backstaff
Date: 1753
Inventory Number: 1993-1-0011
Classification: Backstaff
Subject:
Maker: John Dupee
Cultural Region:
Place of Origin:
Dimensions:
63.6 x 34.8 x 2 cm (25 1/16 x 13 11/16 x 13/16 in.)
Material:
Description:
This is a standard English backstaff. This one, however, is missing the sighting vanes that were essential in making the altitude measurements. The small semi-circle scale is graduated from 0-65°, divided in degrees, while 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 owner of this backstaff would have engraved his (rarely her) name has been left blank.
In Collection(s)
Signedon wood inlay: Iohn Dupee fecit 1753 / For Mr
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.