The rim of this Gurley vernier compass is graduated to 30 minutes. The variation arc on the south arm extends 20 degrees either way, and is read by folded vernier to 2 minutes. Two level vials are on the north arm, and an outkeeper is on the south arm. The side of one vertical sight is graduated to half degrees, for determining angles of elevation or depression. The machine-engraved signature indicates that it was made after 1876. This compass came to the Smithsonian from the University of Missouri at Columbia.
Ref: W. & L. E. Gurley, A Manual of the Principal Instruments Used in American Engineering and Surveying (Troy, N.Y., 1904), pp. 108-120.
W. Skerritt, "W. & L. E. Gurley's Engraving Machine," Rittenhouse 11 (1997): 97-100.
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