backstaff
Date: circa 1775
Inventory Number: 5259
Classification: Backstaff
Subject:
Maker: American
Cultural Region:
Dimensions:
with mounted sights: 36.5 x 63.5 x 12.4 cm (14 3/8 x 25 x 4 7/8 in.)
Description:
This 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 his (rarely her) 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.
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)
Signedunsigned
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.
Curatorial RemarksCould have been made by Benjamin King, of Salem, Massachusetts.