Lietz Reducing Arc

William T. Rhodes (1898-1961) invented the reducing arc while conducting a topographical survey through the rugged terrain along the Merced River in California, in preparation for the All Year Highway to the west entrance of Yosemite National Park. When his design proved practicable, Rhodes submitted a patent application and convinced Lietz to manufacture the device in exchange for royalties.
The first advertisements appeared in 1928, and Rhodes received a patent in 1930. The Rhodes reducing arc was soon popular, especially with highway engineers. Lietz still had some in stock in the late 1980s. Michael Baker Jr., Inc., donated this example to the Smithsonian in 1997. The signature reads "RHODES REDUCING ARC MFD. BY The A. LIETZ CO. SAN FRANCISCO, U.S.A. PATENTED NO. 1,785,284 SERIAL No. 18296."
The Rhodes reducing arc consists of a semicircle attached to a vertical pole, with a sighting tube on the straight edge. With it, a surveyor can take a sight on a vertical range pole, use a tape to measure the slope distance to the pole, and read the horizontal and vertical distances on the gridded half of the arc.
Ref: Doug Morin, "William T. Rhodes and His Reducing Arc," P.O.B. (May 1996): 60-64.
A. Lietz, Engineering, Surveying, Mining and Nautical Instruments (San Francisco, 1928), pp.122-123.
Currently not on view
Object Name
reducing arc
A. Lietz Company
overall: 15 in x 21 in x 2 1/2 in; 38.1 cm x 53.34 cm x 6.35 cm
ID Number
accession number
catalog number
Measuring & Mapping
Surveying and Geodesy
See more items in
Medicine and Science: Physical Sciences
Surveying and Geodesy
Data Source
National Museum of American History, Kenneth E. Behring Center
A. Lietz. Engineering, Surveying, Mining and Nautical Instruments

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