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.
- This instrument has two arms. The German silver tracer arm has a support for the tracer point and is evenly divided by tenths numbered from 10 to 37. Ten units are equivalent to 5mm. The tracer arm fits within a carriage of brass, painted black, that also holds a white plastic measuring wheel and vernier and a metal registering dial. The pole arm is made of brass painted black and is attached to the carriage. The end of the pole arm fits into a rectangular metal weight faced with brass painted black. The weight is marked: G. Coradi Zürich (/) No 759. The bottom of the weight is covered with paper. A cylindrical brass weight fits into a hole on top of the pole arm. The testing rule is missing.
- A wooden case covered with black leather is lined with purple velvet. A paper printed chart glued inside the lid has columns in German for Scales, Position of the vernier on the tracer bar, Value of the unit of the vernier on the measuring roller, and Constant. The values are handwritten. The date on the chart indicates the Coradi firm made serial number 759 on December 28, 1888.
- 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 modified the design into the "compensating" polar planimeter; see MA*321777. Union College donated this instrument in 1964.
- Reference: "People: Gottlieb Coradi," Waywiser, Harvard University Department of the History of Science, http://dssmhi1.fas.harvard.edu/emuseumdev/code/eMuseum.asp?lang=EN.
- Currently not on view
- date made
- Coradi, Gottlieb
- ID Number
- catalog number
- accession number
- Data Source
- National Museum of American History, Kenneth E. Behring Center