# 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).