Bloud-type magnetic azimuth, ivory diptych sundial
Date: circa 1665
Inventory Number: 7519
Classification: Sundial
Dimensions:closed: 1.7 x 8.6 x 10.9 cm (11/16 x 3 3/8 x 4 5/16 in.)
DescriptionThis is a magnetic azimuth sundial made of ivory in an octagonal shape. Incised lines are filled in black. There is a hole to store the pin gnomon, which is missing. The arm to set the top leaf at the proper angle is made of silver.
1a: equatorial sundial for the summer half of the year, with hours I-XII twice, divided into 1/4 hours; polar sundial with hours 8-12-4, divided every 1 hour. Space between the hour scales is filled with a running leaf decoration, flowers, and tendrils. There is a Dieppe-style pecked border.
1b: Lunar volvelle made of pewter with aperture revealing the phases of the moon at different ages, and hours 1-XII twice for using the sundial as a moon dial and tide dial. A latitude scale is along the right edge of the leaf, reading 0-80. Ornamentation includes the running leaf pattern around the volvelle and the Dieppe-style pecked border.
2a: Magnetic compass with paper insert marked with 32 points on the wind rose and divided circle 0-90-0-90-0. Cardinal directions marked in French. In center of wind rose is a gazetteer for 24 cities, mostly French, with their latitudes. The compass needle might be a replacement. On top of the compass insert, there is a pewter hour scale for the magnetic azimuth sundial. It is marked V-XII-VII. Around the compass are hours V-XII-VI, divided every 7 1/2 minutes, for a string-gnomon sundial for 49. The Dieppe-style pecked borders fill in the area around the hour scale and edge of the leaf.
2b: Silver volvelle with a calendar scale to set the magnetic azimuth dial hour scale on the other side of the leaf. The calendar is marked in French months divided into 5 day intervals. A pointing hand serves as index. Inside the calendar scale is a perpetual calendar of the Morland square type. The volvelle is surrounded by a running leaf decoration, and the edge of the leaf has the Dieppe-style pecked ornamental border.
Signedon 1a: C · BLOVD / A · DIEPPE
on 2b: Fait par Charles Bloud ADieppe
FunctionThe magnetic azimuth dial of the form invented and made by Charles Bloud of Dieppe in the mid-17th century was a pocket diptych sundial that found time by the relative position of the compass needle to an hour scale that was adjusted for the date. Bloud-type sundials also had other forms of sundials within them and volvelles for finding the age of the moon, times of tides, and time by moon light.
ProvenanceDavid P. Wheatland, Topsfield, MA; gift to CHSI, ca. 1987.
Published ReferencesSteven A. Lloyd, Ivory Diptych Sundials, 1580-1750 (Cambridge: Harvard University Press, 1992), cat. no. 60.