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Astronomical Compendium
Signed by Christoph Schissler
Dated 1588; Augsburg
Gilt brass; 72 mm in diameter

A circular compendium with two covers hinged above one another on a central box. Each cover has its own hook clasp. There is a fixed suspension ring attached to the central box.

The surfaces are so full of scales and tables that there is little room for decoration: deeply cut stylized flowers and foliage on the top cover and engraved foliage on the base of the spring barrel.

The signature appears round the side of the central box: 'CHRISTOPHORVS SCHISSLER SENIOR ME FACIEBAT AVGVSTAE VINDELICORVM A<NNO> 15.88'.

The outside of the top cover has a Profatius astrolabe-quadrant with the inscription 'TYBVS AD POLI ALTITVDINEM QVODLIBET DIE VENANDAM' against its arc. Within the inscription is a scale of hour angles 1 to 12, each hour divided to 1/2 and 1/8, and double-numbered 1 to 6, 6 to 11. Within is a scale of degrees 0 to 90, divided to 5 and 1, and numbered by 5.

The projection shows the 'TROPICVS CANCRI' as well as the quadrant of the equinoctial, the latter divided to 10, dotted to 2, and numbered by 10. In the projection of the zodiac the signs are given their standard names and each sign is divided to 10 and 2, and numbered by 10. No stars are plotted.

Lines of horizons are engraved and numbered every 5?, from the 'HORIZONTE RECTVS' of the equinoctial to 90?, and back. The same horizon scale also appears on the rotating index from 15 to 90 to 75?, divided and numbered by 5, with each division bisected on the index's beveled edge. The end of the radius carries a zodiac arc with the abbreviated names of the signs (note 'TVR' for Taurus). Each sign is divided and numbered by 10, and further subdivided to 2 on the beveled edge.

The radius also has two pinhole sights for observing altitudes.

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. Although the geographical range is the same as that on similar earlier maps by Schissler, the designed is based on a different model, with different detailing of rivers and mountains, as wel as a distinct treatment of town places (here marked by circular indentations as opposed to the circles with central dots on Epact 57238).

A radial index carries a sliding cursor and a central hole permits the insertion of a wind vane which can be housed in the body of the instrument.

Facing the map is a horizontal string-gnomon dial adjustable for latitudes in the range 42 - 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, except for 42? which is 5 to 12 to 7. The hours are divided to 1/2. The string gnomon is 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 LATITVDI: POLI'. The scale itself runs 42 to 54, divided and numbered by 3, with a single notch per division. A 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 26 mm). The silvered base plate has a direction cross marked 'SE', 'OR', 'ME' and 'OC'. The plate's meridian line terminates in a T-bar at north and the north point of the blued needle terminates in the same way.

The reverse of the dial plate carries a table of 50 latitudes, in round degrees. Most of the places are towns within the area covered by the instrument's map. However, those on the underside of the compass bowl are more wide-ranging, including cities in Italy, France and Spain, as well as 'LONDRN ANG: 52'. Larger territories are also listed, such as 'PORTVGAL 41' and 'CORSICA 41'.

In the centre of the inside back cover is an orthographic ('Rojas') projection of the celestial sphere, 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 'HORAE ORTVS SOLIS' and 'HORAE OCCASVS SOLIS' appear respectively above and below the projected zodiac band. The rule is set against either of two latitude scales on the circumference. The scales are arranged on opposing quadrants and each carry a scale of degrees 0 to 90, divided to 10 and 2, and numbered by 10. The remaining quadrants each carry the inscription 'GRADVS ELEVATIONES POLI'. The appropriate parallels of declination between the tropics carry the standard names of the zodiacal signs.

The back cover carries a lunar volvelle with a scale of hours 1 to 12, 1 to 12, each hour divided to 1/2 and 1/4. The volvelle has a pointer marked 'INDEX', a circular aperture to reveal a diagram of the phases of the moon (with a full moon face), as well as an aspectarium for trine, quadrature and sextile.

Around the volvelle is a scale of hours 1 to 12, 1 to 12, each hour divided to 1/2 and 1/4, and a scale for the age of the moon 0 to 291/2.

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 1/2 and 1/4. The matching sections for 'ORTVS HORE' and 'OCCASVS HORE' are 2 to 10 hours, each divided to 1/2 and 1/4. A descriptive caption is marked around the scales: 'EXTERIOR LVCIS SPATIVM TIBI DENOTAT ORBIS INTERIOR SVRGAT RVTILANS SOL QVANDO CADATVE [sic]'.

Stephen Johnston

Museum of the History of Science, Oxford
Inventory number 49

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