Antique graphometer or semi-circumferentor survey equipment

Description

Second half of the 19
th
century French surveying instrument known as a graphometer or semi-circumferentor. This precise surveying instrument consists of a solid brass body with a semi-circular arc divided into 190 degrees sub-divided by half degrees and marked in 10’s. The center bears a magnetic compass with a sunken central rose marked in French with cardinal and intercardinal points, “N,E,S,O”. The upper rose is marked in a single degrees 0-360 marked by 20’s. Attesting to its quality the compass needle has a brass pivot with an agate cap. This instrument has two sets of sight vanes, two fixed and two on the pivoting arm. Each end of the arm is engraved with a Vernier scale marked from 0 – 30 in single are minutes, one reading left to right and the other right to left. Each of the vanes contains a very fine slit for sighting, and amazingly 3 still retain their original bourse hair sighting lines! The bottom of the instrument is fitted with a ball and socket joint with large thumbscrew, atop a figural walnut box with brass hinges and hok and eye closures. The right end of the box is in unbelievable state of original preservation. Rarely can an object nearly 150 years old be classified as “mint”. But this example comes close. The original bright brass lacquered surfaces are near perfect.