Абрахам бар Ḥия: Математик, астроном және философ

Mathematician, astronomer, astrologer

Abraham bar Ḥiyya ha Nasi (;
c. 1070 – 1136 or 1145), also known as Abraham Savasorda, Abraham Albargeloni, and Abraham Judaeus, was a Catalan Jewish mathematician, astronomer and philosopher who resided in Barcelona. Bar Ḥiyya was active in translating the works of Islamic science into Latin and was likely the earliest to introduce algebra from the Muslim World into Christian Europe. He also wrote several original works on mathematics, astronomy, Jewish philosophy, chronology, and land surveying. His most influential work is his Ḥibbur ha Meshiḥah ve ha Tishboret, translated in 1145 into Latin as Liber embadorum. A Hebrew treatise on practical geometry and algebra, the book contains the first known complete solution of the quadratic equation , and influenced the work of Leonardo Fibonacci.

Abraham bar Ḥiyya was the great grandson of Hezekiah ben David, the last Gaon of the Talmudic academies in Babylonia. Bar Ḥiyya occupied a high position in the royal court, serving as minister of police, and bore the title of governor (נשיא). Scholars assume that Bar Hiyya would have obtained this title in the court of Banu Hud of Saragossa Lerida; there is even a record of a Jewish Savasorda there in the beginning of the 12th century. In his travelogues, Benjamin of Tudela mentions bar Ḥiyya living in Barcelona in the 1160s. According to Adolph Drechsler, bar Ḥiyya was a pupil of Moshe haDarshan and teacher of Abraham ibn Ezra. He was held in high consideration by the ruler he served on account of his astronomical knowledge and had disputes with learned priests, to whom he demonstrated the accuracy of the Jewish calendar. Abraham bar Hiyya is said to have been a great astronomer and wrote some works on astronomy and geography. One tells about the form of the earth, the elements and the structure of the spheres. Other works included papers on astrology, trigonometry, and music. Some scholars think that the Magister Abraham who dictated De Astrolabio (probably at Toulouse) to Rudolf of Bruges (a work that the latter finished in 1143) was identical with Abraham bar Ḥiyya. Although the title "Sephardi" is always appended to his name, Barcelona was at the time no longer under Muslim rule, and therefore not part of Sepharad. Abraham Albargeloni (i. e., from Barcelona) thus belonged to the community of the Jews of Catalonia. Catalonia joined Provence in 1112 and Aragon in 1137, and thus the County of Barcelona became the capital of the Catalan Aragonese Confederation called the Crown of Aragon. The kings of the Crown of Aragon extended their domains to Occitania in what is now southern France. Abraham Albargeloni spent some time in Narbonne where he composed some works for the Jews of Provence, in which he complains of their Provençal Jewry's ignorance of mathematics.

Abraham bar Ḥiyya was one of the most important figures in the scientific movement which made the Jews of Provence, the Jews of Catalonia, Spain, and Italy the intermediaries between Arabic science and the Christian world, in both his original works and his translations. Bar Ḥiyya's Yesode ha Tebunah u Migdal ha Emunah (יסודי התבונה ומגדל האמונה), usually referred to as the Encyclopedia, was the first European attempt to synthesize Greek and Arabic mathematics. Likely written in the first quarter of the 12th century, the book is said to elaborate on the interdependence of number theory, mathematical operations, business arithmetic, geometry, optics, and music. The book draws from a number of Greek sources then available in Arabic, as well as the works of al Khwarizmi and Al Karaji. Only a few short fragments of this work have been preserved. Bar Ḥiyya's most notable work is his Ḥibbur ha Meshiḥah ve ha Tishboret (חיבור המשיחה והתשבורת), probably intended to be a part of the preceding work. This is the celebrated geometry translated in 1145 by Plato of Tivoli, under the title Liber embadorum a Savasordo in hebraico compositus. Fibonacci made the Latin translation of the Ḥibbūr the basis of his Practica Geometriae, following it even to the sameness of some of the examples. Bar Ḥiyya also wrote two religious works in the field of Judaism and the Tanach: Hegyon ha Nefesh ("Contemplation of the Soul") on repentance, and Megillat ha Megalleh ("Scroll of the Revealer") on the redemption of the Jewish people. The latter was partly translated into Latin in the 14th century under the title Liber de redemptione Israhel. Even these religious works contain scientific and philosophical speculation. His Megillat ha Megalleh was also astrological in nature, and drew a horoscope of favourable and unfavourable days. Bar Ḥiyya forecasted that the Messiah would appear in AM 5118 (1358 CE). Abraham bar Ḥiyya wrote all his works in Hebrew, not in Judaeo Arabic of the earlier Jewish scientific literature, which made him a pioneer in the use of the Hebrew language for scientific purposes.

"Form of the Earth" , an astronomical work on the formation of the heavens and the earth, which was to have been followed by a second part on the course of the stars. A portion was translated into Latin by Sebastian Münster and Erasmus Oswald Schreckenfuchs. It appears also that complete translations into Latin and French were made. The Bodleian Library contains a copy with a commentary, apparently by Ḥayyim Lisker. "Calculation of the Courses of the Stars" , the sequel to the preceding work, which is found sometimes in manuscripts with the notes of Abraham ibn Ezra. "Tables" or "Tables of the Prince" (, Luḥot ha Nasi), astronomical tables, called also the "Tables of Al Battani" and the "Jerusalem Tables". There remains doubt as to the particulars: a number of Jewish translators named Abraham existed during the 12th century, and it is not always possible to identify the one in question. Known translations of bar Ḥiyya include:
De Horarum Electionibus, the well known treatise of Ali ben Aḥmad al Imrani. Capitula Centiloquium, astrological aphorisms. A commentary of Aḥmad ibn Yusuf on the Centiloquium, attributed to Ptolemy. De Astrolabio of Rudolph de Bruges. Liber Augmenti et Diminutionis, a treatise on mathematics. In the preface to Ẓurat ha Areẓ, bar Ḥiyya modestly states that, because none of the scientific works such as those which exist in Arabic were accessible to his brethren in France, he felt called upon to compose books which, though containing no research of his own, would help to popularize knowledge among Hebrew readers. His Hebrew terminology, therefore, occasionally lacks the clearness and precision of later writers and translators.

Bar Ḥiyya was a pioneer in the field of philosophy: as shown by Guttmann in refutation of David Kaufmann's assumption that the Hegyon ha Nefesh was originally written in Arabic, Abraham bar Ḥiyya had to wrestle with the difficulties of a language not yet adapted to philosophic terminology. Whether composed especially for the Ten Days of Repentance, as Rapoport and Rosin think, or not, the object of the work was a practical, rather than a theoretical, one. It was to be a homily in four chapters on repentance based on the Hafṭarot of the Day of Atonement and Shabbat Shuvah. In it, he exhorts the reader to lead a life of purity and devotion. At the same time he does not hesitate to borrow ideas from non Jewish philosophers, and he pays homage to the ancient Greek philosophers who, without knowledge of the Torah, arrived at certain fundamental truths regarding the beginning of things, though in an imperfect way, because both the end and the divine source of wisdom remained hidden to them. In his opinion the non Jew may attain to as high a degree of godliness as the Jew.

Bar Ḥiyya's Ḥibbur ha meshīḥah ve ha tishboret contains the first appearance of quadratic equations in the West. Bar Ḥiyya proved by the method of indivisibles the following equation for any circle: , where is the surface area, is the circumference length and is radius. The same proof appears in the commentary of the Tosafists (12th century) on the Babylonian Talmud.