A collection of essays describing the 15th-century astrological treatise De sphaera and the manuscript in which it is contained (Modena, Biblioteca estense universitaria Alpha X 2.14). The manuscript was illuminated by an artist of the Lombard school (thought to be Cristoforo de Predis) for the court of Milan, then made its way to Ferrara and the court of the Este family.
Created in the first decade of the 12th century at Thorney Abbey, a Benedictine monastery in Cambridgeshire. St John's 17 is a compilation of texts, tables, maps and diagrams. It is organized around the central theme of time-reckoning and calendar construction.