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Astronomical Compendium
Signed by Christoph Schissler
Dated 1556; Augsburg
Gilt brass; 70 x 67 x 16 mm

The compendium is almost square, with a central box and a top and bottom cover, hinged at opposing edges of the box. A sequence of vertical gouges decorates the sides of the central box. The only other decoration appears on the inside and outside faces of the front and back covers: in each of their corners there is a symmetrical pattern of engraved foliage.

The accompanying case (86 ? 82 ? 30 mm) is of wood and pasteboard, covered with leather and blind tooled on the lid. There are two crudely decorated brass hinges and a hook clasp. Inside the lid is a printed octagonal sticker numbered in manuscript '1706 25'.

The outer face of the compendium's top cover carries a combined nocturnal and volvelle. The device is set against an outer fixed calendar scale in which the months are named in standard Latin except for 'ONVEMBER'. Each month is divided to 10 and 2, and numbered by 10 (adjusted for the length of the month).

On the volvelle is the title 'NOCTVRNALE . VERSVS ++ POLVM . ARTICVM . VEL . VRSAM . MAIOREM . APLICANDVM'. There is an outer scale of hours 4 to 12 to 8 marked with studs and a pointer at 12.

Within the hour scale are two pairs of rectangular apertures which give the length of day and night for latitudes 50, 48 and 46?. In each pair, one aperture shows the length of day and the other the length of night. A single pair of apertures is used for both 50 and 48?, with their hour scales running, respectively, 8 to 16, 16 to 8 and 8 to 16 to 8. The apertures and thus the scale for 46? is offset at right angles, the hours again running 8 to 16 to 8. The date is set using the volvelle's pointer on the calendar scale and the length of the day and night are read off from small indicators in the apertures. The spring equinox is at 10 March, as expected.

Moving over the volvelle is the 'REGVLA HORE NOCTIS' which is arched to avoid the studs and reaches only to the corners of the plate, reducing its ease of use.

The reverse of the cover carries a lunar volvelle and wind rose. The outer scale is for the age of the moon 0 to 29[1/2] and surrounds a scale of hours I to XII, I to XII, each hour divided to 1/4. The volvelle has a scale of hours at its edge 1 to 12, 1 to 12, each hour divided to 1/4. There is a pointer at 12 and, at the opposite 12, a circular aperture to reveal a diagram of the phases of the moon, with a full moon face. The circular window occupies the space in which the numerals 11, 12 and 1 would have appeared. There is a stud to turn the volvelle. The centre of the volvelle is occupied by a wind rose in which 12 Latin winds are named. A small pointed index can be rotated above the volvelle. It is not clear whether a wind vane was originally provided.

In the central box of the compendium is a horizontal sundial adjustable for latitudes 42 to 54?. The folding gnomon consists of two parts, one of which slides over the other in order to alter the gnomon's angle. The gnomon, which remains upright only with difficulty, is marked 'SCALA LATITVDINVM POLI'. When the gnomon's parts are pushed together the dial is meant for 42?. As the gnomon edge is pulled away it reveals a scale 45 to 54, divided and numbered by 3.

The dial plate has a central hole through which a compass can be seen; the plate is titled 'HOROLOGIVM . HORICONTALE AD . ELEVATIONES . POLI . 42 . 45 48 . 51 54 GRADVS'. The scales for 42, 48 and 54? run 6 to 12 to 6, and alternate with the 45 and 51? scales VI to XII to VI. All these hours are divided to 1/2. Lines for morning hours 4 and 5 and evening hours 7 and 8 are intended to serve for all latitudes.

The reverse of the dial plate has a table for the latitudes of 30 places, each of which is given one of the five latitudes for which the dial is prepared.

The inside of the back cover carries the compass in a raised, revolving bowl. The bowl is 19 mm in diameter and the base plate is engraved with 16 radiating lines. Fixed to the bowl is an index marked 'REGVLA'. Around the compass is an outer scale of degrees 0 to 90 to 0 to 90 to 0, divided to 10 and 2, and numbered by 10. This surrounds a band for directions in which the cardinal points are named 'SEPTENDRIONES', 'ORTVS', 'MERIDIES' and 'OCCASVS'. A cross marks the four intercardinal points and a further eight dots subdivide the remaining intervals. Within this ring is the signature: 'CHRISTOFFERVS . SCHISLER . ME . FECIT . AVGVSTE . ANNO . DOMINI . 15 . 56.'

On the back cover is graphical device for converting between equal and unequal hours. The outer scale of equal hours runs I to XII, I to XII, each hour divided to 1/2 and 1/4. The curved lines of unequal hours are numbered at their intersection with the equinoctial circle 1 to 12 from the 'HORIZON: ORTVS' and 1 to 12 from the 'HORIZO: OCCASVS'. A scale of solar declination is marked with the symbols of the signs and subdivided and numbered as space allows. Around the blank central circle is the title 'HORE . PLANETARVM . INSTRVMENTVM'. The device would presumably have originally had a rotating index to ease its use.

This example shares a number of features, such as the form of the gnomon, in common with another Schissler compendium of 1556 now in Augsburg: see M. Bobinger, Christoph Schissler der ?ltere und der j?ngere (Augsburg, 1954), plate 30.

Stephen Johnston

Museum of the History of Science, Oxford
Inventory number 44317

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