The rim of the mater bears a 360? altitude scale numbered in alphanumerical notation clockwise by 10? starting at the throne leaving the hundreds out, divided to 5? and subdivided to single degrees. The rim is rivetted to the backplate. The inside of the rim has a recess at 12 o'clock underneath the throne to accommodate the tongues of the plates. The inside of the mater is engraved with several circular scales in two sets as follows (from the outside):A.
1) The numbers from 1 to 28 anti clockwise in alphanumerical notation standing the for the 28 years of the solar cycle.
2) The corresponding weekdays numbered 1 to 7 in alphanumerical notation with.
3) The letter 'k' at every fourth year indication leap years.
B.
1) The names of the months as follows in transliteration: 'Yanir, Febrir, Mars, Avril, Mayah, Yunyah, Yulyah, Agust, Setember, October, Novenber, Dejember.
2) The corresponding 'Pasut' (...) in alphanumerical notation: 3, 6, 6, 2, 4, 7, 2, 5, 1, 3, 6, 1; 3) the corresponding 'Kabush' (...) in alphanumerical notation: 3, 6, 7, 3, 5, 1, 3, 6, 2, 4, 7, 2. The throne has a pierced quatrefoil design made up of three layers of metal.
The rete has a semi-quatrefoil design with the star-pointers in the shape of bent daggers sitting on one or triple lobes. Two little knobs are attached to both sides of the double counterchanged equinoctial bar which act as handles to turn the rete. 24 star names are given partially in Hebrew, partially in Arabic in Hebrew script.
The ecliptic is marked with the Hebrew names of the zodiacal signs. Each sign is subdivided to 6?.
The 5 plates are marked on both sides with the circles for the equator and the tropics, azimuths for every 10?, almucantars for every 5? (numbered only on plate 3b in alphanumerical system) and the lines for the unequal hours (numbered only on plate 3b in alphanumerical system). The ten sides are marked in alphanumerical notation and laid out for the following latitudes: 1a) 33?; 1b) 43?; 2a) 35?; 2b) 42?; 3a) 36?; 3b) 40?; 4a) 37?; 4b) 41?; 5a) 38?; and 5b) 39?.
The back of the instrument bears several circular scales as follows (from the outside, all numbers in alphanumerical notation):
1) A concentric altitude scale marked four times 0? to 90? starting at the east west line, numbered by 10?, divided to 5? and subdivided to single degrees.
2) A concentric scale with the Hebrew names of the zodiacal signs, each sign divided to 30?, numbered by 10?, divided to 5? and subdivided to single degrees.
3) An eccentric calendar scale with the names of the months as given above on the ecliptic, is divided to the corresponding number of days, every tenth day marked with divisions to five days and subdivisions to single days. The equinoxes correspond with March 111/2 and September 15.
The bottom half of the vacant space inside these circles is taken up by a double shadow scale marked [zl isr] and [zl hpuk] to the base of 12, every fourth digit numbered, with divisions to single digits. The top half contains two horary quadrants for unequal hours. The alidade is counterchanged without any markings.
The instrument was formerly in the Spitzer collection and was purchased in 1893. It is described and illustrated 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), pp. 113-4, no. 328 (with plate LIII); B. Goldstein, The Hebrew Astrolabe in the Adler Planetarium (Chicago, 1976), reprinted in B. Goldstein, Theory and Observation in Ancient and Medieval Astronomy (London, 1985), paper no. XIX.
Silke Ackermann
