This has an air-driven gyroscope mounted on the index arm in such a way that
it can be moved up and down, that serves as the artificial horizon. The U.S.
Naval Observatory transferred it to the Smithsonian in 1963. The form was
developed in France shortly after World War I, and exhibited at the Paris Air
Show in 1920. Beij referred to it as a Derrien sextant.
Ref: K. H. Beij, "Astronomical Methods in Aerial Navigation," Report of the National Advisory Committee for Aeronautics 198 (1924), p. 21.
Peter Ifland, Taking the Stars (Newport News, 1998), pp. 160-161.