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Refracting Telescope (Almucantar)

Refracting Telescope (Almucantar)

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Seth Chandler earned his living as an actuary but made his mark as an astronomer. His most important scientific achievement was the discovery of what became known as polar motion, the wobble of the Earth around its axis of rotation. He observed this phenomenon with a zenith telescope of his own design—which he called an "almucantar"—for viewing stars as they passed overhead. After the first example proved promising, he had a larger one made.
This telescope came from Chandler’s home in Vermont. It does not seem to be either of the almucantars described in his scientific papers, but it may have been part of the instrument for which he obtained a patent in 1881.
It has a cylindrical draw-tube telescope made of brass that measures 22¾ inches long when closed. The objective lens has a clear aperture of 2 inches. The tube is blackened on the inside, and has no internal diaphragms.
The lenses may have been figured by John Clacey, an optical instrument maker who worked in Cambridge, Ma., in the late 1870s, and who is credited with having made the optical elements of Chandler’s almucantars.
Ref: Seth Chandler, "Altitude Instrument," U.S. Patent 239,315 (1881).
Seth Chandler, “The Almucantar. An Investigation Made at the Observatory in 1884 and 1885,” Annals of the Harvard College Observatory 17 (1887): 1-222.
W. E. Carter and M. S. Carter, “Seth Carlo Chandler, Jr.,” Biographical Memoirs of the National Academy of Sciences (1995): 45-79.
“John Clacey—Optician,” Popular Astronomy 38 (1930): 472-477.
Currently not on view
Object Name
date made
ca 1880
Physical Description
brass (overall material)
overall: 23 3/4 in x 2 1/2 in; 60.325 cm x 6.35 cm
overall: 23 5/8 in x 2 1/2 in; 60.0075 cm x 6.35 cm
ID Number
accession number
catalog number
See more items in
Medicine and Science: Physical Sciences
Science & Mathematics
Data Source
National Museum of American History
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