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 first arm is 9" long. Made of German silver, it has a brass and steel tracer point. The arm is evenly divided into tenths and numbered from 5 to 38. It fits into a brass carriage, painted black, which also holds a white plastic measuring wheel, vernier, and registering dial. Screws on the carriage adjust the length of the tracer arm. The carriage is marked: No 22241.
- An 8" brass (painted black) pole arm fits into a hole in the carriage. A cylindrical brass weight is attached to the other end. The arm is marked: G. Coradi, Zürich Switzerland Keuffel & Esser Co New York. An oblong steel testing plate is marked for 0", 1", 2", and 3". It is also marked: G. Coradi Zürich.
- A wooden case covered with black leather is lined with purple velvet. A printed paper chart is pasted inside the case. The chart has columns 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 in the Position and Constant columns are handwritten in the same hand that indicates the Coradi firm manufactured this planimeter with serial number 22,241 on July 15, 1914. Keuffel & Esser stamped the chart with its model number, 4240.
- Gottlieb Coradi (1847–1929) began to make wheel and disc polar planimeters in the early 1880s. In 1894 he made the pole arm higher than the tracer arm and connected the arms with a ball joint. This "compensating" planimeter could trace in both the clockwise and counterclockwise directions, preventing errors introduced by planimeters made in the Amsler style. In 1901 K&E began selling Coradi's compensating planimeter for $36.00. In 1936 the firm began offering the planimeter under the company's Paragon brand name and charged $49.00. K&E stopped selling the instrument in 1939. The Interstate Commerce Commission transferred this example to the Smithsonian in 1963. ID number 1977.0112.02 is an instruction manual.
- References: Peggy Aldrich Kidwell, "Planimeter," in Instruments of Science: An Historical Encyclopedia, ed. Robert Bud and Deborah Jean Warner (London: Garland Publishing, 1998), 467–469; "The Lang-Coradi Planimeter," in Olaus Henrici, "On Planimeters," in Report of the Sixty-fourth Meeting of the British Association for the Advancement of Science (London, 1894), 496–523, on 515; Clark McCoy, "Collection of Pages from K&E Catalogs for the 4240 Family of Polar Planimeters," http://www.mccoys-kecatalogs.com/PlanimeterModels/ke4240family.htm; Catalogue of Keuffel & Esser, 33rd ed. (New York, 1909), 323; Catalogue of Keuffel & Esser, 38th ed. (New York, 1936), 256.
- Currently not on view
- date made
- Keuffel & Esser Co.
- Coradi, Gottlieb
- ID Number
- catalog number
- accession number
- Data Source
- National Museum of American History, Kenneth E. Behring Center