This octant has an ebony frame, reinforced brass index arm, and ivory name
plate. The ivory scale is graduated every 20 minutes from -3o to +100o and read by vernier with tangent screw to single minutes of arc. There is a telescopic sight, four shades for the index mirror, and three shades for the horizon glass. The U.S. Navy transferred this instrument to the Smithsonian in 1930.
Ref: Gloria Clifton, Directory of British Scientific Instrument Makers
1550-1851 (London, 1895), p. 83.