Alvan Clark & Sons Spherometer

A spherometer is a device used primarily for measuring the curvature of objects such as lenses and curved mirrors. For further information about spherometers, see object MA*315739.
This spherometer was transferred to the Smithsonian by the Naval Observatory. There is no maker indicated on the device, but notes provided by the observatory indicate that the maker was the Clarks. It was acquired for the 1874 U.S. expedition to observe the transit of Venus. Transits of Venus occur in pairs, the most recent being 2004 and 2012. The expedition also took along a Clark telescope and lenses. This item has only a horizontal scale and no vertical scale common to most spherometers, thus it is not as accurate as spherometers with two scales.
Alvan Clark (1804-1887) was the first prominent American telescope maker. In 1846 he went into business with his two sons, Alvan G. and George B. Clark, founding Clark & Sons. At first they repaired scientific instruments, but the firm quickly progressed on to making telescopes. During the second half of the 19th century, five of Clarks' telescopes held the record for world's largest. To aid in grinding lenses, Clark & Sons also made devices such as spherometers. This Clark spherometer is in a box that appears to be homemade out of medical supply box. This spherometer has only a horizontal scale and no vertical scale common to most spherometers. Thus it is not as accurate as spherometers with two scales.
Sydney Observatory, "Nineteenth Century Scientific Instrument Makers," Curatorial Research Series 1, no. 2 (2007).
Warner, D. J., "Alvan Clark & Sons: Artists in Optics," United States National Museum Bulletin 274 (1968): 1-13.
Currently not on view
Object Name
spherometer in wooden box
date made
ca 1800s
Alvan Clark & Sons
Physical Description
metal (instrument material)
wood (box material)
overall: 4 in x 3 1/4 in x 4 in; 10.16 cm x 8.255 cm x 10.16 cm
place made
United States: Massachusetts, Cambridgeport
ID Number
accession number
catalog number
Science & Mathematics
See more items in
Medicine and Science: Physical Sciences
Data Source
National Museum of American History, Kenneth E. Behring Center
Credit Line
U.S. Naval Observatory
Additional Media

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