Equinoctial Ring Dial

Universal Equinoctial Ring Dial J. Field, London, England, ca 1787 Gift of Roger Williams N 3

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The universal equinoctial ring dial was primarily used to determine the time of day. Some instruments could also measure the height of the sun which was useful when trying to determine latitude.

The meridian ring of this dial has a latitude scale divided by 1/2 and numbered by 10s on the front and back (0 to 90 degrees, 90 to 0 degrees). The equatorial ring has an hour ring divided to 2 minute intervals and is numbered with Roman numerals on face and both Roman and Arabic numbers on inner edge. The inner ring pivots perpendicular to outer ring. The bridge attached to the outer ring flips and carries a calendar on one side and zodiac and degree declination scales on the other.

For more information, e-mail collections@MarinersMuseum.org.