This unusual instrument is probably best described as a precise level with a graduated horizontal circle. The telescope is provided with a long and graduated level vial, and an ingenious clamp and tangent screw moving against the silvered vertical arc controls its elevation. This arc extends 20 degrees either way, and is graduated to 10 minutes and read by vernier to 20 seconds. The horizontal circle is silvered, graduated to 15 minutes, and read by opposite verniers with reflecting glasses and magnifiers to 30 seconds. A trough compass and a circular level are mounted above the horizontal circle.
The United States War Department transferred this instrument to the Smithsonian in 1931, in a pine box marked "Capt. M. C. Meigs, Washington Aqueduct -Wurdemann--Grading Transit--1854." That is, it was used by Montgomery C. Meigs, the captain in the United States Army Corps of Engineers who was tasked with surveying the course of a new Washington Aqueduct in 1853. Since William Würdemann was the leading mathematical instrument maker in Washington at that time, it is reasonable that he was asked to
make the instrument needed for this important task.
