Rock Salt Prism
notes: label: Description
content: John Tyndall, an Irish scientist working at the Royal Institution in London, reported in the late 1850s that prisms of rock salt (NaCl) might be used to examine the infra-red region of the solar spectrum, but were difficult to produce and polish. Samuel Pierpont Langley (1834-1906), director of the Allegheny Observatory in Pittsburgh, asked several opticians to produce prisms of this sort, and while their results proved disappointing, John A. Brashear (1840-1920), a local and self-taught instrument-maker, solved the problem. At the 1885 meeting of the American Association for the Advancement of Science, Langley talked about “Some Hitherto Unmeasured Wavelengths” of lines in the infra-red region of the solar spectrum; and Brashear talked about “A Practical Method of Producing Accurate Rock Salt Surfaces for Optical Purposes.” The following year, Langley became the Assistant Secretary of the Smithsonian Institution, and established the Smithsonian Astrophysical Observatory.
label: Description
content: This rock salt prism, which came from the Smithsonian Astrophysical Observatory, was probably figured by Brashear, and used by Langley.
label: Location
content: Currently not on view
setName: label: See more items in
content: Medicine and Science: Physical Sciences
dataSource: label: Data Source
content: National Museum of American History
identifier: label: ID Number
content: PH.247026
label: accession number
content: 46700
label: catalog number
content: 247026
objectType: label: Object Name
content: Rock Salt Prism
physicalDescription: label: Measurements
content: overall: 11 1/2 in x 7 in; 29.21 cm x 17.78 cm
label: Measurements
content: overall: 11 1/2 in x 7 in; 29.21 cm x 17.78 cm