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 the sun, each party had a horizontal telescope—known as a photoheliograph—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. 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: The word “Kerguelan” marked in pencil on the wooden box indicates that this micrometer was used at the observing station on a Kerguelan island in the southern Indian Ocean.
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, Cambridge
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: PH.327708
label: accession number
content: 283654
label: catalog number
content: 327708
objectType: label: Object Name
content: Micrometer
physicalDescription: label: Measurements
content: overall in case: 2 1/8 in x 6 5/16 in x 6 1/4 in; 5.3975 cm x 16.03375 cm x 15.875 cm