Smithsonian - National Museum of American History, Behring Center

 
Physical Sciences Collection - Surveying and Geodesy

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Pocket Compass (prismatic) - click to enlarge

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Pocket Compass (prismatic)

Catalogue number:
PH*314563

Inscriptions:
"U. S. ENGINEERS" and "J. Green N. Y."

Dimensions:
3 inches diameter

Discussion:

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. 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. The United States Weather Bureau transferred this compass to the Smithsonian in 1954.

Further Information:

Compass (pocket)

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