The German research organizationFraunhofer Society, which is Europe's biggest Society for the advancement ofapplied research, is named after him. Fraunhofer lines are used in astronomy to determine the composition of celestial bodies. His epitaph readsAproximavit sidera,Latin for'He brought closer the stars.'[3]
Joseph Fraunhofer was the 11th child, born into aRoman Catholic family[4] inStraubing, in theElectorate of Bavaria, to Franz Xaver Fraunhofer and Maria Anna Fröhlich.[5] His father and paternal grandfather Johann Michael had been master glassmakers in Straubing. Fröhlich's family also came from a lineage of glassmakers going back to the 16th century. He was orphaned at the age of 11 and started working as an apprentice to a harsh glassmaker named Philipp Anton Weichelsberger.[6][7] In 1801, the workshop in which he was working collapsed, and he was buried in the rubble. The rescue operation was led byPrince-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.[6][7]
Joseph Utzschneider, aprivy councilor, 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.[8] In 1806, Utzschneider andGeorg von Reichenbach brought Fraunhofer into their Institute atBenediktbeuern, a secularisedBenedictine monastery devoted to glassmaking. There he discovered how to make fine optical glass and invented precise methods for measuringoptical dispersion.[7]
It was at the Institute that Fraunhofer metPierre-Louis Guinand (de), a Swiss glass technician, who instructed Fraunhofer in glassmaking at Utzschneider's behest.[9] 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.[10] In 1814, Guinand left the firm, as did Reichenbach. Guinand would later become a partner with Fraunhofer in the firm,[9] 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 ofMichael Faraday were unable to produce glass that could rival Fraunhofer.[6][7]
Like manyglassmakers of his era, he was poisoned byheavy 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.[6]
One of the most difficult operations of practical optics during the time period of Fraunhofer's life was accuratelypolishing the spherical surfaces of largeobject glasses. Fraunhofer invented the machine which rendered the surface more accurately than conventionalgrinding. 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.[10]
In 1811, he constructed a new kind offurnace, and during his second melting session when he melted a large quantity of glass, he found that he could produceflint glass, which, when taken from the bottom of a vessel containing roughly 224 pounds of glass, had the samerefractive power as glass taken from the surface. He found that Englishcrown 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.[10]
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 thecolors of thespectrum, making it difficult to accurately measure the angle of refraction. To address this limitation, Fraunhofer performed a series of experiments for the purpose of producinghomogeneous light artificially, and unable to effect his object in a direct way, he did so by means of lamps andprisms.[10]
By 1814, Fraunhofer had invented the modernspectroscope.[11] 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 offire. 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.[10][12]
Continuing to investigate, Fraunhofer detected dark lines also appearing in the spectra of several brightstars, but in slightly different arrangements. He ruled out the possibility that the lines were produced as the light passes through theEarth’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 andsun and carry information about the source of light, regardless of how far away that source is.[2] He found that the spectra ofSirius and other first-magnitude stars differed from the sun and from each other, thus foundingstellar spectroscopy.[13]
These dark fixed lines were later shown to be mostly atomic absorption lines, as explained byKirchhoff andBunsen in 1859,[14] with the rest identified astelluric lines originating from absorption byoxygen molecules in theEarth's atmosphere. These lines are still calledFraunhofer lines in his honor; his discovery had gone far beyond the half-dozen apparent divisions in the solar spectrum that had previously been noted byWollaston in 1802.[15]
Fraunhofer also developed adiffraction grating in 1821, afterJames Gregory discovered the phenomenon of diffraction grating and after the American astronomerDavid Rittenhouse invented the first manmade diffraction grating in 1785.[16][17] 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".[18]
The 9"-aperture refractor telescope with which Neptune was discovered
Fraunhofer produced various optical instruments for his firm.[9] This included the Fraunhofer Dorpat Refractor used by Struve (delivered 1824 toDorpat Observatory), and the BesselHeliometer (delivered posthumously), which were both used to collect data forstellar parallax. The firm's successor, Merz und Mahler, made a telescope for the New Berlin Observatory, which confirmed the existence of the major planetNeptune. Possibly the last telescopeobjective made by Fraunhofer was supplied for atransit telescope at theCity Observatory, Edinburgh,[19] the telescope itself being completed byRepsold of Hamburg after Fraunhofer's death.
^Brand, John C. D. (1995).Lines of Light: The Sources of Dispersive Spectroscopy, 1800–1930. Gordon and Breach Publishers. pp. 37–42.ISBN978-2884491624.
^Fraunhofer (1814–1815),pages 220–221Archived 10 March 2024 at theWayback Machine: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.
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.
I. Bernard Cohen; Henry Crew; Joseph von Fraunhofer; De Witt Bristol Brace (1981).The Wave theory, light and spectra. Ayer Publishing.ISBN978-0-405-13867-6.
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.
