This is a compound monocular with coarse and fine focus, double nosepiece, square stage, inclination joint with handle, sub-stage diaphragm, sub-stage mirror, and horseshoe base. The inscription reads “E. Leitz Wetzlar / No 24997.” The serial number indicates a date of around 1892. The back of the base is marked “48?”
This was used at the Department of Terrestrial Magnetism of the Carnegie Institution of Washington.
Ref: Ernst Leitz, Petrological and Metallographic Microscopes (Wetzlar, 1910), pp. 14-17.