Astrolabe by Jean Fusoris

Jean Fusoris was born in Giraumont in the Ardennes region of France ca. 1365. His father was a pewterer. He studied arts and medicine, attaining the bachelor's degree in 1379, returning after learning his father's craft for his master's degree which was attained in 1391, and served as one of the master's regents in Paris until 1400. Fusoris established a school and opened an instrument workshop in Paris making astrolabes, clocks and other instruments, but he continued to study theology and accumulated various canonries.

He was elected a member of the French embassy in England in 1415, where he met Richard of Courteny, Bishop of Norwich. Norwich bought an astrolabe from Fusoris but did not pay for it. When Fusoris returned to England in an attempt to collect the debt, war broke out between France and England and he was arrested as a suspected spy when he returned. He was exiled to Mezieres-sur-Meuze and later to Reims where he continued to accept and fill commissions for instruments. He died in 1436. In addition to his instruments, Fusoris wrote a treatise on the astrolabe in which he detailed the improvements he incorporated into his instruments and other tracts on mathematics and astronomy.

Fusoris Astrolabe Front

Front of Fusoris astrolabe (Photo courtesy Adler Planetarium and Astronomy Museum)

[Fusoris Astrolabe Back]

Back of Fusoris astrolabe (Photo courtesy Adler Planetarium and Astronomy Museum)

The astrolabe in the picture is from the Adler Planetarium and Astronomy Museum in Chicago, IL, USA (catalog number: W-264). It is 16.3 cm in diameter (6.4 inches) with an overall height of 20.6 cm (8.1 inches). The mater thickness is 0.8 cm (.31 inches).

The mater limb is cast brass and soldered to the hammered back plate. The throne is functional and non-decorative and was cast with the rim of the mater. The limb has an hour scale labeled 12-12 twice with divisions for each 20 minutes. Inside the time scale is an unlabeled scale of degrees with a division for each degree. The degree divisions can be used with the time scale by associating each degree with four minutes of time. The rete has 21 stars of which 20 are labeled. All Fusoris astrolabes had unique star pointers labeled Venter Ceti and Cornu (in the picture they are the two pointers near the limb at about 8 o'clock just below the rule) that are a signature for his instruments. Cornu (beta Arietis) is in the wrong position on all Fusoris astrolabes. All the numerals on the plate are Gothic script and were engraved.

The altitude arcs are drawn for each 2° and the azimuth arcs for each 10°. There are three plates (tympans) for 42°, 36°, 45°, 49° and 52°. The 36° side is probably a later addition as it is in a different hand, the numerals are not in the Gothic style and it includes a crespuscular arc.

The back of the instrument has an eccentric calendar scale, equal/unequal hour conversion scale and a shadow square. The alidade is not original. The date of the vernal equinox is March 11, which is accurate for the date of the instrument.

Fusoris was one of the first philosopher-churchmen to set up a commercial workshop to produce instruments. He was successful and at least 13 of his astrolabes survive. His workshop represented several turning points in the history of instrument manufacture in general and the history of the astrolabe in particular. First, it was unique at the time for a person of his prestige and position to establish a commercial enterprise. Prior to this time, most astrolabes were produced by individuals or nameless guild craftsmen. It cannot be said that Fusoris started a revolution in the instrument industry, but his shop certainly anticipated later ateliers headed by prominent scholars. His influence on the astrolabe cannot be overstated. He was the first to integrate all of the astrolabe elements into a uniquely European instrument and the design elements of Fusoris' astrolabes become virtually universal. Among his innovations were dividing the limb by equal hours, the use of a rule (ostensor) on the front and improvements in the design of the alidade. His elegant and artistic design of the astrolabe components were a milestone compared to the bulky and awkward instruments that preceded his.