This sextant has a brass frame. The silvered scale is graduated every 10 minutes from -5o to +145o and read by vernier
with tangent screw and swinging magnifier to single minutes of arc. It
belonged to Vassar College, and may have been used by Maria Mitchell, who taught astronomy to young women there beginning in 1865.
Ref: Gloria Clifton, Directory of British Scientific Instrument Makers
1550-1851 (London, 1995), p. 106.