Astronomical Images : The author and instruments for astronomy and navigation

Johannes Sacrobosco

Astronomical Images

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. Sphaera mundi, 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 Sphaera, 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 woodcut shows a friar at work with two terrestrial globes. The larger one shows the American continent. The friar is possibly intended to represent Maurus Fiorentinus. This portrait is based on an earlier printed figure of an author, Lodovico de Varthema by the artist Zoan Andrea for Varthema's book Itinerario (Venice: Giorgio Rusconi, 1517), repeated 3 more times (1518, 1520, 1522) and copied twice more before 1530. In the background is an allegory of navigation, demonstrating the practical link between navigation and the basic astronomy of the De sphaera tradition. The whole composition is enclosed in a frame showing constellations and a range of mathematical and astronomical instruments, although the latter are not necessarily accurate in their details, making it difficult to identify precisely the intended objects. Along the top can be seen a carpenter's square (or similar device), an hourglass and a dipytch sundial. The object in the top right-hand corner may be a kind of primitive anemometer. On the left-hand side of the border, below Mercury, are dividers. Underneath these, some form of angle-measuring instrument is shown. This is not likely to be a cross-staff, because it seems to be attached to the arced scale underneath it. Hanging on the left-hand wall, behind the friar, is what is probably intended to be an horary quadrant (although the hour-lines have been put in the bottom left corner rather than at the apex) and an astrolabe (probably astronomical rather than mariner's). Along the bottom are virginals (or a clavichord) and a lute. To the right-hand side, below Venus, is an object with twenty-four divisions, that was probably intended to represent either a nocturnal or a lunar volvelle (there is not enough detail in the inner circle to confirm which). The numbering in the outer ring beyond VII is erratic, presumably partly because of the lack of space. With grateful thanks to Hester Higton for identifying the instruments.