Photometer
notes: label: Description
content: How is energy distributed across the solar spectrum? Samuel Pierpont Langley (1834-1906) tackled this question in the 1880s, while serving as Director of the Allegheny Observatory in Pittsburgh, and he continued this work after becoming the third Secretary of the Smithsonian Institution in 1887 and establishing the Smithsonian Astrophysical Observatory. In a Memoir read to National Academy of Sciences in 1888, Langley mentioned a Rumford photometer, a Bunsen photometer, and an ingenious sector photometer described by Masson. Elsewhere he mentioned a revolving sector (or wheel) photometer.
label: Description
content: When the Smithsonian celebrated its Centennial in 1946, this unmarked sector photometer appeared in the exhibit case featuring Langley and his work. The accompanying label explained: “When in rapid rotation, the eye does not distinguish the separate sectors as holes, but only detects a weakening of the light transmitted by them, which is proportional to the width of the open spaces as compared with the whole circumference of the disk. Means are provided for altering the width of the open spaces at pleasure while the instrument is at full speed.” Charles Greeley Abbot mentioned this instrument in his subsequent account of the S.A.O., terming it “A continuously rotating variable sector invented, of accurate ratio, for photometry. No published description.”
label: Description
content: Ref: S. P. Langley, “Energy and Vision,” Memoirs of the National Academy of Sciences 3 (1888); reprinted in American Journal of Science 36 (1888): 359-379, and Philosophical Magazine 27 (1889): 1-23.
label: Description
content: C. G. Abbot, “Leading Operations of the Smithsonian Astrophysical Observatory, 1895 to 1955” Smithsonian Miscellaneous Collections 131 (1958).
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.247028
label: catalog number
content: 247028
label: accession number
content: 46700
objectType: label: Object Name
content: photometer
physicalDescription: label: Measurements
content: overall: 12 1/2 in x 12 in x 10 1/4 in; 31.75 cm x 30.48 cm x 26.035 cm