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Inventory no. 46769 - Epact entry

Epact number: 38312


Signed by Hans Bamman
Dated 1490; German
Brass; 140 mm in diameter

Main text

Only the mater of this instrument survives. Its back clearly illustrates two astrolabe scales worth commenting on.

The outer scale is the common circle of degrees and immediately within this are the signs and degrees of the zodiac. The next scale, however, separated from the zodiacal scale by a blank space, is a scale of lunar mansions, that is of the 28 sections of the zodiac occupied by the moon in the successive days of a lunar month.

Within this, separated by another blank space, is a calendar scale. The dates on this scale correspond with the positions of the sun in the zodiac on the outermost scale, but it is noticeable that the calendar scale is eccentric, that is, is offset with respect to the zodiacal scale. This is to accommodate the variation in the sun's apparent progress along the ecliptic throughout the year.

Source museum: Museum of the History of Science, Oxford
Museum number: Inventory no. 46,769

Detailed text

The mater comprises a back plate attached to the limb. The throne has a shackle with a rose decoration on both sides and a suspension ring. The limb has a degree scale 0 to 360, divided to 5, subdivided to 1, numbered by 10. The rim is divided for hours, 1 to 12 twice.

The back has an outermost degree scale 90 to 0 to 90 to 0 to 90, divided to 5, subdivided to 1, numbered by 10. Within this is a zodiacal scale, with the names and symbols of the signs, each having a 30-degree scale divided as the degree scale. Next is a scale of the 28 lunar mansions, containing 12 or 13 days, then an eccentric calendar scale, with the Latin names of the months, each with a scale of days, divided to 5, subdivided to 1, numbered by 10 as appropriate. The central space has a double shadow square with scales 0 to 12 to 0 to 12 to 0, divided to 3, subdivided to 1, numbered by 3, and a diagram for unequal hours. Dated '1490' and signed 'h b' with Hans Bamman's triangular mark.

Jim Bennett

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