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Signed by Hans Dorn
Dated 1491; Vienna
Silvered brass; 121 mm in diameter

The instrument consists of a circular disc with an extension on one side which tapers into a v-shaped handle to which a box is fixed.

The front of the disc is engraved for latitude 47? with a circle for the equator, lines for the unequal hours (numbered in Gothic numerals clockwise1 to 12, each line is divided by dots into sections) and the lines for the astrological houses (numbered anticlockwise 1 to 12). Around the rim is a 24 equal hour scale, numbered twice clockwise 1 to 12, and altitude scale 0? to 360?, numbered by 10? and divided to 5? and single degrees.

Rotating over this plate is the circle of the ecliptic, marked with the usual Latin names of the zodiac (some abbreviated). Each sign has a degree scale 0? to 30?, numbered by 10? and divided to 2?. Over this ecliptical circle rotates a ruler.

This side of the instrument can be used for converting equal into unequal hours and for astrological purposes.

The reverse of the disc has several circular scales for use as a nocturnal as follows (from the outside):

1) The ecliptic, marked with the usual Latin names of the zodiac (some abbreviated), each sign having a 30? scale, numbered by 10? and divided to 5? and single degrees.

2) A corresponding calendrical scale marked with the usual Latin names of the months (except 'Meius' and 'Novenber'). For each month the corresponding number of days is given, numbered by 10 and divided to 2. The equinoxes correspond to 11 March and 14 September. The centre of the handle corresponds to 13 June.

3) A semicircle containing an unusually shaped shadow scale to the base 12, numbered by 3 and divided to 1.

4) A scale with the lunar mansions, indicated by the numbers 1 to 28 and the first letter of the corresponding qualities as 's{icca}, t{epida}, h{umida}'.

5) A second calendrical scales, but with the names of the months only indicated by their first letters.

Over this plate rotates a small circular disc connected by four arms to a small hour ring of the same diameter as the whole plate, numbered anticlockwise 3 to 12 to 9, divided to 20 and 4 minutes. Projecting touch pins indicated the hole hours.

The small central disc is marked with the age of the moon 1 to 291/2.

Over this disc rotates another, smaller disc with two arms similar to an alidade with sighting vanes (although the holes are barely usable). This disc has a circular aperture which reveals the phases of the moon on the plate below in blue made from crushed azurite. The disc itself has astrological markings for planetary aspects.

The hole in the centre of the instrument serves as sighting hole for the nocturnal.

The box contains an equatorial dial in the form of a foliate scroll, numbered 3 to 12 to 9, which can be set to the appropriate latitude by means of a foldable arm and a latitude scale on the inside of the bottom of the box. The pin gnomon is missing. The inset compass has a deviation of circa 8?E, the needle is missing and the glass is a replacement. A hole in the lid of the box allows the compass to be seen while the box is closed. The outside and inside of the lid and the inside of the bottom of the box are engraved with the names and latitudes of cities as follows (on the outside of the lid): 'OFEN 48', 'WIEN 48', 'SALCPVRG 48', 'REGENSPVRG 49', 'NURNBERG 49', 'PRAG 50', 'BRESLA 51', 'CRACOVIA 51', 'DANCKA 54', 'LVBECA 54', 'MADBVRG 52', 'WIERCPVRG 50', 'MAIC 50', 'CHOLLN 50', on the inside of the lid: 'PRVCK 52', 'GENT 52', 'SPEIR 49', 'COBLENC 50', 'STRASPVRG 48', 'PASEL 48', 'PERN 47', 'GENIF 46', 'ISPRVK 47', 'POCN 46', 'VENEDIG 45', 'MALAN 45', 'FLORENC 43', 'ROM 42', on the inside of the bottom: 'NEAPOLIS 51', 'IERVSALEM 32', 'CONSTANOPOLIS 44', 'VLLM 48', 'PARIS 48', 'VILACH 46', 'GREC 47'.

The text on the outside of the bottom explains the range of the compass and gives the signature as follows: 'DAS CHOMPAS IST GERECHT AVF ALE LANT VND HAT GEMACHT PRVDER HANNS DORN PREDIGER ORDEN VON WIEN ANNO DOMINI 1491'.

The instrument was purchased in 1894 and 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), p. 47 (with plate XXVIII).

Silke Ackermann

British Museum, London
Registration no. MLA 1894,6-15.1

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