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Inventory no. 49847 - Former Display Label

ASTROLABE and EQUATORIUM of unknown origin
Late 15th century

Unsigned and undated. Brass.

The equatorium is on the other side (see the reverse of this label [below]). On this side is an astrolabe. Rete for twenty-two stars; the positions of five constellations are also shown. The star-pointers derive from the 'wavy flame' type. The design of the rete is very unusual; part of the tracery represents the great circles dividing the ecliptic into its twelve divisions, the names of which are engraved (with two exceptions) on the Capricorn circle and not the ecliptic circle, which is, however, divided into degrees. Over the main rete is a smaller rete consisting only of an ecliptic circle, engraved with a zodiac/calendar scale (0° Aries = 101/2 March; concentric type), and a circular scale numbered 1-28, representing the mansions of the moon. Two plates: (a) an ordinary tablet (with azimuths and without hour-lines) for latitude 45°; a tablet of horizons, engraved also with sixteen equally spaced radial lines, inscribed (reading anti-clockwise from the southern or uppermost line), "ÎICI{V circumflex} MORBI [i. e. inicium morbi]", "1p", "1 IND", "2p", "1 CRISIS", "3p", "2 INDI", "4", "2 CRISIS", "5p", "3 INDI", "6p", "3 CRISIS", "7p", "4 INDI", and "8p". (b) an ordinary plate (without azimuths or hour-lines), uninscribed, but for latitude c.48°; a tablet of twelve astrological houses [see added * note below], each divided into three equal parts, for latitude 45°. The mater is blank. The limb is engraved with a scale of equal hours and in each of the two upper quadrants, a scale of 90°. Fixed to the front of the 'throne' are two sights, and inscribed on the front of the 'throne', the words, "INICI{V circumflex} MORBI" (cf. plate (a) above). There is an alidade, engraved on each arm with a declination scale, one for northern, the other for southern declinations.

An Equatorium

Equatoria are computing instruments which serve to determine planetary positions - usually according to the Ptolemaic system. The equatorium thus complemented the astrolabe, which could be used only for the solution of problems involving the daily rotation of the Sun and stars on the assumption that their positions were first known. (The calendar scale on the back of an astrolabe, used for finding the Sun's positions throughout the year, can be regarded as a rudimentary equatorium.) Many Islamic and European astronomers concerned themselves with the development of the equatorium, which assumed many forms, and a treatise in Middle English on the subject has been ascribed to Chaucer (see the label 'Chaucer and the astrolabe', in the first horizontal case to the right). Some equatoria enabled the user to dispense entirely with astronomical tables, but most required tables of mean planetary motions. Very few metal equatoria are known. The sexagenarium exhibited in this gallery with the quadrants (see the case in the north-east corner) is such an instrument. There is another on the back of an astrolabe in Merton College, there is a fragment in Brussels, and a fine late example (c.1600) in Liverpool.

This equatorium is neither signed nor dated, but dates from the end of the 15th century or the beginning of the 16th. It is the type of equatorium described by Franciscus Sarzosus Cellanus of Aragon in his In aequatorem planetarum, Lib. i 'Fabrica aequatoris', Lib. ii 'Veri motus ac passiones planetarum aequatoris ministeris investigare docens', Paris (Simon Colineus), 1526. A similar equatorium is found in a volume of manuscript pasteboard instruments, of c.1552, in the Bodleian Library, MS Savile 100, f. 8.

On the other side of this equatorium is an astrolabe (see the reverse of this label). To contain the equatorium this side of the instrument has a second mater surrounded by a limb. (The bracket was cast integrally with this limb which was brazed to a second limb with a flat circular plate sandwiched between the two limbs to form a mater on either side.) The limb is engraved with a zodiac scale. Inside the mater fits a plate (like that of an astrolabe) engraved, on one side only, with scales representing the auges of the planets and the mansions of the moon. Above this (like the rete of an astrolabe) is a disc with six arms. Three of the arms serve as indices, and the other three carry small discs each with an index-arm pivoted at its centre. These discs are for (a) Saturn, Jupiter and Mars; (b) Mercury and Venus; and (c) the Moon. On the discs are scales of mean auges; and the indices are marked with points representing the planets. The discs, together with their indices, can slide along their supporting arms; this permits the epicycle to be adjusted, according to the scales engraved on the arms. Above the whole is a rotatable index.

The whole instrument is finely engraved with Roman lettering mixed with some Lombardic, and with late medieval numerals. The planetary symbols are of a very unusual form, and similar symbols have only been noted on a manuscript equatorium (of a different and perfected type invented by Guillaume Gilliszoon de Wissekerke, c.1494) in the Bibliothèque Nationale, Paris, MS Lat. 7276B. The inscriptions on the 'throne' on the other side and plate (a) of the astrolabe, and the purely astrological tablet on plate (b) of the astrolabe, suggest that it was primarily intended for astrological use in connexion with medical practice. It is perhaps of Sourthern French or North Italian origin.

This instrument formerly belonged to the d'Hauteville family and comes from their house at Salon (Provence).

Billmeir Collection

*Note added 9/1/2019. This plate actually has two sequences of 12 main arcs, rather than the single set of 12 expected for houses. It is engraved with each circular arc passing through the north point of the horizon (as in the Regiomontanus house division) but is graduated as if it was a set of unequal (planetary or seasonal) hours, with each hour subdivided into 3. While planetary hours are sometimes used as a rough approximation for the houses, are there any other instances where the houses are used to approximate unequal hours? Note that there are no unequal hours on the main plate for 45 degrees.

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