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FRAUNHOFER, JOSEPH VON (1787-1826)

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Originally appearing in Volume V11, Page 43 of the 1911 Encyclopedia Britannica.
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FRAUNHOFER, See also:JOSEPH VON (1787-1826) , See also:German optician and physicist, was See also:born at See also:Straubing in See also:Bavaria on the 6th of See also:March 1787, the son of a glazier who died in 1798. He was apprenticed in 1799 to Weichselberger, a See also:glass-polisher and looking-glass maker. On the 21st of See also:July 18o1 he nearly lost his See also:life by the fall of the See also:house in which he lodged, and the elector of Bavaria, See also:Maximilian Joseph, who was See also:present at his extrication from the ruins, gave him 18 ducats. With a portion of this sum he obtained See also:release from the last six months of his See also:apprenticeship, and with the See also:rest he See also:purchased a glass-polishing See also:machine. He now employed himself in making See also:optical glasses, and in See also:engraving on See also:metal, devoting his spare See also:time to the perusal of See also:works on See also:mathematics and See also:optics. In 18o6 he obtained the See also:place of optician in the mathematical See also:institute which in 1804 had been founded at See also:Munich by Joseph von Utzschneider, G. See also:Reichenbach and J. Liebherr; and in 1807 arrangements were made by Utzschneider for his instruction by See also:Pierre See also:Louis Guinand, a skilled optician, in the fabrication of See also:flint and See also:crown glass, in. which he soon became an See also:adept (see R. See also:Wolf, Gesch. der Wissensch. in Deutschl. bd. xvi. p. 586). With Reichenbach and Utzschneider, Fraunhofer established in 1809 an optical institute at Benedictbeuern, near Munich, of which he in 1818 became See also:sole manager. The institute was in 1819 removed to Munich, and on Fraunhofer's See also:death came under the direction of G.

Merz. Amongst the earliest See also:

mechanical contrivances of Fraunhofer was a machine for polishing mathematically See also:uniform spherical surfaces. He was the inventor of the See also:stage-See also:micrometer, and of a See also:form of See also:heliometer; and in 1816 he succeeded in constructing for the See also:microscope achromatic glasses of See also:long See also:focus, consisting of a single See also:lens, the constituent glasses of which were in juxtaposition, but not cemented together. The See also:great reflecting See also:telescope at Dorpat was manufactured by him, and so great was the skill he attained in the making of lenses for achromatic telescopes that, in a See also:letter to See also:Sir See also:David See also:Brewster, he expressed his willingness to furnish an achromatic glass of 18 in. See also:diameter. Fraunhofer is especially known for the researches, published in the Denkschriften der Miinchener Akademie for 1814-1815, by which he laid the See also:foundation of See also:solar and stellar See also:chemistry. The dark lines of the spectrum of sunlight, earliest noted by Dr W. H. See also:Wollaston (Phil. Trans., 1802, p. 378), were independently discovered, and, by means of the telescope of a See also:theodolite, between which and a distant slit admitting the See also:light a See also:prism was interposed, were for the first time carefully observed by Fraunhofer, and have on that See also:account been designated " Fraunhofer's lines." He constructed a See also:map of as many as 576 of these lines, the See also:principal of which he denoted by the letters of the See also:alphabet from A to G; and by ascertaining their refractive indices he determined that their relative positions are See also:constant, whether in spectra produced by the See also:direct rays of the See also:sun, or by the reflected light of the See also:moon and See also:planets. The spectra of the stars he obtained by using, outside the See also:object-glass of his telescope, a large prism, through which the light passed to be brought to a focus in front of the See also:eye-piece. He showed that in the spectra of the fixed stars many of the dark lines were different from those of the solar spectrum, whilst other well-known solar lines were wanting; and he concluded that it was not by any See also:action of the terrestrial See also:atmosphere upon the light passing through it that the lines were produced.

He further expressed the belief that the dark lines D of the solar spectrum coincide with the See also:

bright lines of the See also:sodium See also:flame. He was also the inventor of the diffraction grating. In 1823 he was appointed See also:conservator of the See also:physical See also:cabinet at Munich, and in the following See also:year he received from the See also:king of Bavaria the See also:civil See also:order of merit. He died at Munich on the 7th of See also:June 1826, and was buried near Reichenbach, whose decease had taken place eight years previously. On his See also:tomb is the inscription " Approximavit sidera." See J. von Utzschneider, Kurzer Umriss der Lebensgeschichte See also:des See also:Hearn Dr J. von Fraunhofer (Munich, 1826) ; and G.

End of Article: FRAUNHOFER, JOSEPH VON (1787-1826)

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