This sextant was probably made by the John Nixon who worked in London from
1850 to 1869, and who advertised as a "Real Maker of Mathematical
Instruments." It may have been lent to the U.S. Navy for use during World
War I. It came to the Smithsonian in 1930. The silvered scale is graduated every
15 minutes from -5o to +125o and read by vernier with
tangent screw and magnifier to 15 seconds of arc.
Ref: Gloria Clifton, Directory of British Scientific Instrument Makers
1550-1851 (London, 1895), p. 201.