Astronomical Images : Globe with diptych dial

Johannes Sacrobosco

Astronomical Images

<p style='text-align: justify;'>Very little is known about Johannes Sacrobosco except that he was probably British, taught astronomy at Paris University, and died there in the second quarter of the thirteenth century. <i>Sphaera mundi</i>, his major work, was an extraordinarily popular astronomical textbook for several generations. Manuscripts of it circulated through all the main European centres of learning. It was first published in 1472 in Ferrara, and went through dozens of editions up to the mid-seventeenth century. This is from one of the first Italian translations of Sacrobosco's <i>Sphaera</i>, to which Fra Mauro Fiorentino added a short treatise on cosmography, navigation, altimetry and stereometry. Fra Mauro Mattei from Florence or Fiorentino (c. 1493-1556) was a Servite active at the Annunziata Church in Florence. His interests covered several mathematical disciplines, including music (on which a treatise by him survives at the Laurenziana Library). At the beginning of his edition, Fra Mauro included a dedicatory letter to Giovan'Orthega de Carion, from the Annunziata Church, 1537. This Italian translation of Sacrobosco's classic work on the Sphere would have provided a useful resource for those who wanted to improve their knowledge of cosmography but lacked the Latin skills to read the original text, or preferred to read the vernacular version. This figure shows a globe, which the caption describes as 'a cosmographical and terrestrial ball'. The instrument indeed seems to be a terrestrial globe, in that it bears labels for Europe, Asia and Africa. The fact that it is referred to as 'cosmographical' as well as 'terrestrial' may link into the broader agenda of Sacrobosco's work in which the heavens, Earth and circles around them were to be understood together within the field of cosmology. Certain key features of the use of the globe as an instrument are evident in this depiction. A small diptych dial can be seen in the left-hand foreground, the compass of which would have been used to find the meridian line along which the globe had to be aligned. Furthermore, the meridian ring is labelled as the 'Meridiano mobile', or moveable meridian, hinting at the fact that it could be rotated in the horizon ring in order to set the globe for the appropriate latitude.</p>

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