compensating polar planimeter
Date: circa 1920
Inventory Number: 2004-1-0345
Classification: Planimeter
Subject:
Maker: Gottlieb Coradi (1847 - 1929)
Seller: Eugene Dietzgen Company (1885-present)
Cultural Region:
Dimensions:
3.5 x 42 x 6 cm (1 3/8 x 16 9/16 x 2 3/8 in.)
Accessories: pieces of the front of black leather case with clasps; lid of case with paper data sheet; pieces of black leather case lined with green velvet
DescriptionThe planimeter breaks down into three main pieces. The longest piece is a black, rectangular metal bar that sits on top of a large black puck at one end and a silver metal pin at the other end. Secondly, there is a shorter, flat metal tape with a small hole at one end.
The third main piece consists of a shorter black, rectangular metal bar, called the tracer arm. There is a metal roller whose axis is perpendicular to the shorter black bar at one of its ends. Also at that end, there are two short, black rectangular bar offshoots, each perpendicular to the main bar. There is a single hole drilled through the very end of this black bar. These two bars serve to frame and support two measuring devices. One device consists of a flat white disc with incremental measurements from 0 to 9 marked around the circumference. The disc lies flat on top of the black metal bar. There is a black arrow that is attached to the black bar and one end and the other end lies flat on the disc pointing to the measurements. Beneath the disc, parallel to the main bar, there is a thick, silver metal screw. The second measurement device consists of a wheel and the subsection of a wheel, both white with black markings. The axis of both runs parallel to the black bar and connects with the silver metal screw beneath the white disc. The wheel is incrementally marked with the numerals from 0 to 9, and each increment is further subdivided into 10 sections. The wheel subsection has a single unit, one end marked 0 and the other marked 10 with 10 equally spaced lines between them. The wheel subsection serves to increase the accuracy of the readings made on the wheel.
At the opposite end of the smaller black bar from the measurement mechanisms, there is another, silver metal rectangular bar. The latter rests on top of the former so that they overlap for part of its length and then it extends past the black metal bar for the rest of its length. The silver metal bar has a set of etched measurements on part of the subsection that rests atop the black bar. The measurements are equally spaced, with the increment closest to the stylus marked 25 and the increment closest to the measurement mechanisms marked 33. Each increment is subdivided in ten by small lines.
Beneath the section of the black bar above which the incrementally marked silver metal bar sits, there is a silver metal screw. The screw can be loosened to permit users to adjust the placement of the silver metal bar on top of the black metal bar. In between the incrementally marked section of the silver metal bar and the black bar on which it sits there is a short metal pin that rests flat on the top surface of the black bar, directly beneath one of the measurement increments.
At the end of the metal bar that does not rest atop the black bar, there is a black metal clamp. A silver metal stylus next to a small metal stand and brass screw extend below the clamp, and a brass screw extends above it. The black clamp has a depression on either side. Users are meant to put their thumb and middle finger in the depressions and to rest their pointer finger on top of the brass screw, extending above the clamp, when directing the stylus.
When the instrument is assembled, the silver metal pin at one end of the longer black metal bar sits in the hole through the top of the shorter black bar. These holes are located at the two junctions from which the short black offshoots that frame the measuring devices emerge.
There is a white piece of paper inside the case lid with charts of scales.
The Keuffel & Esser Co. manual for a similar model of compensating polar planimeter that details the design and function of the instruments can be found here. Pages 8 - 9 deal specifically with this model, the 4238.
The third main piece consists of a shorter black, rectangular metal bar, called the tracer arm. There is a metal roller whose axis is perpendicular to the shorter black bar at one of its ends. Also at that end, there are two short, black rectangular bar offshoots, each perpendicular to the main bar. There is a single hole drilled through the very end of this black bar. These two bars serve to frame and support two measuring devices. One device consists of a flat white disc with incremental measurements from 0 to 9 marked around the circumference. The disc lies flat on top of the black metal bar. There is a black arrow that is attached to the black bar and one end and the other end lies flat on the disc pointing to the measurements. Beneath the disc, parallel to the main bar, there is a thick, silver metal screw. The second measurement device consists of a wheel and the subsection of a wheel, both white with black markings. The axis of both runs parallel to the black bar and connects with the silver metal screw beneath the white disc. The wheel is incrementally marked with the numerals from 0 to 9, and each increment is further subdivided into 10 sections. The wheel subsection has a single unit, one end marked 0 and the other marked 10 with 10 equally spaced lines between them. The wheel subsection serves to increase the accuracy of the readings made on the wheel.
At the opposite end of the smaller black bar from the measurement mechanisms, there is another, silver metal rectangular bar. The latter rests on top of the former so that they overlap for part of its length and then it extends past the black metal bar for the rest of its length. The silver metal bar has a set of etched measurements on part of the subsection that rests atop the black bar. The measurements are equally spaced, with the increment closest to the stylus marked 25 and the increment closest to the measurement mechanisms marked 33. Each increment is subdivided in ten by small lines.
Beneath the section of the black bar above which the incrementally marked silver metal bar sits, there is a silver metal screw. The screw can be loosened to permit users to adjust the placement of the silver metal bar on top of the black metal bar. In between the incrementally marked section of the silver metal bar and the black bar on which it sits there is a short metal pin that rests flat on the top surface of the black bar, directly beneath one of the measurement increments.
At the end of the metal bar that does not rest atop the black bar, there is a black metal clamp. A silver metal stylus next to a small metal stand and brass screw extend below the clamp, and a brass screw extends above it. The black clamp has a depression on either side. Users are meant to put their thumb and middle finger in the depressions and to rest their pointer finger on top of the brass screw, extending above the clamp, when directing the stylus.
When the instrument is assembled, the silver metal pin at one end of the longer black metal bar sits in the hole through the top of the shorter black bar. These holes are located at the two junctions from which the short black offshoots that frame the measuring devices emerge.
There is a white piece of paper inside the case lid with charts of scales.
The Keuffel & Esser Co. manual for a similar model of compensating polar planimeter that details the design and function of the instruments can be found here. Pages 8 - 9 deal specifically with this model, the 4238.
Signedengraved in black lettering on instrument arm: G. Coradi, Zurich.
stamped on pole arm: Eugene Dietzgen Co.
stamped on pole arm: Eugene Dietzgen Co.
Inscribedin black type on a piece of paper in case lid: 21 April 1914
in white lettering on instrument arm: No 28634
in white lettering on instrument arm: No 28634
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 the 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 black 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 because the user can adjust the length of the tracing arm 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.
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 black 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 because the user can adjust the length of the tracing arm 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.
Curatorial RemarksThe black leather case for the planimeter has fallen apart. The instrument and remaining case pieces are stored in a baby blue cardboard box.