Rowland concave diffraction grating
Date1889
Inventory Number2030
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
Dimensions1.8 x 16 x 13.6 cm (11/16 x 6 5/16 x 5 3/8 in.)
case: 8.8 x 19.7 x 17.5 cm (3 7/16 x 7 3/4 x 6 7/8 in.)
case: 8.8 x 19.7 x 17.5 cm (3 7/16 x 7 3/4 x 6 7/8 in.)
Material
DescriptionThe concave grating, made of speculum metal, sits in a flat wooden box, which can be inserted into a specially designed protective case. The grating itself is divided with 20,000 lines per inch and has a radius of curvature of 652.46 cm.
In Collection(s)
Signedengraved on surface: No 7 March 1889 AE / about 20000 lines to the inch / Radius about 21 ft 5 in / Rowland Concave Grating Definition magnificent / H. S. Rowland
Curatorial RemarksMore information about the use of this grating is found on the handwritten card (see pictures).
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.
Henry A. Rowland
Date: circa 1884
Accessories: wooden box; key
Object number: 2031
Robert W. Wood
Date: circa 1925
Accessories: wooden box
Object number: 2040
