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Joseph von Fraunhofer

Joseph von Fraunhofer

The German physicist Joseph von Fraunhofer (1787-1826) was the first to solve the problem of constructing achromatic lenses of high magnitude.

Joseph von Fraunhofer, the son of a poor glazier, was born on March 6, 1787, in Straubing, Bavaria. An orphan by the age of 12, he became an apprentice to a mirror maker in Munich. He spent his first pennies at the flea market on an elementary textbook of geometry which he studied in his spare time. On July 21, 1801, two houses collapsed in Munich, and of the people buried under the ruins, Fraunhofer was the only one found alive. The incident brought him to the attention of J. Niggl, an optical instrument maker, and J. Utzschneider, a Benedictine from Benediktbeuern. In 1807, when Fraunhofer had already mastered through private studies the best German university textbooks on optics, he was invited to work with a new optical-instrument-making firm established largely through Utzschneider's efforts at Benediktbeuern.

Indicative of Fraunhofer's abilities was his first assignment: the making of achromatic lenses for telescopes. The task implied not only original theoretical work but also the production of highly homogeneous silicates. Fraunhofer's communication on the results of his research appeared in the Denkschriften (Memoirs) for 1814-1815 of the Academy of Sciences in Munich. The paper contained a description of the first use of the dark lines of the solar spectrum (Fraunhofer lines) as reference points for the measurement of refraction indexes.

Fraunhofer's other great achievement concerned the measurement of wavelengths in the optical spectrum. He transformed the spectroscope into a precision instrument, but his finest precision instrument was the micrometer, described in his memoir of 1824 to the Munich Academy. By then he had been "extraordinary visiting member" there for 3 years, in due recognition of the talents of a first-rate physicist whose academic training consisted of spotty attendance of the lowest grades of elementary school.

Fraunhofer's success made his name synonymous with progress. Astronomers considered it a privilege to have their orders accepted by him. The famous refractor he made for the Dorpat Observatory and the heliometer he constructed for the Berlin Observatory gave both institutions positions of unchallenged leadership for several decades.

The privations of youth and his delicate constitution hardly equipped Fraunhofer for glassblowing, which caused in 1824 the first symptoms of a respiratory ailment. Proper attention to his health came too late. He died on June 7, 1826, in Munich at the height of a most promising scientific career.

Further Reading

Information on Fraunhofer is in Theodore F. Van Wagenen, Beacon Lights of Science (1924); Henry Smith Williams, Great Astronomers (1930); and Philip Lenard, Great Men of Science (1933). □

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Fraunhofer, Joseph von

Fraunhofer, Joseph von (1787–1826) German physicist and optician, founder of astronomical spectroscopy. By studying the diffraction of light through narrow slits, he developed the earliest form of diffraction grating. He observed and began to map the dark lines in the Sun's spectrum (1814), now called Fraunhofer lines. Fraunhofer solved many of the scientific and technical problems of astronomical telescope-making.

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