Rowland concave diffraction grating
Datecirca 1884
Inventory Number2031
ClassificationDiffraction Grating
Subject
Maker
Henry A. Rowland
1848 - 1901
Owner
Theodore Lyman IV
1874 - 1954
User
Department of Physics, Harvard University
founded 1884
Cultural Region
Place of Origin
Dimensions22.3 x 17.3 x 7.8 cm (8 3/4 x 6 13/16 x 3 1/16 in.)
box: 27 x 21 x 20.1 cm (10 5/8 x 8 1/4 x 7 15/16 in.)
box: 27 x 21 x 20.1 cm (10 5/8 x 8 1/4 x 7 15/16 in.)
Material
Accessorieswooden box; key
DescriptionThe diffraction grating, made of solid speculum metal, is in its own cover-protected flat box, which slides into the larger travelling case. It is a 5-inch grating made from one of Rowland's newly invented dividing machines. It is divided with 14,438 lines per inch and has a radius of curvature of 651.32 cm.
In Collection(s)
Signedengraved on surface: Rowland's Concave Grating 14438 lines to the inch 24½ ft. radius / Presented to Harvard College (Prof. Trowbridge) by the / Johns Hopkins University Feb 1884
FunctionA diffraction grating is a glass or mirror that has regularly spaced microscopic interruptions to the passage of light (lines) such that light passing through or reflected by it experiences interference phenomena, magnifying its magnitude at some angles and cancelling it at others. As this effect depends on the wavelength of light, a diffraction grating is an effective method of decomposing light into its constituent wavelengths, that will be transmitted at different angles (short wavelengths -- bluer -- are deflected less than longer -- redder -- ones). If one knows the line density (lines per inch) and the angle of deflection (with a spectrometer), one can deduce the exact wavelengths.
Diffraction gratings like this one were often used in astronomy to produce spectra of celestial objects. Begun in 1882, Rowland's gratings were more than an order of magnitude larger and more accurate than any previous one. With these, for instance, it became possible to measure the wavelength of light emitted by atoms to unprecedented accuracy. Rowland himself was able to draw a new and more accurate map of the solar spectrum.
For more information go to the following website.
Diffraction gratings like this one were often used in astronomy to produce spectra of celestial objects. Begun in 1882, Rowland's gratings were more than an order of magnitude larger and more accurate than any previous one. With these, for instance, it became possible to measure the wavelength of light emitted by atoms to unprecedented accuracy. Rowland himself was able to draw a new and more accurate map of the solar spectrum.
For more information go to the following website.
ProvenanceFrom the Department of Physics, Lyman Laboratory, Harvard University.
Historical AttributesSee the note transcribed on the handwritten card (picture), which mentions that this object was a gift from the Johns Hopkins University to Harvard.
