R. Jacob ben Machir ibn Tibbon · c. 1288 (composition; this is a later manuscript copy)
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Jacob ben Machir ibn Tibbon’s treatise on the quadrans novus — the improved astronomical quadrant of his own invention — describing how the instrument is constructed and used for astronomical and time-keeping measurements.
The work is laid out in sixteen gates (she’arim), opening with a table of contents that names them, and it teaches by worked example as much as by rule: the folios carry the instrument’s use for the rising of signs in the oblique sphere as against the right sphere, each followed by examples computed through. A table of fixed stars supplies the coordinates needed to lay out the instrument itself.
The quadrans novus was a genuine improvement rather than a variant. A quadrant is a quarter-circle of brass or wood — cheaper, sturdier and simpler than an astrolabe — and ibn Tibbon’s redesign extended what could be read off one, bringing much of the astrolabe’s functionality onto an instrument that was easier to make and to carry.
This is one of the most influential medieval works on astronomical instruments, and unusually its influence ran outward from Hebrew rather than into it: the treatise passed into Latin, where its author was known as Profatius Judaeus, and was cited by Renaissance astronomers. Ibn Tibbon, working at Montpellier and Marseille, belonged to the family that had made its name translating Arabic science into Hebrew — and here the traffic reverses, with a Hebrew author’s own invention entering the Latin mainstream.
The translated witness is BnF Hébreu 1031, folios 131r–147v — the same richly rubricated Hebrew astronomy anthology that carries ibn al-Aḥdab’s Keli Ḥemda, a Hebrew De Sphaera, and works of ibn Ezra. The manuscript copy is later than the composition of around 1288.