An unrecorded medieval astrolabe quadrant from c. 1300

Summary

A detailed description of an as yet unrecorded astrolabe quadrant in a private collection is presented. A date between 1291 and 1310 is deduced from the calendrical data engraved on it. The characteristics of the newly recorded instrument have been compared with those of six other medieval astrolabe quadrants. The newly recorded instrument appears to present an early, if not the earliest, stage of development in the history of the astrolabe quadrant. In the comparison the newly recorded instrument is also distinguished by the red and black colours applied to differentiate between the superposed scales of the astrolabe quadrant. The names and the positions of the stars on the instruments were used to establish a connection between two of the instruments studied, those in Rouen and Oxford, and a manuscript tradition on the construction of the astrolabe quadrant, exemplified by MS Oxford Ashmole 1522. The data on three other astrolabe quadrants are shown to stem from star lists in treatises on astrolabes. For two instruments, those dated earliest and latest, no such connection was found. Some star names on the newly recorded instrument have hitherto not been recorded. Finally, the competence of the later medieval artisans has been investigated by analysing the accuracy of these instruments.