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Inventory no. 44392 - Epact entry

Epact number: 91986

Astronomical Compendium

Signed by Erasmus Habermel
Late 16th century; Prague
Gilt copper; 105 x 60 x 22 mm

Main text

Shaped like a book, this compendium was intended to act as a set of covers for a notebook which could be bound inside it.

The device includes an adjustable string gnomon sundial and a compass, as well as an assortment of calendrical, astrological and arithmetical tables. Though scarcely a military device it also carries a miniaturised set of gunner's gauge scales, nominally for determining the weight of cannonballs.

The fine gilding and decoration are typical of the work of Erasmus Habermel, court instrument maker to Rudolf II in Prague.



Source museum: Museum of the History of Science, Oxford
Museum number: Inventory no. 44,392



Detailed text

The compendium is shaped in the form of a notebook and its two leaves are mounted on a hollow arched spine. The instrument is fastened with a spring-held clasp which is released by a button. When closed the leaves are held 13 mm apart in order to accommodate the paper or tablets which would originally have been held between its covers.

The outer face of the top cover carries a rectangular grid in one corner of which is the pivot point of an ungraduated index rule. The sides are divided in equal parts, to 90 on the longer and to 60 on the shorter, each side divided to 10, 5 and 1 and numbered by 10. Although the grid is of the same type as that of a sinical quadrant, the device has no clear purpose in its current form since it does not incorporate a scale of degrees.

The inside face carries the signature along the hinged side: 'Pragae fecit Erasmus Habermehl'. There are also three separate tables: 'Tabula Planetarum Diei', giving the signs of the planets ruling over the 12 daytime hours; a Gregorian calendar scale arranged as two parallel lines with each month and zodiac sign divided to 10 and 2 and numbered by 10; a multiplication table with floral decoration giving products from 2 x 2 to 10 x 10.

This cover also carries two small holes near its middle of unknown purpose. If they were intended to receive an attachment it would interfere with motion of the index rule on the outer face and would have no obvious function on the inner face.

The inside face of the lower cover carries a horizontal string gnomon sundial. The folding gnomon support is sprung to the vertical and is adjustable for latitudes of 50, 48, 45 and 42°. The hour scales run 4 to 12 to 8 and are subdivided to quarter hours. In the centre of the face are two tables, one relating the length of day and night and the other the times of sunrise and sunset. The face also carries a compass whose bowl is 26 mm in diameter. The bowl is engraved with the Italian names of the sixteen principal winds.

The outer face has two graphical devices for converting hours; one labelled 'Horae ab Occasu' converts between equal hours and Italian hours; the other labelled 'Horae Planetarum' converts between equal and unequal hours. This face also carries a crested coat of arms.

Each long bevelled side of the inner faces carries a miniature version of one of a gunner's gauge scale: equal parts from 0 to 100, divided to 10, 5 and 1 and numbered by 10; 'Plumbum' to 100; 'Lapis' to 45; and 'Ferrum' to 100.

The outer arched face of the spine carries a table of the latitudes of 15 cities from Rome at 42° to Prag at 50°. One end of the spine is covered by a folding leaf attached to a thin plate with a catch to retain the spine's inner face. Holes in this inner face would have allowed for the binding of the notebook sheets or tablets held in the instrument.

Stephen Johnston

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