Zenith Telescope

Description:

Marked "Troughton & Simms, London" and "U. S. C. S. Z. T. No 1," this is the first of four identical zenith telescopes that Troughton & Simms made for the U. S. Coast Survey. Designed for the determination of latitude by the Talcott method, the telescope arrived in the United States in 1847. In 1891 it was sent to San Francisco for use in the variation of latitude (polar motion) program organized by the International Geodetic Association. C. A Schott, the assistant in charge of the computing division of the Survey, noted at that time that this instrument was far from ideal, its "principal defect" being "a lack of stability; hence demanding great caution in handling it."

This zenith telescope was transferred to the Smithsonian in 1911. Correspondence in the accession file indicates that it was modified by William Wurdemann in 1867, and fitted with two levels in the early 1890s.

Ref: C. A. Schott, "The Variation of Latitude at San Francisco, Cal., as Determined from Observations made by George Davidson, Assistant Coast and Geodetic Survey, Between May, 1891, and August, 1892," United States Coast and Geodetic Survey Report for 1893, Appendix No. 11, p. 447.