Frauenhofer, J von

NAME: Fraunhofer, Josef von

ACHIEVEMENT(S): Frauenhofer lines (spectroscopy)

NICKNAME/ALIAS: None

DATE/PLACE OF BIRTH: 6 March 1787, at Straubing, Bavaria, Germany.

DATE/PLACE/AGE AT DEATH: 7 June 1826, in Munich, Germany. Aged 39

DISCIPLINE: Physicist

FIELD: Physics

LANGUAGE: German

PARENTS: Franz Xaver Fraunhofer (d. 1798) and Maria Anna Frohlich

SIBLINGS: 10 elder siblings

SPOUSE: None

CHILDREN: None

EDUCATION: Limited elementary education

MAJOR WORK: 'Collected Works', 1888

LIFE AND TIMES:

In 1804 Fraunhofer set himself up in business in Munich producing engraving plates for visiting cards, but this project collapsed. In May 1806 he was hired by the optical shop of the Munich Philosophical Instrument Company at Benediktbeuern, which produced scientific instruments.

Dissatisfied with the optical glass available, Fraunhofer then came under the instruction of Pierre Louis Guinand, a master glassmaker. Fraunhofer was now able to combine his

expertise in both the practice and theory of optics with a practical knowledge of glass-making, to the great benefit of the company. As a result he rose to manager of the optical workshop in 1809, and then to business partner and director of glassmaking (over Guinand) in 1811.

At the time he began working in the instrument shop, the European optical trade centred in London, where the leading instrument-makers were <improved on work of> Dollond* and <improved on work of> Ramsden*, but even here the lack of large blanks made of homogeneous, striae-free crown and flint glass, and the comparatively crude calculation of the optical constants of the glass, greatly limited the size and quality of their lenses and confined instrument-makers to trail-and-error methods of construction. Fraunhofer approached lens-making according to optical theory, and decided to calculate the dispersion powers and refractive indices of different kinds of achromatic optical glass with greater accuracy.

In 1813, Fraunhofer first attempted to measure the dispersive power of a given piece of glass by the length of the spectrum it produced, but he found this impossible owing to the absence of sharp edges. He then noticed the characteristic sharp yellow line between red and yellow in the spectrum of many oils and salts and realized this would enable him to plot fixed positions in the spectrum.

In 1814, Fraunhofer began to observe the two bright-yellow lines in flame spectra with a view to using them as a source of monochromatic light in order to obtain get accurate optical values. Comparing the effect of the light from the flame with light from the Sun, he found that the solar spectrum was crossed by many fine, dark lines.

A few of these dark lines had been noticed by the English chemist <anticipated by> Wollaston* in 1802. Fraunhofer identified 574 lines with fixed positions between the red and violet ends of the spectrum, and designated the brightest by the letters A through G, a system of identification still in use.

In 1821 he published a description of the following experiments: having first examined the patterns that result from light diffracted through a single narrow slit, and related the width of the slit to the angles of dispersion of the light, Fraunhofer then increased the number of slits until he had constructed a grating of 260 parallel wires, with which he then made the first quantitative study of spectra produced by diffraction gratings.

The presence of the solar dark lines proved them to be an intrinsic feature of sunlight. Frauenhofer saw that the dispersion of the spectra is greater with a diffraction grating than with a prism.

On examining the relationship between the dispersion and the separation of the wires in the grating, he concluded that the dispersion is inversely related to the distance between successive slits in the grating. By measuring this dispersion, he was able to measure with precision the wavelengths of light of specific colors and the dark lines.

By the 1820s, using the lines of solar spectrum as bench marks, Fraunhofer was able to calculate with unprecedented precision the optical constants of various kinds of glass, and this combination of superior glass, his theoretical design and calculation of lens systems made him the leading producer of optical instruments in Europe.

Among Fraunhofer's most famous instruments were his high-quality telescopes, which led to several important discoveries in astronomy: the nine-and-a-half-inch Dorpat refracting telescope and equatorial mounting used by the German astronomer <instrument used by> Struve* (the discoverer of double stars) and the six-and-a-quarter-inch Konigsberg heliometer with which the astronomer <instrument used by> Bessel* measured the parallax of 61 Cygni in 1838.

Frauenhofer lines in the spectrum of the Sun or other stars were explained by <discovery explained by> Kirchhoff* in 1859:- they were caused by selective absorption the Sun's or star's radiation at specific wavelengths by the various elements existing as gases in its atmosphere About 25,000 Fraunhofer lines are now known to exist in the solar spectrum.

ASSESSMENT: His discovery of spectral absorption lines was a major step in the development of spectroscopy.

EXTRA CONNECTIONS: His work related to that of <work related to> Fox Talbot*

<ideas used by> Vierord* applied his discovery to medicine.

R Walpole*?

ONELINER: Josef von Frauenhofer, who triggered spectroscopy

BIBLIOGRAPHY:

DSB, EB

Biog. Dict of Physicists

JOSEPH VON FRAUNHOFER

L&T: Josef Fraunhofer was born 6 March1787 at Straubing, Bavaria, youngest of the 11 children of Franz Xaver Fraunhofer, an impoverished master glazier, and Maria Anna Frohlich, from a family of glassmakers. Received only limited elementary education. Early life marked by tragedy: mother died in 1797, his father in 1798, yr after he had entered father's glazing workshop. Orphaned Fraunhofer then left Straubing in August 1799 (aged only 12) and was apprenticed for 7 yrs to court mirror maker, Philipp A. Weichselberger, at Munich. JF found apprenticeship tedious, but 2 yrs later was released from it when one night in July 1801 Weichelsberger's workshop-house collapsed, pinning him under wreckage. JF finally released with only minor injuries, but Prince Elector Maximilian Joseph IV of Bavaria heard of weird accident and travelled to scene of disaster: was particularly moved by plight of 14-yr-old JF, and gave him sum of money, invited him to castle in Nymphenburg, and introduced him to his privy councillor Joseph von Utzschneider.

After continuing his apprenticeship with Weichselberger, and working with Benedictine-trained optician Joseph Niggl on Sundays 1801-04, in 1804 JF became a journeyman of decorative glassmaking and cutting, working for Weichselberger. But soon became bored by work, and wanted more education - prevented by Weichselberger: eventually in desperation sought advice of Utzschneider, who in May 1806 offered the 19-yr-old journeyman a position in his Optisches Institut assisting in manufacture of achromatic lenses for refracting telescopes and ordnance surveying instruments. With money gift from Maximilian that he had saved, JF was then able to buy out of his contractual agreement with Weichselberger and to buy books on optics and a glass-cutting machine capable of handling optical glass.

Thus, in May 1806 JF sent to Munich for instruction period before, in early 1807, being transferred to the Bavarian govt's Optical Institute at Benediktbeuern, originally founded in 1802 by Josef von Utzschneider, Georg von Reichenbach, and Josef Liebherr, and which produced scientific instruments. Here, still only 19 years of age, Fraunhofer was able to develop both exceptional manual dexterity and intellectual abilities under tutelage of Ulrich Schiegg, a trained astronomer, and Joseph Niggl, the optics master there from 1804, and attain expertise in practical optics and a useful knowledge of mathematics and optical science. Was F's job to learn how to produce achromatic lenses for theodolites, telescopes, and repeating circles for use by Bureau topographique and the Bavarian Land Registry. JF proved extremely talented, and in 1807 wrote essay on catoptrics which described his newly invneted machine that cd cut segments of hyperbolic mirrors, and also invented a polishing machine.

In 1809, having expressed his dissatisfaction with the optical glass available, Fraunhofer then came under instruction of Pierre Louis Guinand, a master glassmaker. Fraunhofer was now able to combine his expertise in both the practice and theory of optics with a practical knowledge of glass-making, and began manufacturing achromatic lenses for telescopes and microscopes. As a result he rose from journeyman to manager of the optical workshop in 1809, and then to business partner with Utzschneider and director of glassmaking (over head of Guinand, much to G's displeasure, who left 1813) in 1811, at the age of only 24.

During his 20s, despite his lack of formal education, Fraunhofer sought to understand optical theory and apply it to the practical work of constructing lens combinations of minimum aberration. At the time he began working in Utzschneider's workshop, the European optical trade centred in London, where the leading instrument-makers were John Dollond and Jesse Ramsden, but even here the lack of large blanks made of homogeneous, striae-free crown and flint glass, and the comparatively crude determinations of the optical constants of the glass, greatly limited the size and quality of their lenses and confined instrument-makers to trail-and-error methods of construction. Fraunhofer resolved to improve this situation by approaching lens-making according to optical theory, and he set out to determine the dispersion powers and refractive indices of different kinds of achromatic optical glass with greater accuracy. During the following years, he collaborated with Guinand to produce substantial improvements in the homogeneity of optical glass and increases in the size of glass blanks for the production of large-diameter lenses.

In 1813, Fraunhofer first attempted to measure the dispersive power of a given piece of glass by the length of the spectrum it produced, but he found this impossible owing to the absence of sharp edges. He then discovered that the refractive power of a certain type of glass for a given colour could also not be used, owing to the impossibility of fixing the position of the colour exactly in the spectrum, but noticed the characteristic sharp yellow line between red and yellow in the spectrum of many oils and salts which he realized would enable him to plot fixed positions in the spectrum. Thus, in 1814, Fraunhofer began to observe the two bright-yellow lines in flame spectra with a view to using them as a source of monochromatic light in order to obtain more accurate optical values. Then, comparing the effect of the light from the flame with light from the Sun, he found that the solar spectrum is crossed with many fine, dark lines. A few of these dark lines had first been observed by the English chemist William Hyde Wollaston in 1802 but Fraunhofer, using an improved apparatus, was now able to distinguish 574 such lines with fixed positions between the red and violet ends of the spectrum, and to designate the brightest by the letters A through G, a system of identification still in use.

Using the results of his experiments, Fraunhofer was now able to make very accurate measurements of the dispersion and refractive properties of various kinds of glass, and in so doing he greatly improved the performance of the achromatic telescope, and also developed the spectroscope into a precision instrument for the scientific study of spectra. He continued his experiments during the following seven years, and in 1821 published a paper which detailed a number of experiments he had made with a diffraction grating (a device that dispenses light in much the same way a prism does). Having first examined the patterns that result from light diffracted through a single narrow slit, and related the width of the slit to the angles of dispersion of the light, Fraunhofer then increased the number of slits until he had constructed a grating of 260 parallel wires with which he then made the first quantitative study of spectra produced by diffraction gratings. The presence of the solar dark lines proved them to be an intrinsic feature of sunlight, and enabled Fraunhofer to note that the dispersion of the spectra is greater with a diffraction grating than with a prism. Furthermore, on examining the relationship between the dispersion and the separation of the wires in the grating, he concluded that the dispersion is inversely related to the distance between successive slits in the grating. By measuring this dispersion, he was then able to measure with great precision the wavelengths of light of specific colours and the dark lines.

During 1822 Fraunhofer also constructed reflection gratings, which enabled him to extend his investigations to the effect of diffraction on oblique rays. He then developed, using the wave theory of light, a general form of the grating equation still in use today, and calculated a revised set of wavelengths for the major spectral lines, which he published in a paper of 1823. These papers on diffraction gratings would prove important in the subsequent development of spectroscopy, which would much later become a vital tool in the elucidation of atomic structure.

During the late 1810s and early 1820s Fraunhofer also published papers on the design and construction of new instruments, and one paper examining atmospheric light phenomena. However, he never published his researches into glassmaking, nor the methods that he developed for calculating and testing lenses, which he regarded as trade secrets. By the 1820s, using the lines of solar spectrum as bench marks, Fraunhofer was able to determine with unprecedented precision the optical constants of various kinds of glass, and this combination of superior optical glass, his theoretical design and calculation of lens systems, his accurate determination of optical constants, and his use of Newton's rings for the testing of lens surfaces, enabled him to make the Utzschneider-Fraunhofer shop in Munich the leading producer of optical instruments in Europe. Among Fraunhofer's most famous instruments were his high-quality telescopes, which led to several important discoveries in astronomy - among the most were the nine-and-a-half-inch Dorpat refracting telescope and equatorial mounting used by the German astronomer Wilhelm Struve (the discoverer of double stars) and the six-and-a-quarter-inch Konigsberg heliometer with which the astronomer Friedrich Bessel measured the parallax of 61 Cygni in 1838.

From 1814, JF had become sole director of glassmakers at the Optical Institute, and in 1819 his workshop moved from Beneditktbeuern to Munich. As result, during the following years he became active in the affairs of the Bavarian Academy of Sciences at Munich. In 1823, while still pursuing his business career, he accepted the post of Director of the Physics Museum of the Bavarian Academy, and received the honorary title royal Bavarian professor. However, two years later he contracted tuberculosis, from which he died on 7 June 1826, in Munich, Germany, aged 39. During his last years he was elected to several foreign societies, including the Society of Arts in England, awarded the title of doctor of philosophy from the University of Erlangen, and received state honours from Denmark and Bavaria.

During his short career, Fraunhofer had also published his observations on the dark lines in the spectrum, although he could not provide an explanation for them - were explained by Gustav Kirchhoff in 1859 as caused by selective absorption of the Sun's or star's radiation at specific wavelengths by the various elements existing as gases in its atmosphere, and subsequently it therefore became possible to identify the elements in the Sun's atmosphere from a study of the Fraunhofer lines. About 25,000 Fraunhofer lines are now known to exist in the solar spectrum, between the wavelengths of 2,950 and 10,000 angstroms. (One angstrom equals 10-8 cm.).

Fraunhofer and Maximilian: Their alliance happened against backdrop of reformed politics of Bavaria during Napoleon's occupation and the growth of ordnance surveying. Need for precision optical and ordnance surveying instruments was felt throughout the German territories by astronomers and ordnance surveyors who were producing more accurate maps of their regions: Napoleon needed topographical maps of the new territories his troops had acquired, and regional rulers such as Max. I based economic reforms on property taxes - hence, property boundaries had to be determined with much greater accuracy. Until 1800, GB had sold best optical lenses to the Continent; but blockade of 1806 cut off GB from Continent - thus Napoleon assisted in destruction of GB's optical empire, and also guaranteed a market for JF's products across Europe. For Bavaria, changes signalled transformation ofa rural agricultural state into a leader in technological and scientific advances. Was in this context that JF conducted his famous research on achromatic lenses and prisms using solar spectral lines: JF drew upon secretive monastic labour of Benedictine monks and secretive guild practices of artisanal craftsmen from area of Benediktbeuern, Bavaria. JF's lab became a secularized Benedictine monastery whose architecture reflected the importance of labour, silence, and secrecy to the Benedictine order. JF and Utzschneider had many resources at their disposal in order to ensure that recipe and methods for achromatic glass remained secret.

JF's artisanal skills combined with an aggressive, reform-minded Bavarian government gave rise to a precision optical technology that was to become the envy of the world. Maximilian von Montgelas's governmental reforms, backed by Max I, were intended to launch Bavaria to teh technological, scientific, and economic levels of post-Rev France: these reforms shifted the beaucratic power from the clergy of the RC Church to a new group of men - the Beamten, or civil Fservants.

Previous to Max's rule, Bavaria was the most underdeveloped region among the German states. Contemporaries credited Max. for restoring to Bavaria the cultural and scientific status it had had in the Middle Ages, and in particular for his decision to restore the wealth of Bavaria by recreating a community of artisans that had feld to Italy and the Tyrol after Bavaria's devastation during the 30 Yrs War. The reforms of Montgelas transformed Bavaria into a powerful manufacturing and trading nation, and one of most noteworthy enterprises was Utzschneider and JF's Optical Institute.

BIBLIOGRAPHY: DSB, EB, Biog. Dict of Physicists

Jackson, Myles, 'Spectrum of Belief; Joseph von Frauenhofer and the Craft of Precision Optics', Cambridge, Mass. & London: MIT Press, 2000