Jaw Micrometer
date: label: date made
content: 1874
name: label: maker
content: Alvan Clark & Sons
notes: label: Description
content: 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.
label: Description
content: William Harkness, an astronomer affiliated with the U.S. Naval Observatory and the U.S. Hydrographic Office, designed the photoheliograph and the jaw micrometer.
label: Description
content: Ref: Simon Newcomb, ed., <i>Observations of the Transit of Venus, December 8-9, 1874</i> (Washington, D.C., 1880), pp. 30 and 72.
label: Location
content: Currently not on view
place: label: place made
content: United States: Massachusetts, Cambridgeport
topic: label: Subject
content: Science & Scientific Instruments
setName: label: See more items in
content: Medicine and Science: Physical Sciences
creditLine: label: Credit Line
content: U. S. Naval Observatory
dataSource: label: Data Source
content: National Museum of American History
identifier: label: ID Number
content: 2005.3085.01
label: nonaccession number
content: 2005.3085
label: catalog number
content: 2005.3085.01
objectType: label: Object Name
content: micrometer
label: Object Name
content: Micrometer, Gate, Photographic
physicalDescription: label: Measurements
content: overall: 2 1/2 in x 6 in x 6 in; 6.35 cm x 15.24 cm x 15.24 cm
label: Measurements
content: overall: 2 1/8 in x 6 5/16 in x 6 in; 5.3975 cm x 16.03375 cm x 15.24 cm