The Liber Theoreumacie (1214) and the Early History of the Quadrans Vetus

Abstract

The Liber theoreumacie is a neglected work of practical geometry, written in Strasbourg in 1214, which sheds valuable light on the study and practice of astronomy in early thirteenth-century Europe. In this article, I focus on the first two chapters of Book IV, which both deal with the construction of horary instruments. The first of these chapters contains the earliest known account of the type of universal horary quadrant known as quadrans vetus, which is here given a biblical pedigree by labelling it the “sundial of Ahaz.” The second chapter describes a graphical method of inscribing hour markings on the surface of an astrolabe’s alidade, which appears to have been introduced into Latin Europe by the twelfth-century translator John of Seville. A critical edition and translation of the relevant passages will conclude the article.