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Pendulum Sextant - click to enlarge

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Pendulum Sextant

Catalogue number:
NASM 1957-632

"KEUFFEL & ESSER CO. / NEW YORK / 18446" and "U.S. NAVY N 405"

radius 6 inches

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

Further Information:

Keuffel & Esser
Aircraft Sextant