Abraham ibn Ezra the Spaniard (d. 1167) was one of the foremost transmitters of Arabic science to the West. His astrological and astronomical works, written in Hebrew and later translated into Latin, were considered authoritative by many medieval Jewish and Christian scholars. Some of the works he translated from Arabic are no longer extant in their original form, and on occasion his treatises provide information about earlier sources that is otherwise poorly preserved, if at all. Ibn Ezra seems to be the earliest scholar to record one of the seven methods for setting up the astrological houses, and this method was subsequently used by Levi ben Gerson (d. 1344) in southern France.

Euclid discusses the ex aequali relationship twice in the Elements. The first is in Book V (based on definitions 17 and 18, propositions 22 and 23), during his discussion of arithmetical relations between mathematical magnitudes in general. The second is in Books VII–IX (developed using proposition VII,14), where he focuses on arithmetical relations in the case of numbers only. Although the distinction between mathematical magnitudes in general and numbers in particular often seems somewhat forced to contemporary philosophers, it was apparently very real to Euclid. Because Euclid seemed so conscious of the differences between the subject matter of Book V (magnitudes) and Books VII–IX (numbers), he was not much troubled by the differences between his treatment of ex aequali ratios in these two contexts. Later generations of mathematicians, however, found these differences less acceptable and tried to minimize them in various ways. This paper summarizes Euclid's use of the ex aequali relation in developing his mathematics. The paper then outlines the fate of the post-Theonine Greek attempts to “improve” the Euclidean discussion when the Elements entered the Arabic/Islamic intellectual tradition. The study concludes with the attempts by Ibn al-Hayṯam and Ibn al-Sarī to improve the parallelism between the discussions of ex aequali ratios in Book V and Book VII.

The editing of three anonymous Greek texts preserved in the Parisinus Suppl. gr. 643 allows us to clarify certain ideas on the transmission of knowledge in the Mediterranean during the second half of the 13th century. These texts – an introduction to the Physics of Aristotle, one to De generatione et corruptione and a page of Medical Problems – are in fact translations from Latin probably made at Salerno at the end of the Norman period or at the beginning of the Angevin dynasty. They allow us to establish the influence of the Parisian Faculty of Arts on the Sicilian intellectual milieu of the period and to illustrate how, whilst remaining true to its medical vocation, the University of Salerno evolved nonetheless towards a model of general education in the Arts. Finally these texts reveal the considerable influence – both philological and doctrinal – of Arabic learning on the Aristotelian teaching of their author. This very fact, combined with the presence of the Parisinus in Byzantium, in an environment of advanced philological learning, a few decades after its composition, leads us to question our understanding of the Palaeologan Renaissance as well as its independence with regard to the Arabo-latin scholarly tradition of the 13th century.

The Compendium of the Almagest of Averroes, extant only in Hebrew translation, remains unpublished and hardly studied. The present article aims to make it known. It provides a history of the Compendium: its date of writing, translation into Hebrew, and the transmission, reception, and audience of the Hebrew translation, as well as a preliminary study of the text. This includes an annotated outline of its contents, and a discussion of its sources and their critical use by Averroes. The article also contains a translation of significant extracts from the Prologue, with a brief analysis. The Compendium provides direct and relatively early evidence from a leading protagonist of the 12th-century movement by Andalusian thinkers – mostly Aristotelian philosophers – to criticize and reform Ptolemean astronomy.

This article analyzes new material on the history of the amicable numbers. It discusses Hebrew texts which throw new light on the diffusion in Medieval Europe of Ṯābit ibn Qurra's (9th century) work. We find Ṯābit's theorem on amicable numbers in a Hebrew translation, made in Saragossa in 1395, of an arithmetical commentary written by Abū al-Ṣalt al-Andalusī (ca. 1068–1134), and also in an original Hebrew text probably written by the Jewish Provençal scholar Qalonymos ben Qalonymos (1287 – after 1329). These texts lend strong support to the surmise that the Arabic tradition concerning amicable numbers could not have remained unknown to European mathematicians before the work of Descartes and Fermat in the 17th century.

There are three principal philosophical-scientific encyclopaedias written in Hebrew during the Middle Ages: Yehudah ha-Cohen's Midrash ha-Ḥokmah (1245–1247), Shem Tov ibn Falaquera's De'ot ha-Filosofim (ca. 1270) and Gershon ben Shlomoh's Sha'ar ha-Shamayin (end of the 13th century). All three include detailed treatments of zoology, and the last two of botany and mineralogy as well. The principal feature of their treatments is their “theoretical” – not merely “descriptive” – approach: these encyclopaedias do not contain only lists of stones, plants and animals (such as other Arabic and Latin Medieval encyclopaedias), but also attempts at systematization and philosophical arrangement of the various available theories in the fields of mineralogy, botany and zoology qua sciences. An examination of the doctrines and the sources of these texts shows that, while the treatment of zoology relies upon Aristotle's zoological works and, above all, their Compendia by Averroes, the treatment of mineralogy and botany reflects the non-Aristotelian theories of the Brethren of Purity (Iḫwān al-Ṣafā'), rather than such texts as pseudo-Aristotle's De lapidibus and Nicolaus Damascenus' De plantis. In particular, Falaquera's encyclopaedia represents the most convincing effort to provide a truly scientific discussion of mineralogy and botany, comparable to that of his contemporary Albert the Great, and based upon the Brethren, Avicenna and, maybe, some lost works by Averroes.

The Hebrew text On the Heavens and the World, ascribed to Ibn Sīnā, is an interesting and intriguing composition. It dates from the 13th century and was quite influential. It is not a translation of any text of Ibn Sīnā known to us, but is related to the (pseudo-Avicennian) Latin De celo et mundo, which appears in the 1508 Venice edition of translations of Ibn Sīnā. The Latin and Hebrew texts differ widely and the relation between them is far from being clear. Both are in sixteen chapters, the titles of the chapters are the same, but the texts are only roughly similar. The Hebrew text often offers short, incomplete summaries of the Latin arguments. On the other hand it includes many passages which have no parallel in the Latin. There are two possible explanations of the perplexing relationship between the two texts: either that there was more than one version of the Latin (or of the original Arabic) text, or that the translator, Shlomo ben Moshe of Laguiri wrote a kind of paraphrase. The paper shows that the second explanation is correct and offers a preliminary study of the sources and the aims of the Hebrew text.

R. Saadia Ga'on (882–942) of Baghdad sought to avoid anthropomorphism by arguing that scriptural phrases which seem to ascribe materiality to the Deity in fact refer not to God Himself, but rather to a created entity, God's Glory, which he described as a very tenuous “air.” This paper argues that Saadia's conception of a quasi-divine “air” through which God accomplishes His acts in the material world is heavily indebted to the Stoic theory of pneuma. It follows that the immanentist theology of Ḥasidey Ashkenaz (German Pietists), which is known to have been substantially influenced by Saadia, in fine is also indebted to Stoic philosophy and physics.

For many centuries Jews in Arabic-speaking lands have transcribed books written by non-Jews into the Hebrew alphabet; the language remains Arabic, but the writing is Hebrew. This was done mainly for the benefit of those who knew the Arabic language but not the script. The majority of these transcriptions are scientific or philosophical texts. Transcriptions are of value to scholars for two reasons. Some entire texts, or more complete or accurate versions of texts, are preserved only in transcription. In addition, the choice of texts transcribed is very instructive concerning the cultural and intellectual interests of Jews. A century ago the great bibliographer Moritz Steinschneider published a description of the transcriptions known to him. We have undertaken to prepare a full catalogue. In this article we offer a preliminary relisting of those manuscripts that we have examined recently.