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Über dieses Buch

It would seem that S. Munk was the first modern scholar to draw attention to the significance of Levi ben Gerson's Astronomy, surely the most original work on astronomy written in Hebrew in the Middle Ages. Munk (1859, p. 500) called for a specialist to undertake a serious study of this work, but there was little response to his plea in the succeeding century. Indeed, this is the first edition of the Hebrew text of any part of Levi's Astronomy but for the table of contents (Renan, 1893, pp. 624-32), and the poems celebrating the invention of the Jacob Staff that appear in chapter 9 (Carlebach, 191Oa, pp. 152-53). The text of Levi's Astronomy is written in a ponderous Hebrew style but the content sparkles with originality. The Ptolemaic tradition is subjected to a profound critique based on the idea that the planetary models must conform both to Levi's own observations as well as those of the ancients, and the claim that astronomical theory must be philosophically sound. The enduring vigor of the Ptolemaic tradition has been characterized by O. Neugebauer as fol­ lows: "There is no better way to convince oneself of the inner coherence of ancient and medieval astronomy than to place side by side the Almagest, al­ BaWini's Opus astronomicum and Copernicus's De Revolutionibus. Chapter by chapter, theorem by theorem, table by table, these works run parallel" (1957, pp. 205-6).




Levi ben Gerson (1288–1344), sometimes called Gersonides or Leo de Balneolis, is well known as a philosopher, biblical exegete, mathematician, and astronomer (cf. Touati, 1973; and Feldman, 1984). He lived in Orange and occasionally visited Avignon where his brother Solomon was physician to Pope Clement VI. Although the family name was de Balneolis, there is no evidence that he himself was born or ever lived in Bagnols (cf. Shatzmiller, 1972, 1974). Levi did not cite any contemporaries and little is known of his life. More surprisingly, his scientific work was rarely cited in the subsequent literature, though a number of manuscript copies survive both in the original Hebrew and in Latin translations. The works on which Levi depended were all available in Hebrew and there is no reason to believe he read astronomical texts in Latin or in Arabic. A recent article has brought attention to a list of the books in Levi’s library that had not been properly identified in the manuscript catalogue (Weil, 1980, p. 590; cf. Loewinger and Weinryb, 1965, p. 32). Many of the 140 items concerned astronomy and, judging from the incomplete published list, they were all in Hebrew.
Bernard R. Goldstein


[1] Levi ben Gerson said: In previous books we alluded to explanations of some matters that will be explained in this book. [2] Our intention in this book is to investigate how it is possible to establish models for the celestial bodies and their parameters (mispar) in such a way that their observed motions are perfectly represented. [3] Moreover, they should produce agreement with the variation observed in the magnitudes of the planets as well as with physical principles. [4] Later we shall investigate the motions that belong to these celestial bodies with respect to their speeding up and slowing down, their retrograde and direct motions, their inclinations to the north and to the south, as well as all their other properties. [5] Then we shall investigate how the movers of the celestial bodies relate to one to another and how God relates to them, according to the ability of our mind.
Bernard R. Goldstein


In this chapter Levi indicates that his goal is to present an astronomical theory that is satisfactory both from a mathematical and a philosophical point of view. He remarks that this had not been achieved in the past, but he does not criticize any of his predecessors by name. In fact, there are very few authors cited anywhere in his astronomical writings, and none of them was his contemporary. We are told that to complete this task in astronomy, the investigator must be skilled in both mathematics and natural philosophy because this task cannot be split up (§§ 14–17). Levi’s views are similar to those of Ibn al-Haytham (see Introduction), and I am inclined to believe that Levi knew of them: for another example of similarities between the views of Levi and Ibn al-Haytham, see the commentary to chapter 2.
Bernard R. Goldstein


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