Signed by Charles Whitwell
Dated 1595; English
Brass; 388 mm in diameter
This astrolabe is of the type describes by John Blagrave as his 'Mathematical Jewel'. The limb is secured to the plate by a series of screws, the plate has a simple throne, a shackle and suspension ring. The limb has a zodiacal calendar with an outer scale of dates, with the months named in English, divided to 10, to 5 and to 1 day, numbered as appropriate to 10. The zodiac scale had the names and symbols of the signs, and a 30-degree scale for each sign, divided to 10, subdivided to 5 and to 1, numbered by 10. The single-degree divisions are also numbered at the inner edge of the rim to give a degree scale from the throne 90 to 0 to 90 to 0 to 90.
Inside the mater is a universal projection of the saphea type, with lines for every degree of right ascension and declination, the ecliptic line divided for the signs of the zodiac, and the hour lines numbered 1 to 12 and 12 to 1.
One half of the rete has a skeletal grid of meridians and parallels of the same projection with an arc for the southern half of the ecliptic, marked with a zodiacal scale, with the names and symbols for the signs, each with a scale 0 to 30, divided to 5, subdivided to 1, numbered by 10. Stars are engraved and names on the grid and the zodiac. A meridian bar has a scale of degrees, divided to 5, subdivided to 1, numbered only on the half containing the grid, 0 to 90 by 10. The other half of the rete has pointers for named stars and the corresponding northern half of the ecliptic. A diametric bar between the two halves of the rete has a scale, from the centre, 0 to 90 to 270 to 360, divided to 10, subdivided to 5 and to 1, numbered by 10. The edge on the rete has a degree scale, divided to 5, subdivided to 1, numbered only on the half containing the grid, 0 to 90 to 90.
The verso is incomplete, includes an altitude scale on the edge, and is signed: '[star] Charolus Whitwell fecit 1595 [star]'.
Istituto e Museo di Storia della Scienza, Firenze
Inventory no. 1095
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