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Astronomical Compendium
Signed by Christoph Schissler
Dated 1557; Augsburg
Gilt brass; 84 mm in diameter (maximum)

An octagonal compendium with two hinged covers attached at opposite edges of a central box. When closed, the instrument has a depth of 15 mm.

The instrument is signed '.CHRISTOPHORVS. .SCHISSLER. .ME . FECIT. .AVGVSTE. .VINDELICORVM. .ANNO. .DOMINI. .15.57.' in a double-lined border around the sides of the central box.

The outer face of the top cover carries a geographical astrolabe. A rotating circular plate (diameter 70 mm) carries a longitude scale of degrees 0 to 360 at its outer edge, divided to 10 and 2, and numbered by 10. Within the scale is a polar projection of the earth to the Tropic of Capricorn. The continents are named but schematically shaped, and Africa and Asia each include a human figure. There is no North American land mass, only several islands. The oceans are also named and populated with sea monsters and ships. Longitude begins to the west of Africa.

The plate rotates over a scale of hours 1 to 12, 1 to 12, each hour divided to 1/2 and 1/4, and with north and south marked 'SEPTEN' and 'MERIDI', respectively.

Above the geographical plate is a rete representing only the ecliptic. The signs are named as usual (though note 'PISES'), divided to 10 and 2, and numbered by 10. Above the rete is an index marked 'LINEA FIDUCIAE'; the lettering appears to be a later addition.

The reverse of the cover carries an engraved map of central Europe surrounded by an equally divided ring of 12 winds on the pattern 'NORD', 'NORDOST', 'OSTNORD', 'OST', etc. The map is centred near Coburg and reaches to Brussels in the west, L?beck and Rostock in the north and the Alps in the south. The town places are marked by circles with central dots (as opposed to the circular indentations on Epact 63321). A radial index carries a sliding two-handed pointer to indicate the relative bearings of towns. A central hole permits the insertion of a wind vane which, as it is too large to be comfortably housed in the body of the instrument, was perhaps borrowed from elsewhere as a replacement.

Facing the map is a horizontal string-gnomon dial adjustable for latitudes in the range 42 to 54?. It is titled 'HOROLOGIVM HORIZONTALE AD ELEVATIONES POLI 42 45 48 51 54 GRADVS'. There are five hour scales, each running 4 to 12 to 8, with the hours divided to 1/2 and 1/4. The 'string' gnomon is a piece of catgut, threaded through the plate and wound round a barrel on the underside. The barrel contains a watch spring to keep the string taut. At the other end of the string is a brass catch which hooks over the notched end of a folding arc to vary the inclination of the gnomon. The arc is marked on both sides 'SCALA LATITVDINVM POLI'. The scale itself runs 42 to 54, divided and numbered by 3, but there are two notches per division. A silvered spring plate on the underside of the dial plate holds the folding arc upright.

In the centre of the dial plate is the compass (diameter of bowl 22 mm). There is a direction cross marked 'SE', 'ORT', 'ME' and 'OCC'.

The underside of the dial plate carries a table of the latitudes of 42 places, in round degrees. The listed towns appear to fall within the area covered by the instrument's map. The bottom of the compass bowl is decorated with a profiled warrior head in a circular wreath. A name, perhaps 'W Burg', has been scratched beside the head.

In the centre of the inside back cover is a lunar volvelle with a double scale of hours 1 to 12, 1 to 12 and 1 to 24, cut away at the 12 / 24 point to reveal a scale for the age of the moon 0 to 29[1/2]. The volvelle has two pointers, a circular aperture to reveal a silvered diagram of the phases of the moon, as well as an aspectarium for trine, quadrature and sextile. Around the volvelle, and for use with it, is a scale of hours 1 to 12, 1 to 12.

A further double circular scale provides a simple correlation between the length of the day and the time of sunrise, and also between the length of the night and the time of sunset. The length of the day or night ('DIEIS QVANTITAS' or 'NOCTIS QVANTITAS') appears on two sections of the outer scale, from 20 to 4 hours, each hour divided to 1/4. The matching sections for 'SOLIS ORTVS HORE' and 'SOLIS OCCASVS HORE' are II to X hours, each divided to 1/8. A descriptive caption is marked on a raised circular band around the scales: 'EXTERIOR . LVCIS . SPATIVM . TIBI . DENOTAT . ORBIS . INTERIOR . SVRGAT . RVTILANS . SOL . QVANDO . CADATVE [sic]'.

The back cover carries a nocturnal combined with an orthographic projection of the celestial sphere.

The nocturnal is titled on the cover's central circular plate 'NOCTVRNALE . VERSVS . POLVM . ARTICVM . VEL . VRSAM . MAIOREM . APLECANDVM' and its hour scale is marked 'HORE . STELE . MAIOR:'. The scale is numbered 6 to 12 to 8 and is marked with studs. The rotating circular plate is set against a calendar scale around its rim in which each month is named in Latin and divided and numbered by 10 (adjusted for the length of the month). The scale continues on the bevelled edge around the plate with subdivisions to 2 and 1.

Nocturnals usually have an index projecting beyond the edge of the instrument with which to observe the chosen star. The rotating rule of this instrument now appears incomplete and was probably fitted originally with a folding extension piece for observations.

The circular plate also carries an orthographic ('Rojas') projection whose principal function seems to be to determine the time of sunrise and sunset throughout the year. The rotating index is marked 'REGULA . ORTVS . ET . OCCASVS . SOLIS' and the inscriptions 'HORE . ORTVS . SOLIS' and 'HORE . OCCASVS . SOLIS' appear respectively above and below the projected zodiac band. There is a quadrant scale of degrees 0 to 90 for 'ELEVATIONES . POLI', against which the rule is set. The appropriate parallels of declination between the tropics carry the names of the zodiacal signs; as with the rete of the geographical astrolabe, these are in standard form, though 'PISES' again appears.

Many of the elements in this Schissler compendium also feature in other instruments by him; see M. Bobinger, Christoph Schissler der ?ltere und der j?ngere (Basel, 1954).

Stephen Johnston

Museum of the History of Science, Oxford
Inventory number 36175

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