backstaff

Datecirca 1775

Inventory Number5259

ClassificationBackstaff

Subject

Maker American

Cultural Region

Dimensionswith mounted sights: 36.5 x 63.5 x 12.4 cm (14 3/8 x 25 x 4 7/8 in.)

Material

DescriptionThis is a standard English-style backstaff. The small semi-circle scale is graduated from 0-65°, divided in degrees. A small "4" is marked on this arc and the top is decorated with small stars. The large graduated limb has two distinct scales: 65°-90° and 0-25°, the latter divided every 5'. Diagonals are used for precision readings, an early form of vernier. The space where the maker or owner of this backstaff would have engraved their name has been left blank.

The sighting vanes, essential in making the altitude measurements, are not original. They were made in beech wood by Ebenezer Gay in 1979, and marked accordingly.

In Collection(s)

Exhibit 2008--The Matter of Fact

Signedunsigned

Curatorial RemarksVery similar to instrument made by Benjamin King, of Salem, Massachusetts in the collection of the Peabody Essex Museum Decoration almost identical to Gilbert 1740, Greenwich Museum

FunctionThe backstaff was used to measure the altitude of the sun in order to determine latitude. To avoid the intense glare of the sun while observing it, and since the backstaff was not design to hold color filters, the observer made the measurement with his back turned away from the sun, hence the name of this instrument.

ProvenanceDavid Wheatland purchased from Richard Mills, Exeter, New Hampshire, at a "New York show," January 19, 1967. Donated to CHSI April 1977.