«Combustion Tables» in Twelfth-Century Latin Europe: A Preliminary Study

Abstract

The Latin manuscript sources studied in this article jointly document the existence and erstwhile circulation of a highly atypical set of computational tables for planetary longitudes, coupled with extensive tables for ascensions, which served astrologers in Latin Europe as early as the 1130s. An associated text of c.1220 refers to the tables for the five planets as « combustion tables » (tabule combustionis), which reflects the way the tables in question use the time and position of the last conjunction between a planet and the Sun - known in medieval terminology as combustio - as an anchor for calculating the planet’s true ecliptic longitude at a later date within its synodic period. Multiple lines of evidence suggest that the combustion tables as well as the associated solar and ascension tables originally circulated alongside the pseudo-Ptolemaic Iudicia, an astrological work of probable Arabic origin (pre-1138). Overall, the surviving manuscript material raises the possibility that the tables and the Iudicia were at one point a single work that supported astrological computations and judgments at an early stage of their respective development in Latin Europe.