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Signed by Georg Hartmann
Dated 1541; Nuremberg
Gilt brass; 108 mm in diameter

The planispheric astrolabe is made of gilded brass. The instrument is suspended from a ring passing through a swivelling pin fastened to the throne. The throne is decorated on both sides with three eight-petalled rosettes resembling the Hartmann type. All letters and numerals are punched. However, none of the parts carries any marks identifying the fabrication number as the Hartmann astrolabes commonly do.

The outer limb on the front carries an equal hour scale (twice marked from I to XII) and an altitude scale, subdivided into 1? intervals and marked every 10?. The mater is blank.

The rete, rotating freely in the mater around the central pin, carries 24 star-pointers for the following stars: 'CETI AVST', 'HIRCVS', 'CAS', 'VENTER', 'TAVRI ALDEBARAN', 'RIGELA', 'RIGEL', 'HVM OBIONIS', 'ALBT', 'PROCI', 'CANIS MINOR', 'COR LEONIS', 'LVCIDA IDRA', 'ALA CORVI', 'SPICA VIRGO', 'PICA VIDAS', 'FIDICVLA', 'ARTVM', 'EL CVM', 'LCO', 'CIG', 'CELIRA', 'AQVILA' and 'CAPRI'. The counter-changed ruler, rotating over the rete, bears the inscription 'LINEA RECTA' (twice).

Under the rete there is a single central plate, fixed in orientation by a projecting lug and engraved on both sides. On one side a set of almucantars at 3? intervals, a set of azimuth circles at 10? intervals and other positional circles are given for the latitude of 39?. Below the horizon a set of unequal hour curves is given as well as the boundaries of the astrological houses according to the house-division system known in the West as that of Regiomontanus. The reverse, which is laid out for the latitude of 44?, is unfinished. Only the almucantars are drawn at 3? intervals and the unequal hour curves below the horizon (the latter are erroneously projected beyond the tropic of Cancer up to the North point on the horizon). Both latitudes are noted in Arabic numerals whereas on a typical Hartmann astrolabe they are given in Roman numerals. Nor are the latitudes inscribed on the lugs as Hartmann commonly did with his astrolabes.

The reverse carries an altitude scale on the outer rim, subdivided into 1? intervals and marked every 10?. Further inwards is a zodiacal calendar scale for the Julian calendar. The dates for the equinoxes and the solstices are respectively set on March 12.0, June 10.2, September 8.5 and December 10.1. The upper central section depicts a diagram for determining the time in unequal hours from the Sun's altitude. The lower central section features a symmetrical pair of shadow boxes for horizontal and the vertical shadow lengths (marked 'VMB RECTA' and 'VMB VERSA'). Rotating over the back is a counter-changed alidade with vertical sighting slits.

The instrument is signed on the reverse 'GEORGIVS HARTMAN NOREMBERGE FACIBAT ?ANNO?M?D?XLI?'. Again, the notation of the year in Roman numerals instead of Arabic numerals strongly argues that this astrolabe was not the work of Hartmann but that of an inferior contemporary imitator.

The instrument (IC 535, previously catalogued as A 383) was acquired at an auction in 1953. See H. Klemm, Georg Hartmann aus Eggolsheim (1489-1564): Ein Mathematiker, Physiker und Instrumentenmacher von Europ?ischem Rang (Markt Eggolsheim, 1989).

Robert van Gent

Museum Boerhaave, Leiden
Inventory no. 3087

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