Sextant with a double brass frame of the sort introduced by Edward Troughton in London in 1788. The silvered scale is graduated every 10 minutes from -5° to +155° and read by vernier with tangent screw and swinging magnifier to 10 seconds of arc. The "Riggs Brothers, Philadelphia" inscription came into use in 1865, and refers to a firm that sold instruments of this sort to American customers.
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