This 30-inch theodolite was made by Troughton & Simms in London for the United
States Coast Survey, probably in the late 1840s. Only the unusually short trunions, telescope,
small vertical circle, and micrometer eyepiece remain; the standards, graduated horizontal circle,
and tripod base are missing.
Ref: C. A. Schott, "Determination of the Astronomical Azimuth of a Direction," United States
Coast Survey Annual Report (1866), Appendix No. 11.