| Popis: |
The cross-staff is an instrument for measuring angles, invented by Gersonides (1288–1344) in the 1330s. The Latin text describing it, written in 1342, refers to it as baculus Jacob. Between the fifteenth and the eighteenth century, this instrument was widely used in astronomy, surveying, and navigation. Scholars have assumed that the early modern cross-staves have all descended from that of Gersonides. Here I will question this assumption: (i) late-fifteenth-century astronomers do not refer the cross-staff with the term baculus Jacob, but their staff may indeed have its origin in Gersonides’ text of 1342; this hypothesis needs to be checked. (ii) In the surveying literature, German artisans and craftsmen describe the cross-staff and refer to it as “Jakobsstab,” but it is likely an independent invention. I also suggest that the “Jacob” after whom the Jacob’s staff is named is not the Patriarch Jacob (as has been assumed), but St. James (= Jacob) the Great, who in the eleventh century became the object of great veneration. |
