Jaw Micrometer

Jaw Micrometer

<< >>
Usage conditions apply
Downloads
Description
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.
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.
Ref: Simon Newcomb, ed., Observations of the Transit of Venus, December 8-9, 1874 (Washington, D.C., 1880), pp. 30 and 72.
Location
Currently not on view
Object Name
Micrometer
date made
1874
maker
Alvan Clark & Sons
place made
United States: Massachusetts, Cambridge
Measurements
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
ID Number
PH.327708
accession number
283654
catalog number
327708
Credit Line
U.S. Naval Observatory
subject
Science & Scientific Instruments
See more items in
Medicine and Science: Physical Sciences
Data Source
National Museum of American History
Nominate this object for photography.   

Our collection database is a work in progress. We may update this record based on further research and review. Learn more about our approach to sharing our collection online.

If you would like to know how you can use content on this page, see the Smithsonian's Terms of Use. If you need to request an image for publication or other use, please visit Rights and Reproductions.

Comments

Add a comment about this object