Related Object Info
polar planimeter
The planimeter is stored in a rectangular black case that opens with two hinges along one of the long edges. There is a single brass clip on the front of the top half of the case that snaps onto a pin attached to the front of the bottom half of the case when the case is closed. The clasp is embellished with flourishes and engravings. The inside of the case is lined with green felt cloth. The bottom half of the case is contoured to fit the instrument pieces and hold them in place when the case is closed.
The main body of the instrument is black metal and consists of two arms of different lengths. The shorter is the tracing arm and the other will be called the second arm. Each arm has a half circle at one end. The arms are connected with a pivot at that end such that the straight extensions of the arms can be brought nearly together in parallel and a full circle forms at the pivot end.
At the opposite end to the half circle on the tracing arm, there is a metal stylus. The stylus has a brass hour glass shape above the tracing arm and a metal point extending below it. The hour glass component is the tracing handle. The tip of the pointed end rests on the surface below. The stylus is attached to the tracing arm by two metal screws.
At the opposite end to the half circle on the second arm, there is a flat brass extension screwed into a small hole. The brass extension connects to a black metal puck. Underneath this end of the second arm, there is a tiered-funnel-shaped attachment. The funnel attachment has a screw on the side.
At the half circle end of the tracing arm, there is a white measurement mechanism consisting of a white wheel, a white wheel-subsection, and a white disc. The white wheel subsection is fixed, i.e. does not rotate, and is closest to the pivot holding the two arms together. It has one increment marked "0" at one end and "10". This increment is divided in 10 by small black lines. The white wheel is marked in evenly spaced increments from 0 to 9. All the markings are in black type, etched into the white wheel. The axis of each wheel is parallel to the tracing arm. The white disc lies flat, parallel to the top surface of the tracing arm. It is marked from 0 to 9 in evenly spaced increments around the circumference. Each numeral is accompanied by a small black line. In between the white wheel and the white disc there is a metal roller whose axis is parallel to the tracing arm. There is a metal screw running from the center of this roller to a point on the tracing arm at which there is a black metal cube. It has precisely the width that remains between the two planimeter arms when they are rotated together so that the cube touches both arms.