the first law of motion, later rediscovered by Galileo.

The list of his books runs to 200 or so, yet very few of the books have survived. Even his monumental treatise on optics survived only 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-Haytham'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.

Alhacen is featured on the obverse of the Iraqi 10,000 dinars banknote issued in 2003. The asteroid 59239 Alhazen was also named in his honour. And Iran's largest laser research facility, located in the Atomic Energy Organization of Iran headquarters in Tehran is named after Alhacen as well.

Works

Alhacen was a pioneer in optics, engineering and astronomy. According to Giambattista della Porta, Alhacen 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. Alhacen 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.

Alhacen'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) drastically transformed the ancient Greek understanding of vision. Such ancient Greeks as Euclid and Ptolemy believed that sight worked by the eye emitting some kind of rays. The second or "intromission" theory, supported by Aristotle had light entering the eye. Alhacen argued on the basis of common observations (the eye is dazzled or even injured if we look at a very bright light) and logical arguments (how could a ray proceeding from the eyes reach the distant stars the instant after we open our eye) to maintain that we cannot see by rays emitted from the eye. Alhacen developed a highly successful theory which explained the process of vision by rays proceeding to the eye from each point on the object.

Optics was translated into Latin by an unknown scholar at the end of the twelfth or the beginning of the thirteenth century. It was printed by Friedrich Risner in 1572, with the title Opticae thesaurus: Alhazeni Arabis libri septem, nuncprimum editi; Eiusdem liber De Crepusculis et nubium ascensionibus . This work enjoyed a great reputation during the Middle Ages. Works by Alhacen 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.

In his work on optics, Alhacen described sight as the inference of distinct properties of two similar and dissimilar objects. The eye perceives the size, shape, transparency (color and light), position, and motion from cognitive distinction which is entirely different from perceiving by mere sensation the characteristics of the object. The faculty of the mind, for Alhacen, includes perceiving through judgment and inference of distinct properties of similar objects outline and structure. Alhacen continues this body of work by concluding that the discrimination performed by the faculty of judgment and inference is in addition to sensing the objects visible form and not by pure sensation alone. We recognize visible objects that we frequently see. Recognition of an object is not pure sensation because we do not recognize everything we see. Ultimately, recognition does not take place without remembering. Recognition is due to the inference because of our mental capacity to conclude what objects are. Alhacen uses our ability to recognize species and likening their characteristics to that of similar individuals to support recognition associated and processed by inference. Alhacen further concludes that we are processing visual stimuli in very short intervals which allows us to recognize and associate objects through inference but we do not need syllogism to recognize it. These premises are stored infinitely in our souls. He is also credited to have invented the pinhole camera, but the idea was later credited by Della Porta for rediscribing how the camera works.

Notes

David C. Lindberg. Roger Bacon and the Origins of Perspectiva in the Middle Ages. Clarendon Press 1996, p. 11, passim.
D. C. Lindberg, Theories of Vision from al-Kindi to Kepler, (Chicago, Univ. of Chicago Pr., 1976), pp. 60-7.
A. C. Crombie, Robert Grosseteste and the Origins of Experimental Science, 1100 - 1700, (Oxford: Clarendon Press, 1971), p. 147, n. 2.

References

Lindberg, David C. Theories of Vision from al-Kindi to Kepler. Chicago: Univ. of Chicago Press, 1976. ISBN 0-226-48234-0
Omar, Saleh Beshara. Ibn al-Haytham's Optics: A Study of the Origins of Experimental Science. Minneapolis: Bibliotheca Islamica, 1977. ISBN 0882970151

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