Click image to enlarge.

Bubble Sextant

Catalogue number:
NASM 1963-71

Inscriptions:
"KEUFFEL & ESSER CO. / NEW YORK / 61309 / PAT. 1743979" and "AIRCRAFT OCTANT / MARK IV MODEL 1 / SER NO. 1-32 ORDER NO. 35706"

Discussion:
The Mark IV, Model 1 was an improved version of the Mark I, Model 2–lighter and more compact, and with the divided scale on the inside along with the optical train. This example was the first one made in 1932. The U.S. Naval Observatory transferred it to the Smithsonian in 1963.

Ref: T. C. Lonnquest, "Operation and Adjustment of the Mark II Model 2 Octant," Bureau of Aeronautics, Navy Department, Technical Note No. 207 (Nov. 22, 1929).

Lawrence Radford and Noel Davis, "Sextant," U.S. patent #1,743,979.

Further Information:

Keuffel & Esser
Aircraft Sextant