Fraunhofer, Joseph

(b. Straubing, Germany, 6 March 1787; d. Munich, Germany, 7 June 1826)

optics, optical instrumentation.

Fraunhofer represents the highest order of the union of the craftsman and the theoretician. His family and early acquaintances were closely associated with the skilled craft tradition and particularly concerned with the glass and optical trades. As he acquired mastery of lens grinding, lens design, and glassmaking—through apprenticeship and independent study of optical books—Fraunhofer sought not merely to produce lenses which surpassed the best on the market but also to design and produce lenses which approached the optical ideal. In this pursuit he turned to the theoretical study of optics and light, a study which, when combined with his practical experience and understanding, ultimately made him the master theoretical optician of Europe and, as a by-product, led him to make numerous significant contributions to science.

Fraunhofer was the eleventh and last child of a poor master glazier, Franz Xaver Fraunhofer, and Maria Anna Fröhlich. After receiving only a limited elementary education, he entered his father’s workshop. In November 1798, following the death of his parents, Fraunhofer’s guardian apprenticed him to Philipp A. Weichselberger, a dull, unintellectual Munich master mirror-maker and glass cutter. Fraunhofer found his apprenticeship degrading and miserable, as his master discouraged further schooling and isolated him from his peers. Nevertheless, he maintained his goal of becoming a spectacles maker.

The fortunes of the sickly boy took an ironic turn for the better when, on 21 July 1801, the workshophouse collapsed, pinning him under the wreckage for some time. Elector Maximilian Joseph heard of the accident and presented him with the handsome sum of eighteen ducats. With the money Fraunhofer purchased a glass-working machine, books on optics, and release from the last six months of his six-year apprenticeship.

After a short, abortive business venture (producing engraving plates for visiting cards), Fraunhofer returned in November 1804 to work as a journeyman for Weichselberger until May 1806, when he entered the optical shop of the Munich philosophical (scientific) instrument company founded in 1802 by Joseph von Utzschneider, Georg von Reichenbach, and Joseph Liebherr.

Influenced by Ulrich Schiegg, a trained astronomer, and by Josef Niggl, the optics master under whom he served as a journeyman, Fraunhofer developed expertise in practical optics and acquired an interest in and a knowledge of mathematics and optical science. In 1809, in accordance with a contract negotiated between Utzschneider and Pierre Louis Guinand, Utzschneider designated Fraunhofer, who had criticized the available optical glass, to receive from Guinand instruction in his closely kept secrets of glassmaking. Guinand had moved from Switzerland to Bavaria in 1805 at the initiative of Utzschneider in order to supply the optical firm with glass; his tutelage allowed Fraunhofer to combine his understanding of optics with the practical knowledge of glassmaking. This instruction led to a two-year collaboration between Fraunhofer and Guinand that resulted in substantial increases in the size of glass blanks for lenses. fraunhofer’s advance in the firm—from journeyman in 1806, to manager of the optical workshop in 1809, to business partner with Utzschneider and director of the glassmaking (over Guinand) in 1811—was a reflection of his quick grasp of and original contributions to optical science, practical optical work, and glassmaking.

From 1819, when the optical workshop was returned to Munich from Benediktbeuern, he participated actively in the affairs of the Bavarian Academy of Sciences in Munich. In 1823, while still maintaining his active business schedule, he accepted the post of director of the Physics Museum of the academy and received the honorary title royal Bavarian professor. Fraunhofer initiated lectures on physical and geometrical optics shortly thereafter but had to discontinue them because of his frail health. Although he enjoyed neighborhood walks, he had little time for relaxation. Late in 1825 the lifelong bachelor contracted tuberculosis, from which he never recovered. During the last few years of his life Fraunhofer was elected to several foreign societies, including the Society of Arts in England, and received state honors from Denmark and his native Bavaria. The University of Erlangen conferred upon him the title of doctor of philosophy.

Fraunhofer was a blend of mathematically inclined natural philosopher, optical technician, and glassmaker. Although he had little formal education, he sought to understand optical theory and apply it to the practical work of constructing aberrationminimizing lens combinations. At the time he entered Utzschneider’s instrument shop, the optical trade of Europe centered in London, where the leading names were Dollond and Ramsden. Yet even in London the lack of large blanks of homogeneous, striae-free crown and flint glass and the comparatively crude determinations of the optical constants of the glass limited the size and quality of lenses and restricted opticians to trial-and-error methods of optical construction.

Early in the nineteenth century the Munich firm that Fraunhofer joined took the lead in Germany in the manufacture of precision optical instruments and gained a gradual advantage over the London opticians, initially by obtaining the services of Guinand, who improved the making of optical glass. Later, Guinand and Fraunhofer, working together from 1809 to 1813, further improved the homogeneity of optical glass and increased the size of the striae-free blanks, so that large-diameter lenses could be made. Fraunhofer also sought to determine, with significantly greater precision than before, the dispersion and refractive index for different kinds of optical glass, so that he could abandon the traditional trialand-error methods and approach lensmaking according to optical theory and calculation.

In order to determine precisely the optical constants of glass, Fraunhofer in 1814 used the two brightyellow lines in flame spectra as a source of monochromatic light. With improved values for optical constants, he hoped to design and construct lens combinations in which the spherical aberration and coma could be eliminated. While conducting these tests, he observed the effect of the refracting medium on light, comparing the effect of light from flames with light from the sun, and found that the solar spectrum was crossed with many fine dark lines, a few of which William Hyde Wollaston had observed and reported upon in 1802. Designating the more distinct lines with capital letters (A,B,C,D, . . . ,I), he mapped many of the 574 lines that he observed between B on the red end and H on the violet end of the spectrum. Somewhat later he noted that some of these lines appeared to correspond to the bright doublet of lines in many flame spectra; yet he noted further that while the pattern observed for the sun and planets appeared identical, the patterns for the sun, Sirius, and other bright stars differed from one another. These observations stimulated considerable interest for the next half-century among natural philosophers, whose speculations culminated in the classical explanation of absorption and emission spectra made by Kirchhoff and Bunsen in 1859. For Fraunhofer, however, these observations were primarily of importance in his efforts to perfect the achromatic telescope.

In 1821 and 1823, shortly after Fresnel’s studies of interference phenomena had received general attention, Fraunhofer published two papers in which he observed and analyzed certain diffraction phenomena and interpreted them in terms of a wave theory of light. In the 1821 paper he discussed his examination of the spectra resulting from light diffracted through a single narrow slit and quantitatively related the width of the slit to the angles of dispersion of the different orders of spectra. Extending his observations to diffraction resulting from a large number of slits, he constructed a grating with 260 parallel wires.

Although David Rittenhouse and Thomas Young had previously noted some effects of crude diffraction gratings, Fraunhofer made the first quantitative study of the phenomena. The presence of the solar dark lines enabled him to note that the dispersion of the spectra was greater with his grating than with his prism. Hence, he examined the relationship between dispersion and the separation of wires in the grating. Utilizing the dark lines as bench marks in the spectrum for his dispersion determinations, he concluded that the dispersion was inversely related to the distance between successive slits in the grating. From the same study Fraunhofer was able to determine the wavelengths of specific colors of light. Somewhat later he also constructed a grating by ruling lines on glass covered by gold foil and, even later, constructed a reflecting grating. The latter prompted him to consider the effects of light obliquely incident to the grating.

In the paper prepared in 1823, Fraunhofer revealed his continued investigation of diffraction gratings. Using a diamond point, he could rule up to 3,200 lines per Paris inch. He continued his study of the effect of oblique rays, developed formulations based on a wave conception, and calculated a revised set of wavelengths for the major spectral lines. Thus, his earlier observations of the dark lines in the solar spectrum enabled him to make the highly precise measurements of dispersion; then his use of the wave theory of light allowed him to derive, with suitable simplifications, the general formulation of the grating equation still in use today. His other papers focused principally upon the design and construction of new instruments, and one paper examined atmospheric light phenomena.

Fraunhofer’s scientific studies were intimately related to his professional object: the design and production of the finest possible optical and mechanical instruments. Utilizing the lines in the solar spectrum as bench marks, he determined with unprecedented precision the optical constants of various kinds of glass. The combination of superior optical glass, the theoretical design and calculation of lens systems, the accurate determination of optical constants, and the use of Newton’s rings for testing of lens surfaces enabled the Utzschneider-Fraunhofer shop in Munich to wrest leadership in the production of optical instruments from the London opticians during the first quarter of the century.

Although Fraunhofer openly published his observations of the spectral lines and his interpretation of diffraction spectra, he retained as trade secrets his knowledge of optical glassmaking and his methods of calculating and testing lenses. Among his most famous instruments were the nine-and-a-half-inch Dorpat refracting telescope and equatorial mounting used by Wilhelm Struve and the six-and-a-quarterinch Königsberg heliometer with which Friedrich Bessel measured the parallax of 61 Cygni in 1838. Such a detection and measurement of parallax had been sought unsuccessfully since antiquity.

After Fraunhofer’s death, Utzschneider and, later, Siegmund Merz continued the Munich business, actively participating in the movement initiated by Fraunhofer to replace the large reflecting telescopes with the large refractors. Although his Munich optical shop did not continue to lead in innovation during its remaining half-century of existence, Fraunhofer’s approach of combining practical with theoretical knowledge and an understanding of both optics and glassmaking had not only made the German optical industry the leading one in the world but also continued to inspire generations of German optical scientists and industrialists. Fraunhofer’s direct successors in the nineteenth century thus included Josef Max Petzval; Johann Friedrich Voigtländer, Peter Friedrich Voigtländer, and Friedrich von Voigtländer; Carl August Steinheil and Adolph Steinheil; Philipp L. Seidel; Carl Zeiss; Ernst Abbe; and Otto Schott.

BIBLIOGRAPHY

I. Original Works. Fraunhofer’s published works were collected in Eugen C.J. Lommel, ed., Joseph von Fraunhofer’s gesammelte Schriften (Munich, 1888). A review of an unpublished 1807 paper appears in Forschungen zur Geschichte der Optik, 1 (May 1929), 42–51.

II. Secondary Literature. Two important nineteenth-century studies are Joseph von Utzschneider, “Kurzer Umriss der Lebens-Geschichte des Herrn ... Fraunhofer,” in Dinglers polytechnisches Journal, 21 (1826), 161–181; and Siegmund Merz, Fraunhofer’s Leben und Wirken... (Landshut, 1865). Two twentieth-century works have provided the bases for all subsequent studies: the most comprehensive biographical study, by the outstanding Zeiss historian of optics, Moritz von Rohr, Joseph Fraunhofers Leben, Leistungen und Wirksamkeit (leipzig, 1929); and A. Seitz, Josef Fraunhofer und sein optisches Institut (Berlin, 1926). Upon the centennial of Fraunhofer’s death, Naturwissenschaften, 14 (1926), 522–554, was devoted to an evaluation of his work. More recent studies include H. Jebsen-Marwedel, Joseph von Fraunhofer und die Glashiitte in Benediktbeuern (1963); and W. Gerlach, “Joseph Fraunhofer und seine Stellung in der Geschichte der Optik,” in Optik, 20 (1963), 279–292. Twentieth-century literature in English on Fraunhofer is very limited and mostly derived from the works of Rohr and Seitz: Moritz von Rohr, “Fraunhofer’s Work and Its Present Day Significance,” in Transactions of the Optical Society, 27 (1926), 277–294; W. H. S. Chance, “The Optical Glassworks at Benediktbeuern,” in Proceedings of the Physical Society, 49 (1937), 433–443; and Henry C. King, The History of the Telescope (Cambridge, Mass., 1955), passim.

Reese V. Jenkins