John of Sacrobosco and the Calendar

"John of Sacrobosco and the Calendar." John of Sacrobosco was a thirteenth-century writer on quadrivial subjects who nowadays is remembered, if at all, for his treatise on the Sphere. His contemporaries, however, appear to have considered him primarily as a computist, or writer on the calendar. This article attempts to place Sacrobosco in the computistical tradition, and in the process to establish the nature of his contribution to calendar reform. Sacrobosco's computistical treatise, the De anni ratione, has generally been assumed to be the basic text for the liberal arts course of the medieval schools; but since some of its content is of an advanced nature, and both inaccurate and unorthodox, this appears unlikely. It was, in fact, modeled on an earlier schools treatise with which it has been confused, as a comparison between the two treatises shows. Finally, Sacrobosco's contemporaries credited him with having "divided time": this is a reference to his adoption of the system of time measurement using minutes and seconds which is still in use today.