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Physical Sciences Collection - Surveying and Geodesy

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Zenith Telescope

Catalogue number:

"Troughton & Simms, London" and "U. S. C. S. Z. T. No 3"

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


This is one of four zenith telescopes 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 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 and 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.

Further Information:

Troughton & Simms
Zenith Telescope