Pocket Compass (prismatic)

Pocket Compass (prismatic)

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This compass is similar to the one for which Charles Schmalcalder, a London instrument maker, obtained a British patent in 1812. It is designed so that a surveyor can read the card while sighting a distant object. It has a tall folding sight at north, and at south, a shorter sight with a prismatic eyepiece at its base. The floating card is colored bright green; the numbers around its edge read correctly when seen through the prismatic eyepiece.
This example is marked "U. S. ENGINEERS" and "J. Green N. Y." The U. S. Weather Bureau transferred it to the Smithsonian in 1954. James Green was born in England in 1808, moved to the United States around 1832, and opened an instrument shop in Baltimore. He opened a second shop in New York in the early 1840s, and retired in 1885.
Currently not on view
Object Name
Pocket Compass (Prismatic)
Green, James
place made
United States: New York
overall: 3 in; x 7.62 cm
overall: 13/16 in x 4 in x 3 in; 2.06375 cm x 10.16 cm x 7.62 cm
ID Number
catalog number
accession number
Credit Line
U.S. Department of Commerce, U.S. Weather Bureau
See more items in
Medicine and Science: Physical Sciences
Surveying and Geodesy
Measuring & Mapping
Data Source
National Museum of American History
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