Troughton & Simms Zenith Telescope

Marked "Troughton & Simms, London" and "U. S. C. S. Z. T. No 3," this is one of four zenith telescopes that Troughton & Simms made for the U. S. Coast Survey. It was used for the determination of latitude by the Talcott method.
The telescope arrived in the United States in 1848. In 1891, in preparation for the variation of latitude (polar motion) program organized by the International Geodetic Association, this telescope was extensively remodeled. The new features included: an objective lens made by Brashear; diagonal and straight eyepieces made by Kahler; two levels; a striding level; a micrometer with horizontal and vertical parallactic motions; a larger axis for the telescope; a heavier base and vertical axis; wyes to support the telescope; and an improved clamp for the telescope.
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. 449.
Object Name
zenith telescope
Troughton and Simms
telescope aperture: 3 1/4 in; 8.255 cm
telescope: 46 in; 116.84 cm
horizontal circle: 10 1/2 in; 26.67 cm
place made
United Kingdom: England, London
ID Number
accession number
catalog number
Measuring & Mapping
Surveying and Geodesy
See more items in
Medicine and Science: Physical Sciences
Surveying and Geodesy
Data Source
National Museum of American History, Kenneth E. Behring Center

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