With this impressive book, Benno van Dalen presents a part of the outcome of his research at the Ptolemaeus Arabus et Latinus project, focusing on the astronomy of Kūshyār ibn Labbān, a scholar from the province of Gilan (NW Iran) who wrote several astronomical works in Arabic around the year 1000 AD. His al-Zīj al-Jāmiʿ (“The Comprehensive Zīj”—zīj designating an astronomical handbook with tables) was heavily inspired by the scientific tradition of Claudius Ptolemy (2nd century) and provided astronomical tables, instructions for their use as well as some explanations of the underlying models and mathematical proofs. As stated in the preface, the overall aim of Dalen is to give the first critical edition, translation, and commentary of Book II of the Jāmiʿ Zīj, which contains Kūshyār’s core set of chronological, astronomical and geographical tables with some explanatory texts. His study aspires to obtain a clearer picture of the practice of astronomy in Islamic territories around the year 1000.
The book is organized in well-defined parts, containing a comprehensive introduction (part I), the tables edited in a transliterated form (II), the edition of the textual elements (III) and an ample commentary (IV). The publication ends with a series of annexes: two “quick reference guides” which expose (1) an overview of the zījes composed from the 9th to the 14th centuries and used by van Dalen in his commentary, (2) definitions of the most important technical concepts used in his analysis; a glossary in which Arabic terms are transliterated and translated, with references to the present edition; a bibliography and full indexes. The book finishes with 16 colour plates displaying folios from eight manuscripts. The high quality and usefulness of these annexes alone would justify the consultation of van Dalen’s book even by readers who would not be interested in the contents of the Jāmiʿ Zīj itself.
The Jāmiʿ Zīj of Kūshyār has been transmitted in three or four textual versions, contains no less than 55 tables (not counting additional tabular material), and this edition is based on eight manuscripts, among them one in Judaeo-Arabic. By comparison, Ptolemy’s Handy Tables contain 22 Greek tables, mainly known thanks to four manuscripts from which almost all the known manuscript tradition is descended, but no one has yet succeeded in making a complete critical edition. This gives an idea of the impressive task realized by van Dalen, who aimed at recovering the earliest version of Kūshyār’s tables on the one hand and on the other, understanding the specifics of his working methods and scientific activity with reference to his predecessors such as Ptolemy and al-Battānī. This enables the author to obtain a broader comprehension of the history of Kūshyār’s tables and of Islamic astronomy during the late 10th and early 11th centuries.
The critical edition of numerical tables in paper-based format presents numerous, well-known difficulties. Including numerical data and (sometimes voluminous and complex) critical apparatus in a single page can easily discourage the philologist, but also the readers, who need special training or some time to adapt their reading. Some projects such as DISHAS consider digital humanities a possible way to overcome many difficulties in publishing astronomical tables by offering digital editing frames and research tools. In this respect, some may question the usefulness of a highly constrained paper edition. Nevertheless, whether in paper or digital format, the reader still needs a training phase to be able to use critically edited tables—the skills required are simply different—and consulting the tables published by van Dalen is not particularly more tedious than navigating through a digital edition. The book is indeed certainly complex—just like the task the author has set himself—and the consultation of the tables, critical apparatuses and commentaries is not always intuitive, but after a little time of familiarization, the reader can easily navigate between the different sections and find the information he is looking for. Numerical tables are carefully numbered, the structure of the commentaries is clear and the indexes make the book user-friendly despite its complexity.
The audience targeted by the book is varied. Specialists of scientific codices will find helpful manuscript descriptions; historians of science will be able to consult the necessary mathematical and astronomical analyses to understand Kūshyār’s tables, whereas philologists will be interested in the stimulating discussions of editing challenges. The latter issue is the subject of a rich development (pp. 75–87) on how Van Dalen adapted his philological approach to the specificities of the work he edits –in particular for the numerical tables themselves– putting forward a convincing philological method based on several clearly defined criteria (scribal errors, manuscript evidence, mathematical correctness). The editing innovations proposed by the author, such as the introduction of a new system of symbols, are compelling and go beyond a philological approach to Kūshyār’s tables alone. Scribes sometimes miscopied entire rows, columns, or sections of a table. These are not accumulations of single, independent mistakes, and they influence our interpretation of the transmitted table. It is hence necessary that the critical apparatus indicates the specifics of this category of scribal mistake. As van Dalen states, “the purpose of such variants is to show structural differences between the witnesses rather than simply to give any variant individually” (p. 82).
As for the commentary, the most impressive section concerns the tables for Mars (pp. 427–440). Indeed, Kūshyār “states specifically that he found some divergences from Ptolemy’s tables in the results of his own calculations of the true position of Mars” (p. 427). According to the author, Kūshyār probably carried out observations to modify some parameters, and performed a series of numerical corrections (detailed step by step by van Dalen), so that his adjustments contributed to real scientific improvements. As a result, “the average error in the true longitudes of Mars becomes close to zero thanks to Kūshyār’s correction” (p. 435). Despite the complexity of the argumentation, the language is comprehensible, and the hypotheses are always cautious and nuanced, which allows even readers with a limited scientific background to enjoy some insights into the practice of medieval astronomy. Van Dalen succeeds in showing the readers that Kūshyār ibn Labbān was the scientific heir to Ptolemy while making various kinds of improvements, several of them being adopted by later astronomers.
The introduction gives a lot of information about Islamic astronomy, and the historical and scientific context of Kūshyār’s activity. However—and this is my only regret about van Dalen’s publication—the lack of a proper general conclusion which would have gathered in a couple of pages the main results of his inquiry in a narrative form is a bit unfortunate. Nevertheless, the book succeeds in advancing the publication of Arabic astronomical tables by offering a scope that goes beyond the older editions of this type of documentation, which sometimes lacked a thorough philological discussion and were addressed only to an ultra-specialized audience. Historians and philologists of all chronological and cultural backgrounds will benefit greatly from reading van Dalen’s book.
 The Jāmiʿ Zīj is composed of four books. Books I and IV were previously edited and published by Mohammad Bagheri, and Hanif Ghalandari is currently working on the same task for Book III at the Institute for the History of Science in Teheran.