The mater takes the form of a disc without a rim, but bears the usual markings for a 360? altitude scale and a 24 equal hour scale on the outside with markings for a plate on the centre part (see below). The altitude scale is numbered by 10? starting at the east point clockwise, divided to 5? and subdivided to single degrees in an attempt for alternate shading. The hour scale is numbered twice I to XII starting at the throne, divided to 15 minutes by alternate shading.The throne is just an extension of the mater with a circular table with the Latin names of the weekdays with their corresponding numbers (1 for Sunday etc., in the following order: Sunday, Friday, Wednesday, Monday, Saturday, Thursday, Tuesday), and their corresponding planetary symbols. A compass bowl is riveted to the back of the throne.
On the rete 30 Latin star names are given with their corresponding planetary temperaments and magnitudes. In a more cursive script the corresponding 'Arabic' star names have been added. The ecliptic is marked with the usual Latin names of the zodiacal signs with their corresponding symbols, numbered 0 (Aries) to 11. Each sign is divided into 30?, numbered by 10?, divided to 5? and subdivided to single degrees by alternate shading.
The plate is laid out for latitude ('LATI') 48? ('G'). It is marked with the circles for the equator ('Aequator' and 'Aequinotialis') and the tropics ('Tropicus Cancri' and 'Tropscus [sic] Capricornus'), azimuths for every 10? (numbered by 10?), almucantars for every 3? (numbered by 3?), the lines for the unequal hours (numbered 1 to 12) and the markings for the astrological houses in the manner of Regiomontanus (numbered 1 to 12). The twilight line ('LINEA CREPVSCVLINA') and the 'HORIZONT OBLIQUS' are given. Most markings are in the same slightly cursive script as the 'Arabic' star names.
The back of the instrument bears several circular scales as follows (from the outside):
1) A concentric altitude scale marked four times 0? to 90? starting on the east-west line, numbered by 10?, divided to 5? and subdivided to single degrees by alternate shading.
2) A concentric scale with the Latin names of the zodiacal signs with their corresponding symbols and numbered 0 (Aries) to 12, each sign divided to 30?, numbered in Roman numerals by 10?, using the same subdivision as scale 1, each sign also divided into three parts with the corresponding planetary influence.
3) A concentric Gregorian calendar scale marked with the usual Latin names of the months, divided into the corresponding number of days, every tenth day marked with divisions to 5 days and subdivisions to single days, the equinoxes corresponding with March 21 and September 23.
4) A concentric Julian calendar scale marked with the usual Latin names of the months, divided into the corresponding number of days, every tenth day marked with divisions to 5 days and subdivisions to single days, the equinoxes corresponding with March 11 and September 13.
5) a circular scale with the 28 lunar mansions (numbered 1 to 28) with their corresponding qualities ('h{umidus}, s{iccus}, t{epidus}').
6) A circular scale with the Latin names of the winds.
The bottom half of the vacant space inside these circles is divided into the seven sections of the planetary houses (in the order 'SOL, LUNA, MARS, MERCVRIVS, IVPITER, VENVS, SATVRNVS') with the corresponding zodiacal signs. Each section is again divided into seven columns (each twice with the numbers 1 to 12) associated with the planets in the following way: 'DIES SOLIS': [Sun] and 1, 8, 3, 10, [Venus] and 2, 9, 4, 11, [Mercury] and 3, 10, 5, 12, [Moon] and 4, 11, 6, [Saturn] and 5, 12, 7, [Jupiter] and 6, 1, 8, [Mars] and 7, 2, 9. And so forth for 'DIES LUNAE, DIES MARTIS, DIES MERCURY, DIES IOVIS, DIES VENERIS, DIES SATURNI'.
On the right hand side of the top half is a quadrant to the base of 24 on both radii, numbered by 3 with single divisions. The left hand side contains in a cartouche the signature and the date 'THOBIAS VOLCKMER BRAUNSWEIGGENSIS FACIEBAT 1594'. The date seems to have been filled in with red at one point. Underneath this cartouche is a shadow scale to the base of 12, numbered by 3 and divided to single digits. Inside this shadow scale is a horoscope schema, some of the markings with traces of red.
One arm of the rule is marked with northern and southern declinations ('DECLINATIO SEPTENTRIONALIS' and 'DECLINATIO MERIDIONALIS') from 0? to 90? and 0? to 23?, numbered by 10?, divided to 5? and subdivided to single degrees. The other arm bears markings for the solar declinations indicated by the zodiacal signs and marked 'SIGNA COEL ESTICA'.
The counterchanged alidade with sighting vanes is marked 'LINEA FIDUCIAE' on one arm with a linear scale up to 24 (corresponding to the divisions of the quadrant on the back), numbered by 3 with single subdivisions. The other arm bears markings which correspond with the circles on the back of the astrolabe (from the outside): 'ACUS', 'FACIES', 'CALENDA NOVUM', 'CALENDA 'VETUS', 'MANS{IONES}', 'VEN{TES}', 'DIES', 'CHAR{ACTERES}', 'HORAE PLANETA{RUM}', 'NOMI{NES}', 'DOMU{S}', 'EFFIGIES PLANETARUM', 'CHA{RACTER}'.
An extra rule bears the same linear scale up to 24 as one arm of the alidade.
The instrument was bequeathed to the Museum in 1888 by Octavius Morgan and is described in F. A. B. Ward, A Catalogue of European Scientific Instruments in the Department of Medieval and Later Antiquities of the British Museum (London, 1981), p. 119, no. 343.
Silke Ackermann
