The Light of the World

Robert G. Morrison’s book provides the first comprehensive study of the astronomical treatise The Light of the World. It was composed in Judeo-Arabic by Joseph Ibn Naḥmias, who flourished around the turn of the 15th century in the Iberian Peninsula. There is also a later Hebrew recension, which may have been written by Ibn Naḥmias himself, or at least during his lifetime. The kernel of The Light of the World is the structure of the cosmos. Ibn Naḥmias grapples with two opposing world views. The first is Aristotelian, based on the elegant theory that the cosmos is modelled on nine concentric nesting orbs. The Aristotelian world view was able to account for phenomena on earth, but it was unable to provide either accurate astronomical predictions or account for celestial observations, for example the “motion” of the sun around the earth. The second, astronomically superior, theory is Ptolemaic, at the heart of which lie two- and three-dimensional non-concentric motions, such as the eccentric solar model. Ptolemy’s mathematical models became the dominant doctrine in medieval astronomy. Notwithstanding, Ptolemy’s clear breach of the elegant philosophical doctrine of homocentric astronomy did not make the latter disappear. In fact, the Aristotelian Weltanschauung had strong foothold among several leading medieval Muslim and Jewish thinkers, including Maimonides. Furthermore, the Andalusian Revolt against Ptolemaic astronomy during the 11th and 12th centuries (or the Maragha revolution in the 13th and 14th centuries) derived from the conviction that mathematical astronomy alone could not reflect reality. A prominent figure  in the Andalusian revolt was the astronomer Al-Biṭrūjī; and Ibn Naḥmias, less than two centuries later in his Light of the World, further attempted to show that it was indeed possible to devise a homocentric astronomy which could also provide accurate prediction. As demonstarted in Morrison’s book, Ibn Naḥmias was able to improve upon Al-Biṭrūjī’s models.

Morrison’s book is divided into eight chapters, preceded by a detailed introduction which presents the importance of the study of The Light of the World, its textual and historical contexts, its table of contents, the manuscripts and editorial principles, the author, the history of homocentric models, and the distinctive innovations of Ibn Naḥmias’s models. Chapter 1 contains a critical edition of the Judeo-Arabic text, followed by its English translation and diagrams in chapter 2. Chapters 3 and 4 provide the Hebrew recension of The Light of the World and its English translation, respectively. Chapters 5 and 6 are dedicated to a scientific commentary on the Judeo-Arabic text and the novel contributions in the Hebrew recension, respectively. Chapters 7 and 8 present the Hebrew text of Profiat Duran’s response to The Light of the World and its English translation, respectively. Preceding the bibliography and the index at the end of the book, there is a precious glossary of Judeo-Arabic, Hebrew, and English technical terms. As a researcher of medieval Hebrew and Arabic scientific vocabulary, I was delighted to find the Hebrew trigonometric term beq’a designating “sine”–jaib in Judeo-Arabic—(400). The Hebrew term had been coined by Isaac Israeli in his calendrical book Yesod ‘Olam (The Foundation of the World), composed in the Jewish year 5070, which corresponds to 1309/10 CE (14). Until I read Morrison’s book I had been unable to find any other adoption of Israeli’s word in any other medieval Hebrew scientific treatise.  

To summarize, it is easy to see that the dominant Ptolemaic paradigm, the harsh criticism of The Light of the World by Profiat Duran (already during Ibn Naḥmias’s lifetime), and modern criticism, could have thrown The Light of the World into eternal oblivion, but Morrison’s meritorious book has saved it. Furthermore, this book is an important contribution to the ongoing multifocal enterprise of publishing, translating, and fully analyzing medieval treatises in Hebrew and Judeo-Arabic in their own right, regardless of how important, interesting, or scientifically accurate they appear to be. It provides the wider public access to manuscripts which are physically or linguistically inaccessible. By bringing this ignored text to full light, Morrison has successfully shown that, despite the existing prejudices against The Light of The World, it has a place within the history of astronomy, not only in the middle ages but also in Renaissance Italy, through its transmission at the University of Padua. Furthermore, its study contributes much to our understanding of Muslim and Jewish medieval intellectual and cultural histories, as well as linguistic developments of the Hebrew and Judeo-Arabic scientific languages.

Ilana Wartenberg is a Postdoctoral Teaching and Research Assistant in Jewish Studies at the University of Bern.

Ilana Wartenberg

Date Of Review:

January 11, 2019