Joseph von Fraunhofer

Joseph Ritter von Fraunhofer (/ˈfraʊnˌhoʊfər/; German: [ˈfraʊnˌhoːfɐ]; 6 March 1787 – 7 June 1826[1]) was a Bavarian physicist and optical lens manufacturer. He made optical glass and achromatic telescope objective lenses, invented the spectroscope, and developed diffraction grating. In 1814, he discovered and studied the dark absorption lines in the spectrum of the sun now known as Fraunhofer lines.[2]

Joseph von Fraunhofer
Born(1787-03-06)6 March 1787
Straubing, Electorate of Bavaria in the Holy Roman Empire
Died7 June 1826(1826-06-07) (aged 39)
Munich, German Confederation
Known forFraunhofer diffraction, Fraunhofer lines, Fraunhofer distance

The German research organization Fraunhofer Society is named after him and is Europe's biggest Society for the Advancement of Applied Research.

Biography

Joseph Fraunhofer was the 11th child, born in Straubing, in the Electorate of Bavaria, to Franz Xaver Fraunhofer and Maria Anna Frohlich.[3] He was orphaned at the age of 11 and started working as an apprentice to a harsh glassmaker named Philipp Anton Weichelsberger.[4][5] In 1801, the workshop in which he was working collapsed, and he was buried in the rubble. The rescue operation was led by Prince-Elector Maximilian Joseph. The prince entered Fraunhofer's life, providing him with books and forcing his employer to allow the young Fraunhofer time to study.[4][5]

Joseph Utzschneider was also at the site of the disaster, and would also become a benefactor to Fraunhofer. With the money given to him by the prince upon his rescue and the support he received from Utzschneider, Fraunhofer was able to continue his education alongside his practical training.[6] In 1806, Utzschneider and Georg von Reichenbach brought Fraunhofer into their Institute at Benediktbeuern, a secularised Benedictine monastery devoted to glassmaking. There he discovered how to make fine optical glass and invented precise methods for measuring optical dispersion.[5]

It was at the Institute that Fraunhofer met Pierre Louis Guinand, a Swiss glass technician, who instructed Fraunhofer in glassmaking at Utzschneider's behest.[7] By 1809, the mechanical part of the Optical Institute was chiefly under Fraunhofer's direction, and Fraunhofer became one of the members of the firm that same year.[8] In 1814, Guinand left the firm, as did Reichenbach. Guinand would later become a partner with Fraunhofer in the firm,[7] and the name was changed to Utzschneider-und-Fraunhofer. During 1818, Fraunhofer became the director of the Optical Institute. Due to the fine optical instruments developed by Fraunhofer, Bavaria overtook England as the center of the optics industry. Even the likes of Michael Faraday were unable to produce glass that could rival Fraunhofer.[4][5]

His illustrious career eventually earned him an honorary doctorate from the University of Erlangen in 1822. In 1824, Fraunhofer was appointed a Knight of the Order of Merit of the Bavarian Crown by King Maximilian I, through which he was raised into personal nobility (with the title "Ritter von", i.e. knight). The same year, he was also made an honorary citizen of Munich.

Like many glassmakers of his era, he was poisoned by heavy metal vapors, resulting in his premature death. Fraunhofer died in 1826 at the age of 39. His most valuable glassmaking recipes are thought to have gone to the grave with him.[4]

Invention and scientific research
Fraunhofer demonstrating the spectroscope.

One of the most difficult operations of practical optics during the time period of Fraunhofer's life was accurately polishing the spherical surfaces of large object glasses. Fraunhofer invented the machine which rendered the surface more accurately than conventional grinding. He also invented other grinding and polishing machines and introduced many improvements into the manufacture of the different kinds of glass used for optical instruments, which he always found to have flaws and irregularities of various sorts.[8]

In 1811, he constructed a new kind of furnace, and during his second melting session when he melted a large quantity of glass, he found that he could produce flint glass, which, when taken from the bottom of a vessel containing roughly 224 pounds of glass, had the same refractive power as glass taken from the surface. He found that English crown glass and German table glass both contained defects which tended to cause irregular refraction. In the thicker and larger glasses, there would be even more of such defects, so that in larger telescopes this kind of glass would not be fit for objective lenses. Fraunhofer accordingly made his own crown glass.[8]

It was thought that the accurate determination of power for a given medium to refract rays of light and separate the different colors which they contain was impeded by the absence of precise boundaries between the colors of the spectrum, making it difficult to accurately measure the angle of refraction. To address this limitation, Fraunhofer performed a series of experiments for the purpose of producing homogeneous light artificially, and unable to effect his object in a direct way, he did so by means of lamps and prisms.[8]

Discovery of dark absorption lines
Illustration of solar spectrum drawn and colored by Joseph von Fraunhofer with dark lines named after him. (1987 DBP's stamp on 200th anniversary of birthday of Fraunhofer)

By 1814, Fraunhofer had invented the modern spectroscope.[9] In the course of his experiments, he discovered a bright fixed line which appears in the orange color of the spectrum when it is produced by the light of fire. This line enabled him afterward to determine the absolute power of refraction in different substances. Experiments to ascertain whether the solar spectrum contained the same bright line in orange as the line produced by the orange of fire light led him to the discovery of 574 dark fixed lines in the solar spectrum. Today, millions of such fixed absorption lines are now known.[8][10]

Continuing to investigate, Fraunhofer detected dark lines also appearing in the spectra of several bright stars, but in slightly different arrangements. He ruled out the possibility that the lines were produced as the light passes through the Earth’s atmosphere. If that were the case they would not appear in different arrangements. He concluded that the lines originate in the nature of the stars and sun and carry information about the source of light, regardless of how far away that source is.[2] He found that the spectra of Sirius and other first-magnitude stars differed from the sun and from each other, thus founding stellar spectroscopy.[11]

These dark fixed lines were later shown to be atomic absorption lines, as explained by Kirchhoff and Bunsen in 1859.[12] These lines are still called Fraunhofer lines in his honor; his discovery had gone far beyond the half-dozen apparent divisions in the solar spectrum that had previously been noted by Wollaston in 1802.[13]

Invention of optical instruments

Fraunhofer also developed a diffraction grating in 1821, after James Gregory discovered the phenomenon of diffraction grating and after the American astronomer David Rittenhouse invented the first manmade diffraction grating in 1785.[14][15] Fraunhofer was the first who used a diffraction grating to obtain line spectra and the first who measured the wavelengths of spectral lines with a diffraction grating.

Ultimately, however, his primary passion was still practical optics; he once wrote that "In all my experiments I could, owing to lack of time, pay attention to only those matters which appeared to have a bearing upon practical optics".[16]

Telescopes and optical instruments

Fraunhofer produced various optical instruments for his firm.[7] This included the Fraunhofer Dorpat Refractor used by Struve (delivered 1824 to Dorpat Observatory), and the Bessel Heliometer (delivered posthumously), which were both used to collect data for stellar parallax. The firm's successor, Merz und Mahler, made a telescope for the New Berlin Observatory, which confirmed the existence of the major planet Neptune. Possibly the last telescope objective made by Fraunhofer was supplied for a transit telescope at the City Observatory, Edinburgh,[17] the telescope itself being completed by Repsold of Hamburg after Fraunhofer's death.

Works

See also

Notes
  1. Adolf Wißner (1961), "Fraunhofer, Joseph von (bayerischer Personaladel 1824)", Neue Deutsche Biographie (NDB) (in German), 5, Berlin: Duncker & Humblot, pp. 382–384; (full text online)
  2. Kitty Ferguson & Miko Maciaszek (20 March 2014). "The Glassmaker Who Sparked Astrophysics". Nautilus. Retrieved 8 April 2018.
  3. Hockey, Thomas (2009). The Biographical Encyclopedia of Astronomers. Springer Publishing. ISBN 978-0-387-31022-0. Retrieved 22 August 2012.
  4. Myles W. Jackson (2000). "Chapter 1: Introduction". Spectrum of Belief: Joseph Von Fraunhofer and the Craft of Precision Optics. MIT Press. pp. 1–16. ISBN 978-0-262-10084-7.
  5. Daniel Kleppner (2005). "The Master of Dispersion". Physics Today. 58 (11): 10. Bibcode:2005PhT....58k..10K. doi:10.1063/1.2155731.
  6. Ralf Kern: Wissenschaftliche Instrumente in ihrer Zeit. Band 4: Perfektion von Optik und Mechanik. Cologne, 2010. 355–356.
  7. Fraunhofer, Joseph von (1787–1826). plicht.de. 2000. Bibcode:2000eaa..bookE3630. Retrieved 26 March 2011. (in English)
  8. This article incorporates text from a publication now in the public domain: Rines, George Edwin, ed. (1920). "Fraunhofer, Joseph von" . Encyclopedia Americana.
  9. Brand, John C. D. (1995). Lines of Light: The Sources of Dispersive Spectroscopy, 1800–1930. Gordon and Breach Publishers. pp. 37–42. ISBN 978-2884491624.
  10. See:
  11. Fraunhofer (1814–1815), pages 220–221: Original: Ich habe auch mit derselben Vorrichtung Versuche mit dem Lichte einiger Fixsterne erster Grösse gemachte. Da aber das Licht dieser Sterne noch vielmal schwächer ist, als das der Venus, so ist natürlich auch die Helligkeit des Farbenbildes vielmal geringer. Demohngeachtet habe ich, ohne Täuschung, im Farbenbilde vom Lichte des Sirius drey breite Streifen gesehen, die mit jenen vom Sonnenlichte keine Aehnlichkeit zu haben scheinen; einer dieser Streifen ist im Grünen, und zwey im Blauen. Auch im Farbenbilde vom Lichte anderer Fixsterne erster Grösse erkennt man Streifen; doch scheinen diese Sterne, in Beziehung auf die Streifen, unter sich verschieden zu seyn. Translation: With the same device [i.e., spectroscope], I've also made some experiments on the light of some stars of the first magnitude. Since the light of these stars is many times weaker than that of Venus, so naturally, the brightness of the spectrum is also many times less. Notwithstanding, I have seen – without any illusion – three broad stripes in the spectrum of Sirius, which seem to have no similarity to those of sunlight; one of these stripes is in the green, and two in the blue. Also, in the spectrum of the light of other fixed stars of the first magnitude, one detects stripes; yet these stars, in regard to the stripes, seem to differ among themselves.
  12. See:
    • Gustav Kirchhoff (1859) "Ueber die Fraunhofer'schen Linien" (On Fraunhofer's lines), Monatsbericht der Königlichen Preussische Akademie der Wissenschaften zu Berlin (Monthly Report of the Royal Prussian Academy of Sciences in Berlin), 662–665.
    • Gustav Kirchhoff (1859) "Ueber das Sonnenspektrum" (On the sun's spectrum), Verhandlungen des naturhistorisch-medizinischen Vereins zu Heidelberg (Proceedings of the Natural History / Medical Association in Heidelberg), 1 (7): 251–255.
  13. William Hyde Wollaston (1802) "A method of examining refractive and dispersive powers, by prismatic reflection," Philosophical Transactions of the Royal Society, 92: 365–380; see especially p. 378.
  14. See:
  15. Parker AR (March 2005). "A geological history of reflecting optics". Journal of the Royal Society, Interface. 2 (2): 1–17. doi:10.1098/rsif.2004.0026. PMC 1578258. PMID 16849159.
  16. Prismatic and Diffraction Spectra: Memoirs (1899) Tr. & Ed. J. S. Ames p. 10
  17. A Guide to Edinburgh's Popular Observatory, Astronomical Society of Edinburgh
  18. Tr. Brief outline of the life-story of Dr. Joseph von Fraunhofer

References
  • I. Bernard Cohen; Henry Crew; Joseph von Fraunhofer; De Witt Bristol Brace (1981). The Wave theory, light and spectra. Ayer Publishing. ISBN 978-0-405-13867-6.
  • Aller, Lawrence H. (1991). Atoms, Stars and Nebulae, 3rd ed. Cambridge University Press. ISBN 978-0-521-32512-7.
  • Klaus Hentschel: Mapping the spectrum. Techniques of visual representation in research and teaching. Oxford Univ. Press, Oxford 2002.
  • Jackson, Myles W. (2000). Spectrum of Belief: Joseph von Fraunhofer and the Craft of Precision Optics. MIT Press. (German translation: Fraunhofers Spektren: Die Präzisionsoptik als Handwerkskunst, Wallstein Verlag, 2009.)
  • Ralf Kern: Wissenschaftliche Instrumente in ihrer Zeit. Band 4: Perfektion von Optik und Mechanik. Cologne, 2010.
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