# 1911 Encyclopædia Britannica/Neumann, Franz Ernst

**NEUMANN, FRANZ ERNST** (1798–1895), German mineralogist, physicist and mathematician, was born in Joachimsthal on the 11th of September 1798. In 1815 he interrupted his studies at Berlin to serve as a volunteer in the campaign against Napoleon, and was wounded in the Battle of Ligny. Subsequently he entered Berlin University as a student of theology, but soon turned to scientific subjects. His earlier papers were mostly concerned with crystallography, and the reputation they gained him led to his appointment as Privatdozent at Königsberg, where in 1828 he became extraordinary, and in 1829 ordinary, professor of mineralogy and physics. In 1831, from a study of the specific heats of compounds, he formulated "Neumann's law," which expressed in modern language runs: "The molecular heat of a compound is equal to the sum of the atomic heats of its constituents." Devoting himself next to optics, he produced memoirs which entitle him to a high place among the early searchers after a true dynamical theory of light. In 1832, by the aid of a particular hypothesis as to the constitution of the ether, he reached by a rigorous dynamical calculation results agreeing with those obtained by A. L. Cauchy, and succeeded in deducing laws of double refraction closely resembling those of A. J. Fresnel; and in subsequent years he attacked the problem of giving mathematical expression to the conditions holding for a surface separating two crystalline media, and worked out from theory the laws of double refraction in strained crystalline bodies. He also made important contributions to the mathematical theory of electrodynamics, and in papers published in 1845 and 1847 established mathematically the laws of the induction of electric currents. His last publication, which appeared in 1878, was on spherical harmonics (*Beiträge zur* *Theorie der Kugelfunctionen*). He took part in founding the Mathematisch-Physikalisches Seminar, to give students a practical acquaintance with the methods of original research. He retired from his professorship in 1876, and died at Königsberg on the 23rd of May 1895. His son, Carl Gottfried Neumann (b. 1832), became in 1858 Privatdozent, and in 1863 extraordinary professor of mathematics at Halle. He was then appointed to the ordinary chair of mathematics successively at Basel (1863), Tübingen (1865) and Leipzig (1868).