This is a standard marine sextant that was made around 1908 and later
modified for aeronautical use. The modifications include a rapid release handle
on the radius arm, and a bracket by the horizon glass that might have held a
pendulum-type artificial horizon. Ernst G. Fischer, an instrument maker who
spent most of his career with the U.S. Coast & Geodetic Survey, obtained
patents on these features in the early 1920s. There is, in addition, an electric
light over the divided arc, and a battery in the handle. The sighting telescope
is missing. The National Bureau of Standards transferred this instrument to the
Smithsonian in 1957.
Ref: K. H. Beij, "Astronomical Methods in Aerial Navigation," National Advisotry Committee for Aeronautics, Report 198 (Washington, D.C., 1924), pp. 18-19.
E. G. Fischer, "Fine Motion Device for Surveying and Other
Instruments," U.S. patent #1,376,327
E. G. Fischer, "Artificial Horizon," U.S. patent #1,386,695
E. G. Fischer, "Artificial Horizon," U.S. patent #1,409,938
