Coradi Polar Planimeter

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 (/) N^o 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.

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