This is a marine sextant with a gyroscopic artificial horizon. Georges Ernest
Fleurais, a French naval officer, designed the form in the late 1880s, for use
when the natural horizon could not be seen. The first examples were made by A. Hurlimann in Paris. This one was made by Ponthus & Therrode, who took over Hurlimann’s shop in 1900. The U.S. Naval Observatory acquired it around 1912, and transferred it to the Smithsonian in 1963.
The Aeronautical Instruments Section of the National Bureau of Standards
reported in 1924 that this type of instrument could give accurate results, but
did not seem to be "suitable for aircraft because of the time and care
demanded by the observation, the amount of calculation necessary, and the need for two observers."
A label in the box reads: "A. Hurlimann, Ponthus & Therrode
Successeurs / Constructeurs d’Instruments de Précision / 6 rue Victor Considérant, Paris."
Ref: K. H. Beij, "Astronomical Methods in Aerial Navigation," Report of the National Advisory Committee for Aeronautics 198 (1924), pp. 20-21.
G. E. Fleurais, "Gyroscope Collimateur, Substitution d’un repPre
artificiel B l’horizon de la mer," Revue Maritime & Coloniale (1887).
G. E. Fleurais, Horizon Gyroscopique, ModPle Définitif (Paris, 1891).
