radius 12 inches
This octant has an ebony frame and flat brass index arm. The ivory scale is
graduated every 20 minutes from -2o to +100o and read by
vernier and tangent screw to single minutes of arc. There is also a back sight
and back horizon glass used to measure angles greater than 90o. This
instrument was probably made in England around 1800. The U.S. Navy transferred
it to the Smithsonian in 1930.