Established in 1879, the U.S. Geological Survey tested distance measurers to see which best suited their purposes. Those that failed muster were sent to the Smithsonian. This Ferguson Pedograph is one of those instruments.
Ref: Thomas Tapley Helenus Ferguson, “Surveying Instrument,” U.S. Patent 709,313 (Sept. 16, 1902).
Thomas Ferguson, Automatic Surveying Instruments and Their Practical Uses on Land and Water (London, 1904).
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