Gunter's quadrant with declinatory for 51°30'
Date: circa 1690
Inventory Number: 7483
Classification: Astrolabe Quadrant
Dimensions:9.4 x 19.3 x 19.3 cm (3 11/16 x 7 5/8 x 7 5/8 in.)
DescriptionThis brass quadrant is a variant form of Gunter's quadrant with a declinatory on the reverse.
The Gunter's quadrant has the following parts, moving from the apex to the limb:
Plumb line with replacement bob wrapped in leather. The sights are along the right-hand edge.
A table of five bright stars with their right ascensions. The table serves as a key to the stars labeled A-E on the celestial projection below.
A Pegasus Wing 23: 56
B Arcturus 14: 00
C Lyon's [heart] 09: 50
D Bull's Eye 04: 18
E Vultures [heart] 19:35
A calendar scale in four lines, running Winter Solstice to Spring Equinox (R to L); Autumn Equinox to Winter Solstice (L to R); Summer Solstice to Autumn Equinox (R to L); Spring Equinox to Summer Solstice (R to L). The calendar is divided into English months, with graduations every day.
A solar declination scale, marked "Sun's Declination," runing 0 to 23° 31' 30" and marked every 2° up to 20°, and then every 5'.
The left side of the Gunter's quadrant projection shows equal hours VI-XII-VIII every quarter hour and solar declination 0°-23 1/2° with zero marked by the zodiacal symbols for Aries and Libra on the equatorial line.
The right side of the Gunter's quadrant projection shows azimuths 0°-90°-130° every 5°. The ecliptic is marked by a dotted line (with dots at every degree) and labeled with zodiacal symbols. The horizon line is shown. There is a Tudor rose engraved between the hours and azimuths.
Below this, there is a shadow scale marked "Qua Shadowes." The left-hand part of the shadow scale is non-uniformly divided into 100 parts labeled at 10 intervals [0]-1-...-9-1[0], with 10 parts in each interval. The right-hand side of the shadow scale is divided into non-uniform parts from 1 to 50, with a different number of subdivisions in each interval.
Below this along the limb, there is a angle scale divided 0°-90° and 90°-0°, and with subdivisions every 20'.
On the reverse of the quadrant is a declinatory for 51°30'. It consists of a horizontal sundial mounted on a volvelle. The sundial has a removable gnomon that slides in track. The gnomon has its own plumb bob for leveling the declinatory. Hours are marked III-XII-VIII, with subdivisions every 1/8 hour (i.e., every 7 1/2 minutes). The declination scale runs 0°-180°-0° around the edge of the sundial volvelle.
Decorations to the quadrant include geometric patterns with flowers along the gnomon track; a sun face on the horizontal dial; ribbons and a Tudor rose between the ribbons at the ends of the hour scale. The corners of the quadrant have elaborate engravings of fruit and flowers growing out of flower pots.
Signedunsigned
FunctionThe Gunter's quadrant is a type of astrolabe quadrant devised by Edmund Gunter in the early 1620s. Like an astrolabe, it has a planispheric projection of the celestial sphere and local altazimuth coordinates, but these are "folded up" so as to be inscribed on a quadrant rather than a disk. The instrument was used for observations of the sun and stars, astronomical calculations, time finding, and surveying,
The declinatory is a type of dialing instrument--i.e., a tool for laying out the hour lines of sundials. The declinatory was used for determining the orientation of a wall. Having determined the time with the Gunter quadrant on the reverse side of the plate, the edge of the declinatory would be held against the surface of a wall, using the plumb bob on the gnomon to ensure it is level. The gnomon is then rotated until its shadow corresponds to the current time. The index will indicate the angle of the wall to the meridian.
Primary SourcesEdmund Gunter, De Sectore et Radio (London, 1623).
ProvenanceWebster, London, before 1929; Harrold E. Gillingham Collection, 1929; David P. Wheatland, Topsfield, MA, 1949; gift to CHSI, c. 1985.