Troughton & Simms Repeating Circle

Description
This is one of two double repeating circles that Ferdinand Rudolph Hassler, the first superintendent of the U. S. Coast Survey, ordered from Edward Troughton in London in 1812, and that was shipped in 1815. The large circle may be angled from vertical to horizontal to the opposite vertical position. It is graduated to 10 minutes, and read by four verniers and two magnifiers to single minutes.
A repeating circle is a geodetic instrument with two telescopes that is designed to reduce errors by repeated observations taken on all parts of the circumference of a circle. The form was developed by the Chevalier de Borda, first executed by Etienne Lenoir in Paris around 1789, and popular for about 50 years.
Ref: F. R. Hassler, "Papers on Various Subjects Connected with the Survey of the Coast of the United States," Transactions of the American Philosophical Society 2 (1825): 232-420, on 315-320 and pl. VII.
"The Repeating Circle Without Reflection, as made by Troughton," in The Cyclopaedia: or, Universal Dictionary of Arts, Sciences, and Literature, edited by Abraham Rees (London, 1819), Vol. VII, Art "Circle."
Location
Currently not on view
Object Name
repeating circle
maker
Troughton and Simms
Measurements
overall: 32 1/8 in x 26 3/4 in x 17 in; 81.6356 cm x 67.945 cm x 43.18 cm
upper circle: 17 1/2 in; 44.45 cm
circle at base: 13 1/2 in; 34.29 cm
telescope: 24 in; 60.96 cm
place made
United Kingdom: England, London
ID Number
PH*314640
catalog number
314640
accession number
208213
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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