Magnetic Azimuth Sundial, Ivory Diptych of Bloud Type
notes: label: Description
content: This magnetic azimuth dial is of the Bloud type (after Charles Bloud of Dieppe, fl. 1650). The dial is a rectangular ivory diptych. It has a round metal volvelle on the rear face. The volvelle is marked around the edge with the months (in French) and days; there is a seven-column grid of numbers at the center which serves as a perpetual calendar. Rows 1 and 2 give the numbers of months (March = 1), rows 3-7 contain the numbers 1 to 31 with 4 zeroes completing the final row. Volvelles on Bloud dials are supposed to move, but this one appears to be soldered and nailed in place. The inside of the diptych contains a compass bowl with a metal oval hour scale calibrated from VII to XII to V by I, a compass needle which is not resting on its pin, and a printed paper compass bowl insert. The paper insert has latitudes for eighteen cities, mostly French, cardinal directions in French, and an outer scale calibrated from 0 to 90 four times, by 10 degrees. There is an hour scale calibrated from 5 to 12 to 7 by units in the ivory around the compass bowl. The opposite interior face contains a metal volvelle calibrated from I to XII twice by units, with the months and days around the dial's outside edge. A smaller metal dial affixed on top of the volvelle is calibrated from 1 to 30 and is decorated with a floral motif. This dial has a pointer which indicates the date. The front face contains an engraved circular equinoctial dial calibrated from 1 to 12 twice by units with a central polar dial calibrated 8 to 12 to 4 twice. The pin gnomon and string are missing. This dial probably dates from the second half of the 1600s.
label: Location
content: Currently not on view
topic: label: Subject
content: Mathematics
label: Subject
content: Timekeeping
setName: label: See more items in
content: Medicine and Science: Mathematics
label: See more items in
content: Science & Mathematics
dataSource: label: Data Source
content: National Museum of American History
identifier: label: ID Number
content: MA.330848
label: accession number
content: 305777
label: catalog number
content: 330848
objectType: label: Object Name
content: Sundial, Horizontal
label: Object Name
content: sundial
physicalDescription: label: Physical Description
content: ivory (overall material)
label: Physical Description
content: metal (overall material)
label: Measurements
content: overall, closed: 1.5 cm x 7.2 cm x 8.1 cm; 19/32 in x 2 27/32 in x 3 3/16 in