This is a standard "U.S. Navy High Grade Sextant" that was made in
the period 1914-1916 and modified in the early 1920s. It has a Willson bubble
telescope, a Fischer rapid release lever, a drum micrometer, an electrical light
over the divided arc, and a battery in the handle. The National Bureau of
Standards transferred it to the Smithsonian in 1957.
Ref: K. Hilding Beij, "Astronomical Methods in Aerial Navigation," National Advisotry Committee for Aeronautics, Report 198 (Washington, D.C., 1924), pp. 15-16.