"U.S.G.S. No 11"
base 26 inches long; telescope 11.5 inches long
This alidade has a telescope with a level mounted above, and a vertical circle that is silvered, graduated to 30 minutes, and read by vernier to single minutes. The base has six large circular holes, and a circular level vial. The United States Geological Survey transferred this instrument to the Smithsonian in 1907, describing it as a "preliminary type" of alidade devised for the Survey about 1890.