Inventory no. 53801 - Epact entry
Epact number: 93825
Astrolabe
Workshop of Jean Fusoris ?
circa 1400; Paris
Brass; 102 mm in diameter
Main text
This instrument is typical of the astrolabes of the French maker Jean Fusoris, who established in Paris the earliest commercial workshop of which we have any record.
The rete in particular is in his compact and elegant style. Astrolabe plates are made for particular latitudes. One of the plates of this example does not have the latitude value recorded as a number, which is usual; instead it is marked as being for use in Paris.
Source museum: Museum of the History of Science, Oxford
Museum number: Inventory no. 53,801
Detailed text
Mater with limb attached to the back plate, the inside blank, except for 4 dots above the pivot hole. Simple throne, with two ribs and two on the rim of the limb, shackle and suspension ring.
The limb has a scale of hours 0 to 12 twice, divided to 20 minutes, subdivided to 4 minutes, numbered by 1 hour.
Rete for 21 named stars. Ecliptic circle with zodiacal names, each with a scale of 30 degrees, divided to 10, subdivided to 2. Meridian bar counterchanged four times. Four dots close to the pivot hole on the verso.
Four plates, each one fully engraved for only one latitude, as follows: 42° (unfinished verso with a set of unequal hour lines); 45° (unfinished verso with tropics, equator, meridian and east-west lines); 'Parisi' (unfinished verso with tropics, equator, meridian and east-west lines); 52° (verso with tablet of horizons). The projection for each latitude has azimuth lines for every 15 degrees, almucantars for every 3 degrees (every fifth almucantar indicated by short lines and the first and second are numbered '3' and '6' respectively, to show that the progression is by 3), unequal hour lines beneath the horizon, numbered by 2. Each latitude plate has 4 dots on the verso close to the pivot hole and 4 on either side of the lug.
The back has a degree scale on the limb, 0 to 90 to 0 to 90 to 0, divided to 5, subdivided to 1, numbered by 10. The same scale , renumbered in the inside, serves for the zodiacal scale, with abbreviated names of the signs, each with a scale 0 to 30, numbered by 10. Within this is an eccentric calendar scale, with month names in Latin, abbreviated where appropriate, each with a scale of days, divided to 5, subdivided to 1, numbered by 10 as appropriate. The first point of Aires is at 11|1/2| March. In the central space, two quadrants are occupied by an unequal-hour diagram, with lines for hours 0 to 6 to 0; two with a double shadow square, with scales 0 to 12 to 0 to 10 to 0, divided to 4, subdivided to 1, numbered by 4.
Counterchanged alidade, shaped ends, vanes with pinhole sights. One arm of the laidade has a scale of unequal hours. Later bolt and nut.
Jim Bennett