Smithsonian - National Museum of American History, Behring Center

Physical Sciences Collection - Surveying and Geodesy

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Altitude and Azimuth Instrument
Chain, Tape and Base Bar
Compass, Pocket
Compass, Railroad
Compass, Solar
Compass, Surveyor's
Cross, Surveyor's
Electromagnetic Distance Measurement (EDM)
Holland Circle
Range Finder
Repeating Circle
Transit and Equal Altitude
Transit, Geodetic
Universal Instrument
Vertical Circle
Zenith Telescope


Zenith Telescope

A zenith telescope (or sector) is a refracting telescope designed to observe stars as they pass overhead. Robert Hooke made the first instrument of this sort in 1669, hoping to discover evidence of the earth’s annual motion about the sun (or solar parallax). Hooke failed in this endeavor. So too did Samuel Molyneux, who installed a zenith telescope made by George Graham in his observatory in Kew in 1725. James Bradley, however, while observing with Molyneux’s telescope, discovered the aberration of star light, and he later discovered the nutation of the earth’s axis while observing with a smaller instrument also made by Graham.

Portable zenith telescopes could be used for geodetic purposes. Graham made an instrument of this sort for Pierre L. M. de Maupertuis, for his 1736–1737 expedition to Lapland to determine the length of a degree of latitude in northern regions. The first zenith telescope in America was made by John Bird in London in 1763, and purchased by Thomas Penn for Mason and Dixon’s survey of the boundary between Maryland and Pennsylvania.

In 1834, while working on the boundary between Ohio and Michigan, Capt. Andrew Talcott of the United States Corps of Engineers developed a more efficient method of using zenith observations for latitude determinations. Whereas earlier geodesists had observed only those stars that passed within a degree or two of the zenith, Talcott observed pairs of stars that passed at roughly equal distances to the north and south of the zenith, and within a short period of time. The United States Coast Survey adopted Talcott’s method in 1846.


Troughton & Simms (U.S.C.S. No. 1)
Troughton & Simms (U.S.C.S. No. 3)
Troughton & Simms (U.S.C.S. No. 4)
unmarked (Andrew Ellicott)
unmarked (David Rittenhouse)