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Joseph Ritter von Fraunhofer (; ; 6 March 1787 – 7 June 1826) was a German
physicist A physicist is a scientist who specializes in the field of physics, which encompasses the interactions of matter and energy at all length and time scales in the physical universe. Physicists generally are interested in the root or ultimate cau ...
and optical lens manufacturer. He made optical glass, an achromatic telescope, and objective lenses. He also invented the spectroscope and developed
diffraction grating In optics, a diffraction grating is an optical component with a periodic structure that diffracts light into several beams travelling in different directions (i.e., different diffraction angles). The emerging coloration is a form of structur ...
. In 1814, he discovered and studied the dark absorption lines in the
spectrum A spectrum (plural ''spectra'' or ''spectrums'') is a condition that is not limited to a specific set of values but can vary, without gaps, across a continuum. The word was first used scientifically in optics to describe the rainbow of colors ...
of the sun now known as Fraunhofer lines. The German research organization
Fraunhofer Society The Fraunhofer Society (german: Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V., lit=Fraunhofer Society for the Advancement of Applied Research) is a German research organization with 76institutes spread throughout Germany ...
, which is Europe's biggest Society for the advancement of
applied research Applied science is the use of the scientific method and knowledge obtained via conclusions from the method to attain practical goals. It includes a broad range of disciplines such as engineering and medicine. Applied science is often contrasted ...
, is named after him.


Biography

Joseph Fraunhofer was the 11th child, born into a
Roman Catholic Roman or Romans most often refers to: * Rome, the capital city of Italy *Ancient Rome, Roman civilization from 8th century BC to 5th century AD * Roman people, the people of ancient Rome *'' Epistle to the Romans'', shortened to ''Romans'', a let ...
family in
Straubing Straubing () is an independent city in Lower Bavaria, southern Germany. It is seat of the district of Straubing-Bogen. Annually in August the Gäubodenvolksfest, the second largest fair in Bavaria, is held. The city is located on the Danube for ...
, in the Electorate of Bavaria, to Franz Xaver Fraunhofer and Maria Anna Fröhlich. He was orphaned at the age of 11 and started working as an apprentice to a harsh glassmaker named Philipp Anton Weichelsberger. 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. 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. In 1806, Utzschneider and Georg von Reichenbach brought Fraunhofer into their Institute at
Benediktbeuern Benediktbeuern (Central Bavarian: ''Benediktbeiern'') is a municipality in the district of Bad Tölz-Wolfratshausen in Bavaria, Germany, 2 kilometers, or 1.25 miles from Bichl. The village has 3,602 residents as of 31 December 2019. The medieva ...
, a secularised
Benedictine , image = Medalla San Benito.PNG , caption = Design on the obverse side of the Saint Benedict Medal , abbreviation = OSB , formation = , motto = (English: 'Pray and Work') , foun ...
monastery devoted to glassmaking. There he discovered how to make fine optical glass and invented precise methods for measuring optical dispersion. It was at the Institute that Fraunhofer met Pierre-Louis Guinand ( de), a Swiss glass technician, who instructed Fraunhofer in glassmaking at Utzschneider's behest. 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. In 1814, Guinand left the firm, as did Reichenbach. Guinand would later become a partner with Fraunhofer in the firm, 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 Michael Faraday (; 22 September 1791 – 25 August 1867) was an English scientist who contributed to the study of electromagnetism and electrochemistry. His main discoveries include the principles underlying electromagnetic inducti ...
were unable to produce glass that could rival Fraunhofer. His illustrious career eventually earned him an
honorary doctorate An honorary degree is an academic degree for which a university (or other degree-awarding institution) has waived all of the usual requirements. It is also known by the Latin phrases ''honoris causa'' ("for the sake of the honour") or ''ad hono ...
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 Munich ( ; german: München ; bar, Minga ) is the capital and most populous city of the German state of Bavaria. With a population of 1,558,395 inhabitants as of 31 July 2020, it is the third-largest city in Germany, after Berlin and ...
. Like many
glassmaker Glass is a non-crystalline, often transparent, amorphous solid that has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics. Glass is most often formed by rapid cooling (quenching) o ...
s 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.


Invention and scientific research

One of the most difficult operations of practical optics during the time period of Fraunhofer's life was accurately
polishing Polishing is the process of creating a smooth and shiny surface by rubbing it or by applying a chemical treatment, leaving a clean surface with a significant specular reflection (still limited by the index of refraction of the material accordin ...
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. 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 Flint glass is optical glass that has relatively high refractive index and low Abbe number (high dispersion). Flint glasses are arbitrarily defined as having an Abbe number of 50 to 55 or less. The currently known flint glasses have refractiv ...
, 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. 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
color Color (American English) or colour (British English) is the visual perceptual property deriving from the spectrum of light interacting with the photoreceptor cells of the eyes. Color categories and physical specifications of color are associ ...
s of the
spectrum A spectrum (plural ''spectra'' or ''spectrums'') is a condition that is not limited to a specific set of values but can vary, without gaps, across a continuum. The word was first used scientifically in optics to describe the rainbow of colors ...
, 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.


Discovery of dark absorption lines

By 1814, Fraunhofer had invented the modern spectroscope. 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 Fire is the rapid oxidation of a material (the fuel) in the exothermic chemical process of combustion, releasing heat, light, and various reaction products. At a certain point in the combustion reaction, called the ignition point, flames ...
. 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. Continuing to investigate, Fraunhofer detected dark lines also appearing in the spectra of several bright
star A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...
s, but in slightly different arrangements. He ruled out the possibility that the lines were produced as the light passes through the
Earth’s atmosphere The atmosphere of Earth is the layer of gases, known collectively as air, retained by Earth's gravity that surrounds the planet and forms its planetary atmosphere. The atmosphere of Earth protects life on Earth by creating pressure allowing ...
. 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. He found that the spectra of
Sirius Sirius is the brightest star in the night sky. Its name is derived from the Greek word , or , meaning 'glowing' or 'scorching'. The star is designated α Canis Majoris, Latinized to Alpha Canis Majoris, and abbreviated Alpha CM ...
and other first-magnitude stars differed from the sun and from each other, thus founding stellar spectroscopy. These dark fixed lines were later shown to be mostly atomic absorption lines, as explained by Kirchhoff and Bunsen in 1859, with the rest identified as telluric lines originating from absorption by
oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements ...
molecules in the
Earth's atmosphere The atmosphere of Earth is the layer of gases, known collectively as air, retained by Earth's gravity that surrounds the planet and forms its planetary atmosphere. The atmosphere of Earth protects life on Earth by creating pressure allowing fo ...
. 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.


Invention of optical instruments

Fraunhofer also developed a
diffraction grating In optics, a diffraction grating is an optical component with a periodic structure that diffracts light into several beams travelling in different directions (i.e., different diffraction angles). The emerging coloration is a form of structur ...
in 1821, after James Gregory discovered the phenomenon of diffraction grating and after the American astronomer
David Rittenhouse David Rittenhouse (April 8, 1732 – June 26, 1796) was an American astronomer, inventor, clockmaker, mathematician, surveyor, scientific instrument craftsman, and public official. Rittenhouse was a member of the American Philosophical Society a ...
invented the first manmade diffraction grating in 1785. 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".


Telescopes and optical instruments

Fraunhofer produced various optical instruments for his firm. 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 Stellar parallax is the apparent shift of position of any nearby star (or other object) against the background of distant objects, and a basis for determining (through trigonometry) the distance of the object. Created by the different orbital p ...
. 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,A Guide to Edinburgh's Popular Observatory
Astronomical Society of Edinburgh
the telescope itself being completed by Repsold of Hamburg after Fraunhofer's death.


Works


Kurzer Umriß der Lebens-Geschichte des Herrn Dr. Joseph von Fraunhofer
Tr. Brief outline of the life-story of Dr. Joseph von Fraunhofer By Joseph von Utzschneider. Rösl, 1826. *
Prismatic and diffraction spectra
memoirs. By Joseph von Fraunhofer,
William Hyde Wollaston William Hyde Wollaston (; 6 August 1766 – 22 December 1828) was an English chemist and physicist who is famous for discovering the chemical elements palladium and rhodium. He also developed a way to process platinum ore into malleable ingot ...
. American Book Co., 1899.


See also

*
Fraunhofer (crater) Fraunhofer is a lunar impact crater that is located just to the south-southwest of the walled plain Furnerius, in the southeastern part of the Moon. This crater appears foreshortened when viewed from the Earth, and is actually nearly circular ...
* German inventors and discoverers


Notes


References

* * * Klaus Hentschel: ''Mapping the spectrum. Techniques of visual representation in research and teaching''. Oxford Univ. Press, Oxford 2002. * (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.


External links

* * * * * * * * * * {{DEFAULTSORT:Fraunhofer, Joseph von 1787 births 1826 deaths 19th-century German astronomers 19th-century German physicists 19th-century German inventors German Roman Catholics Optical physicists People from Straubing People of the Industrial Revolution German scientific instrument makers Spectroscopists Burials at the Alter Südfriedhof Deaths by poisoning