Details
An exceptionally rare early 15th-Century French brass Medieval Astrolabe,
attributed to Jean Fusoris, c.1400, complete and comprising a mater with soldered limb, four plates, rete, alidade, rule and pin with wedge -- 16cm. (6 5/16in.) diameter, weight 1.2kg (2lb 11oz)
See Illustrations
The very small bracket, with its abbreviated shoulders, is an integral part of the limb. The shackle and ring are missing. The limb (7mm thick) is soldered to the back plate (2mm thick). The inside of the mater has no mathematical lines; there are, however, six crude concentric circles with a man's name, profession, and the year 1518:
PRO:MAGISTRO + PETRO + HILARETO + ANGERIACO~+ SANTONE~~+ MEDICO~~+ 1518
Placed centrally is a pictorial engraving similar to a coat of arms: a large bird holding in its beak a snake or eel, with above, a band with three ears of wheat. There are several casting fissures in the brass. The top of the limb is narrow and is engraved in 360° grouped in fives; each hour is 15°. The numbering is in twice 12 hours, engraved in west European arabic numerals of the early 15th century style.
On the back of the mater is a circle of 360° numbered 90°-0-90°-0-90°. Next is the Zodiac, using the same degree scale, now divided in 30° for each sign. The eccentric calendar scale follows, the months named and divided in days. Here errors are noticable: February 28 is over an earlier number; March 31 is cut over 30. There is evidence of original colour paste in numbers, names and circle, both black and red, presumably rouge. Within the circles is a diagram for the conversion of planetary hours to mean hours, the arcs numbered 1-6-1, and the rectangular tangent scale with sides divided to 12 at the apex. The First Point of Aries is at 11½ March.
The four plates (each c.1mm thick) are inscribed on both sides; they each have a symmetric lug protruding from the meridian line. The stereographic co-ordinate scale has altitude lines every 2° and azimuth lines every 10°. In addition are the unequal hour arcs numbered each two hours 2 to 12. The sides of each plate are inscribed with the latitude for which they were designed, and the name of a prominent city at that latitude is inclluded: Engraved Latitude Modern Latitude
Parisius 48g 50m rome 41g 45m Paris 48° 50' Rome 41° 54'
Poitiers 47 lion 45 Poitiers 46° 35' Lyon 45° 46'
rodis 35g 30m tablet of horizons Rhodes 36° 15'
hiers* 30g 45m tron 24 Jerusalem 31° 47' tropic of Capricorn 23° 27'
(*From an old spelling Hierosalima for Jerusalem)
The rete has a neat arrangement of flame-like star pointers, the framework being four counterchanged bars in the cardinal directions and the ecliptic circle. The ends of the break in the Tropic of Cancer are finished with a dragon's head on the left and star pointer on the right. Between is a fiducial index on the meridian line. There are pointers for 22 stars:
Engraved Modern name Designation
1. Venter Ceti Baten Kaitos \kz\K Cet
2. Cornu Hamal \ka\K Ari
3. Menkar Naris Ceti \ka\K Cet
4. Aldebaren Aldebaran \ka\K Tau
5. Rigil Rigel \kb\K Ori
6. Alhaiot Capella \ka\K Aur
7. Algeuse Betelgeuse \ka\K Ori
8. Alhabor Sirius \ka\K CMa
9. Algomeisa Procyon \kb\K CMi
10. Ydra Alphard \ka\K Hyr
11. Cor leonis Regulus \ka\K Leo
12. Spica Spica \ka\K Vir
13. Eq9 Dubhe \ka\K UMa
14. Alrameth Arcturus \ka\K Boo
15. Elfeta Alphecca \ka\K CrB
16. [?]Lancabri Yed Prior \kd\K Oph
17. Cor Antares \ka\K Sco
18. Alhaue Ras alague \ka\K Oph
19. Wegua Vega \ka\K Lyr
20. Althair Altair \ka\K Aql
21. Ariof Deneb \ka\K Cyg
22. Humerus Scheat \kb\K Peg
(no.16 has been identified from its coordinates. This star does not appear on other Fusoris astrolabes so far located)
The counterchanged alidade is fimbriated along the fiducial edges; the ends are neatly cusped to avoid obscuring the degree scale on the back of the astrolabe. The sight vanes are inset and soldered to the alidade, and have a pinhole and peg sights. The rule is fixed in the instrument by a 'pin', which is a 15mm rod, soldered to a wide (15mm diameter) brass button on one end and cut with a rectangular hole at the other, into which slips the ingenious wedge.
Literature
POULLE, E., Un constructeur d'instruments astronomiques au XVe siècle, Jean Fusoris (Bibliothèque de l'Ecole des hautes études; Paris, 1963)
POULLE, E., Les instruments astronomiques du moyen age (Paris; Brieux, 1983)
WEBSTER, R. & M., Western Astrolabes (Adler Planetarium; Chicago, 1998)
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