Nasıreddin Tusî

Mathematician, astronomer, politician (B. February 21st, 1201, Tus / Khorasan – D. June 25th, 1274, Baghdad). His full name was Ebu Ca'fer Muhammed İbn Muhammed İbnül-Hasan Nasıreddin. He was the pupil of Kemaleddin İbn Yunus and Muînüddin Sâlim, having realized that the mathematical system was about to get destroyed, he succeeded in establishing the system again when he was very young. Thanks to his having a brilliant command of Greek language, he managed to translate many Greek works related to mathematics and astronomy into the Persian and Arabic languages, far better than the ones who had made such translations up to that time. One of the greatest science historians of our time, G. Sarton, points out that the number of the works of Tusî was 61, and this indicates that Tusî showed great efforts in science. The subject fields of these works are arithmetic, geometry, trigonometry, astronomy, optics, mineralogy, geography, medicine, logic, philosophy, ethics, music, and literature.

            Among the positive science writers of the old East, it is rare to encounter with the writers who wrote their works as didactically, appropriately for today’s scientific methods, and systematically as Tusî. He was able to distinguish his own opinions and evidence from the former ones brought by the others, and state the opinions about which he thought as being superior to his opinions. So much so that, in his work titled Kitabı Şeklül Kutta, about the problem of solving the spherical triangles with known angles through the formula of “Şeklü’z Zilî” (tangents theorem), he declared modestly that he did not have the knowledge of a solution method that could be applied to all particular circumstances on the sphere.

            Tusî, bu eserinde Tusî, in Kitabı Şeklül Kutta, carried out such an extensive analysis on the topological synthesis of the various triangles and squares, formed of the big circles on the sphere that it made possible for the modern analytical methods to emerge easily. In short, Tusî, in this work, examined both the plane trigonometry and spherical trigonometry systematically. In this work, Tusî showed that he had deep knowledge of the problems related to the triangles and squares on the sphere. For example, about the solution of the spherical triangle that has known three angles, he was the first to think of the geometric conversion mechanism using the polar triangle, as we do today.

The proof of Euclid’s axiom of parallels, numbered 5, had been a big trouble for many Western mathematicians since the XVIII century. This axiom had not been proved, Euclidean geometry could only preserve its validity through its acceptance or substituting its equivalent. When Tusî came across the numbered 5 axiom, he tried substituting this axiom for a new one. With this new axiom, Tusî proved that the sum of the interior angles of a triangle equaled 180 degrees, and he immediately removed Euclid’s axiom. In the second Tahrir and Kitabı-Şerhi-Masadirat (the interpretation of the geometrical axioms), the 18^th book of Tahrir-ül-Mutavassıtat collection, there are many authentic opinions and findings of Tusî. In brief, Tusî, the brightest star of the world of mathematics of Greece and West, with his axiomatic thoughts, was a courageous pioneer of modern geometry.

At the beginning of the XIII century, positional astronomy was undergoing an unproductive period; the astronomical tables needed being restored. There was no trustworthy astronomical table except for Zic, resulted of the observations made by İbni Yunus in Cebeli Mokattam observatory, in Cairo. By the order of Hulagu, Tusî renovated the Maragheh Observatory. Then, he became a minister and inspector of the pious foundations. He protected his prestige in the palace until his death, even at the period of Abaqa Khan. When he took over Maragheh Observatory, he invited the scholars he trusted from Iraq, Syria, and Turkestan. Most of the devices at Maragheh Observatory were designed and produced by him. Maragheh Observatory had also a rich library, some historians say that this library had 400.000 books and booklets.

Astronomer Tusî wanted 30 years (approximate the time in which Saturn rotates around the Sun) from Hulagu for the restoration of the astronomical tables, providing the data belonging to the astronomical objects, and control and development of Greek and Arabic observations, made before him. Because Tusî had the aim of examining the movements of the planets in the solar system and the geometric codes related to those movements. Instead of the eccentricity or epicyclic systems which had been used to explain the movements of the planets up to his time, astronomer Tusî suggested a theory which was more systematic and convenient for explaining the movements simply. His works in the field of astronomy were collected in Tahrir-ül-Mıcısti, Ttezkere fi-ilmül Hey’e and Zici İlhani. Tusî shared his astronomical theories in Tezkere fil-il-mül Hey’e. In this work of his, Tusî benefited from the works of the great astronomers (Hipparchus, Ptolemy, Al-Battani, Ibn Yunus) who had lived before.

In his mature years, Tusî was imprisoned in famous Kal’atul mevt prison (death castle, 30 km away from Qazvin) by the Abbasid vizier Ibn al-Alkami who saw Tusî’s siding with Caliph Al-Musta'sim as a danger for himself. He was 55 years old when Hulagu released him in 1256. After that date, he spent the remaining eighteen years of his life in a secure and affluent environment, under the aegis of Hulagu. His political view revealed itself through his strong devotion to the doctrine of the Twelve Imams; in addition to his cleverness and ability, his devotion to the doctrine of the Twelve Imams made him the leader of Iranian Shias, who were in the minority against Mogols. Shiism, under the influence of Tusî, was guarded under the invasion of Mongols, and Shias could protect their sacred spaces in southern Mesopotamia.

Among the three mathematicians, Abu al-Wafa, Al-Harezmî and Nasir al-Din al-Tusî, who were the best in the fields of trigonometry, algebra, and geometry, Tusî was the brightest one. We saw the most advanced form of mathematics, especially the field of geometry, with him. He was a high quality man. Tusî, who approached even the oldest information in a critical way, was a great person who enjoyed working until the last day of his life. This well known Turkish scholar, who died in Baghdad, was buried around the mausoleum of Musa al-Kadhim, according to his own will.

Today, most of the works of him, including the original ones, rewritings, and translated works, are in Turkey and in the libraries of the world. Apart from the works below, there is a collection of him titled Tahrir-ül-Mutavassıta or Külliyatı Nasireddin. This collection, which mostly consists of the translated works of the old Greek mathematicians and astronomers, includes also one of his original works titled Kitab-ı fil Şekil Ma’ruf bil Kutla.

HIS WORKS:

MATHEMATICS: Tahrir-i Usul-ül Öklidis, Kitabı fil Şekil Ma’ruf bil Kutla, Tecrid fil Hendese, Kitab-ı Camiül Hesab fi’t Taht ve’t Türab, Kitab-ı Zafer fil Cebir vel Mukabele.

ASTRONOMY: Tahrir el Mıcıstî, Zic-i İlhanî, Tezkere fi ilmül Hey’e, Zic-üş-Şahî, Zübdetü’l İdrak fi Hey’etül Eflak.

  KAYNAKÇA: Prof. Dr. M. Fuad Köprülü /  XIII. Asırda Maraga Rasathanesi Hakkında Bazı Notlar (1942), “Türk Öklit’i Nasireddin Tusî” (Bilim ve Ütopya, Nisan 2000; Prof. Dr. Hamit Dilgan’ın 1956’da İTÜ Matbaasında basılmış “Büyük Türk Alimi Nesreddin Tusî” başlıklı broşürünün sadeleştirilerek yeniden basımı), İhsan Işık / Ünlü Bilim Adamları (Türkiye Ünlüleri Ansiklopedisi, C. 2, 2013) - Encyclopedia of Turkey’s Famous People (2013).