This octant clearly dates from the late eighteenth century. It has a mahogany frame and index arm. The boxwood scale is graduated every 20 minutes from 0 to 90 degrees and read by transversals to 2 minutes of arc. The top of the scale is numbered counterclockwise for zenith distances. There is also a back sight and a back horizon glass that can be used to measure angles greater than 90°.
Currently not on view
Object Name
date made
late 18th century
overall: 7.6 cm x 37.8 cm x 46 cm; 3 in x 14 7/8 in x 18 1/8 in
ID Number
catalog number
accession number
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Medicine and Science: Physical Sciences
Measuring & Mapping
Data Source
National Museum of American History, Kenneth E. Behring Center
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