A GERMAN BRASS ASTROLOGICAL DISC WITH LEATHER CASE
A GERMAN BRASS ASTROLOGICAL DISC WITH LEATHER CASE

Signed and dated 'GEORGIVS HARTMAN NORENBERGE FACIEBAT 1541.'

Details
A GERMAN BRASS ASTROLOGICAL DISC WITH LEATHER CASE
Signed and dated 'GEORGIVS HARTMAN NORENBERGE FACIEBAT 1541.'
This large brass disc is inscribed on one side only. All the letters and numbers are punched with Hartman's characteristic tools. Around the rim is a scale of twnety-four hours, divided to quarter-hour intervals. MITTAG is at the top, and the hours to the right (in roman numerals) run to MITTER NACHT at the bottom, and then back to the top, the hours in Arabic numerals. Labelled at the right 'STVND NACH MITTAG', and to the left 'STVND VOR MITTAG'. Centred on the vertical and below the horizontal diameter of the plate are twenty-four arcs representing planetary, or unequal, hours. With the same centre is a circle divided into the months of the year and the months into single days. At the very centre is a small circle marked with twenty-four hours in Arabic numerals.

Within the month circle, and within the arcs, are the planetary symbols of the Governors of the Planetary Hours. A planetary hour is a twelfth of the time between sunrise and sunset in the case of day hours, and between sunset and sunrise in the case of night hours. These hours are assigned to the seven planets in Ptolemaic order, as given in the table in the upper central part of this disc. With seven planets and twenty-four hours, the first hour of the day gives the planet's name to the whole day, and hence the present day names for the days of the week.

At the top of the disc is an extension in the form of three roundels, the upper most bearing the signature. There is a hole for a suspension ring or cord. The back of the disc is plain. Some old writing in red ink reads 'Instrumentum indicans horas planetarum aereum solidum Normbergae 1541 St. 6 H 3'.

A finely made draw-string, fitted case is made of wood covered with black leather that is fully blind-tooled with a foliate pattern and three armorial shields. One bears the date 1541. The cord is green, and appears to be original.

In association is a disc of paper printed from an engraved plate on one side. It has degree and hour scales, azimuths, almucantars and Houses. The appearance of the letters and numbers is not contemporary with Hatman's disc, and suggests the early seventeenth Century.
10 in. (27.5 cm.) diam.; the case 12 in. (30.5 cm.) diam.
Provenance
Rothschild inv. no. AR1536.
Literature
J.P. Lamprey, 'An examination of Two Groups of Georg Hartmann Sixteenth-century Astrolabes and the Tables used in their Manufacture', Annals of Science, 54, 1997, pp. 111-42.
E. Zinner, Deutsche und niederlndische astronomische Instrumente des 11.-18. Jahrhunderts, Munich, 1956, p. 365.

Lot Essay

No other of this type is recorded. For Hartman's manufacturing technique, see John P. Lamprey, loc. cit.

Georg Hartman (1489-1564)

The extent and significance of the South German instrument-making industry in the fifteenth and sixteenth Centuries is only now becoming fully appreciated. Astronomical instruments were certainly being produced in Central Europe during the second half of the fifteenth Century as a result of the mathematical studies of of such scholars as John of Gmunden (c. 1380-1442), Georg Peurbach (1423-1461), and Johannes Mller (1436-1476), known as regionmontanus, who settled in Nuremberg in 1471. That city, enjoying excellent communications with Italy, North Germany and the Low Countries, and with an established metal-working trade, was ideally suited to become a production centre for mathematical instruments. The leading workshop producing such instruments in the early sixteenth Century was directed by Georg Hartman (the modern spelling of the name is Hartmann; the instruments are signed 'Hartman').

Hartman was born at Eggolsheim in Germany in 1489, and studied mathematics and theology in Cologne. In 1518 he visited Italy, where he became friendly with Copernicus' brother, and began designing sundials. In that same year, he was appointed vicar of St. Sebaldus church in Nuremberg, and he remained there for the rest of his life. He was a distinguished example of the scholar-craftsman, taking a full part in the intellectual life of the city, where he was a contemporary and friend of Albrecht Drer.

The number of his instruments that has survived, as well as indications concerning their manufacture, make it clear that Hartman was a pioneer of quantity production. He made a wide range of instruments, including astrolabes, sundials, quadrants, nocturnals, globes and armillary spheres, and supplied not only the aristocratic market, but also at prices accessible to poor scholars. His correspondence with Archduke Albert of Prussia has survived, revealing that he made instruments for him, and also for King Ferdinand of Bohemia, and other patrons. One of these letters reports Hartman's studies on magnetic declination, which was finally resolved by Robert Norman, and published in 1580.

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