Condy Octant

An octant measures angles by bringing two images together—that of the sun, for instance, and the horizon—and was used primarily to determine latitude at sea. The form was described by John Hadley in London in 1731 and still in use in the early twentieth century.
This example is marked "B. CONDY PHILADELPHIA 1778," the signature being that of Benjamin Condy (d. 1798). It was made during the American Revolution, and there are faint markings on the scale that may read "equality" and "justice." It has a mahogany frame and index arm, and ivory inset. The boxwood scale is graduated every 20 minutes from -5° to +95° and read by ivory vernier to single minutes of arc. There is also a back sight and a back horizon mirror for measuring angles greater than 90°. The radius is 17.75 inches.
Currently not on view
Object Name
Date made
business owner
Condy, Benjamin
Condy, Benjamin
Physical Description
wood (overall material)
brass (overall material)
glass (overall material)
average spatial: 7.9 cm x 42.1 cm x 51.8 cm; 3 1/8 in x 16 9/16 in x 20 3/8 in
Place Made
United States: Pennsylvania, Philadelphia
ID Number
catalog number
accession number
catalog number
Measuring & Mapping
See more items in
Medicine and Science: Physical Sciences
Data Source
National Museum of American History, Kenneth E. Behring Center
Additional Media

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