William Thomson described a new "Marine Azimuth Mirror" at the 1877 meeting of the British Association for the Advancement of Science, and patented the design in Britain and the U.S. This instrument is an example of the improved design, with a reflecting prism in place of the original mirror, that Thomson introduced in the early 1880s. The signature indicates that it was made during the period 1900-1913. The U.S. Coast & Geodetic Survey transferred it to the Smithsonian in 1929.
Ref: William Thomson, "Device for Taking Azimuths," U.S. Patent #210,068.
William Thomson, "Azimuth Instrument," U.S. Patent #402,364.
