Smithsonian - National Museum of American History, Behring Center

Physical Sciences Collection - Surveying and Geodesy

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Zenith Telescope - click to enlarge

Zenith Telescope - click to enlarge

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Zenith Telescope

Catalogue number:

"Troughton & Simms, London" and "U. S. C. S. Z. T. No 1"

Telescope 3.25 inches aperture, 46 inches long; horizontal circle 10.5 inches diameter; vertical arc 5.5 inches radius

This is the first of four identical instruments that Troughton & Simms made for the United States Coast Survey, and that was used for the determination of latitude by the Talcott method. It 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." It was transferred to the Smithsonian in 1911.

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.

Further Information:

Troughton & Simms
Zenith Telescope