Optician, b. at Straubing, Bavaria, 6 March, 1787; d. at Munich, 7 June, 1826. He was the tenth and last son of a poor glass-grinder who was unable to give his boy even the rudiments of knowledge. At the age of twelve he lost both parents and was apprenticed to a mirror-maker and lens-grinder for six years without pay. There he was not permitted to study or even to attend holiday school. The house where he worked collapsed in 1801, burying the boy under the ruins, but not injuring him fatally. This fortunate accident brought him to the notice of court-councillor von Utzschneider, who gave him books on mathematics and optics, and also interested King Max Joseph in him, who made him a present of eighteen ducats. With this money Joseph acquired a grinding-machine and bought his release from the obnoxious apprenticeship. He tried to earn a living at his trade and also as an engraver on metal. Finally, in 1806, he was called to the mathematico-technical institute of Reichenbach, Utzschneider, and Liebherr as an assistant. There he did such excellent work that he became a partner and manager of the optical institute of the firm at Benediktbeuern. In 1814 Utzschneider gave him 10,000 florins and formed with him the new firm of Utzschneider and Fraunhofer. The optical institute was moved to Munich in 1819 and Fraunhofer was appointed professor royal. The University of Erlangen gave him the degree of Ph.D., honoris causâ in 1822. The following year he was appointed conservator of the physical cabinet of the academy at Munich. Nobility, the order of merit, and the honorary citizenship of Munich were conferred upon him in 1824. The Imperial Leopoldina Academy, the Astronomical Society of London, and the Society for Natural Science and Medicine of Heidelberg elected him to membership. Shortly before his death he was made a Knight of the Danish order of Danebrog.

The work of this self-taught mathematical and practical optician was chiefly in developing improved methods of preparing optical glass, of grinding and polishing lenses, and of testing them. His success deprived England of its supremacy in the optical field. He invented the necessary machines, constructed a spherometer, and developed the moving and measuring devices used in astronomical telescopes, such as the screw micrometer and the heliometer. His fame, however, rests above above all on his initiation of spectrum analysis. While studying the chromatic refraction of different glasses he discovered the banded spectra of artificial lights and also the dark lines in the solar spectrum, called now the Fraunhofer lines. He also accomplished an important theoretical work on diffraction and established its laws; he placed the diffraction slit in front of the objective of a measuring telescope and later made and used diffraction gratings with up to 10,000 parallel lines to the inch, ruled by a specially constructed dividing engine. By means of these gratings he was able to measure the minute wave-lengths of the different colours of light. As a Christian, Fraunhofer was faithful and observant even in details. The simple inscription on his tomb reads: Approximaverit sidera. His important memoirs were first published in "Denkschriften" of the Royal Bavarian Academy of Sciences, the one on refraction, spectra, and lines in 1817, and that on diffraction and its laws in 1821. They were soon translated into English and French. His collected works have been published by Lommel (Munich, 1888), and translated in part and edited by Ames (New York and London, 1898).

Sketch of Dr. Jos. Fraunhofer in Pop. Science Monthly, VI, 739; Memoir in Jr. Fr. Institute, VIII, 96; MERZ, Das Leben und Wirken, (Landshut, 1865); BAUERNFEIND, Gedächtnissrede auf F. (Munich, 1887).

WILLIAM FOX