Jaw Micrometer


Hoping to improve our understanding of the distance between the Earth and the Sun, the United States sponsored eight parties to observe the 1874 transit of Venus across the face of the sun, and equipped each with an identical set of apparatus made by Alvan Clark & Sons. For photographing work, each party had a photoheliograph—a horizontal telescope with a lens of 5-inches aperture and nearly 40 feet focal length. To measure the exact distance between the lens and the photographic plate, there was a jaw micrometer. The “Fort Selden, N.U. / F. Thom / 74 / 72” pencil inscription on the box indicates that this jaw micrometer was used at Cerro Roblero (a site near Fort Selden, an Army post in what is now New Mexico) during the transit of Venus of 1882.

William Harkness, an astronomer affiliated with the U.S. Naval Observatory and the U.S. Hydrographic Office, designed the photoheliograph and the jaw micrometer.

Ref: Simon Newcomb, ed., Observations of the Transit of Venus, December 8-9, 1874 (Washington, D.C., 1880), pp. 30 and 72.

Date Made: 1874

Maker: Alvan Clark & Sons

Location: Currently not on view

Place Made: United States: Massachusetts, Cambridgeport

Subject: Science & Scientific Instruments


See more items in: Medicine and Science: Physical Sciences


Exhibition Location:

Credit Line: U. S. Naval Observatory

Data Source: National Museum of American History

Id Number: 2005.3085.01Nonaccession Number: 2005.3085Catalog Number: 2005.3085.01

Object Name: micrometerMicrometer, Gate, Photographic

Measurements: overall: 2 1/2 in x 6 in x 6 in; 6.35 cm x 15.24 cm x 15.24 cmoverall: 2 1/8 in x 6 5/16 in x 6 in; 5.3975 cm x 16.03375 cm x 15.24 cm

Guid: http://n2t.net/ark:/65665/ng49ca746ab-b42b-704b-e053-15f76fa0b4fa

Record Id: nmah_1293480

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