T.C. HARRAN ÜNĠVERSĠTESĠ ĠLAHĠYAT FAKÜLTESĠ

I. ULUSLARARASI KATILIMLI BĠLĠM DĠN VE FELSEFE TARĠHĠNDE HARRAN OKULU SEMPOZYUMU

28-30 Nisan 2006

I. CĠLT

Editör

Prof. Dr. Ali BAKKAL

ġANLIURFA 2006 I. Uluslararası Katılımlı Bilim, Din ve Felsefe Tarihinde Harran Okulu Sempozyumu 369

THE GREAT MUSLIM SCIENTIST THABIT IBN QURRA

Dr Qasim Taa'mneh*

bu'l Hasan Thabit ibn Qurra' Ibn Marwan al-Sabi al-Harrani was an Arab A astronomer and mathematician, who was known as Thebit in Latin. Thabit was born in 836 AD.at Harran (antique Carrhae), Mesopotamia (the land between the Tigris and Eupharates; site of several ancient civilizations) and died in Baghdad in 901 AD. Harran was an important center of astronomy and mathematics which was used to calculate the movement of planets, the prediction of eclipses and other astronomical events. It should not surprise us that such knowledge had survived a thousand years later in that city perhaps because Harranians refused to convert to Christianity and the planetary worship was still part of their religion which made such knowledge necessary. Thabit belonged to the sect of the Sabians,a name mentioned in Qoran which they adopted to join the ranks of the tolerated people. At times they have been confused with the Sabians (Mandanians who have been classified by scholars as Gnostic) living in southern Mesopotamia. This Sect lived in the vicinity of the main center of the Caliphate until 1258 AD, when the Mongols destroyed their last shrine. During Islamic rule, they were a protected minority, and around the time of al-Mutawakkil's reign their town became a center for philosophical, esoteric and medical learning. They were joined by the descendants of pagan Greek scholars who, having been persecuted in Europe, settled in lands that became part of the Abbasid caliphate. The Muslims were greatly interested in Greek culture and science, collecting and translating many ancient Greek works in the fields of philosophy and mathematics. The Sect, with strong Greek connections, had in earlier times adopted Greek culture, and it was common for members to speak Greek in addition to Arabic. There was another language spoken in southeastern Turkey, namely Syriac, which was based on the East Aramaic dialect of Odessa (now Sanli Urfa in Turkey). This language was Thabit ibn Qurra's native language, but he was fluent in both Greek and Arabic. Some resources mentioned that Thabit was a money changer as a young man.

* Dr., Yarmouk University, Department of Planning and Development, Irbed, Jordan 370 I. Uluslararası Katılımlı Bilim, Din ve Felsefe Tarihinde Harran Okulu Sempozyumu

This is quite possible but some historians do not agree; however, he inherited a large family fortune and must have come from a family of high standing in the community. The great Muslim mathematician Mohammed ibn Musa ibn Shaker, who visited Harran, impressed by Thabit's knowledge of languages, and realizing his potential for a scientific career, choose him to join the scientific group at Baghdad that was being patronized by the Abbasid Caliphs. In Baghdad Thabit received mathematical training and also medical training which was common for scholars of that time. In this way Thabit was able to contribute in several branches of science, notably mathematics, astronomy and mechanics, in addition to translating a huge number of works from Greek to Arabic. He was introduced to the Caliph Al-Ma'amun, and attained high favor at court. Thabit returned to Harran but his liberal philosophies led to a religious court appearance when he had to recant his 'heresies'. To escape further persecution he left Harran and returned to Baghdad, the most intellectually vibrant, and probably the largest city at that time, where he was appointed court astronomer. He occupied himself with mathematics, astronomy, mechanics, medicine and philosophy; he translated from Greek Apollonius, Archimedes, Euclid and Ptolemy. Thabit had revised translation of Euclid Elements of Hunayn ibn Ishaq and also had rewritten Hunayn's translation of Ptolemy's Almagest( the great book of an astronomical treatise) and translated Ptolemy's Geography, which later became very well-known. Thabit's translation of a work by Archimedes which gave a construction of a regular heptagon(a polygon with seven sides and seven angles. In regular heptagon all sides and all angles are equal) was discovered in the 20th century, the original having been lost. Thabit's major contribution lies in mathematics and astronomy. He was pioneer in extending the concept of traditional geometry to geometrical algebra and proposed several theories that led to the development of non-Euclidean geometry, spherical trigonometry, integral calculus and real numbers. He criticised a number of theorems of Euclid's elements and proposed important improvements. He applied arithmetical terminology to geometrical quantities, and studied several aspects of conic sections, notably those of parabola and ellipse. A number of his computations aimed at determining the surfaces and volumes of different types of bodies and constitute, in fact, the processes of integral calculus, as developed later. Another important aspect of Thabit`s work was his book on the composition of ratios; in this Thabit deals with arithmetical operations applied to ratios of geometrical quantities . The Greeks had dealt with geometric quantities but had not thought of them in the same way as numbers to which the usual rules of arithmetic could be applied . Thabit started a trend which led eventually to the generalization of the number concept by introducing arithmetical operations on quantities previously regarded as geometric and non-numerical. He also discussed parabolas , angle trisection and magic squares. Thabit`s work on probolas and paraboliods is of particular importance since it is one of the steps taken towards the discovery of the I. Uluslararası Katılımlı Bilim, Din ve Felsefe Tarihinde Harran Okulu Sempozyumu 371 integral calculus . Though he was familiar with Archimedes` results on the quadrature of the parabola , he did not have either of Archimedes` two treatises on the topic . Perhaps most impressive is his contribution to amicable numbers. Re-call , two numbers are called amicable if each number is the sum of the set of proper divisors of the other. Thabit discovered a beautiful rule for finding amicable numbers; he also criticized several theorems of Euclid`s elements and proposed important improvements. In astronomy Thabit was one of the early reformers of Ptolemaic views . He added the ninth sphere to Ptolemic astronomy and played a very important role in the establishment of astronomy as an exact science ( methods , topics and program) which developed along three lines. The theorization of the relation between observation and theory , the 'mathematisation' of astronomy , and the focus on the conflicting relationship between 'mathematical' astronomy and 'physical' astronomy Thabit analyzed several problems on the movements of sun and moon and wrote treatises on sundials(measures time by the position of the sun) . According to Copernicus Thabit determined the length of the sidereal year 365 days , 6 hours , 9 minutes and 12 seconds ( an error of 2seconds ) Copernicus based his claim on the latin text attributed to Thabit . In the fields of mechanics and physics he may be recognized as the establisher of statics . His book Kitab fi`l-qarastun ( The book on the beam balance ) on mechanics was of great importance . It was translated into Latin by Gherard of Cremona and became a popular work on mechanics. In this work Thabit proved the principle of equilibrium of levers and demonstrated that two equal loads , balancing a third , can be replaced by their sum placed at a point halfway between the two without destroying the equilibrium . After giving a generalisation Thabit then considers the case of equally distributed continuous loads and finds the conditions for the equilibrium of a heavy beam . Thabit left his legacy with his son ( Sinan), grandson (Ibrahim) and great grandson (Albattini) who also contributed substantially to our knowledge of geometry, astronomy and medicine. As Thabit himself Sinan was trained in medicine, a topic which his father had studied in Baghdad; he achieved his first major position in which he directed the hospitals and all medical activities in Baghdad. By 931 AD he had gained such authority that all doctors had to be tested by him before being allowed to practise. He awarded eight hundred certificates to medical doctors. Sinan also instituted traveling hospitals and inspected prisons to assure adequate health care. Ibrahim ibn Sinan was a son of Sinan ibn Thabit and a grandson of Thabit ibn Qurra. He had studied geometry in particular tangents to circles, and also studied the apparent motion of the Sun and the geometry of shadows. He was one of the most important mathematicians in the medieval Islamic world. Perhaps his early death in the age of thirty eight robbed him of the chance to make a contribution 372 I. Uluslararası Katılımlı Bilim, Din ve Felsefe Tarihinde Harran Okulu Sempozyumu even more important than that of his famous grandfather. Ibrahim's most important work was on the quadrature of the parabola where he introduced a method of integration more general than that of Archimedes. His grandfather Thabit ibn Qurra had started to view integration in a different way to Archimedes but Ibrahim realised that al-Mahani had made improvements on what his father had achieved. To Ibrahim it was unacceptable that al-Mahani's study should remain more advanced than his grandfather's and tried to do something to excel him. Ibrahim work on the motions of the sun is an astronomical work which discusses the motion of the solar apogee and also provides a critical analysis of the observations underlying Ptolemy's solar theory. The work on the astrolabe includes work on map projections, Ibrahim proves in this work that the stereographic projection maps circles which do not pass through the pole of projection on circles. Ibrahim is also considered the foremost Arab mathematician to treat with mathematical philosophy. Battani, Abu Abdallah Muhammad ibn Jabir ibn Sinan ibn Thabit the great grandson of Thabit, was a famous astronomer, mathematician and astrologer. He has been held as one of the greatest astronomists of Islam and he is responsible for a number of important discoveries in astronomy. Al-Battani determined with remarkable accuracy the obliquity of the ecliptic, the length of the seasons and the true and mean orbit of the sun. He found that the longitude of the sun's apogee had increased by 16°,47' since Ptolemy. This implied the important discovery of the motion of the solar apsides and of a slow variation in the equation of time. He proved, in sharp contrast to Ptolemy, the variation of the apparent angular diameter of the sun and the possibility of annular eclipses. He rectified several orbits of the moon and the planets and propounded a new and very ingenious theory to determine the conditions of visibility of the new moon. His excellent observations of lunar and solar eclipses were used by Dunthorne in 1749 to determine the secular acceleration of motion of the moon. He also provided very neat solutions by means of orthographic projection for some problems of spherical trigonometry. In mathematics, he was the first to replace the use of Greek chords by sines, with a clear understanding of their superiority. He also developed the concept of cotangent and furnished their table in degrees. Among Thabit's writings a large number have survived, while several are not extant. Most of the books are on mathematics, followed by astronomy and medicine. The books have been written in Arabic but some are in Syriac, which was the eastern Aramaic dialect from Odessa. In the middle Ages, Gherard of Cremona translated some of his books into Latin. In recent centuries, a number of his books have been translated into European languages and published. He carried further the work of the Banu Musa brothers and later his sons and grandsons continued in this tradition, with the help of other members of the group. No doubt that their contributions especially in Mathematics and Astronomy, were extremely influential and of great consequence in the development of these sciences. I. Uluslararası Katılımlı Bilim, Din ve Felsefe Tarihinde Harran Okulu Sempozyumu 373

List of references 1. Biography in Dictionary of Scientific Biography (New York 1970-1990). 2. Biography in Encyclopaedia Britannica. 3. Encyclopedia of history of Arabic Science. Roshdi Rashed and Regis Morelon. Vol 1-3.London:Routledge, 1996. 4. (Philip Hitti, "History of the Arabs", Princeton University Press, 10th edition, Macmillan st. Martine Press. 5. F J Carmody, The Astronomical Works of Thabit b. Qurra (Berkeley-Los Angeles, 1960). 6. E A Moody and M Clagett (eds.), The medieval science of weights, Treatises ascribed to Euclid, Archimedes, Thabit ibn Qurra, Jordanus de Nemore, and Blasius of Parma (Madison, Wis., 1952). 7. R Rashed, The development of Arabic mathematics : between arithmetic and algebra (London, 1994). 8. S Brentjes and J P Hogendijk, Notes on Thabit ibn Qurra and his rule for amicable numbers, Historia Math. 16 (4) (1989), 373-378. 9. Y Dold-Samplonius, The 'Book of assumptions', by Thabit ibn Qurra (836-901), in History of mathematics (San Diego, CA, 1996), 207-222. 10. J P Hogendijk, Thabit ibn Qurra and the pair of amicable numbers 17296, 18416, Historia Math. 12 (3) (1985), 269-273. 11. K P Moesgaard, Thabit ibn Qurra between Ptolemy and Copernicus : an analysis of Thabit's solar theory, Arch. History Exact Sci. 12 (1974), 199-216. 12. R Morelon, Tabit b. Qurra and Arab astronomy in the 9th century, Arabic Sci. Philos. 4 (1) (1994), 6; 111-139. 13. A I Sabra, Thabit ibn Qurra on the infinite and other puzzles : edition and translation of his discussions with Ibn Usayyid, Z. Gesch. Arab.-Islam. Wiss. 11 (1997), 1-33 14. A Sayili, Thabit ibn Qurra's generalization of the Pythagorean theorem, Isis 51 (1960), 35-37.