Signedstamped in bottom right of case lid: K + E
written in top right corner of white card inside case: K + E
etched on instrumetn arm: K + E / Keuffel & Esser Co. N.Y./ Made in Germany
Inscribedwritten in pen on tag inside case: 8-20-65
typed on white card inside case: 4236
handwritten on card inside case: serial number 15785
etched in white type on tracing arm: 15785
engraved in flat metal tape: 10 sq. in.
FunctionThe polar planimeter is used for ascertaining the area of any plane surface represented by a figure drawn to any scale, such as indicator diagrams, profiles, architectural plans or sections. The planimeter is placed over top of the diagram in question and the user traces it with the stylus at the end of the short arm of the instrument. The planimeter measures the area of the traced figure. This particular model of planimeter was useful for terrain analysis, cut and fill procedures, and hydrology.
This is a polar planimeter because the intersection point of the tracing arm and the longer black arm is restricted to circular motion. This is the case because the other end of the longer black arm is fixed in place by the brass puck. For linear planimeters, the end of the tracer opposite the stylus moves in a straight line, either in a track or on rollers.
This model of a compensating polar planimeter is further improved by the user's ability to adjust the length of the tracing arm by attaching the silver metal strip extension in either of two holes. It is also equipped with a second measuring device, where regular polar planimeters have only one.
As the user traces a figure on the surface below, the metal roller attached to the tracing arm rolls and slides along accordingly. The measurement mechanisms record this motion and when the user arrives back at the starting point, the recorded motions will be proportional to the area of the figure below.
The Keuffel & Esser Co. Manual for compensating polar planimeters that details the design and function of the instruments can be found here. Pages 5 - 8 deal specifically with this model, the 4236.
Historical AttributesOrigially used in Graduate School of Design classes at Harvard University, including GSD 6104 (Fundamentals of Landscape Technology M3), GSD 6105 (Fundamentals of Landscape Technology M4), GSD 6206 (Landscape Technology), and GSD 6316 (Terrain Analysis), taught by Professors McIntosh, Harris, Jewell, and Ervin.
Primary SourcesKeuffel & Esser Co., "Directions for the Use, Care, and Adjustment of Compensating Polar Planimeters", printed in the United States, 1938.
ProvenanceGiven to CHSI on 5 August 1997 by Niall Kirkwood, Associate Professor of Landscape Architecture, Department of Landscape Architecture, Harvard University Graduate School of Design.