Universal equinoctial ring dial

Universal ring dial 17th century. Brass inscribed 'THO.TOMPION IN FLEET STREET FECIT'. These dials can be used in any latitude (except the polar regions) for telling the time and calculating the altitude of the sun. Thomas Tompion (1639-1713) was renowned for his horological expertise, but also made scientific instruments for members of the Royal Society.

Meridian ring with sliding bridge, suspension loop and tightening screw, engraved on one side with two quadrants, one engraved N[orth] and the other engraved S[outh]. There is a pin-hole at 55° south. The north quadrant scale between 81° and 90° is obscured by the ring stop. The scale of latitude is also engraved with a trefoil motif to indicate the 5° points. The other side of the meridian ring is marked with a graduated, but otherwise unmarked declination scale 0° - 90°, with 5° and 1° subdivisions. The pivoted equinoctial ring is engraved on three sides. One side graduated with Roman numeral hours I - XII twice, the edge and inner face marked with 5 minute, 15 minute and 30 minute intervals. The other side is engraved with a declination scale 0 - 90 in Arabic numerals and there is a pin-hole for measuring the sun's altitude. The bridge is pivoted with a sliding pin-hole gnomon, engraved on one side with the initials of the months and on the other with a declination scale SD 20 - AE - 20 ND and zodiac symbols. The equinoxes are at March and September. The bridge bars are embellished with foliate decoration.