David Rittenhouse Surveyor's Vernier Compass

The magnetic compasses that Americans used to determine property boundaries were inexpensive and expeditious but affected by magnetic variation—the fact that magnetic north seldom coincides with true north, and the relation between the two changes over time. The vernier compass solved this problem. This example is marked "David Rittenhouse PHILADELPHIA." It dates from around 1785, and is probably the first American instrument of its kind; similar instruments were made in Ireland. David Rittenhouse (1732–1796) was a skilled clock and instrument maker, man of science, and master of the American mint.
Ref: D. J. Warner, "True North—And Why It Mattered in Eighteenth Century America," Proceedings of the American Philosophical Society 149 (2005): 372–385.
Currently not on view
Object Name
date made
ca 1785
Rittenhouse, David
overall: 13 3/8 in; 33.9725 cm
needle: 5 1/4 in; 13.335 cm
place made
United States: Pennsylvania, Philadelphia
ID Number
accession number
catalog number
See more items in
Medicine and Science: Physical Sciences
Measuring & Mapping
Surveying and Geodesy
Data Source
National Museum of American History, Kenneth E. Behring Center
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