THE TREATISE on the ASTROLABE by RUDOLF of BRUGES* Knowledge of the Astrolabe and of Stereographic Projection Was Brought To

RICHARD LORCH

THE TREATISE ON THE ASTROLABE BY RUDOLF OF BRUGES*

Knowledge of the astrolabe and of stereographic projection was brought to the Latin West in two main stages: the compilation of the Sententie astrolabii and related texts1 in Spain in the late tenth century and the translation, also in Spain, of major works on the subject in the mid-twelfth century. That further material was gained from Arabic sources will be clear below. It has been shown that the Sententie is partly a translation of al-Khwärizml's account of the use of the instrument, but the introductory material appears to be of Latin origin and there is a middle section that appears to have been written in Latin by someone with an astrolabe and perhaps also Arabic texts in front of him.2 Several of the other tracts in this group give the impression of being compilations or reworkings. On the basis of these texts other, usually clearer, texts were prepared, e.g. the De utilitatibus astrolabii attributed to Gerbert (ca. 945 - 1003)3 and De mensura astrolabii by Hermannus Contractus (1013-1054),4 who worked in the monastery at Reichenau. Some fragments of a translation of Ptolemy's Planisphaerium dating from the Sententie era have recently been discovered.5 In the mid-twelfth century several important works on, or related to, the astrolabe were translated into Latin. In 1143 Hermann of Carinthia translated Ptolemy's Planisphaerium together with some notes by Maslama (d. 1007); further notes by Maslama and his Extra-Chapter were translated by two

* For John North, who gave me so freely of his time and expertise in the sixties when I was his student. I am grateful to Paul Kunitzsch and Menso Folkerts for help with several portions of the text, and to Charles Burnett, who sent me a copy of the Naples manuscript. 1 Edited by MiUas in Assaig d'historia de les idees fisiques i matemàtiques a la Catalunya medieval', vol. I, Estudis universitaris Catalans, Série Monografica I, Barcelona 1931. 2 P. Kunitzsch, 'Al-Khwarizmï as a Source for the Sententie astrolabii\ From Deferent to Equant: A Volume of Studies in the History of Science in the Ancient and Medieval Near East in Honor ofE. S. Kennedy, eds. D. A. King and G. Saliba, New York 1987. 3 Edited by Bubnov in Gerberti opera mathematica, Berlin 1899,109-147. 4 Edited by Drecker from MS Munich Staatsbibliothek, CLM 14836, in 'Hermannus Contractus Über das Astrolab', Isis 16 (1931), 200-219. 5 P. Kunitzsch, 'Fragments of Ptolemy's Planisphaerium in an early Latin translation', Centaurus 36 (1993), 97-101. 56 RICHARD LORCH different scholars, one of whom also translated Maslama's Astrolabe Chapters.6 Two translations were made of Ibn alSaffar's treatise on the uses of the astrolabe: by Plato of Tivoli (active 1133-1145) and by Johannes Hispalensis.7 In some manuscripts of Johannes's translation the text is ascribed to Maslama, Ibn al-Safifar's teacher, but this appears to be a mistake.8 About this time a short description of the astrolabe with a long account of its uses by one Abraham, probably Abraham b. 'Ezra, was translated, apparently from Hebrew.9 Contemporaneous with this translation activity was the composition of several works on the astrolabe in Latin: by Raymond of Marseilles (before 1141)10, Adelard of Bath (1149-1150)11, Johannes Hispalensis, Rudolf of Bruges (1144 or after), Robert of Chester (1147?, 1150?), the otherwise unknown Arialdus and some anonymous tracts.12

6 Hermann's translation was edited by Heiberg in Claudii Ptolemaei opera quae exstant omnia, vol. Π, Opera astronomica minora, Leipzig 1907,225-259. The remaining Maslama pieces are edited in J. Vernet and M. A. Catalâ, 'Las obras matematicas de Maslama de Madrid', Al-Andalus 30 (1965), 15-45, repr. in J. Vernet, Estudios sobre historia de la ciencia medieval, Barcelona 1979, 241-271, and P. Kunitzsch and R. Lorch, 'Maslama's Notes on Ptolemy's Planisphaerium and Related Texts', Sitzungsberichte der Bayerischen Akademie der Wissenschaften, phil.-hist Klasse, Jg. 1994 Heft 2, Munich 1994. 7 The Arabic text was edited by Millâs in 'Los primos tratados de astrolabio en la Espana arabe', Revista del istituto egipcio de estudios islamicos en Madrid 3 (1955), 47-76 (Arabie part) and 35-49 (Spanish part). The Johannes translation was also edited by Milles in Las traducciones orientales en los manuscritos de la Biblioteca Catedral de Toledo, Madrid 1942, 261-284. The Plato translation is edited in R. Lorch, G. Brey, S. Kirschner and Chr. Schöner, 'Ibn-a§-Saffärs Traktat über das Astrolab in der Übersetzung von Plato von Tivoli', Cosmographica et Geographica. Festschrift für Heribert M. Nobis zum 70. Geburtstag, eds. B. Fritscher and G. Brey, vol 1,125-180. 8 P. Kunitzsch, 'Glossar der arabischen Fachausdrücke in der mittelalterlichen europäischen Astrolabliteratur', Nachrichten der Akademie der Wissenschaften in Göttingen, phil.-hist Klasse, Jg. 1982 Nr. 11, Göttingen 1983,480 n. 23. 9 Edited in J. Millas Vallicrosa, 'Un nuevo tratado de astrolabio, de R. Abraham ibn Îzra', Al-Andalus 5 (1940), 1-29. Doubts on the authorship are brought up by R. Levy, 'The Authorship of a Latin Treatise on the Astrolabe', Speculum 17 (1942), 566-569, and Millas replies in J. Millas Vallicrosa, 'Sobre un "Tratado de astrolabio" atribuido a R. Abraham ibn Îzra', Sefarad 4 (1944), 31-88. 10 The treatise is edited in E. Poulie, 'Le traité de l'astrolabe de Raymond de Marseille', Studi medievali 3a Serie, V 2 (1964), 866-900 + 4 plates. 11 Adelard's treatise has been edited by Β. Dickey 'Adelard of Bath: An Examination Based on heretofore Unexamined Manuscripts', (unpublished PhD dissertation, Toronto 1982). It is described in E. Poulie, 'Le traité de l'astrolabe d'Adelard de Bath', Adelard of Bath. An English Scientist and Arabist of the Early Twelfth Century, ed. C. Burnett, London 1987. 12Poulle, 'Raymond' 868 and 'Adelard' 119-120, points to the decade of the 1140's as particularly fruitful. See also E. Poulie, 'L'astrolabe médiéval d'après les manuscrits de la Bibliothèque Nationale', Bibliothèque de l'École de Chartres 112 (1954), 81-103, esp. 84. My list of translators and writers on the astrolabe is largely based on these passages and Kunitzsch, 'Glossar', 476-497.