|Lawrence J. Schoenberg Collection -- Manuscript Number: ljs487 Version:|
|[On the Composition and the Uses of a Combined Nocturnal and Sun Dial]; De confectio baculi Jacob [On Making a Cross-staff] Eastern France, Franche-Comte?|
Physical Description: 12 ff., preceded and followed by three flyleaves, single quire of 12 , lacking leaf or two at the end, also perhaps missing an unidentified leaf at the beginning [perhaps containing a preface?], on paper (watermarks close to Briquet: "Lettres soudees," no. 9755, Luxeuil, 1518-1519; Dole, 1522-1530), written in dark brown ink in a Gothic cursive script on up to 26 lines, on unruled paper, opening initial H with pen flourishing, tables placed in the body of the text, modern inscription imitating Gothic lettering on third front flyleaf: "Cy est manuscript de Astronomie." Bound in a modern half binding of polished tan calf, boards covered with marbled paper, smooth spine with title gilt: "Astronomie" (Sound condition). Dimensions 190 x 145 mm.
Nocturnals and sundials, as well as quadrants and astrolabes, were widely used in Europe in the late Middle Ages and Renaissance, peaking in popularity in the fifteenth and sixteenth centuries. They constitute basic astronomical education tools, also essential to maritime navigation. Knowledge of astronomy was considered to be fundamental in education, and skill in the use of the astrolabe was a sign of proper breeding and education. Geoffrey Chaucer thought it was important for his son to understand how to use an astrolabe, and his 1391 treatise on the astrolabe demonstrates a high level of astronomical knowledge. Astrolabists, such as the famous Jean Fusoris or his student Henri Arnaut, were also fabricators and inventors of other astronomical instruments, a logical extension of their expertise (Jean Fusoris built astronomical clocks for such important patrons as the Duke of Orleans in 1397-1398, as well as the famous Horloge of the Cathedral of Bourges; see Poulle, Un constructeur d?instruments?, 1963, ?Horloges,? pp. 27-40). Gnomonics?the art and science of constructing dials?was a recognized branch of applied mathematics from the Greek antiquity on. The variety and technical precision of ancient sundials and nocturnals that survive show us that ancient dialers were prolific and inventive.
ff. 11v-12v, [ANONYMOUS], De confectio baculi Jacob [On making a Cross-staff ], heading, Baculus Jacob; incipit, ?Si vis baculum Jacobi artificialiter conficere accipe virgam unam quadratum vel rotundam??; explicit, ?[?] spacium inventum inter duas stationes quod significant altitudinem?? [text breaks off].
This is a brief treatise concerning the construction and use of the ?Baculus Jacob? or Cross-staff which appears to be anonymous, but is heavily indebted to Levi ben Gerson?s chapters concerning the ?Baculus Jacob? in his work Wars of the Lord.
The ?Baculus Jacob? or Cross-staff or Jacob?s staff (in French ?arbalestrille?) is an early astronomical instrument used to measure angles. It was mainly used as a navigational instrument and is considered to be functional predecessor of the octant and the sextant, enabling mariners to measure angular separation between two celestial bodies. Levi ben Gershon or Gersonides (1288 -1344), Biblical commentator, mathematician, and astronomer (sometimes referred to as the ?greatest Jewish philosopher after Maimonides?) popularized the ?Baculus Jacob.? He composed in Hebrew around 1318 an important work entitled Wars of the Lord, with Treatise V, Part I devoted to Astronomy, in which one finds the description and uses of the Cross-staff. These chapters were translated into Latin by Peter of Alexandria (see Paris, BnF, MS lat. 7293, ff. 9-17) and Jacob?s staff was called ?revelator secretorum? because the staff allowed many astronomical secrets to be solved.
We have traced only five manuscripts containing this anonymous treatise, found with various titles. These are: Paris, BnF, MS lat. 7717; Paris, BnF, MS lat. 10266 (see E. Poulle, Un constructeur?, 1963, p. 84: ?Deux textes anonyms de la B. N. ont trait a son usage, uniquement geometrique?Si vis artificiose baculum Jacob conficere??); Munich, Universitatsbibliothek, Cod. 746, Gotha, Forschungs- und Landesbibliothek, Chart. B 1423; Jena, Universitatsbibliothek, El. phil. qu. 3; Wolfenbuttel, Herzog August Bibliothek, Cod. Guelf. 1127.