"BUBBLE SEXTANT / U.S. NAVY / BUREAU OF STANDARDS / MODEL NO. 2 / 1924 / NO. 2"
This is one of six instruments that Bausch & Lomb produced for the
Aeronautical Instrument Section of the National Bureau of Standards in 1924. The U.S. Naval Observatory transferred it to the Smithsonian in 1948.
National Bureau of Standards