Instrument maker Gottlieb Coradi established a workshop in Zurich in 1880 and soon began making polar planimeters in the Amsler style. In 1894 he adjusted the pole arm so that it was higher than the tracer arm. He also replaced the pivot connecting the arms with a ball joint. The result, which he called a "compensating" polar planimeter, prevented errors introduced by planimeters made in the Amsler style because Coradi's instrument could trace in both the clockwise and counterclockwise directions. As the relatively large number of Coradi planimeters in the collection suggests, the instruments were widely sold in the United States in the early 20th century—even though they were somewhat more expensive than Amsler planimeters. Because the firm put a label inside each case with the exact date on which each planimeter was manufactured, along with the specific calibration for each instrument, it is easy to identify Coradi planimeters and arrange them in chronological order.
"Planimeters - Polar–Coradi" showing 1 items.
- The citation information for this 40-page booklet is: G. Coradi, The Coradi Planimeters: Description and Instructions for the Use and Testing, with a General Elementary Explanation of Their Operation (Zurich, 1912). Gottlieb Coradi (1847–1929) established a workshop in Zurich in 1880 and began making wheel and disc polar planimeters in the Amsler style soon thereafter. In 1894, he designed the compensating polar planimeter, and by 1900, his firm was selling a precision rolling planimeter.
- This booklet explains the mathematical theory behind planimeters, which are used to measure the area bounded by a curved diagram. Coradi then describes the general parts of a planimeter and provides instructions for the forms manufactured by his workshop: the rolling sphere planimeter (see MA*333660 and 1977.0112.01), the precision disc planimeter (see MA*321745), and the compensating polar planimeter (see 1987.0929.01 and MA*321777). Olaus Henrici (1840–1918), a German mathematician who taught at English universities, helped Coradi prepare the booklet.
- The donor also provided three Coradi pamphlets on the coordinatograph, an instrument for quickly plotting points on a map according to their rectangular coordinates. According to the illustrations at the back of this booklet, Coradi's firm also made integraphs and pantographs.
- References: "People: Gottlieb Coradi," Waywiser, Harvard University Department of the History of Science, http://dssmhi1.fas.harvard.edu/emuseumdev/code/eMuseum.asp?lang=EN; Olaus Henrici, "On Planimeters," in Report of the Sixty-fourth Meeting of the British Association for the Advancement of Science (London, 1894), 496–523.
- Currently not on view
- date made
- Coradi, Gottlieb
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- accession number
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- Data Source
- National Museum of American History, Kenneth E. Behring Center