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In 1813 Fraunhofer built the first spectrograph which could be used to separate sunlight into its various colors for measuring purposes. In 1814 he discovered – independently of the Englishman Wollaston
(1766–1828) – the dark absorption lines in the solar spectrum. These lines are utilized to this very day to determine chemical elements by the spectral analysis conceived by von Kirchhoff and Bunsen in 1859. Around 1817 Fraunhofer examined the diffraction of parallel light rays. He invented the diffraction grating and later produced gratings with 300 lines per millimeter on a ruling machine. He used these to determine the wavelengths of the various color components in white light. Fraunhofer discovered approximately 1500 absorption lines and used them to measure monochromatic radiation and refractive indices.
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Prism spectral apparatus (ca. 1815)
used to measure the Fraunhofer lines. | Large picture: Fraunhofer telescope, "Galle Refractor".
Small picture: Utzschneider 's and Fraunhofer's heliometer. |
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New grinding techniques – he invented the polishing machine and improved Reichenbach’s – and new methods of calculation and testing are attributable to Fraunhofer. They permitted him to produce outstanding achromatic lens elements with larger diameters than was standard at that time. These elements were used in refractor objectives such as the 24 cm Dorpat Refractor, whose construction was commenced in 1824 but whose completion Fraunhofer did not live to see. In 1846 Galle discovered the planet Neptune with a Fraunhofer refractor. With the 15.8 cm heliometer from the Benediktbeuern workshop, F.W. Bessel determined a fixed star parallax for the first time in 1883.
The Fraunhofer Society for the Promotion of Applied Research founded in 1949 is named after the famous physicist. It performs application-oriented research in fields related to the natural and engineering sciences in about 50 institutes.
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