By Andreas Kühne, Richard Lorch, Benno van Dalen, and Joseph W. Dauben on behalf of the Lehrstuhl für Geschichte der Naturwissenschaften, Museumsinsel 1, 80538 Munich, Germany

On 22 June, 2008, Professor Menso Folkerts, Director of the Institute for the History of Science of the Ludwig-Maximilians-Universität in Munich, will celebrate his sixty-fifth birthday. This year he looks back over forty years of successful teaching and research in Oldenburg, Berlin, and Munich. Through his research in the history of science in the widest sense and in particular on medieval mathematical texts, he has long been a leading historian of science.

Menso Folkerts was born in 1943 in Eschwege (Hessen) and went to the Gymnasien in Norden and in Leer (East Frisia). Because he was interested both in ancient languages and in mathematics, he decided to study these subjects in order to become a teacher at a

Through Gericke, Folkerts also came into contact with Joseph Ehrenfried Hofmann (1900–1973), who arranged for Folkert's dissertation to appear in the series "*Boethius. Texte und Abhandlungen der exakten Wissenschaften*." (Eighteen years later, Folkerts became the editor of this series for the history of science, and he is still responsible for *Boethius *today.) In 1967 Hofmann invited Folkerts to give a lecture on his work at the Mathematical Research Institute in Oberwolfach, at a conference on "Problemgeschichte der Mathematik." At that time, the conferences at Oberwolfach, which took place under Hofmann's direction every year, were the most important forum for presenting new results in the history of mathematics. Folkerts regularly read papers at these conferences; later, together with other historians of mathematics, he organized several of them. At Oberwolfach, he met Christoph J. Scriba, who was appointed Professor for the History of Exact Sciences and Technology at the Technical University, Berlin, in 1969, and offered Folkerts the position of *Assistent*. Through cooperation with Kurt Mauel, who was responsible for the history of technology at that time, and through Scriba, Folkerts acquired the knowledge and techniques necessary for a historian of science. Further possibilities of widening his scholarly horizon were offered by the "Driburger Kreis," which met annually in combination with the Deutsche Gesellschaft für Geschichte der Medizin, Naturwissenschaft und Technik. From intense study of manuscripts and numerous visits to libraries, he formed the idea of making a systematic survey of western mathematical texts. On the basis of several important publications he was awarded his *Habilitation* in the "history of the exact sciences and technology, especially mathematics" in 1973.

In the summer of 1976, Folkerts became Professor of Mathematics "with emphasis on professional practice of mathematicians and history of mathematics" at the University of Oldenburg. In Oldenburg, Folkerts developed the project "Materials for the History of European Mathematics in the Middle Ages," which was funded by the Volkswagen Foundation. On the basis of his own research and extensive acquaintance with manuscript collections, an archive of microfilms and paper copies of more than 5000 manuscripts was built up, which is today available at the Lehrstuhl für Geschichte der Naturwissenschaften in Munich. For studies of the mathematical sciences in the Middle Ages this is a unique source.

In 1980, Folkerts was appointed Professor for the History of Science at the Ludwig Maximilians University (LMU) in Munich, and was nominated Director of the Institute for History of Science. When he retires on 30 September, 2008, he will have taught and researched in Munich for more than twenty-eight years. Beginning in the winter semester of 2001/2002, the chair for the History of Science has been a department of the *Historisches Seminar *of the LMU. In his time at the LMU, Folkerts has supervised numerous doctorates and *Habilitationen*; most of the historians of science who received their *Habilitation *at the Institute or *Lehrstuhl* have become professors in German or foreign universities.

Of the numerous research projects undertaken under Menso Folkerts's direction and with his active involvement, only a few can be mentioned here: the establishing of a database of medieval scientific manuscripts, which is today available on-line under the name "Jordanus"; the complete edition of the works of Nicolaus Copernicus (to be finished in 2009); the publication of "Algorismus," a series of books on the history of science; and the co-editorship of ten other scholarly journals and series.

Folkerts has also been active in societies and other institutions for the history of science. Here we should first mention his numerous functions and activities as a member of the National Committee for the History of Science of the German Federal Republic and of the International Committee of the History of Mathematics. He has also been the chief referee for the history of science for the DFG (German Research Foundation), and has been a president of the Deutsche Gesellschaft für Geschichte der Medizin, Naturwissenschaft und Technik, a member of the board of trustees of the Deutsches Museum, and of the Adam Ries Society.

Folkerts's early work was connected with classical philology and with the topic of his dissertation. Later, he made valuable contributions to the history of western mathematics in the early Middle Ages before the translations from Arabic in the twelfth century. Under the influence of Kurt Vogel, Folkerts studied recreational mathematics, particularly collections of mathematical problems. In cooperation with Arno Borst, the author of the authoritative history of the medieval mathematical board-game called "rithmomachia," Folkerts systematically investigated the transmission of the different versions of this game and edited one central text. On the basis of his work on the transmission of mathematical texts in the Middle Ages in collaboration with his friend and colleague, H.L.L. Busard, Folkerts has in the last few years written a bio-bibliographical book on western mathematics between 500 and 1500. This work is now almost complete. Also in collaboration with Busard, Folkerts made a critical edition of an important twelfth-century redaction of Euclid's *Elements *that was the basis of the much-used Campanus edition. Among his most spectacular publications was the edition, with German translation and commentary, of a manuscript that represents the Latin redaction of the oldest Arabic work on calculation with Hindu-Arabic numerals. The Arabic text of this treatise is lost.

Another part of Folkerts's scholarship lay in the mathematics of the fifteenth and sixteenth centuries. On the one hand, he has edited the mathematical works of Nicholas of Cusa (1401–1464); on the other, he has given special attention to the mathematical and scholarly activity of Johannes Regiomontanus (1436–1476). By careful study of manuscripts, he has shown that there are close connections in mathematics between the universities of Erfurt, Leipzig, and Wittenberg, in which school teachers and practitioners of mathematics were involved. One of the topics of practical mathematics was "Visierkunst," with which the contents of barrels were approximated. Folkerts wrote the first general account of the history of this branch of mathematics.

Another important theme in Folkerts's work concerns the mathematical sciences in the nineteenth century, particularly at the University of Göttingen. In the last few years, his work in this period has concentrated on C. F. Gauss (1777–1855) and his activities at the University of Göttingen. Folkerts has completed a database of over 7000 letters written by or sent to Gauss, which can be accessed on the internet at http://gauss.gwi.uni-muenchen.de

Menso Folkerts' scholarly works and his influence as a university teacher have found national and international recognition. He was elected a Corresponding Member of the Académie Internationale d'Histoire des Sciences in 1981, and an Effective Member in 1986. Since 1989, he has been a member of the Deutsche Akademie für Naturforscher Leopoldina, where from 1998 to 2006 he was a Senator and representative of the Section for the History of Science and Medicine. In 1998, he was made a Corresponding Member of the Saxonian Academy of Sciences, and in 1999, he became a Full Member of the Bavarian Academy of Sciences. In the Bavarian Academy, he was elected a member of the Commission for the Publication of the Works of Johannes Kepler in 2006.

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