Signedstamped in gold lettering on the case lid: Keuffel & Esser Co. N.Y.
etched on instrument: Keuffel & Esser Co. N.Y.
Inscribedstamped in gold lettering on case lid: 4238
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 compensating polar planimeter is further improved by the user's ability to adjust the relative placement of the two arms. The longer black bar can be placed in one of two holes on the tracing arm. The length of the tracing arm can also be adjusted by sliding the silver metal bar towards or away from the measurement devices. Compensating polar planimeters are also equipped with two measurement devices 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 8 - 9 deal specifically with this model, the 4238.
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.