‘The separation of liberal and mechanical arts manifested itself clearly in the literature of the [medieval] period’, wrote Edgar Zilsel in 1942. The coming together of scholars and craftsmen, according to the influential Zilsel thesis, caused the emergence of modern science in seventeenth-century Europe. Zilsel’s explanation has been challenged, but his assumption that Latin scholarship and vernacular craftsmanship were different activities practised by different people in the late Middle Ages has remained intact. It is in many cases true that there was a division between scientific and practical cultures, but that dichotomy could be blurred. The ways in which writers blended theoretical and practical material, exploiting the flexibility of the vernacular and moulding it to their needs, are exemplified by the Equatorie of the Planetis.