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. It was made before 1892 when Thomson became Lord Kelvin. The U.S. Naval Observatory transferred it to the Smithsonian in 1966.
Ref: William Thomson, "Device for Taking Azimuths," U.S. Patent #210,068.
William Thomson, "Azimuth Instrument," U.S. Patent #402,364.
