Surveyor's Vernier Compass
date: label: date made
content: ca 1785
name: label: maker
content: Rittenhouse, David
notes: label: Description
content: 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.
label: Description
content: This example dates from around 1785, and is probably the first American instrument of its kind; similar instruments were made in Ireland. The vernier (not easy to see) is on the rim, at north. An inscription reads "David Rittenhouse PHILADELPHIA".
label: Description
content: David Rittenhouse (1732–1796) was a skilled clock and instrument maker, man of science, and master of the American mint.
label: Description
content: Ref: D. J. Warner, "True North—And Why It Mattered in Eighteenth Century America," <i>Proceedings of the American Philosophical Society</i> 149 (2005): 372–385.
place: label: place made
content: United States: Pennsylvania, Philadelphia
setName: label: See more items in
content: Medicine and Science: Physical Sciences
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content: Surveying and Geodesy
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content: Measuring & Mapping
dataSource: label: Data Source
content: National Museum of American History
identifier: label: ID Number
content: 1983.0498.01
label: accession number
content: 1983.0498
label: catalog number
content: 1983.0498.01
objectType: label: Object Name
content: surveyor's vernier compass
physicalDescription: label: Measurements
content: overall: 13 3/8 in; 33.9725 cm
label: Measurements
content: needle: 5 1/4 in; 13.335 cm
label: Measurements
content: overall: 2 3/4 in x 13 1/2 in x 6 1/2 in; 6.985 cm x 34.29 cm x 16.51 cm